bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative and Molecular Genetic Variation in Captive Cotton‐Top Tamarins (Saguinus oedipus)
Authors: Cheverud James , Routman Eric , Jaquish Cashell , Tardif Suzette , Peterson Gloria , Belfiore Natasha , Forman Lisa
Published: March 2003

Most genetic surveys of captive and endangered populations are carried out with single gene characters bearing no direct relationship to life history or other features for which genetic variation needs to be maintained. Quantitative genetic estimates of heritable variation for life‐history traits may be a more direct and appropriate measure of genetic variation for some conservation purposes. Furthermore, recent theoretical and empirical results indicate that genetic variation measured on these two levels may not be concordant. We analyzed heterozygosity at 41 allozyme loci and heritability for body weight in captive cotton‐top tamarins (Saguinus oedipus) from the Marmoset Research Center of the Oak Ridge Associated Universities in order to compare these two levels of genetic variation. Cotton‐top tamarins are a highly endangered species native to Colombia. Many animals currently reside in research facilities and zoological parks. A total of 106 animals were used in the isozyme survey, while data on 364 animals contributed to the quantitative genetic study of body weight. We found a very low average heterozygosity (H = 1%) for this colony. Body weight was moderately and significantly heritable (h2 = 35%). This heritability is within the normal range for natural animal populations. The finding of biologically significant levels of heritability in a population with abnormally low allozyme heterozygosity illustrates the point that low levels of allozyme heterozygosity should not be taken as an indication of overall lack of genetic variation in important quantitative characters such as life‐history traits. Genetic variation required for adaptation of species to future environmental challenges can exist despite low levels of enzyme heterozygosity.
Extinction Dynamics in the American Marten (Martes americana)
Authors: Schneider Richard R. , Yodzis Peter
Published: March 2003

We constructed a model of marten population dynamics and used it to investigate extinction processes across a wide range of parameter values. The model was based on rules governing the behavior and physiology of individual martens and focused on energy balance. Spatial dynamics and demographic and environmental stochasticity were incorporated. The outcome was the probability of extinction and quasiextinction (20 females remaining) over 500 years. Three qualitative forms of extinction were delineated. The first was deterministic extinction, associated with those parameter combinations leading to a negative population growth rate. The second was probabilistic extinction in systems with a strong positive growth rate but restricted population size due to habitat constraint. The transition from 100% persistence to 100% quasiextinction, as the input habitat size was decreased, was abrupt. The final form of extinction was in systems with a growth rate of approximately zero. Prey availability maintained an upper limit on these populations, but otherwise fluctuations in population size were essentially random, leading to nontrivial probabilities of extinction in even relatively large populations. A number of issues requiring further empirical research were identified. These included the relationship between habitat quality and marten reproduction, dispersal patterns and dispersal mortality, the effect of habitat edge on marten reproduction and mortality, and the characterization of the severity and frequency of catastrophic mortality as experienced by marten populations.
The Lower Susquehanna River Gorge and Floodplain (U.S.A.) as a Riparian Refugium for Vernal, Forest‐Floor Herbs
Authors: Bratton Susan P. , Hapeman Jeffrey R. , Mast Austin R.
Published: March 2003

A survey of vernal, forest‐understory herbs was conducted on 52 routes, 10 sample sites each, along the Susquehanna River and its major and minor tributaries in southeastern Pennsylvania and northeastern Maryland. Mature forest stands, as compared to younger successional stands, had a greater diversity and cover of native understory herbs and greater frequencies of K‐selected species such as Trillium flexipes and Dicentra canadensis. Vernal herbs with a high fidelity to the river corridor were likely to be more mesic in habitat preference, to occupy a more limited range of habitats, and to be less tolerant to disturbance than species that are also common in adjacent upland areas. The best vernal wildflower sites, which are usually in mesic or floodplain forest, may also be the most vulnerable to species loss if the canopy is removed or the forest is otherwise disturbed. Disturbance‐sensitive herbs have been nearly extirpated from the Susquehanna tributaries by very intensive human development. Preservation of an appropriate matrix of microhabitats, particularly along the main river and at the mouths of the creeks, is critical to protecting the vernal flora of the region.
Choosing a Management Strategy: Two Structured Decision‐Making Methods for Evaluating the Predictions of Stochastic Simulation Models
Authors: Ralls Katherine , Starfield Anthony M.
Published: March 2003

We describe two structured decision‐making methods—one using a hierarchy of goals and a second using ranking on the sum of weighted criteria—that may be useful for many practical conservation problems, particularly when advisory groups evaluate the output of simulation models. We illustrate both methods by applying them to the problem of choosing a management strategy to address the “mobbing” problem in endangered Hawaiian monk seals. Both methods require estimates of the probabilities of various outcomes, such as a population size of more than 400 seals after 20 years under a specific management regime. We used a simulation model of a small monk seal population to generate these probabilities. Both methods provide an explicit, well‐documented, and reproducible decision process that helps justify the decision. Furthermore, they are easy for those untrained in decision analysis to understand and use, they focus discussion on management objectives, they facilitate an examination of trade‐offs in the light of multiple and sometimes conflicting objectives, they are suitable for use in workshops, and, at least in our example, they lead to management recommendations that are not highly sensitive to minor changes in probability estimates or other factors.
A Gap Analysis of the Management Status of the Vegetation of Idaho (U.S.A.)
Authors: Caicco Steven L. , Scott J.M. , Butterfield B. , Csuti B.
Published: March 2003

We compiled a 1:500,000‐scale map of the actual vegetation of the state of Idaho from existing vegetation maps, LANDSAT MSS satellite imagery, and aerial photography. An accuracy assessment showed 92.7% of the polygons to be correctly classified. The map was digitized as a layer in a Geographic Information System (GIS) using ARC/INFO software. Land ownership was also digitized from existing maps. Ownership tracts were assigned a protection level based on opportunities provided for management for conservation of biological diversity. We then compared the vegetation and management status layers to assess the extent and degree of protection afforded to 71 vegetation and land‐use categories. We identified six vegetation complexes with no protection and five vegetation complexes for which protection is less than 1000 ha each. An additional 18 vegetation types have total protection in the ranges between 1001–5000 ha and 5001–10,000 ha. Most of these 29 vegetation types are shrub‐steppe complexes or conifer/steppe mosaics. Economically valuable montane forests of western redcedar, western hemlock, and grand fir, as well as subalpine woodlands and forests of mountain hemlock, are also poorly represented in protected areas. Most opportunity for increasing protection of these types lies on land managed by federal agencies. Other trends in the data include poor geographic representation, small area of individual protected occurrences, relatively good protection in Idaho but less outside of the state, and protection poor in Idaho but widespread elsewhere. The major limitation of our analysis is a lack of detail on the ecological status of vegetation types. Information on the structure of the forest types as well as data on the understory composition of the shrub‐steppe complexes are lacking. Our study shows gap analysis to be an efficient and useful method of assessing the extent and degree of protection of land‐cover types and associated biodiversity over an area exceeding 200,000 km2.
Handling and Survivorship of African Wild Dog (Lycaon pictus) in Five Ecosystems
Authors: Ginsberg J.R. , Alexander K.A. , Creel S. , Kat P.W. , Mcnutt J.W. , Mills M.G.L.
Published: March 2003

Populations of the African wild dog, Lycaon pictus have declined throughout their range in sub‐Saharan Africa during the last 20 years. It has been hypothesized that handling of wild dogs led to local extinction of a study population in the Serengeti‐Masai Mara ecosystem. In this paper we compare rates of mortality and disappearance in handled (n = 305) versus unhandled (n = 135) dogs to test the hypothesis that handling leads to increased mortality of Lycaon. We examine data from five ecosystems in which Lycaon have been handled. Our data show that there is no effect of handling on the longevity of Lycaon in any ecosystem studied. Given these data, a more parsimonious explanation of the decimation of the Serengeti‐Mara Lycaon population would be that disease alone was responsible for the population collapse and that researcher handling of Lycaon was correlated with, but not causal to, this mortality.
Reproductive Biology of the Rare Orchid, Spiranthes diluvialis: Breeding System, Pollination, and Implications for Conservation*
Authors: Sipes Sedonia D. , Tepedino Vincent J.
Published: March 2003

We examined the breeding system and pollination of Ute lady’s tresses, Spiranthes diluvialis Sheviak, a rare orchid from Colorado and Utah. S. diluvialis exhibits a mixed‐mating system: the degree of selfing depends in part upon the abundance of pollinators visiting the flowers. Outcrossing is promoted by protandrous flowers and by acropetal movement of long‐tongued bees on inflorescences. Male and female phases overlap, however, and flowers are fully self‐compatible. No autogamous or agamospermous fruit set was observed, indicating that a pollen vector is required for reproduction. Observations indicate that bumblebees (Bombus spp.) are the most important pollinators of S. diluvialis. Land managers must include pollinators and pollen‐producing plants in their plans to preserve this rare orchid. The effects of pest management programs on bumblebees and the availability of suitable bee nesting habitat should be considered. Management should strive to maintain floral diversity because other flowering species may facilitate S. diluvialis pollination.
Using Wildlife Communities to Improve Vegetation Classification for Conserving Biodiversity
Authors: O'Neil Thomas A. , Steidl Robert J. , Edge W. Daniel , Csuti Blair
Published: March 2003

Determining which vegetation types organisms perceive similarly and classifying these types into groups that function as similar habitats are necessary steps toward expanding the focus of conservation strategies from single species to ecosystems. Therefore, the methods used to determine these habitat classifications are crucial to the successful design and implementation of these conservation strategies. Typically, this process has been accomplished through best professional judgement. We used quantitative techniques to group vegetation types into habitats based on the occurrence of breeding wildlife species (n = 420) in Oregon. After calculating faunal similarities among all regional vegetation types (n = 130), we used cluster analysis to group vegetation types into wildlife habitats. We classified the original 130 vegetation types into 30 wildlife habitat types that we believe function similarly. We tested this classification to assess whether vegetation types could be correctly classified into habitat types based on wildlife species composition. Discriminant analysis correctly classified 95% of the vegetation types into their wildlife habitat types, strengthening our confidence in this approach. This approach for classifying habitat types allows consistent development of conservation strategies at coarse resolutions and aids in identifying vegetation types where additional biodiversity surveys are needed. Finally, this approach can be refined continuously as the precision of vegetation mapping and our understanding of organism‐habitat associations improve.
Supportive Breeding and Variance Effective Population Size
Authors: Ryman Nils , Jorde Per Erik , Laikre Linda
Published: March 2003

The practice of supporting weak, wild populations through release of individuals bred in captivity is becoming an increasingly important conservation measure. A frequently recommended form of such breeding‐release activity refers to supportive breeding: a fraction of the target population is brought into captivity for reproduction, and the resulting progeny are released to mix with the wild segment of the population. We derived an expression for the variance effective size of a population managed through supportive breeding and discuss its relationship to previously published equations that are based on the assumption of random mating. We show that the effect of supportive breeding may be quite different on the inbreeding and the variance effective sizes. Whereas supportive breeding always results in a reduction of the inbreeding effective number, the variance effective number may either decrease, increase, or remain unchanged. We discuss these observations in relation to conservation management and suggest some general guidelines for supportive breeding situations. Our recommendations include making a distinction between inbreeding and variance effective numbers; taking particular care when dealing with organisms with high reproductive potential; assuring that the amount of drift be no larger than it would be without supportive breeding; and focusing primarily on the variance effective size of a population‐that is, on the effective number directly related to the rate of loss of gene diversity.
Adequacy of Wildlife Habitat Relation Models for Estimating Spatial Distributions of Terrestrial Vertebrates
Authors: Edwards Thomas C. , Deshler Elena T. , Foster Dan , Moisen Gretchen G.
Published: March 2003

In the U.S. National Biological Service’s gap analysis, potential distributions of terrestrial vertebrate species are based on the synthesis of wildlife habitat relation data and then modeled using a vegetation cover map derived from Landsat Thematic Mapper imagery. Using long‐term species lists from eight National Parks in Utah, we evaluated the adequacy of the wildlife habitat relations data generated by gap analysis in predicting species distributions at landscape scales. Omission and commission error rates were estimated for major taxonomic groups and for each national park. Depending on the taxonomic group, omission error ranged from 0 to 25%, whereas commission error ranged from 4 to 33%. Error rates were highest in amphibians and reptiles and lowest for birds and mammals. In general, the error rate declined as the size of the park increased. The Utah wildlife habitat relation models performed well when used to predict the presence or absence of terrestrial vertebrates in eight national parks in Utah and should provide valuable information for making conservation decisions. They also provide a measure of support for the use of these models within the gap analysis framework. Although it is likely that accuracy of wildlife habitat relation models will vary from state to state, and even considerably within a state, the modeling process seems robust enough to provide a reasonably high level of accuracy for use in conservation planning at the ecoregion level.
Microhabitat and Landscape Characteristics Associated with the Threatened Allegheny Woodrat
Authors: Balcom Betsie J. , Yahner Richard H.
Published: March 2003

Populations of Allegheny woodrat (Neotoma magister) in the northeastern U.S. have declined recently for unexplained reasons. The species is believed to be separate from the more widely distributed eastern woodrat (Neotoma floridana; Ord 1818) and is listed as threatened in Pennsylvania. Several hypotheses have been proposed for the decline in N. magister, but little information on the ecology of the species is available to direct conservation efforts. Using a multi‐scale approach, we compared recent microhabitat and landscape characteristics among historical, occupied, and reference sites to pre‐1960 versus post‐1985 landscape characteristics associated with historical woodrat sites. Our analysis suggests that habitat characteristics, such as percent rock cover and aspect, have affected the current distribution of woodrats in Pennsylvania. Differences in microhabitat probably do not account for the disappearance of woodrats from historical sites. We found no evidence that low levels of human activity near nest sites or that forest fragmentation were directly responsible for the observed decline. But we observed increases in residential and agricultural cover near historical sites between the 1950s and 1980s and higher percentages of croplands and other agricultural cover at historical sites than at occupied sites. These land uses are capable of supporting high populations of Great Horned Owls (Bubo virginianus) and raccoons (Procyon lotor). Increased predation by Great Horned Owls and exposure to the raccoon roundworm (Baylisascaris procyonis) have been suggested as potential factors contributing to the decline of woodrat populations in the northeastern United States. Historical sites bad significantly higher percentages of coniferous and mixed forest cover than occupied sites, and the percentage of coniferous forest cover at historical sites increased significantly between the 1950s and 1980s. Therefore, we speculate that changes in forest composition in Pennsylvania may have adversely affected habitat quality (particularly food availability) for Allegheny woodrats and contributed to their extirpation from historical sites.
Isozyme Variation in Echinocereus engelmannii var. munzii (Cacteceae)
Authors: Neel Maile C. , Clegg Janet , Ellstrand Norman C.
Published: March 2003

Assessing the degree of evolutionary differentiation between a rare taxon and its relatives is critical from a biological perspective. Because funding and time are limited, conservation biologists need to set maintainance of truly unique pieces of biodiversity as a higher priority than maintenance of interesting populations of widespread species. Although many factors go into setting priorities, thorough assessment of evolutionary distinctiveness based on multiple lines of evidence is the most basic. We used isozyme characters to assess the distinctiveness of a purportedly rare taxon, Echinocereus engelmannii var. munzii (Munz’s hedgehog cactus), from other common varieties of the same species. We sampled at least 15 individuals from one population in each of the three mountain ranges where E. e. var. munzii is present within the United States plus three corresponding desert populations of a more common variety. To test for clinal variation between mountain and desert populations, we sampled three elevationally intermediate populations in the San Bernardino Mountains. We recognized a total of 104 band patterns for nine enzyme systems. All nine enzyme systems yielded polymorphic zymograms. Although we found substantial intrapopulation variability, no significant isozymic differentiation was apparent among any of the sampled populations. Lack of such differentiation implies that the effects of selection or drift have not been felt or detected in these populations. In terms of these enzyme systems Echinocereus engelmannii var. munzii is not distinct from other members of the species. Although there is no evidence of isozymic distinction, morphological evidence should be included in any decisions to submerge this taxon.
Montane Amphibian and Reptile Communities in Madagascar
Authors: Raxworthy Christopher J. , Nussbaum Ronald A.
Published: March 2003

Abstract; Two habitats in Madagascar, secondary, montane heathland and high plateau prairie, are considered artificial, having been created by human‐set fires soon after the island was colonized less than 2000 years ago. These prairie and secondary heathland habitats are also thought to be degraded and faunistically depauperate. To test the depauperate fauna hypothesis we measured levels of herpetofaunal (amphibian and reptile) endemicity between primary forest, montane secondary heathland, and high plateau prairie. We found no species endemic to high plateau prairie, but a significant percentage of the montane herpetofauna is restricted to post‐fire secondary heathland. These results support the human‐origin hypothesis for prairie, but secondary heathland appears to be a natural, post‐fire successional stage that leads to a climax of sclero‐phyllous forest. This suggests that careful management of montane heathland could establish new dispersal corridors between currently isolated montane forest blocks and, therefore, could offer new opportunities for conservation in Madagascar. Despite widespread burning, the montane heathlands of Madagascar have diverse herpetofaunal communities, demonstrating that these montane communities are not as seriously degraded as previously believed, and that they may be naturally resistant to fire.
Law and Large Carnivore Conservation in the Rocky Mountains of the U.S. and Canada
Authors: Keiter Robert B. , Locke Harvey
Published: March 2003

The law governing large carnivores in the western U.S. and western Canada abounds in jurisdictional complexity. In the U.S., different federal and state laws govern large carnivore conservation efforts; species listed under the Endangered Species Act are generally protected, whereas those subject to state regulation can be hunted, trapped, or otherwise taken. Neither federal nor state environmental or land management laws specifically protect large carnivores, though these laws can be used to protect habitat. A similar situation prevails in Canada. Canadian federal law does not address large carnivore conservation, although the national parks provide some secure habitat. Provincial laws vary widely; none of these laws specifically protect large carnivores, but some provisions can be invoked to protect habitat. Although the two nations have not entered any bilateral treaties to protect large carnivores, several species receive limited protection under multilateral treaty obligations. Despite these jurisdictional complexities, the existing legal framework can be built upon to promote large carnivore conservation efforts, primarily through a legally protected reserve system. Whether the political will exists to utilize fully the available legal authorities remains to be seen.
Genetic Variation of Naturally Colonizing Wolves in the Central Rocky Mountains
Authors: Forbes Stephen H. , Boyd Diane K.
Published: March 2003

Recovery of gray wolf (Canis lupus) populations in North America depends on minimizing human‐caused mortality and enhancing migration from stable source populations to suitable habitat unoccupied by wolves. We used a combination of field observation and DNA microsatellite genotyping to examine natural wolf colonization of Glacier National Park, Montana, and surrounding lands. We found high genetic variation in the colonizing population, showing that these packs were founded by multiple, unrelated wolves from Canada. High dispersal rates, long dispersal distances, and lack of a founding population bottleneck indicate that wolves in the United States and Canada should be viewed and managed as a single population. Restoration in the United States by artificial transplants from Alberta to Yellowstone National Park and central Idaho began in 1995. The transplanted wolves will likely aid demographic recovery, but permanently retaining the high genetic variation of wolves in the United States will require assuring gene flow throughout the central Rocky Mountains.
Inferring Metapopulation Dynamics from Patch‐Level Incidence of Florida Scrub Plants
Authors: Quintana‐Ascencio Pedro F. , Menges Eric S.
Published: March 2003

Spatial structure and dynamics of multiple populations may explain species distribution patterns in patchy communities with heterogeneous disturbance regimes, especially when species have poor dispersal. The endemic‐rich Florida (U.S.A.) rosemary scrub occupies about 4% of the west portion of Archbold Biological Station and occurs scattered within a matrix of less xeric vegetation. Longer fire‐return times and higher frequency of open patches in rosemary scrub provide favorable habitat for many plant species. Occupancy of 123 species of vascular plants and ground lichens in 89 patches was determined by repeated site surveys. About two‐thirds of the species occurring at more than 14 patches had a significant logistic regression of presence on time‐since‐fire, patch size, patch isolation, or their interactions. Species with presence related to the interaction between patch isolation and patch size were primarily herbs and small shrubs specializing in rosemary scrub. These results suggest the importance of spatial characteristics of the landscape for population turnover of these species. An incidence‐based metapopulation model was used to predict extinction and colonization probabilities of those species with presence in rosemary scrub patches related to the studied spatial variables. This is the first attempt to apply incidence‐based metapopulation models to plants. The results showed stronger effects of patch size and patch isolation on extinction probabilities of herbs than on those of woody species. Because of their effect on spatial heterogeneity and habitat availability, fire suppression and habitat destruction may decrease persistence probabilities for these rosemary scrub specialists, many of which are endangered species.
Guidelines for the Design of Conservation Strategies for the Animals of Venezuela
Authors: Rodríguez Jon Paul , Rojas‐Suárez Franklin
Published: March 2003

The geographic distribution of the animals of Venezuela was analyzed as a basis for a series of guidelines to help develop strategies for their conservation. A total of 313 animal taxa is distributed among 24 geographic units, corresponding to the political divisions of the country. Three different criteria were considered in analyzing these data: (1) the number and density of threatened taxa were used to define a ranking system for geographic units; (2) “hotspots” were identified using the distribution of threatened endemics, and (3) a “critical faunas analysis” was used to determine the minimum number of geographic units needed to maximize the number of sampled taxa. The first two criteria emphasize the importance of protecting habitat in the northern portion of the country, where most human intervention has already taken place. But the southern portion of the country is where most of the undisturbed habitat remains. We suggest that the conservation of the animals of Venezuela must follow a mixed strategy, based on two principles: one, aimed mainly at threatened endemics, should focus on the protection of critical habitat north of the Orinoco river, the second, aimed at all threatened animals— particularly high‐risk taxa—should focus on assuring the long‐term persistence of the pristine habitat in the south.
DNA Repair Activity and Resistance to Solar UV‐B Radiation in Eggs of the Red‐legged Frog
Authors: Blaustein Andrew R. , Hoffman Peter D. , Kiesecker Joseph M. , Hays John B.
Published: March 2003

We assessed DNA repair and resistance to solar radiation in eggs of the red‐legged frog (Rana aurora), a species whose populations appear to be in decline. Specifically, we measured the activity of photoreactivating enzyme, photolyase, in R. aurora oocytes. In some species photoreactivation is the most important mechanism for repair of UV‐damaged DNA. We also compared the hatching success of R. aurora eggs subjected to ambient levels of UV‐B radiation with those shielded from UV‐B radiation. We found photolyase levels in R. aurora to be relatively high when compared with other amphibians and hatching success to be unaffected by UV‐B radiation. We suggest that UV‐B radiation is an unlikely cause for declining populations of red‐legged frogs.
Genetic Variation and the Immune Response in Natural Populations of Pocket Gophers
Authors: Sanjayan M.A. , Crooks Kevin , Zegers Gerard , Foran David
Published: March 2003

It is thought that genetic variation can affect the persistence of a population through its influence on disease susceptibility. We assessed genome‐wide genetic variation, variation at a locus involved in the immune system, and acceptance or rejection of skin grafts in three natural populations of the pocket gopher (Thomomys bottae). Multilocus DNA fingerprints confirmed previous allozyme data, revealing high levels of variation among Hastings Reserve pocket gophers and almost complete within‐population identity for individuals from the two Patricks Point populations (Patricks J and Patricks F), although Patricks J animals were dissimilar to animals from Patricks F despite their proximity. Individuals from the high‐variation population consistently rejected within‐population reciprocal skin grafts, whereas Patricks J and Patricks F individuals accepted within‐population grafts. Patricks J and Patricks F individuals were found to be immunocompetent, however, as revealed by the ability of all individuals to reject between‐population grafts, including those that previously accepted within‐population grafts. A DNA heteroduplex analysis was then used to directly characterize variability at DQα, a locus of the immune system’s major histocompatability complex. Both populations low in genetic variation were fixed for unique DQα alleles, whereas observed heterozygosity in the Hastings population was 0.43, ascribable to at least three unique alleles. These data are in accord with previous cheetah skin‐graft results and confirm that skin grafts can be used to assess genetic similarity. We suggest that although many animal populations can persist with extremely low levels of genetic variation in the wild, such populations may be at a greater risk of extinction from particular pathogens because of their genetic uniformity.
Macroinvertebrate Colonization of Woody Debris in Canadian Shield Lakes following Riparian Clearcutting
Authors: France R.L.
Published: March 2003

Deployment of litterfall traps revealed that clearcut logging of boreal riparian forests in northwestern Ontario, Canada resulted in a dramatic shift from once dominant conifers to regrowth composed largely of deciduous trees and reduced the allochthonous inputs of small woody debris to lake littoral zones by over 90%. Due to the rarity of macrophytes in these oligotrophic lakes, littoral macroinvertebrates were found to actively colonize woody debris placed within mesh litter bags. The recalcitrant nature of small woody debris in these lakes (average median persistence time of about 5 years estimated from mass loss data) indicates, however, that this important habitat resource will probably never completely disappear in relation to its projected rate of resupply during post‐disturbance forest regeneration. Colonization rates of twigs and bark contained within the litter bags were not found to differ between coniferous and deciduous species. This indicates that macroinvertebrates in these boreal lakes are merely opportunistic colonizers of woody debris, probably for its use as either a biofilm substrate or a predation refuge. As a result, shifts in tree species composition following riparian clearcutting should not detrimentally affect the taxa richness or organism abundance of aquatic macroinvertebrates in these lakes.
Effects of Livestock Grazing on Stand Dynamics and Soils in Upland Forests of the Interior West
Authors: Belsky A. Joy , Blumenthal Dana M.
Published: March 2003

Many ponderosa pine and mixed‐conifer forests of the western, interior United States have undergone substantial structural and compositional changes since settlement of the West by Euro‐Americans. Historically, these forests consisted of widely spaced, fire‐tolerant trees underlain by dense grass swards. Over the last 100 years they have developed into dense stands consisting of more fire‐sensitive and disease‐susceptible species. These changes, sometimes referred to as a decline in “forest health,” have been attributed primarily to two factors: active suppression of low‐intensity fires (which formerly reduced tree recruitment, especially of fire‐sensitive, shade‐tolerant species), and selective logging of larger, more fire‐tolerant trees. A third factor, livestock grazing, is seldom discussed, although it may be as important as the other two factors. Livestock alter forest dynamics by (1) reducing the biomass and density of understory grasses and sedges, which otherwise outcompete conifer seedlings and prevent dense tree recruitment, and (2) reducing the abundance of fine fuels, which formerly carried low‐intensity fires through forests. Grazing by domestic livestock has thereby contributed to increasingly dense western forests and to changes in tree species composition. In addition, exclosure studies have shown that livestock alter ecosystem processes by reducing the cover of herbaceous plants and litter, disturbing and compacting soils, reducing water infiltration rates, and increasing soil erosion.
Effects of Selective Logging on Forest Bird Populations in a Fragmented Landscape
Authors: Robinson W. Douglas , Robinson Scott K.
Published: March 2003

We evaluated the effects of perforation, or the creation of small gaps, within a mature, deciduous forest in southern Illinois (U.S.A.) on abundances of breeding birds. Openings of 0.02–0.4 ha were created by group and single‐tree selection logging within a 2000‐ha tract of forest. We used point counts to compare abundances of birds in uncut forest with those in similar adjacent forest compartments that were recently cut (1–5 years previously) and less recently cut (10–15 years earlier). Most species of forest birds were not significantly less common in logged tracts. Only Red‐eyed Vireos (  Vireo olivaceus) and Ovenbirds ( Seiurus aurocapillus) were significantly more numerous in uncut forest, but the vireo responded negatively to cuts at sites on ridges only, not in ravines, whereas Ovenbird populations differed substantially among years. Blue Jays (Cyanocitta cristata), important nest predators, were significantly more abundant in cut than uncut forest, but brood parasitic Brown‐headed Cowbirds (  Molothrus ater) showed no consistent differences. Populations of gap‐dependent species such as Hooded Warbler (  Wilsonia citrina), Indigo Bunting (  Passerina cyanea), White‐eyed Vireo (  Vireo griseus), and Carolina Wren (  Thryothorus ludovicianus) were dramatically larger in recently cut forest, with populations of most species reaching a peak 2–3 years after cutting. Between 5 and 10 years after cutting, nearly all gap‐dependent species had returned to population levels comparable to those in uncut forest. Species dependent upon larger gaps, such as Yellow‐breasted Chat (  Icteria virens), Blue‐winged Warbler (  Vermivora pinus), and Prairie Warbler (  Dendroica discolor), were absent. We conclude that the first cutting cycle in selective logging had only a minor effect on the forest bird community composition and created a short‐lived availability of habitat for gap species. In the southern Illinois landscape, selective logging appeared to add little to the existing effects of forest fragmentation. Effects of perforation may differ in more continuously forested landscapes, however, and may be influenced by total basal area of timber removed and by the length of the inter‐cut interval.
Population Structure and Cryptic Evolutionary Units in the Alligator Snapping Turtle
Authors: Roman Joseph , Santhuff Steven D. , Moler Paul E. , Bowen Brian W.
Published: March 2003

The alligator snapping turtle ( Macroclemys temminckii) is a long‐lived, slow‐growing chelydrid turtle found in Gulf of Mexico drainages from Florida to Texas (U.S.A.). Populations are thought to be depleted throughout the range due in part to an increased harvest in the 1960s through 1980s. To identify population and evolutionary units, 420 base pairs were sequenced within the mitochondrial DNA control region of 158 specimens from 12 drainages. Results indicate substantial phylogeographic structuring and strong population‐level separations among river drainages. Eight of 11 haplotypes were observed to be river‐specific, providing diagnostic markers for most drainages. Three partitions are resolved in the mtDNA genealogy, corresponding to the eastern, central, and western portion of the species’ range. These separations coincide with recognized biogeographic provinces. The population structure by river system indicates that many drainages are distinct management units, with the Suwannee River lineage possibly deserving special attention, based on the criterion of genetic distinctiveness. The partitioning of M. temminckii into river‐specific populations illustrates the management framework and conservation challenges that apply to a broad array of riverine species. Drainage‐specific molecular markers may be used to identify the geographic origin of turtle products in the marketplace.
Effectiveness of Predicting Breeding Bird Distributions Using Probabilistic Models
Authors: Beard Karen H. , Hengartner Nicolas , Skelly David K.
Published: March 2003

Abstract: Conservation biologists need to be able to predict species distributions based on easily collected data available at regional scales. We quantified the effectiveness of different types of data for predicting bird distributions for the state of Idaho. We developed probabilistic models to evaluate the ability of vegetation, climate, and spatial autocorrelation data to predict the presence or absence of 40 bird species. We determined the probability of correctly predicting presence and absence for each species using a training‐testing sample methodology. This method involves splitting the data set into two portions: one portion was used to “fit” the models using maximum likelihood, and the second portion was then predicted from the fitted models. The predicted probability of species presence from the second portion of the data was compared to actual presence‐absence values to assess model performance. Overall, differences in average performance among the parameterized models were small. Vegetation, climate, and spatial models each predicted approximately 60% of the presences correctly. Models employing a combination of these factors consistently improved model performance, but only slightly (an approximate 4% improvement). In contrast, the null model correctly predicted just 35% of the presences. Our results suggest that (1) parameterized models are a substantial improvement over a null model but still make frequent mistakes in predicting the presence or absence of species, and (2) data availability may be the most important factor in determining which variables to use to predict species presence‐absence. In some cases, available and relatively inexpensive climate data or incomplete distributional information may be the preferred data option.
Statistical Power of Presence‐Absence Data to Detect Population Declines
Authors: Strayer David L.
Published: March 2003

Abstract: Population declines may be inferred from a decrease in the number of sites at which a species is detected. Although such presence‐absence data often are interpreted informally, it is simple to test the statistical significance of changes in the number of sites occupied by a species. I used simulations to examine the statistical power (i.e., the probability of making the Type II error that no population decline has occurred when the population actually has declined) of presence‐absence designs. Most presence‐absence designs have low power to detect declines of <20–50% in populations but have adequate power to detect steeper declines. Power was greater if the population disappeared entirely from a subset of formerly occupied sites than if it declined evenly over its entire range. Power also rose with (1) increases in the number of sites surveyed; (2) increases in population density or sampling effort at a site; and (3) decreases in spatial variance in population density. Because of potential problems with bias and inadequate power, presence‐absence designs should be used and interpreted cautiously.
Effects of Exploitation and Park Boundaries on Legume Trees in the Sonoran Desert
Authors: Suzán Humberto , Malda Guadalupe , Patten Duncan T. , Nabhan Gary P.
Published: March 2003

Abstract: Legume trees have been harvested in the Sonoyta Valley since 1975. We estimated the effects of this woodcutting along the border between Organ Pipe Cactus National Monument (U.S.A.) and Sonora, Mexico. We placed 10 × 100 m transects in ephemeral watercourses and uplands on both sides of the international boundary at different distances from the border. Mesquite and ironwood trees exhibited significantly higher damage in the Mexican sites than in the protected uplands in the United States. Damage for all the species significantly decreased 500 m from the border, with the exception of ironwood, for which damage remained high within ephemeral watercourses.
Effect of Introduced Mosquitofish on Pacific Treefrogs and the Role of Alternative Prey
Authors: Goodsell Jeff A. , Kats Lee B.
Published: March 2003

Abstract: Mosquitofish (Gambusia affinis) are distributed by many mosquito control programs because of their broad habitat tolerance and because they are considered by some to be effective mosquito predators. As a result, mosquitofish have become established as an exotic species in numerous perennial streams in the Santa Monica Mountains within the last 10–15 years. Previous studies have found that mosquitofish prey heavily on California newt (  Taricha torosa) larvae that inhabit mountain streams. We found Pacific treefrog (  Hyla regilla) tadpoles in the stomachs of 65% of stream‐caught mosquitofish. In both laboratory and field experiments, we found that mosquitofish preyed heavily on treefrog tadpoles, even when high densities of mosquito larvae were presented as alternative prey. Thus, despite apparent high densities of Pacific treefrog populations, our experiments suggest that introduced mosquitofish may negatively affect stream‐breeding H. regilla in the Santa Monica Mountains.
Human Hunting of Nongame Birds at Zuni, New Mexico, U.S.A.
Authors: Taylor Robert V. , Albert Steven K.
Published: March 2003

Abstract: Nongame bird hunting is a critical activity of the Zuni people of the southwestern United States. To help determine whether their current hunting practices may be negatively affecting bird populations on the Zuni Reservation, we interviewed 98 Zuni hunters. Nongame bird hunting was practiced by a large portion of Zuni males (45%); the most active age group was 20‐ to 49‐year‐olds. The rate a species was hunted was not a function of its abundance at Zuni but seemed instead to be related to its cultural demand. Five “species”—bluebirds ( Sialia currucoides, S. mexicana), Northern Flicker ( Colaptes auratus), woodpeckers ( Picoides villosus, P. pubescens, Melanerpes lewis), Steller's Jay ( Cyanocitta stelleri), and American Kestrel ( Falco sparverius)—made up 77% of all birds taken. The two most heavily hunted species were each taken in numbers> 10,000 individuals per year. Although the greatest number of hunters were active in autumn, 31% hunted in spring, despite discouragement by the tribal government. Habitats favored by hunters were coniferous forests and riparian areas. Rates of hunting of nongame birds at Zuni equaled or exceeded those reported for game birds hunted by indigenous hunters in the Neotropics and New Mexico. The Zuni believe that some heavily hunted species are decreasing in number because of hunting. Although we cannot prove this at present, we suggest measures to mitigate possible overhunting, including the creation of refugia and a reduction of spring hunting.
Factors Affecting Population Assessments of Desert Tortoises
Authors: Freilich Jerome E. , Burnham Kenneth P. , Collins Christopher M. , Garry C. Ann
Published: March 2003

Abstract: Desert tortoises have been a subject of controversy since their listing as threatened in 1990. With a wide geographic range and more living individuals than any other listed land animal, biologists have needed to detect population trends against a “noisy” background of strong annual changes. We obtained annual population estimates of desert tortoises over 6 consecutive years at a 2.59‐km2 plot in Joshua Tree National Park, California. Our estimates, based on weekly spring surveys, varied substantially, particularly between wet and dry years. Concurrently, we followed 10 radiotagged animals for 3 years to corroborate the surveys. Population density was determined separately for each year and for all years combined. Our best population estimate was an average of 67 adult tortoises, three times more than the density reported in a 1978 survey of the same site. Annual mortality was low ( <10%), and the animals showed extreme site fidelity. Apparent changes in population size were most strongly related to the animals' varying susceptibility to capture. In dry years, home ranges decreased, captures decreased, and effort required to find each tortoise nearly doubled. Our data confirm that tortoises are likely to be undercounted during dry years and call into question earlier studies conducted during droughts.
Sensitivity of Embryos of Southern Appalachian Amphibians to Ambient Solar UV‐B Radiation
Authors: Starnes Susan M. , Kennedy Caroline A. , Petranka James W.
Published: March 2003

Abstract: Studies suggest that increased ground‐level UV‐B radiation due to stratospheric ozone depletion is adversely affecting many aquatic organisms. In particular, ambient UV‐B radiation can kill or deform amphibian embryos and may be contributing to global amphibian declines. Sensitivity tests have been conducted primarily at northern latitudes (>42° N), where ozone thinning is most prevalent. Studies in southern California and Spain, however, suggest that some amphibians are vulnerable to ambient UV‐B at these lower latitudes. We tested the sensitivity of pond‐breeding amphibians to UV‐B radiation in the southern Appalachian Mountains (35° N; 660 m) of the United States, where stratospheric ozone has declined during the last two decades. We exposed eggs of frogs (  Hyla chrysoscelis, Pseudacris triseriata, Rana sylvatica) and a salamander (Ambystoma maculatum) to three treatments under field conditions that provided maximum exposure to solar radiation: (1) a polycarbonate filter that blocks> 98% of UV‐B (2) an acrylic filter that transmits 80% of UV‐B, and (3) unfiltered sunlight. Survivorship to hatching (
grand mean = 91%) and the percentage of embryos deformed ( grand mean = 4.4%) did not differ significantly among treatments for any species, but differences in the percentage of embryos deformed approached statistical significance for Hyla (p = 0.06) and Pseudacris (p = 0.10). More refined analyses using orthogonal contrasts revealed that deformity rates for both species were significantly lower in embryos that were shielded from UV‐B than in unshielded controls. A pooled analysis of all anurans also indicated that deformity rates were higher in treatments with UV‐B transmitting plates than in those with blocking plates. Collectively, our data suggest that pond‐breeding amphibians in the southern Appalachians currently incur only slight risk from exposure to ambient UV‐B radiation. If ground‐level radiation increases in the future, the risk for certain species could increase significantly.