Habitat destruction has driven many once-contiguous animal populations into remnant patches of varying size and isolation. The underlying framework for the conservation of fragmented populations is founded on the principles of island biogeography, wherein the probability of species occurrence in habitat patches varies as a function of patch size and isolation. Despite decades of research, the general importance of patch area and isolation as predictors of species occupancy in fragmented terrestrial systems remains unknown because of a lack of quantitative synthesis. Here, we compile occupancy data from 1,015 bird, mammal, reptile, amphibian, and invertebrate population networks on 6 continents and show that patch area and isolation are surprisingly poor predictors of occupancy for most species. We examine factors such as improper scaling and biases in species representation as explanations and find that the type of land cover separating patches most strongly affects the sensitivity of species to patch area and isolation. Our results indicate that patch area and isolation are indeed important factors affecting the occupancy of many species, but properties of the intervening matrix should not be ignored. Improving matrix quality may lead to higher conservation returns than manipulating the size and configuration of remnant patches for many of the species that persist in the aftermath of habitat destruction.incidence function ͉ island biogeography ͉ logistic regression ͉ metaanalysis ͉ occupancy H abitat loss and fragmentation are major threats to terrestrial biodiversity (1). Globally, Ϸ40% of land has been converted for agricultural use (2), and regions as diverse as the eastern United States, the Philippines, and Ghana have lost Ͼ90% of their natural habitat (3, 4). Conservation theory and practice are founded on the principle that large habitat patches have more species than small ones and connected patches have more species than isolated ones (5). Although few would dispute this basic premise, we still do not know the general value of patch area and isolation as predictors of species occupancy in fragmented terrestrial systems. Despite hundreds of patch occupancy studies over Ͼ4 decades, there has been no quantitative synthesis of these findings. Several syntheses have examined species-area and diversity relationships (6, 7), but the species occupancy patterns that underlie diversity patterns in fragmented landscapes have been overlooked (8). How important is patch isolation relative to patch size in determining where species occur, and how consistent are these effects across diverse taxonomic groups? These are foundational, yet unanswered, questions for ecology and conservation biology.We synthesized patch occupancy data from 89 studies of terrestrial fauna on 6 continents (Table S1) to determine how patch area and isolation affect species' occurrence patterns. Collectively, these studies recorded the occurrence of 785 animal species (Table 1) in 1,015 population networks surveyed in 12,370 discrete habitat p...

Aim Elucidating patterns in species responses to habitat fragmentation is an important focus of ecology and conservation, but studies are often geographically restricted, taxonomically narrow or use indirect measures of species vulnerability. We investigated predictors of species presence after fragmentation using data from studies around the world that included all four terrestrial vertebrate classes, thus allowing direct inter-taxonomic comparison.Location World-wide.Methods We used generalized linear mixed-effect models in an information theoretic framework to assess the factors that explained species presence in remnant habitat patches (3342 patches; 1559 species, mostly birds; and 65,695 records of patch-specific presence-absence). We developed a novel metric of fragmentation sensitivity, defined as the maximum rate of change in probability of presence with changing patch size ('Peak Change'), to distinguish between general rarity on the landscape and sensitivity to fragmentation per se.Results Size of remnant habitat patches was the most important driver of species presence. Across all classes, habitat specialists, carnivores and larger species had a lower probability of presence, and those effects were substantially modified by interactions. Sensitivity to fragmentation (measured by Peak Change) was influenced primarily by habitat type and specialization, but also by fecundity, life span and body mass. Reptiles were more sensitive than other classes. Grassland species had a lower probability of presence, though sample size was relatively small, but forest and shrubland species were more sensitive.Main conclusions Habitat relationships were more important than lifehistory characteristics in predicting the effects of fragmentation. Habitat specialization increased sensitivity to fragmentation and interacted with class and habitat type; forest specialists and habitat-specific reptiles were particularly sensitive to fragmentation. Our results suggest that when conservationists are faced with disturbances that could fragment habitat they should pay particular attention to specialists, particularly reptiles. Further, our results highlight that the probability of presence in fragmented landscapes and true sensitivity to fragmentation are predicted by different factors.

We counted fecal pellets of snowshoe hares (Lepus americanus) once a year in 10 areas in the southwestern Yukon from 1987 to 1996. Pellets in eighty 0.155-m 2 quadrats were counted and cleared each June on all areas, and we correlated these counts with estimates of absolute hare density obtained by intensive mark-recapture methods in the same areas. There is a strong relationship between pellet counts and population density (r = 0.76), and we present a predictive log-log regression to quantify this relationship, which improves on our previously published 1987 regression, particularly at low hare densities. The precision of density estimates can be improved most easily by increasing the number of sets of quadrats in an area (one set = 80 plots), rather than increasing the number of plots counted within one set. The most important question remaining concerns the generality of this relationship for snowshoe hares living in other habitats in the eastern and southern portions of their geographic range.Résumé : Nous avons compté les boulettes fécales de Lièvres d'Amérique (Lepus americanus) une fois l'an en 10 zones du sud-ouest du Yukon, de 1987 à 1996. Les boulettes ont été comptées chaque juin, puis retirées, dans quatre-vingt quadrats de 0,155 m 2 dans chacune des zones; par la suite, ces nombres ont été mis en corrélation avec des estimations de la densité absolue des lièvres obtenues par des méthodes intensives de capture-recapture dans les mêmes zones. Il y a une forte corrélation entre le nombre de boulettes et la densité de la population (r = 0,76) et nous présentons ici une régression log-log prédictive pour quantifier cette relation, ce qui rend plus robuste la régression que nous avons publiée en 1987, particulièrement lorsque la densité des lièvres est faible. La précision des estimations de la densité peut être raffinée davantage en augmentant le nombre d'ensembles de quadrats dans une région (1 ensemble = 80 parcelles), plutôt que le nombre de parcelles dans chaque ensemble. Il reste à déterminer à quel point cette relation est gé-néralisée chez les lièvres qui vivent dans d'autres habitats dans les portions est et sud de leur répartition.[Traduit par la Rédaction] 4Krebs et al.

A genre of papers has arisen around the premise that ecological progress and communication with non‐specialists are impeded because (1) many ecological terms have multiple meanings and (2) many ecological terms have meanings similar to each other. There is a repeated call for ecological terminology to be standardized and for terms to be defined more concretely. These calls for the standardization of definitions are based on faulty premises about the way language conveys meaning. Most recommendations for definitional reform are unlikely to take hold due to properties of language and they are unlikely to stimulate increased ecological understanding. Precisely delimited definitions are necessary in very few instances, whereas extensive and prescriptive classification can hinder the development of a field by preventing some types of questions from being asked. Useful lexical reviews should focus on the development of ecological knowledge that is signaled by a wealth of terms and meanings, rather than critiquing the terms employed.

Snowshoe hares (Lepus americanus) undergo remarkable cycles and are the primary prey base of Canada lynx (Lynx canadensis), a carnivore recently listed as threatened in the contiguous United States. Efforts to evaluate hare densities using pellets have traditionally been based on regression equations developed in the Yukon, Canada. In western Montana, we evaluated whether or not local regression equations performed better than the most recent Yukon equation and assessed whether there was concordance between pellet‐based predictions and mark‐recapture density estimates of hares. We developed local Montana regression equations based on 224 data points consisting of mark‐recapture estimates and pellet counts, derived from 38 sites in 2 different areas sampled for 1 to 5 years using 2 different pellet plot shapes. We evaluated concordance between estimated density and predicted density based on pellet counts coupled with regression equations at 436 site‐area‐season combinations different from those used to develop the regression equations. At densities below 0.3 hares/ha, predicted density based on pellets tended to be greater than for mark‐recapture; the difference was usually <1 hare per ha on an absolute scale, but at low densities this translated to proportional differences of 1,000% or greater. At densities above 0.7 hares/ha, pellet regressions tended to predict lower density than mark‐recapture. Because local regression equations did not outperform the Yukon equation, we see little merit in further development of local regression equations unless a study is to be conducted in a formal double‐sampling framework. We recommend that widespread pellet sampling be used to identify areas with very low hare densities; subsequent surveys using mark‐recapture methodology can then focus on higher density areas where density inferences are more reliable.

Summary 1.Overwinter mass loss can reduce energetic requirements in mammals (Dehnel's phenomenon). Alternatively, mass loss can result from food limitation or high predation risk. 2. We use data from fertilizer, food-supplementation and predator-exclusion experiments in the Yukon during a population cycle from 1986 to 1996 to test the causes of overwinter mass loss by snowshoe hares ( Lepus americanus ). In all years, some hares on control sites gained mass overwinter. During the increase phase the majority gained mass, but in all other phases the majority lost mass. 3. Snowshoe hares weighing < 1000 g in autumn always gained mass overwinter, as did the majority that weighed 1000 -1400 g. Hares weighing > 1800 g in autumn usually lost mass. 4. Snowshoe hares on the predator-exclosure + food site gained mass overwinter in all years. Hares on the food-supplementation sites lost mass during the decline but gained mass in all other phases. Fertilization had little effect on mass dynamics. 5. Snowshoe hares were more likely to lose mass during winters with low survival rates. Snowshoe hares on the predator-exclosure treatments were more likely to gain mass than were hares on control sites. 6. Overwinter mass loss was correlated with maximum snow depth. At equivalent snow depths, hares on food-supplemented areas lost 98 g ( ± 14·6 SE) less on average than hares on the controls and predator-exclosure treatment. 7. Bone-marrow fat was related to body mass and cause of death. Small hares had the lowest marrow fat. Hares killed by humans had higher marrow fat than those killed by predators; hares that simply died had the lowest marrow fat. Hares on food-supplemented sites had the highest kidney and marrow fat. 8. Overwinter-mass loss for snowshoe hares is explained interactively by winter conditions, food supply, predation risk and autumn mass. Some snowshoe hares lost mass overwinter in all years and on all treatments, suggesting that reducing body mass may facilitate survival, especially in cases where foraging costs are high energetically or increase predation risk.

With climate warming, the ranges of many boreal species are expected to shift northward and to fragment in southern peripheral ranges. To understand the conservation implications of losing southern populations, we examined range-wide genetic diversity of the snowshoe hare (Lepus americanus), an important prey species that drives boreal ecosystem dynamics. We analysed microsatellite (8 loci) and mitochondrial DNA sequence (cytochrome b and control region) variation in almost 1000 snowshoe hares. A hierarchical structure analysis of the microsatellite data suggests initial subdivision in two groups, Boreal and southwestern. The southwestern group further splits into Greater Pacific Northwest and U.S. Rockies. The genealogical information retrieved from mtDNA is congruent with the three highly differentiated and divergent groups of snowshoe hares. These groups can correspond with evolutionarily significant units that might have evolved in separate refugia south and east of the Pleistocene ice sheets. Genetic diversity was highest at mid-latitudes of the species' range, and genetic uniqueness was greatest in southern populations, consistent with substructuring inferred from both mtDNA and microsatellite analyses at finer levels of analysis. Surprisingly, snowshoe hares in the Greater Pacific Northwest mtDNA lineage were more closely related to black-tailed jackrabbits (Lepus californicus) than to other snowshoe hares, which may result from secondary introgression or shared ancestral polymorphism. Given the genetic distinctiveness of southern populations and minimal gene flow with their northern neighbours, fragmentation and loss of southern boreal habitats could mean loss of many unique alleles and reduced evolutionary potential.

Summary 0[ Snowshoe hare "Lepus americanus Erxleben# populations were studied in south! west Yukon during the low phase of the 09!year population cycle[ Food availability and predator abundance were manipulated in a factorial design to determine the importance of each factor in hare dynamics during this phase[ 1[ Food was abundant during the low phase\ and snowshoe hares were not food limited[ 2[ Survival of hares was higher than at any other phase of the cycle\ and predators were scarce\ but ×64) of hare deaths resulted from predation[ 3[ Food addition resulted in higher hare densities and better body condition than on control sites[ There were no observable e}ects of food addition on population rate of increase\ recruitment\ survival or age structure[ 4[ Mammalian predator reduction resulted in higher hare densities\ higher survival\ better body condition and an older age structure[ Relative to control populations\ recruitment was lower and population rates of increase similar[ 5[ The joint manipulation of food addition ¦ predator reduction had greater positive e}ects on hare density and body condition than either single factor manipulation[ Survival was better than on control sites\ and the age structure was older than on control sites[ Population rates of increase were similar\ but recruitment was higher on the control areas[ 6[ We conclude that snowshoe hare dynamics at the low of the cycle are dominated by the interaction of food and predation[ Risk of predation also had indirect e}ects on snowshoe hare age structure and body condition[ Key!words] body condition\ food addition\ population density\ predator reduction\ survival[ Journal of Animal Ecology "0888# 57\ 470Ð483