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Theses and Dissertations Theses and Dissertations
1-1-2007
Herpetofauna Communities and Habitat Conditions in Temporary Wetlands of Upland and Floodplain Forests on Public Lands in North-Central Mississippi
Katherine E. Edwards
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Recommended Citation Edwards, Katherine E., "Herpetofauna Communities and Habitat Conditions in Temporary Wetlands of Upland and Floodplain Forests on Public Lands in North-Central Mississippi" (2007). Theses and Dissertations. 2484. https://scholarsjunction.msstate.edu/td/2484
This Graduate Thesis - Open Access is brought to you for free and open access by the Theses and Dissertations at Scholars Junction. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of Scholars Junction. For more information, please contact [email protected]. HERPETOFAUNA COMMUNITIES AND HABITAT CONDITIONS IN TEMPORARY
WETLANDS OF UPLAND AND FLOODPLAIN FORESTS ON PUBLIC LANDS
IN NORTH-CENTRAL MISSISSIPPI
By
Katherine Elise Edwards
A Thesis Submitted to the Faculty of Mississippi State University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Wildlife and Fisheries Science in the Department of Wildlife and Fisheries
Mississippi State, Mississippi
May 2007
HERPETOFAUNA COMMUNITIES AND HABITAT CONDITIONS IN TEMPORARY
WETLANDS OF UPLAND AND FLOODPLAIN FORESTS ON PUBLIC LANDS
IN NORTH-CENTRAL MISSISSIPPI
By
Katherine Elise Edwards
Approved:
Jeanne C. Jones Kristina C. Godwin Associate Professor of Wildlife and State Director, USDA APHIS Fisheries Wildlife Services (Director of Thesis) Adjunct Faculty of Wildlife and Fisheries (Committee Member)
W. Daryl Jones Bruce D. Leopold Assistant Extension Professor of Professor and Head Wildlife and Fisheries Department of Wildlife and Fisheries (Committee Member) (Committee Member)
Bruce D. Leopold George M. Hopper Graduate Coordinator Dean Department of Wildlife and Fisheries College of Forest Resources
Name: Katherine Elise Edwards
Date of Degree: May 4, 2007
Institution: Mississippi State University
Major Field: Wildlife and Fisheries Science
Major Professor: Dr. Jeanne C. Jones
Title of Study: HERPETOFAUNA COMMUNITIES AND HABITAT CONDITIONS IN
TEMPORARY WETLANDS OF UPLAND AND FLOODPLAIN FORESTS ON
PUBLIC LANDS IN NORTH-CENTRAL MISSISSIPPI
Pages in Study: 115
Candidate for Degree of Master of Science
Temporary wetlands are important breeding sites for herpetofauna, including species of concern, but are often overlooked in conservation planning and management decisions. I conducted surveys of herpetofauna communities and quantified habitat variables surrounding isolated, upland and stream-connected ephemeral pools on Tombigbee National Forest and
Noxubee National Wildlife Refuge in north-central Mississippi from March 2004 – March 2006 to compare herpetile species assemblages between different classes of temporary wetlands, determine use of pools as reproductive sites for amphibians, and determine faunal-habitat relationships for herpetofauna. Species richness and abundance of terrestrial herpetiles differed significantly between upland and floodplain pools. Upland pools contributed substantially more to the diversity of herpetiles than floodplain pools. Upland pools supported significantly greater abundance of larval Ambystomatid salamanders and central newts (larvae and adults). Forest overstory and ground coverage components influenced amphibian abundance such as abundance of mature trees, standing snags, downed woody debris, and litter depth.
ACKNOWLEDGEMENTS
I would like to offer my sincere gratitude to the USDA Forest Service for generously funding my study. I would like to thank Tombigbee National Forest and Noxubee National
Wildlife Refuge for providing access to study sites, and specifically Dave Richardson for his interest and assistance with this study. Special thanks go to Dr. Jeanne C. Jones for her guidance as my major advisor, her professional expertise, and her undying commitment to wildlife conservation. I thank the members of my committee: Ms. Kris Godwin, Dr. W. Daryl Jones, and
Dr. Bruce D. Leopold. Many thanks to Dr. Jarrod Fogarty for pointing me in the right direction when getting started and also teaching me the use of nonparametric statistics. I would like to thank numerous technicians for their enthusiasm and dedication in data collection: Tyler Harris,
Robert Hardy, Matt Brock, Lindsey Singleton, Lindsey Smith, Amanda Mitchell, Will Kouns,
Jason Letson, and Eddie Parham and also fellow graduate students Edith Fogarty, Ray Iglay, and
Joelle Carney for their assistance.
ii
TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS ...... ii
LIST OF TABLES ...... v
LIST OF FIGURE ...... vii
CHAPTER I. INTRODUCTION ...... 1 LITERATURE CITED ...... 5
II. STUDY AREA AND FIELD METHODS ...... 7 STUDY AREA ...... 7 FIELD METHODS ...... 9 Faunal Surveys...... 9 Habitat Data Collection ...... 12 LITERATURE CITED ...... 14
III. HERPETOFAUNA DIVERSITY AND RELATIVE ABUNDANCE IN UPLAND AND FLOODPLAIN EPHEMERAL POOLS ...... 17 INTRODUCTION ...... 17 STUDY AREA ...... 23 METHODS ...... 23 Field Methods ...... 23 Statistical Analyses...... 23 RESULTS ...... 26 DISCUSSION ...... 27 MANAGEMENT IMPLICATIONS ...... 37 LITERATURE CITED ...... 41
IV. LARVAL AMPHIBIAN DIVERSITY AND RELATIVE ABUNDANCE IN UPLAND AND FLOODPLAIN EPHEMERAL POOLS ...... 56 INTRODUCTION ...... 56 STUDY AREA ...... 58 METHODS ...... 58 Field Methods ...... 58
iii
CHAPTER Page
Statistical Analyses ...... 59 RESULTS ...... 60 DISCUSSION ...... 61 MANAGEMENT IMPLICATIONS ...... 67 LITERATURE CITED ...... 69
V. HABITAT ASSOCIATIONS OF REPTILES AND AMPHIBIANS IN UPLAND AND FLOODPLAIN EPHEMERAL POOLS ...... 79 INTRODUCTION ...... 79 STUDY AREA ...... 82 METHODS ...... 82 Field Methods ...... 82 Statistical Analyses...... 83 RESULTS ...... 85 Canonical Correspondence Analysis ...... 85 Habitat ...... 85 Herpetofaunal Richness and Abundance ...... 86 Additional Analyses...... 87 DISCUSSION ...... 87 MANAGEMENT IMPLICATIONS ...... 92 LITERATURE CITED ...... 94
VI. SUMMARY AND CONCLUSIONS ...... 106 LITERATURE CITED ...... 114
iv
LIST OF TABLES
TABLE Page
3.1. Sampling effort of pitfall/funnel trap surveys on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006...... 48
3.2. Reptile and amphibian counts from pitfall/funnel trap surveys on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006...... 49
3.3. MRPP results of abundance of herpetiles detected in pitfall/funnel trap surveys on 10 ephemeral pool sites on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006...... 52
3.4. Kruskal-Wallis results for pitfall/funnel trap surveys on 10 ephemeral pool sites on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006...... 53
3.5. Species list of anuran call count surveys on Tombigbee National Forest an Noxubee National Wildlife Refuge, MS 2004-2006...... 54
3.6. Species list and frequency of detection of fish captured during sweepnet surveys in 10 ephemeral pools on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006...... 55
4.1. Amphibian counts from aquatic surveys in 10 ephemeral pools on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006...... 73
4.2. MRPP results from aquatic surveys in 10 ephemeral pools on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006...... 74
4.3. Kruskal-Wallis results from aquatic surveys in 10 ephemeral pools on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006...... 74
4.4. Periodicity of salamanders, newts, and larvae detected during aquatic surveys in 10 ephemeral pools on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006...... 75
4.5. Periodicity of larval anuran abundance detected during aquatic surveys in v
TABLE Page
10 ephemeral pools on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS, 2004-2006...... 76
5.1. Habitat variables measured from 10 ephemeral pool sites on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS, 2004-2006...... 100
5.2. Habitat variables selected for canonical correspondence analysis to identify parameters affecting reptile and amphibian abundance by class on 10 ephemeral pools sites on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006...... 101
5.3 Average habitat measurements from 10 ephemeral pool sites on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006...... 102
5.4. Correlation coefficients of habitat variables from CCA for reptile and amphibian richness and abundance on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006. Parentheses indicate variance explained by the environmental variables...... 103
5.5. Final scores from CCA for reptile and amphibian richness and abundance on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006...... 103
5.6. Dominant faunal-habitat associations from CCA on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006...... 104
vi
LIST OF FIGURES
FIGURE Page
2.1 Tombigbee National Forest, Ackerman Unit and Noxubee National Wildlife Refuge in north-central Mississippi, USA 2004-2006...... 15
2.2. Design of sampling techniques, pitfall trap (without exclusion), pitfall trap with “predator-guard”, and funnel trap, along drift fence array for herpetofaunal study on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS, from 2004-2006...... 15
2.3. Experimental design for herpetofaunal community study on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS, 2004-2006...... 16
2.4 Plot design of vegetation sampling at ephemeral pools on Tombigbee National Forest and Noxubee National Wildlife Refuge MS, 2004-2005...... 16
4.1 Larval salamander and newt abundance from aquatic surveys in 10 ephemeral pools on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006...... 77
4.2 Larval anuran abundance from aquatic surveys in 10 ephemeral pools on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006...... 78
5.1 Canonical correspondence analysis for habitat associations and herpetofaunal richness and abundance from the first 2 axes...... 105
vii
CHAPTER I
INTRODUCTION
Reptiles and amphibians play a significant role in the structure of vertebrate communities and are crucial for monitoring the integrity of wetland habitats (Russell et al. 2002). They represent important members of the food web and are among the top predators of invertebrates in forested habitats (Wyman 1998). Reptiles and amphibians are also among the most numerous organisms found on forest floors representing a large percentage of forest biomass, though often overlooked due to their inconspicuous natures (Gibbons 2003a). Amphibians, in particular, serve as a principle indicator species of habitat quality in wetlands, because they are especially sensitive to changes in water quality and habitat alteration (Russell et al. 2002).
Over the past few decades, concern over the global decline of reptiles and amphibians and the subsequent loss of biodiversity has led to an increased need in proactive conservation measures regarding habitat protection and conservation. Specifically, the protection of isolated temporary wetlands has been proposed to address breeding habitat requirements for most amphibians and aquatic reptiles (Gibbons 2003b; Dodd and Cade 1998). Isolated, temporary wetlands, or ephemeral pools, serve as important breeding sites for amphibians including many threatened and endangered species that use these pools exclusively, such as the Mississippi gopher frog, Rana sevosa (Dodd and Cade 1998). Ephemeral pools serve as breeding sites in areas that are otherwise hundreds of meters from the nearest water source (Asmus 2003). A survey conducted by Moler and Franz (1987) on the Southeastern Coastal Plain found that of the
29 species of anurans native to the area, 10 species breed primarily or exclusively in isolated
1 2 wetlands, whereas 10 other species use the habitat opportunistically (Russell et al. 2002). In addition, ephemeral pools provide water, cover, and foraging opportunities for many reptile species and support unique plant and animal communities not present in larger wetland habitats
(Walker 2001). Primary factors including habitat loss and degradation, environmental pollution, introduced invasive species, and global climate change have led to complete loss or severe alteration of many temporary wetlands making them unsuitable breeding sites for amphibians
(Gibbons 2003b.)
Under traditional guidelines of the Clean Water Act, ephemeral pools are afforded minimal protection against development. The United States Army Corp of Engineers (USACE) has used size as the primary criteria to establish jurisdiction over wetlands, implementing regulatory and protection measures for wetlands larger than 0.13 ha but generally allowing the development of those < 4.0 ha in size (Snodgrass et al. 2000). During the past 200 years, an estimated 53% of original wetlands have been lost as a consequence of human activities (Dahl
1990). Due to recent changes following the U.S. Supreme Court’s SWANCC decision in 2001, additional jeopardy was placed on ephemeral pools defined as isolated waters that are intrastate and not connected to navigable waters or adjacent to navigable waterways and tributaries.
Because of this designation, ephemeral pools are not under regulatory jurisdiction of USACE and are not afforded protection by Section 404 of the Clean Water Act (U.S. DOE 2003).
On public lands, most riparian areas and floodplain pools are protected under streamside management zones (SMZs) that buffer streams from the potential impact of silvicultural activities, with the goal of leaving the streams and riparian habitat intact for fish and wildlife
(Dickson and Wigley 2001). Amphibians and reptiles are reported to be more prevalent in SMZs of 30.48- 96.01m in width of either side; however, most SMZs on public lands are typically ≤
30.48m and even less on private lands, < 19.81m (Yarrow and Yarrow 1999; Mississippi Forestry
3 Association 2000). Therefore, floodplain pools would theoretically receive protection on public lands from two sources, SMZs and Section 404, as they are adjacent to waters protected under the
Clean Water Act. On the other hand, upland pools, receive no additional protection from disturbance by either source.
Effective conservation and management of reptile and amphibian communities can only occur with a thorough understanding of their ecology and the determination of specific habitat requirements needed at each stage of their life histories. Due to the biphasic nature of most amphibians, conservation measures should be targeted not only at the protection of ephemeral pools but also to the surrounding terrestrial habitat. Information on species richness and abundance in upland and floodplain ephemeral pools on public forested lands of central
Mississippi is limited. By determining habitat conditions that may influence the herpetofaunal community, I will be able to identify areas that support breeding amphibians and determine species richness and abundance of herpetofaunal communities of ephemeral wetlands. With this information, I can offer land managers community characteristic trends and approaches for prioritization of pools and habitat conditions that support herpetofaunal communities. The data collected during this study will be used to aid resource managers in future land use planning aimed at the conservation of herpetofauna and forest biodiversity.
This study addressed the following objectives:
1) Measure herpetofauna species diversity in ephemeral pools located on Tombigbee
National Forest and Noxubee National Wildlife Refuge.
2) Measure amphibian usage of ephemeral pools as breeding sites by determining
amphibian larvae in pools.
4 3) Measure habitat characteristics at all ephemeral pools to determine conditions which may
influence amphibian communities.
4) Compare amphibian species richness, abundance, and community characteristics as they
relate to isolated upland pools and floodplain pools.
5) Compare habitat characteristics between isolated upland pools and floodplain pools.
5 LITERATURE CITED
Asmus, J. L. 2003. Diversity of riverine turtles and pool-breeding amphibians on public lands in northcentral Mississippi. Thesis, Mississippi State University, Mississippi State, Mississippi, USA.
Dahl. T.E. 1990. Wetlands: losses in the United States 1780’s to 1980’s. U.S. Fish and Wildlife Service, Washington, D.C., USA.
Dickson, J.G. and T.B. Wigley. 2001. Managing forests for wildlife. Pages 83-94 in J.G. Dickson, ed. Wildlife of southern forests: habitat and management. Hancock House Publishers, Blaine, Washington, USA.
Dodd, C. and B. Cade. 1998. Movement patterns and the conservation of breeding in small, temporary wetlands. Conservation Biology 12(2): 331-339.
Gibbons, J. W. 2003a. Chapter 17- Societal values and attitudes: history and conservation. Pages 214-227 in R. D. Semlitsch, editor. Amphibian conservation. Smithsonian Institution Press, Washington, D.C., USA.
Gibbons, J. W. 2003b. Terrestrial habitat: a vital component for herpetofauna of isolate wetlands. Wetlands 23(3): 630-635.
Mississippi Forestry Association. 2000. Best management practices for forestry in Mississippi.Third edition. Mississippi Forestry Commission, Jackson, Mississippi, USA.
Moler, P.E. and R. Franz. 1987. Wildlife values of small, isolated wetlands in the southeastern coastal plain. Pages 234-241 in R.R. Odum, K.A. Riddleberger, and J.C. Ozier, editors. Proceedings of the third southeastern nongame and endangered wildlife symposium. Georgia Department of Natural Resources, Atlanta.
Russell, K. R., H. G. Hanlin, T. B. Wigley, and D. C. Guynn. 2002. Responses of isolated wetland herpetofauna to upland forest management. Journal of Wildlife Management 66(3): 603-617.
Snodgrass, J. W., M. J. Komoroski, A. L. Bryan Jr., and J. Burger. 2000. Relationships among isolated wetland size, hydroperiod, and amphibian species richness: implications for wetland regulations. Conservation Biology 14(2): 414-419.
U.S. Department of Energy. 2003. Clean Water Act information brief: the Supreme Court’s swancc decision. DOE/EH-412/0016r.
Walker, J.L. 2001. Sensitive plant communities. Pages 48-71 in J.G. Dickson, ed. Wildlife of southern forests: habitat and management. Hancock House Publishers, Blaine, Washington, USA.
Wyman, R. L. 1998. Experimental assessment of salamanders as predators of detrital food webs: effects on invertebrates, decomposition, and the carbon cycle. Biodiversity
6 and Conservation 7:641-650.
Yarrow, G.K. and D.T. Yarrow. 1999. Managing for non-game wildlife. Pages 256-283 in G.K.Yarrow and D.T. Yarrow, eds. Managing wildlife: on private lands in Alabama the Southeast. Sweetwater Press, Birmingham, Alabama, USA.
CHAPTER II
STUDY AREA AND FIELD METHODS
STUDY AREA
Mississippi is located within the humid subtropical climatic region of North America and is characterized by temperate winters (0 C-15 C) and hot summers (21 C-38 C). The annual mean temperature for the northern part of the state is 16.67 C and precipitation normally ranges from
127cm to 165cm across the state from north to south (Mississippi State University Department of
Geosciences 2006).
Study sites were located on Tombigbee National Forest and Noxubee National Wildlife
Refuge in Oktibbeha and Winston Counties, north-central Mississippi (Figure 2.1). These lands were managed by the U.S. Forest Service and U.S. Fish and Wildlife Service, respectively
(Asmus 2003).
Ten ephemeral pools were selected by the study preceding my work within the Hilly
Coastal Plain of north-central Mississippi (Asmus 2003). Six floodplain pools were selected, 5 of which were located east of Highway 25 on Tombigbee National Forest, Ackerman Unit, in the
Mill Creek floodplain (33°11’N, 88°58’W), Township 16N, Range 13E and one located in the
Yellow Creek floodplain, Township 16N, Range 14E within Noxubee National Wildlife Refuge in Winston County, MS. Four upland pools were chosen, located on Noxubee National Wildlife
Refuge in the area east of Bevil Hill Church (33°12’N, 88°54’W), Township 16N, 14 E (Asmus
2003). The floodplain pools were shallow oxbow sloughs that were connected to streams by
7
8 seasonal lotic overflows. The upland pools were impounded or constructed as water sources for livestock and wildlife prior to 1960. These pools were not hydrologically connected to any perennial lotic systems (Asmus 2003). Duration of pool hydroperiod depended on precipitation levels in upland pools and precipitation and flooding in floodplain pools. All pools had the tendency to become dry during summer to early fall at least every several years, if not annually
(Asmus 2003).
Floodplain pools were located within bottomland hardwood forest dominated by oaks
(Quercus spp.), hickories (Carya spp.), tupelos (Nyssa spp.), sweetgum (Liquidambar styraciflua), yellow poplar (Liriodendron tulipifera), and green ash (Fraxinus pennsylvanica).
Midstory species included American hornbeam (Carpinus caroliniana), elm (Ulmus spp.), switchcane (Arundinaria gigantea), deciduous holly (Ilex decidua), common pawpaw (Asimina triloba), and Virginia creeper (Parthenocissus quinquefolia). Understory consisted of greenbriar
(Smilax spp.), honeysuckle (Lonicera japonica), viola (Viola spp.), partridge-berry (Mitchella repens), blackberry (Rubus argutus), and panicgrass (Dicanthelium spp.) (Asmus 2003, Edwards unpublished data).
Upland pools were located within mixed pine-hardwood forest dominated by loblolly pine (Pinus taeda), persimmon (Diospyros virginiana), oaks, sweetgum, and tupelo gums.
Midstory species included sassafras (Sassafras albidum), winged sumac (Rhus copallinum), red maple (Acer rubrum), buttonbush (Cephalanthus occidentalis), and American beautyberry
(Callicarpa americana). Understory consisted of blackberry, wild grape (Vitis spp.), honeysuckle, greenbriar, beggar-lice (Desmodium spp.), and lespedezas (Lespedeza spp.) (Asmus 2003,
Edwards unpublished data).
9 FIELD METHODS
Faunal Surveys
Pools were sampled to determine species richness and abundance of amphibian and reptile communities within the pool proper and in adjacent terrestrial habitats. A sampling schedule for all faunal surveys may be found in Table 2.1. Sampling methods included use of three trap designs: pitfall traps, double-ended funnel traps, and pitfall traps combined with a wire anti-predator exclusion cover along a straight-line silt drift fence array (Figure 2.2).
Pitfall traps were installed by burying a 22.02L bucket until the top openings’ were even with the grounds’ surface. Buckets were installed ten m apart in a line conforming to the perimeter of the pool. Silt fencing was installed between the buckets and the bottom portion of the fence was partially buried to direct travel of herpetiles into the pitfall traps (Heyer et al.
1994). Fences were installed typically within 1 m of the pool’s high water mark (Asmus 2003).
One-half of the pitfall traps installed had no wire exclusion cover, whereas half of the pitfall traps were combined with an exclusion cover attached over the bucket’s opening. The cover was constructed by cutting a piece of welded utility wire (Range Master 14 Gauge) and bending it to form a cage over the top of the pitfall traps, measuring 30.48 cm x 30.48 cm x 10.16 cm. Two holes were drilled into the bucket, approximately 2.5 cm from the top on opposite sides of the bucket for attachment of the exclusions. One side of the guard was permanently attached by securing it with a non-removable cable tie. The other side was attached by using a reversible cable tie to allow easy access in checking traps and removal of organisms.
Due to periodic flooding, all pitfall traps had a rafting object (a small piece of 5.08 cm x
10.16 cm wood) to allow for the floatation of organisms caught in the traps. Open pitfall traps
(without exclusion) were shaded by propping up the bucket lid with a piece of wood. Excluded traps were shaded by placing the bucket lid on top of the predator guard while leaving the sides
10 open and accessible for traveling organisms. The designation of which traps remained unguarded and which received exclusion was accomplished through random selection of buckets on each drift fence array.
Five funnel traps were randomly placed along the drift fence at each site between pitfall
traps. Funnel traps were constructed of mesh insect netting with a body length of 60.96 cm and an
opening diameter of 20.32 cm (Heyer et al. 1994). Funnel traps were placed directly against the
drift fence and secured in place by a cable tie attached to a wooden stake that was driven into the
ground in front of the trap. Traps were shaded by raising a wooden coverboard (30.48 cm x
30.48 cm) over top of the trap and securing it to the wooden stake.
All traps were opened simultaneously for 5-10 consecutive days every 30 days, from
March 2004 through March 2006, without regard to rainfall events or other weather related variables (Figure 2.3). Lids were placed on the buckets to prevent capture of animals during non- surveying periods. During survey periods, information on date, time, and observers was recorded daily at each site. Data on weather conditions including wind velocity (calm, light, strong), precipitation, relative humidity (%), barometric pressure (in), and general condition (rain, snow, sleet, etc) was recorded. Daily rainfall data were obtained from the nearest National Oceanic and
Atmospheric Administration weather station at the Department of Geosciences, Mississippi State
University (Asmus 2003). Habitat measurements including water temperature (°C, °F), water pH, water clarity, soil temperature (°C, °F), soil pH, and soil moisture (%) was collected daily (Heyer et al. 1994; Asmus 2003). Data on capture-bucket number, species identification, abundance, gender (if discernable), age (larva, metamorph, juvenile, or adult), snout to vent length (SVL) in mm, total length (TL) in mm, and mass (g) was recorded daily at each site for all herpetiles.
Species identifications were accomplished using Conant and Collins (1998) and measurements were taken according to Petranka (1998). In the event that traps contained high numbers of
11 animals (>50), I recorded length and mass of a representative sample (ca. 25) of captured individuals to speed processing and minimize stress to animals. All individuals were counted.
Twice monthly during spring, summer, and fall (March 2004-March 2006), anuran call counts were conducted at night to locate species not readily captured in pitfall or funnel traps
(Heyer et al. 1994). Call count surveys were used to enhance detection of species but were not included in abundance estimates. We conducted surveys at each ephemeral pool site by quietly approaching the ponds, and listening motionless for ≥10 minutes to detect presence of vocalizing anurans. Data were collected regarding air and water temperature, moon phase, general sky conditions (cloudy, fog, rain), and wind speed. Calling anurans were classified according to
Heyer et al. (1994) as follows: 1= individuals can be counted, there is space between calls; 2= calls of individuals can be distinguished but there is some overlapping of calls; 3= calls are constant, continuous, and overlapping, there is a full chorus (Heyer et al. 1994).
Amphibian larvae were sampled monthly at each ephemeral pool during spring, summer, and fall, from April 2004 through March 2006. A 500 μm mesh sweepnet (25.4 cm x 45.7 cm) was used capture amphibian species present in the pool. Two surveyors sampled until approximately 80% of the littoral zone had been swept for a maximum of 30 minutes of sweep- netting spent at each pond. Vertebrate species identification were accomplished using Conant and Collins (1998), Petranka (1998), and McDiarmid and Altig (1999). Measurement including total length (TL) in mm for larva, and total length and snout-vent length (SVL) in mm for adults was recorded (Heyer et al. 1994). Invertebrate taxa were identified to taxonomic order (Leahy
1987) and fish taxa were identified at least to family (Ross 2001). Data on water pH, water temperature (°C, °F), depth (cm), and clarity were recorded at each site (Heyer et al. 1994).
12 Habitat Data Collection
Habitat characteristics were measured at each site to determine vegetation structure and composition. This information was used to determine relationships between habitat features and amphibian communities. Systematically placed, nested sampling plots were established to measure plant community characteristics (Asmus 2003). Four baseline starting points were determined at each site by first estimating the center of the pool and aligning this point with the 4- cardinal directions of a compass. In each of the cardinal directions, a starting point was chosen on the interior of the pool, 1-3 m from the pool edge (Asmus 2003). The distance from the pool edge was determined randomly. Due to the small nature of the pools, a larger distance could not be used due to overlapping of plots. From this point, I established a 20-m transect in each of the 4 cardinal directions away from the center of the pool. Starting at zero, the center location of the nested plots was established 5 meters from (perpendicular) the baseline every 10 meters out to 20 meters. A circular 1-m2 hoop made of plastic piping was placed over each sampling point to measure understory cover. Ten-m2 and 100-m2 square plots were centered over the measuring hoop to measure midstory and overstory, respectively. This system produced 24 nested plots at each pool (Asmus 2003). Understory (<1m tall) species composition and percent coverage were recorded within each 1- m2 hoop. Forest floor litter depth was measured in cm using a metric ruler at the center of each 1- m2 plot. Midstory (>1m and <6m tall) species composition and
heights were recorded in the 10-m2 plots. Overstory (>6m tall) species composition, diameters at
breast height (dbh), and ground line diameter (gld) were recorded within each 100-m2 plot (Hays
et al.1981). Within 100-m2 plots, snags and downed logs were identified by log type (pine or
hardwood) and their diameter and decay category recorded using techniques described by Hunter
(1990). Vegetation identification was accomplished using Miller and Miller (1999). Visual
obscurity was measured using a Nudds board at two of the cardinal directions, chosen randomly.
13 Six visual obscurity classes (0-0.5m, 0.5-1.0m, 1.0-1.5m, 1.5-2.0m, 2.0-2.5m, and 2.5-3.0m high) were measured at 20m from a randomly chosen bearing. Canopy closure was measured with a densitometer along the transect line at 0m, 10m, and 20m and at points perpendicular to these measurements on the outer edge of the 100-m2 plot in each of the four directions (Hays et
al.1981). This approach produced 36 densitometer readings per site (Figure 2.4). Sampling was
begun in October 2004 but was not completed prior to the arrival of dormant season. Habitat
measurements for all sites were then repeated during the growing season between June 2005-July
2005. Extensive damage to hardwoods was incurred at 4 floodplain pool sites following
Hurricane Katrina in August 2005. Therefore, canopy coverage, leaf litter, and Nudd’s board
readings were repeated following the hurricane damage in October 2005.
14
LITERATURE CITED
Asmus, J. L. 2003. Diversity of riverine turtles and pool-breeding amphibians on public lands in northcentral Mississippi. Thesis, Mississippi State University, Mississippi State, Mississippi, USA.
Conant, R., and J. T. Collins. 1998. A field guide to reptiles and amphibians: eastern and central North America. Houghton Mifflin Co., New York, New York, USA.
Hays, R., L. C. Summers, and W. Seitz. 1981. Estimating wildlife habitat variables. Office of Biological Services, Fish and Wildlife Service, U.S.D.I., Washington, D.C., USA.
Heyer, W. R., M. A. Donnelly, R. W. McDiarmid, L. A.C. Hayek, and M. S. Foster, editors. 1994. Measuring and monitoring biological diversity: standard methods for amphibians. Smithsonian Institution, Washington D.C., USA.
Hunter, M.A., Jr. 1990. Wildlife, forests, and forestry: principles of managing forests for biological diversity. Prentice-Hall, Englewood Cliffs, New Jersey, USA.
Leahy, C. 1987. Peterson first guides to insects of North America. Houghton Mifflin Co., New York, New York, USA.
McDiarmid, R.W., and R. Altig, editors. 1999. Tadpoles: the biology of anuran larvae. University of Chicago Press, Chicago, Illinois, USA.
Miller, J.H. and K.V. Miller. 1999. Forest plants of the southeast and their wildlife uses. Southern Weed Science Society, Auburn, Alabama, USA.
Mississippi State University Department of Geosciences, Office of the Mississippi State Climatologist. 2006 Aug 24.
Petranka, J.W. 1998. Salamanders of the Unites States and Canada. Smithsonian Institution Press, Washington, D.C., USA.
Ross, S.T. 2001. Inland fishes of Mississippi. University Press of Mississippi, Jackson, Mississippi, USA.
15
Figure 2.1. Tombigbee National Forest, Ackerman Unit and Noxubee National Wildlife Refuge in north-central Mississippi, USA 2004-2006.
Figure 2.2. Design of sampling techniques, pitfall trap (without exclusion), pitfall trap with “predator-guard”, and funnel trap, along drift fence array for herpetofaunal study on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS, from 2004-2006.
16
Figure 2.3. Experimental design for herpetofaunal community study on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS, 2004-2006.
Figure 2.4. Plot design of vegetation sampling at ephemeral pools on Tombigbee National Forest and Noxubee National Wildlife Refuge MS, 2004-2005.
CHAPTER III
HERPETOFAUNA DIVERSITY AND RELATIVE ABUNDANCE IN UPLAND AND
FLOODPLAIN EPHEMERAL POOLS
INTRODUCTION
The southeastern region of the United States contains a diversity of forested habitats including upland and bottomland hardwood forest, pine-flatwoods, cypress-tupelo gum swamps, mixed pine-hardwood forest, pine plantations, and other habitats such as rivers, caves, marshes, and isolated wetlands (Gibbons and Buhlmann 2001). These areas support the greatest herpetofaunal biodiversity in North America with 116 amphibian and 104 reptile species known to exist in this region alone. Many of these species are endemic species of the southeastern U.S.
(Gibbons and Buhlmann 2001). Most are found within forested ecosystems and directly depend on forests for either all or part of their life cycles (Gibbons and Buhlmann 2001). The greatest biodiversity of herpetofauna is found within the Atlantic and Gulf Coastal Plains of the southeastern U.S. (Gibbons and Buhlmann 2001). During the last 100 years, the southeastern
Coastal Plains have experienced dramatic shifts in land-use practices that have greatly altered the landscape: agriculture, pine plantations, and other human activities. These land-use trends have resulted in the loss and fragmentation of old-growth forests, bottomland hardwood forests, and temporary wetlands that once dominated this region (Dickson 2001; Gibbons and Buhlmann
2001).
In the past, most management strategies and conservation efforts have focused on game
species with little attention given to the nongame species, such as herpetofauna. As a result, 17 18 limited information exists for many species regarding basic life-history strategies and factors influencing population dynamics. Biologists have now begun to realize the importance reptiles and amphibians play in the biological communities in which they live. Amphibians have very important functions in the food chain of aquatic and terrestrial systems (Reaser 2000). Reptiles and amphibians play essential roles in the consumption of insects, including species known to be noxious to humans (Gibbons and Buhlmann 2001). In the absence of fish, amphibians may represent the top predators in freshwater systems, consuming invertebrates and other vertebrates, and aquatic vegetation. They also serve as important prey sources (Reaser 2000). Many amphibians and their larvae are depredated by large aquatic salamanders (sirens, amphiumas), salamander larvae (Ambystomatids), frogs (Ranids), mammals (Procyon lotor), birds, crayfish, and aquatic invertebrates (Odonate nymphs) (Jones and Taylor 2005; Petranka 1998). Amphibian and reptile eggs are greatly consumed by aquatic, terrestrial, and semi-aquatic predators. Aquatic and semi-aquatic reptiles also serve as efficient scavengers in aquatic systems, controlling the amount of decaying organic material present (Gibbons and Buhlmann 2001). Consequently, reptiles and amphibians influence the population dynamics of other organisms, as well as nutrient cycling, leaf litter decomposition, and energy flow (Petranka 1998; Reaser 2000).
Differing life history requirements and unique adaptations allow aquatic, semi-aquatic, and terrestrial species of reptiles and amphibians to utilize various wetland habitats and wetland ecotones (Jones and Taylor 2005). One category of wetland, temporary ponds (also known as ephemeral pools), are especially important for the reproductive success of pond-breeding amphibians, including rare species such as the Flatwoods salamander (Ambystoma cingulatum) and Mississippi gopher frog (Rana sevosa) (Petranka 1998; Bailey et al. 2006). These species are obligate breeders of temporary wetlands. Ambystomatid salamanders, numerous treefrogs, toads,
19 and other frogs are dependent upon these wetlands for breeding, oviposition, and larval development (Hairston 1996; Semlitsch et al. 1996; Petranka 1998).
Naturally occurring ephemeral pools include isolated depressional wetlands such as vernal ponds, Carolina bays, prairie potholes, and playa lakes and also river or stream-connected floodplain pools (Tiner et al. 2002; Jones and Taylor 2005). Brooks (2000) related seasonal forest pond function to aquatic islands in a sea of terrestrial forest. Seasonal climatic changes cause dramatic shifts in the appearance of ephemeral and vernal pools, causing water to collect during winter and spring rains, and change volume in response to varying weather patterns (USEPA
2003). During normal rainfall years in the southeast, ephemeral pools contain water during winter (November-February) and spring (March-May) (Jones and Taylor 2005). Summer through early fall is generally characterized by a dry period due to lesser seasonal rainfall and water recharge from lotic systems (Jones and Taylor 2005). During a single season, pools may fill and dry several times, and in years of drought, pools may remain dry (USEPA 2003). Differences in hydrology, including seasonal flood pulses, quantities of water discharge, and flood duration influence the plant and animal communities within upland and stream-connected wetlands (Jones and Taylor 2005). In stream-connected pools, extensive flooding or flooding for long durations can result in lesser species richness and abundance in areas that become heavily inundated.
Scouring by floodwaters may result in loss of eggs, larvae, and adult amphibians from breeding pools. Floodwaters that flow into pools and areas of floodplains may act as a dispersal agent for amphibians into new alternate habitats. Coincidentally, floodwaters also may introduce aquatic predators, such as fish, into breeding ponds (Horton and Grant 1998; Mills et al. 1995). Lack of pool connectivity with rivers or streams may act as a barrier to dispersal for species unable to travel distances to reach an alternate water source (Mills et al. 1995). Stream-isolated pools are not subjected to the potential disturbance caused by the scouring effect or surface water recharge
20 of floodplain waters. Wetland permanence of these ponds is influenced by rainfall and groundwater recharge (Dickson 2001).
Temporary pools have been shown to support unique species assemblages that are not found in permanent wetlands (Snodgrass et al. 2000). Hecnar and M’Closkey (1996) found no relationship between amphibian species richness and pond size among 97 ponds in southwestern
Ontario, Canada. Primary factors thought to influence herpetofaunal communities include hydroperiod or wetland permanence, predation, forest fragmentation, and human disturbance.
Lack of water during drought-years influences reproductive success and survival of pool-breeding amphibians, and in part, is responsible for the year-to-year larval recruitment and population fluctuations of pond amphibians and aquatic reptiles (Congdon and Gibbons 1996; Semlitsch et al
1996; Taylor and Scott 1997; Holomuzki 1997). Due to intermittent periods of drying, temporary wetlands usually lack well-established populations of predaceous fish, thus increasing their importance for aquatic amphibians, their eggs, and aquatic larvae (Jones and Taylor 2005).
Temporary pools play an essential role in the reproductive success of many species, but most amphibians spend most of their lifetimes along wetland ecotones or in surrounding terrestrial habitat. Newts (Notophthalmus spp.) generally metamorphose into a juvenile eft stage and remain on land for 1-3 years before returning to ponds to mature (Conant and Collins 1998;
Petranka 1998). Many anuran species occupy underground burrows or “forms” during most of their adulthood, surfacing occasionally to feed and migrate to ponds for breeding (Jones and
Taylor 2005). Ambystomatid salamanders are known to spend most of adulthood in terrestrial habitat, returning only to the pools for breeding. In addition to pond-breeding amphibians, other groups such as the terrestrial woodland salamanders (Plethodon spp.), utilize leaf litter, downed woody debris, and decaying logs for foraging, laying eggs, and development (Petranka 1998).
21 Numerous reptile species also utilize wetlands and associated ecotones. Aquatic turtles,
such as mud turtles (Kinosternon spp.), require well-drained terrestrial habitat for nesting and
egg-laying (Jones and Taylor 2005). Burke et al. (1993) found that female mud turtles
(Kinosternon subrubrum) remained dormant on land several meters from the wetland edge for
days or weeks prior to egg-laying. Water snakes (Nerodia spp.) inhabit aquatic habitat, but require terrestrial habitat for nesting and overwintering. Woody debris, stumps, and leaf litter provide foraging sites for snakes and lizards while logs and downed wood provide basking sites for many species including northern fence lizard (Sceloporus undulatus), green anole (Anolis carolinensis), and eastern cottonmouth (Agkistrodon piscivorus) (Jones and Taylor 2005).
Temporary pools and their terrestrial ecotones also may be important habitats for rare or sensitive species. One species known to use temporary pools, the tiger salamander (Ambystoma
tigrinum), is currently listed as extirpated from the state of Mississippi although it is listed for
historical occurrence. Four herpetofauna species are listed as tier 2 in the state of Mississippi,
Webster’s salamander (Plethodon websteri), crawfish frog (Rana areolata), alligator snapping
turtle (Macrochelys temminckii), and the red milksnake (Lampropeltis triangulum syspila)
(Mississippi Museum of Natural Science 2005). These species require timely conservation
measures due to rarity, restricted habitat, and habitat vulnerability. Another species, the southern
red salamander (Pseudotriton ruber vioscai) is listed as tier 3, species with unknown or
decreasing population trends or vulnerable habitat (Mississippi Museum of Natural Science
2005). Except for the tiger salamander, none of these species are known to be obligate breeders of
temporary wetlands, however, potential exists for these species to occur in adjacent terrestrial
areas (Petranka 1998). Increased knowledge of pool-dependent herpetiles and conservation of
ephemeral pools and adjacent terrestrial habitats can create proactive management approaches
22 that limit the potential landscape level population declines in common and rare species that depend on temporary wetlands.
This knowledge is especially important due to the current status of small temporary wetlands. Following the U.S. Supreme Court’s SWANCC decision, isolated wetlands were not given federal protection under the Clean Water Act if they were not deemed connected to or immediately adjacent to navigable bodies of water or waters used for commerce. Due to this designation, many temporary wetlands were left vulnerable to development (Asmus 2003).
Floodplain pools, such as those in this study, receive regulatory consideration from the Clean
Water Act, as they are adjacent to waters under jurisdiction of the U.S. Army Corp of Engineers
(Asmus 2003). These wetlands also may be afforded some protection due to the maintenance of streamside management zones (SMZs) on public and private lands. Retention of SMZ’s is voluntary on private lands in Mississippi and defined by agency management plans on public lands (Dickson and Wigley 2001; Forest Service and Forest Service unpublished data). In contrast, upland pools of < 2 ha receive no protection on private lands and protection is based on importance to biological diversity on public lands. Thus, public land managers need increased information on the role of these ephemeral wetlands in maintaining herpetile diversity on public forest lands. By identifying which areas serve as important breeding sites for herpetiles we can identify areas of the greatest conservation need and suggest approaches to conservation planning.
This study was designed to assess herpetofaunal communities occurring within two types of temporary wetlands located on public forest lands: isolated, upland ephemeral pools which were artificially created and floodplain ephemeral pools which are filled through lotic overflow of adjacent creeks and streams. The primary goal was to determine if these habitats support similar species assemblages and to identify any species of special concern occurring on these lands.
23 STUDY AREA
I conducted field experiments on 10 ephemeral pool sites located on Tombigbee National
Forest, Ackerman Unit (6 sites) and Noxubee National Wildlife Refuge (4 sites) in Oktibbeha and
Winston Counties, north-central Mississippi. Upland ephemeral pools (4 pools) were created artificially prior to the 1960’s as standing water sources for livestock and game species and were hydrologically isolated from streams, rivers, or other perennial waterbodies (Asmus 2003).
Floodplain pools (6 pools) were shallow oxbows and sloughs formed through scouring from the lotic overflow of adjacent creeks and streams (Asmus 2003). Details on study site location and habitat description are provided in Chapter II.
METHODS
Field Methods
Field data was collected from March 2004 through March 2006 using straight-line drift fence arrays combined with three trap designs; pitfall trap, pitfall trap combined with an anti- predator exclusion, and double-ended funnel trap. Anuran call count surveys were conducted from June 2004 through March 2006 to detect species not readily captured during trapping surveys. Field methods are described specifically in Chapter II. Data on species richness and abundance in this chapter were obtained from 23 pitfall/funnel trap surveys and 24 anuran call count surveys on 10 ephemeral pool sites.
Statistical Analyses
Faunal response variables included species richness and abundance of amphibians, species richness and abundance of reptiles, and individual species abundance. Sampling effort varied by site due to an unequal number of upland and floodplain sites, an unequal number of
24 traps of each design on 3 upland sites, and weather-related disturbances and management practices which restricted sampling and site access (i.e., prescribed burning, flooding). Sampling effort by site can be found in Table 3.1. Counts were standardized using catch/unit effort to adjust for sampling biases among sites. To account for differences in sampling intensity, total number of traps available for each site were calculated and then multiplied by number of trap days each site was opened. Catch/unit effort was calculated for each species as total number of captured individuals per site divided by the adjusted number of trap days for that site (Fogarty 2005).
The following hypotheses were investigated:
1. H0 : Species richness of amphibians is similar in upland and floodplain pools.
H1 : Species richness of amphibians differs between upland and floodplain pools.
2. H0 : Abundance of amphibians is similar in upland and floodplain pools.
H1 : Abundance of amphibians differs between upland and floodplain pools.
3. H0 : Species richness of reptiles is similar in upland and floodplain pools.
H1 : Species richness of reptiles differs between upland and floodplain pools.
4. H0 : Abundance of reptiles is similar in upland and floodplain pools.
H1 : Abundance of reptiles differs between upland and floodplain pools.
Species richness was calculated for upland and floodplain pools as total number of species detected during the study by pitfall/funnel trap arrays. Amphibian and reptile species richness were calculated separately. I used a one-way Analysis of Variance (PROC GLM, SAS
9.1) to determine if species richness varied significantly between pool types (Freund and Wilson
2003).
I used multi-response permutation procedure (MRPP) to determine if herpetofauna abundance differed between upland and floodplain ephemeral pool types. MRPP is considered a
25 non-parametric alternative to discriminant function analysis (DFA) for testing the hypothesis of no difference between 2 or more groups decided upon a priori to analysis (McCune and Mefford
1999). I categorized the capture data from pitfall/funnel trap surveys by Order into anurans
(Order Anura), salamanders (Order Caudata), turtles (Order Testudines) and snakes (Order
Serpentes) (Conant and Collins 1998). Study sites (n=10) were categorized according to pool type as either upland or floodplain pools. MRPP did not allow for number of species included in analysis to exceed number of study sites. Species with negligible capture numbers (< 3 captures per pool type) were omitted from analysis.
If a significant difference was found using MRPP analysis, I conducted a Kruskal-Wallis test (PROC NPAR1WAY, SAS 9.1) to determine if individual species abundance varied significantly according to pool type. Kruskal-Wallis is considered a non-parametric equivalent to a one-way Analysis of Variance yet relaxes the assumptions of normality and homogeneity of variance required for parametric analyses (Conover 1980).
I used Renkonen’s Index to quantify the similarities of reptile and amphibian communities between floodplain and upland pools (Krebs 1989). The index is a percentage similarity index defined as P = ∑ minimum (p1i, p2i); where, P = percentage similarity between upland and floodplain sites; p1i = percentage of species i in floodplain pools; p2i = percentage of species i in upland pools. Renkonen’s Index can be viewed as a scale from 0 (no similarity
between pool types) to 100 (complete similarity between pool types) (Krebs 1989).
26 RESULTS
Pitfall/funnel trap arrays were opened simultaneously at all 10 ephemeral pool sites for
23 trap periods that varied between 5 to 10 days long (222 days total) and produced 2,211 trap days. Trap captures yielded 34 herpetile species and 6,713 individuals during study (Table 3.2).
On upland sites, 17 amphibian species (5,383 individuals) and 16 reptile species (218 individuals) were captured. On floodplain sites, 14 amphibian species (1,013 individuals) and 11 reptile species (99 individuals) were captured. Species richness differed significantly between upland and floodplain ephemeral pools for amphibians (F1,8 = 4.98, P =0.056) and reptiles (F 1,8 = 8.23,
P =0.021).
MRPP found significant separation of groups for 4 of the Orders analyzed: salamanders
(T = -2.921, P = 0.014, A= 0.234), snakes (T = -4.508, P = 0.003, A = 0.233), lizards (T = -4.017,
P = 0.005, A =0.246) and turtles (T = -2.482, P = 0.018, A = 0.161). Thus, abundance of
salamanders, snakes, turtles, and lizards differed between upland and floodplain pools. Due to
low capture numbers and MRPP restrictions, two species of anuran, southern cricket frog (Acris
gryllus) and spring peeper (Pseudacris crucifer), were omitted from MRPP analysis (McCune
and Mefford 1999). Anurans did not have a significant separation (T = -0.768, P =0.184, A
=0.006) (Table 3.3).
Kruskal-Wallis test indicated that abundance of 7 herpetofauna species differed between pool types (Table 3.4). While results from the MRPP analysis did not show separation for anurans, the Kruskal-Wallis test showed that Cope’s grey treefrog (Hyla chrysocelis; P = 0.036) was more abundant in upland pools. Mole salamander (Ambystoma talpoideum; P = 0.033) and central newt (Notopthalmus viridescens louisianensis; P = 0.018) were more abundant in upland pools. Five-lined skink (Eumeces fasciatus; P = 0.055), green anole (Anolis carolinensis; P
27 =0.019), and northern fence lizard (Sceloporus undulatus; P = 0.010) showed significant differences in abundance, as did, cottonmouth (Agkistrodon piscivorus; P = 0.006).
The Renkonen Index values for amphibians and reptiles were 0.2754 and 0.0328,
respectively, with a total index value of 0.3082 for all herpetofauna. This total index value
indicated that approximately 30.82% of the herpetofaunal community was similar between upland
pools and floodplain pools. Amphibian communities were 27.54% similar between upland and
floodplain sites, whereas, only 3.08% of the reptile communities were similar between pool types.
Although data from anuran call count surveys were not included in statistical analyses, 12
species were heard vocalizing on floodplain sites whereas 13 species were heard vocalizing on
upland sites (Table 3.5). Three additional species, (Hyla avivoca, H. cinerea, and H. squirella)
were detected using call counts but were not detected through trapping.
DISCUSSION
Species richness and abundance of herpetiles varied significantly between upland and
floodplain ephemeral pools. Of the individual species that differed in abundance between pool
types, greater numbers were found for all species on upland sites versus floodplain sites. Three
amphibian species that I detected at greater abundance levels in my study, Cope’s gray treefrog,
mole salamander, and central newt, have been reported as breeders of temporary wetlands which
supports my findings (Kats et al.1988; Petranka 1998; McDiarmid and Altig 1999).
Amphibian occurrence and abundance of selected species may have been related to many
biotic and abiotic factors such as pool periodicity, hydroperiod, and presence of aquatic predators.
Temporary ponds that dry seasonally or annually are especially important to pool-breeding
amphibians because they generally lack fish. Selected amphibian species including bullfrogs,
cricket frogs, green frogs, and green treefrogs can coexist in ponds containing fish because they
28 possess anti-predator behaviors and skin toxins. However, studies have shown that most pool-
breeding amphibians are eliminated by predatory fish (Heyer et al. 1975; Bradford 1989; Hecnar
and M’Closkey 1997; Petranka 1998). Cope’s gray treefrog uses temporary and permanent ponds
for breeding (Kats et al.1988). In the northern portion of its range, it often breeds in vegetation
choked ponds with fish, but prefers temporary pools lacking fish in the South (L.B. Kats et al.,
personal observations). Cope’s gray treefrog is known to be palatable to fish and would,
therefore, benefit from pools lacking fish (Kats et al. 1988). Due to the low sample size of Cope’s
gray treefrog (n=12) in this study, however, limited assumptions can be made. In my study, mole
salamanders were more abundant in upland pools that contained fewer species of fish predators
than floodplain pools during the study period. These finding were similar to those who reported
that mole salamanders have a strong tendency to use fish-free habitats and are found rarely in
ponds with predatory fish, such as bluegill (Lepomis macrochirus), that are voracious predators of
salamander eggs and larvae (Semlitsch 1988). Presence of predatory fish does not preclude pond
usage of central newts as terrestrial efts and aquatic adults are unpalatable and toxic to most
predators (Hulbert 1970; Brodie et al. 1974).
Presence of fish was detected at 3 of the upland pools and all 6 floodplain pools. Fish
species collected at upland sites were banded pygmy sunfish (Elassoma zonatum), bluegill sunfish (Lepomis machrochirus), and Johnny darter (Etheostoma nigrum); whereas, floodplain sites contained more species including pirate perch (Aphredoderus sayanus), bluegill, banded pygmy sunfish, Johnny darter (Etheostoma nigrum), blackspotted topminnow (Fundulus
olivaceus) and mosquitofish (Gambusia affinis) (Table 3.6). All of the fish species detected are
known to inhabit shallow margins of streams, ponds, and sloughs typically within vegetated areas
and feed on a variety of aquatic insects and insect larvae, such as dipterans, chironomids,
mayflies, hemipterans, as well as, microcrustaceans (Ross 2001). Maximum sizes for these
29 species ranged from 5cm (banded pygmy sunfish) to 30cm (bluegill sunfish). Of the species detected, the 3 species known to attain the largest size were blackspotted topminnow (maximum
10cm), pirate perch (maximum 11.5cm), and bluegill. None of these species are known to feed primarily on amphibian larvae. Due to size of these species and their ability to seek out larger prey, however, amphibian eggs, larvae, and metamorphs are vulnerable to opportunistic feeding by these species. Bluegills, in particular, have been documented as efficient predators on salamander eggs and larvae, as well as, some anuran tadpoles (Semlitsch 1988). A study conducted by Smith et al. (1999) found that the density of larval gray treefrogs (Hyla versicolor) showed a negative association with the density of adult bluegills, attributed to depredation of tadpoles by bluegills.
All of the three largest species were represented in floodplain pools, whereas, topminnow and pirate perch were absent from upland pools. I hypothesize that stream connectivity of floodplain pools had a greater tendency for predator presence through the recharge of water from perennial water sources, such as streams or rivers. Stream connectivity of floodplain pools could have led to the introduction of fish predators during flooding events. The increase in water recharge and hydroperiod due to soil saturation of floodplains may have led to greater permanence of surface water which might have enabled more fish species to survive and grow larger. On the other hand, upland ponds were hydrologically isolated and fish present in these pools were likely human introduced which might explain the presence of smaller fish species and overall reduced richness of fish found within ponds.
In my study, floodplain pools had greater richness of fish species, including species known to opportunistically feed on amphibian larvae, and these pools were found to have lesser abundance of amphibians. The reduced abundance of amphibians in floodplain pools may have been due to direct predation. Additionally, presence of fish also may have indirectly influenced
30 amphibian diversity by altering density of aquatic invertebrate prey available to developing amphibians. Bluegills are known to feed on prey items that are common for Ambystomatids and central newts. Ambystomatids are vulnerable to predation by bluegills, however, central newts are known to be unpalatable and are, therefore, not at high risk. Competition with fish over available prey may have influenced abundance of species not directly affected by predation, such as newts. Smith et al. (1999) found that newt abundance decreased in response to greater bluegill density. This reduction was attributed to the decline of prey items, specifically Daphnia spp., with increasing adult bluegill density. The combination of predation and potential for limited prey availability due to presence of a greater number of fish species, may have resulted in less species diversity of amphibians in floodplain pools.
In my study, fewer fish species were found in upland pools than floodplain pools potentially leading to less predation pressure for amphibian larvae of some species. Though fish were detected at most upland sites (3 of 4), larger species, such as bluegill, occurred only on two upland sites, with the greatest frequency of detection for this species found at site “J”. This upland pool was found to have the second least number of captures of pond-breeding salamanders
(n=13) through the study period but produced high numbers of captures for toads such as
Bufonids (n=147) and eastern narrowmouth toads (n=182). However, some species inevitably where affected by predation, such as salamanders, other species may have benefited by presence of few fish species by the control of aquatic invertebrate predators such as odonates, coleopterans, and hemipterans that are often eaten by fish (Smith et al. 1999).
Although ponds contained fish predators, amphibian species assemblages also may have been influenced by within-class predators. The establishment of species colonizing an area is thought to depend on the resident biota already present and may involve trophic relationships, competition, and predation between different species and conspecifics (Wilbur and Alford 1985;
31 Connell and Slatyer 1977). Habitat characteristics also may play a major role in determining suitability of a site and will be discussed in Chapter V. Amphibians that breed early may serve as important predators of later hatching larvae, potentially gaining a size advantage against predators present later during the season (Alford 1999). In my study, marbled and mole salamanders were found to move to breeding ponds during late summer and early fall, whereas, spotted salamanders generally appeared later during winter. Previous studies supporting these findings have found that these species are nearing metamorphosis at the time A. maculatum are hatching and are large enough to depredate eggs and newly hatched larvae, as well as, injure conspecifics (Stenhouse et al. 1983; Stewart 1956). Larvae of spring-breeding anurans also may be vulnerable to depredation because transformation for Ambystomatids does not occur until March-September, forcing predator and prey to coexist. Additionally, in my study, mole salamander populations at 3 upland sites contained permanently aquatic adults presenting a potential larval predator presence year- round for larval salamanders and anurans, even those breeding early in the season.
Though the immediate effect of predation is the reduction of local populations, it also may serve to increase species diversity of pool-breeding amphibians in complex communities.
Results of my study show that, except for the bullfrog (Rana catesbeiana), anuran species richness and abundance was greater for all species on upland sites containing mole salamanders and central newts which function as predators, though significance was only found for Cope’s gray treefrog. Mole salamanders and central newts are often found inhabiting the same ponds as they share strong dietary overlap, with ostracods, cladocerans, and chironomid larvae composing most of their diets (Petranka 1998). Morin (1981) found that newts (Notopthalmus spp.) function as keystone predators and can control the structure of artificial-pond communities, and research suggests this may be true in their natural environment. Central newts are predators on eggs and larvae of spring-breeding frogs and Ambystomatid salamanders (Bishop 1941; Fauth 1990; Gill
32 1978; Hamilton 1932; Walters 1975; Wilbur and Fauth 1990; Wood and Goodwin 1954).
Notopthalmus has been found to alter the structure of the larval anuran community by preying on the competitively dominant species allowing for inferior competitors to multiply and increase abundance (Paine 1966; Dayton 1971, 1975). In some instances, predation may be sufficient to nearly eliminate certain species from ponds (Morin 1983). Fauth (1999) found that in a study of
12 predators in South Carolina ponds, only Ambystoma talpoideum was identified as a strong keystone predator and anuran species richness was 36% greater in ponds containing mole salamanders, whereas, Morin (1995) predicted that salamanders similar in size to that of the mole salamander would also be functionally equivalent as keystone predators of larval anurans. As this study was not designed to examine complex predator-prey relationships, future studies should seek to investigate effects of predators on pool-breeding amphibians with special detail given not only to abundance of predators but particularly composition of fish, invertebrate, and amphibian communities residing within temporary ponds.
In addition to increased abundance of amphibians, four reptile species, five-lined skink, green anole, northern fence lizard, and cottonmouth, were more abundant on upland pool sites.
Upland sites used in this study were more xeric than floodplain sites and had more open forest canopy leading to warmer temperatures that may have attracted these species for basking. Upland terrestrial habitat adjacent to wetlands has been found to be extremely important for hydrophilic reptiles for basking, nesting, hibernating, and aestivating (Semlitsch and Bodie 2003).
Differences in temperature and vegetation surrounding upland pools also may have resulted in different prey assemblages of invertebrates than found on floodplain sites allowing for greater species diversity of reptiles on uplands.
Results from Renkonen’s Index indicated that approximately 31% of the herpetofaunal community was similar between upland and floodplain temporary pools. Amphibians were 28%
33 similar, whereas, reptiles were only 3% similar between pool types. These results combined with the results of MRPP and Kruskal-Wallis indicated that the species richness and abundance was significantly greater at upland pools versus floodplain pools. The 31% similarity score can conversely be thought of as a “difference score” with 69% of the herpetofaunal community being neglected if management plans continue to afford protection solely to floodplain pools. The estimate of similarity found for reptiles may have been underestimated due to the survey methods used. Drift fences were placed to encompass most of the pool’s perimeter to capture breeding amphibians moving to and from the pond. However, reptiles were captured using these methods, only a subset of the terrestrial area surrounding the pond was surveyed, potentially excluding reptiles and woodland salamanders not found directly surrounding the pools.
In addition to upland pools supporting a larger species assemblage, two locally rare species, the southern red salamander (Pseudotriton ruber visocai) and the red milksnake
(Lampropeltis triangulum syspila) were detected at two upland sites. The southern red salamander is not an obligate breeder of temporary wetlands but may use the terrestrial areas surrounding these wetlands during drought or when another nearby water source in unavailable, thus increasing the importance of upland pools.
Evidence suggests that pond-breeding amphibian populations are structured as clusters of metapopulations across a landscape and require connectivity among populations. Populations are centered on discrete breeding sites and rather than having constant low-level reproductive success each year that characterizes many mammals and birds, local populations persist by periodically producing large numbers of metamorphosing juveniles followed by years with little or no reproduction (Gill 1978; Semlitsch 1983; Berven 1990; Pechmann et al. 1989). Breeding synchrony, or explosive breeding, is common in many pool-breeding amphibians and may involve a single reproductive event or several explosive bouts over a prolonged breeding season
34 (Heyer et al. 1975; Crump 1983; Newman 1987). Although anurans did not statistically differ between pool types in my study, anuran abundance was greater in upland pools (n=4,746) than floodplain pools (n=848). Eastern spadefoot toads, Scaphiopus holbrookii holbrookii, represented >65% of anuran captures on upland sites and <1% of anuran captures on floodplain sites. Spadefoot toads are fossorial in nature, preferring loose or sandy soils representative of upland habitats, and engage in explosive breeding events lasting 1-2 days typically during summer following heavy rains (Gosner and Black 1955; Conant and Collins 1998; Wright 2002;
Greenberg and Tanner 2004). In my study, breeding events were documented at only one upland pool (pond G) in the summers of 2004 and 2005. In 2004, only adults were captured, whereas, in
2005, metamorphs and adults were captured, with metamorphs comprising approximately 92% of total spadefoot captures. Spadefoot larvae also were sampled using sweep-netting and were only documented at pond G during one sampling session in summer 2005 and not found at any other pond. This evidence leads me to conclude that substantial recruitment occurred during 2005 and either did not occur during 2004 or was missed due to periodicity in sampling effort and the short larval period of spadefoot toads. Studies by Greenberg and Tanner (2005) support my findings.
They found that breeding events with >175 adults captured occurred in only 1-2 ponds per sampling period and in only 4 of the 9 study years. Recruitment ranged from 0-4648 individuals among ponds but substantial recruitment occurred during only 5 of 23 breeding events.
Multiple successive years of reproductive failure due to natural conditions, such as pond drying, drought, fish predation, and flood scour, can lead to decline and extinction of local populations. These breeding sites exist in discrete patches and connectivity of these critical wetlands is often disrupted due to fragmentation caused by agriculture, silviculture, and urban development, leaving the conjoining habitat unsuitable to support these species. Small temporary wetlands, uplands or floodplains, often represent “source” populations for breeding amphibians
35 and depend on habitat connectivity and recolonization from neighboring populations when local populations decline (Gill 1978; Sjogren-Gulve 1994). These ponds may produce large numbers of dispersing juveniles for several years and then decline (Semlitsch 2005). For the recolonization and rescue of declining populations to occur, individuals must have a suitable habitat adjacent to breeding pools.
Most species cannot migrate long distances due to physiological constraints and are likely concentrated within 200-300m of the breeding ponds for foraging and overwintering (Semlitsch
1998; Gibbons 2003). Isolated wetlands with no hydrologic connection are more restricted than permanent wetlands and riparian habitats that offer potential for aquatic travel for reptiles and amphibians (Gibbons 2003). These wetlands may still be biologically linked, however, if connected by an accessible terrestrial corridor allowing for animal movements (Gibbons 2003).
Scott (1994) reported that up to 7% of newly metamorphosed marbled salamanders dispersed overland to breed in non-natal pools. Similarly, copperbelly watersnakes (Nerodia erthrogaster neglecta) traveled overland more than 0.5 km in Indiana and cottonmouths moved several km due to wetland drying (Gibbons 2003).
In my study, immediate areas surrounding all study sites were surrounded by forested habitats of >65 years of age; thus, this study was not designed to investigate fragmentation and habitat loss. Investigation of habitat conditions within different forest stands is reported in
Chapter V. Future research should address fragmentation of pool habitats due to habitat loss or adjacent barriers such as timber production, agricultural land-use, or urbanization. Specifically, I recommend that future studies include investigations of the effects of roads on herpetofauna of ephemeral pools. Construction of forest roads has become an increasing form of natural disturbance even on lands dedicated to the conservation of wildlife (national forests, national wildlife refuges, parks, preserves) and results in a relatively permanent change in habitat and a
36 barrier to dispersal for less mobile taxa, such as reptiles and amphibians (Schonewald-Cox and
Buechner 1992; deMaynadier and Hunter 2000). These barriers may present significant challenges for species needing to migrate for breeding, foraging, and overwintering through direct mortality from vehicles, habitat degradation due to sedimentation and pollution, and desiccation due to open habitat condition of roads (Stamps et al. 1987; Reh and Seitz 1990; Ashley and
Robinson 1996). Additionally, there is an increased risk of mortality due to edge-adapted predators including raccoons, skunks (Mephitis macroura), hawks (Accipiter spp., Buteo spp.),
and snakes (deMaynadier and Hunter 2000). Current guidelines for best management practices on
public forest lands, recommend streamside management zones of 35-60 feet on both sides of
intermittent stream banks though no official recommendations exist for ephemeral pools
(Mississippi Forestry Association 2000). Due to the lack of federal regulation ephemeral pools
receive and the proximity of these ponds to roads, local populations of herpetofauna using these
upland areas remain increasingly vulnerable to further habitat degradation that may limit dispersal
and rescue of declining populations. All upland pools in this study were bordered on >1 side by a road in close proximity (< 30 m) and most floodplain pools were located close to bulldozed fire- lanes. DeMaynadier and Hunter (2000) found that anurans were not limited by roadside barriers, whereas, significantly fewer salamanders crossed roads opting for travel through continuous forest instead. Future studies should examine the relationship between herpetofauna richness and abundance, proximity of pools to roads and firelanes, and associated road mortality.
To support the array of different herpetofaunal species at all life stages, a mosaic of terrestrial and aquatic habitat must be present with protective measures taken to minimize disturbance and further fragmentation (Semlitsch and Bodie 2003). Additionally, ponds with varying hydroperiods are needed to support pool-breeding species with varying larval periods.
37 Therefore, conservation of upland and floodplain ephemeral pools are necessary to protect the diversity of herpetofauna species occurring on public lands in central Mississippi.
MANAGEMENT IMPLICATIONS
The primary threat to the long-term viability of amphibian populations is the loss or degradation of suitable habitat due to human activities (Blaustein et al.1994; Dodd 1997; Alford and Richards 1999). Exotic species, development, silviculture, and chemical contamination may degrade or destroy breeding sites and peripheral terrestrial habitat. Upland pools used in this study, had greater species richness and abundance than floodplain pools. Currently, isolated upland pools receive no federal protection against development or degradation aside from residing on public forest and refuge lands. Due to differences in communities detected in my study, upland pools contribute substantially >70% for amphibians and 95% for reptiles to the diversity of herpetofauna on public lands in central Mississippi. Due to their ephemeral nature, small size, and seasonal hydroperiods they are often overlooked as wetlands and consequently overlooked during forest management and land-use planning (Semlitsch 2005). Depending on when surveys are conducted for forest management, public land managers may not realize the presence of ephemeral pools if the timing of surveys coincides with times when pool surface water is absent.
For a diversity of herpetofauna species to receive protection, upland and floodplain ephemeral pools need to be considered in management plans and conservation action must be extended to adjacent terrestrial habitat and not strictly the pond itself. Upland forest habitats are essential for feeding and overwintering of many reptiles and amphibians, as well as essential breeding sites for many amphibians and aquatic reptiles. Semlitsch (2005) recommended the designation of core terrestrial areas and buffer zones surrounding temporary pools similar to
38 streamside management zones used to protect riparian fauna. He recommended an aquatic buffer of 60m encompassing the breeding pond to prevent contamination and siltation of the water.
Outside this zone, core terrestrial habitat should be designated from the shoreline up to 200m to protect juveniles and adults of the breeding population (Semlitsch 1998; Richter et al. 2001). The width of the core habitat is determined by the average dispersal distance of herpetiles from the wetland to summer and wintering sites (Bailey et al. 2006). An additional 50m should surround core habitat to provide a buffer against land-use practices that may further degrade habitat quality and be detrimental to herpetofauna (Murcia 1995; Semlitsch and Jensen 2001). Construction sites and roads should be limited or relocated > 60m from wetlands to prevent harmful edge effects
(Keenan and Kimmins 1993; deMaynadier and Hunter 1995). Additionally, the installation of culverts or tunnels is recommended to direct travel of animals under or away from roads (Bailey et al. 2006).
In addition to conserving habitat around the breeding site, key areas used as corridors for dispersing juveniles should be determined. Because amphibians are physiologically limited in their dispersal capabilities, distances from the nearest breeding site should be examined and the creation of artificial ponds should be considered in areas where dispersal distances may be too great to allow successful recolonization or rescue of declining populations. Upland ponds used in this study were created artificially for livestock and as standing water sources for upland game species. These pools are > 40 years in age and are surrounded by mixed pine-hardwood forest
>65 years of age. This study’s results show the propensity for recolonization of constructed ponds and the value of these ponds for reptiles and amphibians in upland forests. A similar study done by Quinn et al. (2001) found that amphibian species richness was similar in artificial ponds constructed for livestock and natural temporary ponds. He also emphasized that wetland permanence and elevation were key characteristics in determining amphibian occurrence
39 regardless of wetland origin. In areas where habitat connectivity has been disrupted, artificial ponds may serve a valuable resource for joining populations and serving as breeding sites when
“source” ponds are no longer being used. Bailey et al. (2006) stress the need to conserve naturally occurring seasonal ponds, as well as construction of farm ponds to ensure habitat diversity for herpetofauna. Stratman (2000) recommends the creation of artificial wetlands that are small (0.2-
1.0 ha), multi-shaped, and have shallow basins (0.5-1.0 m deep). A diversity of hydroperiods lasting from 30 days to 1-2 years is needed to encompass the multitude of breeding amphibian species and to increase production of metamorphs and juveniles (Semlitsch 2005). Constructed ponds should occur at 100-200m intervals to aid in dispersal, however, naturally occurring seasonal wetlands should not be disturbed to create artificial ponds (Bailey et al. 2006).
The survey method used in this study was designed to capture herpetiles moving to and from the breeding pond and may have underestimated reptiles and amphibians not using the ponds for breeding but using the terrestrial areas nonetheless. Additionally, excluded pitfall and funnel trap designs are inherently biased against capturing larger testudines and the exclusive cover may have provided a surface for more agile species of lizard to climb and escape capture.
Depredation of pitfall and funnel traps by raccoons also was evident on our sites, but degree of capture bias in un-excluded pitfall traps is unknown. For future studies, I would recommend a combination of faunal surveys including pitfall/funnel trapping, time or area-constrained searches, and auditory surveys to detect the multitude of species occurring in these areas. The combination of these survey methods could increase the probability of detecting rare or secretive species and species which may be excluded due to trapping biases.
The focus of this study was to determine the usage of upland and floodplain temporary pools by the herpetofaunal community and to determine which areas serve as important breeding sites or support rare species, thus, warranting further conservation measures. This study did not
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48 Table 3.1. Sampling effort of pitfall/funnel trap surveys on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006.
# Excluded Total # Total # # Pitfall Pitfall # Funnel Site Site Type Surveys Days Open Traps Traps Traps
A Floodplain 23 222 5 5 5 B Floodplain 23 222 5 5 5 C Floodplain 23 222 5 5 5 D Floodplain 23 222 5 5 5 E Floodplain 23 217 5 5 5 F Upland 23 222 4 5 5 G Upland 23 222 6 4 5 H Upland 23 218 3 5 5 I Floodplain 23 222 5 5 5 J Upland 23 222 5 5 5
Table 3.2. Reptile and amphibian counts from pitfall/funnel trap surveys on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006.
Floodplain Upland Floodplain Upland Taxon Common Name N N CPUE CPUE
Order Anura Frogs and toads Acris gryllus Southern cricket frog 0 1 0.0000 0.0003 Bufo spp. True toads 218 264 0.0661 0.1490 Gastrophyrne carolinensis Eastern narrowmouth toad 325 403 0.0978 0.2234 Hyla versicolor chrysoscelis Cope’s gray treefrog 3 9 0.0009 0.0038 Pseudacris crucifer Northern spring peeper 1 13 0.0003 0.0048 Pseudacris triseriata feriarum Upland chorus frog 25 36 0.0076 0.0197 Rana catesbeiana Bullfrog 91 47 0.0275 0.0423 Rana clamitans clamitans Bronze frog 109 171 0.0330 0.0877 Rana sphenocephala Southern leopard frog 72 121 0.0217 0.0624 Scaphiopus holbrookii holbrookii Eastern spadefoot toad 4 3681 0.0012 1.1068 Subtotal 848 4746 0.2561 1.7002 Species Richness 9 10
Order Caudata Salamanders Ambystoma maculatum Spotted salamander 47 119 0.0144 0.0509 Ambystoma opacum Marbled salamander 41 64 0.0124 0.0319 Ambystoma talpoideum Mole salamander 45 434 0.0137 0.1517 Eurycea longicauda guttolineata Three-lined salamander 5 6 0.0015 0.0034 Notophthalmus viridescens louisianensis Central newt 0 5 0.0000 0.0017 Plethodon mississippi Mississippi slimy salamander 22 9 0.0066 0.0095 Pseudotrition ruber vioscai Southern red salamander 0 1 0.0000 0.0003
49
Table 3.2 Continued.
Floodplain Upland Floodplain Upland Taxon Common Name N N CPUE CPUE Subtotal 160 638 0.0486 0.2494 Species Richness 5 7
Order Squamata Suborder Serpentes Snakes Agkistrodon piscivorus Eastern Cottonmouth 1 9 0.0003 0.0031 Coluber constrictor priapus Southern Black Racer 2 1 0.0006 0.0009 Diadophis punctatus stictogenys Mississippi Ringneck 1 0 0.0003 0.0000 Heterodon platirhinos Eastern Hognose 0 1 0.0000 0.0003 Lampropeltis triangulum syspila Red Milksnake 0 1 0.0000 0.0004 Nerodia erythrogaster flavigaster Yellowbelly Water Snake 0 2 0.0000 0.0006 Nerodia sipedon pleuralis Midland Water Snake 0 1 0.0000 0.0003 Thamnophis sauritus sauritus Eastern Ribbon Snake 0 2 0.0000 0.0007
Subtotal 4 17 0.0012 0.0063 Species Richness 3 7
50
Table 3.2. Continued.
Floodplain Upland Floodplain Upland Taxon Common Name N N CPUE CPUE
Order Squamata Suborder Lacertilia Lizards Anolis carolinensis Green Anole 17 43 0.0051 0.0188 Eumeces fasciatus Five-lined Skink 39 55 0.0118 0.0296 Eumeces laticeps Broadhead Skink 17 18 0.0051 0.0108 Sceloporus undulatus Northern Fence Lizard 5 49 0.0015 0.0175 Scincella lateralis Ground Skink 14 22 0.0042 0.0113
Subtotal 92 187 0.0277 0.0880 Species Richness 5 5
Order Testudines Turtles Chelydra serpentina Common Snapping Turtle 1 2 0.0003 0.0009 Pseudemys concinna River Cooter 0 1 0.0000 0.0003 Kinosternon subrubrum subrubrum Eastern Mud Turtle 1 9 0.0003 0.0032 Terrapene carolina triunguis Three-toed Box Turtle 2 1 0.0006 0.0009
Subtotal 4 13 0.0012 0.0053 Species Richness 3 4
51
Table 3.3. MRPP results of abundance of herpetiles detected in pitfall/funnel trap surveys on 10 ephemeral pool sites on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006.
Test Total Total Total Statistic Effect Size Floodplain Upland Abundance Group P-value (T) (A) Abundance Abundance Both Pool Types
Amphibians
Anurans 0.184 -0.768 0.006 847 4,732 5,579
Salamanders 0.014 -2.921 0.234 160 638 798
Reptiles
Snakes 0.003 -4.508 0.233 4 17 21
Lizards 0.005 -4.016 0.246 92 187 279
Turtles 0.018 -2.482 0.161 4 13 17
52 53
Table 3.4. Kruskal-Wallis results for pitfall/funnel trap surveys on 10 ephemeral pool sites on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006.
Taxon P-value Mean score (F) Mean score (U) Anurans Bufo spp. 0.201 4.500 7.000 Eastern Narrowmouth Toad 0.088 4.167 7.500 Northern Spring Peeper 0.072 4.250 7.375 Upland Chorus Frog 0.285 4.667 6.750 Bullfrog 0.394 6.167 4.500 Bronze Frog 0.088 4.167 7.500 Southern Leopard Frog 0.201 4.500 7.000 Eastern Spadefoot Toad 0.153 4.417 7.125 Cope’s Grey Treefrog 0.036 3.917 7.875 Southern Cricket Frog 0.221 5.000 6.250 Salamanders Mississippi Slimy Salamander 0.669 5.833 5.000 Marbled Salamander 0.392 4.833 6.500 Mole Salamander 0.033 3.833 8.000 Spotted Salamander 0.136 4.333 7.250 Three-lined Salamander 0.741 5.750 5.125 Central Newt 0.018 4.000 7.750 Southern Red Salamander 0.221 5.000 6.250 Lizards Ground Skink 0.088 4.167 7.500 Five-lined Skink 0.055 4.000 7.750 Broadhead Skink 0.108 4.250 7.375 Green Anole 0.019 3.667 8.250 Northern Fence Lizard 0.010 3.500 8.500 Snakes Eastern Ribbon Snake 0.068 4.500 7.000 Midland Water Snake 0.221 5.000 6.250 Yellowbelly Water Snake 0.221 5.000 6.250 Red Milksnake 0.221 5.000 6.250 Eastern Hognose 0.221 5.000 6.250 Southern Black Racer 1.000 5.500 5.500 Cottonmouth 0.006 3.500 8.500 Mississippi Ringneck 0.414 5.833 5.000 Turtles Eastern Mud Turtle 0.072 4.250 7.375 Common Snapping Turtle 0.648 5.250 5.875 Three-toed Box Turtle 0.693 5.750 5.125 River Cooter 0.221 5.000 6.250
54 Table 3.5. Species list of anuran call count surveys on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006.
Taxon Common Name Floodplain Upland Acris gryllus Southern cricket frog 9 9 Bufo fowleri Fowler’s toad 9 9 Gastrophyrne carolinensis Eastern narrowmouth toad 9 9 Hyla avivoca Bird-voiced treefrog 9 9 Hyla cinerea Green treefrog 9 9 Hyla versicolor chrysoscelis Cope’s gray treefrog 9 9 Hyla squirella Squirrel treefrog 9 9 Pseudacris crucifer Northern spring peeper 9 9 Pseudacris triseriata feriarum Upland chorus frog 9 9 Rana catesbeiana Bullfrog 9 9 9 9 Rana clamitans clamitans Bronze frog 9 9 Rana sphenocephala Southern leopard frog 9 Scaphiopus holbrookii holbrookii Eastern spadefoot toad
Table 3.6. Species list and frequency of detection of fish captured during sweepnet surveys in 10 ephemeral pools on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006.
Floodplain Upland # Sites # Surveys # Sites # Surveys Taxon Common Name Detected Detected Detected Detected Family Aphredoderidae Pirate Perch Aphredoderus sayanus Pirate Perch 1 1 0 0
Family Centrarchidae Sunfishes Elassoma zonatum Banded Pygmy Sunfish 2 3 2 3 Bluegill Sunfish 1 1 2 3 Lepomis machrochirus Family Cyprinodontidae Killifishes Fundulus olivaceus Blackspotted Topminnow 1 2 0 0
Family Percidae Perches Etheostoma nigrum Johnny Darter 4 4 1 1
Family Poeciliidae Livebearers Gambusia affinis Mosquitofish 2 4 0 0
55
CHAPTER IV
LARVAL AMPHIBIAN DIVERSITY AND RELATIVE ABUNDANCE IN UPLAND AND
FLOODPLAIN EPHEMERAL POOLS
INTRODUCTION
All anurans and many salamanders of southeastern floodplains spend their adult life stages in terrestrial habitats or wetland ecotones but depend on aquatic habitats for breeding, egg- laying, and larval development (Hairston 1996; Semlitsch et al. 1996; Petranka 1998). Aquatic larvae grow and develop, feeding primarily on zooplankton and aquatic insects, until metamorphosis is achieved and juveniles disperse into the surrounding terrestrial area (Semlitsch
1998). Adult amphibians can breed repeatedly during their lifetimes and species, such as
Ambystoma talpoideum, have shown an affinity of returning to natal ponds for breeding each time
(Semlitsch 1998; 2002). Isolated, temporary wetlands provide important sites for amphibian reproduction and recruitment, because they generally lack an abundance of fish and invertebrate predators that may compete with and prey on amphibian larvae (Semlitsch and Bodie 1998). For example, breeding activity of 41,776 female amphibians and the production of 216,251 metamorphosing juvenile amphibians was documented at a small ephemeral wetland (0.5 ha) in
South Carolina over a 16-year monitoring period (Semlitsch et al. 1996; Semlitsch and Bodie
1998).
56 57 Although ponds may be able to support large species assemblages, species composition of larvae and metamorphs can vary across ponds (Morin 1983). Larvae and metamorphs sampled within different ponds may not constitute the entire species richness of a pond or the various species that may potentially use these ponds for breeding. Temporary ponds are characterized by cyclic patterns of nutrient availability and unpredictable cycles of drying and filling which may alter the species composition of the community (Alford 1999). Existing habitat patches often fill and dry in response to seasonal weather patterns that vary between sites and years (Alford 1999).
Use of aquatic habitats varies among species and is determined by factors such as length of larval period and environmental factors including hydroperiod, food availability, competition, temperature, contamination, and predation (Semlitsch 2002). Mineral nutrients and high quality detritus are likely to be most available early in each episode of filling and drying (Barlocher et al.
1978; McLachlan 1981a, b; Osborne and McLachlan 1985; Wassersug 1975). Differences in time of spawning can have tremendous consequences in larval survival and maturation due to the ephemeral nature of ponds. Spawning before temporary pools have completely filled increases the risk of desiccation (Alford 1999). Larvae of species that spawn early during the hydroperiod cycle experience different ecological conditions from those that reproduce later (Wilbur and
Alford 1985). For example, larvae of species that spawn during summer may experience high mortality rates from desiccation during drought years.
Length of larval period also may influence larval survival and maturation rates.
Amphibian species exhibit different larval periods, ranging from 12 days for spadefoot toads
(Scaphiopus spp.) to 1-2 years for bullfrogs (Semlitsch 2002). Due to different larval periods, ponds are differentially favored by certain amphibians depending on hydroperiod length. Thus, a variety of pools with varying hydroperiods may be necessary to ensure breeding sites for all local species (Semlitsch 2002). Additionally, some species such as Ambystoma talpoideum, may
58 survive as paedomorphic adults requiring presence of pooled water during their entire lifetime
(Petranka 1998).
Loss of small wetlands used by breeding amphibians can have landscape-scale impacts on amphibian populations, potentially changing metapopulation dynamics by reducing ecological connectivity, limiting breeding sites, and reducing species populations (Semlitsch and Bodie
1998). Based on current status of knowledge of pool-breeding amphibians, I sought to determine the diversity of amphibian larvae occurring over a 2-year period in floodplain-connected and isolated upland temporary pools of public forestlands in north-central Mississippi.
STUDY AREA
I conducted field experiments on 10 ephemeral pool sites located on Tombigbee National
Forest, Ackerman Unit (6 sites) and Noxubee National Wildlife Refuge (4 sites) in Oktibbeha and
Winston Counties, north-central Mississippi. Details on study site location and vegetative composition are provided in Chapter II.
METHODS
Field Methods
Field data collection was accomplished from April 2004 to March 2006. Aquatic
sampling was not conducted during November, December, and January to limit disturbance to the
ponds during salamander breeding seasons and protect egg masses from potential damage. Field
methods and sampling schedule are described specifically in Chapter II. Species data reported in
this chapter were obtained from 27 sweepnet surveys on 10 ephemeral pool sites.
59 Statistical Analyses
Faunal response variables included species richness and abundance of larval amphibians and individual species abundance.
The following hypotheses were investigated:
H0 : Species richness of larval Ambystomatid salamanders, newts, and anurans is similar between upland and floodplain pools.
H1 : Species richness of larval Ambystomatid salamanders, newts, and anurans differs between upland and floodplain pools.
H0 : Abundance of larval Ambystomatid salamanders, newts, and anurans is similar between upland and floodplain pools.
H1 : Abundance of larval Ambystomatid salamanders, newts, and anurans differs between upland and floodplain pools.
Species richness was calculated for upland and floodplain pools as total number of species detected during the aquatic sweep-net surveys. I used a one-way Analysis of Variance
(PROC GLM, SAS 9.1) to determine if species richness varied significantly for larval salamanders, newts, and anurans between upland and floodplain pools (SAS Institute 1999).
I used multi-response permutation procedure (MRPP) to determine if larval amphibian abundance differed between upland and floodplain ephemeral pools. MRPP is considered a non- parametric alternative to discriminant function analysis (DFA) for testing the hypothesis of no difference between 2 or more groups decided a priori to analysis (McCune and Mefford 1999). I divided capture data from pitfall/funnel trap surveys by Order into anurans (Order Anura) and salamanders (Order Caudata) (Conant and Collins 1998). Study sites (n=10) were categorized according to pool type as either upland or floodplain pools. MRPP did not allow for number of species included in analysis to exceed number of study sites. Species with negligible capture numbers (< 10 total captures) were omitted from analysis. (Fogarty 2005).
60 If a significant difference was found using MRPP analysis, I conducted a Kruskal-Wallis test (PROC NPAR1WAY, SAS 9.1) to determine if individual species abundance differed significantly between pool types. Kruskal-Wallis is considered a non-parametric equivalent to a one-way Analysis of Variance (Conover 1980).
I used Renkonen’s Index to quantify the similarities of amphibian larvae in upland and floodplain pools (Krebs 1989). This similarity index is defined as P = ∑ minimum (p1i, p2i); where, P = percentage similarity between upland and floodplain sites; p1i = percentage of species i in floodplain pools; p2i = percentage of species i in upland pools. Renkonen’s Index can be viewed as a scale from 0 (no similarity between pool types) to 100 (complete similarity between pool types) (Krebs 1989).
RESULTS
Twenty-seven sweepnet surveys at 10 ephemeral pools yielded captures of 15 amphibian species and 2,179 individuals (Tables 4.1, 4.4, 4.5). On upland sites, 14 amphibian species and
1,038 individuals were detected. On floodplain sites, 12 amphibian species and 1,141 individuals were detected (Tables 4.4 and 4.5). Species richness did not significantly differ for anurans (F1,8
= 2.76, P = 0.135) or salamanders (F 1,8 = 0.93, P = 0.363) between upland and floodplain pools.
MRPP found significant separation of groups for abundance of Ambystomatid salamanders and newts (T= -2.740, P = 0.021, A= 0.258; Table 4.2). Due to low number of captures and MRPP restrictions, southern cricket frog (Acris gryllus), eastern narrowmouth toad
(Gastrophyrne carolinensis), and bird-voiced treefrog (Hyla avivoca) were omitted from MRPP analysis. No significant separation was found for anurans (T= 0.297, P = 0.552, A = -0.010).
Kruskal-Wallis test yielded 2 amphibian species, southern cricket frog and central newt showing significant differences in abundance between pool types (Table 4.3). Southern cricket
61 frog (P =0.068) and central newt (Notopthalmus viridescens louisianensis; P =0.018) were found to be most abundant in upland pools.
The Renkonen Index value for amphibian larvae was 0.613. This index value indicates that approximately 61.34% of the larval amphibian communities were similar between upland and floodplain sites.
I detected amphibian larvae over a 9-month period of each study year (Tables 4.4 and
4.5). Southern cricket frog tadpoles were detected during July and August. True toad tadpoles were detected from March-August with greatest detectability occurring between June-July.
Eastern narrowmouth toad tadpoles were detected only during August. Treefrogs were detected
June-September with the greatest number of captures in August. True frogs were detected March-
October with the greatest number of captures between May-August. Upland chorus frogs
(Pseudacris triseriata feriarum) were solely detected in July. Eastern spadefoot toads were solely detected in September. Northern spring peepers (Pseudacris crucifer) were heard vocalizing at upland and floodplain pools; however, no larvae were captured during sweepnet surveys.
Ambystomatid salamanders were captured February-July, whereas, central newts were captured
March-October with greatest numbers June-July.
DISCUSSION
Species richness of larval salamanders, newts, and anurans did not differ significantly between upland and floodplain pools, whereas, abundance of Ambystomatid salamanders and central newts showed significant differences between isolated upland and floodplain pools in at least one analysis method. All Ambystomatid salamanders showed greater abundance in upland pools and central newts (larvae and adults) used upland pools exclusively. Larvae of anuran species that were most common in upland and floodplain pools were bronze frog (Rana clamitans clamitans), true toads (Bufo spp.), and southern leopard frog (Rana sphenocephala). Southern
62 cricket frog and eastern spadefoot toad larvae (Scaphiopus holbrookii holbrookii) were found in upland pools exclusively, whereas, eastern narrowmouth toads were found solely in floodplain pools.
Characteristics of spawning sites chosen by adults affect ecology of larvae by defining which species of competitors and predators are likely to be present and whether habitat conditions are favorable for breeding, development, and subsequent recruitment (Alford 1999). Inherent characteristics of pool hydrologic regimes may affect species composition of the amphibian breeding community. Stream-connected floodplain pools receive recharge from overflow following rainstorms. While this phenomena may lead to a more predictable and continuous supply of water than isolated pools, the flow and scouring effect of floodplain waters may be detrimental to amphibian eggs and larvae and may be responsible for the introduction of fish and invertebrate predators (Horton and Grant 1998).
Some amphibian species are generalists and can survive and reproduce in a variety of habitats, even in the presence of predators. Selected species, including some Ranid and Hylid species, possess anti-predator behaviors and skin toxins that allow them to colonize pools containing fish or shift microhabitat use to avoid predation, and not be restricted to a specific habitat (Taylor 1983; Morin 1986; Petranka et al. 1987; Stangel and Semlitsch 1987; Kats et al.
1988; Lawler 1989, Petranka 1998). Bronze frogs and southern leopard frogs are generally ubiquitous throughout their range, and are common residents in temporary and permanent freshwater habitats, including sloughs, swamps, oxbows, stream channels, and ephemeral pools
(Wright and Wright 1961, Conant and Collins 1998). Similarly, true toads are found within a variety of habitat types due to special skin adaptations and fossorial habits allowing these species to persist in more xeric habitats and not be restricted solely to mesic soils representative of floodplains (Jones and Taylor 2005).
63 Other species are more specialized in choice of breeding sites due to vulnerability of eggs
and larvae to predation or habitat disturbance. Ambystomatids typically breed in temporary pools
lacking predacious fish that pose a significant threat to their eggs and larvae. In my study, > 85%
of larval Ambystomatid captures were collected from upland pools. Central newts are unpalatable
and toxic to most predators and use temporary and permanent ponds for breeding in both upland
and bottomland habitats (Hulbert 1970, Brodie et al.1974, Gates and Thompson 1982; Petranka
1998; Semlitsch 1988). However, in my study, 100% of central newt captures were from isolated
upland ephemeral pools. Upland pools in my study contained fewer fish species than floodplain
pools and were not subjected to disturbance caused by flood pulse waters potentially making
these ponds more favorable as reproductive sites for both Ambystomatids and central newts.
In my study, 3 anuran species differed in usage of upland and floodplain pools as
reproductive sites. Southern cricket frogs (n=3) and eastern narrowmouth toads (n=8) bred solely
in upland and floodplain pools, respectively, however, due to low capture numbers few
assumptions can be made. Eastern spadefoot toads (n=60) bred exclusively at one upland pond
(pond G) and tadpoles were documented on only one sampling occasion between 2004-2006.
In addition to larval amphibians captured in my study, 12 paedomorphic mole
salamanders (Ambystoma talpoideum) were captured in 3 upland pools. Salamanders and newts exhibit complex life cycles and may develop through either metamorphosis or an alternative life cycle called paedomorphosis. Paedomorphosis is a heterochronic developmental pathway in which individuals reproductively mature and live an aquatic existence while retaining larval characteristics, such as external gills and tail fins (Jackson and Semlitsch 1993; Denoël et al.
2005). Presence of paeodomorphism has been observed in 57 species of salamanders and newts and is common in certain species of Ambystoma (Petranka 1998; Denoël et al. 2005). Local populations of mole salamanders may consist entirely of terrestrial adults or a mixture of gilled
64 and terrestrial adults (Petranka 1998). Gilled adults tend to dominate permanent or semi- permanent ponds (Heintzel and Rossell 1995; Scott 1993; Semlitsch and Gibbons 1985;
Semlitsch et al. 1990). The propensity to become paedomorphic has been thought to be determined by a genetic component and environmental factors (Harris 1987). Tompkins (1978) indicated that a recessive gene was possibly responsible in coding for paedomorphosis during cross-breeding experiments of paedomorphic and metamorphic individuals, whereas, more recent studies suggest a more complex genetic basis (Harris et al. 1990; Voss and Shaffer 1997).
Environmental factors including density of conspecifics, desiccation rate, temperature, and food availability have been shown to affect paedomorphic development (Harris 1987; Semlitsch 1987;
Semlitsch et al. 1990; Svob 1965; Sprules 1974; Voss 1995; Ryan and Semlitsch 2003). Studies have shown, however, that local populations differ in their tendency to metamorphose when faced with the same environmental factors, lending support that paedomorphic development also contains a heritable component (Semlitsch and Gibbons 1985; Semlitsch et al. 1990). In my study, all sites that contained paedomorphic mole salamanders also contained metamorphic individuals.
Results from Renkonen’s Index indicated that approximately 61.35% of the larval amphibian community was similar between upland and floodplain temporary pools. Currently, isolated upland temporary pools receive limited protection through federal wetland regulation and protection is based on importance to biological diversity on public lands (see Chapter III). In terms of conservation measures, this means that 38.65% of the larval amphibian community would be neglected if management plans continue to afford protection solely to floodplain pools.
Though species richness for larval amphibians did not differ between upland and floodplain pools in my study, upland pools supported several pool-breeding species, including one species exhibiting an alternative life-cycle, not found in floodplain pools. Although paedomorphism is common in species of Ambystoma, paedomorphic mole salamanders were found only in upland
65 pools in my study and may represent a locally distinct population because this alternative
development is thought to be heritable. If upland pools continue to be overlooked in conservation
and management planning, local populations of pool-breeding amphibians using these ponds may
decline or be eliminated.
Differences in species detectability and periodicity of sampling in my study resulted in
difficulty determining areas that serve as the most important reproductive sites for pool-breeding
amphibians and also for gaining accurate abundance estimates for larval amphibians. In my study,
difference in detectability was of special concern for anuran species, particularly species that are
episodic breeders or species exhibiting shortened larval periods. For example, eastern spadefoot
toads exhibit a short larval period lasting from 12-60 days (Wright and Wright 1961; Semlitsch
2002). Explosive breeding events were documented for this species at one upland pond (pond G)
in summer 2004 and summer 2005 with >200 adults captured during each event by pitfall/funnel
trap surveys (see Chapter III). Eastern spadefoot toad tadpoles were detected only at this pond
and during only one sampling occasion in September 2005 with 60 tadpoles captured by
sweepnetting, however, >3,000 spadefoot metamorphs were observed exiting the pond within an
8-day period post-sweepnetting. Without witnessing the emergence of newly transformed metamorphs and relying solely on sweepnet capture data, I would have concluded that the pond had limited breeding success for spadefoot toads between 2004-2005. Due to the shortened larval period and the tendency of spadefoots to not breed annually, however, I concluded that my sampling intensity of bi-monthly sweepnetting was not sufficient to detect species that may transform and emerge 2-3 weeks post-spawning. More frequent sampling would be required to ensure detection of these species.
Adult eastern narrowmouth toads were common species at upland and floodplain pools
(see Chapter III), with pitfall/funnel capture numbers >100 per trap period on several occasions.
66 However, only 8 narrowmouth tadpoles were captured using sweepnetting between 2004-2006, and tadpoles were found only in floodplain pools. Narrowmouth tadpoles are suspension feeders and have a larval period of 20-70 days (Wright and Wright 1961). These traits should have made it easier to detect tadpoles because they would likely be located foraging along the water’s surface and bi-monthly sampling should have been sufficient to detect tadpole presence prior to transformation and emergence. Sweeping occurred along the littoral zone of each pond so it is possible that shifts in microhabitat use to escape capture may have resulted in an underestimate of this species’ larvae. Another alternative is that there was a reduction in reproductive success in my ponds for narrowmouth toads and that these ponds may be serving as biological “sinks” due to in-pool conditions or adjacent barriers, such as roads and bulldozed firelanes that may limit movement to suitable breeding areas. However, amphibian reproduction is known to fluctuate, and production of large numbers of juveniles may occur at ponds for several years only to be followed by declines in subsequent years (Gill 1978). Long-term monitoring would be necessary to determine intermittent use of these ponds as breeding sites and natural fluctuations in pool- breeding amphibian populations.
Connectivity of local amphibian populations and barriers to dispersal remains a crucial issue for long-term viability of pool-breeding amphibians (see Chapter III). Breeding adults show a strong preference to return to natal ponds, and most dispersal occurs during the juvenile stage
(Oldham 1966; Gill 1978; Breden 1987; Berven and Grudzien 1990). Frequent reproductive failure in local populations has been observed in many locations due to environmental factors such as drought (Dodd 1993, 1995; Semlitsch 2002). With low recruitment and limited dispersal capabilities, amphibian populations are extremely vulnerable to local extinctions (Semlitsch
2002). Results of my study indicated the importance of temporary pool sites for supporting diverse amphibian assemblages using these pools for breeding. Generalist anuran species bred frequently in upland and floodplain pools, whereas, upland pools were used extensively by
67 Ambystomatid salamanders and newts. Additionally, paedomorphic salamanders and anurans exhibiting explosive breeding events used selected upland pools and were not found in floodplain pools. For conservation measures to encompass the entire suite of breeding amphibians surrounding these ponds, upland and floodplain pools should be protected from loss or degradation.
MANAGEMENT IMPLICATIONS
For future studies and natural resource planning, accurate sampling is crucial for identifying areas that serve as important reproductive sites for pool-breeding amphibians. Due to species differences in larval period and microhabitat use, timing, location, and method of sampling are crucial to determine the suite of species using upland and floodplain pools at varying times of the year. Presence of either egg masses, larvae, or metamorphs could be detected for varying species throughout the year and sampling during each month of the year is necessary to capture all species detected in my study. For example, additional sampling should be conducted during the breeding season between November-March to identify egg masses and tadpoles of northern spring peepers (Pseudacris crucifer) (Conant and Collins 1998). With the recommendation that surveys should be conducted year-round, one consideration that must be made is the potential disturbance to the pool environment and subsequent negative impacts on egg masses and larvae that may occur with an intensive sampling approach. In my study, sweepnet surveys were limited to spring, summer, and fall to avoid damage to egg masses layed by salamander species breeding in late fall/winter. The reduction of surveys during this time may have underestimated salamander usage of these ponds for breeding. Additionally, sweepnet surveys concentrated on the littoral zone of each pool and may have biased abundance estimates.
Species that use specific microhabitats for foraging, that seek refugia due to differences in diel patterns, or exhibit escape responses when approached by the sweepnet may have been
68 underestimated. Thus, consideration should be given to sampling methods that are less disruptive and more inclusive of microhabitats that may be favored by different species.
Due to biases revealed through comparisons of larval amphibian captures to captures of metamorphs emerging from pools and disturbance associated with sweepnetting, I recommend that future studies incorporate a more passive survey approach and more comprehensive sampling of aquatic habitats to quantify amphibian larvae in temporary pools. An aquatic funnel trap technique described by Wilson and Dorcas (2003) may be an appropriate alternative to sweepnetting. Wilson and Dorcas (2003) compared the efficiency of aquatic funnel traps to timed sweepnetting in stream habitats. Funnel traps were constructed of plastic liter soda bottles of varying sizes and placed in various microhabitats within streams. Traps were left for one-week sessions and checked every other day. Their results showed that funnel traps yielded a greater diversity of amphibian species and life stages than sweepnetting and no in-trap mortality was observed. This method is relatively passive when compared to sweepnetting and would not likely result in damaging effects to egg masses and larvae. This method also would present a detailed account of larval microhabitat use within ephemeral pools, potentially revealing species that were undetected due to a secretive nature or species which may have been missed when using sweepnetting as a sampling method.
Several species showed affinity to breeding in upland pools over floodplain pools including Ambystomatid salamanders, central newts, and eastern spadefoot toads. For research studies targeting these species I would recommend focusing sampling efforts on upland pools, however, I would not discount use of floodplain pools by these species due to their proximity to upland habitats. Furthermore, floodplain pools may be important during years of drought providing source populations of some amphibian species or the rescue of declining populations.
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Table 4.1. Amphibian counts from aquatic surveys in 10 ephemeral pools on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006.
Floodplain Upland Floodplain Upland Taxon Common Name N N CPUE CPUE Order Anura Frogs and toads Acris gryllus Southern cricket frog 0 3 0.00 0.75 Bufo spp. True toads 429 187 71.50 46.75 Gastrophyrne carolinensis Eastern narrowmouth toad 8 0 1.33 0.00 Hyla avivoca Bird-voiced treefrog 3 1 0.50 0.25 Hyla cinerea Green treefrog 13 2 2.17 0.50 Hyla versicolor chrysoscelis Cope’s grey treefrog 109 4 18.17 1.00 Pseudacris triseriata feriarum Upland chorus frog 58 18 9.67 4.50 Rana catesbeiana Bullfrog 2 11 0.33 2.75 Rana clamitans clamitans Bronze frog 305 417 50.83 104.25 Rana sphenocephala Southern leopard frog 167 101 27.83 25.25 Scaphiopus holbrookii holbrookii Eastern spadefoot toad 0 60 0.00 15.00
Subtotal 1094 804 182.33 201.00 Species Richness 9 10 9 10
Order Caudata Salamanders Ambystoma maculatum Spotted salamander 29 54 4.83 13.50 Ambystoma opacum Marbled salamander 2 8 0.33 2.00 Ambystoma talpoideum Mole salamander 16 132 2.67 33.00 Notophthalmus viridescens louisianensis Central newt 0 40 0.00 10.00
Subtotal 47 234 7.83 58.50 Species Richness 3 4 3 4 73
74
Table 4.2. MRPP results from aquatic surveys in 10 ephemeral pools on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006.
Test Statisti Effect Size Floodplain Upland Total Group P-value c (T) (A) Abundance Abundance Abundance
Anurans 0.552 0.297 -0.010 1083 800 1898
Salamanders 0.021 -2.740 0.258 47 234 281
Table 4.3. Kruskal-Wallis results from aquatic surveys in 10 ephemeral pools on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006.
Taxon P-value Mean Score (F) Mean Score (U) Anurans Bufo spp. 0.669 5.833 5.000
Bird-voiced Treefrog 0.879 5.417 5.625 Bronze Frog 0.136 4.333 7.250 Bullfrog 0.117 4.417 7.125 Cope’s Grey Treefrog 0.741 5.125 5.750 Eastern Narrowmouth 0.224 6.167 4.500 Toad Eastern Spadefoot Toad 0.221 6.250 5.000 Green Treefrog 0.793 5.667 5.250 Southern Cricket Frog 0.068 4.500 7.000 Southern Leopard Frog 0.392 4.833 6.500 Upland Chorus Frog 0.256 4.667 6.750
Salamanders Central Newt 0.018 4.000 7.750 Marbled Salamander 0.648 5.250 5.875 Mole Salamander 0.163 4.417 7.125 Spotted Salamander 0.279 4.667 6.750
75 Table 4.4. Periodicity of salamanders, newts, and larvae detected during aquatic surveys in 10 ephemeral pools on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006. MONTH SPECIES JAN FEB MAR APR MAY JUN Ambystoma maculatum NA 16 17 6 33 11 Ambystoma opacum NA 0 0 0 2 3 Ambystoma talpoideum ** NA 10 1 51 26 34 Notophthalmus viridescens NA 0 1 4 0 13 louisianensis *** SPECIES JULY AUG SEPT OCT NOV DEC Ambystoma maculatum 0 0 0 0 NA NA Ambystoma opacum 0 5 0 0 NA NA Ambystoma talpoideum ** 19 6 0 1 NA NA Notophthalmus viridescens 15 5 0 2 NA NA louisianensis ***
Note: Abundance for each species was summed across years to represent the total number of captures from 2004-2006. NA= Non-applicable, surveys were not conducted during these months. ** A. talpoideum abundance includes paedomorphic adults captured during sweep-netting [July (4), Aug (4), Apr (4)]. *** N. v. lousianensis abundance includes adults captured during sweep-netting [Mar (1), June (7), Oct (2)].
76 Table 4.5. Periodicity of larval anuran abundance detected during aquatic surveys in 10 ephemeral pools on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS, 2004-2006. MONTH
SPECIES JAN FEB MAR APR MAY JUN Acris gryllus NA 0 0 0 0 0 Bufo spp. NA 0 21 26 27 203 Gastrophryne carolinensis NA 0 0 0 0 0 Hyla avivoca NA 0 0 0 0 3
Hyla cinerea NA 0 0 0 0 0 Hyla chrysoscelis NA 0 0 0 0 0
Rana catesbeiana NA 0 6 1 0 0 Pseudacris triseriata NA 0 3 0 8 0 feriarum Rana clamitans clamitans NA 0 1 34 112 168 Rana sphenocephala NA 13 60 2 2 58 Scaphiopus holbrookii NA 0 0 0 0 0 holbrookii
SPECIES JULY AUG SEPT OCT NOV DEC
Acris gryllus 1 2 0 0 NA NA Bufo spp. 312 27 0 0 NA NA Gastrophryne carolinensis 0 8 0 0 NA NA Hyla avivoca 1 0 0 0 NA NA Hyla cinerea 1 12 2 0 NA NA Hyla chrysoscelis 1 108 4 0 Rana catesbeiana 1 5 0 0 NA NA Pseudacris triseriata 65 0 0 0 NA NA feriarum Rana clamitans clamitans 130 211 11 55 NA NA Rana sphenocephala 45 54 24 10 NA NA Scaphiopus holbrookii 0 0 60 0 NA NA holbrookii Note: Abundance for each species was summed across years to represent the total number of captures from 2004-2006.
77
35.00 30.00 25.00 20.00 Floodplain 15.00 Upland 10.00 5.00 0.00 AMMA AMOP AMTA NOVL Catch per Unit Effort (# Effort per Individuals) Unit Catch Species Code
Note: Species codes are as follows: AMMA= Ambystoma maculatum; AMOP= Ambystoma opacum; AMTA= Ambystoma talpoideum; NOVL= Notopthalmus viridescens louisianensis.
Figure 4.1 Larval salamander and newt abundance from aquatic surveys in 10 ephemeral pools on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006.
78
120.00
100.00
80.00 Floodplain 60.00 Upland 40.00
20.00
0.00
Catch per Unit Effort (# Individuals) H YCI CGR UFO ACA YAV H YCR STR ACA ACC ASP A B G H H P R R R CHO S Species Code
Note: Species codes are as follows: ACGR= Acris gryllus; BUFO= Bufo spp.; GACA= Gastrophryne carolinensis; HYAV= Hyla avivoca; HYCI= Hyla cinerea; HYCR= Hyla chrysoscelis; PSTR= Pseudacris triseriata feriarum; RACA= Rana catesbeiana; RACC= Rana clamitans clamitans; RASP= Rana sphenocephala; SCHOH= Scaphiopus holbrookii holbrookii.
Figure 4.2 Larval anuran abundance from aquatic surveys in 10 ephemeral pools on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006.
CHAPTER V
HABITAT ASSOCIATIONS OF REPTILES AND AMPHIBIANS IN UPLAND AND
FLOODPLAIN EPHEMERAL POOLS
INTRODUCTION
Wildlife management has traditionally focused on game species and their associated habitats, whereas, little attention has been given to reptiles and amphibians from a management perspective until recent decades (Bury 1988; Gibbons 1988; deMaynadier and Hunter 1995).
Amphibians have been well recognized as important indicator species of freshwater wetland habitats; however, many aspects concerning amphibian ecology are still lacking such as key environmental elements that may affect their abundance and distribution (Wellborn et al. 1996;
Skelly 1997, 2001; Alford 1999; Skelly and Kiesecker 2001). With limited information available, forest managers are faced with the difficult task of protecting wildlife habitat and maintaining biodiversity while managing for the production of forest products (Hunter 1990; Sharitz et al.
1992; Moore and Allen 1999).
In general, habitat conditions that are conducive to retaining habitat quality for
amphibians include closed canopy, larger forest patch sizes, retention of older age class hardwood
forest, leaf litter, and deadwood cover. These features enhance habitat quality by providing
invertebrate food resources, creating moist microsite conditions, and increasing structural cover
(Fitch 1954; Petranka 1998). However, many species of amphibians exhibit biphasic life histories
and different habitat conditions may be needed for varying stages of life history (Duellman and
79 80 Trueb 1986, Halverson et al. 2003). For example, Halverson et al. (2003) found that woodfrogs were able to breed in wetlands across a light gradient, whereas, spring-peepers required different habitat conditions between the larval stage and adulthood. Spring peepers were excluded from wetlands maintaining heavy canopy cover during embryonic and larval phases but depend on forested terrestrial environments post-metamorphosis (Delzell 1958; Halverson et al. 2003).
Research has indicated that distribution of herpetofauna species within an ecosystem may be related to differential use of habitats due to species life history requirements, movement of individuals between habitat patches, and colonization of new and unused habitats (Galat et al.
1998, Mills et al.1995). Specifically, habitat conditions found to influence assemblages of salamanders are water quality and availability; forest canopy coverage, structure, and composition; availability of cover, such as deadwood and detrital layers; incidence of nonpoint and point source pollution; forest patch size and interspersion; riparian corridor width; and wetland size, permanence, and interspersion (Conant and Collins 1998; Rudolph and Dickson
1990; Petranka 1998; Semlitsch 1998; Gibbs 1998a; Horton and Grant 1998; Semlitsch and Bodie
1998). Abiotic factors that influence habitat conditions within floodplain systems include hydrologic regime, flood pulse intensity and duration, topography, hydrology, wetland permanence (hydroperiod), water quality, and connectivity to river or stream (Galat et al. 1998,
Petranka 1998).
In the Southeastern Coastal Plain, seasonal isolated wetlands are an integral habitat component for many aquatic and semi-aquatic herpetofauna species, particularly pool-breeding amphibians. These temporary wetlands have been shown to support widely distributed species as well as unique species assemblages not found within permanent wetlands (Wellborn et al. 1996;
Snodgrass et al. 2000). Though isolated wetlands can be found at high densities in managed forests, their tendency to remain dry for periods of time coupled with their small size, often make these pools inconspicuous and not included on topographic maps or included in management
81 decisions (Kirkman et al.1999, Wigley 1999). The hydroperiod and duration of surface water of pools affects the faunal composition and reproduction of species using temporary pools (Brooks and Hayashi 2002). Reduction of pool size due to drying and increased competition can slow growth and increase the larval period and preclude amphibian larvae from attaining body size enough to metamorphose and disperse before habitat desiccation (Holomuzki 1997). Larvae born in long duration pools tend to be large at metamorphosis, a life history trait related to greater terrestrial fitness in temperate amphibians (Scott 1994). In wetlands that are dry for longer periods, competition for limited resources and predation rates may be more intense during brief wet periods (Snodgrass et al. 1999).
For conservation measures to be effective, protection and restoration of wetlands used by
herpetofauna must be coupled with protection of adjacent terrestrial habitat, though these issues have typically been addressed separately in the past (Porej et al. 2004). Many amphibians rely on temporary ponds for breeding, however, amphibians spend most of their lifetimes in surrounding terrestrial habitat. Most amphibians have small home ranges and rarely travel more than several hundred meters during their lives (Gibbons et al. 2000). Pond-breeding amphibian populations are believed to function as clusters of metapopulations across a region in which habitat connectivity among populations is crucial for the rescue and recolonization when local populations decline
(Gill 1978; Sjogren-Gulve 1994). Semlitsch (1997, 2005) presented the idea of including terrestrial “buffer zones” surrounding isolated wetlands and the designation of core terrestrial habitat for pond breeding salamanders, because they depend on aquatic and terrestrial habitats to complete their life cycle and maintain viable populations. Semlitsch (1998) provided guidance on adequate buffer width to protect salamanders, such as Ambystomatids, reporting that protective buffers extending 164m from the wetland edge should protect 95% of the amphibian populations.
According to Burke and Gibbons (1995), a 275-m wide upland buffer around wetlands protected
100% of the nesting and hibernation sites of freshwater turtles; whereas 73-m buffers protected
82 90% of these essential sites (Burke and Gibbons 1995). Snodgrass et al. (1999) found that wetland size was not a good predictor of hydroperiod or amphibian species richness and therefore, other measures should be used in conservation planning (Snodgrass et al. 1999).
Most research concerning effects of forest management on herpetofauna has focused on stream-associated amphibians, whereas, information regarding habitat associations and amphibians surrounding temporary wetlands remains sparse (deMaynadier and Hunter 1995).
Based on the current status of knowledge of pool-breeding amphibians, I sought to determine habitat conditions that may influence herpetofaunal communities in stream-connected and isolated, upland temporary pools of public forestlands in north-central Mississippi. I also sought to determine if measured habitat characteristics differed between floodplain and upland temporary pools.
STUDY AREA
I conducted field experiments on 10 ephemeral pool sites located on Tombigbee National
Forest, Ackerman Unit (6 sites) and Noxubee National Wildlife Refuge (4 sites) in Oktibbeha and
Winston Counties, north-central Mississippi (Asmus 2003). Details on study site location and vegetative composition are provided in Chapter II.
METHODS
Field Methods
Field methods are described specifically in Chapter II. Habitat measurements were
originally begun in October 2004 but were not completed prior to the arrival of dormant season.
Habitat measurements for all sites were then repeated during the growing season between June
2005-July 2005. Extensive damage to hardwoods was incurred at 4 floodplain ephemeral pool
83 sites following Hurricane Katrina in August 2005. Canopy coverage, leaf litter, and Nudd’s board readings were repeated following the hurricane damage in October 2005.
Statistical Analyses
The following hypotheses were investigated:
H0 : Habitat conditions surrounding and within pools does not influence amphibian species richness or abundance.
H1 : Habitat conditions surrounding and within pools does influence amphibian species richness or abundance.
H0 : Habitat conditions surrounding and within pools are similar in upland and floodplain pools.
H1 : Habitat conditions surrounding and within pools differ between upland and floodplain pools.
A detailed account of herpetofauna pifall/funnel trapping results including species richness and abundance of amphibians and species richness and abundance of reptiles can be found in Chapter III. A list of habitat variables included in analysis can be found in Table 5.1.
Determining if habitat conditions influenced herpetofaunal richness and abundance was a two- step process. I used data reduction techniques to eliminate environmental variables exhibiting little variance among ephemeral pool sites and variables that were correlated (Fogarty 2005).
First, I used Principal Components Analysis (PCA) to reduce the habitat data set to a smaller number of variables that represented most of the variation between pool sites (PROC
PRINCOMP, SAS 9.1; McCune and Grace 2002). PCA is a basic eigenvector analysis that requires one data matrix, in this case, habitat variables by pool site, and determines which variables contribute most to the overall variance of the data set relative to one another (Johnson
1998; Fogarty 2005). Then, I used Canonical Correspondence Analysis (CCA) to identify environmental variables that were related to measured herpetofaunal community structure (Table
5.2; McCune and Grace 2002). CCA also is an eigenvector analysis technique but pairs two
84 matrices together, one with sample units x species and the other with sample units x environmental variables (McCune and Grace 2002). CCA uses multiple linear regression to constrain an ordination of one matrix on variables in the second matrix (McCune and Grace
2002).
CCA matrices were constructed for environmental variables, amphibian richness and abundance, and reptile richness and abundance. Southern cricket frog (Acris gryllus) and northern spring peeper (Pseudacris crucifer) were omitted from the amphibian abundance due to low capture numbers (< 3 captures per pool type) but were included in models on amphibian species richness. Additionally, eastern spadefoot toads (Scaphiopus holbrookii holbrookii), an explosive breeder, were not included in the amphibian abundance estimate due to highly variable capture rates ranging from no captures to > 3,600 captures, however, spadefoot toads were included in models on amphibian species richness.
Select environmental variables measured during this study were omitted at this stage of analysis including climatic, weather related, and hydrological variables including water pH, water temperature and depth, soil pH and moisture, precipitation, and air temperature. These measurements were taken during monthly trap surveys and will be combined with data collected by Asmus (2003) to produce a 5-year data set. Analysis on this data will be completed as part of a doctoral research project in which I will determine specific habitat associations and generate predictive models of abundance for herpetile groups over years and climatic variation.
I used multi-response permutation procedure (MRPP) to determine if habitat variables reduced by PCA differed between upland and floodplain ephemeral pool types. MRPP is considered a non-parametric alternative to discriminant function analysis (DFA) for testing the hypothesis of no difference between 2 or more groups decided a priori to analysis (McCune and
Mefford 1999). Study sites (n=10) were categorized according to pool type as either upland
(isolated from floodplain) or floodplain pools (located within stream floodplain).
85 If a significant difference was found using MRPP analysis, I conducted a Kruskal-Wallis test (PROC NPAR1WAY, SAS 9.1) to determine if individual environmental variables varied significantly by pool type. Kruskal-Wallis is considered a non-parametric equivalent to a one-way
Analysis of Variance yet relaxes the assumptions of normality and homogeneity of variance required for parametric analyses (Conover 1980).
I used Renkonen’s Index to quantify the similarities of environmental variables between
floodplain and upland pools (Krebs 1989). The index is a percent similarity index defined as P =
∑ minimum (p1i, p2i); where, P = percentage similarity between upland and floodplain sites; p1i = percentage of habitat variables i in floodplain pools; p2i = percentage of habitat variables i in
upland pools. Renkonen’s Index can be viewed as a scale from 0 (no similarity between pool
types) to 100 (complete similarity between pool types) (Krebs 1989). All variables listed in Table
5.1 where included for calculation of the similarity index which the exception of pool type.
RESULTS
Canonical Correspondence Analysis
Habitat
Results presented in this chapter are based solely on measurements taken during the
2005-growing season. I began habitat analysis with 30 environmental variables measured at
ephemeral pools sites (n=10) (Table 5.1). PCA eliminated 9 variables that showed weak
associations with the first several eigenvectors. Due to CCA restrictions, an additional 12
environmental variables were eliminated from analysis. Variables included in CCA were based
upon their associations from PCA, as well as, their perceived biological importance to
86 herpetofaunal community structure and function as reported by current literature. The 10 x 9 habitat matrix consisted of ephemeral pool sites x environmental variables and was used in combination with the matrix below for CCA (Table 5.2). Average measurements for habitat variables included in CCA are listed in Table 5.3.
Herpetofaunal Richness and Abundance
A 10 x 4 matrix was constructed of ephemeral pool sites x herpetofaunal parameters including amphibian species richness, amphibian abundance, reptile species richness, and reptile abundance. The first two axes of the CCA ordination accounted for 96.0 % of variance in species data as explained by the environmental variables (Fig.5.1). The first axis was the most important and explained 58.1 % of the variance. Environmental variables strongly correlated with the first axis were overstory count, log count, snag count, and snag diameter (Table 5.4). The second axis accounted for 37.9 % of the variance. Environmental variables associated with the second axis were ground cover density (Nudds A), log decay, overstory count, bare ground, snag diameter, and litter depth. Of the species data, amphibian abundance was the only variable found to influence ordination, thus, inferences can only be made about this response variable as it relates to environmental variables. Ter Braak (1986) states that an ordination diagram can be used to show dominant patterns in community composition related to measured habitat characteristics. By examining an ordination diagram using biplot scores, I concluded that the approximate center of the distribution for amphibian abundance was intermediate along the environmental gradients as denoted by its position close to the center on the ordination diagram (Figure 5.1).
87 Additional Analyses
MRPP found no significant separation of groups for upland and floodplain ephemeral pools (T = 1.208, P = 0.898, A = -0.036). Because no significant difference was found using
MRPP, further analysis using the Kruskal-Wallis test was not conducted.
The Renkonen Index value for habitat was 0.9850. This indicates that approximately
98.50 % of the measured environmental variables were similar between upland pools and floodplain pools.
DISCUSSION
In my study, analysis related measured habitat characteristics to summary variables for reptiles and amphibians based on community-level indices. Overall, amphibians were most abundant in areas with intermediate levels of sampled environmental factors and inferences could not be made for reptiles. However, species-specific habitat requirements may differ along each environmental gradient due to variability in physiology and activity patterns of herpetofauna, and individual species needs may be missed when making broad generalizations at the community level. Thus, I recommend that further analysis be conducted examining faunal-habitat associations for individual species of herpetiles. Furthermore, analysis should incorporate information on water quality and weather conditions in addition to vegetative structure to determine how they relate to herpetofauna.
Results of my study support previous findings that structure and composition of forest overstory and ground coverage components such as snags, downed woody debris, and detritus were important factors influencing herpetofauna, however specific associations could not be made for herpetiles. Previous studies have found that reptiles and amphibians responded differently to abundance of standing snags potentially related to the influence of canopy gaps on life-history traits of herpetofauna. Areas containing numerous snags likely produce warmer and
88 drier microsite conditions as more light would penetrate and reach the forest floor due to lack of crown closure in areas containing snags. Reptiles would likely benefit from these conditions as higher light levels lead to increased prey abundance and warmer temperatures required for thermoregulation, egg incubation, and development of hatchlings, whereas amphibians are particularly vulnerable to desiccation and may be negatively impacted by these conditions (Goin and Goin 1971; Blake and Hoppes 1986; Deeming and Ferguson 1991; Petranka 1998). Previous studies found that amphibians, including mole (Ambystoma talpoideum), marbeled (Ambystoma opacum), and slimy salamanders (Plethodon gluttinosus), were captured more frequently in unharvested mature forests compared to forests containing canopy gaps due to selective logging practices (Cromer et al. 2002). In contrast, lizard and snake abundance was found to be highest in forests containing canopy gaps compared to mature forest with closed-canopy conditions
(Greenberg 2001). Additionally, differing responses of herpetiles to snag abundance may be related to predator presence associated with standing snags. Forests containing abundant snags may contain dense populations of meso-mammal predators, such as raccoon (Procyon lotor) that
use cavities and decaying wood for den sites and foraging opportunities (Yarrow and Yarrow
1999). Amphibians have limited mobility compared to reptiles and may be more susceptible to
depredation in areas containing abundant predators due to snag availability (Zug et al. 2001).
Snags provide a valuable source of downed woody debris that may be utilized to varying
degrees by reptiles and amphibians. Areas containing numerous snags would likely contribute to
abundant deadwood on the forest floor over time. Numerous sources have cited the importance of
downed woody debris for providing cover, basking, reproductive, and foraging opportunities for
reptiles and amphibians (Hunter 1990; Petranka 1998; Fogarty 2005; Jones and Taylor 2005;
Bailey et al. 2006). Coarse woody debris is beneficial for protecting against extreme weather and
retaining moisture and has been found to contain abundant insect prey (Boddy 1983; Harmon et
al. 1986; Hanula 1995). The majority of amphibians captured during my study were pool-
89 breeders, many of them fossorial in nature. Several sources have discovered that coarse woody debris may be of less significance for species seeking underground refuge, such as
Ambystomatids, as compared to more surface-active species, such as terrestrial woodland salamanders (Plethodon spp.) and reptiles that use woody debris for cover, foraging, and basking
(Williams 1970; Douglas 1981; Semlitsch 1983; Loredo et al. 1996; Madison 1997; Madison and
Farrand 1998; Trenham 2001). Although reptiles and terrestrial salamanders may not rely heavily on deadwood, woody debris may provide important cover for these species in areas lacking other forms of sufficient ground cover such as leaf litter.
Detrital layers provide cover and protection of refugia for numerous species of herpetofauna. Detritus may offer protection to burrows of fossorial species by limiting erosion and, like downed wood, may buffer against extreme fluctuations in temperature and help retain moisture during dry periods (Williams and Gray 1974; Geiger et al. 1995; Moseley et al. 2004).
Furthermore, leaf litter has been found to serve as important reproductive and foraging sites.
Whereas, most pool-breeding salamanders are aquatic breeders, marbled salamanders, a common species on my study sites, oviposit on land and rely heavily upon leaf litter for the construction of nests in dried beds of ephemeral pools and along pond margins (Noble and Brady 1933; Petranka
1998). Additionally, red efts (Notopthalmus spp.) use leaf litter extensively for foraging and are known to form feeding aggregates around food sources such as rotting mushrooms (Petranka
1998). Prey availability has also been linked to litter depth with shallow litter containing reduced abundance of arthropods compared to deeper litter (Seastedt and Crossley 1981; Shure and
Phillips 1991; Siira-Pietikainen et al. 2003).
Protective measures targeting reptile and amphibian assemblages of temporary ponds should focus on retaining key habitat characteristics, such as those identified in my study, within core use areas as these elements are essential for forage, moisture, reproduction, overwintering, and cover for numerous herpetofauna species. Maintenance of moist microsite conditions
90 including leaf litter and deadwood are especially important for amphibians close to breeding ponds as they are physiologically limited in their dispersal capabilities and most pool-breeders are generally located within several hundred meters of ephemeral pools. The designation of core terrestrial habitat and buffer strips surrounding temporary pools has been proposed by several authors similar to streamside management zones used to protect riparian fauna (Murcia 1995;
Semlitsch 1997, 1998, 2005; Richter et al. 2001; Semlitsch and Jensen 2001; Bailey et al. 2006).
Amphibians depend on dispersal connections for the rescue of local populations when population numbers decline and these connections are especially important in landscapes that have been fragmented or altered by humans (Gibbs 1998b). I recommend that further research examine movement patterns including dispersal distances and use of corridors for pool-breeding amphibian assemblages on public lands.
Results of MRPP and Renkonen’s Index showed that vegetative characteristics did not
differ surrounding upland and floodplain ephemeral pools. These results conflict with personal
observations that upland sites were pine-dominated, xeric, and had more open forest canopy,
whereas, floodplain pools were surrounded by bottomland hardwood forest, had saturated soils,
and closed–canopy conditions in surrounding terrestrial areas. Canopy cover ranged from
approximately 44-94% for upland pools, whereas, canopy cover was > 80% for all floodplain
pools. These perceived differences lead me to believe that sampling effort was insufficient to
detect true differences and that pool types may have only been superficially similar. Sampling
was standardized regardless of differences in size or shape of each pool, however, pools varied
greatly from small semi-circular ponds (243 m2) to long, linear sloughs (2,291 m2). Although the total amount of area sampled at each site was the same, a disproportionate amount of sampling occurred at smaller sites in terms of sampling pool perimeter. For small pools, such as pools of surface area < 243 m2 , the entire perimeter was sampled by this design, however, due to the
overall length of some floodplain pools, only a portion of pond perimeters were sampled.
91 Ephemeral pools typically lacked an abundance of emergent vegetation or canopy cover within the pool proper due to their periodicity of filling and drying. This may account for my overall finding of no difference, as habitat conditions immediately surrounding ephemeral pools may be more similar to one another in terms of vegetative communities based on hydrology.
Habitat conditions surrounding upland and floodplain pools also were potentially affected
by natural and anthropogenic disturbances including flood scour, prescribed burning, and
herbicidal control of vegetation. Full effects of these disturbances on the structure and
composition of forest stands, however, may not have been revealed due to sampling efforts
focused around the pool proper. Intense flooding events associated with stream-connected pools
potentially have favored bottomland hardwood tree species adapted to moist-soil conditions over
time, whereas, upland areas were dominated by loblolly pine (Pinus taeda) and not subjected to
this type of disturbance regime. On the other hand, upland forests, surrounding study pools were
subjected to occasional prescribed burning and selective thinning of forest stands that may alter
canopy cover and forest floor components such as downed woody debris and litter abundance.
The type and extent of disturbance surrounding all study sites is unknown as past management history for these lands was unavailable. Differences in habitat composition and structure may only have been evident at greater distances from the pond and sampling efforts should be extended to identify variation within these habitats. Most pool-breeding amphibians are concentrated within several hundred meters of ephemeral pools, whereas, my transect line only extended 20 m and may have been insufficient for quantifying differences in habitat at a larger scale. I recommend that transect lengths be extended to > 50 m from pond edge as this distance
would likely give a more accurate picture of forest stands surrounding ephemeral ponds.
Furthermore, based on my findings and experience, I suggest that future studies investigate the
influence of disturbance, including prescribed fire and herbicide on herpetofauna surrounding
ephemeral wetlands, also the effects timber harvesting and site preparation techniques, such as
92 disking and piling of slash on these assemblages. Additionally, I recommend quantification of macro-stand conditions such as connectivity by forest corridors that may be used by herpetofauna.
MANAGEMENT IMPLICATIONS
Based on my study, I recommend protection of upland and floodplain ephemeral pools and associated terrestrial habitats to promote and conserve herpetofaunal diversity on public forested lands in Mississippi. I propose the use of a habitat mosaic approach suggested by
Semlitsch and Bodie (2003) for differences in habitat preferences between reptiles and amphibians. This approach would include maintaining terrestrial areas in forested habitats of multiple seral stages from early-mid successional forest to benefit reptile species and late- successional hardwood forest for amphibians with numerous isolated wetlands of varying hydroperiods to serve as breeding ponds. Ground coverage components including downed woody debris and leaf litter should be retained in core use areas for herpetofauna, generally within 200-
300 meters of ephemeral pool edges, as most pool-breeding amphibians spend most of their lives within terrestrial areas surrounding these wetlands.
I concur with Semlitsch (1997, 2005) who recommended maintenance of terrestrial
buffers around ephemeral wetlands for amphibian conservation. Maintenance of buffers and
connective corridors in mature hardwood forest interspersed with mixed pine-hardwood forest
could provide valuable habitat for reptiles and amphibians. Connectivity of forest patches is
crucial for the recolonization and rescue of amphibian populations and especially important in
fragmented landscapes where alternate habitat is unsuitable or unavailable.
To maintain forest patches in multiple stages of succession, forest management
techniques including prescribed burning and mechanical site preparation may be necessary
though the impact of these practices on herpetofauna remains unclear. Prescribed burning on
93 shortened-intervals (< 3 years) may reduce forest floor components, such as deadwood cover and leaf litter, found to be important for thermoregulation, moisture, forage, and reproduction of herpetiles. This would be particularly important for forest-dwelling amphibians, especially woodland salamanders.
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Table 5.1. Habitat variables measured from 10 ephemeral pool sites on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS, 2004-2006.
Variable Measurement
LITTER Mean depth (cm) of litter at center of 24 1-m2 sample plots GRNDCVR Mean # of plant species <1 m height from 24 1-m2 sample plots %BRGRND Mean percentage cover of bare ground from 24 1-m2 sample plots %DEBRIS Mean percentage cover of debris from 24 1-m2 sample plots MIDCNT Mean # midstory trees <6 m height from 24 10-m2 sample plots MIDSP Mean # midstory tree species <6 m height from 24 10-m2 sample plots MIDHT Mean midstory tree height (m) from 24 10-m2 sample plots OVCNT Total # overstory trees >6 m height from 24 100-m2 sample plots OVERSP Mean # overstory trees >6 m height from 24 100-m2 sample plots OVPINE Total # overstory pine trees >6 m height from 24 100-m2 sample plots OVRDBH Mean diameter at breast height (ft) for overstory trees >6 m height from 24 100-m2 sample plots BA Total basal area (cm2) of overstory trees in 24 100-m2 sample plots OVRGLD Mean ground-line diameter (ft) for overstory trees >6 m height from 24 100- m2 sample plots SNAGCNT Total # standing snags in 24 100-m2 sample plots SNAGPINE Total # standing pine snags in 24 100-m2 sample plots SNAGDIAM Mean diameter of standing snags in 24 100-m2 sample plots SNAGDECAY Mean level of decay of standing snags in 24 100-m2 sample plots LOGCNT Total # downed logs in 24 100-m2 sample plots LOGDIAM Mean diameter of downed logs in 24 100-m2 sample plots LOGDECAY Mean level of decay of downed logs in 24 100-m2 sample plots POOLSA Total surface area of pool (m2) POOLVOL Maximum volume of pool (m3) %CANOPY Percentage closed canopy cover from densitometer NUDDSA Means Nudd’s board reading at 2 randomly chosen directions 0.5 m above ground NUDDSB Means Nudd’s board reading at 2 randomly chosen directions 1.0 m above ground NUDDSC Means Nudd’s board reading at 2 randomly chosen directions 1.5 m above ground NUDDSD Means Nudd’s board reading at 2 randomly chosen directions 2.0 m above ground NUDDSE Means Nudd’s board reading at 2 randomly chosen directions 2.5 m above ground NUDDSF Means Nudd’s board reading at 2 randomly chosen directions 3.0 m above ground POOLTYPE General pool type (upland or floodplain ephemeral pool)
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Table 5.2. Habitat variables selected for canonical correspondence analysis to identify parameters affecting reptile and amphibian abundance by class on 10 ephemeral pools sites on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006.
Variable Measurement SNAGCNT Total # standing snags in 24 100-m2 sample plots OVPINE Total # overstory pine trees >6 m height from 24 100-m2 sample plots SNAGDIAM Mean diameter of standing snags in 24 100-m2 sample plots OVCNT Total # overstory trees >6 m height from 24 100-m2 sample plots LOGDECAY Mean level of decay of downed logs in 24 100-m2 sample plots %BRGRND Mean percentage cover of bare ground from 24 1-m2 sample plots LOGCNT Total # downed logs in 24 100-m2 sample plots NUDDSA Means Nudd’s board reading at 2 randomly chosen directions 0.5 m above ground LITTER Mean depth (cm) of litter at center of 24 1-m2 sample plots
Table 5.3. Average habitat measurements from 10 ephemeral pool sites on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006.
SITE SNAGCNT OVPINE SNDIAM OVCNT LOGDECAY BRGRND LOGCNT NUDDSA LITTER A 11.00 0.00 10.40 187.00 3.30 30.94 76.00 3.00 2.86 B 8.00 4.00 10.60 192.00 2.80 24.21 71.00 2.50 3.10 C 22.00 3.00 8.15 229.00 2.87 7.33 91.00 2.50 4.19 D 21.00 11.00 11.35 266.00 2.87 30.58 355.00 2.00 2.26 E 29.00 42.00 13.22 218.00 2.40 21.50 118.00 1.00 1.63 F 16.00 42.00 8.72 185.00 2.91 31.25 81.00 1.50 3.44 G 14.00 12.00 4.42 46.00 1.74 20.23 54.00 2.50 1.53 H 11.00 5.00 9.34 134.00 2.94 34.08 143.00 5.00 2.04 I 7.00 35.00 5.34 101.00 2.30 23.21 145.00 1.00 1.53 J 54.00 3.00 19.29 209.00 2.66 18.96 122.00 2.00 3.26 Note: Acronyms are as follows: SITE= study site letter ; SNAGCT= total # overstory snags; OVPINE= total # overstory pine trees; SNDIAM= mean diameter of snags; OVCNT= total # overstory trees; LOGDECAY= mean level of decay of downed logs; BRGRND= mean percentage cover of bare ground; LOGCNT= total # downed logs; NUDDSA= mean Nudd’s board reading 0.5m above ground; LITTER= mean litter depth.
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103 Table 5.4. Correlation coefficients of habitat variables from CCA for reptile and amphibian richness and abundance on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006. Parentheses indicate variance explained by the environmental variables.
CC1 CC2 Habitat Variable (58.1 %) (37.9 %) SNAGCT -0.261 0.062 OVPINE -0.064 0.060 SNDIAM -0.225 -0.264 OVCNT 0.299 -0.390 LOGDECAY 0.149 -0.734 BRGRND -0.182 -0.351 LOGCNT 0.225 0.049 NUDDSA -0.170 -0.442 LITTER 0.139 -0.313
Note: Acronyms are as follows: SNAGCT= total # overstory snags; OVPINE= total # overstory pine trees; SNDIAM= mean diameter of snags; OVCNT= total # overstory trees; LOGDECAY= mean level of decay of downed logs; BRGRND= mean percentage cover of bare ground; LOGCNT= total # downed logs; NUDDSA= mean Nudd’s board reading 0.5m above ground; LITTER= mean litter depth.
Table 5.5. Final scores from CCA for reptile and amphibian richness and abundance on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006.
Species Data CC1 CC2 Raw Data Totals Amphibian species richness 3.629 -2.457 0.0382 Reptile species richness 1.861 -2.648 0.0216 Amphibian abundance 0.030 0.436 0.8376 Reptile abundance -2.044 -2.136 0.1000
Table 5.6. Dominant faunal-habitat associations from CCA on Tombigbee National Forest and Noxubee National Wildlife Refuge, MS 2004-2006.
LOG LOG NUDDS SNAGCT OVPINE SNDIAM OVCNT DECAY BRGRND CNT A LITTER Amphibian - - + + + + + + + richness Reptile richness - - + + + + + - - Amphibian + + - - - - + - - abundance Reptile + - + + + + - + + abundance
Note: Acronyms are as follows: SNAGCT= total # overstory snags; OVPINE= total # overstory pine trees; SNDIAM= mean diameter of snags; OVCNT= total # overstory trees; LOGDECAY= mean level of decay of downed logs; BRGRND= mean percentage cover of bare ground; LOGCNT= total # downed logs; NUDDSA= mean Nudd’s board reading 0.5m above ground; LITTER= mean litter depth.
104
105
Note: Acronyms are as follows: AMRICH= amphibian species richness; AMABUND= amphibian abundance; REPRICH= reptile species richness; REPABUND= reptile abundance; SNAGCT= total # overstory snags; OVPINE= total # overstory pine trees; SNDIAM= mean diameter of snags; OVCNT= total # overstory trees; LOGDECAY= mean level of decay of downed logs; BRGRND= mean percentage cover of bare ground; LOGCNT= total # downed logs; NUDDSA= mean Nudd’s board reading 0.5m above ground; LITTER= mean litter depth.
Figure 5.1. Canonical correspondence analysis for habitat associations and herpetofaunal richness and abundance from the first 2 axes.
CHAPTER VI
SUMMARY AND CONCLUSIONS
Reptiles and amphibians are an integral component in the structure of vertebrate communities and are principle indicator species for the health of wetland ecosystems (Russell et al. 2002). Forest management plans, however, have traditionally overlooked herpetofauna in favor of game species or charismatic groups such as mammals or birds leaving a disparity of knowledge concerning faunal-habitat relationships for this group (Gibbons and Buhlmann 2001).
Over the past few decades, concern has grown over the global pattern of decline of herpetofauna largely due to habitat loss and degradation and the subsequent loss of biodiversity. Temporary isolated wetlands have been identified as key reproductive sites for many amphibians and aquatic reptiles, including many threatened and endangered species (Dodd and Cade 1998). These wetlands, referred to as ephemeral pools, receive minimal protection through federal regulation concerning water quality issues and development (Snodgrass et al. 2000; (U.S. DOE 2003). Much of the information available regarding habitat associations of herpetofauna is based on species residing within forested riparian zones, whereas, little attention has specifically been given to ephemeral pool habitats until recently (deMaynadier and Hunter 1995).
I conducted surveys on amphibian and reptile communities located on Tombigbee
National Forest (TNF) and Noxubee National Wildlife Refuge (NNWR) in north-central
Mississippi from March 2004 through March 2006 to compare herpetile species assemblages between isolated, upland and stream-connected floodplain ephemeral pools, determine use of these pools as reproductive sites for amphibians, and determine habitat characteristics that may
106 107 influence herpetofaunal communities. Inferences made from results of this study are restricted to
TNF and NNWR and similar physiographic areas in north-central Mississippi. Ten ephemeral pools sites were chosen, 6 floodplain ephemeral pools within bottomland hardwood forest and 4 isolated, upland ephemeral pools within mixed pine-hardwood forest. Reptiles and amphibians were surveyed monthly using pitfall/funnel trap arrays, whereas, amphibians were additionally sampled using anuran call count surveys and aquatic sweep-netting for larvae and aquatic adults.
Habitat measurements were taken during the 2005-growing season to determine conditions that may influence herpetofaunal communities.
Species richness and abundance of herpetiles during terrestrial surveys varied significantly between upland and floodplain ephemeral pools with upland pools contributing substantially more to the diversity of amphibians and reptiles on public lands in north-central
Mississippi than floodplain pools. Seven species differenced in abundance between pool types, including three species known to rely on temporary pools for breeding, Cope’s gray treefrog,
(Hyla chrysocelis), mole salamander (Ambystoma talpoideum), and central newt (Notopthalmus viridescens louisianensis). Greater numbers were found for these species on upland sites versus floodplain sites and central newts were found to use upland pools exclusively. Additionally, two species listed as locally rare in the state of Mississippi, southern red salamander (Pseudotriton ruber visocai) and red milksnake (Lampropeltis triangulum syspila) were captured at two upland sites. Eastern spadefoot toads (Scaphiopus holbrookii holbrookii) also were more common in upland ponds and were captured in great numbers (> 3,600) during explosive breeding events.
Approximately 39 % of the larval amphibian community differed between upland and floodplain ephemeral pools. Species richness of larval salamanders, newts, and anurans did not differ significantly, whereas, abundance of Ambystomatid salamanders and central newts showed significantly greater abundance in upland pools than floodplain pools and central newts (larvae and adults) used upland pools exclusively. Southern cricket frog (Acris gryllus) and eastern
108 spadefoot toad larvae also were found in upland pools exclusively, whereas, eastern narrowmouth toads tadpoles (Gastrophryne carolinensis) were found solely in floodplain pools. In addition to larval amphibians captured in my study, upland pools supported one species of salamander exhibiting an alternative lifestyle, paedomorphic mole salamanders.
Results of my study support previous findings that structure and composition of forest overstory and ground coverage components such as snags, downed woody debris, and detritus were important factors influencing herpetofauna, however specific associations could not be made for herpetiles. Habitat community similarity indices showed that habitat conditions did not differ between isolated, upland and floodplain ephemeral pools. These findings may be accurate, however, they conflict with personal observations of study site differences between pool types concerning midstory, overstory, and forest canopy conditions. Canopy cover ranged from approximately 44-94% for upland pools, whereas, canopy cover was > 80% for all floodplain pools. These perceived differences lead me to believe that sampling effort was insufficient to detect true differences and that pool types may have only been superficially similar.
In my study, upland sites of mixed pine-hardwood forest supported greater herpetofauna diversity than hardwood-dominated forests. These results are contradictory to published research findings that mature bottomland forests with closed-canopy conditions typically support a more diverse array of herpetofauna (Fitch 1954; Petranka 1998). In my study, terrestrial areas surrounding stream-connected floodplain pools generally contained a greater abundance of overstory trees than upland sites, were composed predominantly of hardwoods, had closed forest canopy, and copious amounts of detritus all of which are thought to favor increased richness and abundance of amphibians. One possible explanation for this is that flooding events associated with stream-connectivity of these pools may have led to an increase in water recharge and hydroperiod and the introduction of fish predators not present at upland ponds. Fish were present at both upland and floodplain pools, however, floodplain pools were found to have greater
109 richness of fish species, including larger species such as blackspotted topminnow (Fundulus olivaceus), pirate perch (Aphredoderus sayanus), and bluegill (Lepomis macrochirus), known to opportunistically feed on amphibian eggs, larvae, and metamorphs. An abundance of fish predators also may alter density of aquatic invertebrates available for consumption by developing amphibians. Additionally, floodwaters may provide unsuitable breeding habitat for some species due to the possible detrimental effect of scour on amphibian egg masses and larvae (Horton and
Grant 1998; Mills et al. 1995). Future studies should seek to investigate the role of predator-prey relationships between invertebrate and fish assemblages and the pool-breeding amphibian community.
Another possible explanation for the preference for upland ponds is the reduced dispersal
capabilities of amphibians. All upland pools in this study were bordered on >1 side by gravel or
paved roads potentially inhibiting them from moving to more desirable habitat. It may not be that
pine-dominated habitats were more favorable but that they may pose the only suitable habitat
within a restricted range. Additionally, some salamanders are also known to return to the same
ponds during subsequent years for breeding and the extent to which this occurs is relatively
unknown (Semlitsch 1998; 2002). Some species may potentially return to known breeding sites
even when habitat conditions surrounding these sites have become degraded. I recommend that
further research examine movement patterns and use of corridors for pool-breeding amphibians
assemblages on public lands, as well as effects of timber harvesting and silvicultural activities on
habitat conditions surrounding ephemeral pools. Evaluation of presence or absence of corridors
and measurement of habitat features within corridors also is warranted.
Upland ponds used in this study were created artificially for livestock and as standing
water sources for upland game species. This study’s results show the propensity for
recolonization of constructed ponds and the value of these ponds for reptiles and amphibians in
110 upland forests, in particular, larvae, juveniles, and adults of pool-breeding salamanders and newts. Upland ponds, however, receive minimal protection from development and degradation as a result of the 2001 U.S. Supreme Court’s SWANCC ruling, declaring that isolated wetlands that are both intrastate and not connected to navigable bodies of water or waters used for commerce are not afforded protection under the Section 404 of the Clean Water Act (U.S. DOE 2003).
Floodplain pools, on the other hand, receive regulatory consideration, as they are adjacent to waters under jurisdiction of the U.S. Army Corp of Engineers and may be afforded additional protection by occurring within streamside management zones (SMZs) (Asmus 2003). In contrast, upland pools of < 2 ha receive no protection on private lands and protection is based on importance to biological diversity on public lands.
For a diversity of herpetofauna species to receive protection, upland and floodplain ephemeral pools should to be considered in management plans and conservation action must be extended to adjacent terrestrial habitat and not strictly the pond itself. Semlitsch (2005) proposed the designation of core terrestrial areas and multiple buffer zones surrounding temporary pools similar to SMZs to protect habitat necessary for breeding, aestivation, overwintering, etc. and prevent contamination and degradation of both terrestrial and aquatic habitats due to human land- use practices. Distances for core zones and buffers depend on the dispersal distances of selected herpetofauna species but are generally recommended up to 200 m from the shoreline to protect most of the breeding populations (Semlitsch 1998, 2005; Richter et al. 2001). To prevent negative edge effects, construction sites and roads should be limited or relocated > 60m from wetlands
(Keenan and Kimmins 1993; deMaynadier and Hunter 1995). Additionally, the installation of culverts or tunnels is recommended to direct travel of animals under or away from roads (Bailey et al. 2006). For areas in which dispersal distances to alternate ponds are too great, the creation of
111 artificial ponds should be considered to allow successful recolonization or rescue of declining populations.
Sampling methods used in this study proved effective for capturing most species of herpetofauna. However, I recommend the inclusion of additional methods and the modification of others given the nature of temporary wetland habitats and their associated biota. Pitfall and funnel trapping was useful for capturing most surface-active species but may have underestimated arboreal or fossorial species that used these ponds for breeding. Additionally, pitfall traps have known capture bias against larger species of snakes and frogs that may be able to readily escape traps, such as adult Ranids. Excluded pitfall and funnel trap designs also biased captures against testudines due to the size of the diameter opening of the funnel trap and the width of wires on the exclusion cover, only allowing for smaller species or individuals to be captured. The exclusion cover also may have provided a surface for more agile species of lizard to climb and escape capture. Another consideration that must be taken into account is the degree of trap mortality associated with this sampling method. Traps were checked every day to minimize mortality, however, intense flooding events and weather-related variables such as cold temperatures caused occasional mortality of herpetofauna and incidental mammals captured due to drowning or exposure. Additionally, depredation of captured herpetofauna by meso-mammals, predominantly raccoons (Procyon lotor), was evident on several upland sites adding to increased mortality and survey bias. Raccoons and other meso-mammal predators, including opossums (Didelphis virginiana), inhabit mesic forests adjacent to perennial water sources increasing the likelihood of depredation of pool-breeding amphibians using these same areas (Chamberlain and Leopold
2001). Though no rare species detected on my sites were obligate breeders of temporary pools, several amphibian species listed as rare in the state rely on forested habitats and riparian areas containing these wetlands. Concern must be taken when using these methods in areas where rare species may exist to limit the potential negative impact they may have on populations that may be
112 declining or have unknown population trends. I recommend a combination of faunal surveys including pitfall/funnel trapping, time or area-constrained searches, and auditory surveys to detect the multitude of species occurring in these areas. The combination of these survey methods would increase the probability of detecting rare or secretive species and species which may be excluded due to trapping biases. However, use of active searches and anuran calling surveys would result in less mortality associated with trapping.
The sampling method and timing of aquatic surveys also presented difficulty in determining the species composition of pool-breeding amphibians using upland and floodplain ephemeral pools and accurately estimating abundance of larval amphibians and aquatic adults.
Larvae of several species, including eastern narrowmouth toad and eastern spadefoot toad, were found in minute numbers compared with the numbers of adults present at each breeding pond.
However, in the case of spadefoot toads, thousands of metamorphs were witnessed exiting a breeding pond only days after the pond was swept for larvae with minimal captures. I attribute this to the periodicity in which ponds were swept and believe that more frequent sampling would be necessary using this method to detect species with shortened larval periods or preference for microhabitats not found within the littoral zone. However, frequent sampling may cause harm to egg masses and larvae or disturb habitat features required for breeding such as debris serving as refugia and attachment sites for eggs. I recommend that future studies incorporate aquatic funnel trapping as described by Wilson and Dorcas (2003) to sample amphibian larvae in temporary wetlands. This technique was found to be passive compared with sweepnetting used in our study and may pose less of a threat to egg masses and larvae. This method also would present a detailed account of larval microhabitat use within ephemeral pools, potentially revealing species that were undetected due to a secretive nature or species which may have been missed when using sweepnetting as a sampling method. Wilson and Dorcas (2003) suggested that traps be left for one-week sessions to be checked every other day. This sampling schedule would compliment the
113 schedule I used for pitfall and funnel trapping, minimizing the number of field days required for researchers and limiting incidental disturbance to habitat and breeding populations of amphibians that comes with conducting field surveys.
Habitat measurements were standardized regardless of differences in size or shape of upland and floodplain pools potentially undersampling larger pools and leading to a misrepresentation of similarities between these habitat types. I recommend that future studies allocate sampling efforts in proportion to pool size and designate areas of high priority (i.e., pool perimeter, littoral zone) prior to sampling to encompass the full array of potential breeding areas for amphibians and limit potential bias against larger ponds. Most amphibians are likely concentrated within 200-300m of the breeding ponds; however, vegetation transects established in my study only measured a small portion of the terrestrial area potentially used by amphibians
(Semlitsch 1998; Gibbons 2003). I recommend that transect lengths be extended to > 50 m from
pond edge as this distance would likely give a more accurate picture of forest stands surrounding
ephemeral ponds.
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