The following document differs from my MS thesis in format only. All text, data and figures are identical to those found in the bound volume available from the library at Montana State University, Bozeman, Montana 59717, USA. I have changed only those details of format necessary to conform to the limitations of html.
INFLUENCES OF UNGULATE CARCASSES ON COLEOPTERAN
COMMUNITIES IN YELLOWSTONE NATIONAL PARK, USA
by
Derek Scott Sikes
A thesis submitted in partial fulfillment
of the requirements for the degree
of
Master of Science
in
Entomology
MONTANA STATE UNIVERSITY
Bozeman, Montana
November 1994
ii
APPROVAL
of a thesis submitted by
Derek Scott Sikes
This thesis has been read by each member of the thesis committee and has been found to be satisfactory regarding content, English usage, format, citations, bibliographic style and consistency, and is ready for submission to the College of Graduate Studies.
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______________________ Date |
_______________________________ Chairperson, Graduate Committee |
______________________
Date
_______________________________
Head, Entomology
______________________
Date
_______________________________
Graduate Dean
In presenting this thesis in partial fulfillment of the requirements for a master's degree at Montana State University, I agree that the Library shall make it available to borrowers under the rules of the Library.
If I have indicated my intention to copyright this thesis by including a copyright notice page, copying is allowable only for scholarly purposes, consistent with "fair use" as prescribed in the U.S. Copyright Law. Requests for permission for extended quotation from or reproduction of thesis in whole or in parts may be granted only by the copyright holder.
Signature__________________________[signed: Derek Sikes]
Date_______________________________[signed: 28 November 1994]
I thank my committee members Michael Ivie, Kevin O'Neill, John Varley and William Kemp for their input, encouragement and support of this thesis. I also thank John Varley for his interest in and financial support of this project. The methodological knowledge obtained from, and the financial skills of LaDonna Ivie ensured that this project ran smoothly. I thank, R. Anderson, G. Ball, D. Gustafson, R. Hoebeke, M. Ivie, A. Kirejtshuk, J. Klimaszewski, R. Miller, K. Phillips and C. Seibert for their identifications of specimens. The work of R. Moore, C. Youmans, S. Rose and others, who initiated this research project in 1978, and Dr. Moore's willingness to release the material for my thesis research is gratefully acknowledged. I am very thankful to M. Becker for his assistance in the field and the lab. The assistance of D. Gustafson in data processing and general analyses was invaluable. I thank those who provided miscellaneous assistance, such as M. Lavin, T. Weaver, K. Miller, and E. Nance. A great debt is owed to Michael Ivie, whose support and relentless high standards have driven me to achieve more than I thought possible. Finally, I am enormously grateful to my wife, Melissa Sikes, for her friendship and support.
This research was funded by NPS Work Order # YELL-93-03, Cooperative Agreement # 1268-1-9001, a grant from Yellowstone National Park and the Western Region of the National Park Service to Michael Ivie and LaDonna Ivie, and by the Montana Agricultural Experiment Station, Project # 156.
RESULTS
AND DISCUSSION....................... 61 62 63 78 84 87 88 CONCLUSIONS.................................. 96 SUGGESTIONS
FOR FUTURE RESEARCH.............. 98 REFERENCES
CITED............................. 103 APPENDICES................................... 118 119 132 134 141 147 154
Abundance:
Coleopteran.........................
Abundance:
Species.............................
Species
Diversity: Abundance &
Richness............................
Species
Occurrence..................
Species
Richness....................
Principal
Components Analysis.......
Appendix A -
Family
Species List....
Appendix B -
1978
Sample Collection.
Appendix C -
Bionomics..............
Appendix D -
Complete
1978 Species-to-Trap
Type-Association............
Appendix E -
Complete
1993 Species-to-Trap-
Type-Association...........
Appendix F -
Raw
Data...............
Community ecology is a relatively young and fast growing science. The rapid growth and immaturity of the field has lead to multiple definitions for numerous terms. Until a consistent usage is finally worked out, a glossary is required such as presented here to unambiguously define frequently used terms.
community. Assemblage of species that share at least one arbitrarily chosen, but biologically important characteristic.
family-species list. A master list that contains the identification numbers and names of taxa employed for a given research project.
fauna. The assemblage of resident animal species within a defined area.
morpho-species. A species whose classification is based only on gross, external morphology.
parataxonomy. The identification of specimens to morpho-species by technical-level personnel using only visual comparison with other specimens.
sample. All specimens captured in a single trap during a single trap period.
species abundance. The number of individuals of a given species.
species occurrence. The presence of a species in a sample, regardless of its abundance.
species richness. The number of species in a sample, data set, community, etc.
trap day. One trap active during one day.
trap period. Time span from the opening of a trap to the collection of the sample.
trap unit. One trap during one trap period.
My research tested the hypothesis that "The presence of large vertebrate carcasses will not affect the local richness, abundance and occurrence of taxa", and addressed three areas of scientific ignorance: (1) terrestrial ecosystem carrion ecology, (2) Nearctic large vertebrate carrion ecology, and (3) United States National Park biodiversity. To test this hypothesis, Coleoptera were sampled adjacent to ungulate carcasses and 40 meters distant via pit-fall trapping during 1978 and 1993 in the Lamar Valley of Yellowstone National Park, USA.
The two data sets, 1978 and 1993, contained a combined total of 23,365 adult beetles in 445 species. These beetles were trapped within habitat types representing 28% of the non-forested and 3% of the forested area within the park, and in sites that differed little in physiognomy--all shared glacial till soils of andesitic origin, similar elevations and were semi-arid.
The analyses conformed to standard community ecology protocol with the primary objective being the unambiguous documentation of what effect carcasses had, if any, on the fauna at a site. Many species that are documented carrion associates showed carrion associations, however, species with no recorded saprophilic tendencies were found to be significantly represented in the carrion community. The family Silphidae ranked first in abundance, due to the species Thanatophilus lapponicus (Herbst). The family Staphylindae was the most species rich (124 species) and the family Carabidae ranked second in species richness (57 species) and third in abundance.
The results caused me to reject the null hypothesis of no carcass effect and demonstrate that while a carcass is present, beetle abundance and species richness in a habitat greatly increases. This research documents some aspects of the complex and diverse impacts that result from the input of ungulates carrion into an ecosystem. Consequently, knowledge of one of the least known and more ecologically important and diverse faunas of Yellowstone National Park has been augmented considerably.
The field of ecology is often divided into four scales of focus: the study of organisms, the study of populations, the study of communities, and the study of ecosystems. However, a great deal of overlap exists between these subdisciplines. This study is focused primarily on the community and ecosystem levels. To begin to determine how large vertebrate carcasses effect ecosystem functioning requires an investigation of the communities that make up ecosystems. Specifically, this study attempts to test the hypothesis that "The presence of large vertebrate carcasses will not affect the local richness, abundance and occurrence of taxa".
Decomposers contribute significantly to the cycling and dissemination of energy in an ecosystem (Putman 1983; Price 1984; Begon et al. 1986). In most terrestrial systems, decomposers are responsible for over 95% of total community metabolism (Putman 1983). Decomposer species are found in virtually all higher-level heterotrophic taxa, from bacteria and fungi to vertebrates (Begon et al. 1986). Even some plant species are classified as decomposers (loc. cit.). Some decomposers are specialists, such as brown rot fungi that feed primarily on lignin-based residues, others are generalists, such as grizzly bears that scavenge dead tissues only on occasion. Some ecosystems, like those in caves, are composed primarily or only of decomposers and their predators, because they lack autotrophs and primary consumers. The majority of the organic remains consumed by decomposers are vegetative in origin (Putman 1983). The decomposition of animal remains is not understood as well as the decomposition of vegetation and appears to constitute but a small part of the total biomass decomposed within ecosystems (loc. cit.).
However, some of the more dramatic decomposer communities are associated with animal remains, principally because, unlike vegetative remains, they are spatially and temporally rare, rich sources of energy and nutrients. These communities can contain a great diversity of species (Hanski & Koskela 1977) and play a major role in the cycling of energy and nutrients within an ecosystem (Smith et al. 1989; Parmenter & Lamarra 1991). The more noticeable carrion-associated taxa are vertebrate scavengers such as coyotes, grizzly bears, bald eagles, vultures, lions, hyenas, and jackals, (Houston 1978; Richardson 1980; Mattson et al. 1991) yet the bulk of the diversity and complexity of the carrion community involves invertebrate taxa (Putman 1978a). In general, decomposer communities are, in their structure and dynamics, as complex as or more complex than other communities more commonly studied by ecologists (Begon et al. 1986). However, relatively little is known about how carrion decomposition effects ecosystem functioning. The majority of what is known regarding the effects of decomposition on ecosystem functioning was obtained from research on leaf-litter decomposition (e.g Odum 1957; Olson 1963; McClaugherty et al. 1985; Rustad 1994; Vitousek et al. 1994).
Most investigations of carrion communities fall into one of three categories, (1) species composition and the succession of decomposer taxa (e.g. Howden 1950; Bornemissza 1957; Reed 1958; De La Cruz 1964; Payne 1965; Payne et al. 1968; McKinnerney 1977, 1978; Coe 1978; Braack 1981, 1986, 1987; Jirón & Cartín 1981; Seastedt et al. 1981; Shubeck et al. 1981; Abell et al. 1982; Norrbom 1983; Lord & Berger 1984a, 1984b; Hanski & Hammond 1986; Schoenly & Reid 1987; Hegazi et al. 1991; Terron et al. 1991; Biernbaum & Wenner 1993), (2) seasonal and habitat associations, and natural history of carrion community species (e.g. Walker 1957; Johnson 1975; Katakura & Fukuda 1975; Denno & Cothran 1975; Anderson 1982), and (3) forensics (e.g. Yovanovitch 1888; Megnin 1894; Johnston & Villeneuve 1897; Motter 1898; Schoenly 1992). Additional studies of various aspects such as competition among decomposer taxa (e.g. Prior & Weatherhead 1991), behavioral ecology (e.g. Scott 1990), vertebrate scavenger resource use (Houston 1978) and conservation (e.g. Klein 1989) have also been conducted.
Good reviews of decomposer and carrion community ecology are those of Putman (1983), Begon et al. (1986), and Doube (1987). These reviews stress the importance of such communities to the overall functioning of ecosystems. Heal and MacLean (1975) mapped the relative contribution of different trophic groups to consumption and assimilation of net primary production for a hypothetical grassland community. They estimated that decomposers were responsible for 84.8% of the consumption of matter and 90.8% of the assimilation. De la Cruz' (1964) empirical study of litter decomposition in Costa Rica revealed that herbivores consumed only 5% of the available vegetative matter, the rest was removed by decomposers.
Doube (1987) and Putman's (1983) reviews of carrion and dung communities covers the more well-studied aspects of these communities. Carrion communities are often considered jointly with dung communitigs because they share many features. These communities and others, like those associated with rotten fruit or logs, are characterized primarily by their association with spatially and temporally rare, discrete and ephemeral patches of highly concentrated energy (Doube 1987). A number of factors have been identified that influence the structure and dynamics of these communities. A few of these factors include the mass of the energy resource and its consequent "lifespan" (e.g. Coe 1978; Kuusela & Hanski 1982; Schoenly & Reid 1983; Kneidel 1984) the seasonal availability of the resources (e.g. Putman 1983; Braack 1986), habitat type and elevation (e.g. Peck & Forsyth 1982; Hanski & Hammond 1986), competition (e.g. Kuusela & Hanski 1982; Kneidel 1984; Prior & Weatherhead 1991) and historical biogeography and latitude (Doube 1987; Hanski & Cambefort 1991).
Although a great deal of research has been conducted on carrion communities, most has been descriptive (Doube 1987; Schoenly & Reid 1987; Hanski & Cambefort 1991). This is not true of decomposer ecology research in general, which has a rich literature of experimental studies, but rather of carrion ecology research in particular. Few attempts have been made to apply general ecological theory to these systems in an experimental manner. Some of the few carrion ecology studies that have been experimental include Kneidel (1984), Klein (1989), Ives (1991) and the studies of Schoenly et al. (1983, 1987, 1991, 1992). Schoenly and Reid (1987) state:
"Although much is known of [carrion] communit[ies] from a purely descriptive viewpoint, we are aware of no quantitative tests of the decay stage concept, or of any statistical or numerical analyses of the carrion arthropod community in general" (loc. cit.).
Theory built from the study of resource use and species distributions predicts that numerous changes should be observable as a result of the introduction of a large, rich, temporally limited food resource into a habitat. Also, many observational studies mentioned above have provided information that supports such predictions and may be useful in the designing and testing of hypotheses.
A first step towards a quantitative understanding of carrion communities would be to devise an objective means to identify such communities. Without a method to differentiate carrion communities from non-carrion communities scientists have only anecdotal, natural history studies on which to base future work.
One of the most basic approaches to achieve a quantifiable differentiation of carrion-associated from non-carrion associated taxa is the use of control measurements to isolate and identify the effect on the local biota of introducing a large carrion resource into a habitat. This approach has rarely been employed in carrion ecology research. One of the three studies I am aware of that included control sampling was performed by Bornemissza (1957) during an investigation of the effects of carrion decomposition on soil faunas in Australia. He sampled the soil fauna beneath five 0.62 kg carcasses, 10 cm and 40 cm distant and, using Berlese extraction, found faunistic differences between carcass and control samples. He found a reduction in the abundance of 29 soil taxa beneath the carcasses. His results included a comparison of the mean number of Acari and Collembola found per sample and showed that most of the carcass samples had significantly fewer of these taxa than did the controls. Ants and earwigs were the only two taxa present in control samples that showed increased abundances at the carcasses. Sixteen taxa were identified as associated with the carcasses, but absent from the controls (and thus inferred to not be members of the normal soil fauna). He inferred that the fauna of the control community played an insignificant part in the decomposition of the carcasses. However, although the research was well-designed and well-executed in many ways, his general approach was one of a natural history investigation and many elements important to a rigorous analysis were missing from his report (e.g. sample sizes) and taxonomic level of identification varied among taxa.
Walker (1957) also performed a decomposition ecology investigation that included control sampling. His study was excellent for the time period and compared three replicates of four pit-fall trap types within four different habitats (=four sites) in Tennessee, USA. His traps types were (1) unbaited, (2) baited with fish carrion, (3) baited with cantaloupe, and (4) baited with cornmeal. Walker collected 444 arthropod species that were almost all identified to species. He attempted to identify the variables (temperature, time, rain, habitat, bait type) that were responsible for the richness, abundance and occurrence of species. Additionally, Walker explicitly tested the null hypothesis that the bait in a trap would not affect the biota. For each baited trap type Walker presented a table of species whose sample sizes were such that they strongly indicated (P<0.05) the null hypothesis was false. Although Walker's study was primarily descriptive rather than hypothetico-deductive, and suffered from numerous methodological shortcomings (e.g. he used live-traps and removed specimens by hand--thereby allowing many flying insects to escape, he had only one trapping site per habitat type, etc.), the concept of including the background ecology into his investigation and objectively determining species' associations with trap types was novel at the time, and has remained so.
A third study that incorporated control trapping was performed by Putman (1978a) in the United Kingdom. Putman used mouse carcasses and employed a moat-style pit-fall trap to collect and differentiate carcass associated arthropods from those of control traps. His research was entirely descriptive and unfortunately lacking in statistical, experimental, taxonomic, and basic scientific expertise. Putman, similar to Walker's (1957) study, statistically quantified the strength of association between taxa and carcasses. Unfortunately his results consist only of P-values (no test statistics nor degrees of freedom) for selected comparisons of unspecified abundances of various higher level taxa between unspecified numbers of trap units. He did not indicate what statistical test was used to generate his P-values, how many individuals were trapped, how far his control traps were placed from his carcass traps, how many traps were used, how many sites were used (although he did compare two habitat types), how many species were trapped, and only a few species were identified (most were lumped at the level of order or family). Although Putman's attempt was laudable, the lack of scientific rigor greatly reduced the value of his contribution to the question investigated.
What Walker, Bornemissza and Putman shared is the appreciation that a carrion resource modifies the communities within the habitat. A carcass can be considered like any other perturbation of a habitat, such as a pollutant or a fire. To unambiguously document if a habitat perturbation has an affect on the biota, it is necessary to use a careful experimental design (Green 1979; Hurlbert 1984; Stewart-Oaten et al. 1986). A number of investigators have discussed the relationship of background habitat communities to carrion communities studied (e.g. McKinnerney 1977, Schoenly and Reid 1983), yet only Walker, Bornemissza and Putman attempted to provide empirical documentation of the relationship between a carrion community and the local background community.
In this study, I attempted to use an experimental design analogous to that of Walker (1957), Bornemissza (1957), and Putman (1978a) but I incorporated modifications from progress in ecological, experimental hypothesis testing, entomological sampling, and community ecology research. This investigation tests the hypothesis that the local occurrence, richness and abundance of taxa are not affected by the presence of large, vertebrate carcasses.
This hypothesis is dependent on the Resource Diversity Hypothesis, the Resource Concentration Hypothesis and the Island or Patch Size Hypothesis (Price 1984). These hypotheses predict, respectively, that species richness is positively correlated with resource abundance, that species are more likely to find, stay and reproduce in areas of greater resource concentration, and that species richness is positively correlated with the size of the area of resource distribution (loc. cit.).
It has been argued that there is a need for more experimental and statistically rigorous ecological research that unites descriptive research with the theoretical (e.g. Connor & Simberloff 1979, 1986; Strong 1980, 1983; Quinn & Dunham 1983; Simberloff 1983; Loehle 1987; Drew 1994). Nevertheless, many areas of ecology, such as carrion community ecology that are based on a wealth of observational data have not seen their hypotheses experimentally tested. Too often, good descriptive research is not used to test hypotheses and experimental research is performed with small sample sizes (e.g. Kneidel 1984; Schoenly & Reid 1987; Schoenly 1991, 1992). This probably results from the scarcity of studies that combine the specialties of taxonomists with those of theoretical ecologists.
Of the four levels generally considered in the study of ecology, the organism, the population, the community, and the ecosystem, carrion ecology has been well studied within the first and third. The second and last levels, that of the population and ecosystem, are poorly understood. Population aspects are not addressed here, but remain a fertile field for future research. There exist few studies that focus on the question of what roles carrion plays in ecosystem functioning. Because this study focuses on aspects of how a carrion source impacts the ecosystem (by assessing changes in community structure), a discussion of what is known regarding ecosystem-focused carrion ecology is warranted.
Decomposers within an ecosystem generally feed on vegetable matter, animal tissues or animal dung. The role of vegetable matter decomposition within an ecosystem has received a great deal of attention in the literature (e.g Odum 1957; Olson 1963; McClaugherty et al. 1985; Rustad 1994; Vitousek et al. 1994), but the decomposition of animal products has received relatively little (Parmenter & Lamarra 1991).
The few studies that have addressed the influences of animal carrion and wastes to ecosystem functioning have focused on non-terrestrial ecosystems. The majority of these studies have dealt with the contribution by fish to aquatic ecosystem nutrient cycling (e.g. Meyer & Schultz 1985; Cederholm & Peterson 1985; Andersson et al. 1988; Cederholm et al. 1989; Brabrand et al. 1990; Minshall et al. 1991; Parmenter & Lamarra 1991). These studies have gone far in documenting the ecological contributions of the vertebrates in the system. Richey et al. (1975) inferred that phosphorus and nitrates made available from the decomposition of salmon carcasses significantly effected the biota of Taylor Creek (Lake Tahoe drainage, Nevada). Parmenter and Lamarra (1991) concluded that in some aquatic ecosystems the contribution to nutrient cycling from the decomposition of animal tissues can be substantial and in such cases, should be considered in the formulation of nutrient budgets, cycle dynamics, and management strategies. Dahl (1979) approached carrion ecology from a different perspective, focusing on evolutionary patterns of adaptations by benthic, marine, carrion-feeding, lysianassid amphipods. It appears that, generally, the research done on terrestrial carrion ecology has been more anecdotal/observational and community or behavior oriented, whereas the research done on aquatic carrion ecology has been more experimental/quantitative and ecosystem oriented.
Putman (1978b,c) documented the contribution of carrion to carbon dioxide production, and energy and organic matter flow within a terrestrial system. Because so little is known of terrestrial ecosystem carrion ecology, discussions of the importance of carrion reduction, carrion biomass and carrion communities to terrestrial ecosystem functioning can only be based on inference. In the following, I provide some information from which the importance of carrion to terrestrial ecosystem functioning can be inferred.
Although small vertebrate species must contribute a significant percentage of total vertebrate carrion input into a system (perhaps the majority, depending on the ecosystem), the focus of this study on larger vertebrate species argues for a general limitation of the discussion to sources of large vertebrate carrion.
Young (1994) presents a review and analysis of literature on large mammal die-offs applicable to wildlife conservation (with a die-off defined as a rapid peak-to-trough decline of 25% or more in estimated population numbers). Young's review indicates that large vertebrate die-offs should be considered a natural component of such species' population dynamics. Given the potential biomass and energy made available from a catastrophic, large mammal die-off, such as a 90% loss in a herd of bison, it seems reasonable to assume that such die-offs would play a role in many aspects of ecosystem functioning. No carrion study has directly compared a large die-off with the normal background density of carrion input nor has any study compared large vertebrate carcasses (>50kg) to small ones. However, it seems reasonable to postulate that the greater the mass of carrion the greater the richness, diversity and ecological impact.
Schoenly and Reid's investigation of the influence of carcass size on carrion community structure (1983) supports this prediction. They found that within the Chihuahuan desert, greater carcass mass correlates with greater carrion species richness. Although in their data set, the largest carcasses were only 2.5 kg, if this model holds true, the largest carcasses should display the greatest species richness (all other factors being constant).
It has been observed that species diversity increases as resource availability increases, (see Resource Diversity Hypothesis, Price 1984). I predict that communities associated with carcasses will show greater species diversity in regions of higher carrion concentration, such as the northern range of Yellowstone National Park. This greater resource availability might allow species that are generally less competitive in regions of sparser carrion resources or on smaller carcasses to coexist with their competitors.
Previous
Research
Employing Large Carcasses
Surprisingly few studies have been performed using large vertebrate carcasses. One study of particular relevance to my research was performed by Douglas Houston. Houston (1978, 1982) evaluated elk carcasses as a food resource for the predator-scavenger vertebrate fauna in the Northern range of Yellowstone National Park. He monitored 1,084 elk carcasses and reported that between 75-80% of the necromass, estimated to represent ca. 19,000-35,000 kg, was consumed by vertebrate scavengers annually during the years 1974-1978. The scavenger fauna was composed of seven to nine species of vertebrate, four of which were birds. Houston concluded that the necromass made available by the large population of elk in the park was a very important source of food for those vertebrates found exploiting the carcasses. Houston (1978) documented the consumption of insect larvae that were feeding on the carcasses by six species of insectivorous birds (chipping sparrows: Spizella passerina Bechstein, Audubon's warblers: Dendroica audoboni Townsend, western tanagers: Piranga ludoviviana Wilson, mountain bluebirds: Sialia currucoides Bechstein, robins: Turdus migratorius L., and Brewer's blackbirds: Euphagus cyanocephalus Wagler. He also reported that bears fed on the insect larvae, which were most likely either fly maggots or the immatures of the silphid beetle Thanatophilus lapponicus (Herbst). Houston's work clearly complements my research by demonstrating some aspects of the importance of large carcasses to the fauna of the region.
Another study that has employed large vertebrate carcasses was performed by Parmenter, a researcher who has addressed the question of how carrion impacts ecosystem function. He investigated nutrient and biomass loss rates from numerous terrestrial vertebrates, including mule deer in Wyoming (R. R. Parmenter pers. comm.). McKinnerney (1977) cited natural history observations of deer carcass decomposition made by a National Park Service Ranger, in Big Bend National Park. Another large vertebrate, carrion ecology investigation conducted in the Nearctic region was a short-term observational study of the arthropods associated with harbor seal carcasses located within the intertidal zone along the north eastern coast of the United States (Lord & Berger 1984).
The majority of investigations that have used large vertebrate carcasses were African or Indian (Morris 1928; Curry-Lindahl 1961; Coe 1978; Richardson 1980; Braack 1981, 1986, 1987). This is most likely due to the high density of large vertebrates in Africa and India.
Smith et al. (1989) investigated perhaps the largest carcass and the most rare and interesting of all carrion faunas yet studied. They discovered the remains of a 20 m long blue or fin whale at a depth of 1240 m in the Santa Catalina Basin. The fauna associated with the remains was distinct from that of the well-studied basin floor. At least six metazoan species and a diverse assemblage of sulfurphilic bacteria were found associated with the remains. The metazoans (four bivalves, a limpet and a snail) had not been previously found within the Santa Catalina Basin. Unlike terrestrial carrion ecology research, which is primarily anecdotal, their findings were discussed within the perspective of the entire benthic ecosystem, speculating what influences such whale carcasses might have had on the evolution, distributions, and abundances of deep-sea species.
Large Vertebrates: Paleoecology
The large vertebrate fauna of the New World is less diverse that that of Africa. This, however, has not always been the case. Around 10,000 years ago the number of genera of large mammal species in the Nearctic was close to that of Africa (Martin 1966). Given this history in the Nearctic, it seems safe to assume (and evidence suggests) that some aspects of the Nearctic ecosystem today originated in the past as a result of large vertebrate influences that are no longer present (Janzen & Martin 1982; Mack & Thompson 1982; Janzen 1983; Webb 1983; Janzen 1986; Milchunas et al. 1988). Studies of the evolution of ecosystem organization have indicated that large vertebrates, such as those in Africa today (e.g. McNaughton 1976, 1978, 1985) and in the remaining pockets of the Nearctic grasslands (e.g. Coppock et al. 1983), have been involved in coevolutionary relationships that have shaped many aspects of the flora (such as phenology) and fauna (such as dung beetle diversity) (Mack & Thompson 1982). A wealth of studies have been conducted on the issue of vertebrate influences on ecosystem structure and dynamics (e.g. Ruess & McNaughton 1987; Seagle & McNaughton 1992). For example, Ruess & Seagle (1994), in an analysis of soil microbial patterns and dynamics in the Serengeti, discuss the contribution of ungulate urine and dung to the soil ecosystem, but do not mention ungulate carrion contribution.
Considering the potential resources, the Pleistocene megafauna of the Nearctic could have supported large carrion communities. Martin (1973) estimated an average preextinction biomass of large mammals for unglaciated North America, north of Mexico at 9,429 kg/km2. Such density of potential carrion suggests that the decomposition of these resources played a more significant ecological role in the past than currently. Another comparison with modern Africa supports this idea. Within the Serengeti ecosystem, Houston (1979) estimated some 40 million kg worth of ungulates die annually. Predators consume 14 million kg of this total, vertebrate scavengers 12 million kg and the remaining 14 million kg are removed by invertebrates, fungi, bacteria, and weathering.
Although the current Nearctic mega-fauna is comparatively small, this does not prevent investigation into historical and current megafaunal influences on Nearctic ecosystems. The restriction of remaining New World megafauna (e.g Bison bison) to ecological islands such as Yellowstone National Park (YNP), indicates some degree of corresponding restriction, simplification, and perhaps extinction of the carrion communities associated with these vertebrates may have occurred.
Of course, most of the species in such carrion communities may not be restricted to these ecological islands. Rather, I expect only those community aspects (such as high species richness) that are unique to regions of dense sources of large vertebrate carrion to be restricted to regions such as YNP.
An investigation into the influences of large vertebrate carcasses on Nearctic invertebrate communities is long overdue. A first step towards obtaining such an understanding is the establishment of quantitative information regarding how a carcass modifies its local habitat. This information could be important if an ecosystem is being managed for maintenance of biological diversity. The knowledge that many species may be dependant on large sources of carrion might be important to ecosystem managers. Traditional knowledge of ungulate biology includes information on feeding habits, the effects of grazing, population variables such as natality and mortality, parasites, pathogens, vertebrate scavengers and predators (e.g Houston 1982). However, of all the ecological relationships between ungulates and other species of the ecosystem, a major area of ignorance is the relationship of ungulates to members of the invertebrate carrion community. To fully understand how large vertebrates affect ecosystem functioning, the invertebrate carrion ecosystem must be incorporated.
Invertebrates are the least-studied animals within the National Park System (Vogel, 1989; Ginsberg 1993, 1994). Thus, with almost nothing known about most invertebrate taxa, virtually any investigation into their ecology produces new information. Such basic faunistic information might be incorporated into the Biological and Conservation Data System of the Greater Yellowstone Conservation Data Center [a Natural Heritage Program funded by the Nature Conservancy with logistical support from the National Park Service (Feigley 1993)].
The paucity of information available about the insects within our national parks is striking in light of what has been discovered regarding the roles insects play in the functioning of our biosphere. Insects outnumber any other animal taxon in individuals and species [ >75% of the species on Earth are insect (Ginseberg 1993; Briggs 1994 and references therein)]. Wilson (1987) states that, within a hectare of Brazilian rain forest, there exists about 200 kg (dry weight) of animal tissue, 93% of which is attributable to invertebrates. It has been documented repeatedly that insects can and do consume and produce more biomass and cycle more nutrients than other animal groups in terrestrial ecosystems (e.g. Odum et al. 1962; Golley & Gentry 1964; Carlisle et al. 1966; Wiegert & Evans 1967; Lugo et al. 1973; Mattson & Addy 1975; Kitchell et al. 1979; Wilson 1987, 1988, 1992; Hölldolbler & Wilson 1990).
The purpose of my investigation was to experimentally investigate for the first time in the New World (to the best of my knowledge) a large-carcass, invertebrate carrion community. Given the lack of experimental research investigating decomposer community ecology, this research will provide an important baseline from which further experimental, ecosystem-focused work can proceed. The test of the null hypothesis that the local occurrence, richness and abundance of taxa are not affected by the presence of large, vertebrate carcasses will establish data supporting or rejecting what has, to date, only been assumed. A rigorous comparison of carrion and non-carrion communities that will provide unequivocal support for previous, anecdotal, natural-history information has not been performed (K. Schoenly pers. comm.). This hypothesis has, in the paraphrased words of Loehle (1987) -muddled along in a plausible but unconfirmed state, and is long overdue for rigorous testing.
For the purposes of the discussion below, the formal hypotheses tested state:
H0: The presence of a large vartebrate carcass does not affect the local occurrence, richness, and abundance of Coleopteran taxa, in comparasin to an area otherwise similar, but lacking a large vertebrate carcass.
H1: The local occurrence, richness, and abundance of Coleopteran taxa are affected by the presence of a large vertebrate carcass in comparison to an area otherwise similar, but lacking a large vertebrate carcass.