bluuebunny/crossref_metadata_2025 huggingface dataset:
A Practice‐based Approach to Ecosystem Management
Authors: Brunner Ronald D. , Clark Tim W.
Published: March 2003

Ecosystem management is a rapidly evolving philosophy or paradigm of natural resource management intended to sustain the integrity of ecosystems. The problem is that principles of ecosystem management are unsatisfactory for practical purposes. Three major approaches to the problem are evaluated: (1) clarification of the goals of ecosystem management, (2) construction of a better scientific foundation for management decisions, and (3) comparative appraisal of current practices. The evaluation concludes that neither of the first two approaches is necessary or sufficient for better management decisions because better decisions depend upon the complexities of particular contexts. The third, practice‐based approach makes the most of the limited human capacity to cope with the complexities of ecosystem management in order to improve principles of ecosystem management, to inform particular management decisions through improved principles, and to incorporate clearer goals and a better scientific foundation as they become available. The evaluation draws on experience and disciplines beyond conservation biology and natural resource management, including policy sciences.
The Sustainability of Subsistence Hunting in the Neotropics
Authors: Alvard Michael S. , Robinson John G. , Redford Kent H. , Kaplan Hillard
Published: March 2003

Hunting is an important component of native subsistence strategies in Amazonia. It is also a serious threat to biodiversity in some areas. We present data on the faunal harvests of two native Neotropical subsistence hunting peoples, Machiguenga bow‐hunters and Piro shotgun hunters of Peru. The rate of annual harvest per square kilometer of catchment is estimated and compared to rates of sustainable harvest calculated by Robinson and Redford (1991). We used indicators of prey abundance to test for the depletion of species that hunters killed in numbers greater than what the model predicts to be sustainable. As predicted, we found the strongest evidence for local depletion of the large primates at the Piro site. The woolly monkey ( Lagothrix lagothricha) harvest at the Machiguenga village and the deer ( Mazama americana) and collared peccary (Tayassu tajacu) harvests at both sites were not predicted to be unsustainable and we found no evidence for depletion. Machiguenga bow hunters killed spider monkeys (Ateles paniscus) in quantities that were slightly above what the model predicted to be sustainable, yet we found no evidence for depletion. Differential species vulnerability, catchment size, and consumer population size could be important factors in determining sustainability.
A Habitat‐Based Metapopulation Model of the California Gnatcatcher
Authors: Akçakaya H. Reşi̇t , Atwood Jonathan L.
Published: March 2003

We present an analysis of the metapopulation dynamics of the federally threatened coastal California Gnatcatcher (Polioptila c. californica) for an approximately 850 km2 region of Orange County, California. We developed and validated a habitat suitability model for this species using data on topography, vegetation, and locations of gnatcatcher pair observations. Using this habitat model, we calculated the spatial structure of the metapopulation, including size and location of habitat patches and the distances among them. We used data based on field studies to estimate parameters such as survival, fecundity, dispersal, and catastrophes, and combined these parameters with the spatial structure to build a stage‐structured, stochastic, spatially‐explicit metapopulation model. The model predicted a fast decline and high risk of population extinction with most combinations of parameters. Results were most sensitive to density‐dependent effects, the probability of weather‐related catastrophes, adult survival, and adult fecundity. Based on data used in the model, the greatest difference in results was given when the simulation’s time horizon was only a few decades, suggesting that modeling based on longer or shorter time horizons may underestimate the effects of alternative management actions.
Disappearance and Return of Plethodontid Salamanders to Clearcut Plots in the Southern Blue Ridge Mountains
Authors: Ash Andrew N.
Published: March 2003

The disappearance and return of plethodontid salamanders on clearcuts has been monitored since 1979 in the southern Blue Ridge Mountains at three sites near Highlands, North Carolina. Salamander abundance on 225 m2 plots located on clearcuts and in nearby forest was determined by nightly non‐destructive searches. Abundances on clearcut and forest plots at a given site were compared for each year in which sampling occurred. Numbers of salamanders on clearcut plots decreased to 30–50% of forested plots in the first year after logging and were almost zero by the second year. Decreases in standing crop and moisture content of leaf litter seem responsible for salamander disappearance. Salamanders returned to clearcuts 4–6 years after cutting, and their numbers increased rapidly. Linear regressions estimate that salamander numbers on clearcut plots will equal or exceed numbers on forested plots by 20–24 years after cutting. The pattern of salamander return to clearcuts appears closely correlated with the timing of litter layer reformation. All sex and age classes of the most common species, Plethodon jordani, disappear from clearcuts at equal rates, whereas the earliest colonizers are predominantly large adults. Plethodon oconaluftee, a desiccation‐resistant species, exists on regenerating clearcuts in disproportionately large numbers. Large adults of all species, including Plethodon oconaluftee, may be better able to withstand the drier, sparse litter cover of young, regenerating stands. Adults might move to clearcuts to avoid competition from smaller and immature salamanders restricted to mature forests with abundant, moist litter.
Extinction of a Species of Land Snail Due to Infection with a Microsporidian Parasite
Authors: Cunningham Andrew A. , Daszak Peter
Published: March 2003

Snails of the genus Partula are highly endangered, with many species occurring solely in captivity. Captive populations experience periodic crashes, some of which have resulted in extinction. Pathologic investigations of the last individuals of a species that had undergone such a crash (Partula turgida) showed infection with a protozoan parasite as the cause of death. The parasite was identified as a member of the microsporidian genus Steinhausia, other members of which are known to cause mortality in aquatic pulmonate snails. We believe this is the first definitive report of an infectious disease causing the extinction of a species.

 Extinción de una especie de Caracol Terrestre Debido a una Infección por un Parásito Microsporidio 

Los caracoles del género Partula estan altamente amenazados junto con muchas especies existiendo únicamente en cautividad. Las poblaciones cautivas experimentan colapsos periódicos, algunos de los cuales han resultado en extinciones. Investigaciones patológicas de los últimos individuos de una especie que ha pasado por este tipo de colapso (Partula turgida) muestran infecciones de un protozoario parásito como la causa de su muerte. El parásito ha sido identificado como un miembro del género Steinhausia, otros miembros de este género han sido identificados como los causantes de mortalidades en caracoles pulmonados acuáticos. Creemos que este es un reporte definitivo de una enfermedad infecciosa causante de la extinción de una especie.
Functional Ecosystems and Biodiversity Buzzwords
Authors: Goldstein Paul Z.
Published: March 2003

Abstract:Several increasingly popular paradigms in conservation remove organismal information and life‐history requirements from management planning with claims that species‐specific information is not necessary to the understanding and management of “ecosystem function” and may therefore be discarded. Although several authors have called attention to the fact that ecosystem management has not yet been articulated sufficiently to comprise an adequate paradigm for wildlife protection, there has been a series of suggestions paralleling ecosystem management’s popularity that the perceived or imagined emergent properties of communities should be at the root of conservation planning. Such reductions most commonly take the form of abstracted species diversity measures that may be irrelevant or misleading with respect to site‐specific planning and to the monitoring of specific management treatments. Following earlier examinations of ecosystem management, I emphasize that several of its apparent outgrowths may be too vague to inform specific recommendations, that the historical mechanics of “ecosystem processes” are essentially unknowable, and that anecdotal definitions of ecosystems allow one to justify virtually any protocol as management. The primacy of process‐dependent, landscape‐functional considerations in conservation planning is specious in the absence of species‐ and population‐specific information, which should form the foundation for understanding such processes in the first place. Only by viewing nature in terms of the relationships between processes and organisms, rather than in terms of emergent properties of organismal assemblages or abiotic factors divorced from organismal data, can conservation plans claim to protect biological elements.
Nesting Success of Neotropical Migrant Songbirds in a Highly Fragmented Landscape
Authors: Friesen Lyle , Cadman Michael D. , MacKAY R. Jock
Published: March 2003

Abstract:Small forests in agricultural landscapes are generally thought to be population sinks where the nesting success of Neotropical migrant songbirds is too low to sustain populations. In 1996 and 1997, we assessed the nesting success and productivity of Wood Thrushes ( Hylocichla mustelina) and Rose‐breasted Grosbeaks ( Pheucticus ludovicianus) in the Region of Waterloo, a highly fragmented agricultural landscape with 14% forest cover in southwestern Ontario. We located 154 Wood Thrush nests and 63 Rose‐breasted Grosbeak nests in 26 small forest fragments (3–14 ha) and 15 large fragments (26–140 ha). We used the Mayfield method to determine nesting success. Across all sites nesting success was 51% for Wood Thrushes and 46% for Rose‐breasted Grosbeaks. Nesting success and productivity rates were used in a simple population growth model that suggested that the Wood Thrushes but not the Rose‐breasted Grosbeaks were a self‐sustaining population. Forest size and distance of nests to the nearest forest edge (measured in five distance classes ranging from 0 to over 100 m) did not significantly affect the nesting success or productivity of either species. Brown‐headed Cowbirds (  Molothrus ater) parasitized 47% of all Wood Thrush nests and 10% of all Rose‐breasted Grosbeak nests; parasitism significantly reduced Wood Thrush productivity but not that of Rose‐breasted Grosbeaks. Our findings challenge the prevailing notion that small woodlots in a farmed landscape are invariably habitat sinks and offer additional incentive for habitat protection in settled landscapes where small forest fragments are often all that remain for conservation purposes.
The Role of Guesswork in Conserving the Threatened Sand Skink
Authors: McCoy Earl D. , Sutton Phillip E. , Mushinsky Henry R.
Published: March 2003

Because we possess little understanding of what constitutes optimal habitat for the threatened sand skink, any individual charged with choosing among habitat fragments to promote recovery of the species will need to employ some guesswork. We examined the relative values of employing two kinds of guesswork, “uneducated guesswork,” from literature descriptions of optimal habitat, and “educated guesswork,” from expert judgments of optimal habitat. The rank order of seven areas of scrub habitat in central Florida based on abundance of the sand skink (Neoseps reynoldsi) was compared with the rank order of the areas based on literature descriptions and on expert judgments. Ranks of areas based on expert judgments predicted ranks of areas based on sand skink abundance much better than did ranks of areas based on literature descriptions. Our results show, on the one hand, how uneducated guesswork could challenge recovery of the sand skink and, on the other hand, how educated guesswork could support its recovery.
Hybridization between Wolves and Dogs
Authors: Vilà Carles , Wayne Robert K.
Published: March 2003

Concern has been expressed that European populations of gray wolves (Canis lupus) have extensively hybridized with domestic dogs (C. familiaris). We reviewed and analyzed surveys of mitochondrial and biparentally inherited genetic markers in dogs and wild populations of wolf‐like canids. Although dog‐wolf hybrids have been observed in the wild, significant introgression of dog markers into wild wolf populations has not yet occurred. Our investigation suggests that hybridization may not be an important conservation concern even in small, endangered wolf populations near human settlements. The behavioral and physiological differences between domestic dogs and gray wolves may be sufficiently great such that mating is unlikely and hybrid offspring rarely survive to reproduce in the wild.
Mechanisms of Reduced Trillium Recruitment along Edges of Old‐Growth Forest Fragments
Authors: Jules Erik S. , Rathcke Beverly J.
Published: March 2003

Abstract: Studies of plants in fragmented habitats have focused on single ecological processes, such as seed production or seed dispersal, that may be altered by increased fragmentation and that operate as the mechanism(s) that increase extinction probability. We examined a suite of potential mechanisms to explain demographic shifts toward extinction in populations of Trillium ovatum, a long‐lived herbaceous perennial found in the understory of western North American conifer forests. Past work has shown that populations of T. ovatum found within ∼65 m of forest‐clearcut edges in southwestern Oregon have had almost no new recruitment since the edges were formed. We hypothesized that changes in abiotic conditions and biotic interactions present along edges are responsible for reduced recruitment. In eight populations in eight separate fragments, we evaluated the relationship of distance of the populations to the forest edge with respect to six processes: flowering phenology (timing), seed production, pollination‐ and resource‐limitation of seed set, seed dispersal, seed predation, and germination. Those factors that showed a significant relationship with edge distance were then compared with recruitment of younger age classes. Two processes were significantly different near edges and were highly correlated with decreased recruitment: decreased seed production due to changes in pollination and increased seed predation by rodents. Our study (in conjunction with previous studies) suggests that several ecological processes show no significant relationship with edge distance and can be eliminated as possible mechanisms of reduced recruitment: flowering phenology, resource‐limitation of seed set, seed dispersal, germination, herbivory, and survivorship of established plants. Edges influence some but not all components of a plant's life history. Thus, determining shifts in only one part of a life history will be inadequate for testing the prediction of increasing extinction probabilities in fragmented landscapes. Future studies should include enough information to conduct comprehensive analyses, such as matrix projections and sensitivity analyses.
Long‐Term Changes in the Avifauna of Barro Colorado Island, Panama, a Tropical Forest Isolate
Authors: Robinson W. Douglas
Published: March 2003

Since its isolation from the mainland more than 85 years ago, 65 bird species have disappeared from Barro Colorado Island, Panama. Because of these extinctions the island is often used as a model for the study of faunal relaxation, or loss of species through time. The most recent survey of the island’s bird community was completed in 1970. Between June 1994 and May 1996 I surveyed the island and observed 218 species, including 5 species never before recorded. Three relatively sedentary species have experienced severe population declines since Willis’s 1970 survey and may be on the brink of disappearing from the island. Willis estimated 500 Slate‐colored Grosbeaks (Pitylus grossus), whereas I found only two pairs of this conspicuous midstory‐dwelling finch. Two cotingas—Speckled Mourner (Laniocera rufescens) and Rufous Piha (Lipaugus unirufus)—have declined by 85–95%. I did not locate any individuals of 36 other species that were present during the 1970s. Most (21) of these are uncommon aquatic or nocturnal species, which I may have missed during my surveys, or are rare to uncommon edge species that probably move frequently to and from the island. Seven species, however, are primarily inhabitants of second‐growth forest and have been lost probably because of continuing successional maturation of the forest, including changes in land use around the laboratory clearing. Seven forest‐dwelling species disappeared during the 1970s and have not recolonized. I detected only one sedentary forest‐dwelling species, Great Currasow (Crax rubra), that previously had been reported as missing from the island. The nearly complete lack of recolonizations by such forest‐interior species suggests that local extinction from tropical forest isolates may be extremely persistent. Tropical forest reserves as small as Barro Colorado Island (1600 ha) may not preserve high levels of regional avian diversity over long periods of time.
Plethodontid Salamander Response to Silvicultural Practices in Missouri Ozark Forests
Authors: Herbeck Laura A. , Larsen David R.
Published: March 2003

Abstract:
There is little information on the effects of tree harvest on salamander populations in the midwestern United States. We present data on plethodontid salamander densities in replicated stands of three forest age classes in the southeastern Ozarks of Missouri. Forest age classes consisted of regeneration‐cut sites <5 years old, second‐growth sites 70–80 years old, and old‐growth sites> 120 years old. Salamander abundance on 21, 144‐m2 plots was determined by area‐ and time‐constrained searches. We also compared age‐class habitat characteristics, including downed woody debris, canopy cover, ground area cover, herbaceous vegetation, and woody vegetation. Salamander density was lowest in newly regenerated forests and highest in forests> 120 years old. Comparisons of recently regenerated forests with mature forests> 70 years old indicated that terrestrial salamanders were reduced to very low numbers when mature forests had been intensively harvested. This reduction may result from a decrease in microhabitat availability. Forest age‐class comparisons further indicated that salamander abundance slowly increased over time after forests had regenerated. Management decisions that take into account plethodontid salamander abundance and their response to forest structural diversity are important components in sustaining ecosystem integrity while maximizing economic yield.
Temporal Changes in Allele Frequencies Provide Estimates of Population Bottleneck Size
Authors: Luikart Gordon , Cornuet Jean‐Marie , Allendorf Fred W.
Published: March 2003

Abstract:Monitoring temporal changes in genetic variation can provide estimates of effective population size (  Ne  ) that are useful for detecting population bottlenecks. We used Monte Carlo computer simulations to quantify the bias and precision of theNeestimates obtained from temporal changes in allele frequencies at allozyme and microsatellite loci. The estimates ofNeoverestimated the trueNeby 12–200% after 1–10 generations of a bottleneck of effective size 4. This magnitude of bias, however, is not likely to cause bottlenecks to go undetected or to cause misguided management recommendations. The bias was nearly negligible for bottlenecks of effective size ≥10, until approximately five bottleneck generations had passed. Three causes of the bias are the loss of alleles, the assumption that the increase in variance in allele frequencies with time is additive (instead of multiplicative), and the assumption that selfing can occur when it cannot. We derived a new equation that substantially reduces the bias. The precision ofNeestimates was sufficient that, when trueNewas 4, the 95% confidence interval bracketing aNeestimate was <25 in 95% of 500 simulations (when only five microsatellite loci were monitored and when 30 individuals were sampled with a sampling interval of one generation). When the trueNewas 20, however, only 80% of the confidence intervals were <50 when we sampled 45 individuals and 20 microsatellite loci (i.e., loci with five alleles). High power to detect a bottleneck of effective size 4 can be achieved by monitoring only five microsatellite loci having five alleles each and sampling 30 individuals with a sampling interval of one generation. But achieving high power to detect bottlenecks of sizeNe= 20 requires approximately 20 polymorphic microsatellite loci and 45 individuals with a one‐generation sampling interval.
Estuarine Vegetated Habitats as Corridors for Predator Movements
Authors: Micheli Fiorenza , Peterson Charles H.
Published: March 2003

Abstract: The spatial proximity of one habitat to another can strongly influence population and community dynamics. We investigated whether the proximity of intertidal oyster reefs to vegetated estuarine habitats, salt marshes, and seagrass beds, affects the abundance and community structure of benthic macroinvertebrates on reefs and predator‐prey interactions between mobile predators and bivalves living on reefs. Benthic macroinvertebrate abundance was highest on reefs spatially separated from salt marshes. Macroinvertebrate species richness was highest on reefs separated from both salt marshes and seagrass beds. Comparisons of predation on juvenile bivalves transplanted to reefs for 7–12 days indicated that survivorship of clams was greatest on reefs spatially separated from both salt marshes and seagrass beds, whereas reef proximity to vegetated habitats did not affect the survivorship of oysters. The foraging behavior of blue crabs may explain patterns of macroinvertebrate abundance and clam survivorship among reefs with different proximity to vegetated habitats. In experiments conducted in 30‐m2 field enclosures, blue crabs had higher predation rates on hard clams transplanted onto artificial reefs adjacent to salt marshes or seagrass beds than on reefs separated from both habitats by unvegetated sand bottom. Thus, vegetated habitats appeared to act as corridors by facilitating the access of blue crabs to oyster reefs and enhancing the intensity of blue crab predation. Such an understanding of the effects of landscape characteristics of estuarine habitats on their value as habitats for estuarine organisms can be used to predict the consequences of habitat fragmentation on ecosystem function and to improve strategies for habitat and species conservation and restoration.
Erosion of Heterozygosity in Fluctuating Populations
Authors: Vucetich John A. , Waite Thomas A.
Published: March 2003

Abstract: Demographic, environmental, and genetic stochasticity threaten the persistence of isolated populations. The relative importance of these intertwining factors remains unresolved, but a common view is that random demographic and environmental events will usually drive small populations to the brink of extinction before genetic deterioration poses a serious threat. To evaluate the potential importance of genetic factors, we analyzed a model linking demographic and environmental conditions to the loss of genetic diversity in isolated populations undergoing natural levels of fluctuation. Nongenetic processes—environmental stochasticity and population demography—were modeled according to a bounded diffusion process. Genetic processes were modeled by quantifying the rate of drift according to the effective population size, which was predicted from the same parameters used to describe the nongenetic processes. We combined these models to predict the heterozygosity remaining at the time of extinction, as predicted by the nongenetic portion of the model. Our model predicts that many populations will lose most or all of their neutral genetic diversity before nongenetic random events lead to extinction. Given the abundant evidence for inbreeding depression and recent evidence for elevated extinction rates of inbred populations, our findings suggest that inbreeding may be a greater general threat to population persistence than is generally recognized. Therefore, conservation biologists should not ignore the genetic component of extinction risk when assessing species endangerment and developing recovery plans.
Genetic Diversity, Population Size, and Fitness in Central and Peripheral Populations of a Rare Plant Lychnis viscaria
Authors: Lammi Antti , Siikamäki Pirkko , Mustajärvi Kaisa
Published: March 2003

Abstract: Genetic diversity is expected to decrease in small and isolated populations as a consequence of bottlenecks, founder effects, inbreeding, and genetic drift. The genetics and ecology of the rare perennial plant Lychnis viscaria (Caryophyllaceae) were studied in both peripheral and central populations within its distribution area. We aimed to investigate the overall level of genetic diversity, its spatial distribution, and possible differences between peripheral and central populations by examining several populations with electrophoresis. Our results showed that the level of genetic diversity varied substantially among populations (  Hexp = 0.000–0.116) and that the total level of genetic diversity (mean Hexp = 0.056) was low compared to that of other species with similar life‐history attributes. The peripheral populations of L. viscaria had less genetic variation (mean Hexp = 0.034) than the central ones (0.114). Analysis of genetic structure suggested limited gene flow (mean FST = 0.430) and high differentiation among populations, emphasizing the role of genetic drift (  Nem = 0.33). Isolation was even higher than expected based on the physical distance among populations. We also focused on the association between population size and genetic diversity and possible effects on fitness of these factors. Population size was positively correlated with genetic diversity. Population size and genetic diversity, however, were not associated with fitness components such as germination rate, seedling mass, or seed yield. There were no differences in the measured fitness components between peripheral and central populations. Even though small and peripheral populations had lower levels of genetic variation, they were as viable as larger populations, which emphasizes their potential value for conservation.
On the Use of Surrogate Species in Conservation Biology
Authors: Caro T. M. , O'Doherty Gillian
Published: March 2003

Abstract: Conservation biologists have used surrogate species as a shortcut to monitor or solve conservation problems. Indicator species have been used to assess the magnitude of anthropogenic disturbance, to monitor population trends in other species, and to locate areas of high regional biodiversity. Umbrella species have been used to delineate the type of habitat or size of area for protection, and flagship species have been employed to attract public attention. Unfortunately, there has been considerable confusion over these terms, and several have been applied loosely and interchangeably. We attempt to provide some clarification and guidelines for the application of these different terms. For each type of surrogate, we briefly describe the way it has been used in conservation biology and then examine the criteria that managers and researchers use in selecting appropriate surrogate species. By juxtaposing these concepts, it becomes clear that both the goals and selection criteria of different surrogate classes differ substantially, indicating that they should not be conflated. This can be facilitated by first outlining the goals of a conservation study, explicitly stating the criteria involved in selecting a surrogate species, identifying a species according to these criteria, and then performing a pilot study to check whether the choice of species was appropriate before addressing the conservation problem itself. Surrogate species need to be used with greater care if they are to remain useful in conservation biology.
Population Density as a Predictor of Genetic Variation for Woody Plant Species
Authors: Gram Wendy K. , Sork Victoria L.
Published: March 2003

Abstract:As the focus of conservation biology shifts toward multispecies and ecosystem conservation and management, a principal question becomes how we manage species to conserve their long‐term evolutionary potential. Few criteria exist for prioritizing which populations within a species should be protected to conserve maximal genetic variation. We designed this study to explore the genetic consequences of using population density as a criterion for selecting populations of woody plant species for conservation. Population density may be an effective gauge of genetic variation for two reasons. First, density often reflects ecological population size, particularly for continuously distributed species, and density is much easier to measure in the field than population size. Second, from an individual species' perspective, population density may be an indicator of habitat quality. We evaluated the relationship between standard genetic diversity indices and densities of seedlings, small trees, and large trees, and we investigated the association between genotypic composition and density measures with canonical correlation analysis for three common tree species (Carya tomentosa, Sassafras albidum, andQuercus alba) from the Missouri Ozarks. We found that population density was not correlated with genetic diversity in large populations of plant species, but density was associated with genotypic composition of populations. That is, populations with small densities had different genotypes than those with large densities. To sample a maximal amount of regional genotypic variation, we recommend choosing plant populations representing a range of densities. Findings from our study should be generally applicable to plant populations that have occupied habitats long enough for natural selection to affect local genotypic composition. Used in conjunction with other established criteria, population density may be a useful rule of thumb for conservation practitioners concerned with the maintenance of adaptive genetic variation in plant species.
Ecological Interactions, Social Organization, and Extinction Risk in African Wild Dogs
Authors: Vucetich John A. , Creel Scott
Published: March 2003

Abstract: The conservation of wild dogs depends on the persistence of small populations because African wild dog ( Lycaon pictus) populations are low in density, are limited by range loss, and are often restricted to parks containing fewer than 100 adults. Although major limiting factors for wild dog populations have been identified, including interspecific competition and diseases, such factors have not been translated into extinction risk. To assess wild dog extinction risks, we used individual‐based simulations constructed from data from a 6‐year field study in the Selous Game Reserve, Tanzania. Our simulations predicted that extinction risk for wild dogs was extremely sensitive to competition with lions. Extinction rates (  for periods as short as 20 years) rose sharply to near 1.0 when lion populations exceeded moderate densities (approximately 110–140 lions/1000 km2). This prediction is remarkably consistent with, and highlights, ecological processes that may be responsible for recent patterns of extinction among wild dog populations. Infectious diseases that kill adults, such as rabies, also reduced population persistence if they increased mortality by ≥0.3 and occurred at average intervals of ≤10 years. In contrast, diseases killing only pups, such as canine parvovirus, had weaker effects on persistence. Although persistence declined sharply for mean litter sizes ≤6, persistence was unaffected by increasing mean litter size above its normal range (i.e., 8–12 in Selous). Increasing mean pack size from typical levels reduced extinction risk, but reproductive suppression may set an upper limit on pack size. Although the risk of extinction for 20‐ to 100‐year time frames was appreciable for many realistic ecological and demographic conditions, even low immigration rates substantially increased persistence probabilities. Active management to mitigate the effects of interspecific competition, facilitate dispersal among populations, or augment population size appears essential for wild dog conservation.
Extinction Rates of North American Freshwater Fauna
Authors: Ricciardi Anthony , Rasmussen Joseph B.
Published: March 2003

Abstract: Since 1900, 123 freshwater animal species have been recorded as extinct in North America. Hundreds of additional species of fishes, mollusks, crayfishes, and amphibians are considered imperiled. Using an exponential decay model, we derived recent and future extinction rates for North American freshwater fauna that are five times higher than those for terrestrial fauna. Assuming that imperiled freshwater species will not survive throughout the next century, our model projects a future extinction rate of 4% per decade, which suggests that North America's temperate freshwater ecosystems are being depleted of species as rapidly as tropical forests.
Season‐Long Fecundity, Survival, and Viability of Ovenbirds in Fragmented and Unfragmented Landscapes
Authors: Porneluzi Paul A. , Faaborg John
Published: March 2003

Abstract:From 1992–1995, we compared the season‐long fecundity of marked Ovenbirds ( Seiurus aurocapillus) on three sites in large ( >2000‐ha) forest patches in a fragmented landscape in central Missouri (U.S.A.) with four sites in a contiguously forested landscape of almost 2 million ha in the Missouri Ozarks. Our purpose was to determine to what extent the negative effects of fragmentation on nests affect individual bird's annual productivity. To measure annual productivity, we determined the proportion of territorial males that ultimately succeeded in raising young in a season and multiplied this proportion by the average brood size obtained from nest observations. Fewer pairs successfully raised young in the fragmented landscape (50 ± 11%) than in the unfragmented landscape (70 ± 7%). In the fragmented landscape, 25 ± 6% of pairs raised at least one Brown‐headed Cowbird ( Molothrus ater), whereas only 1 ± 1% of pairs raised cowbirds in the unfragmented landscape. Lower season‐long success and increased brood parasitism led to annual productivity of 0.70 and 1.47 juvenile females per female in the fragmented and unfragmented landscapes, respectively. Territory size (mean = 2.76 ha) was not affected by landscape, but density was lower in the fragmented landscape (1.6 ± 0.41 males per 10 ha) than in the unfragmented landscape (2.2 ± 0.32). The ratio of second‐year to after‐second‐year males did not vary with landscape. Male pairing success (67 ± 6%) and survival (0.621 ± 0.21) was not affected by landscape. We concluded that it was unlikely that sites in the fragmented landscape contained viable Ovenbird source populations, whereas populations in the unfragmented Ozark region were likely to be sources in most years. Nevertheless, any changes in the Ozarks that increase nest predation or parasitism may have consequences for the regional population of Ovenbirds and other forest‐breeding Neotropical migrants in the midwest.
Gray Whales and the Value of Monitoring Data in Implementing the U.S. Endangered Species Act
Authors: Gerber Leah R. , Demaster Douglas P. , Kareiva Peter M.
Published: March 2003

Abstract: Many scientists lament the absence of data for endangered species and argue that more funds should be spent acquiring basic information about population trends. Using 19 years of abundance estimates for the eastern North Pacific gray whale (Eschrichtius robustus), we sampled subsets of the original survey data to identify the number of years of data required to remove the population from the U.S. Endangered Species Act's (ESA) list of endangered and threatened wildlife. For any given duration of monitoring, we selected all possible combinations of consecutive counts. To incorporate variability in growth rates, we extracted a maximum likelihood estimator of growth rate and confidence interval about that growth rate on the assumption that the population changes can be approximated by a simple diffusion process with drift. We then applied a new approach to determine ESA status for each subset of survey data and found that a quantitative decision to delist is unambiguously supported by 11 years of data but is precariously uncertain with fewer than 10 years of data. The data needed to produce an unequivocal decision to delist gray whales cost the National Marine Fisheries Service an estimated U.S. $660,000, a surprisingly modest expense given the fact that delisting can greatly simplify regulatory constraints. This example highlights the value of population monitoring in administering the ESA and provides a compelling example of the utility of such information in identifying both imperiled and recovered species. The economic value of such data is that they provide the foundation for delisting, which could ultimately save much more money than the collection of the data would ever cost.
An Experiment Testing whether Condition and Survival are Limited by Food Supply in a Reintroduced Hihi Population
Authors: Armstrong Doug P. , Perrott John K.
Published: March 2003

Abstract: The Hihi (Stitchbird, Notiomystis cincta) is an endemic New Zealand honeyeater that after European colonization survived on only one offshore island. Attempts to reintroduce Hihi to other islands have been unsuccessful, with populations slowly declining. The main hypothesis for these declines was an inadequate year‐round supply of carbohydrate food (nectar and fruit) due to human impacts on the forest habitat. When Hihi were reintroduced to Mokoia, another island with regenerating forest, we tested whether survival was limited by carbohydrate food in the year after release. We conducted an “on‐off” experiment in which ad libitum sugar water was available to birds for 2 out of every 4 weeks. We compared the masses of individual birds at the end of on and off periods to identify times when birds lost condition with no supplementary food and would be likely to starve. We also used mark‐recapture analysis of resighting data to test whether mortality rates were higher when supplementary food was unavailable. The only effect of the supplementary food was that Hihi spent less time foraging for nectar and fruit and more time foraging for invertebrates. There was no time of year when birds lost mass when the food was taken away, and survival rates were not significantly lower when supplementary food was absent. The low (38%) annual survival rate could not be accounted for by shortage of carbohydrate food, and population viability analysis suggests that the population is likely to slowly decline. Our experiment shows that declines of reintroduced Hihi populations may be unrelated to food supply and that alternative hypotheses should be developed and tested. Our results also show the importance of using experimental methods, when possible, to test hypotheses about factors thought to be limiting reintroduced populations.
Single Species as Indicators of Species Richness and Composition in California Coastal Sage Scrub Birds and Small Mammals
Authors: Chase Mary K. , Kristan William B. , Lynam Anthony J. , Price Mary V. , Rotenberry John T.
Published: March 2003

Abstract: Individual species may be useful as indicators of biodiversity if an association exists between the presence of a species and another component of biodiversity. We evaluated 40 species of birds and small mammals, including 11 species of conservation concern, as potential indicators of species richness and species composition in southern California coastal sage scrub habitats. This habitat, which is the target of large‐scale conservation planning, has been greatly reduced by human development and supports many plants and animals of conservation concern. We asked whether there is an association between the presence of a potential indicator species and the species richness and composition of the bird or small‐mammal community in which it is found. We used point counts and live‐trapping to quantify the distribution of birds and small mammals, respectively, at 155 points in 16 sites located in three counties. Of the few species we found associated with species richness, some were associated with higher species richness and others with lower richness, and species of conservation concern were not more frequently associated with species richness than were common species. Ordination analysis revealed a geographic gradient in coastal sage scrub bird and small‐mammal species composition across southern California, and 18 of the species we evaluated were associated with the composition of the bird and small‐mammal community in which they were found. Our results suggest that efforts to conserve bird and small‐mammal biodiversity in coastal sage scrub should not focus exclusively on rare species or on locations with the highest species richness, but instead should focus on a diverse suite of species that are representative of the range of variation in communities found in coastal sage scrub habitats.
Functional Equivalency between Rice Fields and Seminatural Wetland Habitats
Authors: Elphick Chris S.
Published: March 2003

Abstract:Evaluating the potential for anthropogenic habitats to act as surrogates for the natural habitats they replace is a key issue in conservation biology. In California, flooded rice fields are used by numerous aquatic birds during winter. If this habitat functions similarly to more natural wetlands, increased flooding may help replace the extensive wetlands that occurred in the region prior to agricultural development. I tested whether food abundance, perceived predation threat, foraging performance, and the way in which birds allocate their time to different behaviors differed between flooded rice fields and seminatural wetlands for several species of aquatic bird. When appropriate, I also compared flooded and unflooded fields. Invertebrate densities did not differ among habitats. Seminatural wetlands had less rice grain but more seeds from other plants than the two rice habitats. The frequency with which predators passed over a feeding area was lower in flooded fields than in unflooded fields or seminatural wetlands. Most differences in feeding performance and time allocation among habitats were small and statistically insignificant. For some species, feeding efficiency was greater in seminatural wetlands than in flooded fields. Increasing attack rates and the amount of time spent feeding when in flooded fields, however, may allow birds to compensate for reduced efficiency. Multivariate analyses showed that group size, predation threat, time of day, date, and water depth often were associated with behaviors, but that these variables rarely accounted for habitat differences. Flooded fields apparently provide equivalent foraging habitat to seminatural wetlands and, because of reduced predation threat, may be a safer habitat for waterbirds. Thus, if managed appropriately, one of the world's dominant forms of agriculture can provide valuable waterbird habitat.
Fragmentation of Landscape as a Cause for Genetic Subdivision in Bank Voles
Authors: Gerlach Gabriele , Musolf Kerstin
Published: March 2003

Abstract: We studied the barrier effects of various roadways on the genetic subdivision of bank vole (Clethrionomys glareolus) populations. Allele frequencies, genetic variability, and genetic distances of natural populations were calculated based on polymorphism of seven microsatellite markers. We compared bank vole populations in control areas without such barriers with animals from both sides of a country road, a railway, and a highway. Using F and R statistics, we demonstrated significant population subdivision in bank vole populations separated by the highway, but not in populations on either side of the other roadways or in the control area. Correlations between geographic and genetic distances were revealed by an extended method based on a Mantel analysis. This allowed us to measure genetic barrier effects and express them as additional geographic distances. For instance, statistically significant differences in allele frequencies in all seven loci examined existed among populations in southern Germany and Switzerland, which are separated by the Rhine River and Lake Constance. The real geographic distance between bank vole populations in Konstanz and those in Lengwil, Switzerland, was 6 km. According to this analysis the genetic barrier effect of the Rhine could be defined as an additional distance of 7.7 km. This study shows for the first time that not only old geographic barriers but also more recent fragmentation of landscape by, for example, highways has an important effect on gene flow and the genetic substructuring of populations, which should be considered in future environmental impact assessments.
Influence of Landscape Scale on Farmland Birds Breeding in Semi‐Natural Pastures
Authors: Söderström Bo , Pärt Tomas
Published: March 2003

Abstract: Little attention has been paid to fragmentation effects on organisms living in open habitats in which species may have high mobility and generalized habitat use. We investigated landscape effects on 23 farmland bird species breeding in 72 semi‐natural dry pastures distributed equally among three landscape types (agricultural‐dominated, mosaic, and forest‐dominated) in southcentral Sweden. There were generally higher local abundances of farmland birds in pastures located in agricultural‐dominated and mosaic landscapes than in forest‐dominated landscapes. Species feeding on a mixed diet as well as resident species and temperate migrants were most numerous in pastures located in agricultural‐dominated landscapes and least numerous in forest‐dominated landscapes. While controlling for the effects of local pasture area and vegetation structure, we found that the local abundance of 18 ( 78%) farmland bird species was significantly associated with the composition and structure of the surrounding landscape. The landscape distance that explained the largest part of local variation in abundance varied among species according to the size of their breeding territories or foraging home ranges. Our results suggest that habitat use of farmland birds breeding in pastures is affected both by suitable foraging habitats in the surrounding landscape and by nest sites within local pastures. Despite the generally higher abundances of farmland birds in pastures located in agricultural‐dominated landscapes, most species of European and Swedish conservation concern had higher abundance in pastures located in more forested landscapes. Thus, the rapid loss of semi‐natural dry pastures in forest‐dominated landscapes is a serious threat to the future of these species in Sweden.