MOVEMENT DYNAMICS OF THE FORKED FUNGUS BEETLE, Bolitotherus cornutus PANZER (COLEOPTERA: TENEBRIONIDAE)
BRIAN M. STARZOMSKI Centre for Wildlife and Conservation Biology Acadia University, Wolfville, Nova Scotia Canada, BOP 1x0
B .Sc. Joint Advanced Major, Saint Francis Xavier University, 1996
Thesis submitted in partial fulfillment of the requirements for the Degree of Master of Science (Biology)
Acadia University Fa11 Convocation 2000
O by BRIAN MARTIN STARZOMSKI 2000 I, Brian M. Starzomski, grant permission to the University Librarian at Acadia University to reproduce, loan, or distrubute copies of my thesis in microform, paper or electronic formats on a non-profit basis. I, however, retain the copyright in my thesis.
Signature of Author
Date Table of Contents
List of tables ...... v List of figures ...... vi List of boxes ...... vi .. List of fodas...... vu... Abstract ...... , ...... VU Acknowledgements ...... ix General Introduction...... :...... 1 References ...... 8
Chapter 1 :Movement dynamics of Bo lito~orheremscornutus ...... -13
Abstract ...... 14 Introduction...... 15 Smdy Organisms ...... -18 Methods ...... 19 Results ...... 28 Discussion ...... 41 References ...... -46
Chapter 2: Choice test ...... -51
Absîract ...... -32 ]Introduction...... 53 Methods ...... 35 Results ...... -...... 60 Discussion ...... 6 1 References ...... -65
Generd Conclusions...... 68 References ...... -70 List of Tables
Chapter 1 .
Table I . treatments...... -22
Table 2. Parameter moments for experimental treatments...... 30
Table 3 . Kruskd-Wallis and Nemenyi tests ...... 31
Table 4. Autocorrelation measure ...... -32
Chapter 2 .
TabIe 1. Variables measured...... 59
Table 2. Responses by sex ...... 60 List of Figures
Chapter 1.
Figure 1. Diagram of Experimental Mode1 System ...... 20
Figure 2. Net Squared Displacement of al1 glued individuais...... 26
Figure 3 . Log-transfonned move distances...... 29
Figure 4 . Theoretical Net Squared Displacement, Adults ...... 33
Figure 5 . Theoretical Net Squared Displacement, Tenerds...... 34
Figure 6. Path representations (Release 1) ...... 35
Figure 7 . Paîh representations (Release 2) ...... -36
Figure 8 . Path representations (Release 3) ...... 37
Figure 9 . Path representations (Release 4) ...... titi...... 38
Figure 10 . Path representations (Teneral Release 1 )...... 39
Figure 1 1. Path representations (Teneral Release 2) ...... 40
Chapter 2.
Figure 1. Diagram of choice-test experiment...... -58 vii
List of Formulas
Chapter 1. . . Fonnula (1.1) Trappabd~ty...... ,,,, .... .-..--..----.--.--..-..-...-. .--.--....-..*--.------.-. .-..--.-- 25 Formula (1 -2) Net squared displacernent in Correlated Random Walk ...... 27
Formula (1 -3) Autocorrelation function..-.. -.- ...- ..., . .-...... -. .---.-... ..--.....--.--.. -.. .-....-. ..-27 I used Capture-Mark-Recapture methods to measure and model movement in the forked fungus beetle, Bolitotherus cornufus Panzer (Coleoptera: Tenebrionidae). Age, sex, and mode of movement (whether by walking or flying) were expIicitly treated. The objectives of the study were to examine the movement abilities of the different sexes, the teneral and adult stages of the forked fungus beetle life cycle, and aiso to look at whether the beeties are walking or flying over the scale examined. An experimental model system constructed of patches of logs hosting the fungus Fomes fornentarius (Polyporaceae) was used to folIow the movements of B. cornutus. Trappability did not differ between the groups released, and the analysis revealed that both sexes moved in a similar fashion. Adults moved more, and Mer, over the first 28 days of each release than tenerals. Movement of all individuals was confined to an area roughly 50 metres in radius. A percentage of both adults and tenerals had their elytra glued to test for fiight in this species. No difference in movement was detected between glued and non-glued individuals. Over 4000 trapnights of flight intercept trap data, as well as 15 days of logs suspended above the ground failed to show any evidence of flight. I conclude that i) flight is not an important mode of movement over the spatial scale exaniined, ii) adult beetles move Merand more often than tenerals, iii) most movement is confined to an area of 50 m radius near the release point. Implications for B. cornutus population and metapopdation structures are discussed. Additionally, an experhent was done to explore the ability of the forked fungus beetle, Bolitotherus cornutus, to detect its fimgal host, Fomes fomentarius by chemosensory methods. A choice-test was conducted using a tube with F. fomentarius at one end, and Coprinus atramentarius (Coprinaceae) at the other. A weak effect of the beetle being able to detect the F. fornentarius over the C. atramentarius was detected, females more often chose the F. fornentarius than males, and larger individuals more often than smaller.
Kqwords: Bolitotherus, Tenebnonidae, Fomes, chemoattraction, choice test, dispersal, movernent, coneIated random walk Acknowledgements
A great number of people contributed in one way or another to the completion of this manuscript. To Dr. Patrick Farrell in the Statistical Consuking Centre, thanks for stats conversations and good books. Thanks are due to Daniel Kehler and Sonja Teichert for providing a tough act to follow, as weii as many ideas. Next, the graduate students of the Acadia University Biology Department. Special thanks to Matt Hoider, Meg
Krawchuk, Julie McKnight and Mateo Yorke for great conversations with a gifted group.
Drs. Dave Shutler and Phil Taylor deserve special recognition for their intellect and suggestions dong the way. My advisor, Dr. Soren Bondrup-Nielsen, cannot be given enough credit, as his steady patience, quick mind and wit shaped this thesis fiom start to finish. His wife, Pia, deserves thanks as well, for beans, eggs, coffee, and the fun of 14 acres in maton. Finally, 1cannot begin to express my reliance on, and gratitude to, my partner, Meghan Mulcahy. Meghan's uncornmon patience and strength in the presence of esoteric undertaking such as that contained herein helped rernind me that there was a life away fiom ecology, mathematics, and the cornputer screen. Meghan, this is as much yours as mine. General Introduction
Ecology as practiced today is a relatively young science, having its practical origin in the 1960s and 1970s, when it became rooted in quantitative analysis of ecosystem fiinction, pattern, and process. The first ambitious atternpts at producing broadly applicable theory based on rigorous collection and mathematical synthesis of data began at this the. Examples include: MacArthur and Wilson 1967, the theory of
Island Biogeography to mode1 comrnunity structure; Levins 1970, an early foray into modeling the population dynamics of single species in fiactured habitat; and May 1973, who attempted to model the eEects of complexity on ecosystem, food web and co111i11unity stability. These works stimulated much Mer research in fiagmented landscapes.
Habitat and biodiversity conservation concerns fieleci this growth in ecology, with the Theory of Island Biogeography (MacArthur and Wilson 1967) being used to ex~!ahand predict many organisms' response to habitat fragmentation (e-g. Janzen 2 968,
O'Comell and BoIger 1997), and also as a model to create simple rules for the design of nature reserves (initiating a surpnsingly dirty and fi-actious debate seldom seen in professional science, e-g. Diamond 1976, Simberloff and Abele 1976).
What these early attempts at modeling lacked was an explicit treatment of scale, and had over-simplifïed assumptions conceming organism movement abilities. Much of the current research and theory in the ecological sub-disciplines of landscape ecology and conservation biology (direct descendants of this early modeling work) is concemed with this concept of scale (Fahrig 1992, HoIling 1992, Levin 1992, May 1994, Hanski and
Gilpin 1997, Keitt 1997, Roland and Taylor 1997, Tilman and Kareiva 1 997, Carroll and Pearson 1998, Kehler and BondnipNielsen 1999). How organisms persist over various temporal and spatial scales is examined in these studies, especially in the context of disturbed environments.
'Disturbed environrnents' and 'temporal and spatial scales7 co~otebroad topics, and much of present ecologicai research confines itself to the disîurbed environments of fkagmented landscapes, and spatial scale.
Metapopulation theory is the most popular fiamework for modeling the persistence of organisms in hgrnented landscapes (Hanski and Gilpin 1997). This subtly awkward theory models the persistence of an organism in a fiagmented landscape by considering that the overd population of organisms in the landscape is composed of a number of locaily breeding popuIations in some or aii of the suitable habitat. Each locdy breeding population has a chance of extinction, and also of interaction with other populations through movernent (which process can also re-establish a population after extinction) (Hanski and Sïmberloff 1997).
It is in Iight of this set of conditions that ecologists have come to realize the importance of movement as the 'glue' that holds these various elements together. How organisms move (e.g. by walkîng or flying), if they disperse fkom their natal sites, or whether they wander in a home range nearby, retumïng on occasion over time, become important considerations for piecùig together the population/metapopulation structure and function. Understanding these strategies is very important in preparing conservation measures for species at risk, as in, for example, the Spotted Owl (Strix occidentalis) in
Noahwestern North America (Turchin 1W8), and the European buttedy Proclossiana eunomia (Neve er al. 1996). This work considers the extent of movement, and focuses on two special cases of
this movement: dispersal and ability to orient to suitable habitat (habitat location) (Jonsell
and Nordlander 1995), and Merconsiders the scale(s) that movement takes place on.
The technical te- used in describing animal movement are not agreed upon, and - are problematic (Swingland and Greenwood 1983). For the purposes of this paper,
dispersal is defined as the process occurring when individds leave their existing home
range and do not retum (Stenseth and Lidicker 1992). This results in what Turchin
(1 998) calls spatial spread of a population. Dispersal is important in population fomding
and transfer of genetic material @udd and McEvoy 1996), in providing immigrants to
boost declining populations (Eirown and Kodric-Brown 1977), to re-establish a local
population after extinction (den Boer 1979, Warren 1996), and to increase population and
metapopulation size and persistence (Hansson 1991).
Habitat location refers to how an organism hds a potential habitat site duruig a
movement between sites. This may occur in a variety of ways, for instance by sight, by
attraction to a mate (pheromones) (see Tamaki 1985 and Haynes and Birch 1985 for
reviews), by following a chemicd path produced by conspecifics (Haynes and Birch
1985), or as this study considers, by chernicals produced by a food resource (kairomones)
(e.g. Phelan and Lin 199 1, Pierce et al. 1991, Phillips et al. 1993, Jonsell and Nordlander
1995, Faldt et al. 1999).
Though it is recognized that dispersal of organisms is very important in
explaining their (likelihood of) persistence in a fiagmented environment, the dispersal
literature is less well-developed than many others in ecology due to the inherent difficulty in collecting good data. Because they involve both a spatial and temporal component,
these data are complicated to collect and adyze (Dempster 1991, Turchin 1998).
It is important to know when in the He cycle organisms rnove, and in particular, disperse: is dispersal occurrïng soon derbirth (Le. natal dispersal), or at some other time
(Greenwood and Harvey 1982, Harrison l989)? Timing of movement may be important for several reasons; for instance, to exploit food resources, to participate in mating, and in deciding what age group provides the founding members of a new population
@ansson 1991). As well, the timing of animal movement may have less theoretical and more applied importance in designing management regimes, specifically by biasing the timing of intnisive resource extraction (for example) to times when movement may take the organism of interest from the affected site to another, more stable location. This study aims to investigate the timing of movement and dispersal in the forked fiingus beetle, and contribute to closing some of the gaps discussed, specifically in the areas of organism dispersal and movement in spatially heterogeneous landscapes.
Because Bolirotherus cornutus inhabits a temporally variable and spatially isolated habitat (the perennial sporocarps (Polyporaceae), described in detail below), it can be expected to conform to the dispersai abilities hypothesized for organisms inhabiting such ephemeral resources. This theory states that organisms inhabiting habitats that do not persist for long periods of time relative to the lifespan of an organism can be expected to have very good powers of dispersal, to facilitate establishment of new populations in another spatial location when the natal site is exhausted (den Boer 1970,
Gadgil 1971, den Boer 1979, Hanski 1989, Hansson 1991). Previous work on B. cornutus (Barlow 1996, Lundrigan 1997, Teichert 1999,
pers. obs.) has uncovered Iimited movement between habitat patches in studies of natural
and experimentai populations, though Kehler and Bondrup-Nielsen (1999) suggest that
beetles may be able to move long distances to isolated habitat patches.
Study systern: Forkedf.irngus beetles moving amongst spatial& isolatedfùngal patches
The forked fungus beetIe, Bolitotherus cornutus Panzer (Coleoptera:
Tenebnonidae), provides an excellent organism to use in a study of movement.
Common, widespread, and resident in a fiagmented habitat, it is easily followed using a
Capture-Mark-Recapture methodology (Heatwole and Heatwole 1967, Conner 1989,
Whitlock 1992, Lundrigan 1997). It is obligately associated with several species of fungi, most commonly the perennial Fornes fomentarius (Polyporaceae) (Mathewman and Pielou 1971, Kehler and Bondrup-Nielsen 1999). One of the 'esoteric microfauna', the large numbers of individuals of B. cornutus that can be marked and recaptured al!owed a large amount of information to be collected in a short period of time.
F. fomentarius is a dead-wood decomposing fungus found throughout mixed and hardwood forests in Nova Scotia, inhabiting dead and dying white birch (Bemlcz papyrifera Marsh), yellow birch (Betula lutea Michx. f), beech (Fagus grandgolia
Ehrh.) and Populur spp., discrete locations that are easy to find. F. fomentarius has a life-span of about 10 years (Schwarze 1990), and B. cornutus has been known to live up to 5 years (Bondrup-Nielsen, unpublished data). Though F. fomentarius persists longer than the average B. cornutus life span, it appears that B. cornutus occupies F. fomentarius only at certain age classes or decomposition levets of the fungus, thus making the effective residence the for B. cornutus somewhat less than the 10 years stated above
(Bondmp-Nielsen, unpublished data). In North Amerka, B. cornutus is likely the leading
killer of live F. fomentorius sporocarps (Mathewrnan and Pielou 1971).
Previous work indicates that B- cornutus is a slow and seldom moving organisrn,
but anecdotd evidence suggests that it is able to move on Sequent occasions over many
hundreds to thousands of metres.
B. cornutus completes its entire life cycle on the sporocarps of the perennial fungi
host (Liles 1956, Heatwole and Heatwole 1967, Pace 1967). Eggs are laid on the surface
of the fûngi, and the larvae tunnel through and feed on the context for a penod of 8 to 12
months before pupating and emerging fiom the sporocarp as tenerals (Liles 1956). In
previous movement studies, only the post-teneral (adult) life stage was marked in
Capture-Mark-Recapture studies (Corner 1989, Whitlock 1992, Whitlock 1994, Teichert
1999). This study explicitly includes age in an analysis of movement and dispersal, to
avoid missing dispersers before they are marked.
Study Objectives
1 used Capture-Mark-Recapture (CMR) techniques to study the movement of an
organism in a forested habitat by cornparing dispersa1 activity of newly emerged (teneral)
and over-wintered (adult) forked fungus beetles, Bolitotherus cornuzus (Panzer), at the scale of a small forest stand. Also, mode of movement, whether wallwig or flying, was examined. A tivo-way choice experiment was conducted in the laboratory to quanti@ the
ability of the individuals to choose potential habitat by a mechanism other than sight. Finally, the spatial scale at which the movement took place was examined. and implications for what defines a population of B. cornutus are discussed. References
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1 used Capture-Mark-Recapture methods to measure and mode1 movement in the forked fungus beetle, Bolitotherus cornutus Panzer (Coleoptera: Tenebrionidae). Age, sex, and mode of movement (whether by walking or flying) were explicitly treated. The objectives of the study were to examine the movernent abilities of the different sexes, the teneral and adult stages of the forked fungus beetle life cycle, and also to look at whether the beetles are walking or flying over the scale examined, An experimental mode1 system constmcted of patches of logs hosting the fungus Fomes fomentarius was used to foIlow the movements of B. cornutus. Trappability did not differ between the groups released, and the analysis revealed that both sexes moved in a similar fashion. Adults moved more, and further, over the first 28 days of each release than tenerais. Movement of al1 individuals was confined to an area roughly 50 metres in radius. A percentage of both adults and tenerafs had their eIytra glued to test for flight in this species. No difference in rnovement was detected between glued and non-gIued individuals. Over 4000 trapnights of flight intercept trap data, as well as 15 days of patches suspended above the ground failed to show any evidence of flight. 1 conclude that i) flight is not an important mode of movement over the spatial scale examined, ii) adult beetles move fürther and more often than tenerals, iii) most movement is confined to an area of 50 m radius near the release point. Implications for B. cornutus population and metapopulation structured are discussed.
Keywords: Dispersal, rnovement, correlated random walk, Tenebrionidae, Bolitothew, Fomes, Experimental model system Introduction
Habitat tragmentation and degradation resulting corn hurnan pressure on natural environments are threatening the viability of ecosystems around the world (Wilcove et al.
1986, Noss and Cooperrider 1994). Fragmentation causes a decrease in some or al1 suitable habitat for some species, and division of the rernaining habitat into smaller and more isolated patches Wilcox and Murphy 1985). Many questions of organism persistence and changes in ecology in these environments remain unanswered (Dempster 1991, Didharn et al. 1996).
Because insects compose one of the Iargest parts of global biodiversity (Kim 1993), their response to this hgmentation is of paramount importance. However, only a small percent of insect species have been described, and very Iittle is known about the movement and dispersa1 abifities of the species that have been described (Harrison 1989, Hansson et al.
1992, Midtgaard 1996).
Metapopulation theory (Hanski and Gilpin 1991, Harrison 1994, Hanski and Gilpin
1997) and Island Biogeography theory (MacArthur and Wilson 1967) have been employed to mode1 the fragrnented ecosystem. What Island Biogeography theory is to cornmunities, metapopulation theory is to populations, and in recent years, metapopulation ideas have corne to dominate theories of spatial population dynamics (Hanski 1991, Hanski and Gilpin 199 1,
Hanski and Gilpin 1997). The concept of the metapopulation has been applied to fi-agrnented insect populations to explain population dynamics over time (Hanski and Thomas 1994, Hill et al. 1996, Neve et al. 1996). Metapopulation theory suggests that animal movement and dispersa1 through landscapes is very important in maintaining a population of organisms over landscape levels (Hanski 1991, Hanski and Gilpin 1991).
Dispersa1 is defined as the process occurring when individuals leave their existing home range and do not renirn (Stenseth and Lidicker 1992). The response of an organisn; to fragmentation is in part determined by its dispersal abiIity and fiequency (Fahrig and
Memm 1994). Dispersal rnay maintain regional populations when local extinctions occur
(den Boer 1979, Warren 1996), can provide immigrants to boost declining populations
(Brown and Kodric-Brown 1977), and is important in population founding and gene flow
(Rudd and McEvoy 1996). If hgmentation causes habitats-to be separated by more than the
dispersal distance of an organism, dispersa1 rnay no longer take place, and the species rnay
become extinct. Altemately, fragmentation may cause an increase in dispersa1 distances, and organisms rnay need to expend more energy to find new habitat (Matthysen et al. 1995).
Metapopulation theory is important in conservation ecology, and good theory concerning the spatial extent of an organism's population~metapopulationis needed. That is, when applying the concept of a metapopulation to an organism, care must be taken to carefully define the boundaries of a metapopulation. For instance, in popuIations of B. cornutus, is this scale the log hosting fungal sporocarps, the patch (clusters of sporocarp- hosting Iogs separated from one another by less than 1 metre), or a group of patches of some size? Whitlock (1994) suggested that each log constituted a population in this species, which contrasts with Teichert's (1999b) findings that there is spatial autocorreIation in B. cornutus separated by less than 50 m. Teichert's (1999b) study indicates that a circle with a diameter of 50 rn containing multiple sporocarp patches better defines a population of B. cornutus. In this paper, 1 analyzë movement of individuals of B. cornutus to investigate this population structure firther.
Studies rnay focus on movement and dispersal to temporally and spatiaIIy variable habitat patches (Matter 1996), but few consider timing of dispersa1 events. It is important to know when in the life cycle organisrns disperse: is dispersa1 occurring soon after birth (Le. natal dispersal), or at some other time (Greenwood and Harvey 1982, Harrison 1989)?
Timing of dispersa1 rnay be important for several reasons; for instance, to exploit food resources, to participate in mating, and in deciding what age group provides the founding
members of a new population (Hansson 1991). These factors have important implications for
the population dynamics of spatially isolated organisms such as Bolitotherus comutus.
Past studies have recorded infkequent instances of inter-patch movements (defined as
moves between logs, or a group of logs less than 1 metre apart, hosting Fornes fomentarius)
in forked fiingus beetles (Barlow 1996, Lundrigan 1997, Bondrup-Nielsen et al. unpublished). 1 thus hypothesized that much of the movement between patches in the wiId was the result of newly-ernerged, or teneral beetles, that had completed a dispersa1 event pnor to being marked in a study. This experïment tests whether tenerals are the dominant dispersers among populations of BoZirothew comutus.
Flight in this species has only been recorded once, and then under very artificial conditions in the laboratory (Teichert 1999a). To test how important flight is in wild populations of B. cornutus, 1 performed experiments that controlled the ability of individuals to fly, and used traps that capture flying individuals.
Capture-Mark-Recapture (CMR) studies cm be used to quanti@ movements by following organisms through time and space (Neve et al. 1996, Rudd and McEvoy 1996,
Lundrigan 1997, Turchin 1998). By recapturing an organism and recording its new spatial and temporal coordinates, a cokction of moves, or patti, can be constnicted. By analyzing this path, a great deal of information can be interpreted about how an organism moves in its environment. Correlated Random Walk (CRW) provides a powerful method for analyzing path data (Kareiva and Shigesada 1983). Deviations fiom the expected CRW response can be interpreted to investigate how both individuals and populations of organisms are moving in their environment.
In this paper 1: 1) by marking and following the movements of B. cornutus in a field tracing study, test the prediction that tenerals move more often and further than adults; 2) investigate whether individuals move by flight or by walking at the scale up to 135 m through
experimental manipulation of flight ability; 3) look at what sex is responsible for the
rnajority of the movernent by comparing male and female movement; and 4) look at what the
behavioural factors are in detennining spatial spread of a population by comparing actual and
theoretical movements, as described below.
Study Organisms
Much of the life history of the forked fùngus beetle, Bolitothem cornutus Panzer
(Tenebrionidae), is well known, and its genetics and behaviour have been studied in detail
(Mes 1956, Brown and Siegfried 1983, Conner 1989% Corner 1989b, Whitlock 1994). B.
cornutus Iives on the sporocarps of the bracket fungi Fomes fomentarius, Ganoderma
applanatum, and Ganoderma tsugae (Pace 1967, Mathewman and Pielou 1971). During the
summer breeding season, approximately 20 eggs are laid by the adult female on the surface of these fûngi, and the hatched larvae tunnel through the sporocarp to feed, while the aduIts feed on the underside (Liles 1956). Both adults and young survive the winter within the sporocarps (Mes 1956, Pace 1967). The animals are most active at night (Liles 1956), though they are easily observed during the day. Only males have pronotal horns that may
Vary in size, making it easy to sex individuals in the field (Liles 1956, Heatwole and
Heatwole 1968). Individuals measure about 10 mm in length, and are hmlessly and permanently marked with enamel paint. Forked fungus beetles have been described as living in temporally unstable and spatially heterogeneous environments (Whitlock 1992), and have been recorded moving over short distances, fiom habitat patch to habitat patch (Heatwole and
Heatwole 1968). Sporocarps last for up to 10 years (Schwarze 2994), and are thus a potential resource for several generations of beetles. Their movements are easily followed using
Capture-Mark-Recapture technique (Barlow 1996, Lundrigan 1997).
Methods
An experimental mode1 system (Ims and Stenseth 1989, Wiens et al, 1993) was constructed, consisting of a spatial arrangement of Fomes fomentarius fungal sporocarps in a forested environment (Figure 1). The fungal sporocarps were arranged to mimic the naturai occurence of F. fomentarius in the mixed wood forests of northeastem North Amerka.
Logs hosting sporocarps of F. fomentarius were collected fiom locations in western
Nova Scotia by cutting of host trees with a chainsaw, to allow for continued growth of the fungus after removal from its in situ location. These Iogs were used as "patches" in the experimental mode1 system (EMS), and hereafier the term "patch" refers to one experimentally introduced log in the EMS. Each log hosts an approxirnately equal volume of live, intact sporcarps, compared to that of al1 the other "patches" (estimated by eye).
Attempts to remove Fmesfornentmius sporocarps from their host trees, and then nail these sporocarps to another iog failed (Whitlock 1994, Lundrigan 1997). In these instances, the reattached sporocarps would quickly die and be invaded by other fungi, likely because they were no longer connected to the inner-log mycelia that provide them with nuîrients.
The study site consisted of 90 patches arranged in a 9 by 10 rectangle, with patches spaced 10 m from one another, to allow movernents up to 135 m. AI1 patches hosting sporocarps were thoroughly searched for forked fungus beetles, prior to the start of the experiment, to insure that no beetles were present prior to experimental -releases. No barriers were placed on the perimeter, and organisms could move on and off the site. This Figure 1. Diagram of experimental mode1 system. Each .represents a patch (sporocarp- covered log), and each O a release site. This system takes the fom of a square grid with 10 metre spacing. The numbers above patches show the staggered arrangement of flight intercept traps, with 1 representing ground level (0.5 m above ground); 2, mid-canopy (5 m above ground); and 3, canopy (within 1 rn of treetop). The dark lines ( - ) represent trails. experimental model system was located in a well-drained, mixed wood forest on the South
Mountain, Kings County, Nova Scotia (4S05'N, 64"2S7W).
Adult beetles used in the experiment were collected frorn locations throughout
western Nova Scotia by visiting sites where large numbers of F. fomentarius and G.
. applanatum were found. Beetles could be found on the fungal sporocarps, and taken back to
the lab to be marked. Tenerals were collected as larvae with their associated sporocarp in the
autumn and winter of 1998/early 1999 from several different sites in western Nova Scotia,
and raised over the winter. Fungi were chosen by looking for sporocarps with large numbers
of the characteristic eggs of B, cornutus on the cuticle. The sporocarps were stored in a
caged, outdoor roorn at Acadia University's animal care facility. Tenerals began to emerge
fiom the sporocarps in late July 1999, and were then coIlected and marked for release. In
addition to tenerals being defined by their late emergence fiom fungal sporocarps, it was
noted that the posterior quinone-producing glands used in defense (Conner et al. 1985) were
a light yellow colour, rather than the dark orange to brown of the adults (personal
observation). Beetles that were raised in sporocarps in the lab and collected were described
as tenerals only if they met the above two criteria. Individuals that were found in laboratory
sporcarps and had orange glands were considered to be past the teneral stage (adults), and not
used in the experiment. Al1 collected adult and teneral beetles were kept in a 45 cm by 30 cm
by 30 cm terrarium with moss and Fomes fomentarius sporocarps, and released in the study
site within 7 days of their collection.
To distinguish individuals, al1 beetles were marked using Testor's Non-MetaIIic
Enamel Paints pnor to reiease in the study area. Each was given a unique pattern of five
coloured dots, one on the pronotum, and two on each elytra.
To test whether tenerals move more often and further than adults, both adult and
tenerai B. cornufusof both sexes were released into the experimental model system. Moves in al1 cases were defined as the straight-line distance fiom the patch the beetIe was previously
captured on, to the new capture patch.
Six reieases of beetles were conducted (Table 1). Sixty adult beetles were released
on both 10 June and 17 June, 1999. Two further groups of 60 adult beetles were released on
27 June and 11 July, 1999, with half of the males and fernales glued in each release. Finally,
60 tenerals were released on both 3 August and 20 August, with half of both males and
females glued each tirne (see Methods). In each of the releases, half of the beetles were male,
and half female. Beetles were released on 'release patches', a collection of 5 patches
arranged in an 'X' shape, separated by 5 m. These release patches were placed in the
experimental mode1 system, between the regular lines of patches (Figure 1)- Twelve (12)
beetles were released on each patch; 6 males, and 6 females. A thorough search for beetles at
al1 potential habitat sites (sporocarps) in the study area was made daily in June, July, and
August, to 15 September. Al1 searches were conducted in the early moming, begun within 30
minutes of the daily start time of al1 other searches throughout the summer, and lasted for 70 to 80 minutes. Introduced beetles fiom previous releases were not removed fiom the
experimental mode1 system when new releases were conducted.
Table 1. Summary of experimental treatments. Release D.ate Number Treatment(s) Adult 1 10 June 60 Sex Adult 2 17 June 60 Sex Adult 3 27 June 60 Sex, Glue Adult 4 11 July 60 Sex, Glue TeneraI 1 3 August 60 Sex, Age, Glue TeneraI 2 20 August 60 Sex, Age, Glue To determine if flight was occurring, 1 prevented some of the beetles released from flying, changed the position of patches, and attempted to capture flying beetles in flight intercept traps.
Prevention of flight was accomplished by using Lepage's 5-minute Epoxy glue to seal the suture between the elytra on the dorsal side of selected individual beetles. A small dab of glue over the elytral suture (less than 1 mm by 1 mm) was used. The elytra in the
Coleoptera are structures that have been modified fiom wings, to function as protection for the delicate wings that they cover. To fly, a beetle must mise the elytra to expose the wings-
By gluing the elytra shut, the beetle is prevented fiom flying, by preventing it fiom opening its wings. In field trials, this proved an effective method, with only 2 individuals (-3%) showing signs of glue spots deteriorating to the point where the individual might be able to open its elytra. However, no beetle, glued or otherwise, was ever observed in flight.
Forty-five flight intercept traps were used to capture flying beetles. These traps consisted of interlocking, perpendicular panels of transparent Plexiglas measuring 60 cm ta11 by 30 cm wide, with a conical collecting base that ended in a plastic container. The plastic collecting container consisted of an unbaited 100 ml plastic jar filled with 10% ethylene glycol, to preserve captured invertebrates. These traps were suspended as near as possible to the experirnental Fomes fomentmius patches on the release grid, at 3 heights: canopy (within
1 m of the tops of trees, at approximately 10 m above the forest floor), mid-canopy (on average, 5 rn above the forest floor), and 50 cm above ground Figure 1). A staggered pattern was used with the traps placed above every second patch location. Fifteen of each class of traps was used, in a repeating pattern of ground, mid-canopy, and canopy heights. A total of
4365 trap days were recorded among the three classes of traps. The traps were sampled and invertebrates greater than 0.25 mm, large enough to be distinguished as invertebrates using a
Wildm dissecting microscope at 25 power, were recorded. Beginning 1 September and continuing to 15 Septernber, half of the patches were
suspended 1 m above the ground using heavy-gauge twine tied to tree branches, Any B.
cornutus that were resident on these patches were removed and released on the ground
directly beIow the suspended patches. Each hung patch was visited daily during the normal
course of checking the experimental site.
The analyses of Bolitotherus cornutus movement data were conducted using non-
parametric Kniskal-Wallis tests (Zar 1998) followed by Nemenyi multiple cornparisons (Zar
1998), 2-tests, and Autocorrelation Function (ACF) in S-Plus Professional 4.5 (Mathsoft
1998). Non-parametric tests were used due to the non-normal (right-skewed) distributions of move distances. Further mode1 fitting was done using the Correlated Random Walk
framework after Kareiva and Shigesada (1983) and Turchin (1998). To look for differences
in move distances between groups of beetles, several Kmskal-Wallis tests were performed on untransformed data, using S-Plus Professional Version 4.5 (Mathsoft 1998). A one-way
Analysis of Variance in S-PIUSProfessional 4.5 (Mathsoft 1998) was used to investigate differences in trappabilities between the 6 releases of B. cornutus.
For Kmskal-Wallis tests, only data fiom the first 28 days of each release were used, to standardize the number of days of moves between each treatment. This was due to the last release of tenerals only covering 28 days. The use of 28 days as the cut-off for this analysis does not cause a loss of a significant amount of rnovement data. Analysis of net squared displacement (MD) data plotted against time indicates that movement for B. cornutus individuals tends to level off near 28 days, with the majority of moves taking place in the first
30 days after release (Figure 1). In a random walk model, this curve is expected to increase approximately linearly with time (Turchin 1998). A leveling-off of NSD with time is consistent with an organism seîtling down in a territory, or reaching the limits of its movement ability (Turchin 1998). As weI1, the aim of the experiment was to study farked fungus beetle movement and the distances individuals could be expected to move. Thus, the study system is not affected by problems related to storage prior to release (agitation, etc.), as the moevements were the focus of this study.
To compare the between-release observations, a trappability measure was calculated to judge the equality of recapture between releases. Trappability was calculated using the following:
T = (MIR - 2) 1 (TDR) (1 -1)
Where NDR= number of days recaptured and TDR= total days it could have been recaptured.
Correlated Random Walk analysis was performed using the procedure outlined in
Kareiva and Shigesada (1 983), and Turchin (1 998). Theoretical Net Squared Displacement
(NSD, R:), calculated using equation 12, was plotted against the number of moves, and
compared with the observed NSD. Observed NSD was calculated by averaging R: for each
- different n (move number) (Kareiva and Shigesada 1983). Theoretical NSD was calculated
as follows:
R: = nmz + 2rni (iY/l-v) x (n - (1-9") / (1-9) ) (1 -2)
where ml = mean move length, ma = mean squared move Iength, $ = average cosine of the
turning angle, and n = number of moves.
Confidence intervals for the theoretical NSD were computed by bootstrapping 1000
samples of the calculated NSD for al1 moves at each n to produce a standard error for each n.
This standard error was then multiplied by the appropriate two-tailed t-value to produce a
confidence interval for the theoretical NSD at each move number (Efion and Tibshirani 1993,
Davison and Hinkley 1997, Turchin 1998, Venables and Ripley 1999). A 2-test was
performed on each pair of values (one each fiom the observed and theoreticai NSD) to test
for differences between theoretical and observed NSD. For adults, higher order
autocorreIations in the turning angles (i.e. autocorrelations in turn angle above Lag 1) were
calculated. FoIlowing the methods in Turchin (2998), these autocorrelations were computed
using formula 1.3:
Autocorrelation Measure: (S-O)/(S+O) (1 -3)
where S = a pair of turns in the same direction, and O = a pair of tums in the opposite
direction.
Al1 possible pairs of turning angles are calculated for each lag (2 through 6 here), and
are assigned to one of two categories: S, turns in the same direction (either lei%-left, right- right, or no turn); 0, ~msin opposite direction (either lefi-rïght, or nght-lefi). For each lag
d, a value between -1 and 1 is calculated, with -1 indicating fi111 negative autocorrelation
between turn angles at lag d, and 1 indicating full positive autocorrelation between turn
angles,
Results
Cornparison of Releases
Trappability is the probability of recapture of an individual B. cornutus while that
individual was present in the experimental mode1 system, and as such was selected as the best
measure to compare the different releases. To ensure that there were equal trappabilities among groups, a one-way Analysis of Variance was performed using the pooled trappability
data across al1 6 releases (Table 2). No significant difference in trappabilities between the 6 groups was detected (F = 0.50, DF=5, p=0.78).
The effecr of age on move distance
A Kruskal-Wallis test conducted on the rnean move distances of each individual in unglued treatments of teneral and adult Bolitorherus cornutus (Figure 3) showed there was a significant difference between male and female teneral and adult beetles (X2 = 14.7, DF=3, p=0.02). The non-parametric Nernenyi multiple cornparisons test was used to Iocate the individual differences between groups, with significant differences in move distance shown between Female Adult and Fernale Teneral @<0.005), and between Male Adult and Female
Teneral (pc0.02) (Table 3). In both of these cases the adult beetles moved fürther. iia
TFG TFNG TMG TMNG AFG AFNG AMG AMNG F M
Type
Figure 3. Log-transformed move distances for first 28 days of each treatment release. (TFG=
Teneral female, glued; TFNG = Teneral female, non-glued; TMG = TeneraI male, glued;
TMNG = Teneral male, non-glued; AFG = Adutt female, glued; AFNG = Adult female, non- glued; AMG = Adult male, glued; AMNG = Adult male, non-glued; F = Adult female, first release; M = Adult male, first release). White bar is the median, box encloses 1 SD on either side of the mean, outer bars enclose 95% of the data, width of bars is proportiona1 to number of moves represented for each class of beetIes. When the step lengths (distance rnoved between recaptures) of adults were
considered, 341 of 347 step lengths (98.3%) were less than 50 m in Iength, and only 5 of 184
individuals (2.7%) made moves greater than 50 m. Al1 teneral moves were less than 50 m-
Table 2. Parameters for experimental treatments. Proportion Trappability Mean Proportion Release movingf7 *SD* Distance(m@SD* recaptured * Adult 1 0.86 0.34d=0.21 15.1~13.85 0.85 Adult 2 0.88 0.34*0,25 11.699.93 0.82 Adult 3 0.95 0.4W0.26 12.74*12.28 0.98 Adult 4 0.86 0.4=0.28 12.3210.41 0.98 Teneral 1 0.49 0.37h0.28 5.43*2.56 0.95 Teneral2 0.44 0.43*0.29 5.36*6.08 0.95
* calculated using first 28 days of release f-Proportionmoving refers to moves between patches.
me effect of sex and potential forjlight on move distance
Among tenerals, there was no significant difference in mean distance rnoved by either glued or un-glued males and females (X2 = 1.64, DF=3, p=0.65, Kruskal-Wallis test). For male and female adults, there was no significant difference between the glued and un-glued individuals (X2 = 2.05, DF=3, p=0.56). There thus appears to be no difference in move distance between the different sexes in B. cornutus at the 135 rn scale measured in this study. Also, the glued and unglued beetles show no difference in move distance, suggesting that the movement at the scale measured is by walking, not flight.
Flrght Intercept Trap Data
Over 5800 total macro-invertebrates (defined as an invertebrate larger than 0.25mm) were captured in flight intercept traps suspended above the ground during the experiment, which covered 97 nights- More than 2000 of these were Coleoptera. No Bolitotherus
cornutus were recorded.
Table 3. KruskaI-Wallis test and Nemenyi multiple cornparisons of move distances among non-glued male and female adults and tenerals. * indicates significant difference between groups.
Kruskal-Wallis x2 = 14.7
Nemenyi Multiple Cornparisons
p-val ue Adult Female vs. Adult Male ~0.50 Adult Female vs. Female Teneral <0.005* Adult Male vs. Female Teneral e0.02" Female Teneral vs. Male Teneral >0.5
Patches Suspended Above the Forest Fluor
For the Iast 15 days of the experiment, haIf of the patches in the experïmental mode1 system were suspended lm above the forest floor, and the B. cornutus individuals inhabiting them removed and placed on the forest floor below the patch. No forked fungus beetles were recorded recoionizing these patches, though many of them had been occupied pior to the hanging of the patches. Correlated Randorn Walk Analysis
Because no difference was found between the sex and glue classes, correlated random
walk analysis was conducted using the pooled data fiom a11 releases for each of adult and
teneral classes. Correlated Random Walk theory assumes that there are no first order
correlations in movement parameters between moves. Analysis of autocorrelations in move
length and tuming angle, using the Autocorrelation function in S-Plus 4.5, prior to
computation of theoretical Net Squared Displacement showed no first-order correlations. 1 thus proceeded to cakulate NSD using a Correlated Randorn Walk hework using formula
1.2. Figures 4 and 5 show the results of plotting Net Squared Displacement against
number of moves for adults and tenerals. Both adult and teneral theoretical NSDs over- predict the spatial spread of the population (2-test for adults, al1 p-values <0.00 1).
The Autocorrelation Measure for turn direction was caIculated for the adult, but not teneral, B. cornutus due to the larger number of moves in the adult age class. Autocorrelation
in turn direction for adult B. cornutus reached maximums at lags 5 and 6, where there was maximum positive autocorrelation in turn direction (that is, tums separated by lags of 5 and 6 are most likely to be in the sarne direction) (Table 4). Figures 6 through 11 show the pathways of B. cornufus individuals, sorted by release number. These plots show the tendency of B. cornutus paths to turn back on thernselves, resulting in the beetle being confined to a small home range, with a radius of 50 m.
Table 4. Autocorrelation measure for each lag d for adult B. cornutus. Lag (42 3 4 5 6 Mean -0.014 0.321 0.111 0,810 0.857 SE 0.736 0.736 0,469 0.09 1 0.051 n 61 28 9 7 7 Number of moves
Figure 4. ~heoreticalNet Squared Displacement (m2) (open circles) and Actual Net Squared
Displacement (m2)(circles with horizontal bars) versus Number of Moves, for al1 adult
Bolitotherus cornutus. Bars around theoretical NSD points are 95% confidence intervals. Number of moves
Figure 4. Theoretical Net Squared Displacement (m2) (open circles) and Actual Net Squared
Displacement (m2) (circles with horizontal bars) versus Number of Moves, for al1 teneral
~aiitotheruscornutus. Bars around theoretical NSD points are 95% confidence intervals. x-coordinate
Figure 6. Paths followed by individuai beetles of Adult Release 2. Each dot represents a stopping point (Fornesfomentarius patch), and each line the move from Patchi to Patchi+,.X and Y coordinates are the actual coordinates fiom the experimental grid, each 10 metres fiom one another. The release point coordinates are centered on (6.5, -6.0). x-coordinate
Figure 7. Paths followed by individual beetles of AduIt ReIease 2. Each dot represents a stopping point (Fomesfomentarius patch), and each line the rnove fi&n patchi to patchi+,.X and Y coordinates are the actual coordinates fiorn the experirnental grid, each 10 metres from one another. The release point coordinates are centered on (4.5, -4.5). I I I I I I O 2 4 6 8 10 x-coordinate
Figure 8. Paths followed by individual beetles of Adult ReIease 3. Each dot represents a stopping point (Fumesfomentarius patch), and each line the move fiom Patchi to Patchi+,.X and Y coordinates are the actual coordinates fiom the experimental grid, each 10 metres from one another. The release point coordinates are centred on (9.5, -7.5). x-coordinate
Figure 9. Paths followed by individual beetles of Adult Release 4. Each dot represents a stopping point (Fomesfomentarius patch), and each line the move fiom Patchi to pat~h~+~.X and Y coordinates are the actual coordinates from the experïmental grid, each 10 metres from one another. The release point coordinates are centred on (9.5, -7.5). Figure 10. Paths followed by individual beetles of Teneral Release 1. Each dot represents a stopping point (Fumes fomentarius patch), and each line the move fiom Patchi to patchçi. X and Y coordinates are the actual coordinates from the experimental grid, each 10 metres from one another. The release point coordinates are centred on (7.5, -4.5). O 2 4 6 8 10 x-caordinate
Figure 11. Paths folïowed by individual beetles of Tenerai Release 2. Each dot represents a stopping point (Fomes fomentarius patch), and each Iine the move from patchi to Patchi+,.X and Y coordinates are the actual coordinates from the experimental grid, each 10 metres from one another. The release point coordinates are centred on (4.5, -4.5). Discussion
My hypothesis was that teneral forked fiingus beetles, BoZitotherus cornutus Panzer
(Tenebrionidae), were the dominant movers amongst the life history stages. This was rejected. In fact, the adult beetles moved further, on average.
What was surprising in this study was the fact that the tenerals moved Zess than the adults. I had originally hypothesized that tenerals moved more often than adults to explain why 1 was not seeing a large number of movers in the natural system study (Bondrup-Nielsen et al., unpubiished), in 1995-98. In other studies (Johnson 1969, DingIe 1978), timing of dispersal was found to be controlled by the 'oogentsis flight syndrome', where dispersal was related to the undeveloped ovaries of fernales, particuiarly during a brief, post-teneral penod
(Messina 1982). However, the life history of B. cornutus differs markedly from the insects in the above studies. For example, the goldenrod leaf beetles Trirhabda virgata and T. borealis
(Coleoptera: Chrysomelidae) studied by Messina (1982) had a maximum Me span of about 7 months. BoZitotherus cornutus can live up to 5 years, and overwinters in diapause several times. Teneral B. cornutus may need to overwinter once to reach sexual and physical maturity, at which tirne they have the hlly developed musculature necessary for movement.
Because glued and non-glued beetles were moving similar distances, the experiment where the elytra were glued suggests that most or al1 of the movement I observed arnong the sporocarp covered patches in the experimental mode1 system was by walking. This is further supported by the complete lack of captures of B. cornutus in flight intercept traps, and also the absence of individuals colonizing (or retuming to) patches suspended above the forest floor. In another study of insects captured using flight intercept traps, near the Orono campus of the UniversiS. of Maine, of thousands of trapped insects, only one B. cornutus was noted, caught in a canopy trap at 30 m (S. Thomas, pers. comm.). In a recent study by Teichert (1999b), individual B. cornutus were found to exhibit
spatial autocorrelation in an area with a diarneter of approximately 50 metres. This is similar to the area that contained the majority of forked fungus beetle movements in this study, and may represent the area that a population of B. cornutus uses as a home range. Wiens (1989) defines 'domains' as regions of scale where processes operate. The above area may be the domain of movement by walking for the forked fungus beetle. Correlated Random Walk analyses support this, as it can be seen fiom Figures 4 and 5 that theoretical net squared displacement overpredicts the spatial spread of B. cornuhcs adults and tenerals. At higher
Iags, beetles tended to follow a move in one direction with a move in the same direction (Le.
Left-Left, or Right-Right). This results in a spiral pattern, and over time individuals tum back toward the release point. Hence, the Correlated Random Walk Net Squared
Displacement overpredicts the spatial spread of the populations, as positive autocorrelations in hirn angles mean that the beetle path turns on itself. This suggests that the beetles confine their movements to a certain spatial extent, as the number of direction reversals increases with move number.
The area enclosed within a circle of 50 rn radius suggests the scale at which a population of B. cornutus should be defined. Because Correlated Random Walk analysis deaIs with moves based on the distance from the release point that the beetle is at any step, the use of the approximately maximum move distance of 50 rn is a legitimate bound on their movements for this analysis. Previous studies (e-g. Heatwole and Heatwole 1967, Co~er
1989, Whitlock 1992, Whitlock 1994, Lundrigan 1997) have considered B. cornutus populations to be confined to one sporcarp-hosting Iog, or a group of sporcoarp-hosting logs separated by less than 1 m (Lundrigan 1997). This study suggests that the population definition be expanded to include al1 B. cornutus inhabiting Fornes fomentarius within an area with a 50 m radius. Also, the movement between patches within this scale is not dispersal, but simply movement within a home range. The metapopuIation concept applied
to B- cornutus in the wild shouId be modified. 1 suggest that if wild populations of B.
cornutus do exist in a metapopulation structure, then the size of individual populations is on
the order of the area delimited by a circle with an approximately 50 rn radius, and movement
is common within this area, Dispersal operates between these 50 m radius areas, movement
within them.
It is instructive to consider what effects the edge of the experimental mode1 system
may have had on the rnovements of the forked fingus beetles used in this study. If the edge
of the study site was reflective, that is, if beetles that wandered near the edge were turned
back toward the interior of the grid, this would bias the movernent results 1 found. There is
no reason to suspect that this was the case. In fact, several observations suggest that the edge
of the system provided no barrier to the movements of forked fungus beetles. The majority
of the moves observed took place distant fiom the boundary of the study grid, and there is no
evidence that beetles moving near the grid edge biased their movements away fiom that edge.
Several individuals were observed to have moved off the grid to logs hosting Fomes
fomentarius nearby. Thus, beetles were free to move off the grid, and the edge does not seem
to have biased their movements.
The scale on which forked fungus beetIes do the majority of their moving in this
study is similar to the spatial definition of a B. cornutus population proposed by Teichert
(1999b). It is interesting that Teichert (1 999b) used data fiom a natural study system (not an
experimental model system), and that hm data was fkom a site that had two distinct groups of
patches of Fomes fomentarius, with diameter 50 m, that contained the populations. Both the
study site of Teichert (1999b), and the experimental model system of this study were Iocated
in rnixed Acadian forest, subject to gap dynamics (Runkle 1985). Because Fomes fomentarius and other fimgal species that host B. cornutus colonize dead and dying trees, groups of patches of F. fomentarius and other hngi may be clurnped at a scale of
approximately 50 m radius in response to the injury of trees through the processes goveming
the formation of forest gaps (e.g. windfall, Iightening strikes, pest attacks). These gap
dynamics are prevalent in forests throughout the range of B cornutus, and it is conceivable
that B. cornutus populations have yolved to walk through a home range with a radius of 50
m in response to the fungus patches that are formed through the above processes. As well,
the forked fungus beetle can live for at least 5 years in nature, and the amount of resources
found in one sporocarp-hosting log may not be suff~cientto ensure the survival of the beetle
over this time period. Beetles rnay move within the larger area as a way of sampling
sporocarps of various decay levels on many trees. More work to test this hypothesis is
needed.
It rnay be that the forked fungus beetle exhibits two scale-dependent modes of
movement, as first proposed by Kehler and Bondrup-Nielsen (1999). Above the 50 m
distance, movement rnay be dominated by flight, instead of walking. While this study found
no evidence of individuals flying, it has been recorded in the past (Teichert 1999a). Though
Capture-Mark-Recapture experiments tend to oversarnple less vagile individuals (Turchin et al. 1991), 1 atîempted to reduce this sampling error by using flight intercept traps and hung patches to look for flying B. cornutus, with no success. Perhaps flight in B. cornutus is used
only in longer-distance dispersa1 events, especially in highly fiagmented landscapes, where
individuals are forced to cross an inhospitable matnx. Some evidence for this exists: B. cornutus in fragmented forest sites tend to be more closely related to one another than those
in continuously forested sites, when considered at the same spatial scale (Bondmp-Nielsen, unpublished, but see the Knutsen et al. (2000) study that shows the opposite for the closely related European Tenebrionid, Bolitophagus reticulatus). When considered in light of the
results of my experirnent, which shows that walking movements tend to be concentrated in a very small area where resources are plentifil, Bondrup-Nielsen's study rnay indicate that
flight is operating across matrices in fragmented habitat.
An alternative explanation for the lack of flight observations may be related to the
experimental mode1 system set-up. Because individuals could only be sarnpled at introduced
- patches of Fomes fomentarius, beetIes making movements that do not involve stopping on
these patches would be undersampled. Such would be the case if female forked firngus
beetles were moving according to the 'oogenesis-flight syndrome' (Johnson 1969, Dingle
1978), where individuals do not typically respond to food or oviposition sites (in this case the
F. fomentarius sporocarps).
No difference in average or maximum move distances was noted between the sexes,
nor was there a difference in the proportion of each moving. This is surprising, as previous
work (Lundrigan 2997) found a much higher proportion of females making moves, and
suggested that females make movements related to oviposition. This may simply be a result
of the previous study being conducted in a natural environment where the F. fomentarius
sporocarps were not as uniformly distributed thmugh the landscape, and suitable oviposition
sites were more dificult to locate. In addition, Lundrigan (1997) used a smaller area (a circle
with radius 15 m), and F. fomentarius sporocarps that were dead, rather than the random
mixture used in the experimental mode1 system of the present study.
In conclusion, 1 found no evidence that tenerals are the dominant dispersers in
Bolitotherus cornutus populations; in fact, the data suggest that the aduit beetles move more
often and further. There is no distinct difference in movement between the sexes, as both
males and females move at a similar rate. Flight does not seem to be an important mode of
movement, at least at the scaIe considered in this experiment. There was no difference in
movement rate or distance between glued elytra and non-glued beetles. Finally, movements
of beetles seem to be confined to an area with a radius of approximately 50 m. References
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Zar, J.H. 1996. Biostatistical analysis. 3" edition. Prentice-Hall, New Jersey. pp. 197-23 1. Chapter 2. The ability of the forked fungus beetle, BoZitotherus cornutus Panzer (Coleoptera: Tenebrionidae), to detect its fimgal host Fumes famentarius (Polyporaceae), in preference to a non- host fimgal species. 1conducted an experiment to explore the ability of the forked fungus beetle, Bolitotherus cornutus Panzer (Coleoptera: Tenebrionidae), to detect its fungal host, Fornes fomentarius (Polyporaceae) by chemosensory methods. A choice-test was conducted using a tube with F. fomentarius at one end, and Coprinus atmmentarius (Buil. ex Fr.) Fr. (Coprinaceae) at the other. A weak effect of the beetle being able to detect the F. fomentarius over the atramenturius was detected. As well, femaies more often chose the F- fomentarius than males, and Iarger individuals more ofien than smaller.
K~~wo~s: Bolitothew, Fornes, volatileç, chernoattraction, choice test, kairomones Introduction
Fragmentation of habitat and the resulting spatial isolation of habitat patches is a common landscape phenornenon, and the processes associated with it have been often studied (Brown and Kodric-Brown 1977, Dempster 1991, Fahrig and Merriam 1994,
Didham et ai. 1996, Matter 1996, Kehler and Bondmp-Nielsen 1999, and many others).
Fragmentation causes a decrease in some or all suitable habitat for some species, and division of the remahbg habitat into smaller and more isolated patches (Wilcox and
Murphy 1985). Many questions of organism persistence and changes in ecology in these envkonments remain manswered (Didham et al. 1996). Because insects compose one of the largest parts of global biodiversity 1993), theu response to this fragmentation shodd be of paramount importance. However, little is known about the response of many insects to this fkagmentation and isolation of habitat @ut see Hanski and Kuussaarï
1995, Thomas and Hanski 1997). This study examines a poorly understood mechanism, specifically the sensitivity to kairomones (chernical volatiles fiom food) used by the forked hgus beetle, BoZitotherus cornutus Puizer (Tenebrïonidae), to find its food resources.
Fra,omentation of habitats in the range of B. cornutus is a very common and well described process, resulting in los of habitat, increased isolation of habitat, and the creation of an intervenîng matrix of unsuitable habitat between fonnerly connected habitat patches (Wilcox and Murphy 1985, WiIcove et al. 1986, Hanski 1991, Fahrig and
Merriam 1994, Harrison 1994). This maaix between habitat patches may provide a boundary to animal movement by conventional means (e.g. sight). Chemoattraction may increase the permeability of this barrier. The forked fûngus beetle (Bolitotherus cornutus Panzer) has been described as
inhabiting a habitat that is variable in both space and time (Whitlock 1992), and thus is an
example of an animal that must occasionally move to bdresources. Kehler and
Bondrup-Nielsen (1999) found that the primary resource of the forked fungus beetle, the polypore hgiFomes fomentarius (Polyporaceae), could be fiom 1 to 900m distant in very fiagmented Annapolis Valley habitat. This IeveI of dispersion of resources for a slow and apparently seldom-moving species (Pace 1967, Heatwole and Heatwole 1968,
WhitIock 1994) such as B- cornutus may suggest that there is a chemical cue to the resources that the beetles use to find the widely dispersed sporocarps of Fomes fornen tarius.
Though in a forested region the attraction to a sporocarp by chemical cues may not be the primary process occurring (in the presence of large numbers of carps relatively nearby in the normal forested habitat, sight alone may be sufficient to locate the resource), there may be cases where chemoattraction is the dominant process,
Many authors have described the phenomenon of chemical attractants, especially sex hormones, or pheromones (Tamaki 1985, Haynes and Birch 1985), and a number of studies have demonstrated the existence of attractive hormones fiom food, or kairomones
(Phelan and Lin 1991, Pierce et a[. 1991, Phillips et al. 1993, ~onselland Nordlander
1995, Faldt et al. 1999). Jonsell and Nordlander (1995) used window traps containing, respectively, chopped Fomiropsis pinicola and Fomes fomentarius in a field experiment to test the hypothesis that Cisid beetles (Cisidae) living on F. fomentarius would be preferentially caught in the baited traps, and their results indicated that individuals were in fact captured more often in the baited traps than the unbaited control (1.3 to 2 times
more often),
The main objective of this study was to test the hypothesis that the forked fungus
beetle would be attracted to its main fimgal host, Fomes fornentarius (Fr.) Kickx
(Polyporacae), rather than to another species of fungus. This was tested using a
laboratory choice experimenf where iodividuals were presented with two fungal choices,
Fomes fornentarius, and Coprinus atramentarius (Bull. ex Fr.) Fr. (Coprinaceae), that is
not a species of fungus that B. cornutus is associated with. Additionally, measured
variables (body size, hom size, sex) eecting the response of B. cornutus are analyzed.
Methods
The forked fungus beetle, BoZitotherus cornutus Panzer (Tenebrionidae), is a
common inhabitant of eastern North American forests. B. cornutus completes its entire
life cycle on the hiting bodies of polypore shelf hgi (Polyporaceae) (Pace 1967).
Individuals have been observed to live up to 5 years (Bondrup-Nielsen, unpublished
data).
B. cornutus lives primarily on the sporocarps of the bracket fungi Fomes fornentarius, Ganoderma applanatum, and Ganoderma tsugae (Pace 1967, Liles 1956,
Matthewman and Pielou 1971), with individuals inçequentiy found on Fornitopsis pinicola, Piptoporus betulenris, Russula spp. and Lactarius spp. (personal observation).
During the summer breeding season, approximately 20 eggs are laid by the female on the surface of the F. fomentarius and Ganoderma species. Afier die eggs hatch, larvae tunnel through the sporocarp to feed, while the adults feed on the pore tubes and spores of the underside ciles 19%)- Both adults and young survive the winter within the sporocarps
(Liles 1956, Pace 1967). B. cornutus is1 thus obligately dependent upon the füngi, with
Fomes fomentarius representing the most commonly occupied species in Nova Scotia
(Bondmp-Nielsen unpublished data, pers. obs.).
Fomes fomentarius is perennial, with the hgal carps (fruiting bodies) survivîng for up to 10 years (Schwarze 1994). F. fomentarius has a wide distribution tbroughout
Asia, Afiica, Europe and North America (Schwarze 1994). These fungi are found invading dead and dying trees, aiding in the decompositional process (Schwarze 1994).
In Nova Scotia, Fomes fomentarius is very common in forests composed of its host trees, white birch (Betula papyrifera), yellow birch (Betula lufea), beech (Fagus grandfolia), and large-toothed aspen (Populus grandidentata), though there is a wide dispersion, with distances to nearest host trees on the order of 1 to 900 metres (Kehler and Bondrup-
Nielsen 1999).
B. cornutus has been descnbed as living in temporally unstable and spatially heterogeneous environments (Whïtiock 1992), and has been recorded moving hfiequently over short distances, fkom habitat patch to habitat patch (Heatwole and
Heatwole 1968). It has been estimated that only 30% of adults move between fungus patches in a lifetime (Whitlock 1992).
Adult beetles used in the experiment were collected in the field, by visiting forested sites known to have large numbers of host fùngi. Individuais were located by looking on and around fungal carps on the host trees.
To distinguish individuals al1 beetles were marked, using Testor's Non-Metallic
Enamel Paints, with a unique pattern of five coloured dots, one on the pronotum, and two on each el- BeetIes were sexed by looking for the pronotai horns that ody males
possess.
A laboratory choice experiment was conducted to determine if B. cornutus
chooses Fomes fomentarius sporocarps more often than non-food items- Individual
beetles were offered a choice of Fomes fomentarius or Coprinus utramentarius. The füngi were placed at opposite ends of a piece of plumbing tube, cut in half length-wise and rneasuring 4 cm by 30 cm- Each end of the tube was covered with window screening, to prevent the beetle fkom leaving the tube, and the fungi was placed on the outside of this screen, beyond the reach of the beetle. On a glass sheet measuring 45 cm by 82 cm, 10 to 12 tubes were spaced 3 cm apart and weighted down to prevent airflow through any part of the tube but the ends (Figure 1). Pnor to placing the tubes on the glass sheet, the suface of the glass was dusted with a fine covering of flour, by filtering the flour through a cloth. The path of the beetle could be traced by looking at where it had moved through the flour. The beetles were placed at the mid-point of each tube, perpendicular to the long axis of the tube (see Figure 11, and equidistant fiom both the F. fomentarius and C. atramentarius fun@. The experiment was run 6 Gmes, each for 30 minutes, with 12 individuals each time, except for the first 2 nins, where 10 individuals were used. The response of the beetle was recorded by noting which end of the tube
(whether on F. fomentarius or C. atramentarius) the beetle was found. At the end of each experiment, the glass sheet was washed with soap and water to remove any traces of flour or fungus, and then redusted with flour. A random number table was used to position the fimgi for each nin, to reduce the effect of residuai fungus and beetle on the glas Figure 1. Choice . test experiment set-up, run 1. Each tube (thick black Iine) is perpendicular to the long axis of the glas sheet. Each fungus is placed outside the tube, one on either end (F = Fomes fomentarius, C = Coprinus atrarnentorius). In the experiment, forked hgus beetles wodd be placed in the middle of the tube, aligned perpendicular to the long axis of the tube (in this representation, beetles would face the top edge of the sheet). Sm-six individuals were tested, though 8 were removed fiom the andysis as they did not move fkom the original release point. Thus, 58 total îndividuals were used in the analysis, and their responses compared to test for differences in ability to sense the food source. Each individual was tested ody once, to avoid learned responses. In Run 1,
5 females and 5 males were used; Run 2, 6 females and 4 males; Run 3, 6 females and 6 males; Run 4, 5 females, and 7 males; Run 5, 6 females and 6 males; and Run 6, 10 females and 2 males- Measured variables are shown in Table 1,
Chi-square goodness of fit tests were performed to test the deviation fiom the expected nul1 fiequencies of the responses. A heterogeneity Chi-square andysis was performed to avoid pooling heterogeneous data. This test ensures that data fiom more than one population of subjects is not cornbined (Zar 1996). Yates' correction was used in testing the pooled data due to the low degrees of fieedom. Two- and three- dimensional contingency tables were constnicted to test the independence of the variables.
Table 1. Variables measured in Bolifotlteruscornutus experiment for use in statistical rnodels.
Variables measured
Variables Range MeanlSD TRIAL 1 to 6 SEX Male or FemaIe COLOUR ID colour given to 58 individuals HORN LENGTH In mm 0-3 .O BODY LEWGTH In mm 7.4-12.0 BODY CLASS BINARY, O = CIOmm, 1 =llOmm CHOICE F, fornentarizlr or C. atramentarius PATH BINARY, O = Straight, 1 = Wandered Results
Fift/-eight total msponses were used, consisting of 23 males and 35 femaies.
Overall, individuais moved toward the Fomes fomentarius 37 times, and the C.
ahamentarius 21 times. The number of individuals that moved to the F. fomentarius
offering was significantly higher than those that rnoved to the C. ahamentarius offering,
with X2=3 .879 (1 DF, P < 0.05).
Sex had a significant effect on choice, with femaies more often moving toward F. fimentarius than males (X2=4.544, 1 DF, P < 0.05).
Table 2. Beetle choice by sex. Note that B. cornutus chooses Fomes fomentarius most
often.
Sex Fumes fomentarius Coprinus- atramentarirts Total Male 14 9 23 Female 23 12 35 Total 37 21 58
No significant interaction was found between Sex, Choice and Path (X2=2.545574
DF, P>0.05), though there was a significant interaction between Sex Choice, and Size
(X2=13.980374 DF, P < 0.01), with larger fernales choosing F. fornenrarius more often than smaller. Discussion
It is not surprishg that a preference for Fomes fomentarius was shown over the
Coprinus atrmentariur. Given that the ability to hdhabitat is essential for an
organisrn, traits that increase this ability are likely to be present in a population. To
survive in its naturally patchy habitat, Bolitothenrs cornufus must be able to fmd its
hgaihosts, which are ofien very widely dispersed throughout the forest. With such a
small percentage of the forest area hosting Fumes fomentarius and other food fungi, the
slow-moving forked fungus beetle rnay need a cue operating outside the visual reah to
locate and home in on potentiai habitat.
However, we know little about the metabolism of B. cornurus, and it may be that
it can find F. fomentarius or other fûngi simply by wallcing through the forest, going days
or weeks between bouts of feeding. B. cornutus is a long-lived species, ofien surviving at
least 5 years in the wild (Bondrup-Nielsen, pers. corn.), and spends up to 8 months of
the year in diapause, when it does not eat at ail. Several days of walking to another set of
F. fomentarius sporocarps may not cause a heavy strain to the beetle. As well, like many
. other Coleoptera that feed on perennial fungi (Hanski 1989), B. cornutus is polyphagous.
In Nova Scotia, B. cornufus has been found feeding on several perennial polypore fungi,
as well as many annual poIypores, and a number of ground Basidiomycetes (RussuLa spp.
and Lactarius spp. (Russulaceae)) (pers. obs.). The food resources contained in these
ofien widely scattered hgimay provide enough energy for B. cornutus to undertake
long (spatially and temporally), searching joumeys to find new habitat, in which chernical
cues to the fûngi play little or no role. The response of the beetie in moving more ofien to the F. fomentarius than the
Coprinus atramentarius may in fact not be related to a choice of F. fomentarius over C.
atramentarius, but rather to a noxious effect of C. azramen~urius. The beetie response
may have been to a factor in the C. atramentarius that repelled B. cornutus, rather than an
attractant effect of the F. fomentarius. Whiie B. cornu tu.^ are polyphagous on many
species of hgi, C. atrarrzentarius is not known to be one of them. C. atramentarius may
produce a volatile that B. cornutur must avoid, thereby producing the response that was
recorded. This is unlikely, however, as the experiment stiU recorded many instances of
beetles moving toward the C. atramenrarius. If there was a noxious effect of C.
atramentariur, there likely wouid have been no beeties that selected this fungus dukg
the experiments.
In a simiIar experiment, Heatwole and Heatwole (1968), found that in a Y-maze
treatment of responses to fungus odours, individuals were either right-tuners or left
tumers, demonstrating no discernible responses to odour. However, in the preliminary
stages of my experiment, some individuais were introduced to the tubes several times,
with no fungus at either end, and showed no tumllig preference (Le. they were not right
or left tumers).
While care was taken to conduct the experiment in a controlled setting that
negated the effect of sight, this mechanism cannot be ded out entirely. Al1 triais were conducted in noctumai conditions, with a fine mesh screen over the ends of the tubes to prevent the beetles both fiom escaping and seeing the fungi. However, B. cornutus is a nochrmal insect, and rnay have been able to see through the screen to a greater extent than was theorized. It would be instructive to conduct this experiment using only models
or photos of various fûngi to test what the role of sight is in BoZitotherus cornutus-
Finally, ail individuals used in this experiment were stored in an aquarium with
Fomes fornentarius sporocarps. The response rnay have been an artifact of the storage.
Individuals may have simply moved preferentially to the species they had been stored
with. The effect of storage shouId be minimized, however, because al1 F. fornentarius
sporocaps were collected fiom F.fomentarius that were unoccupied by B. cornutus, and
thus should not have been individually farniliar to the beetles.
The fact that a greater percentage of females moved to the F. fomentarius may be expIained in a variety of ways. Many organisms have a biased sex ratio amongst dispersers. For instance, in birds, females often disperse more than males (Greenwood and Harvey 1982), and in many mammals, the males disperse more than femdes
(Stenseth and Lidicker 1992). It rnay be that femdes are the dominant dispersers in B. cornutus, and females have best developed the abiIity to interpret the chernical volatiles of Fomes fornentarius. This rnay be a result of females making moves related to oviposition, or to find suitable mates. These results should be interpreted with care, as the number of male beetles used in the study was low.
The result that beetles greater than IOmm in length chose F. fomentarius more often than Coprinus rnay be related to movement ability. Larger individrds rnay have greater reserves of energy, and rnay be the dominant movers in the wild. Perhaps these larger individuals have the best developed chemo-sensory organs, and are best able to sense the chernicd volatiles of the F. fornentarius. Jonseli and Nordlander (1995) used window traps that measured attraction of
Coleoptera to chopped Fomes fomentarius and Fornitopsis pinicola sporocarps, and
attracted no Bolitophagus retimlatus. B. reticulattcs is ecologically very similar to B.
cornutus, essentially filling a simifar niche space as B. cornutus in the woodlands of
northeastem Europe (Midtgaard 1996). Other Coleoptera, especially members of the
Cisidae, waich fly, were commonly caught in the traps (Jonsell and Nordlander 1995).
When combined with O captures of forked fungus beetles in 4365 trap days using
unbaited flight intercepter traps at canopy, mid canopy and 50 cm above the forest
(Chapter l), and only one (laboratory obsenied) set of flights (Teichert 1999), the
evidence seems to point to forked fungus beetles very rarely, if ever, flying to new
sporocarps.
Severai avenues for Merinvestigation are suggested by this experiment. A
larger number of individuais would lend some statistical power to the results, and help to
illuminate some of the her divisions between classes of movers to Fomes fornentarius.
Another experiment using only photos or replicas of the fungi would be interesting to
look at the effects of vision on the individual responses. Also, it wodd be instructive to
conduct another choice experiment using only proven fimgal food sources as choices, to
look at the effect of attraction rather than repulsion in B. cornutus responses.
To conclude, this study shows several important results: 1) There is a preference
for Fomes fornentarius over Coprinus airamentarius, 2) a larger proportion of females
than males choose F. fomentarius , and 3) larger individuals more often choose F. fornentarius. References
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1 used Capture-Mark-Recaphire (CMR) techniques to study the dispersal of an
organisrn in a forested habitat by comparing timing of dispersal of newly emerged (teneral)
and over-wintered (adult) forked fungus beetles, Bolitofherus cornutus Panzer (Coleoptera:
Tenebrionidae), at the scale of a smail forest.stand. In addition, a choice test was conducted
to look at whether B. cornutus was chemoattracted to chemical volatiles produced by its .host
fimgus, Fomes fomentarius (F'olyporaceae).
In the Capture-Mark-Recapture experiment, 1 found no evidence that tenerals are
the dominant dispersers in Bolirotherus cornutus populations. In fact, the data suggest that the adult beetles are moving more ofien and further, as demonstrated in Kruskal-
Wallis tests and Correlated Random Wallc analysis (Kareiva and Shigesada 1983). There is no distinct difference in movement parameters for either of the sexes, as both males and females move at a similar rate. Flight does not seem to be an important mode of movement, at least at the scale considered in this experiment. Over 5800 total macro- invertebrates were captured during the experiment, in almost 4500 trap-nights. More than 2000 of these were Coleoptera No Bolitothents cornutus were recorded. There was no difference in rnovement rate or distance between ghed elytra and non-giued beetles.
Finally, movements of beetles seem to be confined to an area with a radius of approximately 50 m, suggesting that this is the spatial 'domain' (Wiens 2989) of this mode of movement.
The choice test experiment shows severd interesting results. First, there is a preference for Fomes fomentarius over Coprinus atramentarius. This is not unexpected, as
C. cztramentarius is not a fungus that B. cornutus is typicdly associated with. A larger proportion of females than males chose F. fomentariw in choice tests. This may be related to differences in bebaviour between the two sexes. Fernales rnay move to other fûngi to oviposit (Lundrigan 1997), and thus to find fhgi for oviposition, and may have better developed chernosensory apparatus than males. However, Chapter 1 of this paper shows that both males and females move at the same rate, and casts doubt on this hypothesis.
Further work is needed to address this question,
FinalIy, larger individuals more ofien chose F. fomentarius. This may reflect the differing movement abiiities arnong the sizes, with larger individuals being the dominant movers, and thus having better developed chemosensory organs. These effects are weak, however, and care should be taken not to overgeneralize.
In conclusion, this study demonstrates that Bolitotherus cornutus is moving often by walking, with the adults mabg the majority of the moves. In addition, there is an ability of
B. cornutus to chernosense its fimgal host. References
Kareiva, P- M. and Shigesada, N. 1983. Analyzing insect movement as a correlated random walk. OecoIogia 56: 234-23 8-
Lundrigan, T. A. 1997. Movement rates as an indicator of dispersal potentid in the forked fungus beetle Bolifotherus cornutus. B.Sc. Honours Thesis, Acadia University, Nova Scotia.
Wiens, J. A. 1989. Spatial scaling in ecology. Functional Ecology 3: 385-397.