Distribution, Abundance, Microhabitat Use and Interspecific Relationships Among Terrestrial Salamanders on Vancouver, Island, British Columbia
ty
Theodore M. Davis B.S., Portland State University, 1968 M.Sc., University of Victoria, 1991
A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of
DOCTOR OF PHILOSOPHY
in the Department of Biology
We accept this dissertation as conforming m the required standard
Dr. P. T. Gregory, sjiipervi^r (Department of Biology)
Dr. G. A. Allen, Departmental Member (Department of Biology)
Dr. N_LiMneston,, Departmental Member (Department of Biology)
Dr. E. A. Roth, Outside Member ^Department ofAnthropology)
Dr. N. L. Staub, External Examiner (Biology Department, Gonzaga University)
© Theodore M. Davis, 1996 University of Victoria
All rights reserved, This dissertation may not be reproduced in whole or in part, by photocopying or other means, without the permission of the author, ii Supervisor: Dr. Patrick T. Gregory
Abstract
A fundamental aim of ecology is the study of patterns of distribution
and abundance of organisms. These patterns can be influenced by intrinsic
responses to environmental conditions, interspecific interactions, or both.
If individuals of similar co-existing species use the same limited resources,
competition can result in resource partitioning, but this pattern can also be
the result of intrinsic differences.
On Vancouver Island, British Columbia, two ecologically similar
plethodontid salamanders, Plethodon vehiculum and Aneides ferreus, are
each common only where the other species is uncommon. I described
their distribution and abundance, investigated differential microhabitat
use, and evaluated interspecific interactions between them.
At each of nine sites I established arrays of six 0.3 x 2 m artificial
cover objects (ACOs). Each ACO consisted of three boards arranged to
create multiple microhabitats. ACOs allow sampling without disturbance
of natural cover, provide a standard sampling unit, and minimize observer
bias. In 1992 and 1993,1 checked 228 ACOs every other week, but less often
in 1994. I also searched natural microhabitats and investigated distribution
and abundance with time-constrained searches at 16 additional sites.
I collected data on 2790 salamanders. At the northern sites, A. fe rre u s was relatively abundant compared to P. vehiculum, but the iii situation was reversed in the south. I found no differences in site characteristics that would explain this pattern. Salamander abundance was reduced in clearcuts, but there was no difference among old-growth, mature, and immature sites.
The density of P. vehiculum in Coldstream Provincial Park was exceptional. In one area, surface density was 1.8 individuals/m2, but 200 m away there was <0.03 individuals/m2. From censuses in fenced plots elsewhere, I estimated that <24% of the P. vehiculum population was on the surface at any particular time. Thus, by extrapolation, there are at least
75,000 P. vehiculum/ha in one area of Goldstream Park.
The density of P. veh icu lu m was <0.1 individuals/m2 across wide areas of forest habitat with occasional patches of higher density. Surface abundance wras correlated with the area of ground covered by coarse woody debris (CWD) and with surface moisture, and abundance varied by a factor of 12 over a distance of 50 m.
I collected microhabitat data o.i 1306 salamanders. Of the A. ferreus,
95% were under the bark on logs or within logs. In. contrast, 67% of the P. v e h ic u lu m were under CWD on the soil and 20% were within logs.
Aneides ferreus used logs in an early stage of decay, and P. vehiculum , when under bark on logs oi within logs, used logs in a late stage of decay.
Under ACOs, 98% of the A . ferreus were found between boards, whereas
85% of the P. veh icu lu m were found on the soil under boards.
Microhabitat use by Ensatina eschscholtzii and Taricha granulosa was iv similar to that of P. vehiculum, except that 23% of the T. granulosa were on the surface.
In staged encounters, there was no aggression or predation between
A . ferreu s and P. veh icu lu m . In laboratory and outdoor enclosures, microhabitat selection was not influenced by the presence of the other species. Thus, differential microhabitat use is due to intrinsic differences, and is not the result of interspecific interactions.
The distribution and abundance of these species is not explained by interspecific interactions or site characteristics as measured in this study.
Examination of habitat features at a finer scale might explain differences in distribution and abundance, but the requirements of these species could be so similar or correlated that differences might not be found. Additional sites need to be investigated to determine the detailed pattern of distribution of these species on Vancouver Island and adjacent islands. Examiners:
Dr. P. T. Gregory, Su^brvisor (Department of Biology)
Dr. G. A. Allen, Departmental Member (Department of Biology)
Dr. N. Lfy/ngston, ^Dep^tmental Member (Department of Biology)
Dr. E. A. Roth, Outside Member (Department of Anthropology)
Dr. N. L. Staub| External Examiner (Biology Department, Gonzaga University) vi Table of Contents
Abstract ..... b Table of Contents ...... vi List of Tables ...... - ...... x List of Figures...... xi Acknowledgments xi v
Chapter 1: Introduction ...... 1
Objectives...... 7
Interspecific interactions among salamanders...... 11
N atural History...... 18 Clouded Salamanders (Aneidesferreus) ...... 19 Western Red-backed Salamander (Plethodon vehiculum) 20 Ensatina Salamanoer (Ensatinaeschscholtzii) ...... 21 Rough-skinned Newt (Taricha granulosa)...... 22
Chapter 2: Methods ...... —25
Methodological Overview...... 25 Artificial cover objects (ACO s)...... 25 General methodology ...... 27
Detailed Methodology...... 32 Study sites...... 32 Artificial cover objects (ACOs)...... 33 A C O P lots ...... 37 Fenced Plots...... 40 Sampling Frequency ...... 41 Area constrained searches(ACSs) ofACO plots ...... 42. Handling of salamanders ...... 42 Statistical methods ...... ,.43 vii
Chapter 3: Population Ecology...... 44
Methods...... 45 Area-constrained searches (ACSs) of natural cover in ACO plots...... 45 Body condition ...... 47 Statistical methods ...... 48
Results...... 49 Seasonal variation in surfaceabundance ...... 49 Variation inabundance among sites...... 59 Variation inabundance among species...... 59 Population structure...... 72 Body condition ...... 79 Movement across fences ...... 88 M o v e m e n t s...... 88 Population size in fenced andunfenced ACO plots...... 89 D e n s ity ...... 92
Discussion...... 95 Seasonal variation in surfaceabundance ...... 95 Variation inabundance among sites...... 97 Variation inabundance among species ...... 98 Metapopulation effects ...... 99 Population structure ...... 101 Population size and density...... 104
Chapter 4: Goldstream Provincial Park ...... 107
Methods...... 107
Results...... I ll
Discussion...... ,...... 113 viii Chapter 5: Time-constrained Searches of Secondary Sites ...... 117
Methods...... 117 Site selection ...... 117 Search Order ...... 118 Time-consirained searches ...... 121
Results...... 123
Discussion...... 127
Chapter 6: Site and Plot Characteristics, Climatic Conditions, and Abundance ...... 133
Methods...... 134 Site characteristics ...... 134 Site characteristics in relation to salamander abundance...... 136 Plot characteristics in relation to salamander abundance...... 137 Climate and Weather ...... 138
Results „...... 139 Site characteristics ...... 139 Site characteristics in relation to salamander abundance ...... 143 Plot characteristics in relation to salamander abunaance...... 146 Climate and Weather ...... 150
Discussion...... 150 Site characteristics ...... 150 Site characteristics in relation to salamander abundance ...... 155 Plot characteristics in relation to salamander abundance...... 156
Chapter 7: Microhabitat U se ...... 159
Methods...... 161
Results...... 163 Variation in natural microhabitat use among species ...... 163 Variation in natural microhabitat use among size classes ...... 167 ix Variation in ACOmicrohabitat use among species...... 174
Discussion...... 177
Chapter 8: Interspecific interactions ...... 181
Methods...... 183 Salamanders ...... 183 Staged encounters...... 184 Use of cover object...... 185 Habitat selection in field enclosures...... 186 Interspecific predation ...... 188
Results...... 189 Staged encounters...... 189 Use of cover object...... 189 Habitat selection in field enclosures...... 190 Interspecific predation ...... 190
Discussion...... 193
Chapter 9: Summary...... 196
Synopsis...... 208 Artificial cover objects (ACOs) ...... 208 Distribution and abundance among ...... sites 210 Distribution and abundance within sites...... 210 Microhabitat use...... 211 Interspecific interactions ...... ,.212 Directions for further research...... 212
Literature Cited ...... 217 X
List of Tables
Table 1. Salamanders of Vancouver Island British Columbia ...... 5
Table 2. Comparisons of the mean number of salamanders found per search by site from April 1 to October 1,1992 and 1993...... 58
Table 3. Comparisons of the mean number of salamanders found per search from April 8 to May 15,1993 and 1994 ...... 60
Table 4. The number of salamanders found under ACOs on 8 searches of primary sites between April 8,1993 and August 12,1993...... 61
Table 5. The number of salamanders found under ACOs on matched searches of primary sites...... 64
T able 6. Probability of finding at least one individual of a species on searches of ACO and searches of natural cover ...... 71
Table 7. Number of individual Taricha granulosa found in fenced and unfenced plots at Lake Cowichan, 1992-1994 ...... 93
Table 8. Density of Plethodon vehiculum in Goldstream Provincial Park, Vancouver Island, B.C. on May 1, 1994 ...... 112
T a ble 9a. Location o f sites searched on the first day of 2-hr time constrained searches (TCSs), in the spring of 1993 ...... 119
Table 9b. Location of sites searched on the second day of 2-hr time constrained searches (TCSs), in the spring of 1993 ...... 120
Table 10. Number of salamanders found on time-constrained searches of 20 -12 sites on southeastern Vancouver Island, BC...... 124
Table 11. Habitat characteristics at forested primary sites ...... 140-141
T a b l e 12. Terrestrial microhabitat use by four species of salamanders on Vancouver Is*and, B.C ...... 164 xi
List of Figures
Figure 1. Location of study sites O:: iricouver Island, British Columbia, Canada ...... 28
Figure 2. Diagram of an artificial cover object (ACO)...... 35
Figure 3. Location of sample plots at Lake Cowichan ...... 38
Figure 4. Seasonal variation in number of salamanders, including recaptures, found under artificial cover objects (ACOs) at Goldstream Provincial Park, 1992-1994 ...... ,...... 50
Figure 5. Seasonal variation in number of salamanders, including recaptures, found under artificial cover objects (ACOs) at Lake Cowichan, 1992-1994...... 52
Figure 6. Seasonal variation in number of salamanders, including recaptures, found under artificial cover objects (ACOs) at the GVW sites, 1992-1994...... 54
Figure 7. Seasonal variation in number of salamanders, including recaptures, found under artificial cover objects (ACOs) at the RMC sites, 1993...... 56
Figure 8. Salamander abundance among nine sites on Vancouver Island, B. C ...... 62
Figure 9. Proportion of salamander species based on searches of ACO, 1992-1994...... 66
Figure 10. Proportion cf salamander species based on searches of natural cover in ACO plots, 1992-1994...... 68
Figure 11. Size-frequency histograms by season for P lethodon ve h ic u lu m found under ACOs at Goldstream Provincial Park, 1992-94...... 73
Figure 12. Size-frequency histograms by season for Plethodon ve h ic u lu m found under ACOs at Lake Cowichan, 1992-94 ..... 75 xii
Figure 13. Size-frequency histograms for Plethodon vehiculum found under ACOs and natural cover at Lake Cowichan and the Greater Victoria Watershed (GVW), 1993-1994 ...... 77
Figure 14. Size-frequency histograms for Plethodon vehiculum found at Lake Cowichan in fenced ACO plots, 1992-1S94 ...... 80
Figure 15. Size-frequency histograms by season for Aneides ferreus (n=12.3) found under ACOs at the RM.C sites, 1993...... 82
Figure 16. Size-frequency histograms for Taricha granulosa found under ACOs at Lake Cowichan and the GVW sites ...... 84 ilgure 17. Mass-length relationships of Plethodon vehiculum and Aneides ferreus...... 86
Figure 18. Cumulative number of salamanders caught in unfenced and fenced plots at Lake Cowichan, 1993-94 ...... 90
Figure 19. Map of Goldstream Provincial Park showing location of ACO plot and transects for quadrat sampling ...... 108
Figure 20. Number of salamanders found on time-constrained searches (TCSs) of secondary sites on Vancouver Island, B.C 125
Figure 21. Proportion of Plethodon vehiculum found on time- constrained searches (TCSs) of secondary sites on Vancouver Island, B.C ...... 128
Figure 22. Scattergrams showing correlations between salamander abundance and site characteristics for the forested primary study sites ...... 144
Figure 23. Scattergrams showing correlations between the abundance of Plethodon vehiculum and two plot characteristics for Lake Cowichan and the Greater Victoria Watershed (GVW) sites combined ...... 147
Figure 24. Scattergrams showing correlations between the abundance of Plethodon vehiculum and area of CWD ...... 151
Figure 25. Normal temperatures and total precipitation per month for study sites on Vancouver Island, B.C ...... 153 Figure 26. Microhabitat use among four species of salamanders: Aneides ferreus, Ensatina eschscholtzii, Plethodon v e h ic u lu m , and Taricha granulosa...... 165
Figure 27. The proportion of logs used by decay class ioxPlethodon v e h ic u lu m and Aneides ferreus...... 168
Figure 28. The proportion of logs by decay class and the proportion of logs used by decay class at Lake Cowichan and Rosewall Creek...... 170
Figure 29. Microhabitat use by SVL (mm) for P lethodon v e h i c u l u m...... 172
Figure 30. ACO microhabita!: use by species...... 175
Figure 31. Microhabitat selection in field enclosures by P lethodon v e h ic u lu m and Aneides ferreus, singly and with each other...... 191 xiv
Acknowledgments
I thank Guillaume Audet, Sophie Boizard, Jeannine Caldbeck, Logan Caldbeck, Aziza Cooper, Lisa Crampton, Christian Engelstoft, Trent Garner, Jennifer Harris, Kristina Lauridsen, Lynn Norman, Kristiina Ovaska, and Laura Smith for their assistance in the field. Aziza Cooper helped record much of the field data and I thank her for her dependability and careful attention to detail and accuracy. She also entered data into the computer, and helped with the tedious task of observing staged encounters. I thank the authorities of the British Columbia Ministry of Environment, Lands and Parks who allowed me access to the site in Goldstream Park, the staff of the Greater Victoria Water District for access to sites under their control, and Douglas Pollard, Valin Marshall, and Tony Trofymow of Forestry Canada for their support and use of equipment. Patrick Gregory provided helpful advice and encouragement throughout this study, and carefully reviewed an earlier version of this manuscript. I thank my committee members for their valuable comments. This study was carried out while I held a Natural Sciences and Engineering Research Council (NSERC) Postgraduate Scholarship in 1991- 1992 and 1992-1993. Additional support was provided by the King-Platt Fellowship, 1993-1994, Additional funding was provided by grants to P. T. Gregory from the Forestry Practices Component of Forestry Canada’s Green Plan, and through the British Columbia Ministry of Environment, Lands and Parks, Wildlife Branch. Chapter 1: Introduction
A primary goal of ecologists is to identify and explain patterns of distribution, abundance, and diversity of organisms (e.g. Brown 1984;
Begon et al. 1990; Ricklefs and Schluter 1993; Krebs 1994). Of particular interest are patterns of distribution and abundance of ecologically similar sympatric species, and the ecological and behavioral processes that produce thjse patterns. Similar species may be found in the same habitats because they use similar resources and their behavioral and physiological responses to environmental conditions are similar. Alternatively, some species may be rare and others common at one location, but the relative abundances may be reversed elsewhere. Such patterns can be the result of intrinsic differences and similarities among species and their responses to particular environmental and resource conditions, but interspecific interactions among similar species, either competition or predation, also can have profound effects on when and where organisms are found, their abundances, and which species coexist. Individuals of similar species may use the same resources, and if these resources are limited in supply, competition can result in resource-partitioning or competitive exclusion.
Thus, ecologists have long been interested in how similar, coexisting species differ in their use of resources (Darwin 1859; Allee et al. 1949; 2 Hutchinson 1959; Mayr 1963; Jaeger 1974; Schoener 1974,1989; Connell 1980;
Hairston 1980b; Toft 1985; den Boer 1986).
Although competition for limited resources can result in resource partitioning, other mechanisms can produce the same pattern. Observed differential resource use may be due to either (1) independently derived differences among species, expressed as physiological, morphological or behavioral adaptations, or constraints, (2) interactions among species that happened in the past ("Ghost of Competition Past", Connell 1980), (3) current interactions, or (4) some combination of all these elements. If interspecific interactions are occurring, they may be direct or indirect
(Abrams, 1987), but the strongest interactions in amphibians that use similar resources are likely to be direct interference competition or predation (Toft 1985). Experimental manipulations of natural populations can provide evidence for current competition (Schoener 1983; Connell
1983), but there are no obvious methods that distinguish between independently evolved differences and differences that arose because of interactions in the evolutionary past (Begon et al. 1990).
Ecological similarity among species is often, but not always, correlated with their degree of phylogenetic relatedness. Thus, most experimental studies of competition have focused on closely related species
(Connell 1983, Schoener 1983). However, there are many cases of distantly related organisms competing for resources. Classic examples include competition among barnacles, mussels, and algae for space (Lubchenco and 3 Menge 1978), among fish and ducks for invertebrate prey (Eriksson 1979), and among rodents and ants for seeds (Brown et al. 1979). Nevertheless, as emphasized by Darwin (1859: chapter 3), competition is generally most intense between closely related species because similar morphology implies similar resource requirements: "As species of the same genus have usually, though by no means invariably, some similarity in habits and constitution, and always in structure, the struggle will generally be more severe between species of the same genus, when they come into competition with each other, than between species of distinct genera." Homoplasy is characteristic of terrestrial plethodontid salamanders (Wake 1991) and where they are syntopic they should use similar resources and should compete for those resources when those resources are limited in supply.
My overall goal is to determine whether similar, related species of terrestrial plethodontid salamanders on southeastern Vancouver Island differ in their distribution and abundance. If they differ, how do they differ and why? What are the ecological consequences of these differences?
These salamanders are similar in body size and shape, have similar life histories, require similar environmental conditions, and use similar resources. Where such species are in contact and compete for resources, they should either evolve differences in resource use or there should be some shift in resource use by one or both species in response to the presence of the other. Similar species also may partition resources because of species-specific morphological, physiological, or behavioral constraints. 4 Thus, the pattern of differential resource use may be the result of a combination of species-specific traits and interspecific interactions (Toft
1985).
All six species of salamanders found on Vancouver Island are either entirely terrestrial or have an adult terrestrial stage (Table 1). The three plethodontid species (Family Plethodontidae), Aneides ferreus (Clouded
Salamander), Plethodon vehiculum (Western Red-backed Salamander), and Ensatina eschscholtzii (Ensatina Salamander), are entirely terrestrial: they lay their eggs on land, the hatchlings are terrestrial, and they do not require standing or running water during any part or their life cycle. The other three species, Taricha granulosa (Rough-skinned Newt), A m b y s to m a g racile (Northwestern Salamander), and Ambystoma macrodactylum
(Long-toed Salamander), have a terrestrial adult stage, but they must return to water to reproduce. These species lay their eggs in temporary or permanent ponds or creeks. The eggs develop into aquatic larvae that eventually transform into terrestrial salamanders. However, A . gracile are facultatively neotenic (Duellman and Trueb 1986), and in some B. C. populations most individuals reproduce while retaining the larval external morphology (Eagleson 1976).
A m b ysto m a is the most diverse and widespread genus of Family
Ambystomatidae (Nussbaum et a l 1983). This family is morphologically similar to, but distantly related to the Plethodontidae (Duellman and Trueb
1986; Larson and Dimmick 1993). Taricha belongs to the Salamandridae, a TABLE 1. Salamanders of Vancouver Island, British Columbia. Data from Green and Campbell (1984), Stebbins (1985), and Leonard et al. (1993). SVL = snout-vent length; TL = total length.
Family Species name Size Reproductive mode/habitat Typical terrestrial habitat SALAMANDRIDAE Rough-skinned Newt, 60-90 mm SVL Eggs and larvae aquatic/ Under or within logs or leaf litter; Taricha granulosa 120-180 mm TL lakes, ponds, swamps, and noctumally and diumally active on slow moving streams. surface.
AMBYSTOMAT1DAE Northwestern 75-100 mm SVL Eggs and larvae aquatic / Terrestrial habitat poorly known. Salamander, 150-200 mm TL lakes, ponds, and slow Underground burrows, occasionally Ambystoma gracile moving streams. under or within logs.; some populations may be neotenic.
Long-toed Salamander, 40-60 mm SVL Eggs and larvae aquatic/ Terrestrial habitat poorly known. Ambystoma 80-120 mm TL temporary pools, small Underground burrows, under rocks, macrodactylum lakes, ponds, and slow bark and logs on soil or within leaf moving streams. litter.
PLETHODONTIDAE Clouded Salamander, 48-66 mm SVL Eggs terrestrial; direct Under bark on logs or within logs. Aneides ferreus 80-110 mm TL development/ cavities within logs.
Ensatina Salamander, 40-60 mm SVL Eggs terrestrial; direct Talus, under rocks, bark and logs on Ensatina eschscholtzii 80-120 mm TL development/ cavities soil or within leaf litter. below surface or under or within logs.
Western Red-backed 40-55 mm SVL Eggs terrestrial; direct Talus, under rocks, bark and logs on Salamander, 80-110 mm TL development/ in cavities soil or within leaf litter and Sword Plethodon vehiculum below surface. Fem bases. 6 family closely related to the Ambystomatidae (Larson and Dimmick 1993).
Four of these species, A. ferreus, P. vehiculum, E. eschscholtzii, and
A. macrodactylum, have very similar adult morphologies. They have
smooth skins, are relatively slender, and there is substantial overlap in the
range of adult body sizes (Table 1). The other two species, T. granulosa and
A. gracile, are larger and much more robust. The skin of T. gra n u lo sa may be dry and granular, depending on the sex and time of year. All these species have wide distributions in similar moist forest habitats and commonly coexist.
Two :necies, A . ferreu s and P. vehiculum, are found throughout
Vancouver Island, at least at lower elevations, and can be locally very abundant. Ovaska and Gregory (1989) studied the population ecology of a dense population of P. vehiculum in Goldstream Provincial Park (48°28'
N, 123°32' W). I had found A . ferreu s nearby, but densities appeared to be low, although focused searches were not possible because such searches require the removal of bark from logs, which is rather destructive and also is prohibited in the park. In contrast, I found A . ferreus to be abundant farther north (49°27' N, 124°46' W), but P. vehiculum appeared to be relatively uncommon (Davis 1991). Casual observation suggested that habitat characteristics and weather conditions were similar among these and other sites. Also, microhabitat differences appeared to exist between these species, and although this question had not been formally addressed at this stage, Corn and Bury (1991) soon reported differences in the use of 7 CWD between these species in Oregon. These patterns suggested that interspecific interactions might be occurring between these species, or that the sites differed in conditions or resources important to these species, or both. Of particular interest was whether the presence of one species affects microhabitat selection in the other as it does in some plethodontid salamanders in eastern North America (see Interspecific interactions among salamanders., below).
Thus, A . fe rre u s and P. v e h ic u lu m are the species of most interest in this study. The closely related E. eschscholtzii will be considered where numbers captured allow. Taricha granulosa, very different in morphology and life history from the plethodontids, will provide an interesting contrast in certain circumstances. Both species of A m b y sto m a were infrequently captured, so presence/absence data only will be reported.
O bjec tiv es
There are four primary objectives of this study:
1) To determine the general pattern of distribution and abundance of Aneides ferreus and Plethodon vehiculum, and to explore how and why abundance varies among sites. These two species of terrestrial salamanders coexist on southeastern Vancouver Hand, but on preliminary searches, A, ferreu s was relatively more abundant at northern locations whereas P, 8 v eh icu lu m dominated in the south. This suggested that their distribution and abundance was influenced by climatic conditions, interspecific interactions, or both. Also, abundance appeared :o vary among sites locally at the scale of a km or less, and, within a site, at much smaller scales (<100 m), so I investigated salamander abundance within sites in relation to local structural and biological conditions.
This objective was partly motivated by the issue of declining amphibian populations (Pechmann and Wilbur 1994; Blaustein and Wake
1995). Although there are no reports of declines of terrestrial salamanders in undisturbed environments, systematic monitoring has been rare, so if declines have occurred, they have not been recorded. There is concern that the fragmentation or loss of temperate old-growth forests might reduce amphibian diversity and abundance in western North America
(Herrington and Larsen 1985; Aubry et a l 1988; Bury and Corn 1988;
Gibbons 1988; Raphael 1988; Welsh and Lind 1988; Hansen et al. 1991), of which terrestrial plethodontid salamanders make up a considerable fraction. Because the forests of southeastern Vancouver Island are highly fragmented by logging, I sampled some sites that represent an approximate
Ci 'noseries from clearcut to old-growth forest to see what effect disturbance might have on salamander populations. However, the majority of the sites were relatively undisturbed.
2) To document the nature and extent of differential microhabitat use between these species. Time, habitat and food type are considered the 9 three most important primary resource dimensions, with habitat and diet being the most important for vertebrates (Pianka 1969; Huey and Pianka
1983; Toft 1985; Schoener, 1974,1989). Toft (1985), in an extensive review of the literature on resource-partitioning in reptiles and amphibians, found that except for amphibian larvae and snakes, habitat is the resource dimension partitioned first by amphibians and reptiles. Salamanders and lizards tend to be opportunistic feeders, so differences in prey type are generally attributable to habitat (Toft 1985).
Because terrestrial salamanders are euryphagic and there is considerable overlap in the diet of sympatric species, differential use of prey in similar habitats is primarily related to body and jaw size (e.g. Maiorana
1978; Jaeger 1972; Harestad and Stelmock 1983; Lynch 1985). Thus, if there is differential use of prey, it could be a function of body and jaw size, an artifact of microhabitat partitioning, or both. Also, if food is a limiting resource, competition should occur for high-quality feeding microhabitats as a proximate limiting resource. Alternatively, microhabitat space per se, used as daytime retreats or nesting sites, might be the ultimate resource
(Jaeger 1980b; Hairston 1987; Jaeger and Walls 1989; Gabor and Jaeger 1995).
Thus, I chose microhabitat use as the most obvious niche dimension to investigate in these species. A fundamental assumption here is that resources are limiting for these species. The basis for this assumption is covered in the next section. 10 3) To develop and apply a number of sampling and censusing methods appropriate for terrestrial salamanders. A principal obstacle to accomplishing the above objectives was the lack of unbiased sampling methods. Therefore, a major aim of my work was to develop such methods, especially the use of artificial cover objects. This objective also was partly motivated by the issue of declining amphibian populations.
Lack of standardized methodology makes comparison among sites and studies difficult or impossible, so there has been considerable effort in developing standardized methods (Heyer et al. 1994). My work is a contribution to that effort.
4) To evaluate the importance of interspecific interactions between
A . fe rreu s and P. vehiculum . This was done using a variety of experimental approaches. A standard method of assessing intra- and interspecific interactions in terrestrial salamanders is to stage encounters between individual salamanders (e.g. Cupp 1980; Jaeger 1984; Keen and
Sharp 1984; Nishikawa 1985; Ovaska 1987b, 1993; Davis 1991; Staub 1993), and I did this for these species. Salamander-salamander predation was investigated by offering hatchling P. veh icu lu m to adult A. ferreus.
Finally, I experimentally investigated microhabitat selection in these species in the laboratory and under semi-natural conditions. 11
I nterspecific interactions a m o n g salamanders
Similar species of terrestrial salamanders are able to coexist if they feed at different times, feed on different size prey, or use different microhabitats (Burton 1976; Fraser 1976a). For example, in Oregon, three syntopic species of terrestrial salamanders ( Aneides ferreus, Ensatina eschscholtzii, and Batrachoseps wrighti) differ in their use of different
decay classes of coarse woody debris (CWD; Bury and Corn 1988). Similarly, in the Oregon coast range mountains, Corn and Bury (1991) found that
Plethodon vehiculum, E. eschscholtzii, and A . fe rreu s differ in their use of
CWD by decay class, or by their specific locations within or under CWD, or both. Such microhabitat partitioning may result from each species being
better able to exploit critical resources in slightly different microhabitats, or
because one species, through interspecific competition, forces another into
a different microhabitat (Schoener 1974,1982,1983; Hairston 1987). These
factors may operate concurrently, but where differences in resource use
among species are intrinsic, competition for resources or interspecific
predation will be rare or absent.
Some species of terrestrial salamanders use the same or similar
microhabitats, but differ in the use of other resources. Bury and Martin
(1973) found that Aneides lugubris, A. ferreus, E, eschscholtzii, and
Batrachoseps attenuatus consume different sizes, types, and numbers of
prey in Redwood forests in California. Aneides lugubris were found 12 primarily in open, non-forested areas (74.1% of captures), occasionally in second-growth forests (19.3% of captures), and never in old-growth forests.
The other species were relatively rare in the open areas, but common in both second- and old-growth forests. Microhabitats used by all species were similar, and individuals of different species were sometimes found under the same cover object. Differential use of prey may be related to morphological and behavioral differences among these species, but it is not known if competition for cover objects occurs among them.
Several species of terrestrial salamanders in eastern North America are known to partition microhabitats through interspecific interference competition. For example, Plethodon cinereus excludes P. Shenandoah from areas of deep, moist soil through interspecific aggression (Jaeger 1970;
Jaeger 1971a,b; Jaeger 1972; Jaeger and Gergits 1979; Wrobel et al. 1980). As a result, P. Shenandoah is confined to islands of xeric talus that are physiologically unsuitable for P. cinereus (Jaeger 1971b).
Similarly, the semiaquatic Desmognathus fuscus moves to microhabitats significantly farther from a stream when in the presence of
Desmognathus monticola (Keen, 1982), but juvenile D. m onticola shift from rocks to wood in the presence of adult D. fu sc u s(Southerland 1986).
Keen and Sharp (1984) showed that resident D. m onticola were more aggressive toward D. fu s c u sintruders than toward conspecific intruders.
Among several species of Desmognathus, territorial aggression can grade into predation (Keen and Sharp 1984; Southerland 1986). 13 Interspecific predation is known to affect microhabitat use and abundance among several species in this genus (Southerland 1986; Hairston 1986,
1987). For example, D. quadramaculatus and the ecologically similar
Gyrinophilus porphyriticus may affect distribution and microhabitat use by
Desmognathus ochrophaeus (Formanowicz and Brodie 1993).
If the body sizes of individuals are sufficiently different, interspecific predation also might occur among terrestrial salamanders. For example, aggressive behavior by Ambystoma maculatum toward P. cinereus can lead to predation or interference competition, and may affect the distribution of
P. cinereus among microhabitats on the forest floor (Ducey et al. 1994). In general, adult terrestrial salamanders might prey on hatchling or juvenile salamanders of their own or other species, but very few species have been examined with this in mind. Powders (1973) described an apparent case of cannibalism in Plethodon teyahalee (=P. glutinosus), but such predation must be rare because there are no reports of vertebrate parts in the stomach contents of terrestrial salamanders (e.g. Dumas 1956; Storm and Aller 1947;
Altig and Brodie 1971; Jaeger 1972; Bury and Martin 1973; Lee and Norden
1973; Burton 1976; Stelmock and Harestad 1979; Lynch 1985; Whitaker et al.
1986).
Although direct interspecific interactions generally favor one species over another, in some cases a more balanced relationship is possible. For example, in the Black Mountains of North Carolina and the Great Smoky
Mountains of North Carolina and Tennessee, Plethodon jordani and P. 14 teyahalee compete for space strongly enough that their distributions
overlap only along a narrow elevational band (Hairston 1951,1980a, 1987).
Presumably, the altitude at which each species occurs depends on intrinsic
physiological and behavioral responses to physical conditions that vary
with altitude. Plethodon jordani is favored in the cooler, moister
microhabitats that occur at higher elevations as well as in deep ravines and
north-facing slopes. Plethodon teyahalee is favored in the warmer, dryer
microhabitats that occur at lower elevations (Hairston 1949; Hairston
1980a). However, in the Balsam Mountains of North Carolina, which are
geographically between the other two ranges, there is a broad band of
overlap between the two species (Hairston 1951; Hairston 1980a). In field
experiments, Hairston (1980a,b) was able to show that interspecific
competition is much stronger where the overlap is narrow than where the
overlap is broad. Also, individuals from the Great Smoky Mountains, where competition is strong, are more aggressive than individuals from
ihe Balsam Mountains, where competition is weak (Nishikawa 1985).
Other experiments showed that neither prey nor foraging microhabitats are the object of competition, but that space, perhaps for nesting sites, is the most likely limiting resource (Nishikawa 1985; Hairston et al. 1986;
Hairston 1987).
Such a relatively symmetrical relationship can also be the result of a shift in competitive abilities at different life stages. Wilbur (1980) suggested that two species may coexist if one species is competitively superior in the 15 larval stage while the other has an advantage in the adult stage. Such an ontogenetic switch in competitive abilities occurs in A m b y sto m a ta lp o id eu m and A. maculatum. These species have an aquatic larval stage, but become terrestrial at metamorphosis. In the larval stage, A. ta lp o id eu m is aggressively superior to A. maculatum (Walls and Jaeger
1987), but the relationship is reversed at metamorphosis (Walls 1990). It is not known if competition between these species in the terrestrial stage causes a shift in resource use.
Aggressive behavior has been observed between other terrestrial salamanders. Grant (1955) observed territorial defense in captive Eurycea bislineata and Hemidactylium scutatum. Thurow (1975) observed aggressive interactions among several species of Plethodon. Ovaska (1993) reported that P. d u n n ishows aggressive behavior toward P. vehiculum, and Smith and Pough (1994) demonstrated that D. ochrophaeus displaces P. cinereus from cover objects. However, the ecological effects of these interactions in nature, if any, are unknown.
Although interspecific interactions among terrestrial salamanders can profoundly affect local abundance and diversity, few studies have been carried out for species in western North America. Maiorana (1978) found that when large prey were scarce, there was substantial overlap in prey size between A. lugubris and B. attenuatus, but she concluded that prey were less important in limiting populations than the availability of burrows of different sizes. However, the importance of interspecific competition 16 between these species is unclear, and there are no experiments that demonstrate competition for burrows or territoriality. Lynch (1985) found that four species of terrestrial salamanders, A. lugubris, A. flavipunctatus,
B. attenuatus, and E. eschscholtzii, despite considerable dietary overlap, exhibited significant differences in the size of prey taken. Competition for food or space among these species is plausible, but again, no experimental work has been done. Dumas (1956) studied Plethodon dunni and P. vehiculum where their ranges overlap in western Oregon. He found slight differences in microhabitat use and in the variety of prey consumed by these species, but there was much overlap. Ovaska and Davis (1992) found that these species recognize and display toward each others' fecal pellets
(which are used in chemical communication), and Ovaska (1993) observed attacks and agonistic display behavior by P. d u n n toward i P. vehiculum .
However, much work needs to be done to clarify the extent and significance of these interspecific interactions in nature.
Most of the work on intra- and interspecific interactions among terrestrial salamanders has focused on species from the central
Appalachian Mountains (Hairston 1987). However, life history patterns, including the nature and extent of interspecific interactions, may be different elsewhere. For example, because of climatic differences between the eastern and western United States, the timing of surface activity, courtship, and oviposition by salamanders in the two regions are very 17 different (Houck, 1977). Similarly, patterns of resource use and community structure may differ between the two regions.
Such differences may also exist between northern and southern regions. For example, warm, dry summers may limit surface activity for several months in California, but in the relatively wet Pacific Northwest and on Vancouver Island, salamanders may be able to remain on the surface for longer periods. Finally, because there are fewer species dividing up the available resources, the northern species may be less subject to interspecific competition and predation than southern species. It is notable that neither Ovaska (1987b) nor I (Davis 1991) found territorial behavior in
P. vehiculum or A. ferreus, respectively, but similar species in the eastern
United States [e.g. P. cinereus (Jaeger et a l 1982) and Aneides aeneus (Cupp
1980)] are territorial. Also, in Washington State, P. d u n n i,which is restricted to rocky splash zones near streams, is more aggressive than the wider ranging plethodontid salamanders with which it coexists (Ovaska
1993). This suggests that Canadian populations of P. cinereus might have very different selection pressures than populations of P. cinereus in the central Appalachians. The specific prediction is that individuals from northern populations would be less aggressive and less territorial than individuals from southern populations. 18
N a t u r a l H isto r y
Plethodontid salamanders lack lungs so the exchange of respiratory
gases occurs across the highly vascularized skin and buccal cavity. As a requirement of transcutaneous gas exchange, the skin is very permeable to water, and the body size is small, making these salamanders especially susceptible to desiccation and restricting them to moist microhabitats
(Shoemaker et al. 1992). Nevertheless, many plethodontid salamanders, including the three species on Vancouver Island, are completely terrestrial during their entire life cycle. Females lay and brood small clutches of eggs in the early summer. The larval stage is passed in the egg, and young hatch in the autumn as miniature replicas of the adults (McKenzie 1970; Ovaska and Gregory 1989; Davis 1991). Amphibians are ectothermic and heat is obtained mainly from the external environment (Hutchison and Duprd
1992). Thus, their surface activity is constrained by moisture and temperature.
On Vancouver Island, these salamanders can be found at the surface fairly easily throughout most of the year, but disappear during the coldest part of the winter when beinw-freezing temperatures force them underground or deep inside logs. Dry conditions late in the summer and in early autumn can have a similar effect. Peak abundance at the surface is usually in the spring or early summer (Ovaska and Gregory 1989, Davis
1991; Davis and Gregory 1993), but surface abundance can increase 19 dramatically at any time of the year if conditions are favorable. Resources
such as mates and prey are obtained primarily at the surface and little or no
feeding is thought to take place underground (Jaeger 1972,1980c; Fraser
1976a,b; Maiorana 1976). Thus, their ability to grow and reproduce is
directly related to the length of time that they spend near the surface
(Houck 1977; Jaeger 1980b; Semlitsch and West 1983). They are
opportunistic predators, feeding on small terrestrial invertebrates.
Clouded Salam ander (Aneides f e r r e u s ) - The geographical
distribution of this species is strikingly disjunct: Vancouver Island, British
Columbia, and south of the Columbia River in Western Oregon and northwestern California (Wake 1965). In British Columbia, A. ferreus are found on Vancouver Island at altitudes less than about 600 m, and are well established on many of the smaller islands nearby (Davis and Gregory
1993). They can be found in moist terrestrial habitats such as under exfoliating bark and in cracks and cavities of decomposing logs, stumps, and snags, in talus, and occasionally in trees (Nussbaum et al. 1983;
Stebbins 1985; Davis and Gregory 1991; Leonard et al. 1993). They are very site-specific and most movements of individuals are less than 2 m between captures that may be many months apart (Davis 1991). Peak abundance at the surface occurs in June (Davis 1991). Courtship and mating take place in the spring, and females lay small clutches of eggs in cavities within decomposing logs in the early summer (McKenzie 1970; Davis and Gregory 20 1993). Prey consists of small terrestrial arthropods, especially insects (Storm
and Aller 1947; Bury and Martin 1973; Stelmock and Harestad 1979;
Whitaker et al. 1986).
W estern Red-backed Salam ander (P l e t h o d o n v e h i c u l u m ) - This
species is found from southern Oregon to southern British Columbia, west
of the Cascade and Coast mountains (Stebbins 1985; Leonard et al. 1993). In
British Columbia, it is found throughout Vancouver Island and on the
mainland in the Fraser Valley as far east as Hope (Green and Campbell
1984). Curiously, this salamander has not been recorded from any of the
Gulf Islands and is absent from most of the other islands surrounding
Vancouver Island. This contrasts dramatically with A . ferreu s (see above).
Plethodon vehiculum are found within leaf litter and Sword Fern
(Polystichum munitum) bases, under moss, rocks or CWD on the forest floor, and under or among rocks on talus and rock outcrops (Bury et al.
1991; Corn and Bury 1991; Leonard et a l 1993). They favor damp, but not wet, shady areas of the forest and can be very abundant (Ovaska and
Gregory 1989). Cvaska (1988b) reported a high degree of site-specificity and small home ranges. Most movements of individuals between captures over a two-year period were less than 3 m. On Vancouver Island, salamanders move from underground retreats during warm wet weather, so peak surface abundance occurs in the spring and autumn, depending on recent weather conditions (Ovaska and Gregory 1989). Courtship and 21 mating occur mainly in October and November, but eggs are laid the following summer (Ovaska and Gregory 1989). Eggs and nests are not well documented, probably because eggs are laid beneath the surface and are difficult to locate (Leonard et al. 1993). Hatchlings appear in the autumn and take two to three years to reach sexual maturity (Ovaska and Gregory
1989). Prey consists of a variety of terrestrial invertebrates (Dumas 1956).
Ensatina Salam ander (E n s a t i n a eschscholtzii ) - This species is found from extreme northwestern Baja California to southern British Columbia, west of the Sierra Nevada mountains in California (but absent from the
Great Valley of California), west of the Cascade crest in Oregon and
Washington, and on eastern Vancouver Island, the adjacent mainland, and up the Fraser valley to Boston Bar in British Columbia (Green and
Campbell 1984; Leonard et al. 1993). These salamanders can be found in damp microhabitats under rocks or CWD on the forest floor, at the entrance of rodent burrows, under or among rocks on talus, and particularly within and under bark piles at the base of snags and stumps, but are almost never found in perpetually wet areas (Corn and Bury 1991;
Leonard et al. 1993). They are difficult to find during the day, but may be abundant on the surface at night during warm wet weather, and are sometimes observed on paved roads when conditions are favorable. This species has not been studied in British Columbia, but its ecology and 22 genetics have been studied in California (Stebbins 1954; Wake and Yanev
1986; Jackman and Wake 1994).
If disturbed, individuals may show a defensive display and produce a milky poison on the dorsal side of the tail. Also, the tail is easily autotomized, usually at the basal constriction, leaving a predator with a writhing noxious tail while the salamander escapes (Green and Campbell
1984; Leonard et al. 1993).
Rough-skinned Newt (T a r i c h a g r a n u l o s a ) - This species is found in the humid coastal forests from southeast Alaska to Northern California, primarily west of the Cascade and Coast Range mountains (Leonard et al.
1993; Stebbins 1995). It is much larger than the plethodontid salamanders described above, uses lungs in gas exchange and has a relatively thick skin.
Thus, it is probably less subject to desiccation than the plethodontid species.
In the water, adult T. granulosa prey on a variety of invertebrates, especially amphipods and insects, and on frog tadpoles (Chandler 1918;
Efford and Tsumura 1973; Lefcort and Eiger 1993). In the terrestrial phase, these salamanders eat a wide variety of invertebrates including earthworms, snails, spiders, mites, springtails, and a variety of adult and larval insects (Chandler 1918).
On Vancouver Island, T. granulosa lay a series of single eggs in ponds from April to July (Oliver and McCurdy 1974). Larvae develop over the summer and transform by the end of August. At higher altitudes, 23 some larvae may overwinter and transform the following summer
(Chandler 1918). After metamorphosis, the young leave the water until they reach their 4th or 5th year when they become sexually mature and return to the pond to breed. On southern Vancouver Island, Oliver and
McCurdy (1974) found that adult males normally remain permanently aquatic, but adult females migrate from breeding ponds to overwinter cn land. However, at Marion Lake, B.C., which is on the mainland, Efford and
Mathias (1969) reported that males as well as females left the water by mid-
October and returned early in the spring. This is the same pattern reported by Chandler (1918) and Pimentel (1960) near Corvallis, Oregon. Mass migrations of newts to breeding ponds are limited to females only
(Pimentel 1960). Details of the activities and natural history of T. granulosa during the terrestrial phase are unknown.
Breeding males develop a swollen vent, high tail crest, smooth skin, and cornified, melanized nuptial pads (Oliver 1974). Nonbreeding males have a granulated skin as do females at all times. Sexes can be distinguished by anatomical details of the cloaca (Stebbins 1954:45).
The skin of T. granulosa contains high concentrations of tetrodotoxin (TTX), a neurotoxin, which functions as a defense against predators (Brodie 1968; Brodie and Brodie 1990). Thus, they are virtually immune to predation by fish, and unlike many other aquatic amphibians, are able to coexist with fresh water salmonids (Efford and Mathias 1969;
Efford and Tsumura 1973; Taylor 1984). However, Brodie and Brodie (1991) 24 found that skin extracts of newts from Reed Island (an island adjacent to
Vancouver Island) were at least three orders of magnitude less toxic than
skin extracts of newts from the Willamette Valley, Oregon. They concluded that Reed Island T. granulosa have little or no TTX in their skins, and assumed that this applies to all Vancouver Island T. granulosa.
However, Macartney and Gregory (1981) found that garter snakes
(Thamnophis ordinoides and T. e ltg a n s ) that were force fed T. granulosa from Vancouver Island exhibited symptoms of TTX poisoning. 25
Chapter 2: Methods
In this chapter, I provide an overview and justification of the use of artificial cover objects (ACOs), details of the main site locations, the location of plots within sites, and a description of ACOs and their arrangement within plots. I also describe fences that were used t o enclose some ACO plots as well as sampling frequency, searches of natural cover in
ACO plots, the handling and measurement of salamanders and other general methodological details. Detailed methodology relevant to particular chapters only is described in those chapters.
M ethodological O v er v iew
Artificial cover objects (ACOs) - Estimation of temporal and spatial variation in abundance is of fundamental importance in ecology and conservation biology. Estimates of relative abundance of terrestrial amphibians in space and time are often made using unit-effort searches of natural cover objects and microhabitats (Corn and Bury 1990). Methods include time- or area-constrained searches, surveys of coarse woody debris
(CWD), and quadrat, transect and patch sampling (Corn and Bury 1990; 26 Heyer et al. 1994). However, because of disturbance of the natural habitat,
these methods may be unsuitable where repeated searches of the same area
are needed, or where disturbance of the natural habitat is unacceptable or
prohibited. For example, Aneides ferreus is typically found under bark on
logs or within logs (Da vis 1991), and one thorough search of this
microhabitat can be very destructive. Such destructive sampling is
unacceptable where more than one sample is needed and may be
prohibited in parks and reserves. Also, searches of natural cover among
sites that differ in the amount and type of CWD may not be comparable because some types of cover may be difficult to search efficiently, resulting in unequal search effort. Finally, search effort may vary among individual searchers (Heyer et al. 1994) or through time with the same individual (T.
Davis, unpublished data; see Chapter 9).
To overcome some of these difficulties, unit-effort pitfall trapping may be used to estimate relative abundance. This has the advantage that the amount and type of CWD and individual effort are independent of the trapping effort. However, the capture rate varies widely among species
(Buhlmann et al. 1988; Bury and Corn 1987; Corn and Bury 1990; Welsh
1990; Welsh and Lind 1988), and many species, probably because they are relatively site-tenacious, are not readily trapped (Welsh and Lind 1988).
Also, the traps must be checked frequently to prevent accidental mortality of the various vertebrates that may be caught. 27 In principle, ACOs can overcome many of these difficulties (Grant et al. 1992; Heyer et a l, 1994). They are especially useful when repeated sampling is necessary, are relatively easy to sample, result in little or no damage to the natural habitat, and can attract species that are difficult to trap in pitfall traps. Unlike sampling with pitfall traps, sampling with
ACOs can be opportunistic with no risk of mortality from failure to check the traps frequently (Grant et al. 1992). Because ACOs can be checked repeatedly over long periods, rare species can eventually be detected without damage to the natural habitat that could result from repeated searches of natural cover. In conjunction with mark-recapture methods,
ACOs can be used to monitor individual movements and to estimate life- history parameters and abundance. Also, they can be used to investigate the relationship between habitat characteristics and abundance, and differential microhabitat use among species. Because ACOs can be of a standard size and number, and are independent of the amount and type of
CWD and individual searching effort, they should give more reliable estimates of relative abundance across sites that differ in structure than do searches of natural cover.
General methodology -The study sites were limited to southeastern
Vancouver Island, from Goldstrean1 Provincial Park, north to Rosewall
Provincial Park, and west to Lake Cowichan (Fig. 1), I selected nine main
(primary) study sites to monitor with ACOs. Within these sites, I 28
Figure 1. Location of study sites on Vancouver Island, British Columbia,
Canada. Primary study sites with ACOs are indicated by large
black dots and the following notation: RMC = Rosewall,
McNaughton and Cook Creeks; LC = Lake Cowichan; GVW =
Greater Victoria Watershed (4 sites); GS = Goldstream Provincial
Park. Black squares and open squares indicate secondary sites,
with the open squares representing sites that were not searched
on the second and third searches (Chapter 5). Other locations
(Chapter 9) are indicated by black dots and place names. • Woss
Miracle Beach Provincial Park
Denman Is. RMC
Port Albemi Cleland Is. Tofino
i® Portland Is.
126 Carmanah Valiey U ^ S * f v . Provincial Park 125 Victoria Jordan River K> SO 30 established two to six circular plots, each approximately 10 m in diameter.
Within each plot, I haphazardly arranged six 0.3 x 2 m ACOs. Each ACO
consisted of three boards arranged to create multiple microhabitats. I
periodically searched for salamanders under the ACOs, and this is the
primary source of my field data.
For two field seasons, I checked 228 ACOs at approximately two week intervals. In the third field season, ACOs were checked less often. After recording the snout-vent length (SVL), weight and sex, and marking the salamanders by toe-clipping, I released the salamanders at the same spot where they were captured. At one site (Lake Cowichan), some plots were fenced to restrict the movement of salamanders in order to take a census of them. Additional sampling was done by unit-effort searches of surface microhabitats. These included time-constrained searches (TCSs; time- limited equal-effort searches of all available microhabitats) and area- constrained searches (ACSs; area-limited equal-effort searches of all available microhabitats). Detailed within-site sampling was done with randomly placed lxlm quadrats along equally spaced parallel transects at one site (Goidstream), and by within-site comparison of the 10-m-diameter plots at other sites (Lake Cowichan, Greater Victoria Watershed sites). To assess the general distribution and abundance of salamanders on southern
Vancouver Island, an additional 16 secondary sites plus four of the primary sites were searched with TCSs. 31 I collected data on the general habitat features of the primary sites within 12 x 12 m plots centered on the 10-m-diameter ACO plots. Within these plots, I recorded the amount and type of all coarse woody debris
(CWD), and measured the diameter at breast height (DBH) of each tree and identified the species. I also estimated the percentage of bare ground, the percentage area covered by understory plants, and measured and counted
Sword Ferns (Polystichum munitum), as these were thought to provide shelter for salamanders.
I recorded the microhabitat in which each salamander was found.
The ACOs contained two microhabitats: 1) under wood on soil, and 2) under wood on wood. Natural microhabitats searched on TCSs and ACSs included, in part: under logs or other CWD on the ground, under bark on logs and within logs, within Sword Fern bases, in moss, and under rocks. I found some salamanders on the surface when conditions were favorable.
I noted weather conditions and temperature at the time of each search, and supplemented these data with observations obtained from
Environment Canada weather stations.
I investigated microhabitat use in the laboratory and in outdoor enclosures, and interspecific interactions in staged encounters between individual salamanders in the laboratory. 32
D e t a il e d M e t h o d o l o g y
Study sites - There were nine primary study sites (Fig. 1). Four sites were in the Greater Victoria Watershed (GVW; 48°34’ N, 123°39' W, 200-
250 m), three near Rosewall Creek Provincial Park (RMC; Rosewall Creek:
49°27' N, 124°46' W, <50 m; McNaughton Creek: 49°27’ N, 124°46' W, <50 m; Cook Creek: 49°27' N, 124°45' W, <50 m), and one each at Goidstream
Provincial Park (48°28‘ N, 123°32’ W, <50 m), and the University of
Victoria research property (Jeannie Simpson Resource Centre) on Marble
Bay, Lake Cowichan (48°50’ N, 124°10' W, Lot 29,163 m). The GVW sites can be found within the following polygon numbers from the Greater
Victoria Water District Forest Cover Maps: GVW clear-cut: 753; GVW immature: 640; GVW mature: 699/V; GVW old-growth: 648 and 650.
Polygon numbers from Forest Cover Map 92F.47 (Ministry of Forests,
British Columbia) for the Rosewall, McNaughton, and Cook Creek sites
(RMC) are 205 and 207,202, and 194, respectively.
The GVW clear-cut site was logged and burned in 1985 and forest seedlings were planted in 1986. The McNaughton Creek site was logged in
1977 and planted with forest seedlings in 1988. All the other sites were forested, but had been selectively logged (not clear-cut) or otherwise disturbed within the last 100 years. Nevertheless, all the forested sites contained at least a few very old trees (estimated at >200 years) and a similar suite of dominant tree species and understory plants. The dominant trees were Douglas-fir ( Pseudotsuga menziesii) and Western
Hemlock (Tsuga heterophylla), but Western Red Cedar (Thuja plicata), Red
Alder ( Alnus rubra), and Broadleaf Maple (Acer macrophyllum) were
common as well. Little light penetrated the forest canopy, ground
vegetation was generally sparse, and some areas were virtually devoid of
undergrowth. At all the forested sites, Sword Fern { Polystichum
m u n itu m )was usually the dominant ground species, but in some areas
Salal (Gaultheria shallon) was dominant. Logs and woody debris, in
various states of decomposition, were common. The GVW sites were
selected by Forestry Canada to study the effect of forestry practices on carbon
and nutrient dynamics and biodiversity in Douglas-fir and Western
Hemlock coastal forests, and approximately represent a chronoseries [GVW
old-growth (> 150 years), GVW clear-cut (10-20 years), GVW immature (40-
60 years), and GVW mature (80-100 years)].
Sixteen secondary sites and four primary sites were used to assess the
general distribution and abundance of salamanders on southeastern
Vancouver Island. Details of secondary site selection are in Chapter 5.
Artificial cover objects (ACOs). - An individual artificial cover object
(ACO) consisted of a baseboard and two top boards. A large and massive
cover object was needed to resist moisture loss and temperature changes; I judged that a 1.8 m long x 30.5 cm wide x 5 cm thick board to be about the
largest baseboard that could be reasonably carried by one person into the 34 study sites. The space beneath the baseboard was cleared of vegetation, and the board was placed flat on the soil surface. Two 1.8 m long x 15.3 cm wide x 2.5 cm thick top boards were placed on top of the baseboard. Strips of cedar lath nailed to the baseboard separated the top boards from the baseboard in such a way as to create a wedge-shaped space between the top boards and the baseboard (Fig. 2). Rain water dripped through the crack between the two top boards into this space. This created a complex microhabitat so that a salamander could be found on the soil under the baseboard, or between the baseboard and the top boards. Commercial lumber is often treated with fungicides that may harm amphibians, so untreated full dimensional lumber was used. Each baseboard was individually labeled at one end with both a metal tag and a marking pen.
The ACOs contained two basic microhabitats: on soil under the baseboard and on top of the baseboard under the top boards. Although the spaces under the top boards were wedge-shaped in cross section, because of the arrangement of the cedar lath spacers, the height of the space was different for each of the two boards (Fig. 2b). The edge of one top board rested directly on the baseboard and the other edge was raised above the baseboard by the cedar lath spacer in the center of the baseboard by approximately 7 mm. The other board rested on the same spacers in the center of the baseboard (7 mm high), but the outer edge rested on a double layer of cedar lath spacers (14 mm high). 35
Figure 2. Diagram of an artificial cover object (ACO). (a) The baseboard
portion (viewed from above) of an ACO (previously published
in Heyer, et al., 1994, p. 148). Strips of cedar lath (7 x 38 mm, or
0.27" x 1.5") in lengths of 46 cm (18") and 61 cm (24") are attached
with galvanized nails along the middle and one edge of the base
board, respectively. The strips along the edge are doubled, so
that the lath raises above the baseboard about 14 mm (0.55").
The baseboard is placed on the ground with the lath strips facing
up. Top boards (2.5 x 15 x 180 cm, or 1" x 6" x 72") are placed on
top of the lath strips, creating wedge-shaped spaces, (b) Cross-
section of the ACO showing spaces created between the top
boards and the baseboard. 15 cm 30 cm I 61 cm 30 cm 46 cm I \ 115 cm 180 cm
Top boards
spacers
Baseboard "sN
30 cm
o\w 37 ACO Plots - At every primary site except Goldstream, six ACOs were arranged around natural logs and other debris within 10-m-diameter plots
(78.5 m2). Each of the GVW sites and the Lake Cowichan site had six such plots (36 ACOs/site). At the RMC sites, there were two plots per site (12
ACOs/site). At the Goldstream site, 12 ACOs were arranged within a single
150 m2 plot. At all sites, the edge of any one ACO was at least 2 m from the edge of any other ACO. Logs and other large natural cover objects were not
disturbed and the ACOs were placed among them as space allowed. This resulted in a roughly uniform distribution of ACOs within the 10-m-
diameter plots, but haphazardly oriented.
Within a site, I located plots at least 50 m from any road or the forest
edge. Edge effect is thought to be minimal at this distance or greater
(Murcia 1995). For all sites except Goldstream, I established the location of
the first plot by convenience, but the other plots were located at pre
determined distances from the first plot, and from one another, so that
they were established without regard to local variation in habitat. At Lake
Cowichan, ACO plot centers were about 40 m apart and the centers of
fenced plots without ACOs were spaced about 25 to 30 m between the ACO
plots (Fig. 3). At the GVW sites, ACO plot centers were 40 m apart in an
arrangement similar to the ACO plots at Lake Cowichan. At the RMC sites,
where there were only two plots per site, the plots were 100 m apart. At
Goldstream, the single ACO plot was established at essentially the only 38
Figure 3. Location of sample plots at Lake Cowichan. Open circles with
solid perimeter represent fenced ACO plots. Open circles with
dotted perimeter represent unfenced ACO plots. Filled circles
represent fenced plots without ACOs. Numbers indicate plot
numbers. Filled squares and rectangles represent buildings.
Scale is approximate. 39 N
s s s / ✓ ✓ ✓ ✓ \✓ ✓
100 m Lake Cowichan 40 place in the park where 1) salamanders were known to be abundant and 2)
the ACOs were out of view of hikers (see Chapter 4).
Fenced Plots - On June 9-12,1992, when conditions were dry and few
salamanders were at the surface, fences were put around three of the six
ACO plots at Lake Cowichan. Three plots without ACOs were also fenced
at this site (Fig. 3). The purpose of these fences was to prevent immigration
or emigration into or out of the plots so that I could take a census of the population within a plot. Starting on May 17,1993,1 removed all salamanders that were found on nine searches of ACOs and on six searches of natural cover within the plot. These salamanders were kept in 1-liter glass jars at the University of Victoria until the termination of the census
(June 1994) at which time they were returned to the plots.
Each fence enclosed a roughly circular space, 11.3 m in diameter, around all six ACOs of a plot. Thus, each fence enclosed an area of approximately 100 m2. Logs were cut or removed where necessary, but disturbance was kept to a minimum. Trees, stumps or roots occasionally foteed the fence to deviate from a circular path, but an effort was made to compensate for this by enclosing more or less area further along the perimeter so that all the fences enclosed plots of roughly the same area.
The fences consisted of a strip of 10 mil clear plastic, 60 cm wide, supported by a wooden framework of 2x2 stakes (3.8 x 3.8 x 50 cm) joined at the top with 1x2s (2 x 3.8 cm). The lower edge of the plastic was buried in 41 the soil to a depth of about 15 cm where possible, but tree roots sometimes made burying the edge impossible. In all cases, the lower edge was carefully sealed by either stapling it to roots or by packing soil around it.
Terrestrial salamanders are good climbers, so the top edge of the fence was capped with a 15 cm wide strip of aluminum flashing to create an overhang on both sides of the plastic. Salamanders (both P. vehiculum and A. ferreus), were unable to climb over the flashing when encouraged to do so •' a the laboratory. Thus, the fence restricted surface movements, but did not prevent movement through subterranean passages. Searches of enclosed plots and removal of salamanders as part of a census are described in Chapter 3.
Sampling Frequency At- the Goldstream, Lake Cowichan and
Watershed sites, ACOs were put in place in December 1992, and were checked during daylight hours, usually in the morning, about once every 2-
3 weeks from the beginning of March 1992 until the end of September 1993, except when the temperature was below freezing. Some ACO plots were also checked in the spring of 1994. At the RMC sites, ACOs were put in place in February 1993 and checked about once every 2-3 weeks from the beginning of March 1993 until the end of October 1993. 42 Area constrained searches(ACSs) of ACO plots - Three ACSs were
made of all plots in the GVW sites in 1992, and 13 searches of all the plots
at Lake Cowichan in 1992-93. Details are presented in Chapter 3.
ACSs are area-limited equal-effort searches of all available
microhabitats. Equal effort is achieved by through searches of a unit area,
regardless of how long it takes to search the area. On these searches, every
piece of debris on the ground within the search area was overturned, as
well as bark on logs, except where damage would occur to the cover object.
All cover was replaced to its original position after being moved.
Handling of salamanders - Salamanders were weighed to the nearest
0.1 g with a Pesola® spring scale, and measured from the tip of the snout to
the anterior angle of the vent (snout-vent length, SVL) to the nearest 0.1
mm with vernier calipers. If it was raining or windy, accurate
measurements of mass were difficult to obtain, so under these conditions,
the salamanders were not weighed. If eggs were visible through the
abdominal wall, I estimated the number of eggs present, although I did not attempt to verify these estimates by dissection. I sexed adult Plethodon veh icu lu m by sliding a moistened finger anteriorly on the underside of the snout. The protruding premaxillary teeth can be felt in males, but not in females (Ovaska 1987a). No attempt was made to determine the sex of the other species. For each salamander, I recorded the ACO microhabitat (on wood or on soil) and the distance (to the nearest 10 cm) from the marked 43 end of the baseboard. To mark salamanders individually, I clipped a
unique combination of 1-3 toes from each salamander, but never more
than one toe from each foot. I released each salamander at its original location within 15 minutes of capture.
Statistical methods - Calculations were done with Microsoft EXCEL®,
(5.0 for Macintosh™, Microsoft Corporation, Redmond, WA), SYSTAT®
(5.2 for Macintosh™, SYSTAT, Inc. Evanston, IL), or SPSS® for Windows™
(6.0, SPSS Inc., Chicago, IL). Before comparing two means with t-tests, I used the F-test (= variance ratio test, Zar 1984:122-3). If the variances were homogeneous, I used the standard t-test, but if they were not, I used a modified t-test that is calculated with separate variances (Zar 1984:130-1).
Both t-tests assume that the underlying distribution is normal, but are robust to deviations from this assumption. However, the F- test is seyerely and adversely affected by non-normal distributions. To test for normality I used Lilliefors test (Wilkinson et al. 1992). If there were questions about the assumptions of the parametric tests, I used nonparametric tests. If there were multiple t-tests, I reduced the a level to a /n where n was the number of tests (Zar 1984). The minimum level of significance was set at a=0,05.
For all contingency tables, no expected values were less than 1.0 and no more than 20% were less than 5.0 (Zar 1984). I applied the Yates' correction for continuity in %2 tests whenever df=l (Zar 1984). 44
Chapter 3: Population Ecology
The distribution and abundance of terrestrial salamanders can be affected by the availability of resources required by each species (e.g. Fraser
1976a,b; Maiorana 1978; Jaeger 1980b,c), the environmental conditions to which each species is adapted (Heatwole 1962; Jaeger 1971b, 1980a,c;
Maiorana 1976; Wyman and Hawksley-Lescault 1987), interspecific interactions such as competition (e.g. Jaeger 1970,1971a; Wrobel et al. 1980,
Hairston 1980a,b; Nishikawa 1985; Walls 1990) or predation (Keen and
Sharp 1984; Southerland 1986; Hairston 1986), or a combination of these factors (Hairston 1987). A fundamental goal of this study is to identify and explain the distribution and abundance of two similar coexisting species of terrestrial salamanders, P. vehiculum and A. ferreus. By examining the natural history and population ecology of these species among sites and through time, patterns of distribution and abundance can be identified, and the nature of the factors that influence these patterns should be clarified.
Therefore, in this chapter I describe how abundance varies seasonally, among sites, and among species. I also estimate absolute abundance within fenced plots at Lake Cowichan. I make estimates of the surface abundance at Goldstream in the next chapter. 45 Terrestrial salamanders are subject to desiccation, so dispersal and home range size are probably limited by the availability of suitable microhabitats (Jaeger 1980c). Cover objects are used primarily as retreats during daylight hours and when conditions are unfavorable, and are therefore an essential resource for activities that take place on the surface such as feeding and mating. Thus, terrestrial salamanders are not expected to move far from a suitable cover object once it is discovered. This may explain why many species are site-tenacious (e.g. P. vehiculum: Ovaska
1988a; A. ferreus: Davis 1991) or territorial (e.g. P. cinereus: Jaeger 1981;
Jaeger et al. 1982; Mathis, 1990; Aneides aeneus: Cupp 1980; P. jordani and
P. teyahalee: Nishikawa 1985; P. dunni: Ovaska 1993).
M e t h o d s
Details of study site locations, description and use of ACOs, construction of fences, handling of salamanders, and other methodological details can be found iri Chapter 2.
Area-constrained searches (ACSs) of natural cover in ACO plots In - addition to regular searches of ACOs, I searched the natural cover within 6 m of the center of each of the ACO plots. In these ACSs, care was taken not to break open logs or otherwise damage the cover objects. The GVW plots 46 were searched three times in the spring of 1992. Lake Cowichan plots were
searched ten times in the spring of 1992, and three more times in the spring
of 1993. All salamanders found on these searches were marked and
released.
On April 24,1994, at Lake Cowichan and Goldstream Park, in
addition to regular ACO searches, searches of natural cover were done on
the 12 x 12 m plots used for habitat assessment (see Chapter 6). The 12 x 12
m plots were centered on the 10-m-diameter ACO plots. These searches
served as an independent estimate of surface abundance and as a basis of
comparison with the ACO searches done at the same time. For both
searches, P. vehiculum were classified according to size class as hatchling
(<25 mm SVL), juvenile (25 - 40 mm SVL ) or adult (> 40 mm SVL). These
size classes were suggested by size-frequency histograms and are similar to
those used by Ovaska and Gregory (1989). Based on size-frequency
histograms, T. granulosa were classified as either juveniles (< 40 mm SVL)
or adults (> 40 mm SVL).
I examined the possibility that ACOs were attracting more
salamanders than would normally occur in that plot without ACOs. I
compared the mean number of salamanders found per search in fenced
and unfenced ACO plots, including recaptures, before and after the fences
were in place. If there was no difference in the mean number of
salamanders found on searches of the two groups of plots before the fences were in place, then an increase in the number of salamanders in the 47 unfenced plots relative to the fenced plots would indicate that salamanders were attracted to the ACO. Also, I compared the proportion of recaptures previously found under ACOs that moved to natural cover with the proportion of recaptures previously found under natural cover that moved to ACOs.
Starting on May 17,1993, until 18 September 1993, all salamanders found were removed from the fenced plots at Lake Cowichan. These included all animals found on nine searches of ACOs and six searches of all natural cover within the fenced areas. This was done to make cover objects available to salamanders that might be elsewhere because of the presence of salamanders already under the cover objects.
I plotted the cumulative number of salamanders against time to estimate the total population within the fenced plots and compared these figures to similar data from unfenced plots to determine if salamanders were moving into the plots in the absence of fences. This census was previously discussed in Chapter 2.
Body condition - If sites vary in resources or conditions important to salamanders, this might be result in variation in body condition among sites. Thus, I investigated variation in body condition of salamanders among sites. The body condition of each individual was calculated as the deviation (residual) from a regression of ln (mass) on /«(SVL) for all sites combined. Recaptures were not included, and because all sites were 48 sampled throughout the year, seasonal effects were ignored. I tested
among-site variation in mean body condition with ANOVA. Because
either P. vehiculum or A . ferreu s were rare or absent at some sites, not all
sites could be compared for both species. For P. vehiculum, site
comparisons were made among GVW clearcut, GVW immature, GVW
mature, GVW old-growth, Goldstream, Lake Cowichan, and Rosewall and
Cook Creeks combined. For A. ferreus, site comparisons were made among
all GVW sites combined, Lake Cowichan, Rosewall Creek, McNaughton
Creek, and Cook Creek.
Statistical methods - For general comments, see Chapter 2. To
compare relative abundance among sites, I used searches of ACOs that were
less than one week apart among sites. If there were equal numbers of
ACOs at each site, Friedman's test was used (Zar 1984). If the null
hypothesis of equal medians was rejected, observations were considered
independent and pairwise comparisons of medians were done with %2
goodness-of-fit (GoF), rather than with ordered rank sums, because the
number of blocks was always < 15 (Gibbons 1993). If there were unequal
numbers of ACOs at each site, %2 GoF tests were used. Expected frequencies were based on the number of ACOs inspected at each site. Recaptures were not included in these analyses. Contingency tables were used to analyze 49 the relative abundances of species within sites. All searches were used in these analyses, but recaptures were not included.
R e s u l t s
Seasonal variation in surface abundance - Salamanders virtually disappeared from the surface during the coldest part of the winter, and few salamanders were on the surface during the driest part of the summer in
July and August (Figs. 4-7). Visual inspection of Figs. 4-7 suggested that the number of salamanders found per search was greater in 1993 than in 1992, and greater in 1994 than in 1993. To test this hypothesis for 1992 and 1993,1 restricted my analysis to all searches between April 1 and October 1 in both years. Based on the nine searches that had the highest number of salamanders at each site in each year, there was an overall increase in the mean number of salamanders found per search (t(2) )06=2.5, P=0.014). An even more extreme result was obtained when all searches between April 1 and October 1 were used (t(2)/133=3.5, P=0.001). Goldstream, Lake Cowichan and the Greater Victoria Watershed (GVW) had more salamanders per search in 1993 than in 1992, but the difference was not significant for Lake
Cowichan (Table 2.). In late April, 1994, Goldstream had more than twice as many salamanders under ACOs than at any time in the previous two years
(Fig. 4). At both Lake Cowichan and the GVW sites, the mean number of 50
Figure 4. Seasonal variation in number of salamanders, including
recaptures, found under artificial cover objects (ACOs) at
Goldstream Provincial Park, 1992-1994. Each column represents
a search of all ACOs. The height of each column indicates the
number of salamanders found on that particular search. At least
one salamander was found on every search, so every search is
represented by a column. Plethodon vehiculum was the only
species found at this site. Note the change in scale in 1994. 51
50 -T- 1992 Q) l 40 3<0 30 CO «l-i o 20 & 1 0 --
n EL Jan-1 Apr-1 Ju Sep-30 Dec-31
50 CO 1993 I 40 ^ jj 30 ttt CO e 2 0 - - na> ,0 10
- i r r J ] flj Jan-1 Apr-2 Jul-2 Oct-1 Dec-31
120 CO 1994 -§ 100 §
a}
C
Jan-1 Jul-2Oct-1Apr-2 Dec-31 52
Figure 5. Seasonal variation in number of salamanders, including
recaptures, found under artificial cover objects (ACOs) at Lake
Cowichan, 1992-1994. Each column represents a search of all
ACOs (n=36). The height of each column indicates the number
of salamanders found on that particular search. At least one
salamander was found on every search, so every search is
represented by a column. The label "reduced sampling effort"
indicates that only data from the three unfenced plots is shown
after this time because salamanders were being removed from
the fenced plots. The height of each column indicates the
number of salamanders found on that particular search, and the
columns are subdivided by species. Open column = Plethodon
v e h ic u lu m , Stippling = Taricha granulosa. Cross-hatched
column = Ensatina eschscholtzii. S3 VO VO to i-> S3 NJ CO CO o cn o cn o cn number of salamanders 52
a. c n fD Q. to to o cn 0 9 cn cn number of salamanders — N> n co V 3 4* VO to to to co co o cn o cn number of salamanders o cn o cn Jan-1 Apr-2 Jul-2 Oct-1 Dec-31 54
Figure 6. Seasonal variation in number of salamanders, including
recaptures, found under artificial cover objects (ACOs) at the
GVW sites, 1992-1994. Each column represents a search of all
ACOs (n=144). The height of each column indicates the number
of salamanders found on that particular search. At least one
salamander was found on every search, so every search is
represented by a column. In 1994, only 48 ACOs were inspected
on each search, so tnis represents reduced sampling effort. The
height of each column indicates the number of salamanders
found on that particular search, and the columns are subdivided
by species. Open column = Plethodon vehiculum. Stippling =
Taricha granulosa. Cross-hatched column = E n sa tin a
eschscholtzii. 50 -T- 1992 •V 4 0 - -
« 3 0 - -
o 2 0 - -
1 0 --
Jan-1 Apr-1 Jul-1 Sep-30 Dec-31
50 1993 «-( s 40 6 30
(A 20 O) I 1 0 -- g ___ -a!. 4 Jan-1 Apr-2 Jul-2 Oct-1 Dec-31 1993
50 1994 I 40
30 m cn [L 20 §3 ,Q 10 His Jan-1 Apr-2 Jul-2 Oct-1 Dec-31 56
Figure 7. Seasonal variation in number of salamanders, including
recaptures, found under artificial cover objects (ACOs) at the
RMC sites, 1993. Each column represents a search of all ACOs
The height of each column indicates the number of salamanders
found on that particular search. At least one salamander was
found on every search, so every search is represented by a
column. The height of each column indicates the number of
salamanders found on that particular search, and the columns
are subdivided by species. Open column = P lethodon
v e h ic u lu m . Stippling = Taricha granulosa. Cross-hatched
column = Ensatina eschscholtzii. Black = Aneides ferreus. number of salamanders
!-» t-» fO to 03 03 o cn o cn © 01 o cn o 3 — i nr j i 111 1 m 1 1 1 u . 11111 [ 1111 j 1111 i i rrj
h* vt> roa VO n - u> d)
c n T a b l e 2. Comparisons of the mean number of salamanders found per search by site from April 1 to October 1,
1992 and 1993. For Lake Cowichan, only unfenced ACO plots were used (plots 1,3,5). GVW = Greater Victoria
Watershed, all sites combined. x= mean, SD = standard deviation, n= number of searches. Comparisons were made with t-tests, with significant difference (*) at a=0.05/3 = 0.017 (Zar 1984).
1992 1993
Site (no. of ACO) X SD n X SD n t df P
Goldstream (12) 18.9 8.0 13 34.4 9.7 10 4.2 2 1 0.002 *
Lake Cowichan (18) 6.3 2.8 12 8.9 4.9 11 1.6 21 0.226 ns GVW (144) 6.7 5.3 13 23.0 12.9 9 4.1 20 0.001 *
oocn 59 salamanders was greater in 1994 than in 1993, but the difference was not statistically significant (Table 3).
Variation in abundance among sites - Abundances of salamanders
(all species combined) varied greatly among sites (Table 4, %z goodness-of-fit
(GoF), x2=1081.4, df=8, PcO.OOl; Fig. 8). There were many fewer salamanders captured in the clearcut sites compared to tire forested sites
(Table 5, GVW sites, Friedman's test, %r2=29.2, df=3, PcO.OOOl; Table 5, RMC sites, Friedman's test, Xr2=8.7, df=2, P=0.013). However, there were significant differences in the numbers of salamanders (all species combined) among forested sites as well (Table 4, %2 GoF, %2=768.6, df=6,
PcO.OOl; Table 5, Lake Cowichan and Goldstream, x2=259.0, df=l, PcO.OOl).
When the Goldstream site was excluded from the analysis, there were still significant differences in the relative abundances of salamanders among forested sites (Table 4, x2 GoF, x2=27.4, df=5, PcO.OOl). However, if both
Goldstream and Lake Cowichan were excluded from the analysis, there were no significant differences among forested sites (Table 4, x2 GoF, %z=>6.2, df=4,0.10>P>0.25).
Variation in abundance among species - At most sites, P leth o d o n veh icu lu m was the most common salamander, but relative abundances T a b l e 3. Comparisons of the mean number of salamanders found per search from April 8 to May 15,1993 and
1994. For Lake Cowichan, only unfenced ACO plots were used (plots 1,3,5). For the Greater Victoria Watershed
(GVW) sites, four plots (2,3,5, 6) in the GVW old-growth site and four plots (1,2,3,4) in the GVW immature site were used. x= mean, SD = standard deviation, n= number of searches. Comparisons were made with t-tests, with significant difference at a=0.05/2 = 0.025 (Zar 1984). The Mann-Whitney U test gave similar results.
1993 1994
Site (no. of ACO) x SD n x SD n t df P Lake Cowichan (18) 13.0 3.4 4 23.5 7.2 4 2.6 6 0.039 ns GVW (48) 15.0 7.0 4 22.5 1.9 4 1.2 6 0.29 ns
OsO TABLE 4. The number of salamanders found under ACOs on 8 searches of primary sites between April 8,1993 and August 12,1993. Each search included all sites and took from 2 -7 days to complete (x=3.8 days, SD=1.5). For Lake Cowichan, unfenced plots only were used. The number of salamanders does not include recaptures within the interval.
no. of no. of P le th o d o n A n e id e s E n sa tin a T a rich a total no. of Site searches ACOs v e h i c u l u m fe r r e u s eschscholtzii g r a n u lo s a salamanders
GVW clearcut 8 36 6 0 0 0 6
GVW immature 8 36 52 1 1 9 63
GVW mature 8 36 41 1 2 2 46
GVW old-growth 8 36 32 0 6 4 42
Lake Cowichan 8 18 34 0 1 18 53
Coldstream 8 12 179 0 0 0 179
Rosewall Creek 8 12 8 14 0 0 22
McNaughton Creek 8 12 0 2 1 0 3
Cook Creek 8 12 3 14 0 1 18
ON Figure 8. Salamander abundance among nine sites on Vancouver Island B.
C., based on eight searches from April 8,1993 - August 12,1993
(Table 4). The column height represents the number of
salamanders per ACO for each site. Sites: GVWim = GVW
immature; GVWma = GVW mature; GVWog = GVW old-
growth; GS = Goldstream; LC = Lake Cowichan; RC = Rosewall
Creek; MC = McNaughton Creek; CC = Cook Creek. The total
number o e salamanders represented in this diagram is n=432. Plethodon vehiculum
Aneidesferreus
Taricha granulosa
GVWccGVWma Ensatim eschscholtzii GVYVim GVWog TABLE 5. The number of salamanders found under ACOs on matched searches of primary sites. Between March 4,1992 and September 26,1993,30 searches were done of the four GVW sites; each search took one day to complete. Between March 29,1992 and September 18,1993,29 searches were done of the Lake Cowichan and Goldstream sites; each search of the two sites took place within a period of seven days (x=2.4 days, SD=1.7). At Lake Cowichan, unfenced plots only were used. For the RMC sites, 12 searches were done between March 9, 1993 and October 19,1993 and each search of the three sites was completed in one day. The number of salamanders does not include recaptures within the interval.
species no. of no. of P le th o d o n A n e id e s E n s a tin a T a rich a total no. of Site searches ACOs v e h i c u l u m fe r r e u s eschscholtzii g r a n u lo s a salamanders
GVW dearcut 30 36 15 0 0 0 15 GVW immature 30 36 113 3 5 12 133 GVW mature 30 36 83 5 8 10 107 GVW old-growth 30 36 35 0 10 14 111
1 Lake Cowichan 29 18 110 0 1 55 166 1 Goldstream 29 12 432 0 0 0 432
Rosewall Creek 12 12 14 29 1 0 44 McNaughton Creek 12 12 0 5 1 0 6 Cook Creek 12 12 7 22 0 3 32
£ 65 varied greatly among species (Fig. 9). Only P. vehiculum was found under
ACOs at Goldstream, but I have found A . ferreus elsewhere in the park, and an E. eschscholtzii was found in the stomach of a Common Garter
Snake, Thamnophis sirtalis, in this area (P. T. Gregory, pers. comm.). At
Lake Cowichan, both P. vehiculum (proportion of salamander species at this site: 67%, n=231) and Taricha granulosa (32%, n=110) were common under ACOs, but I found just one E. eschscholtzii and no A . ferreu s or
Ambystoma macrodactylum. However, these species are known from other searches of this site (Fig. 10). At Lake Cowichan, the ratio of P, v e h ic u lu m to T. granulosa was significantly different from the ratio in the forested GVW sites (%2=44.3, df=3, P=0.0001). However, among the forested
GVW sites, the ratios of P. vehiculum (85%-87%, n=267) to T, granulosa
(8%-10%, n= 31; Fig. 9) were similar (%2=0.29, df=2, P=0.87). Also, the relative abundance of P. vehiculum, T. granulosa, and £, eschscholtzii (2%
-12%, n= 23) was similar among the forested GVW sites (%2=8.5, df=4,
P=0.07). Aneides ferreus (0%-3%, n=6 and Ambystoma macrodactylum
(0%-2%, n=3) were relatively rare at these sites. In the GVW clearcut, only
P. vehiculum (n=15) was found under ACOs, although I found A , ferreu s and E. eschscholtzii on searches of natural cover (Fig. 10).
The relative abundance of species found under ACOs were very different at the RMC sites (Fig. 9). Aneides ferreus (69%-86%, n=62) was more abundant than P, vehiculum (0%-29%, n-17), and although more 66
Figure 9. Proportion of salamander species based on searches of ACOs,
1992-1994. Columns indicate the proportion of each species by
site, not including recaptures. Species are arranged from left to
right in the following order : P v = Plethodon vehiculum, Tg =
Taricha granulosa, A f= Aneides ferreus, Ee = Ensatina
eschscholtzii, Am = Ambystoma macrodactylum. The legend is
for all three plots. Numbers at the top of the columns indicate
the number of individuals found. Search effort was equal
among the Greater Victoria Watershed (GVW) sites, and equal
among the Rosewall, McNaughton and Cook Creek sites, but not
among other sites. indicates that the species has not been
found at that site on these or other searches. 67
100%
80% — 85
40% —
20% —
0% E%££li GVW GVW GVW GVW clearcut im m ature mature old-growth
C'24 100% □ P v n ■ A f 80% N Ee 231 HE A m 60%
40% 110
20%
0%- 0 4 ? 0 Lake Cowichan Goldstream
Rosewall McNaughton 68
• Figure 10. Proportion of salamander species based on searches of natural
cover in ACO plots, 1992-1994. Ali available microhabitats were
searched. Columns indicate the proportion of each species by
site, not including recaptures. Species are arranged from left to
right in the following order : Pv = Plethodon vehiculum, Tg =
Taricha granulosa, A f = Aneides ferreus, Ee = Ensatina
eschscholtzii, Am = Ambystoma macrodactylum, The legend is
for all three plots. Numbers at the top of the columns indicate
the number of individuals found. Search effort was equal
among the Greater Victoria Watershed (GVW) sites, and equal
among the Rosewall, McNaughton and Cook Creek sites, but not
among other 's. indicates that the species has not been
found at that site on these or other searches. 69
1 0 0 % -n 45 29 45 1 2 80% -
60%
40% -
20% 1 I 0 1 ? 1 1 0% I m • sao 0 Oi GVW GVW GVW 1 GVW clearcut im m ature mature old-growth
100% -r-
80% 477
60%
40%
20% —
0% Lake Cowichan Goldstream
Rosewall McNaughton Cook 70 individual P. vehiculum were found at Rosewall Creek than at Cook
Creek, the relative abundance of these species was similar between these
two sites (xc2=2.6, df=l, F=0.10). Taricha granulosa (0%-3%, n=l) and E.
eschscholtzii (0% 2%, n=l) were rare. Ambystoma macrodactylum was not
found at the RMC sites.
The relative abundance of species found on searches of natural cover
was similar to that found on searches of ACOs (compare Figs. 9 and 10).
Plethodon vehiculum was the most abundant species at Goldstream and
the GVW sites, with the other species relatively rare or absent. At the
GVW sites, there was no difference in the ratio among species found
between the two kinds of sampling (%2=5.0, df=2, P=0.08). Although P.
ve h ic u lu m was the most abundant species at Lake Cowichan, T. granulosa
was common compared to other species. However, relatively more T. granulosa were found under ACOs than were found on searches of natural
cover at Lake Cowichan compared to the number of P. veh icu lu m found
on the two kinds of searches (xcz=8.9, df=l, P=0.003).
The probability of finding P. vehiculum at Lake Cowichan or the
GVW, with either a search of 36 ACOs (« 60 minutes) or searches of natural
cover in three 10-m-diameter plots (~ 60 minutes), was close to 1.0 (Table 6).
The chances of finding rarer species using ACOs was less than with
searches of natural cover, but all species were eventually discovered with
ACOs, but not at all sites. T a b l e 6. Probability of finding at least one individual of a species on searches of ACO and searches of natural cover. Based on tuned searches at Lake Cowichan and Greater Victoria Watershed (GVW) 1992-93. Searches of the natural cover in three 10-m-diamet plots and searches of 36 ACOs are assumed to each take 60 minutes. Number in parentheses after search type indicates the number of 60 minute searches. ACO searches were selected to match searches of natural cover by date to control for seasonal variation, except for last row which includes 34 ACO searches in the GVW and 41 ACO searches at Lake Cowichan. P v = Plethodon vehiculum; A f = Aneides ferreus; Ee = Ensatina eschscholtzii, Tg = Taricha granulosa; Am = Ambystoma macrodactylum.
site search type (no.) P v A f Ee T g A m
GVW natural (6) 1.00 0.33 0.33 0.67 0.00
GVW ACO (6) 1.00 0.33 0.50 0.50 0.00
Lake Cowichan natural (13) 1.00 0.23 0.23 0.77 0.00
Lake Cowichan ACO (13) 0.92 0.00 0.00 0.62 0.00
Lake Cowichan + GVW natural (19) 1.00 0.26 0.26 0.73 0.00
Lake Cowichan + GVW ACO (19) 0.94 0.12 0.16 0.59 0.00
Lake Cowichan + GVW ACO (75) 0.96 0.11 0.29 0.68 0.03 72
Population structure - Size-frequency histograms of P. vehiculum by
season, based on captures under ACOs at Goldstream in 1992, suggest that
individuals in their first year of life form a distinct size class, but these size
classes are not obvious in the 1993 histograms from the same site (Fig. 11).
Similarly, size-frequency histograms, based on captures under ACOs at
Lake Cowichan, suggest three size classes for the summer and fall of 1992 and the spring of 1993, but size classes were unresolved in the other seasons (Fig. 12). A size-frequency histogram based on ACO captures from the spring of 1992 through the summer of 1993 at Lake Cowichan failed to show any distinct size classes (Fig. 13a). However, a size-frequency histogram based on surface searches of natural cover made at the same time revealed three distinct size classes (Fig. 13b). Comparison of these histograms suggest that the smaller size classes may avoid using ACOs.
Contingency table analysis comparing the distribution of salamanders among four arbitrary size classes (<25, 25-35, 35-45, >45 mm SVL) against all searches of ACOs and surface searches support this hypothesis (%2 = 15.612, df=3, p=0.0014). A similar result was obtained from the GVW sites (Fig.
13c,d; r =11.645, df=3, p=0.0087).
Size-frequency data from the search of ACOs and natural cover on
April 24,1994 at Goldstream Park and Lake Cowichan suggest a similar pattern. Combining the data from the two sites results in a statistically 73
Figure 11. Size-frequency histograms by season for Plethodon vehiculum
found under ACOs at Goldstream Provincial Park, 1992-94.
Males are represented by cross-hatched columns, females and
juveniles by white columns. For individuals captured more
than once in a season, the mean SVL was used. 74
Spring 1992 Spring 1993 20-, 20-,
1 5 -
1 10- Jaf :
T l I I I r TTTTTTTT'I I I 18 22 26 30 34 40 44 48 52 56 SVL (mm) SVL (mm)
Summer 1992 Summer 1993 25-, 2 0 -,
5 - 5 -
SVL (mm) SVL (mm)
Fall 1992-W inter 1993 Fall 1993-W inter 1994 12 —,
2 - H i
SVL (mm) SVL (mm) 75
Figure 12. Size-frequency histograms by season for Plethodon vehiculum
found under ACOs at Lake Cowichan, 1992-94. Males are
represented by cross-hatched columns, females and juveniles by
white columns. For individuals captured more than once in a
season, the mean SVL was used. 76
Spring 1992 Spring 1993 10-i 12-,
§
4 - iiiii 18 22 26 30 34 40 44 48 52 56 SVL (mm) SVL (mm)
Summer 1992 Summer 1993 6 -,
5
4
g 3 S' \ sJ I 2 * 2 - 1 a ! 0. 18 22 26 30 34 40 44 48 52 56 SVL (mm) SVL (mm)
Fell 1992 Fall 1993 - Spring 1994 2 5 -,
1 0 -
SVL (mm) SVL (mm) 77
Figure 13. Size-frequency histograms for Plethodon vehiculum found
under ACOs and natural cover at Lake Cowichan and the
Greater Victoria Watershed (GVW), 1993-1994. Males are
represented by cross-hatched columns, females and juveniles by
white columns. For individuals captured more than once in a
season, the mean SVL was used. a. Found under ACOs at Lake
Cowichan, n=192. b. Found on searches of natural cover at Lake
Cowichan, n=504. c. Found under ACOs at GVW, n=281. d.
Found on searches of natural cover at GVW, n=129. ACO ACO 25- (Lake Cowichan) 35-, (GVW)
20-r o ' 15- 3g : c r cr 2 10- 10 5 - otrrhrr z iiiiii 16 20 24 28 32 36 42 46 50 54 58 16 20 24 28 32 36 42 46 50 54 58 SVL (mm) SVL (mm)
natural cover (Lake Cowichan) natural cover 70 1 4 1 (GVW) 12'
10 -
U S 8 S'tu 6:
20 4- m 24-i I. i l l 0 i l l 16 20 24 28 32 36 42 46 50 54 58 16 20 24 28 32 36 42 46 50 54 58 SVL (mm) SVL (mm) 79 significant difference in the distribution of juveniles and adults between the two types of searches (xc2=8.84, df=l, p=0.003).
These results suggested that it would be useful to look at the population structure of animals collected within the fenced ACO plots. In these plots salamanders were either found under ACOs or on searches of natural cover. There was a significant difference between the two kinds of searches in the number of juveniles (SVL< 40 mm) and adults (SVL > 40 mm) (xc2=34.61, df=l, p=0.0001, Fig. 14).
For A . ferreu s caught under ACOs at Rosewall Creek and Cook
Creek, size-frequency histograms suggest three size classes in the spring and summer, but fall hatchlings were not found (Fig. 15a,b,c). A size-frequency histogram for 1993 shows two peaks with modes at 36 and 50 mm SVL (Fig.
15d).
Because relatively few T. granulosa were captured (299 individuals),
I combined data from the GVW sites (41 individuals) and Lake Cowichan
(258 individuals) sites. Size-frequency histograms (Fig. 16a,b) show two or three size classes, but whether or not these represent age classes is unknown.
Body condition - The relationship between body mass and length
(SVL) for P. vehiculum and A , ferreus is illustrated in Fig. 17. There were no amorig-site differences in body condition for either species (P. 80
Figure 14. Size-frequency histograms forPlethodon vehiculum found at
Lake Cowichan in fenced ACO plots, 1992-1994. For individuals
captured more than once in a season, the mean SVL was used,
a. Salamanders (n=81) found on searches of ACOs within fenced
plots, b. Salamanders (n=169) found on searches of natural
cover within fenced ACO plots. 81
ACOs 16 14 ^
12 - 10 u § 8 §< 0) 44 6 4 ^
m m 2 - m m m 0 TTTTI 18 22 26 30 34 38 42 46 50 54 58 62 66 SVL (mm)
natural cover 16
t* io
18 22 26 30 34 38 42 46 50 54 58 62 66 SVL (mm) 82
Figure 15. Size-frequency histograms by season for Aneides ferreus found
under ACOs at the RMC sites, 1993. For spring, n=27; summer,
n=52; and fall, n=44. For individuals captured more than once
in a season, the mean SVL was used. 83
Spring 1993 6 i 5 - 4- a>c 3-i £ 2 -
n i i i i i i i i i i i i 20 24 28 32 36 40 44 48 52 56 60 SVL (mm)
Summer 1.993
i I I 20 24 28 32 36 40 44 48 52 56 60 SVL (mm)
Fall 1993 12-,
GU crS 6- Si * 4 -
SVL (mm) Figure 16. Size-frequency histograms for Taricha granulosa found under
ACOs at Lake Cowichan and the GVW sites. For individuals
captured more than once in a season, the mean SVL was used.
For spring and summer 1992, n=93; fall 1992, n=81; spring and
summer 1993, n=88; spring 1994, n=39. Spring and Summer 1992 Spring and summer 1993 25 -i
2 0 - ojc 3 4>
«« SS 22 26 30 34 38 42 46 50 54 22 26 30 34 38 42 46 50 54 58 62 SVL (mm) SVL (mm) 86
Figure 17. Mass-length relationships of Plethodon vehiculum and A n e id es
fe r r e u s . 87
4-, Plethodon vehiculum • • 3.5 n=1161 3 2.5 ^ >59 CA 2 6 1.5 -f
1-^ 0.5-=
0 “T" ~l------\~ ~ r ~ 10 20 30 40 50 60 SVL (mm)
5 1 Aneides ferreus n=69 • 4 -
CA CA S 2-1 «*a * '
0 - | | | , ! j 20 30 40 50 60 70 SVL (mm) 88 v e h ic u lu m ,FM154 = 0.78, P = 0.58; A. ferreus, F4 64 = 0.72, P = 0.58), although the sample size for P. vehiculum at the Rosewali creek sites (n-6), and for
A . ferreu s at Lake Cowichan (n-4) were very small.
Movement across fences - There were 157 animals that were marked and released (4 A . fe rreu s, 1 E. eschscholtzii, 115 P. veh icu lu m ,and 37 T. g ra n u lo sa) within 5 m of the outside of the fences. There were 159 recaptures of 98 individuals in all searches of fenced plots at Lake
Cowichan. Of these, only two animals (both P. veh icu lu m) apparently crossed fences. One animal was found in plot 6 (fenced) on October 10,
1992, March 7,1993, and April 13,1993. It was then found in plot 3
(unfenced) on May 31,1993, and in plot 6 again on April 13,1994. These plots are at opposite ends of the block of plots (Fig. 3), so this apparent movement is probably spurious, due to an error in either reading or recording the toeclip mark. The second animal was found outside the fence at plot 6 on April 19,1993, but inside the fence on May 17,1993. Thus, a few salamanders may have moved into or out of the fenced plots, but overall, there was very little movement of salamanders across fences.
M o v e m e n ts - In general, P. veh icu lu m and A . ferreu s were site- tenacious. For P. veh icu lu m ,73% of the first recaptures were under the same AGO and there were no differences in site tenacity among four size classes (<25,25-35,35-45, >45 mm SVL; 4.23, df=3, P=0.24). For A. 89 ferreu s, 80% of the first recaptures were under the same ACO and there was no difference in site tenacity between juveniles and adults (/c2=1.64, df=l,
P=0.20).
On 15 occasions, searches at Lake Cowichan included searches of natural cover within plots as well as searches of ACOs. For P. vehiculum, counting only the first recapture of any individual, the proportion of recaptures previously found under ACOs (n= 37) that were found under natural cover was 13.5%. The proportion of recaptures previously found under natural cover (n=12) that moved to ACOs was 17%, but the difference between the proportions was not significant (xc2=0.041, df=l,
P=0.84). Thus, the proportion of recaptures previously found under ACOs that moved to natural cover was the same as the proportion of recaptures previously found under natural cover that moved to ACOs.
Population size in fenced and unfenced ACO plots In the - fenced
ACO plots, some P. vehiculum were still being caught in 1994, but the upward trend in cumulative numbers of previously uncaught salamanders may have begun to reach an asymptote (Fig. 18a). In contrast, unfenced
ACO plots showed a relatively greater increase in the number of new salamanders caught in the spring of 1994 (Fig. 18b). There was a significant difference in the mean number of new individuals found per search of
ACOs in 1994 between the two unfenced plots with the smallest increase in 90
Figure 18. Cumulative number of salamanders caught in unfenced and
fenced plots at Lake Cowichan, 1993-94. Recaptures not
included, a. Fenced ACO plots. Filled circle - Plot 2; open square
= Plot 4; filled triangle = Plot 6. b. Unfenced ACO plots. Filled
circle = Plot 1; open square = Plot 3; filled triangle ••= Plot 5. c.
Fenced plots without ACO. Filled circle = Plot 7; open square =
Plot 8; filled triangle = Plot 9. 91
1 2 0 - i fenced ACO plois
100 - QJ & 80
rs 40- 3 20
Apr-6 Oct-23 r ~ May-11 ' Nov-27 ' Jun-15 1992 1993 1994
120 unfenced ACO plots y 100 -
8 0 -
60- 4 0 -
2 0 -
Apr-6 Oct-23 May-11 Nov-27 1992 1993
120-n fenced plots without ACO 100 2
40 2
Apr-6 Oct-23 May-11 Nov-27 Jun-15 1992 1993 1994 92 numbers (Plots 3 and 5, n=14 and n=17, respectively; x =3.9, SD=2.2) and the three fenced ACO plots (Plots 2,4, and 6, n=7, n=8, m d n=9, respectively; x =2.0, SD=1.6; t(1)18=2.23, P=0.02), but not in 1992-1993 (ACO fenced: x=0.7,
SD=0.8; ACO unfenced: x=0.7, SD=1.0; t(1)13g=0.07, P=0.5). However, one unfenced plot (plot 1, Fig. 18b) had a significantly higher mean number of new individuals per search compared to the other unfenced ACO plots from 1992-1994 (plot 1: x=2.4, SD=2.1; plots 3 and 5: x= l.l, SD=1.6; t(1)94=3.4,
P=0.0006).
After the fences were installed, up until the time when salamanders were removed from the fenced plots (May 17, 1993), there was no difference in the mean number of salamanders caught per search between fenced and unfenced ACO plots (ACO fenced: x=10.0, SD=9.7; ACO unfenced: x=6.3,
SD=6.1;t(2)48=2.01,P=0.11).
For T. granulosa, the mean number of salamanders found in fenced plots was less than the number of salamanders found in unfenced plots
(fenced: x =0.5, SD=1.0; unfenced: x=1.0, SD=1.4; t(2)m=2.6, P=0.01). In 1993, fewer individual T. granulosa were found in fenced ACO plots than in unfenced ACO plots (Table 7; t(2)4=3.9S,,P=0.016). In 1994, there was a difference between fenced and unfenced ACO plots (t(2)4=l,17, P=0.03). In most plots, there were only 2-6 new individuals/plot captured in 1994, but plot 6 contained 11 new individuals (Table 7). Table 7. Number of individual Taricha granulosa found in fenced and unfenced plots at Lake Cowichan, 1992-1994. Numbers in columns indicate the number of newly caught individuals in that year.
plot 1992 1993 1994 total
1 ACO 5 8 6 19 (unfenced)
3 ACO 18 13 6 37 (unfenced)
5 ACO 2 15 2 19 (unfenced)
2 ACO 7 2 6 15 (fenced)
4 ACO 8 1 5 14 (fenced)
6 ACO 19 4 11 34 (fenced)
7 (fenced) 14 8 0 22
8 (fenced) 4 3 0 7
9 (fenced) 9 8 0 17 94 D e n sity - Based on cumulative frequency plots described above, the total number of individual P. vehiculum in each of the fenced plots with
ACOs was 63,50, and til (x=58.0) salamanders (plots 2, 4, and 6, respectively), and in each of the fenced plots without ACOs was 19,30 and
31 (x=26.7) salamanders (plots 7,8, and ± .' pectively, Figs 18b,c), This
converts to a minimum mean density of 0.6 salamanders/m2 in the fenced plots with ACOs, and to 0.3 salamanders/m2 in the fenced plots without
ACOs.
The maximum number of P. vehiculum found on the surface in any fenced ACO plot at any particular time, searching all cover and ACOs, was no more than 24% of the animals estimated to be in the plot by the cumulative numbers of individuals caught.
The search of natural cover on April 24,1994 in the 12 x 12 m habitat assessment plots at Lake Cowichan produced 53 P. veh icu lu m and 5 1. g ranulosa. The ACO search on the same day produced 25 P. vehiculum , one T. granulosa and one E. eschscholtzii. This results in a surface density of 0.1 P. veh icu lu m / m2 at Lake Cowichan. If this represents 24% of the population, then the total density would be 0.4 P. v e h ic u lu mm2 / if all the salamanders were at the surface. At Goldstream Park on the same day, the search of natural cover produced 54 P. vehiculum and 106 were found under ACOs. This results in a surface density of 0.56 P. ve h ic u lu m/ m2 at the ACO plot in Goldstream park. 95
D isc u ssio n
Seasonal variation in surface abundance - As I pointed out in
Chapter 1, surface activity in terrestrial salamanders is important because it
affects foraging and mating behavior. For example, Frazer (1976a) showed
that little or no feeding takes place below the surface in P. cinereus and P.
hoffm ^ ii. Thus, the ability of a terrestrial salamander to grow and reproduce is probably directly related to the amount of time it spends near the surface (Houck 1977; Jaeger 1980b; Semlitsch and West 1983).
Patterns of surface activity in terrestrial salamanders are strongly influenced by climate (Houck 1977). In the eastern United States, most rainfall occurs from late March through October, but during the winter
(December through March), temperatures are near or below freezing.
Thus, eastern terrestrial salamanders in upland areas tend to be active from
April through October, but are inactive during the winter. In the western
United States, rains usually begin in the autumn (September or October) and continue through the relatively mild winter until spring (April or
May). Therefore, most western species (especially in California) are active from October through April, but are inactive through the relatively dry summer.
In Oregon, Peacock and Nussbaum (1973) found P. vehiculum on the surface in all months except August. On Vancouver Island, where winter conditions are somewhat more severe, Ovaska and Gregory (1989) 96 found that surface activity in P. vehiculum was confined to the autumn
(September - November) and spring (March - June), but occasional salamanders were seen on mild winter days, suggesting a direct role for temperature in influencing activity. Below-freezing temperatures in the winter, and dry conditions in July and August, probably forced the salamanders underground. However, I had found that although A . ferreus also disappeared during the coldest part of the winter, individuals were fairly abundant even during the driest part of the summer (Davis 1991).
These different patterns of surface activity may be related to microhabitat use. I found that the soil ruder most natural cover on the ground became dry during the summer, but wood under the bark on larger logs remained moist throughout the year (Davis 1991). Because P. ve h ic u lu m were largely absent from the bark-on-log microhabitat, and their usual microhabitat under coarse woody debris (CWD) on the soil was relatively dry, they were difficult to find in July and August. In contrast, A. ferreu s was common in the relatively moist conditions under bark-on-log microhabitat. Microhabitat use is discussed in detail in Chapter 7.
That local moisture conditions can influence seasonal activity patterns was demonstrated by Rosenthal (1957). In a natural area in
California he could not find individuals of Aneides lugubris near the surface during the dry season (June - October), but found that they remained near the surface of masonry walls in an urban area if the walls were artificially moistened. 97 Although the aquatic life history ofTaricha granulosa has been well
studied (e.g. Chandler 1918; Efford and Mathias 1969; Oliver and McCurdy
1974; Taylor 1984), and Pimentel (1960) investigated movements into and out of ponds, I know of no detailed studies of the terrestrial ecology of this species. Surface abundance of T. granulosa was reduced during the driest part of the summer and the coldest part of the winter. P lethodon v e h ic u lu m and A . fe rre u s had a similar pattern of surface abundance, but there was considerably less variation in surface abundance of T. granulosa relative to the other species. One possible explanation for this is that oecause T. granulosa have a larger body size and thicker skin relative to the other species, and thereby a reduced surface to volume ratio and better resistance to dehydration, under desiccating conditions they are better able to resist moisture loss and so can remain on the surface longer than the plethodontids. This suggests that a larger proportion of the T. granulosa population is on the surface at times when temperature and moisture have caused many P. vehiculum to disappear underground.
Variation in abundance among sites The - density of terrestrial salamanders can vary hugely from one site to the next, but it should be noted that the abundances reported in Figs. 4-7 cannot be compared directly across all sites. The Goldstream site yielded more salamanders at any particular time than any other site, even though the sample was based on only 12 ACOs (Fig. 4). The Greater Victoria Watershed (GVW) in Fig. 6 98 represents 144 ACOs divided among 4 sites, one of which was a clearcut, whereas the RMC sites (Fig. 7) had 36 ACOs divided equally among three sites, one of which was a clearcut. The Lake Cowichan site (Fig. 5) had 36
ACOs. Thus, the Goldstream site supports a much larger population of salamanders than any of the other sites (Fig. 8). In contrast, there were about equal numbers of salamanders among the three forested GVW sites.
This suggests that abundance may be similar across wide areas and that areas of relatively high abundance are local and patchy. I investigate the extent of the dense population of P. vehiculum at Goldstream in Chapter 4.
Variation in abundance among species A -striking result of this study is the extreme difference in the ratio of P. veh icu lu m to A . ferreu s between the forested RMC sites and the other forested sites. This may represent a difference in local site conditions such as amount and size of
CWD, a geographical difference that may be related to climatic conditions, metapopulation phenomena related to landscape effects, chance historical events, or a combination of any or all of these factors. The influence of local site conditions, climate, weather, and gross habitat features are explored in Chapter 6. Here I discuss the possible effects of metapopulation dynamics.
Metapopulation effects Fragmentation - of natural habitats and their plant and animal populations has led to considerable theoretical and 99 practical interest in metapopulation dynamics (e.g. Hanski 1991,1994;
Hanski and Gilpin 1991; Hansson 1991; Harrison 1991; Howe and Davis
1991; Hanski and Thomas 1994; Hanski et al. 1994; Schemske et al 1994;
Diffendorfer et a l 1995; Watkinson and Sutherland 1995). Levins (1970) defined a metapopulation as a 'population of populations', an assemblage of local populations connected by occasional dispersal. Small, isolated populations may be subject to stochastic extinction, but a metapopulation may persist due to a balance between local extinctions and recolonizations
(Hanski 1991). Pulliam (1988) noted that populations of most species occupy a mosaic of habitat patches that vary in quality. Populations in these habitat patches can be divided into sources and sinks, depending on whether or not local reproduction is sufficient to balance mortality. In a source population at equilibrium, natality is greater than mortality and emigration is greater than immigration. In a sink population, natality is less than mortality and equilibrium is maintained by immigration from one or more source populations (Watkinson and Sutherland 1995).
Many of the classic examples of metapopulations are derived from studies of amphibians (e.g. Gill 1978; Sinsch 1992; Gulve 1994 ). However, metapopulation dynamics have not been demonstrated for terrestrial salamanders, but aspects of their natural history suggest that such a model might be appropriate. Aneides ferreus eggs are suspended in cavities under bark on logs, and in cavities within logs, but P. vehiculum lays eggs in burrows or cavities below the surface (Dunn 1942; Guppy 1946; Storm 1947; 100 Davis 1991; Leonard et al. 1993). This suggests that logs of a particular size and decay class may be important in maintaining a source population of A. fe rre u s, but are of little or no importance to P. vehiculum. Thus, a location that contains a suitable nesting log for A . ferreu s may be a source area in one decade, but may become a sink area in the next as the nesting log passes beyond some optimum decay class [analogous to Gill's (1978) spatially shifting reproductive source ponds for the Red-spotted newt,
Notophthalmus viridescens]. If such ephemeral nesting logs within the same stand are of different ages, source areas could shift from log to log and populations of A . ferreus should persist indefinitely. However, where the result of logging is relatively even-age forests that contain uniform types, amounts, and decay classes of CWD, or where stands of original forests are small and separated by clearcuts, populations of A . ferreu s may decline, but
P. vehiculum might be relatively unaffected. Such metapopulation dynamics do not explain the high densities of A . ferreu s on small isolated islands adjacent to Vancouver Island, nor why P. veh icu lu m is absent from these islands. Also, it appears that P. vehiculum is relatively scarce where
A . ferreu s is abundant.
Populations of salamanders were reduced in clearcuts, but there was no difference among the three forested GVW sites. This suggests that small-scale local disturbance has no long-term population consequences, but leaves open the question of landscape and metapopulation effects.
Also, because the GVW sites are small, contiguous with sites of various 101 ages, and except for the GVW clearcut, contain trees of various ages, they
represent a chronoseries only approximately. For example, the GVW
immature and old-growth sites are part of the same contiguous forest and
represent only local variation within that forest.
Population structure - Ovaska and Gregory (1989), who searched all
available surface microhabitats in plots in Goldstream Park, found that P.
v eh icu lu m juveniles formed a distinct size-class throughout their first year
of life. In an earlier study (Davis 1991), I searched under bark on logs and within logs at the Rosewall and Cook Creek sites, and obtained similar results for A. ferreus. For both species, the size-frequcrtcy hi stograms showed a second peak that probably represented salamanders in their second year of life. The second peak tended to merge into the third peak, which probably consisted of several older age classes. Size-frequency histograms of P. vehiculum ,based on surface searches from Lake
Cowichan and the GVW sites, suggest the same pattern (Figs. 13b,d; 14).
However, size-frequency histograms based on the ACO searches generally failed to show the first or second peak (Fig. 14). This is evidence that the smaller size classes of P. veh icu lu m do not use ACOs as much as the larger size classes. For A. ferreus, the size-frequency histograms (Fig. 15) were similar to those I reported elsewhere, based on searches of natural microhabitats (Davis 1991). However, the fall hatchlings are entirely missing from the ACO searches and the smaller size classes may be 102 underrepresented in the spring. Thus, for this species also, the smaller size classes are poorly represented in samples based on searches of ACOs.
There are at least four possible explanations for this pattern. First, larger salamanders might have a requirement for larger cover objects than smaller salamanders, and so might be more selective in their use of cover objects. Second, predators of juvenile salamanders might be more abundant under ACOs than in other microhabitats. Third, the appropriate size prey for juvenile salamanders might be less abundant under ACOs than elsewhere. Finally, larger salamanders might exclude smaller salamanders from ACOs.
Apparently, adding ACOs to an area increases the local surface density of salamanders (see Population size and density, below), suggesting that the ACOs provide favorable microhabitats and such microhabitats might be defended. Although neither Ovaska (1987b) nor I (Davis 1991) could detect territorial behavior in P. vehiculum or A. ferreus, respectively, adult-juvenile interactions were not investigated. In iheory, there should be greater competition between adults than between adults and juveniles, but juveniles may be easier to displace than adults by territorial adults.
Also, adult salamanders might exclude non-related juveniles for the benefit of related juveniles. Where several unrelated adults occupy a single cover object, all juveniles might be excluded.
This suggestion is made more plausible by the observation that juvenile P. cinereus have active postcloacal glands (Simons et al. 1995). 103 These glands may function in kin recognition (Jaeger and Gabor 1993), but
the function in neonates and juveniles is unknown. Jaeger et al. (1995)
found that there was considerable overlap in the size of prey taken by
juvenile and adult P. cinereus, suggesting that competition for prey occurs
between juvenile and adult salamanders when prey becomes scarce. Also,
Jaeger et al. (1995) found that juvenile P. cinereus were attracted to
territorial pheromones of adults, and spent more time near and less time
escaping from adults found under the same cover object than with adults
found under other cover objects. Adult male P. cinereus were less
aggressive toward juveniles than toward adult males, and adults were
more tolerant of juv tiles with which they had cohabited than with juveniles that had been found under other cover objects. This suggests
that kin recognition (Waldman 1988) and behavior that benefit kin may be occurring in this species (Jaeger et al. 1995).
Kin recognition has been reported in several species of salamanders
(Jaeger and Forester 1993; Jaeger et al. 1995). For example, kin recognition allows female P. cinereus (Bachmann 1984) and Desmognathus ochrophaeus (Forester et al. 1983) to locate their eggs, and results in reduced aggression among related larval Ambystoma opacum (Walls and lvoudebush 1991), and reduced cannibalism among related larval A. tig rin u m (Pfennig and Collins 1993). In terrestrial plethodontid salamanders, the possible advantages for juveniles remaining together with their parents include the protection of juveniles from predators, and 104 the exclusion from favorable cover objects of non-related juveniles that are potential competitors (Jaeger and Forester 1993).
Although smaller salamanders seem to be underrepresented under
ACOs, this is relative to searches of natural surface microhabitats. The true proportion of salamanders in each size class remains unknown, because neither sampling method has been tested with a population in which the size structure of the population is known independently. However, size structures based on searches of natural cover are likely to be closer to the true size structure of the population because more microhabitats are sampled than are sampled on searches of ACOs.
Population size and density - The unfenced plots with ACOs showed an increase in the cumulative number of new individual P. vehiculum in
1994, but the fenced ACO plots did not. However, there was no difference in the mean number of salamanders, including recaptures, found per search between unfenced and fenced ACO plots. This suggests that although there might have been immigration and emigration into and out of the unfenced plots, because there was no net increase in the total number of salamanders between fenced and unfenced plots, any tendency of ACOs to attract salamanders must have occurred before the fences were put in place, Also, no net movement of salamanders toward ACOs was detected by comparing proportions of salamanders moving to and away from the ACOs, but the number of recaptu/es was small, so this is not a 105 compelling result. The unfenced ACO plot that had the most new
individuals (Plot 1, Fig. 3; Fig. 18b) was surrounded by a virtually
continuous blanket of Sword ferns which may have facilitated movements
of salamanders into and out of the plot. All the other plots lacked this
feature.
Finally, nearly twice as many individual salamanders were caught in
fenced plots with ACOs compared to fenced plots without ACOs. This
suggests that ACOs attracted salamanders before the fences were installed.
Alternatively, more salamanders may have been found in ACO plots because ACOs may have provided cover so that salamanders could be at
the surface earlier in the year, or ACOs may have simply facilitated the capture of salamanders. Any or all these factors could explain the higher numbers of salamanders in fenced ACO plots compared to fenced plots without ACOs.
If cover objects are limiting, adding ACOs can be seen as habitat enhancement, and the number of salamanders found within an ACO plot might be higher than it would be without ACOs. If ACOs were attracting more salamanders than would normally occur in that plot, the proportion of recaptures previously found under ACOs that moved to natural cover should lower than the proportion of recaptures previously found under natural cover that moved to ACOs, at least soon after the ACOs are put in place. Such movement was not detected, but there are several reasons why this might be so. First, of the 49 recaptures ofP. vehiculum that could be 106 analyzed in this way, only 12 were of individuals previously found under natural cover. Thus the sample size was small, so the expected movements might be missed. Second, the sample was taken over a two- year period, after the ACOs were in place. Equilibrium was probably reached early in the sampling period, but there were too few recaptures to detect any early trends. Finally, P. vehiculum are site-tenacious, so movements to new cover objects are rare. A more definitive experiment would involve marking a large proportion of salamanders within a plot before establishing the ACOs, followed by intensive monitoring of ACOs and natural cover.
For T. granulosa, the fenced ACO plots had fewer new individuals than the unfenced ACO plots, suggesting that the fences prevented salamanders from moving into the plots. However, the situation was different in 1994, when all plots had similar numbers of newly caught individuals, except for plot 5 (unfenced) which had only 2 new individuals and plot 6 (fenced) which had twice as many new salamanders as any other plot. There is no obvious explanation for these results. Plot 5 had the maximum number of new individuals in 1993. Salamanders may have been moving into plot 6 through subterranean passages, but this is speculation. Overall, few T. granulosa were caught, and this makes explaining these data difficult. 107
Chapter 4: Goldstream Provincial Park
Based on searches of ACOs, the density of P. vehiculum in
Goldstream Provincial Park is exceptional, and supports a much larger population of terrestrial salamanders than any of the other primary sites
(Chapter 3). Ovaska and Gregory (1989) reported high densities of P. v eh icu lu m in plots about 100 m north of the ACO plot, but the spatial extent of this dense population is unknown. In this chapter I estimate the surface density of P. vehiculum over a larger area in Goldstream Park, and compare these results to the densities of other populations of terrestrial salamanders reported in the literature.
M e t h o d s
Five areas in Goldstream Park were selected for sampling (Fig. 19).
Area 1 included the Ovaska and Gregory (1989) plots, and Area 2 included the ACO plot. The three other areas were selected b) convenience, but all had dense forest canopies and superficially appeared to be similar to Areas
1 and 2. The areas were searched using randomly placed quadrats along parallel transects (Heyer et. al. 1994). In each area, 4 parallel 100-m 108
Figure 19. Map of Goldstream Provincial Park showing location of ACO
plot and transects for quadrat sampling. Transects (100 m long)
are indicated by horizontal lines. There were four transects in
each of five areas labeled 1-5. The location of the plots studied by
Ovaska and Gregory (1989) are labeled 'A' and 'B'. 109
Freeman King Visitor Centre 110 transects, 20 m apart, were followed in an East-West direction starting from a convenient trail or road. Along each transect, ten 1 m2 quadrats were searched for salamanders. The location of quadrats along a transect was randomized by dividing the transect into 1 m quadrats and randomly selecting ten quadrats, with the stipulation that quadrats must be at least 2 m apart. As shown in Fig. 19, some transects ran into barriers before they terminated. These transects were extended by moving 10 m north or south and then followed back parallel to the original transect. There were four crews of two people/crew. In each area, crews were randomly assigned to one of the four transects.
The edges of the quadrats were defined with a 1 x 1 m quadrat frame.
To avoid biases due to subtle differences in search images and technique, one person in each crew did all the searching while the other recorded the data. To avoid having the salamanders escape from the quadrat before they were discovered, searching began at the perimeter and moved in toward the center. All debris (rocks, pieces of bark or wood, leaves) was removed from the quadrat, but was returned when the search was finished.
Salamanders were sexed and weighed after the entire quadrat was searched and all salamanders located.
All searches were done during daylight hours on May 1, 1994. ACOs were checked before and after the quadrat searches to ensure that salamanders were at the surface at the beginning and end of the day, I ll
R e s u l t s
The Victoria International Airport Station recorded a mean temperature of 8.5°C and 0.4 mm of rain on May 1,1994. At Goldstream, the sky was overcast in the morning, but cleared in the afternoon. The ground was moist, but not wet. During the previous five days there was 7.8 mm of rain and mean daily temperatures were between 10.2°C and 11.3°C.
The twelve ACOs at Goldstream produced 112 P. veh icu lu m in the morning on this date, and a cursory inspection of ACOs in the afternoon
(after the quadrat searches) indicated that the salamanders were still present under cover on the surface.
Quadrat searches gave a mean density of 0.75 P. vehiculum/m2 in
Goldstream Park. The density of salamanders was much higher in Areas 1 and 2 than in the other three areas sampled (nested ANOVA, F(1)415=6.70,
0.0025 T able 8. Density of Plethodon vehiculum in Goldstream Provincial Park, Vancouver Island, B.C. on May 1,1994. Total number of salamanders based on four transects per area with ten 1 m2 quadrats randomly placed along each transect. See Fig. 19 for the location of transects. total number of mean density of Area Plethodon vehiculum Plethodon vehiculum /m 2 SD 1 72 1.8 1.88 2 59 1.5 1.91 3 12 0.3 0.56 4 5 0.125 0.40 5 1 0.025 0.16 total 149 0.75 1.43 113 D isc u ssio n Based on searches of ACOs and natural cover, I recorded densities as high as 0.56 individuals/m2 over an area of 288 m2 (Chapter 3). The highest surface density of P. vehiculum was found in Area 1 (Fig. 19) where quadrat searches produced 1.8 individuals /m 2. In Areas 1 and 2 combined, peak surface densities are about 16,500 salamanders/ha (1.65 individuals/m2). The mean surface density among the five areas sampled in Goldstream Park was 7500 salamanders/ha. Coincidentally, the most salamanders (n=112) found under ACOs at any time during this study were found on the same day that quadrat searches were done, suggesting that the quadrat-based density estimate is high for this site. However, on April 24, 1994, nearly the same number of salamanders (n=110) were found under ACOs. The mean number of salamanders found on 7 searches of ACOs in the spring of 1993 was x=35.6, SD=1.0, range 23-47. Thus, the number of salamanders under ACOs/search in 1994 was over twice the maximum number found on any search in 1993. However, the variance in 1993 is relatively small, suggesting that the increase in 1994 was due to a general increase in the number of salamanders using ACOs, and not because conditions brought an exceptional number of salamanders to the surface. Nevertheless, the density based on quadrat searches (1.8 individuals/m2) is higher than the maximum number of P. vehiculum found by Ovaska and 114 Gregory (1989) in a 100 m2 plot in Area 1 (1.4 individuals/m2), and one- third higher than the mean number of salamanders found on six searches from March to May, 1984 (1.2 individuals/m2). Based on these numbers, the average surface density in the spring is probably about one-third lower than the quadrat-based sample resulting in an estimate of 5,000 salamanders/ha over the entire area of the park that I sampled. If these numbers represent less than 24% of the total population (Chapter 3), then there are at least 70,000 P. vehiculum I ha. in Areas 1 and 2. This estimate is the highest reported surface density for plethodontid salamanders in western North America of which I am aware. Stebbins (1954) estimated that there were between 600 to 700 E. eschscholtzii/acre (240 to 280/ha) at his study site in California. Bury (1983) found 420 salamanders/ha (0.042 salamanders/m2) in old-growth redwood forests in northern California. Corn and Bury (1991) reported an average of 744 plethodontid salamanders/ha in old-growth forests in Oregon, with no site having more than 1300 plethodontid salamanders/ha and no site having more than 300 P. vehiculum/ha. On Vancouver Island, Dupuis el al. (1995) found a mean density of 1450 salamanders/ha at three old-growth forest sites in the spring of 1991 and 1992. The density of P. vehiculum in Goldstream Park is comparable to the relatively high densities of terrestrial salamanders found in eastern North America. Burton and Likens (1975a) reported 2,583 salamanders/ha in the Hubbard Brook Experimental Forest in New Hampshire. Merchant 115 (1972) estimated the mean density of salamanders in the Great Smoky Mountains to be 1.1/m2, but this was revised by Hairston (1987) to 0.7 salamanders/m2. Mathis (1991) reported a density of 2.8 P. c in e re u s/m2 in Virginia, which was based on mark-recapture data using the Schnabel method. The highest daytime surface densities of terrestrial salamanders reported in North America are for P. cinereus on Blackrock Mountain, Virginia, which Jaeger (1979) found to vary between 0.8 and 4.0 salamanders/m2 based on 22 days of searching in the spring and summer of 1974. The mean surface density was 2.2 salamanders/m2 (22,000 salamanders/ha). The high density areas in Goldstream Park have very rocky soil substrates that grade into talus (rock rubble). Corn and Bury (1991) and Bury et al. (1991) found a strong association between the abundance of P. v e h ic u lu m and the presence of talus. Thus, fo r P. veh icu lu m , the presence of talus may be more important than the age of the stand or the amount of CWD. The ACO plots were re1 /ively devoid of cover that could be overturned, and had a less ro :ky substrate than the rest of Area 2, which is less rocky than Area 1. These factors probably account for the lower density in the ACO plot (0.56 individuals/m2, Chapter 3) compared to the quadrat searches which sampled a larger area. All the GVW forested sites, the Lake Cowichan site, and the Rosewall and Cook Creek sites have about the same density of salamanders (Fig. 8), which suggests that abundance may be 116 relatively low across wide areas, whereas areas of relatively high abundance, such as at Goldstream, are probably local and patchy. 117 Chapter 5: Time-constrained Searches of Secondary Sites In Chapter 3 I showed that the northern sites had relatively more A. fe rre u s than the southern sites and relatively fewer P. vehiculum. However, it was not known if this represented the general pattern of distribution and abundance along the southeastern coast of Vancouver Island, or if these sites were exceptional in some way. A number of secondary sites, located between the northern and southern primary sites, were used to address this question. In this chapter I report on time- constrained searches (TCS) of these secondary sites. M e t h o d s Site selection - Potential secondary sites were selected from current British Columbia Ministry of Forests Forest Cover Maps by identifying all stands that were of age class 7 (121-140 years) or older, at an altitude of less than 200 m, between Sooke Lake (48°33' N, 123°41' W) and Rosewall Creek Provincial Park (49°27' N, 124°47' W), and within 20 minutes driving time from the main highway which runs along the southeastern coast of Vancouver Island, Highway 19. Some sites thus identified could be 118 eliminated from consideration because they were obviously inaccessible. Other sites, particularly in the GVW, were eliminated because they were adjacent to primary sites. All sites were close enough to Highway 19 so that several sites could be searched on the same day, thereby avoiding the problems created by searching different sites on different days. Of the 41 potential secondary sites that fit the above criteria, 15 proved to be inaccessible, 2 were very unproductive and contained small, stunted trees with little canopy closure, 8 suffered from substantial edge effect from nearby clearcuts as judged by light penetration or were very fragmented, and 3 had recently been logged. Thus, 13 sites were chosen from the original 41. An additional 3 sites were found serendipitously and 4 primary sites (GVW mature, Lake Cowichan, Cook Creek and Rosewall Creek) were used as well (Fig. 1). Details of site locations are given in Table 9a,b. Search Order - The 20 sites were searched with 2 person-hour TCSs per site (see below). The sites were searched according to a pre-determined order based on approximate north-south geographical position, except that every other site vas searched on the first day, and the remaining sites were searched the following day. On the first day, searches began at the most southern site and finished at the most northern site, but the direction was reversed on the second day. T able 9a. Location of sites searched on the first day of 2-hr time constrained searches (TCSs), in the spring of 1993. Searches were done on April 26-27,1993, June 2-3,1993, and June 16,17,1993. The sites are listed in the order in which they were searched, ‘primary site; +first search only. Unless otherwise indicated, most recent Forest Cover Map Series as of April 1993, Ministry of Forests, Province of British Columbia. 2Forest cover map, Scoke Lake Watershed, Greater Victoria Water District. Forest site cover map1 polygon latitude longitude description *GVW mature Sooke 699/V 48° 34’ 123° 39’ Enter from Leechtown main near W end of Sooke Lake Lake2 'Shawnigan Lake N 48° 39’ 123° 40’ From N end of W Shawnigan Lake Rd., 0.3 km S 'Mayo Road 92B.071 L. 18 48° 47’ 123° 51’ West side of Mayo Rd., 1.6 km S from Cowichan Lake Rd. *Lake Cowichan 48° 50’ 124° 10’ UVIC property on Marble Bay, Lake Cowichan, Lot 29. Chemainus River I 48° 54' 123° 46’ 2.0 km from HWY on S side of Chemainus River Rd. 'Nanaimo Lakes 49° 5' 124° 00’ 8.6 km past first RR tracks on Nanaimo Lake Rd. Little Mountain 92F.029 124 49° 18' 124° 19’ Park at large turnout 0.6 km from bottom of Little Mtn. Rd. Follow trail for 5 min, then down to flat area. 'Powerline 92F.037 241 48° 23' 124° 38’ Take Cochrane Rd. (0.8 km N of Big Qualicum River). On S side of Rd. at 3.8 km from HWY 19 Crosley RoaJ. 92F.047 112 49° 26' I24042’ Take Crosley Rd., 15 km N of Bowser on HWY 19 for 15 km. On N side of Rd. ‘Rosewall Creek 92F.049 205 & 207 49° 27' 124° 46’ NE of ACO plots; new Island Highway now covers this site T able 9b. Location of sites searched on the second day of 2-hr time constrained searches (TCSs), in the spring of 1993. Searches were done on April 26-27,1993, June 2-3,1993, and June 16,17,1993. The sites are listed in the order in which they were searched, “primary site; +first search only. JMost recent Forest Cover Map Series as of April 1993, Ministry of Forests, Province of British Columbia. Forest polygon site cover map1 number latitu de longitude description *Cook Creek 92F.049 194 49° 27' 124° 45’ W side of HWY 19,1 km S of Cook Cr. Thames Creek 92F.047 528 49° 26' 124° 40’ Walk 3.5 min SE on RR tracks on HWY 19 at Cobum Rd. to Thames Cr.; W side of tracks R ailroad 92F.038 13 49° 22' 124° 33’ NE side of HWY 19,0.4 km S of Baylis Rd. ‘Craig Creek 92F.029 202 49° 17' 124° 15’ On E side of HWY 19,0.4 km S of Parksville bypass to HWY 4 ‘Christy Road 49° 01' 123° 51’ From HWY 19, take Chrisly Rd. (1.2 km N of Ladysmith signal ligfit) for 2.0 km. W side of Rd. Chemainus River II 48° 54’ 123° 46’ 2.6 km from HWY 19 on S side of Chemainus River Rd. Hillcrest Road 92B.082 2852 48° 49' 123° 48’ 2.9 km N from HWY 18, W side of Hillcrest Rd. Riverbottom Road 48° 47' 123° 46’ S side of Riverbottom Road, 0.7 km W of junction with Stoltz Rd. ’Shawnigan Lake 48° 36' 123° 38’ 0.2 km N of junction of S Shawnigan Lake Rd. and Leechtown South Main Shawnigan Lake 3 48° 35’ 123° 37 3.9 km from HWY 19 on S Shawnigan Lake Rd, on S side of Rd. 121 There were three searches of these sites: 1) April 26-27, 1993, 2) June 2-3,1993; and 3) June 16-17,1993. On the first and third searches, we searched all available microhabitats (under CWD on ground, under bark on logs, within logs, within Sword Fern bases, in leaf litter, under rocks, under and within moss). On the second search, so that the pattern of distribution of A . ferreu s would be better defined, we limited ourselves to microhabitats favored by that species: under bark on logs and in cracks and cavities within logs. All twenty sites were searched on the first search, but this proved to be an exceptionally arduous task, so only 12 sites were searched on the second and third searches. The sites that were rejected either produced few salamanders on the first search or lacked sufficient undisturbed area for additional searches. Time-constrained searches - TCSs are equal-effort searches as measured by the number of person-hours spent searching. They are used to estimate the relative abundance of amphibians within habitat types (Corn and Bury 1990; Heyer et al. 1994). In general, each 2-person-hour search was confined to an area of about 2,500 m2. For searches limited to bark on logs and in cracks and cavities within logs, the area searched depended on the numbers and sizes of the logs, but always covered a larger area than the normal searches. The crew size was from four to six people. One person was the data recorder, I measured and marked the 122 salamanders, and the remaining people did the searching. When an animal was found, the time spent by the searcher assisting in the collection of data was added to the end of the search so that a full unit of collecting time was achieved. When not occupied with data collection, the recorder and I helped search, and the time spent collecting was adjusted accordingly. Tools used on the TCSs were crowbars and light axes. Bark on logs was removed and the decayed wood removed layer by layer. To survey as much habitat as possible, no more than about 10 minutes was spent on any single object, regardless of the object's size. Logs and rocks were rolled over when possible. Moderate size debris (10 cm or more in diameter) was checked, but, in general, searching through leaf litter or turning over very small objects was avoided. Piles of bark or wood were thoroughly searched and moss was peeled from logs. Some habitat destruction is unavoidable when searching the natural environment, but this was minimized by returning cover objects to their original positions when possible. The temperature at ground level was taken at each site as the search began, and weather conditions were noted. Salamanders were weighed, measured and toe-clipped as described in Chapter 2. For each salamander, I recorded the microhabitat according to the scheme outlined in Chapter 7. 123 R e s u l t s Unfortunately, suitable sites to search were not found between 49°2' N and 49°16' N latitude. This area is highly fragmented and much of it has been converted to agricultural land or is used for human habitation. This left a substantial gap between the northern and southern areas (Fig. 1). Weather conditions were reasonably constant for the two days of each search. During the first search, the weather was cloudy with light rain to overcast conditions with a mean ground temperature among sites of 9.5°C, SD=1.5° C, Tmln=7° C, Tmax=13° C. The second search had similar conditions with rain to partly cloudy with a mean ground temperature of 13.8° C, SD=1.3° C, Tmin=ll° C, Tmax=15° C. During the third search, conditions were sunny to partly cloudy with a mean ground temperature of 16.1° C, SD=2.5° C, Tmin=12° C, Tmax=21° C. The primary purpose of these searches was to determine the general pattern of distribution and abundance of two species, P. vehiculum and A. ferreu s. However, other species of salamanders were found in low numbers. Overall, 467 salamanders were caught in 88 person-hours of searching. Of these salamanders, 83.3% were P. vehiculum, 12.2% were A. ferreu s, and other species accounted for 4.5% of the total number caught (Table 10). Variation in abundance among sites was high (Fig. 20). Also, at each site, the first search produced many more salamanders than the third T able 10. Number of salamanders found on time-constrained searches of 20 - 12 sites on southeastern Vancouver Island, B.C. Each search represents 2 hours searching per site. Percentages of the total number of salamanders caught on each search are given in parentheses. Species Date of search N o. of Plethodon Aneides Taricha E nsatina Amhystoma Amhystoma Totals (1993) sites vehiculum ferreus granulosa eschscholtzii macrodactylum gracile April 26,27 20 265 (90.1%) 15 (5.1%) 4 (1.4%) 8 (2.7%) 2 (0.7%) 0 (0.0%) 294 June 2,3 12 25 (40.3%) 36 (58.1%) 1 (1.6%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 62 June 16,17 12 99 (89.2%) 6 (5.4%) 4 (3.6%) 0 (0.0%) 1 (0.9%) 1 (0.9%) 111 Totals 389 (83.3%) 57 (12.2%) 9 (1.9%) 8 (1.7%) 3 (0.6%) 1 (0.2%) 467 Figure 20. Number of salamanders found on time-constrained searches (TCSs) of secondary sites on Vancouver Island, B.C. Each column represents the number of salamanders found at a particular site. Open columns represent P. vehiculum; black columns represent A. ferreus. Sites are arranged along the x-axis by latitude. Searches on April 26-27,1993 and June 16-17,1993 were of all available microhabitats. The searches on June 2-3, 1993 were restricted to under bark on logs and cavities within logs. number of salamanders number of salamanders number of salamanders ■fc* l-» I—» t-» l-J © N J ^ O n O O O N J ^ O v to Ol 00 0 0 © N Ov 00 O K) it^ On » ° o o o o 1.11 I i i i I i i i I i i i I i i i I i i i I i i i I i i i I 0 3 03_o I i i i i II I I I I I I I I I I I I I I I I I I I ° q o “T Z- 2 3 n» z D> -— N**r~t- ct- c ? = a a z re re - i > N> 0 3 N3 Ovi VO S 3 VO 0 3 4*. - 4*. vO - vo 4* vo o — o vO _ vo p 0 3 w - 1 0 3 0 3 □ O o S 3 Ov 127 search. At the same 12 sites, the first search produced 200 salamanders, but the third search produced only ill salamanders. However, for most of the sites, the proportion of salamanders caught was similar between these searches (Fig. 21; P. vehiculum : x2=18.1, df=ll, P=0.08). The second search, which was restricted to under bark on logs and in cracks and cavities within logs, produced a greater proportion of A . ferreu s (58.1%) than on the other two searches (5.1% and 5.4%, respectively). D isc u ssio n These results confirm that the northern sites have relatively more A . ferreu s than the southern sites and relatively fewer P. veh icu lu m . Somewhat drier sites with less canopy cover had fewer salamanders, but there was nothing particularly obvious that would distinguish between many of the sites and would account for this variation. Variation in site characteristics is explored more formally in the next chapter. There was a similar proportion of the total number of salamanders caught at most sites on the first and third searches, but there was considerable variation at a few sites (Fig. 21). For example, about 8% of the P. vehiculum found on the first search were found at Chemainus River II, but 14% were found on the third search. Similarly, at the GVW mature 128 Figure 21. Proportion of Plethodon vehiculum found on time-constrained searches (TCSs) of secondary sites on Vancouver Island, B.C. Sites are ordered by the proportion of P. vehiculum caught on April 26-27,1993. 129 ", April 26-27,1993 Shawnigan Lake 3 June 16-17,1993 GVW mature Chemainus River II Thames Creek Riverbottom Road Hillcrest Road Chemainus River I T" T I I I I I I 0% 5% 10% 15% 20% 25% proportion of P. vehiculum 130 site, about 3% of the P. veMculum were found on the first search, but 8% were found on the third search. The most extreme variation was four, i at Chemainus River I which produced 22% of the P. vehiculum found on the first search, but only 8% on the third search. Recall that the areas searched at each site were adjacent, but not identical. In all cases, the sites appeared to be homogeneous, but these results suggest that salamander populations are very patchy within a site and that fine scale habitat features may greatly influence the surface abundance of terrestrial salamanders. This is consistent with the results of the last chapter and will be revisited in Chapter 6. Weather conditions are known to affect the surface abundance of terrestrial salamanders (Houck 1977), and there is a strong seasonal effect on capture rates in these species (Davis 1991, Ovaska and Gregory 1989; Chapter 3). The first search, with rain and cloud, produced approximately twice as many salamanders as the third search, which had clear and partly cloudy skies. This suggests that TCSs are most effective when it is lightly raining or wet and overcast, and that when estimating relative abundance among sites, searches should be done under the same conditions, preferably on the same day. Weather conditions on the first few days before a search are probably as at least as important as the conditions on the day of the search. 131 Variation within sites, combined with seasonal and daily variation in weather conditions, suggests that TCSs can lead to spurious conclusions. Thus, a single TCS of a site means little when attempting to estimate relative abundance among sites. Other methods of sampling, such as quadrat or transect sampling, will give more reliable results because they are more likely to achieve a representative sample of the habitat matrix (Heyer et al. 1994), but all sampling methods need to be repeated several times to account for changes in temperature and moisture that occur over a season. These observations support Bury and Corn (1988) and Corn and Bury (1990) who caution that TCSs should not be used across stands or environmental gradients. The number of salamanders collected on TCSs could vary among stands because the types, numbers, and biomass of logs differ among stands, independent of the actual numbers of salamanders present. For example, Bury (1983) and Bury and Martin (1973) found more A . ferreus in clearcuts than in older forests. This could have been because the salamanders were easier to find in the downed material, and not because they were actually more abundant in clearcuts. The results of the second search, which was restricted to under bark on logs and in cracks and cavities within logs, illustrate the importance of targeting species-specific microhabitats. Surface searches of all microhabitats may be biased against some species because some microhabitats are easier to search than others. Thus, surface searches may 132 be very misleading as a measure of relative abundance among species within a site. These searches sampled a relatively small number of sites, and many more sites are needed to firmly establish what appears to be a geographical pattern of distribution, preferably with randomly placed quadrats rather than TCSs. It would be interesting to explore sites north of Rosewall Creek and sites along the south coast of the island. However, there are some serious practical difficulties. First, surface abundance varies according to weather conditions, so that searches done on different days are not comparable. This problem can be addressed by sampling each site several times during the year, but that is costly and time-consuming. Second, because of forest fragmentation and human activities, there are very few undisturbed sites left on this part of Vancouver Island. Therefore, the natural pre-disturbance distribution may be impossible to determine. These issues are discussed further in the last chapter. 133 Chapter 6: Site and Plot Characteristics, Climatic Conditions, and Abundance The results of the last three chapters indicate that the densities of A. ferreu s are relatively high at the northern sites (Cook Creek and Rosewall Creek) compared to Lake Cowichan and the sites further south. In contrast, the densities of P. vehiculum are relatively low at the northern sites compared to the southern sites. One possible explanation for this pattern is that there are site-specific characteristics that favor one species over another. For example, differences in the amount and type of CWD, or the density of Sword Fern (Polystichum munitum) among sites could influence salamander numbers, presumably because both provide cover for terrestrial salamanders. Climatic differences among sites also might be important. Differences in temperature or precipitation among sites could directly favor one species of salamander over another because of physiological differences between species. Also, climatic effects on other organisms might influence salamander abundance. For example, climatic differences may control the abundance of predators, prey, or determine the species composition of trees 134 and understory plants among sites, any of which could influence salamander fecundity, survival, and growth. Casual observation suggested that the forested primary sites were very similar to one another in terms of CWD, dominant tree species, understory plants, and physical conditions, but in this chapter I will compare the general site characteristics and climatic conditions among sites more formally. There are two primary objectives of this chapter. The first objective is to determine if there exist site-specific characteristics that would distinguish the northern and southern sites. These characteristics could be structural, biological or physical. The second objective is to explore the relationship between salamander abundance (as indicated by ACOs) and plot characteristics. M e t h o d s Site characteristics - The center of each 10-m-diameter ACO plot (see Chapter 2) was used as the center of a 12 x 12 m square plot within which characteristics of the plot were measured. Each 12 x 12 m plot was subdivided into nine 4 x 4 m quadrats for ease of measurement. Within each 4 x 4 m quadrat I estimated the percentage of bare ground, and the percentage area covered by Sword Fern ( Polystichum munitum), Salal (Gaultheria shallon), and Oregon Grape (Mahonia nervosa). These were 135 averaged to give percentages for the entire plot. I also measured the diameter of Sword Fern bases, the height and diameter of stumps and snags and their decay classes, and the DBH of all trees higher than 2 m. For decay classes of stumps and snags, see the section on decay classes of logs in Chapter 7. At the Goldstream site, because of restrictions on where plots could be placed within the park, the twelve ACOs were arranged differently than at the other sites. Therefore, the habitat assessment plot, instead of being a square plot with an area of 144 m2, was arranged so that all ACOs were included in two contiguous rectangular plots, each with an area of 144 m2. The amount, type, and decay class of all CWD with a smallest dimension of 10 cm or larger was recorded for each plot. For the calculation of the area of ground covered by bark, pieces of bark were measured in two dimensions and assumed to be rectangles. For volume estimation, bark was assumed to be 1 cm thick. The volume of a log was assumed to be given by the product of the length of the log and its cross- sectional area, the latter based on the average of two diameter measurements, one at each end of the log. The area of ground in contact with each log was estimated separately because there were portions of some logs that were not in contact with the ground. Species and decay class were also recorded (for decay classes, see Chapter 7). For some logs in a late stage of decay, the species was not obvious, but coniferous species (Douglas fir, Western Hemlock, and Western Red Cedar; for Latin names, see Chapter 2) 136 could be distinguished from deciduous species (Red Alder and Broadleaf Maple). Differences in general habitat features among sites based on plot characteristics were compared by ANOVA. The Rosewall and Cook Creek sites were combined to increase sample size (combined total of n=4 plots), but Goldstream was left out of this analysis because there were only two plots and they were contiguous. The GVW and Lake Cowichan sites had six plots each. If there were statistically significant differences among sites using ANOVA, t-tests were used make comparisons between pairs of sites. Site characteristics in relation to salamander abundance - The analysis of site characteristics in relation to salamander abundance was constrained a priori by small sample size: there were nine sites, two of which were clearcuts. However, I explored the relationship among site characteristics and abundance of salamanders by calculating Pearson correlation coefficients and inspecting scattergrams. The clearcut sites were excluded from this analysis because few salamanders were found in the clearcuts, and many of the clearcut characteristics were not directly comparable to the forested site characteristics, or could not be measured in the same way. Variables were the number of Sword Ferns, the area of Sword Fern bases, the volume of Sword Fern bases, the number of trees by size class, the area of CWD covering the ground, the volume of CWD, the volume of CWD plus the volume of stumps, the volume of CWD of logs 137 by decay class, and the number of each species of salamander/ACO found on 8 matched searches (Table 4, Chapter 3). Plot characteristics in relaHon to salamander abundance- 1 investigated the relationship between salamander abundance and plot characteristics within sites. To increase the power of the analysis, the plots in the forested GVW sites were pooled (n=18). This is reasonable because there was no difference in abundance (Chapter 3), or site characteristics among the three sites (see results, below), they were less than 2.2 km apart, and two of the sites were contiguous. I explored the data with Pearson correlation coefficients, partial correlation coefficients, and scattergrams. With highly correlated and non-independent variables (e.g. area of CWD and volume of CWD), only the variable with the strongest correlation was retained for further analysis. A similar approach was taken for the Lake Cowichan site, where the abundance of salamanders was greater, but the number of plots was smaller (n=6). For the GVW sites, data from 1992 and 1993 were used, but only data from 1992 were used in the Lake Cowichan analysis because of the possible effect of fences around ACO plots. Finally, the plots from the forested GVW sites and Lake Cowichan were combined to explore relationships suggested by the separate analyses. The number of searches was equal among the GVW and Lake Cowichan sites, and data from 1992 only were used for the reason given above. 138 A related issue is whether the distribution of salamanders among plots changes as ACOs age. If abundance under ACOs is a reflection of other plot characteristics, then the distribution of salamanders among plots should remain constant from year to year. I analyzed frequency distributions among plots for Lake Cowichan and GVW using contingency tables. For Lake Cowichan I used the unfenced ACO plots only in 1992, 1993, and 1994. For the GVW sites I used data for 1992 and 1993 only. Climate and Weather - The climate on southern Vancouver Island is characterized by mild, wet winters with some snow and temperatures typically near or below freezing from December to February. Summers are generally dry, but under the cover of a dense forest canopy, spaces under bark and in decaying wood can remain relatively moist. Normal monthly temperatures and precipitation were taken from Environment Canada (1993). Not all weather stations record both temperature and precipitation, and some stations have incomplete records for some months. Thus, in some cases, I used temperature and precipitation normals from more than one station to represent the normals at a particular site. Because the Goldstream site (48°28' N, 123°32' W, <50 m) and at the Victoria International Airport Station (48°39' N 123°26' W, 20 m) are at approximately the same elevation, I assumed that their temperature normals were similar. For precipitation normals, I used the closest station to the Goldstream site, the Victoria Highland Station 139 (48°25' N, 123°30' W, 152 m). For the GVW sites (48°34’ N, 123°39' W, 200- 250 m), I used precipitation normals from the Sooke Lake North Station (48°3r N, 123° 39' W, 231 m), and temperature normals from the Shawnigan Lake Station (48°31' N, 123°37' W, 137 m). For Lake Cowichan (48°50' N, 124°10' W, 163 m), I used both temperature and precipitation normals from the Cowichan Lake Forestry Station (48°50'N, 124°08' W, 177 m). For the RMC sites (49°27’ N, 124°46' W, <50 m), I used temperature and precipitation normals from the Qualicum River Fisheries Research Station (49°24' N 124°37' W, 8 m), which are very similar to the incomplete temperature and precipitation data from the Mud Bay Station (49°28' N, 124°27' W, 11m). R e s u l t s Site characteristics - Habitat characteristics of the forested primary sites are presented in Table 11. Although there was considerable variation in the species and size classes of trees among sites, neither Goldstream nor Rosewall and Cook Creeks combined (RC sites) appeared to be exceptional, except that the RC sites had fewer coniferous trees than the other sites (all forested sites except Goldstream, ANOVA, F=3.16, df=4, P=0.03). There were no differences in the mean number of deciduous trees per plot among sites (F=0.61, df-4, P=0.66). However, there were significant differences Table 11. Habitat characteristics at forested primary sites. Values in body of table are means of 12x12 m plots with standard deviation in parentheses. CWD = coarse woody debris. DBH = diameter at breast height. Rosewall Creek and Cook Creek are combined (RC sites). Deciduous species include Maple and Alder. Coniferous species include Douglas Fir, Hemlock, and White Pine, texcluding Cedar. sites Goldstream GVW immature GVW mature GVW old-growth Lake Cowichan RC sites No. of Plots (n) 2 6 6 6 6 4 No. of trees DBH 0-29 cm 4.3 (4.0) 6.8 (5.2) 11.5 (4.4) 7.0 (3.0) 11.2 (7.8) 7.5 (3.9) No. of trees DBH 30-59 cm 1.7 (2.9) 2.7 (2.2) 4.0 (2.3) 2.0 (2.1) 4.5 (1.0) 1.8 (1.5) No. of trees DBH >60 cm 1.0 (0.6) 0.5 (0.5) 0.8 (0.8) 1.2 (1.2) 0.2 (0.4) 0.5 (1.0) % Bare ground 87.3 (0.6) 30.0 (8.2) 19.1 (16.0) 0(0) 78.9 (15.2) 31.7 (21.3) % Salal 0(0) 4.7 (3.2) 3.9 (4.0) 26.0 (25.0) 29.0 (71.0) 1.4 (2.8) % Sword Fern 4.2 (2.7) 54.4 (6.1) 13.0 (7.9) 13.7 (26.8). 10.9 (7.8) 58.3 (10.8) % Oregon Grape 0(0) 2.0 (2.8) 7.8 (8.7) 5.1 (7.2) 6.5 (8.4) 0.83 (1.7) Area of CWD (nr) 18.4 (25.3) 9.5 (3.8) 10.2 (4,5) 15.0 (11.5) 18.2 (6.8) 11.0 (8.0) Volume of CWD (m3) 18.16 (25.6) 3.0 (3.4) 2.1 (1.4) 4.8 (4.8) 4.9 (2.0) 4.8 (43) Table 11. (continued) sites Goldstream GVW immature GVW mature GVW old-growth Lake Cowichan RC sites No. of Sword Fems 19.5 (6.4) 92.0 (34.9) 26.5 (16.4) 32.0 (35.8) 54.5 (100.0) 120.3 (18.9) Vol. Sword Fem base (m3) 0.15 (0.00) 0.58 (0.20) 0.07 (0.06) 0.33 (0.71) 0.25 (0.52) 0.69 (0.23) No of Alder trees 0(0) 1.5 (2.0) 0.5 (0.8) 0(0) 0(0) 0.5 (1.0) No. of Maple trees 1.2 (2.0) 0(0) 0(0) 0.3 (0.5) 0(0) 1.3 (1.5) No. of Cedar trees 7.0 (1.4) 0.2 (0.4) 7.3 (4.3) 0.7 (0.8) 1.8 (1.9) 5.3 (4.4) No. of Douglas Fir trees 0(0) 3.0 (4.3) 5.8 (3.5) 1.8 (1.2) 0(0) 1.5 (1.0) No. of Hemlock trees 0(0) 5.3 (3.1) 2.5 (2.2) 7.3 (2.3) 14.0 (5.5) 1.8 (2.1) No. of White Pine trees 0(0) 0(0) 0.2 (0.4) 0(0) 0(0) 0(0) No. of coniferous treest 0(0) 8.3 (6.3) 8.5 (4.2) 9.2 (2.6) 14 (5.5) 3.5 (3.0) No. of deciduous trees 1.2 (2.0) 1.5 (2.0) 0.5 (0.8) 0.3 (0.5) 0.8 (2.0) 0.5 (1.0) 142 among sites in terms of the mean number of cedar trees per plot (F=7.36, df=4, P=0.0006), but there was no difference between the GVW mature and the RC sites (t=0.74, df=8, P=0.48). There was no difference in the mean number of trees by size class per plot among sites (DBH 0-29 cm, F=0.88, df=4, P=0.48; DBH 30-59 cm, F=2.22, df=4, P=0.10; DBH >60 cm, F=1.38, df=4, P=0.27). The percentage of bare ground varied considerably among sites (F=2.80, df=4, P<0.0001), but there was no difference between the GVW immature site and the RC sites (t=0.18, df=8, P=0.86). There was no difference in the percentage of ground covered by Salal per plot among sites (F=0.8, df=4, P=0.53). Goldstream had 3.4 times as much as volume of CWD as any other site, but the area covered by CWD was similar to Lake Cowichan (Table 11). Otherwise, there was no difference in the area of ground covered by CWD among sites (F=1.48, df=4, P=0.24), or in the volume of CWD among sites (F=0.88, df=4, P=0.49). The mean number of Sword Ferns per plot at the RC sites was greater than at the other forested sites, but there was no difference between the RC sites and the GVW immature site (F=2.9, df=4, P=0.05; t=1.5, df=8, P=0.18). The GVW immature site had significantly more Sword Ferns than the GVW mature and GVW old-growth sites CF=8.6, df=2, P=0,003), However, there was no difference in the volume of the Sword Fern bases among sites (ANOVA, F=1.75, df=4, P=0.17). 143 Site characteristics in relation to salamander abundance There - were two site characteristics that were significantly correlated with abundance of salamanders. First, the volume of logs of decay class 5 was highly correlated with the abundance of P. vehiculum (r=0.97, PcO.OOl). But the scattergram (Fig. 22a) shows that this result was almost entirely due to the Goldstream site. When Goldstream was removed from the analysis, there was no relationship between this site characteristic and the abundance o f P. vehiculum (r=0.06, P=0.92). No other correlations were significant for P. vehiculum. Second, the volume of logs of decay class 4 was correlated with the abundance of T. granulosa (r=0.81, P=0.028). The scattergram (Fig. 22b) suggested that this relationship was fairly consistent over the range of the data. However, note that T. granulosa were not found at two of the seven sites. No other correlations were significant for T. granulosa. No significant correlations were found between any habitat characteristics and the abundance of A. ferreus. Because the Goldstream site had many more salamanders/ACO than the other sites, outliers were created making the correlation coefficients and scattergrams difficult to interpret. I expected that the abundance of P. veh icu lu m would be correlated with the area of CWD and/ or the area of Sword Fern bases. Therefore, I calculated Pearson correlation coefficients for these key habitat features without the Goldstream site. There was no significant correlation between the abundance of P. vehiculum and the 144 Figure 22. Scattergrams showing correlations between salamander abundance and site characteristics for the forested primary study sites. LC = Lake Cowichan; GS = Goldstream; GVWim = GVW immature; GVWma = GVW mature; GVWog = GVW old- growth; RC = Rosewall Creek; CC = Cook Creek, a. The relationship between abundance of P. vehiculum and the volume of logs of decay class 5. b. The relationship between the abundance of T. granulosa and the volume of logs of decay class 4. 145 Plethodon vehiculum n=30 7 o u N< H(A 13 CD 4 8 12 16 Volume of decay class 5 logs (m3) Taricha granulosa LC 0.6-4 n=39 8 0.5- < "aa> 04 TJ § 0.3 # GVWim ■S 0.2 CD # CC # GVWog 0.1 GVWma Qg 0 T 0 RC 2 4 6 8 10 12 14 Volume of decay class 4 logs (m3) 146 area of CWD (r=0.80, P=0.57) or the area of Sword Fern bases (r=-0.28, P=0.59). However, the partial correlation coefficient for the area of CWD, controlling for the area of Sword Fern bases, was significant (r=0.88, P=0.05). Plot characteristics in relation to salamander abundance Among - plots in the forested GVW sites there was a positive relationship between the number of P. veh icu lu m caught and the amount of CVvD. All variables associated with CWD showed a similar positive relationship, but the strongest was for the area covered by CWD (r=0.70, P=0.001, Fig. 23a). There were weaker correlations associated with the volume of logs of decay class 2 (r=0.48, P=0.045) and decay class 4 (r=0.51, P=0.03), and with the number of trees of size class 30-59 cm DBH (r=0.48, P=0.043). For T. granulosa, only the volume of sword ferns was significant (r=0.62, P=0.006), but examination of the scattergram suggested that the correlation was strongly influenced by one ortlier. When that outlier was removed, the correlation was not significant (r=0.22, P=0,40). For Lake Cowichan, the number of salamanders was not significantly correlated with any plot characteristics (all correlation coefficients, P>0.05). However, when combined with the GVW sites, several correlations were significant. The abundance of P. vehiculum and area of CWD were positively correlated (r=0.80, P <0.0001, Fig, 23b), Also, there was a positive correlation between the abundance of P. vehiculum and the number of trees in size class DBH 30-59 cm (r=0,54, P=0,007, Fig. 147 Figure 23. Scattergrams showing correlations between the abundance of Plethodon vehiculum and two plot characteristics for Lake Cowichan and the Greater Victoria Watershed (GVW) sites combined. Sites: OG = GVW old-growth; MA = GVW mature;. IM = GVW immature; LC = Lake Cowichan. (a) The relationship between the abundance of P. vehiculum and the Area of CWD for the GVW sites only, (b) The same as (a), but including Lake Cowichan. (c) The relationship between the abundance of P. vehiculum and the number of trees in size class DBH=20-59 cm. 148 30 1______I______I______L CA Plethodon vehiculum I 25-1 n=229 I 20 A ▲ a W 15 1 C - VM ▲ • ffl OG O ffl a io • MA & b3* • ▲ IM • □ LC a 1 1 T...... 1 ... . 1 10 15 20 „ 25 30 35 Area of CWD (m ) 30 _L □ Plethodon vehiculum 3 25 -1 n=189 6 2 0 - : □ « 15 ^ Mh O □ 53 10^ □ c 0 Q] I CD T 0 10 15 20 25 30 Area of CWD (m ) 30 □ CA Plethodon vehiculum S 25 n=189 1 H I 20-1 □ □ in ffl □ 10 S3 b • A ▲ • A cs • • ! ffl 1------1------r 1 2 3 4 5 6 Number of trees (DBH 30-59 cm) 149 23c)/ and a negative correlation between abundance of P. vehiculum and the number of trees in size class DBH >60 cm (r=-0.58, P=0.003). However, when either of these tree size classes were held constant, the partial correlations between salamander abundance and tree size class were not significant. Also , there was a positive correlation between the area of CWD and the number of trees in size class DBH 30-59 cm (r=0.43, P=0.035) and a negative correlation between the area of CWD and the number of trees in size class DBH £60 cm (r=-0.57, P=0.004). When these size classes were held constant, the correlation between the abundance of P. veh icu lu m and the area of CWD remained significant (r=0.70, P<0.0001). This implies that these tree size classes are correlated with CWD, but do not influence salamander abundance directly. No correlation coefficients were significant for T. granulosa. Contingency table analysis of the distribution of salamanders among plots by years suggested that ACOs continue to reflect plot attributes as ACOs age. At Lake Cowichan, there was no difference in the distribution of the number of salamanders (recaptures included) among unfenced plots among years (x2=8.2, df=4, P=0.09). For the GVW forested sites, the distribution among plots was the same between years (%2=16.0, df=13, P=0.25), although four plots had to be removed from the analysis because of expected values <1 (Zar, 1984). However, there was a significant correlation in 1992 between the abundance of P. veh icu lu m and the area of CWD 150 (r=0.80, P=0.0001), but not in 1993 (r=0.45, P=0.058, Fig. 24). A similar result was obtained when the unfenced ACO plots at Lake Cowichan were added to the data set, expect that the correlations were significant in both years (1992: r=0.80, P<0.0001; 1993: r=0.59, P=0.002). Climate and Weather - Monthly temperature normals varied between -0.6°C and 24°C, but were similar among sites (Fig. 25; ANOVA for minimum and maximum monthly normals, F=0.27, df=4, P=0.9, and F=0.40, df=4, P=0.8, respectively). Mean yearly normal total precipitation was greatest at Lake Cowichan (2147 mm/year) and least at Goldstream (1137.4 mm/year), but there was no significant difference in mean monthly precipitation among sites (ANOVA, F=1.62, df=4, P=0.18). The mean yearly normal total precipitation at Rosewall and Cook Creeks was 1292.5 mm/year. D isc u ssio n Site characteristics - For most site characteristics, including temperature and total precipitation normals, there were no differences among jites that would explain the differential abundance of P, vehiculum and A, ferreus. Although there were significant differences among sites for some habitat features, the Rosewall and Cook Creek sites, where A . ferreus 151 Figure 24. Scattergrams showing correlations between the abundance of Plethodon vehiculum and area of CWD in (a) 1992 and (b) 1993 for the Greater Victoria Watershed (GVW) sites. Sites: OG = GVW old-growth; MA = GVW mature;. EM = GVW immature. number of salamanders number of salamanders N ) NJ CO NJ NJ CO Cn Cn © cn © O cn o Cn O Cn O o O -I 1 1 1 1 1 1 ■ 1 1 1 ‘ ■ ' ' 1 ■ ' ' ■ * 1 ■ ■ « * ‘ 1 ■ 1 1 c n - Rn •-t> o o fl)&• □ Cn □ OHh VO a VO VO n VO D NJ w ^ NJ N> o ° N>KJ cn OJ c o o © co co cn cn rocn 153 Figure 25. Normal temperatures and total precipitation per month for study sites on Vancouver Island, B.C. Open circles represent mean minimum and maximum temperatures per month. Columns represent mean total precipitation per month. Data is from Environment Canada (1992). TEMPERATURE (DC) TEMPERATURE (°C) 61 01 o U1 09 < _ o NJ TOTAL PRECIPITATION (mm) TOTAL PRECIPITATION (mm) TEMPERATURE (°C) TEMPERATURE (°C) M M KJ KJ 01 u °88888§is TOTAL PRECIPITATION (mm) TOTAL PRECIPITATION (mm) 155 were relatively abundant, were not significantly different from at least one other site where A . ferreu s were relatively rare and P. vehiculum were relatively common. Thus, the site characteristics measured in this study do not suggest an explanation for the differential abundance of these two species of salamanders. Goldstream stands out as having 3.4 times as much volume of CWD as any of the other sites, but the area of ground covered by CWD at Goldstream is similar to the area of ground covered by CWD at Lake Cowichan (Table 11). Examination of the data showed that one 12 m log with an average diameter of 175 cm accounted for 80% of the volume of CWD at Goldstream. Although there are other large logs at Goldstream, they are not common and are not found in some areas where salamanders are known to be very abundant (see Chapter 4). Because I focused on a few small plots within a site, sample size was small and the chance that the sample is not representative of the site is high. Thus, there may be site characteristics that would differentiate these sites, but if they exist, those characteristics were not measured at the appropriate scale in this study. Site characteristics in relation to salamander abundance - In general, any relationship between salamander abundance and site characteristics among sites was obscured by small sample size. There were too few sites with large numbers of A . ferreu s to make any firm conclusions regarding site characteristics and abundance, except that none of the site 156 characteristics measured seemed to be correlated unambiguously with abundance for this species. Similarly, the significant correlation between the number of T. granulosa with the volume of logs of decay class 4 is difficult to interpret because of small sample size. This applies to both the number of T. granulosa found on the 8 matched searches (n=39) and the number of sites (n=5) where they were present. Finally, there was a significant correlation between the abundance of P. veh icu lu m and the area of CWD on the ground when the area of Sword Fern bases was held constant. These results suggest that if the relationship between abundance and these site characteristics are to be clarified, sampling of salamander abundance and measurement of site characteristics needs to be done over a larger area within a site, preferably with a randomized sampling design, and that more sites are needed to increase sample size. Clearly, CWD is important as cover for P. veh icu lu m ,but there are no site differences that I measured that explain the differential pattern of distribution and abundance of A . ferreu s and P. veh icu lu m between the northern and southern sites. Plot characteristics in relation to salamander abundance The - number of P. veh icu lu m found under ACOs was correlated with the amount of surface area of ground covered by CWD within a plot. This suggests that cover objects limit the distribution and abundance of this species. Because these salamanders use cover objects at the surface from 157 which to forage (Fraser, 1976b; Maiorana, 1976) and find mates, this result is not surprising. They may also use cover objects as retreats from predators and unfavorable weather conditions. Inspection of Fig. 23b shows that the relationship between abundance of salamanders and amount of CWD is consistent among sites and suggests that surface abundance of salamanders is very dependent on the availability of suitable cover objects at the scale of a few meters. However, the correlation was not as good in the second year of the study, and the absolute number of salamanders found under ACOs increased (Fig. 24; see Chapter 3). This implies that the number of salamanders found under an ACO was a function of the habitat characteristics in the immediate vicinity of the ACO in the first year, but that the effect diminished over time. Apparently, where there is an abundance of natural cover and salamander densities are high, salamanders will colonize ACOs at a faster rate compared to plots with less cover and fewer salamanders. However, salamanders will eventually find the ACOs in plots with little cover, and other conditions being equal, the number of salamanders in that plot will increase. Thus, adding ACOs to a plot increases the amount of cover in the plot and so can be thought of as habitat enhancement. The number of salamanders found under an ACO should continue to reflect the amount of cover in a plot and other conditions, but the effect of natural cover will decrease because a significant fraction of that cover will be the ACO itself. Adding ACOs to plots in the 158 GVW and at Lake Cowichan increased the area of CWD in each plot by 12.5% to 101.2%. 159 Chapter 7: Microhabitat Use Habitat, food type, and time are generally considered to be the three primary resource dimensions that define an organism's niche (Huey and Pianka 1983; Toft 1985; Schoener 1974,1989), with time being more important for invertebrates than vertebrates (Schoener 1974). Differential habitat use in this assemblage of salamanders is most appropriately studied at the microhabitat level (see Chapter 1). In theory, if competition occurs for a limited resource, then the degree of partitioning of the resource should be positively correlated with the intensity of competition (Schoener 1989). If competition is not occurring now, but was intensive in the past, then differential resource use should be high. High differential resource use can also be the result of independent evolutionary histories, but if there is little differentiation and no current competition, then the resource must be abundant and not limiting. Although microhabitat selection by terrestrial salamanders is an important aspect of their natural history, only a few studies have explicitly examined differences among coexisting species in the Douglas-fir forests of northwestern North America (for a summary of studies outside this area, see Chapter 1), and none has attempted to investigate the underlying ij ?chanism. Differential microhabitat use was investigated in Oregon by 160 Bury and Corn (1988). They found that most A .fe r r e u s and Batrachoseps w rig h ti (Oregon Slender Salamander) were associated with logs, but there was some partitioning of the log microhabitats between these species. In contrast, about half of the E. eschscholtzii were associated with logs and the rest were spread among other microhabitats. In Washington, Aubry et al. (1988) found E. eschscholtzii most often in bark piles at the bases of moderately decayed snags, whereas P. vehiculum were found most often under logs in contact with the ground. Corn and Bury (1991) reported that in the Oregon Coast Range, A. fe rreu s (n=166) were usually found under the bark on logs or within logs, but rarely in contact with the ground. Plethodon vehiculum (n=40) were found most often in contact with the ground, but about 30% were found within logs. However, there was differential use of different decay classes of logs by these species: A .fe rre u s used younger decay classes, and P. v e h ic u lu m used older decay classes, although the result for P. vehiculum was not statistically significant. Ensatina eschscholtzii (n=lll) were captured most often inside logs, especially in older decay classes, but were found in contact with the ground more often than A, ferreus, but not as often as P. vehiculum. These results are similar to what I found for A. fe rreu s and P. veh icu lu m on Vancouver Island (Davis 1991), but in both studies the sample size for P. vehiculum was relatively small. I have three objectives in this chapter. First, I document differential microhabitat use among P. vehiculum and A .fe r r e u s in more detail than 161 has been done previously. I also describe microhabitat use by E. eschscholtzii, and T. granulosa to the degree that numbers captured allow. Second, comparisons of size-frequency distributions from ACO and non- ACO searches suggested that there is differential use of microhabitats by size-class (Chapter 3) and I explore that idea here. Third, I compare natural microhabitat use with the microhabitats provided by ACOs. These microhabitats are presumably equivalent to those under-log-on-the-soil, and under bark or within wood, respectively. M e t h o d s The following microhabitat categories were adopted: 1. Under bark on ground (plus decay class of bark). 2. Under log on ground (plus decay class). 3. Under bark on bark (plus decay class) 4. Under bark on log (plus decay class of log). 5. Within log (plus decay class). 6. Under bark on a snag or stump (plus decay class) 7. Within wood on a snag or stump (plus decay class) 8. On surface of bark on ground (plus decay class). 9. On surface of log (plus decay class). 162 10. On or within forest floor litter. 11. Under moss. 12. Within moss. 13. Under rock. 14. Within Sword Fern base. 15. In rocks or talus. The decay classes of large woody debris or logs were defined as follows (Bury and Corn, 1988): (1) intact, recently downed trees; (2) logs with loose bark; (3) logs without bark and partly rotted stem; (4) deeply decomposed logs with invasion by roots of other plants; and (5) hummocks of wood chunks and organic material. The decay state of loose bark was classified as: 1) intact, new bark, 2) breaks into large solid pieces, and 3) easily breaks into small blocky pieces. Inspection of the data suggested collapsing the main categories into five summary categories for the purpose of contingency table analysis: 1) Under bark on bark (i.e. between pieces of bark on soil surface), 2) CWD on soil (i.e. under bark, wood, or logs on soil surface), 3) Log (i.e. under bark on logs or within logs; includes snags and stumps), 4) Other (i.e. Sword Fern bases, within moss, under rocks), and 5) Surface (i.e. not under any kind of cover). The ACOs contained two basic microhabitats: 1) on soil under the baseboard and 2) on top of the baseboard under the top cover boards. The microhabitat under the base board and on the soil surface was probably equivalent to spaces under natural CWD on the ground. Presumably, the microhabitat on the baseboard but under the top boards was similar to natural cavities in logs or under bark on logs. R e s u l t s Variation in natural microhabitat use among species - There were striking differences among species in microhabitat use (Table 12; Fig. 26; contingency table, %2=397.9, df=12, P=0.0001), Aneides ferreus was found almost exclusively under bark on icgs or in cavities within logs (94.6%). Plethodon vehiculum used this microhabitat to some extent (19.6%), but was mostly found under CWD on the soil surface (56.9%). Similarly, E. eschscholtzii was sometimes found under bark on logs or in cavities within logs (23.5%), but was usually found under CWD on the soil surface (70.6%). Taricha granulosa was also usually found under CWD on the soil surface (52.8%), but was found on the surface (23.3%) more often than any other species, and its distribution among microhabitats was significantly different from that of P, vehiculum (contingency table, %2=71.7, df=4, Table 12. Terrestrial microhabitat use by four spedes of salamanders on Vancouver Island, B.C. Each individual is counted on its first capture only. The data are from 28 sites, but most of the P. vehiculum (n=498), E. eschscholtzii (n=5) and T. granulosa (n=146) were found at Lake Cowichan, and most of the A . ferreu s were found at Rosewall Creek (n=55) or Cook Creeks (n=10). spedes summary category microhabitat Aneides Ensatina Plethodon Taricha granulosa ferreus eschscholtzii vehiculum CWD on soil Under bark on ground 2 4 179 34 Under logon ground 1 8 399 52 bark on bark | Under bark on bark 0 0 58 19 Under bark on log 86 0 69 5 logWithin log 17 r* 122 10 Under bark on a snag or stump 0 1 0 Within wood on a snag or stump 0 1 7 0 On surface of bark on ground 0 0 3 2 surface On surface of log 1 0 3 2 On or within forest floor or litter 0 0 59 34 Under or within moss 2 0 82 3 other Under rock on ground 0 1 19 0 Within SwTord Fem base 0 0 14 2 Total number of salamanders 111 17 1015 163 165 Figure 26. Microhabitat use among four spedes of salamanders: A n eid es ferreus, Ensatina eschscholtzii, Plethodon vehiculum, and Taricha granulosa, 'bark on bark' = between pieces of bark on soil surface. 'CWD on soil' = under bark on logs or with logs, including snags and stumps, 'other' = sword fern bases, within moss, under rocks, 'surface' = not under any kind of cover. 100% ■ bark on bark n CWD on soil □ log 80% M oth er sN surface 60% 40% i i 1 20% 0% T Am ides Ensatina Plethodon Taricha n = lll n=l 7 n=1015 n=163 o\0>> 167 P=0.0001). Aneides ferreus and P. vehiculum were associated with logs of different decay classes when found under bark on a log or within a log (Fig. 27a,b; x2=143.2, df~3, P-0.0001). A neides ferreu swas most strongly associated with decay class 3 logs, whereas P. vehiculum was most closely associated with decay classes 4 and 5. That this was not due to differential densities of different decay classes of logs among sites can be seen in Fig. 28a,b. The proportion of logs in each decay class was very similar between the Lake Cowichan and the Rosewall Creek sites (Fig. 28a). Also, the total volume of logs between the two sites was similar (Lake Cowichan: 6.1 m3/12 x 12 m plot; Rosewall Creek: 4.3 m3/12 x 12 m plot). The abundance of A . ferreu s at Rosewall Creek and P. vehiculum at Lake Cowichan (Fig. 28b) was similar to the overall pattern in Fig. 27a,b, and is not related to the availability of logs of a particular decay class. Variation in natural microhabitat use among size classes For - P. veh icu lu m , the distribution among microhabitats was the similar for all size classes (Fig, 29; contingency table, %7=17.2, df=12, P=0.14). For A. 168 Figure 27. The proportion of logs used by decay class for Plethodon v e h ic u lu m and Aneides ferreus. Recaptures not included. 169 Plethodon vehiculum (n=189) ^3 Bark on log □ Within log 10%- decay class Aneides ferreus (n=103) Bark on log □ Within log 60%- 50%- 999999 20%- 10%- 3 4 decay class 170 Figure 28. The proportion of logs by decay class and the proportion of logs used by decay class at Lake Cowichan and Rosewall Creek, a. The proportion of logs by decay class at Lake Cowichan and Rosewall Creek, b. The proportion of logs used by decay class by P. v e h ic u lu m and A . ferreu s at Lake Cowichan and Rosewall Creek. 171 80% - • □ Lake Cowichan 70 % - H Rosewall Creek 60 % -= 50% -: • 40% i - 30% -= • 20% 10% 4- 0 %' H ® HP 3 4 decay class ■ Aneides ferreus (n=31) 100% - t □ Plethodon vehiculum (n=89) 60% - 40% - 20% i 3 4 decay class 172 Figure 29. Microhabitat use by SVL (mm) for Plethodoti vehiculum. 'bark on bark' = between pieces of bark on soil surface. 'CWD on soil' = under bark on logs or with logs, including snags and stumps, 'other' = sword fern bases, within moss, under rocks, 'surface' = not under any kind of cover. ■ bark on bark CWD on soil □ log 70% m other s surface 50% - 20 % - 25-34 35-44 n=275 n=334 SVL (mm) 3 174 ferreu s, too few salamanders in the smallest size classes were captured to allow comparison among size classes (see Chapter 3), and most individuals were found under bark on logs (Table 12). For T. granulosa, three size classes were created to increase cell size in contingency table analysis (< 25 mm, 25-45 mm and >45 mm SVL). Even so, there were too few captures in the 'Log' and 'other' microhabitat categories to be included in the analysis. For the remaining categories ('Bark on bark', 'CWD on soil', and 'surface'), there were no differences in the distribution among microhabitats by size class (contingency table, %2=7.4, df=4, P=0.13). Variation in ACO microhabitat use among species - There were significant differences among species in their use of soil and wood microhabitats (Fig. 30; All species: %z=266.2, df=3, P<0.0001; P. vehiculum vs. T. granulosa, %c2=36.1, df=l, P<0.0001). Plethodon vehiculum (n=1004) were usually found on soil (84.8%), whereas A . ferreus (n=62) were strongly associated with wood (98.4%). Nearly two-thirds (61.8%) of the T. g ranulosa (n=110) were found on soil. Almost all (96.7%) of the E. eschscholtzii (n-30) were found on soil. The preceding numbers do not include recaptures, 175 Figure 30. ACO microhabitat use by species. Data are from all sites combined. Recaptures are not included. P v = P lethodon vehiculum, Tg = Taricha granulosa, A = f Aneides ferreus, Ee = Ensatina eschscholtzii. n = number of salamanders for each pair of columns. Each pair of columns sums to 100%. 100% wood n=1004 n=110 ■ 177 D isc u ssio n These results confirm the observation of Corn and Bury (1991) and my observation (Davis 1991) that A . ferreus are usually found under bark on logs or within logs, but rarely in contact with the ground, whereas P. veh icu lu m is usually found on the soil under a cover object. Corn and Bury (1991), who searched 536 logs among 18 sites in Oregon and Washington, reported that about 30% of the P. vehiculum they found (n=40) were found within logs. In 1988-1990,1 had a larger sample of P. veh icu lu m (n=136), but all the data were from a single site, Rosewall Creek (Davis 1991). In 1992-1993, with a much larger sample (number associated with logs, n=590) among 28 sites, I found that 20.7% of the P. vehiculum associated with logs were within logs, but this represents just 12.0% of the individuals found in all microhabitats (n=1015). However, Corn and Bury (1 °9l) reported that the proportion of A . ferreus found within logs (56%) was higher by a factor of more than three than the proportion that I found within logs (16.4%, but 15.3% of all microhabitats). Because we made every reasonable effort to dismantle and break open logs on our searches of natural cover, these differences among studies are probably related to the availability of logs that can be taken apart, and suitable microhabitats within them, and not searching intensity, Thus, there may be differences in microhabitat use between the two areas, probably correlated with the 178 microhabitats available. Additional work needs to be done to resolve this question. Similarly, Bury and. Corn (1988) reported that 81% of the A . ferreus (total: n=79) they found in Oregon and Washington were associated with logs, either inside logs (34%) or under the bark on logs (47%). Although 93.7% of the A . ferreus (total: n = lll) that I found were associated with logs, only 15.3% were inside logs whereas 77.5% were under the bark on logs. Again, these different results may be due to differences in search methods or differences in the proportions of logs that could be torn apart. Many of the logs at Cook and Rosewall Creeks were Broadleaf Maple or Red Alder, species that are relatively rot resistant and difficult to split open. Thus, there may have been a higher proportion of salamanders inside logs, but inaccessible. Alternatively, more spaces under bark may have been available at my sites than at those sampled by Bury and Corn (1988). These observations are consistent with data on the use of ACO microhabitats and clearly demonstrates the importance of suitable cover objects when attempting to monitor a particular species. Most of the P. veh icu lu m (84.8%) were found under the base board on the soil whereas nearly all the A ferreus (98.4%) were found on wood under the top boards. If the wood microhabitat had not been made available, it is unlikely that many A . ferreu s would have been found, even in areas where they are relatively abundant. In natural microhabitats, 79.8% of the P. vehiculum were found associated with the soil surface (under CWD or rocks on the 179 soil, on bark on the ground, under bark on bark on the ground, within moss, forest floor litter, or Sword Fern bases) and 92.8% of the A . ferreus were found under bark on logs or within logs. Although size-frequency distributions from ACO and non-ACO searches suggested differential use of microhabitats by size-class (Chapter 3), there was no direct evidence from searches of natural microhabitat for this effect. Except for P. vehiculum, the sample size was small in some microhabitat categories or size classes, and this makes analysis for those species problematic. If microhabitat partitioning by size-class exists for these species, more detailed observations of the nature and size of natural cover objects will be required. In addition to showing that these species have distinct preferences for specific sites associated with logs, Bury and Corn (1988) and Corn and Bury (1991) found differences in the decay classes of logs used by these species. Aneides ferreus was most abundant in younger (class 2) logs, a result similar to what I reported here. Bury and Corn (1988) observed that B. w rig h ti was found more often in older logs (class 4 and 5), a result similar to what Corn and Bury (1991) and I found for P, vehiculum . 1 found few E. eschscholtzii (n=17), so I cannot compare abundance among decay classes, but Bury and Corn (1988) found that this species (n=52) was generally evenly distributed among all decay classes of logs. Corn and Bury (1991) reported that E. eschscholtzii (n=lll) were captured most often inside logs (60%), especially in logs of decay classes 4 and 5, and were found 180 in contact with the ground more often than A. ferreus, but not as often as P. vehiculum. 181 Chapter 8: Interspecific interactions Where species of terrestrial salamanders coexist, interspecific interactions can potentially have significant effects on their distribution, abundance, and microhabitat use. Such interactions can be direct or indirect (Abrams, 1987), but indirect interactions among terrestrial salamanders have not been studied. Indirect interactions, such as 1) exploitation competition or 2) interaction with a third species, are likely to be less important than direct interactions (Toft 1985). Two types of direct interactions are possible, interference competition and predation, either of which could result in differential microhabitat use. Several species of terrestrial salamanders are known to partition microhabitats as a result of interspecific interference competition, and I reviewed these cases in Chapter 1. Predation among terrestrial salamanders where plethodontids are involved is less well studied, but large Ambystoma maculatum will attack and sometimes eat P. cinereus (Ducey et a l, 1994). Maiorana (1978) observed that Batrachoseps attenuatus actively avoids Aneides lugubris in the field and laboratory, and suggested that A. lugubris may prey on B. attenuatus. However, because of the avoidance response, successful predation in nature may be rare. Predation among several semiaquatic genera, particularly species of Desmognathus, 182 can cause microhabitat shifts in the prey species (Keen and Sharp 1984; Southerland 1986; Hairston 1986, 1987; Formanowicz and Brodie 1993). The data on distribution and abundance from the last few chapters show that at sites where the density of P. vehiculum is relatively high, the density of A . ferreu s is relatively low. Conversely, where the density of A. fe rreu s is relatively high, P. vehiculum is relatively rare. Also, there is clearly differential microhabitat use between these species. Plethodon v e h icu lu m is usually found in contact with the soil, but this is rarely the case for A . ferreu s, which is usually found under bark on logs or within logs. Also, when P. vehiculum is found in logs, the logs are usually in an older decay class, but A . ferreu s is usually found in logs in a younger decay class. These patterns suggest that there may be interspecific interactions between these species that regulate the behavior and abundance of either or both species. Thus, one of the primary objectives of this study is to evaluate the importance of interspecific interactions between P. vehiculum and A. ferreus. In general, evidence for interspecific interactions can be obtained by either manipulations of populations in the field, by experiments in outdoor enclosures, or by laboratory experiments. Field experiments involve manipulation of populations of one species, such that if significant interspecific interactions are occurring, there will be a positive or negative effect on the second species. This requires a site where both species are reasonably abundant so that the effects of the manipulation can be 183 monitored. Such experiments have been done for some species of terrestrial salamanders (Hairston 1987), and I reviewed some of this work in Chapter 1. Field enclosures allow controlled experiments with replication under nearly natural conditions (e.g. Jaeger 1971a; Keen 1982, 1985; Wilbur 1984; Hairston 1989). In laboratory experiments, either staged encounters (e.g. Wrobel et al. 1980; Keen and Sharp 1984; Ovaska 1993; Ducey et al. 1994), or displacement from favorable cover objects or microhabitats (e.g. Keen 1982, 1985; Carr and Taylor 1985; Southerland 1986; Smith and Pough 1994) can demonstrate interspecific aggression. In this chapter, I use field enclosures to investigate microhabitat use by P. ve h ic u lu m and A . ferreu s singly and together, and use laboratory experiments to determine if individuals interact directly in staged interspecific encounters, or interact by exclusion of individuals from cover objects or territories. M e t h o d s Salamanders - On October 19-20, 1993,1 captured twenty-four A. fe rreu s near the Rosewall Creek site. I maintained these salamanders individually in 1-L glass jars filled with moist moss under a 12 h light: 12 h dark photoperiod at 10°C, and fed them termites (Z ootermopsis augusticollis), wingless Drosophila, or both, ad libitum at least once a 184 week. All animals appeared to be healthy at the time of the experiments, at which time they were transferred to food-quality plastic tubs (24 x 24 cm, 10 cm in height) with tight-fitting lids. I made holes in the sides of the tubs for ventilation, and put a moist paper towel on the bottom of each tub as well as a small wooden cover object. On April 21, 1994,1 captured ten P. vehiculum at Lake Cowichan and on April 25, 1994, fifteen P. veh icu lu m just outside of Goldstream Provincial Park. I kept these animals individually in food-quality plastic tubs (above), and fed them ad lib itu m both termites and D rosophila at least once a week. All salamanders were kept in the plastic tubs at room temperature (20°C) under natural photoperiod conditions for at least ten days before the start of the experimental trials described below. Staged encounters - 1 divided sixteen A . ferreu s into two size classes, large and small. Eight of the A . ferreu s were in the larger size class and ranged in size (SVL) from 58.3 - 66.0 mm, x=61.0, SD=2.5. The other eight A . ferreus were in the smaller size class with a range of 36.4 - 46.0 mm, x=40.3, SD=3.7. I used eight adult P. vehiculum with a SVL range of 42.8 - 51.6, x=47.6 mm, SD=2.9. I maintained the salamanders individually in food-quality plastic tubs as described above. 185 There were six classes of staged encounters, each with eight replicates. Large A . ferreus were introduced to small A . ferreus residents and P. vehiculum residents. Small A . ferreu s were introduced to large A. fe rre u s ,’esidents and P. veh icu lu m residents. Finally, P. veh icu lu m were introduced to large and small A. ferreus. Thus, there were 48 trials and each animal was used four times, twice as resident and twice as an intruder. Pairings were randomized, as well as the order of the trials, expect that at least 1 h was allowed between trials for any individual salamander, and no pair of salamanders encountered each other more than once. Observers washed their hands in tap water before and after handling a salamander. Under low light conditions, an intruder was gently placed in the tub of the resident, the cover object was removed, and a piece of glass was placed over the top of the tub. Each trial lasted 10 minutes, during which behavior of the salamanders was observed and recorded. All observations were made from behind a blind, at room temperature (20°C) during daylight hours on May 5, 1994. Use of cover object To- investigate use of cover objects, I set out 20 food-quality plastic tubs (as described above) with a wet paper towel and a wooden cover object in each tub. On May 10,1994,1 put one salamander into each of the 20 tubs. These resident salamanders consisted of ten adult P, veh icu lu m , and ten adult A. ferreus. The SVL of the P, vehiculum in 186 this experiment ranged from 41.7 - 51.8 mm, x=47.2, SD=3.2. The SVL of the A . ferreu s ranged from 36.4 - 66.0 mm, x=50.3, SD=10.0. The tubs containing resident salamanders were set out randomly on the laboratory table, the temperature was about 20° C, and the photoperiod was the same as the natural photoperiod. On May 12, 1994 an A . ferreu s was put into each of the tubs containing a resident P. vehiculum, and a P. vehiculum was put into each of the tubs containing a resident A. ferreus. The pair of salamanders was left overnight and the position of each with respect to the cover object was checked the next morning. After the experiment, the intruders were removed from the tubs, and the paper towels changed. To allow the residents time to establish occupancy, they were left in the tubs and the experiment was repeated on May 17,1994. Feeding was as described above. Habitat selection in field enclosures To - investigate microhabitat use, I built six cages that contained various microhabitats. These cages were set up outside on private property at 665 Latoria Road, Colwood, B.C. The site was surrounded by a mature (=100 year old) Douglas-fir ( Pseudotsuga m en ziesii) forest which formed a canopy over the cages and shaded them from direct sunlight. The ground vegetation was dominated by Salal (Gaultheria shallon). 187 Each cage wus 122 cm long, 61 cm wide, 61 cm deep and framed in wood. I covered the ends and bottom with 10 mm thick plywood. To allow the movement of small arthropods into the cages, I covered the sides and top with 3 mm mesh hardware cloth. I drilled small holes in the plywood bottom for drainage. I positioned the cages about 2 to 3 m apart and parallel to each other, buried the bottom of each cage to a depth of 20 cm, and filled each cage with soil level to a depth of 20 cm. On the soil in each cage, I placed two pieces of Douglas-fir bark, and two split logs (rounds) of Douglas-fir with bark loosely attached. Each piece of bark on the soil was about 10-15 cm x 40-50 cm. The rounds were about 40 cm long, 30 cm in diameter, and split horizontally along the long axis. I loosened the bark on the top half of each round and placed a 6.5 mm x 38 mm x 60 mm cedar block under the bark at one end of each round. This created a space under the bark on the rounds. I also placed a cedar block of the same dimensions in the split in each round, which created a space between the split halves. All the rounds and bark were from the same log, which was solid and which I felled in the summer of 1986. I used twenty-four A . ferreu s in this experiment. They ranged in size (SVL) from 36.4 - 66.0 mm, x=49.9, SD=9.58. The salamanders were ranked according to SVL and divided into four size classes with six salamanders in each size class. The resulting size classes (SVL in mm) were: 36-41; 43-47; 48-59; 60-66. 188 On May 28, 1994,1 put 4 adult P. vehiculum (SVL: x =47.4, SD=3.0, range 41.7 - 51.8 mm) in each cage. Three days later I recorded their locations in the cage with respect to the following microhabitat categories: 1) on the surface, 2) under bark on soil, 3) under bark on leg, 4) in crack in log, 5) under log on soil. Then, I added four A . ferreu s to each cage (one salamander, randomly assigned, from each of the four size classes, above), and checked the locations of all salamanders two days later. I removed all the P. vehiculum that could be found and checked the location of the A. ferreu s the following day. All observations were made between 07:30 and 08:30 hours. Interspecific predation - I investigated the possibility that adult A. fe rr e u s prey on hatchling P. veh icu lu m . Five hatchii.^ P. veh icu lu m (SVL: x=19.4, SD=0.78, range 18.6 - 20.7 mm) were used in this experiment. One hatchling was put in each of five food-quality plastic tubs (as described above) containing a large resident A . ferreus (SVL: x =61.06, SD=1.32, range 59.5 - 63.0 mm) that had not been fed for 5 days. The salamanders were checked at 1,3 and 8 days later. 189 R e s u l t s Staged encounters Because- the tubs were relatively small, the salamanders usually either came into physical contact with each other, or reacted in some way toward the other salamander during the trials. In 81.3% of the trials there was either physical contact between members of a pair (48.0%) or some other reaction toward the other salamander (33.3%) such as looking toward, approaching, moving away, or nose tapping. No agonistic behavior was apparent in any trial, and the frequency of nose tapping, looking toward, moving toward and moving away was about the same for both species (x2=3.4, df=3, P=0.34). In general, both species seemed to be aware of the presence of the other salamander (by nose tapping, looking toward or approaching), but then ignored the other salamander (by walking away, or by crawling under or over the other salamander). In three cases, the P. vehiculum crawled under a large A. ferreus, essentially treating it as a cover object. U se o f cover object - There was no difference between the two trials in the number of salamanders of each species that was under the cover object (xc2=0.01, df=l, P=0.91), so the data from the two trials were combined, Plethodon vehiculum was under cover more often (75%) than was A . ferreus (42.5%) and the difference was statistically significant (%c2=7A, df=l, P=0.l _ 6). However, in 15 out of 40 tubs (37.5%), both salamanders were under the cover object. When the salamanders were under the same cover object, in 79% of the cases the salamanders were in contact with each other. Residents were not under the cover object more often than intruders (both species: %c2=0.05, df=l, P=0.82; A . ferreu s or P. veh icu lu m resident: %C2=0.O, df=l, P=1.00). Habitat selection in field enclosures - For the purpose of statistical analysis, the microhabitats of 'bark on soil' and under log on soil' were combined, as were the microhabitats 'under bark on log' and 'within log'. Using these two microhabitats only, there were no differences for either species in the use of microhabitats with or without the other species being present (Fig. 31; P. vehiculum: xu2=0.003, df=l, P=0.95; A. ferreus: xc2=0.04, df=l, P=0,84). However, there were significant differences in microhabitat use between species (excluding 'surface', x2=46.8, df=3, P=0.0001), with P. ve h ic u lu m most often found in contact with the soil (86%) and A . ferreu s most often found either under the bark on the logs (52%) or within the cracks in the logs (25%). Interspecific predation - None of the P. veh icu lu m hatchlings were eaten by the adult A. ferreus. There was no indication that the hatchlings were hiding from the adults. Two salamanders were in contact on the last 191 Figure 31. Microhabitat selection in field ei„ ' "ures by Plethodon v e h ic u lu m and Aneides ferreus, singly and with each other, l-'v = P. ve h ic u lu m; A f = A, ferreus. 192 Plethodon vehiculum □ Pv alone W Pv with Af Bark on soil Log on soil Bark on log Within log Surface Aneides ferreus 80% 70% □ Af alone 60% i ^ Af with Pv 50% 40% 30% 20% 4 10% 0% 1 1------1------5------1 Bark on soil Log on soil Bark on log Within log Surface 193 day of the experiment. At the end of the experiment I offered the A. fe rreu s termites. Each A . ferreus ate three termites in less than 5 minutes. D isc u ssio n There was no evidence in staged encounters, the co ver object experiment, the microhabitat experiment, or in the predation experiment of any interaction between these species. These results strongly suggest that the patterns of distribution, abundance, and differential microhabitat use found in these species are entirely the result of intrinsic differences between them, and have nothing to do with current interspecific interactions. In the cover object experiment, P. vehiculum was more often under cover objects than A. ferreu s, but in o^er one-third of the cases both salamanders were under the same cover object, suggesting that this differential use of cover objects is unlikely to be the result of species interactions and is probably the result of intrinsic behavioral differences. In general, A. ferreu s gives the impression of being more active and exploratory in captivity than P. vehiculum. For example, in an experiment not reported here in detail, A ferreus took less time (x=48.4 seconds) to move along a horizontal ramp and go down a hole than did P. vehiculum (x =170.0 seconds; t=2.69, df=10, P=0.02). Thus, there were probably fewer A. 194 fe rreu s under cover objects compared to P. vehiculum because of higher activity levels in A. ferreus. Also, when the salamanders were under the same cover object, they were often in contact with each other, suggesting tolerance or indifference toward each other. This was even the case in the predation experiment where the sizes of the salamanders differed greatly. Despite this tolerance, the two species moved into different microhabitats in the enclosure experiment whether the other species was present or not. This is consistent with the microhabitat use by these species described in Chapter 7. Hatchling P. veh icu lu m ought to be ideal prey items for large A. ferreus'. they appear to be relatively defenseless, are locally abundant, and have no chitinous parts as do many invertebrate prey. Although terrestrial plethodontid salamanders are thought to be a high-quality prey item for a predator (Burton and Likens 1975b), the skin secretions of several species are noxious to shrews and leave an astringent or burning taste in the mouth of humans (Brodie et al. 1979). The adhesive effects of plethodontid skin secretions may be even more important in predator defease, and can completely immobilize a snake predator (Arnold 1982). However, Ducey et a l (1994) did not report adverse reactions in A. m a cu la tu m during or after eating P. cinereus, but P. cinereus were often able to brace against the head of the predator, pull free, and successfully escape. Thus, because of their potentially noxious skin secretions and ability to escape, P. veh icu lu m may be an undesirable prey item for A. 195 fe rreu s. Whatever the reasons, the large adult A . ferreu s that I tested showed no interest in hatchling P. vehiculum as prey. 196 Chapter 9: Summary A primary objective of this study was to determine the general distribution and abundance of P. vehiculum and A . fe rreu s on southeastern Vancouver Island. The results of ACO searches and TCSs indicated that the density of A . ferreus was relatively high at the northern sites (Cook Creek and Rosewall Creek) compared to Lake Cowichan and the sites further south. In contrast, the density of P. vehiculum was relatively low at the northern sites compared to the density at the southern sites. There is a large area between these sites that I was unable to sample adequately because much of the land, at least at lower elevations, has been converted to use for human habitation and agriculture, and the surrounding forests are highly fragmented. In general, undisturbed old- growth stands below 600 m elevation, and with an area greater than 10 ha, are very rare on the east side of central and southern Vancouver Island. Therefore, it may be impossible to determine the historical pattern of distribution and abundance of these salamanders. The biogeography ofA . ferreus on Vancouver Island is an especially interesting problem. There is evidence that sites north of my study sites have densities comparable to the densities at Rosewall Creek. For example, A . fe rreu s are common at Miracle Beach Provincial Park (pers. obs.; for this 197 and other locations discussed below, see Fig. 1, p. 28). Stelmock and Harestad (1979) found 15 A. ferreu s in six hours of searching in July near Woss (2.5 A. ferreus/h). They found 21 A. ferreus and one P. veh icu lu m on other searches in the same general area. I found 4.6 A. ferreus for every P. veh icu lu m under ACOs at the RMC sites and eleven A. ferreu s and one P. vehiculum at Rosewall Creek on a 2 h TCS focused on CWD (5.5 A. ferreus/h). In contrast, searching all microhabitats, produced three A. fe r r e u s and thirteen P. veh icu lu m at the same site on an earlier 2 h search (1.5 A. fe r r e u s /h and 6.5 P. vehiculum/h; Fig. 21). Thus, because it is not known how comparable the searches by Stelmock and Harestad (1979) are to those in this study, it is not possible to compare the abundance of salamanders at the sites near Woss with the RMC sites. However, the abundance of A. ferreu s is clearly higher, and the abundance of P. v e h ic u lu m is likely lower at Woss than at many of the sites I studied in the southern part of my study area. In contrast, Dupuis et al. (1995) sampled nine forested sites (stand age 17 - 500+ years) and two clearcuts near Port Alberni and found only two A. ferreus , but 562 P. vehiculum . Elevations of the sites were not reported, but all microhabitats were searched in ACSs. It would be interesting to search those sites targeting microhabitats favored by A. ferreus, Other sites on Vancouver Island have relatively high densities of A. fe rre u s. For example, sites in the vicinity of Jordan River may have relatively dense populations (pers. obs.), but more searches in this area are 198 needed to confirm this impression. On the west coast of Vancouver Island near Tofino, A . ferreu s are common and can be found in both forests and clearcuts (pers. obs.). They appear to be common at lower elevations in Carmanah Valley Provincial Park, but are rare at higher elevations. Many plethodontid salamanders are restricted to particular elevations (Hairston 1951,1987), and transects along an elevational gradient at sites on the west coast of Vancouver Island would help to address this question for A. fe r r e u s . Clearly, more searches of potential sites on Vancouver Island are needed to properly assess the distribution and abundance of this species. Generally, based on the seasonal abundance data from ACOs and data in Davis (1991), this should be done in from about mid-April to mid-July, and from the beginning of October to mid-November. Other months are unlikely to yield many animals, even if the absolute density is high. Searches of CWD focused on large, younger decay class logs are probably the best method for sampling this species, but ACOs could be used at sites where densities are known to be high for the purpose of detecting the timing of surface abundance. More frequent searches of many more ACOs than I had at Rosewall Creek and Cook Creek are needed to determine the precise weather conditions under which individuals of this species move from relatively inaccessible retreats deep inside logs to under the bark on logs where they are more accessible. 199 The other interesting aspect of the biogeography of this species concerns its disjunct distribution (see Chapter 1). Habitats on the mainland of British Columbia and in Washington state appear to be suitable for A. ferreu s, but colonization has not occurred. Jackman (1993) has shown that A . ferreu s from Vancouver Island are genetically nearly identical to those in California, and more distantly related to A . ferreu s in Oregon. He suggests thatA . ferreu s was introduced to Vancouver Island in the nineteenth century in shipments of bark from tan oaks from California. According to this hypothesis, salamanders dispersed from point sources at Victoria and Nanaimo to the present distribution on Vancouver Island in less than 150 years. Although this may explain the genetic similarities between these populations, it is inconsistent with what we know about the distribution, ecology and natural history of this species. Based on recaptures of 176 individuals, I found that the mean distance moved between captures of A . ferreus was less than 3 m and there was no significant relationship between the number of days between captures and the distance moved (Davis 1991). Also, 76% of the movements were <, 2 m and 94% were < 10 m. The longest distance moved by any individual between captures was about 40 m. The straight line distance from Nanaimo to Tofino is about 145 km, but because the path is constrained by fjords and large, long lakes, the shortest distance on tend is about 170 km, not taking into account changes in elevation. Thus, a salamander population would have to spread at an average rate of over 1 km/year to 200 spread from Nanaimo to Tofino to achieve the current distribution. Upon reaching Tofino, the salamanders would have to quickly spread to Cleland Island (Jarernovic 1978), which seems wildly unlikely given that they have not crossed the Columbia River from Oregon to Washington since the end of the Pleistocene. Several other islands adjacent to Vancouver Island have large populations of this species [e.g. Thetis Island (pers. obs.), Denman Island (J. Blake, pers. comm.), and Portland Island (C. Engelstoft, pers. comm.)]. Equally problematic is the population at Woss (Stelmock and Harestad 1979; Harestad and Stelmock 1983), which is over 200 km from Nanaimo. The other problem with Jackman's (1993) hypothesis is that the generation time in these salamanders is 3-4 years and fecundity is low: the average number of eggs per clutch reported in the literature is 10.4 (Dunn 1942, Storm 1947, Davis 1991). All of this suggests that the current distribution of A . ferreu s in British Columbia is the result of dispersal that occurred over a time span much longer than Jackman suggests. The biogeography ofP. vehiculum in British Columbia is equally interesting. Found throughout much of Vancouver Island and the mainland, it appears to be absent from many if not all of the Gulf Islands. This animal is often very abundant and relatively easy to find, so systematic searches in the appropriate season on the Gulf Islands should estabiish this point. Extensive searches have been done on Thetis Island yielding many A. ferreus, T, granulosa, one A. macrodactylum, but no P. veh icu lu m (T. Davis and J. Caldbeck, unpublished data). One of the 201 highest densities of P. vehiculum found on TCSs was at the Chemainus River site, which is located on Vancouver Island at approximately the same latitude as Thetis Island. Although there was substantial variation in abundance among sites, there was considerable variation in abundance within sites as well. The most extreme case is in Coldstream Park where surface densities varied by a factor of 72 over a distance of 200 m (Areas 1 and 5, Fig. 19). Also, the total number of salamanders found under ACOs differed by a factor of more than 12 between plots 50 m apart in the GVW old-growth site, with the more productive plot being obviously wetter. But adjacent plots in the GVW mature and GVW immature stands varied by factors of more than 6 and more than 3, respectively, without obvious differences in surface moisture. At Lake Cowichan, over an area of about 1 ha, abundance varied among plots by a factor of 4.8. Dupuis et a l (1995) found that the density of P. vehiculum was four to six times higher within 10 m of streams compared to habitats more than 30 m from streams in mature (52-72 years) forests, an effect attributed to moisture differences. This effect was not observed in old-growth stands (330-500+ years). However, we have seen that P. veh icu lu m is associated with CWD and logs in a late stage of decay. Such material may be more abundant near streams in managed forests for a variety of reasons including increased rates of decay near streams, greater density of downed trees, and less disturbance by logging operations. In old- growth forests, CWD and logs in a variety of decay states are more likely to 202 be abundant everywhere. Also, Corn and Bury (1991) and Bury et a l (1991) found a strong correlation between the abundance of P. vehiculum and the presence of talus. They concluded that the presence of talus may be more important than other variables in the environment. Thus, subtle changes in local moisture conditions, the amount of CWD, the decay state of logs, and the presence or absence of talus may affect the density of P. vehiculum across a star d that appears homogeneous. The second major objective of this study was to document the nature and extent of differential microhabitat use between these species. I confirmed my impressions (Davis 1991) and those of Corn and Bury (1991) that A . ferreu s is usually found under the bark on logs or in cavities in logs of younger decay classes, but is rarely found in contact with the soil. In contrast, P. vehiculum was thought to be found most often under CWD on the soil, and when found in logs uses older decay classes, but the sample sizes for these conclusions were small (n=40 and n=12, respectively; Corn and Bury 1991). With my much larger sample size (n=590 and n=122, respectively), this result can now be considered firm, and is not associated with the presence or absence of the other species. Ther, are several possible explanations for these patterns of distribution, abundance and differential microhabitat use. First, there may be climatic differences among sites that directly favor one species of salamander over another because of physiological differences between these species with respect to temperature and moisture. However, no 203 significant differences among sites were detected (Chapter 6). Second, there may be climatic differences among sites that could indirectly favor one species of salamander over another. For example, climatic differences might control the abundance of predators, prey, or determine the species composition of trees and understory plants among sites. Although I did not sample availability of predators or prey, I found no significant differences in the flora among sites that would explain the differential abundance of P. veh icu lu m and A. ferreus. Third, there may be site- specific differences, independent of climatic differences, that favor one species over another. For example, differences in the amount and type of CWD among sites, soil pH, or substrate structure could influence salamander numbers. At the Goldstream site, the talus-like substrate may have a positive effect on the abundance of P. vehicu lu m ,but there were no site differences that suggest that A . ferreus should be more abundant at some sites rather than other sites. Fourth, if metapopuktion dynamics are important for either of these species, and this has yet to be demonstrated, then salamander abundance may be affected by the degree of forest fragmentation at the landscape level. This issue was discussed in Chapter 3. Fifth, chance historical events may have produced the current pattern. This includes stochastic processes related to colonization and local extinction (MacArthur and Wilson 1967), local or large-scale geological events, fires, or disturbance by humans. 204 The third major objective of this study was to develop a number of sampling and censusing methods appropriate for terrestrial salamanders. There are a wide variety of techniques available for sampling terrestrial salamanders (Heyer et a l 1994), and these were briefly outlined in Chapter 2, where I justified the use of artificial cover objects (ACOs). In this study, ACOs proved successful for sampling terrestrial salamanders, and I discuss their advantages and disadvantages here. There are several advantages of ACOs compared to other methods. First, unlike TCSs or other searches of natural cover, they result in little or no damage to the natural habitat. For some species, such as P. vehicu lu m , repeated searches of natural cover objects can be done without serious modification of microhabitats (e.g., Ovaska and Gregory 1989), ahhough some microhabitats, such as within logs o r under bark on logs, must be avoided. However, for other species, such as A . ferreus that inhabit logs that must be taken apart, modification of the habitat can be a serious concern. Second, ACOs can attract species that are difficult to trap in pitfall traps (for pitfalls, see Welsh and Lind 1988). However, ACOs should contain species-specific microhabitats if the target species are to be successfully sampled. Third, ACOs provide a standardized sampling unit. Searching natural cover among sites that differ in the amount and type of CWD may not be comparable because some types of cover many be difficult to search efficiently, resulting in unequal search effort. Finally, observer bias is minimized compared to searches of natural cover. 2.05 On the TCSs of April 26-27,1993 (Chapter 5), there were significant differences in the number of salamanders caught among the five collectors (%2=22.6, df=4, PcO.OOl). The mean number of salamanders caught per collector was x=58.4, SD=18.2 with a range of 32-77 salamanders. Variation among collectors in experience, motivation, physical condition, and psychology can probably account for these differences. In contrast, because the collector is concentrating on a relatively small, well defined area, salamanders are much harder to overlook with ACOs (compared to searches of natural cover), and the other collector-associated variables are of much less importance. However, there are several disadvantages to using ACOs. First, because the suitability of ACOs as cover objects varies among species, they can provide only measures of relative abundance among similar sites and not among species within sites. Also, the suitability of ACOs as cover objects varies among size classes, so the size-structure of the sample is not necessarily representative of the size-structure of the population. Second, establishing ACOs essentially creates new microhabitat, and the effect of this on salamander populations is unknown, but capture rates will increase locally. Third, through processes of decay and invasion by fungi and arthropods, the nature of the ACOs may change through time, although this should be consistent across similar sites and subject to the same conditions that natural CWD experiences. In Chapter 7,1 showed that A. 206 fe rreu s uses logs in younger decay classes and P. vehiculum uses logs in older decay classes. Extending this to ACOs. we would expect that numbers of A . ferreu s found under ACOs should decrease over time and the number of P. veh icu lu m increase, without any change in the size of either popuktscn. This could be controlled by replacing some proportion of the ACOs yearly, eventually achieving a stable age distribution of ACOs. Finally, although they are generally easier to install than pitfall traps with drift fences, their installation is labour-intensive, and they are costly per salamander found compared to searches of natural cover, especially if salamander densities are low. The results of Chapter 3 indicate that ACOs were biased against younger size classes for unknown reasons. In other species, similar effects can be imagined. For example, in a territorial species like P. cinereus, one may be sampling territorial males only, while a much larger population of "floaters" (non-territorial individuals awaiting access to a suitable cover object) might be missed (R. Jaeger, pers. comm..). In general, species richness is probably much more efficiently sampled by searches of natural cover than by using ACOs. For example, I found A . ferreu s at the Coldstream and Lake Cowichan sites on searches of natural cover, but not under ACOs. This result agrees with Pearman et al. (1995) who found in Ecuador that day or night transect searches of natural cover resulted in observations of more species than did searches of simple artificial cover objects. This is probably because more types of microhabitats 207 are inspected on searches of natural cover than on searches of ACOs, even when the ACOs are configured to have complex multiple microhabitats. ACOs used to monitor surface abundance at a site are probably best set out systematically along parallel transects. Random distribution of ACOs is desirable form a statistical point of view, but this would complicate the physical task of checking them. Systematic sampling will likely give a representative sample as long as some feature of the habitat does not vary with the same period as the distance between sampling points. Based on the results from Goldstream and Rosewall and Cook Creeks, one would expect to find at least two P. veh icu lu m per ACO or about 0.5 A . ferreus per ACO during peak surface abundance at sites where the densities are relatively high. Thus, 36 ACOs will give a reasonable sample at most sites. This is the number of ACOs I had at Lake Cowichar. and at the GVW sites. Once installed, these can be checked, including taking measurements of salamanders, in about 1 h by two people. For P. veh icu lu m ,single boards laid on the soil are probably optimally efficient, but much could be done to optimize ACOs for A. ferreus. Clearly, boards placed directly on the ground are nearly useless. Various arrangements of boards or other materials could be tested. For example, 1x12 (2.5 x 30 cm) boards could be stacked with spacers between them, either leaning on logs or set directly on logs. Such experimentation should be done at a site where densities are high, such as at the Rosewall 208 Creek and Cook Creek sites. (Unfortunately, the Rosewall Creek site no longer exists as the new Island Highway has been placed directly over it.) The forth major objective of this study was to evaluate the importance of interspecific interactions between A . ferreu s and P. veh icu lu m . Interspecific interactions between these species, either predation or competition, could affect population size. However, as a result of intrinsic differences in microhabitat preferences, there appears to be little chance of contact between P. veh icu lu m and A . fe rreu s in the wild. These intrinsic differences could be the result of competition in the evolutionary past or independent evolutionary development (Connell 1980). When these species do come in contact with each other, no significant interactions occur, at least under the conditions in my experimental tests. Therefore, the abundance and distribution of these species can be considered independently of each other. S y n o psis Artificial cover objects (ACOs) - ACOs were useful for repeated sampling of salamander populations. They have the advantages of 1) being non-disruptive to the natural habitat, 2) attracting species that are difficult to trap in pitfall traps. 3) providing a standardized sampling unit, and 4) minimizing observer biases and errors. In terms of the relative abundance 209 of species, ACOs produced approximately the same proportions among species as searches of natural microhabitats. However, for species richness it is probably more efficient to search the natural habitat directly (Pearman et al. 1995). Searches of natural habitats are biased by the availability of microhabitats that can be searched, the microhabitats that are targeted, variation in skill and motivation among individual collectors, and details of the search procedure. Despite the advantages of using ACOs, there are several difficulties or biases associated with ACOs. The efficiency with which ACOs attract salamanders varies among species. Thus, if certain species are to be captured in reasonable numbers, species-specific microhabiats must be built into ACOs (e.g. space between wood for A. ferreus). Smaller size classes of A . fe rreu s and P. vehiculum are not found under ACOs as often as they are found on searches of natural microhabitats. Also, as ACOs age, they are invaded by fungi and arthropods, and conditions under ACOs may change over time, thereby becoming more or less attractive to particular species of salamanders. In general, because ACOs represent new habitat, they probably attract salamanders. This results in an increase in local surface density by immigration from the surrounding habitat. Thus, capture rates may increase as salamanders discover ACOs, although the overall population size remains the same. .210 Distribution and abundance among sites- At the primary sites, I collected data on 2278 individual salamanders with an additional 812 recaptures. Quadrat seraches at Goldstream Park yielded 149 P. vehiculum (Chapter 4). On TCSs of primary and secondary sites (Chapter 5) I collected data on 467 salamanders. Finally, on an opportunistic search near Rosewall Creek, I collected another 45 A. ferreus. The density of A . ferreus was relatively high at the northern sites (Cook Creek and Rosewall Creek) compared to Lake Cowichan and the sites farther south. In contrast, the density of P. veh icu lu m was relatively low at the northern sites compared to the density at the southern sites. I found no significant differences among sites in terms of climate or site characteristics that would explain this pattern of distribution and abundance. At Goldstream Provincial Park, the abundance of P. veh icu lu m was greater by more than an order of magnitude than the mean abundance of the other forested sites in the south. Abundance of salamanders among all the forested sites except Goldstream generally varied by less than a factor of 2. Salamander abundance is greatly reduced in clearcuts, but there was no difference in the number of salamanders found among the old-growth, mature, or immature sites in *he GVW. Distribution and abundance within sites - According to estimates made in fenced ACO plots, no more than 24% of the P. veh icu lu m are at the surface at any particular time. On average, only about 10% of the 211 population can be located on the surface during times of peak surface abundance in the spring and fall. One of the highest densities of terrestrial salamanders reported in North America is in Goldstream Provincial Park. Areas with a rocky substrate have surface densities of about 1.65 P. vehiculum/m2, suggesting that there are at least 70,000 individuals/ha in this area. However, surface density within Goldstream Park varies by a factor of 72 over a distance of 200 m. In general, the density of P. vehiculum appears to be relatively low (surface densities of approximately 0.1 salamanders/m2 or less) across wide areas of forest habitat with occasional small patches of very high densities, probably associated with a rocky substrate. In areas without a rocky substrate, the abundance of P. vehiculum was closely correlated with the area of ground covered by CWD and moisture, so that in an apparently homogeneous site, abundance can vary by a factor of 12 over a distance as little as 50 m. Microhabitat use - Over 1300 salamanders were found on searches of natural microhabitats. Aneides ferreus is usually found under the bark on logs or in cavities in logs of younger decay classes, but is rarely found in contact with the soil. In contrast, P. vehiculum is found most often under CWD on the soil and when found in logs, uses older decay classes. With ACOs, 98% of the A . ferreus were found in the wood microhabitat on top of 212 the baseboard, and 85% of the P. vehiculum were found on the soil under the baseboard. Taricha granulosa was found on the surface more than the other species, but otherwise its distribution among microhabitats was similar to the distribution of P. vehiculum. Very few E. eschscholtzii were caught, but their distribution among microhabitats was also similar to that of P. vehiculum. Interspecific interactions When- A . fe rreu s and P. vehiculum come in contact with each other, no significant interactions occur, either competition or predation, at least under the conditions in my experimental tests. Also, there is no evidence that microhabitat selection is influenced by the presence of the other species. Therefore, the abundance and distribution of each of these species is independent of the other species. Directions for future research- 1 have shown that P. vehiculum and A . ferreu s use different microhabitats, and that this due to intrinsic differences between these species, and is not because of interactions between them. This microhabitat partitioning could be the result of independent evolutionary histories, or the result of competition in the past (Connell 1980). I have also shown that the abundance of salamanders can vary greatly across sites that appear superficially to be similar. Also, local abundance can greatly vary within a site over surprisingly short distances. Finally, the northern sites had relatively more A . ferreu s and fewer P. 213 veh icu lu m , whereas the situation was reversed at the southern sites. In Chapter 3,1 discussed the possible role that forest fragmentation and metapopulation dynamics might play in creating this distribution. In Chapter 4 ,1 discussed the importance of talus for P. vehiculum. Earlier in this chapter I discussed questions suggested by the biogeographic distribution of these species. To identify the process or processes that create these patterns of distribution and abundance, several approaches are possible. First, it would be useful to study the detailed distribution of A . ferreu s and P. vehiculum on Vancouver Island and adjacent islands. Earlier in this chapter, I outlined some of the areas that are of particular interest. Museum records should be investigated and verified, and gaps in the data base filled in systematically. Are there areas were both species are abundant, or is the pattern I found with my limited number of sites typical? Also, is the apparent geographical decline in abundance of A . ferreu s from north to south real, or is this an artifact of a small number of study sites? The limited data we have suggest that the pattern is real, but more sites need to be searched to establish this point. If the pattern is real, is it related to climate or is it a result of forest fragmentation or some other factor? If this pattern is a result of climate, which is slightly drier and warmer in the south, it poses a puzzle because of the existence of populations of A . ferreus in Oregon and northern California. ACOs might be established and monitored in key areas that would serve as reference sites to determine 214 when salamanders are near the surface, and then abundance could be estimated with TCSs and surveys of CWD by trained collectors. Hairston (1987) suggested that nesting sites might be the ultimate limiting resource for P. teyahalee and P. jordani, and this might be the case for the Vancouver Island species as well. For P. vehiculum, talus might be favorable for nesting, foraging, or both. Corn and Bury (1991) and Bury et al. (1991) found that the abundance of P. veh icu lu m was correlated with talus, and this should be investigated for Vancouver Island. For A. ferreus, nesting logs of a particular size and decay state might be limiting. Sites were A . ferreu s are abundant need to be identified and the amount and type of CWD measured. If a correlation is found between abundance and logs of a particular size and decay state, nesting logs might be identified. Based on the three clutches I found at the Rosewall and Cook Creek sites (Davis 1991), suitable nesting logs are probably >0.5 m in diameter and in decay class 3. Terrestrial salamanders are small, inconspicuous, and their abundance at the surface is very dependent on local microhabitat features and recent weather conditions. This makes the identification of high- density populations labor-intensive, because the assessment of any particular site requires intensive sampling at a relatively fine scale several times during a season. ACOs can help in this regard because they are easily checked, and represent a standard search unit so that a series of searches over a season can be compared directly. Thus, periods of peak surface 215 abundance can be identified during which more intensive sampling can be done. For P. vehiculum, point quadrat sampling (Heyer et al. 1994), such as I used at Goldstream Provincial Park (Chapter 4), is probably the best method because it lends itself to statistical analysis and samples a variety of habitat types. For A. ferreus, patch sampling (Heyer et al. 1994), in which logs of a particular size and decay class are searched, is probably the most efficient method. In spite of these sampling difficulties, once a dense population is located, large numbers of salamanders can be found dependably year after year. Hairston (1987) reported that population size in some terrestrial plethodontid salamanders in eastern North America appears to be relatively stable over a period of several years (at least eight years for P. jordani; also, see Jaeger et al. 1995 for P. cinereus), and this appears to be the situation at at least some of the sites I have studied. The abundance of A . ferreus at the RMC sites has apparently remained relatively stable over a period of five years (1989-1994; Davis 1991, and this study). 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Prentice-Hall, Englewood Cliffs, New Jersey. YI.IA Surname: Davis Given Names: Theodore Michael Place of Birth: Portland, Oregon, USA Educational Institutions Attended: Oregon State University 1964-1966 Portland State University 1966-1968 University of New Mexico 1969 University of Victoria 1986-1996 Degrees Awarded: B.S. Portland State University 1968 M.Sc. University of Victoria 1991 Honours-and Asyands: King-Platt Memorial Award 1988 King-Platt Memorial Award 1989 President's research scholarship 1990 President's research scholarship 1991 NSERC 1991-1993 President's research scholarship 1992 NSERC 1992-1993 King-Platt Fellowship 1993-1994 Samuel Simco Bursary 1995 Publications: Davis, T. M. 1991. Natural history and behaviour of the Clouded salamander, Aneides ferreus Cope. M.Sc. Thesis. University of Victoria, Victoria, B.C. Davis, T. M. 1994. Contributor toG. M. Fellers and C. A. Drost. Sampling with artificial cover pp. 146-150. In W. R. Heyer, M. A. Donnelly, R. W. McDiarmid, L. C. Hayek, and M. S. Foster (eds.). Measuring and Monitoring Biological Diversity: standard methods for amphibians. Smithsonian Institution Press, Washington, D.C. Davis, T. M. (in press). Standardized methodology for the inventory of biodiversity: terrestrial salamanders. Wildlife Branch, B. C. Ministry of Environment. Davis, T. M. (in press). Non-disruptive Monitoring of Terrestrial Salamanders with Artificial Cover Objects on Southern Vancouver Island, British Columbia. In D. M. Green, (ed.). Amphibians in decline. Society for the Study of Amphibians and Reptiles. Davis, T. M. and P. T. Gregory 1991. Status report: the Clouded salamander, Aneides ferreus, in British Columbia. Wildlife Branch, B. C. Ministry of Environment. Ovaska, K., and T. M. Davis. 1992. Fecal pellets as burrow markers: intra- and interspecific odour recognition by four western plethodontid salamanders. Anim. Behav. 43:931-939. PARTIAL COPYRIGHT LICENSE I hereby grant the right to lend my dissertation to users of the University of Victoria Library, and to make single copies only for such users or in response to a request from the Library of any other university, or similar institution, on behalf or for one of its users. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by me or a member of the University designated by me. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Title of Dissertation: Distribution, Abundance, Microhabitat Use and Interspecific Relationships Among Terrestrial Salamanders on Vancouver Island, British Columbia Author ______(__ r Theodore M. Davis April 25, 1996