Showing papers on "Habitat destruction published in 2000"

Biodiversity hotspots for conservation priorities

Abstract: Conservationists are far from able to assist all species under threat, if only for lack of funding. This places a premium on priorities: how can we support the most species at the least cost? One way is to identify 'biodiversity hotspots' where exceptional concentrations of endemic species are undergoing exceptional loss of habitat. As many as 44% of all species of vascular plants and 35% of all species in four vertebrate groups are confined to 25 hotspots comprising only 1.4% of the land surface of the Earth. This opens the way for a 'silver bullet' strategy on the part of conservation planners, focusing on these hotspots in proportion to their share of the world's species at risk.

A survey and overview of habitat fragmentation experiments.

Abstract: Habitat destruction and fragmentation are the root causes of many conservation problems. We conducted a literature survey and canvassed the ecological community to identify experimental studies of terrestrial habitat fragmentation and to determine whether consistent themes were emerging from these studies. Our survey revealed 20 fragmentation experiments worldwide. Most studies focused on effects of fragmentation on species richness or on the abundance(s) ofparticular species. Other important themes were the effect offragmentation in interspecific interactions, the role of corridors and landscape connectivity in in- dividual movements and species richness, and the influences of edge effects on ecosystem services. Our com- parisons showed a remarkable lack of consistency in results across studies, especially with regard to species richness and abundance relative to fragment size. Experiments with arthropods showed the best fit with the- oretical expectations of greater species richness on larger fragments. Highly mobile taxa such as birds and mammals, early-successional plant species, long-lived species, and generalist predators did not respond in the "expected" manner. Reasons for these discrepancies included edge effects, competitive release in the habitat fragments, and the spati.al scale of the experiments. One of the more consistently supported hypotheses was that movement and species richness are positively affected by corridors and connectivity, respectively. Tran- sient effects dominated many systems;,for example, crowding of individuals on fragments commonly was ob- served afterfragmentation, followed by a relaxation toward lower abundance in subsequentyears. The three long-term studies (?14 years) revealed strong patterns that would have been missed in short-term investiga- tions. Our results emphasize the wide range of species-specific responses to fragmentation, the need for eluci- dation of behavioral mechanisms affecting these responses, and the potentialfor changing responses to frag- mentation over time.

Biodiversity. Extinction by numbers

Abstract: Habitat destruction, especially of the humid forests in the tropics, is the main cause of the species extinctions happening now New work documents the uneven, highly clumped distribution of vulnerable species on the Earth, and pinpoints 25 so-called ‘biodiversity hotspots’ Seventeen of them are tropical forest areas, and here reduction of natural habitat is disproportionately high Nonetheless, identification of this pattern should enable resources for conservation to be better focused

Ecological basis of extinction risk in birds: habitat loss versus human persecution and introduced predators.

Abstract: Understanding the ecological mechanisms that underlie extinction is fundamental to conservation. It is well established that not all taxa are equally vulnerable to extinction, but the reasons for these differences are poorly understood. This may be, in part, because different taxa are threatened by different mechanisms. Theoretically, sources of extinction risk that perturb the balance between fecundity and longevity, such as human persecution and introduced predators, should be particularly hazardous for taxa that have slow rates of population growth. In contrast, sources of extinction risk that reduce niche availability, such as habitat loss, should represent a particular threat to taxa that are ecologically specialized. Here we test these predictions by using a phylogenetic comparative method and a database on 95 families of birds. As theory predicts, extinction risk incurred through persecution and introduced predators is associated with large body size and long generation time but is not associated with degree of specialization, whereas extinction risk incurred through habitat loss is associated with habitat specialization and small body size but not with generation time. These results demonstrate the importance of considering separately the multiple mechanisms that underlie contemporary patterns of extinction. They also reveal why it has previously proven so difficult to identify simple ecological correlates of overall extinction risk.

The Ecology of Tropical Asian Rivers and Streams in Relation to Biodiversity Conservation

Abstract: ▪ Abstract Tropical Asian rivers support a rich but incompletely known biota, including a host of fishes, a diverse array of benthic invertebrates, and an assemblage of mammals adapted to riverine wetlands. River ecology is dominated by flow seasonality imposed by monsoonal rains with profound consequences for fishes and zoobenthos. Information on life histories, feeding, and the trophic base of production of these animals is summarized. Widespread use of allochthonous foods by fishes and zoobenthos is apparent. Migration by fishes is often associated with breeding and results in seasonal occupation of different habitats. Riverine biodiversity is threatened by habitat degradation (pollution, deforestation of drainage basins), dams and flow regulation, as well as over-harvesting. Conservation efforts in tropical Asia are constrained by a variety of factors, including lack of ecological information, but the extent of public awareness and political commitment to environmental protection are likely determinan...

Habitat alteration and the conservation of African primates: case study of Kibale National Park, Uganda.

Abstract: Tropical forests and the animals they support are being threatened byaccelerating rates of forest conversion and degradation In a continuallyfluctuating sociopolitical world, it is often impossible to protect areasfrom such conversion until the political environment is suitable to pur-sue conservation goals, by which time, the forests have often been con-verted to other uses This reality suggests a need for inquiry into whichprimate species can persist after different types of disturbances and howquickly primate communities can recover from disturbance Here we ex-amine the persistence of primate populations in disturbed habitats byproviding a case study of patterns of primate abundance in areas of KibaleNational Park (766 km

Species richness and parasitism in a fragmented landscape: experiments and field studies with insects on Vicia sepium.

Abstract: Effects of habitat fragmentation on species diversity and herbivore-parasitoid interactions were analyzed using the insect community of seed feeders and their parasitoids in the pods of the bush vetch (Vicia sepium L.). Field studies were carried out on 18 old meadows differing in area and isolation. The area of these meadows was found to be the major determinant of species diversity and population abundance of endophagous insects. Effects of isolation were further analyzed experimentally using 16 small plots with potted vetch plants isolated by 100–500 m from vetch populations on large old meadows. The results showed that colonization success greatly decreased with increasing isolation. In both cases, insect species were not equally affected. Parasitoids suffered more from habitat loss and isolation than their phytophagous hosts. Minimum area requirements, calculated from logistic regressions, were higher for parasitoids than for herbivores. In addition, percent parasitism of the herbivores significantly decreased with area loss and increasing isolation of Vicia sepium plots, supporting the trophic-level hypothesis of island biogeography. Species with high rates of absence on meadows and isolated plant plots were not only characterized by their high trophic level, but also by low abundance and high spatial population variability. Thus conservation of large and less isolated habitat remnants enhances species diversity and parasitism of potential pest insects, i.e., the stability of ecosystem functions.

Depressed pollination in habitat fragments causes low fruit set.

Abstract: In central New South Wales, Australia, flowers of Acacia brachybotrya and Eremophila glabra plants growing in linear vegetation remnants received less pollen than conspecifics in nearby reserves. Pollen supplementation increased fruit production by both species, indicating pollen limitation of fruit set. Together these observations explain why fruit production by these species was depressed in linear-strip populations relative to nearby reserves. This study confirms that habitat fragmentation can lead to decline in pollination and subsequent fruit set in wild plant populations. Disrupted pollination interactions of the kind documented in this study may offer a substantial challenge to the conservation of biodiversity in fragmented landscapes.

Impacts of habitat fragmentation and patch size upon migration rates

Abstract: A spatially explicit model (MIGRATE) was used to investigate the effects of habitat loss and fragmentation on the ability of species to migrate in response to climate change. Illustrative simulations were run using parameters that represent the reproductive and dispersal characteristics of the wind-dispersed tree Tilia cordata (small-leaved lime). Hierarchically structured landscapes with different patch sizes and overall habitat suitability levels were generated at a 1-km resolution for a 200 × 800 km area. Simulated migration rates slowed markedly when habitat availability fell below ∼25% of the landscape area, especially in landscapes composed of fewer larger patches. The implication of these results for the management of landscapes for species conservation is discussed.

Rapid extinction of the moas (Aves: Dinornithiformes): model, test, and implications.

Abstract: A Leslie matrix population model supported by carbon-14 dating of early occupation layers lacking moa remains suggests that human hunting and habitat destruction drove the 11 species of moa to extinction less than 100 years after Polynesian settlement of New Zealand. The rapid extinction contrasts with models that envisage several centuries of exploitation.

Preemptive Habitat Destruction Under the Endangered Species Act

Abstract: This paper examines the extent to which landowners have preemptively destroyed endangered species' habitats in order to avoid potential landuse regulations prescribed under the Endangered Species Act (ESA). Under the ESA it is not only illegal to take (kill) an endangered species, but it is also illegal to damage their habitat. Our application is to red-cockaded woodpeckers (RCWs) in the forests of North Carolina. RCWs are an endangered species that live in old growth pine forests throughout the Southeast. Our primary hypothesis is that the closer a landowner is to known populations of RCWs, the more likely the landowner will take action to destroy the habitat for RCWs, primarily by "prematurely" cutting their pine forest. By preventing the establishment of an old growth pine stand, the landowner can insure that RCWs do not inhabit their land and avoid ESA regulations that limit or prohibit timber harvest activity. Two empirical questions are addressed: How does the potential for ESA regulation affect the harvest probability of a particular forest plot? How does the potential for ESA regulation affect the age at which a forest will be harvested? Data on over 1,000 individual forest plots from the U.S. Forest Service's Forest Inventory and Analysis (FIA) and a 1997-98 North Carolina State University (NCSU) survey of over 400 landowners are used to test predictions about the probability of harvest and the age of timber when it is harvested. The location of RCW populations is used to construct various measures of the probability that a forest plot will become inhabited by RCWs and thus subject to ESA restrictions on land use. Probit regressions estimate the probability that a plot is harvested and OLS regressions - corrected for harvest selection bias - estimate the age at which a plot is harvested. In all our estimates we find that increases in the proximity of a plot to RCWs increases the probability that the plot will be harvested and decreases the age at which the forest is harvested. These findings indicate that the ESA, at least for RCWs in North Carolina, actually reduces the amount of endangered species habitat.

Overview, Critical Assessment, and Conservation Implications of Koala Distribution and Abundance

Abstract: Regional and national surveys provide a broadscale description of the koala's present distribution in Australia. A detailed understanding of its distribution is precluded, however, by past and continuing land clearing across large parts of the koala's range. Koala population density increased in some regions during the late 1800s and then declined dramatically in the early 1900s. The decline was associated with habitat loss, hunting, disease, fire, and drought. Declines are continuing in Queensland and New South Wales. In contrast, dense koala populations in habitat isolates in Victoria and South Australia are managed to reduce population size and browse damage. Current understanding of koala distribution and abundance suggests that the species does not meet Australian criteria as endangered or vulnerable fauna. Its conservation status needs to be reviewed, however, in light of the extensive land clearing in New South Wales and Queensland since the last (1980s) broadscale surveys. Consequently, we recommend that broadacre clearing by curtailed in New South Wales and Queensland and that regular, comprehensive, standardized, national koala surveys be undertaken. Given the fragmentation of koala habitat and regional differences in the status of the koala, we recommended that studies on regional variation in the koala be intensified and that koala ecology in fragmented and naturally restricted habitats be developed. More generally, the National Koala Conservation Strategy should be implemented.

Synthesis of linkages between benthic and fish communities as a key to protecting essential fish habitat

Abstract: Several essential fish habitats lack the protections necessary to prevent degradation because of failure to integrate the scientific disciplines required to understand the causes of the degradation and failure to integrate the fragmented state and federal management authorities that each hold only a piece of the solution. Improved protection of essential habitat for demersal fishes requires much better synthesis of benthic ecology, fisheries oceanography, and traditional fisheries biology. Three examples of degraded habitat for demersal fishes and shellfishes are high-energy intertidal beaches, subtidal oyster reefs, and estuarine soft bottoms. In each case, both scientific understanding of and management response to the problem require a holistic approach. Intertidal beach habitat for surf fishes could be protected by constraints on the character of sediments used in beach nourishment and restriction of nourishment activity to biologically inactive seasons. Subtidal oyster-reef habitat for numerous crabs, shrimps, and finfishes could be protected and restored by reduction of nitrogen loading to the estuary and elimination of dredge damage to reefs. Estuarine soft-bottom habitat for demersal fin- and shellfishes could also be protected by reduction of the nutrient loading of the estuary, which could prevent associated problems of nuisance blooms and low dissolved oxygen. Although a broad general understanding of the nature of habitat degradation exists for each of these three examples, the interdisciplinary science needed to sort out the separate and interactive contributions of all major contributing factors is incomplete. Adopting the holistic approach embodied in the principles of ecosystem management sets a course for addressing both the scientific inadequacies and the management inaction.

The effects of future urban development on habitat fragmentation in the Santa Monica Mountains

Abstract: A site suitability model of urban development was created for the Santa Monica Mountains in southern California, USA, to project to what degree future development might fragment the natural habitat. The purpose was to help prioritize land acquisition for the Santa Monica Mountains National Recreation Area and examine to what extent projected urban development would affect distinct vegetation classes. The model included both environmental constraints (slope angle), and spatial factors related to urban planning (proximity to roads and existing development, proposed development, and areas zoned for development). It implemented a stochastic component; areas projected to have high development potential in the suitability model were randomly selected for development. Ownership tracts were used as the spatial unit of development in order to give the model spatial realism and not arbitrarily `develop' grid cells. Using different assumptions and parameters, the model projected the pattern of development from ∼5 to ∼25 years hence (based on recent development rates in the area). While <25% of the remaining natural landscape is removed under these scenarios, up to 30% of core (interior) habitat area is lost and edge length between natural vegetation and development increases as much as 45%. Measures of landscape shape complexity increased with area developed and number of patches of natural habitat increased four- to nine-fold, depending upon model parameters. This increase in fragmentation occurs because of the existing patterns of land ownership, where private (`developable') land is interspersed with preserved park lands.

Implications of endemics-area relationships for estimates of species extinctions

Abstract: Species are disappearing at unprecedented rates because of habitat destruc- tion. Lack of detailed knowledge about total numbers of species and their global or regional distributions, however, makes it difficult to quantify extinction rates precisely. Current estimates of extinction rates attributed to habitat destruction generally rely on species-area relationships. Many of the predictions based on species-area relationships, however, appear to overestimate the extent of current species extinction. In a previous paper, we used the species-area relationship as our starting point to derive a relationship for the areal distri- bution of endemics within a habitat, or an "endemics-area relationship." The endemics- area relationship is logically and mathematically consistent with the species-area relation- ship, but it provides additional information about the distribution of species within a biome. In this paper, we use the endemics-area relationship to improve estimates of species ex- tinction rates attributed to habitat destruction or conversion. At low levels of habitat de- struction, estimates of species loss using the endemics-area relationship are significantly lower than existing estimates, but a rapid rise in predicted species loss when a threshold of habitat loss is exceeded suggests that extrapolation of recent rates of species loss may underestimate future species extinctions under continued land clearing.

Prediction and assessment of local stream habitat features using large‐scale catchment characteristics

Abstract: SUMMARY 1 Knowledge of what a habitat should be like, in the absence of the effects of human activities, is fundamental to local stream habitat assessment It has been suggested that stream habitats are influenced by large-scale catchment features This study aimed to identify these relationships so that local-scale habitat features could be predicted from larger-scale characteristics 2 Fifty-one reference sites from the Upper Murrumbidgee River catchment, south-eastern Australia, were classified on the basis of the local features of their stream habitat Large-scale variables, namely catchment area, stream length, relief ratio, alkalinity, percentage of volcanic rocks, percentage of metasediments, dominant geology and dominant soil type, provided sufficient information for classifying 69% of reference sites into appropriate reference site groups 3 A model created using these large-scale catchment variables was able to predict the local habitat features that were expected (E) to occur at a site in the absence of the effects of human activities These were compared with observed (O) local habitat features to provide an observed-to-expected (O:E) ratio, an assessment score of the habitat at a site The departure of this ratio from 1 enables identification of those sites that may be impacted A list of habitat features that are expected at a site can provide targets for habitat restoration or enhancement 4 For impacted sites, when habitat assessment from the habitat predictive model was compared with biological assessment from the Australian River Assessment System (AUSRIVAS) predictive model, it was possible to identify whether habitat degradation or water quality degradation was the cause of biological impairment Such assessment may make it possible to identify rehabilitation goals relevant to the biota

Assessing and protecting endangered marine species

Abstract: Documented extinctions of marine and anadromous species are rare, but extinction of species and extirpation of major populations have occurred - there are cases of near extinction - and there may be undocumented extinctions. Factors associated with known extinctions and near extinctions include specific life-history characteristics (e.g. low fecundity, high age at maturity, low mobility), habitat degradation, high value and high susceptibility to harvesting, ecological specialization. Harvesting mortality, targeted or incidental, is implicated in some known extinctions or near extinctions, and may act synergistically with other threats. Criteria to make assessments of risk of extinction more consistent have been developed, but given the limited experience to date with extinctions in the marine environment there have been questions about applying these to some marine species. The wide range of life history characteristics in marine species suggests that a range of approaches to assessing extinction risk will be needed. Protocols for defining significant population units are also required since protection of populations is part of protecting endangered species. Keeping species and populations well away from endangered status should be the main goal of conservation programmes. Implementation of precautionary conservation frameworks for exploited species could be a sound approach to preventing “endangerment”.

Effects of Habitat Disturbance and Protected Areas on Mammals of Peninsular Malaysia

Abstract: I studied a network of small forested areas (2–2744 ha) that are protected as forestry research control sites and nature reserves in Peninsular Malaysia. These areas are officially known in Malaysia as Virgin Jungle Reserves ( VJRs). They are unlogged and are usually part of a larger, generally logged forest. I examined the effects of habitat disturbance on the species richness and composition of the mammal communities in seven of these protected areas ( 70–304 ha) and in adjoining logged forest, exotic monoculture plantation, or “farm bush.” Thirty-eight species of mammals were recorded through direct observation, identification of tracks, or other signs. The size of the remaining area of natural forest, including both logged and unlogged forest but not including exotic timber plantations, or farm bush, was the most important factor affecting the mammal communities in all seven areas. The presence of species followed a nested subset pattern. A loss of large herbivores and carnivores, in particular, was apparent between areas of natural forest of 6551 to ≥10,000 ha. When areas of natural forest of ≤459 ha were considered, size continued to be critical; a sharp loss in mammal species richness was apparent between 70 and 164 ha. The area of the natural forest in which a protected area was located largely determined the mammal species richness and composition in the protected area. Differences in habitat quality accounted for the differences in mammal communities between protected areas and their adjoining vegetation. The preservation of small undisturbed areas can effectively enhance certain mammal communities in a disturbed landscape. The survival of some mammal species, however, including the largest carnivores and herbivores, will be determined by the area of surviving forest as a whole. A positive management strategy would be to retain large, continuous areas of forest wherever possible, in preference to fragmenting forest, and to build on existing small protected-area networks, such as the VJR network in Peninsular Malaysia, so that logged forests contain a rich mix of undisturbed protected areas.

Modular Habitat Refugia Enhance Generalist Predators and Lower Plant Damage in Soybeans

Abstract: Promoting generalist predators in agriculture via habitat manipulation has gained much interest in biocontrol research. Straw shelters have been used by Chinese farmers for .2,000 yr to provide temporary spider refugia during cyclic farming disturbances. This method, however, has not been systematically investigated on larger scales in western-style agriculture. Our prelim- inary observations indicated a significant decrease in the abundance of spiders (76%) and their egg sacs (75%), after conventional tillage of soybeans (Glycine max (L.) Merr.). We hypothesized that providing alternative habitats in tilled fields could conserve predatory assemblages following this major disturbance. We used modular habitat refugia constructed of chicken wire loosely filled with bedding straw to provide temporary habitats for epigeic predators in a soybean field. Refugia held 5—36 times the spider density compared with open field, and the production of spider egg sacs was enhanced 18—87 times. Almost 60% more spider species were found in refugia than in open field. Abundance of harvestmen, carabids, and staphylinid beetles also significantly increased in habitat refugia. Increased habitat cover and provision of alternative prey in habitat refugia may have caused this dramatic predator increase. Soybean seedlings grown withi n1mo fhabitat refugia suffered 33% less insect damage compared with plants at control locations. Decrease in seedling damage, however, did not significantly increase soybean seed production. Applications of discrete habitat refugia may provide an alternative to habitat manipulation techniques to conserve and augment arthropod predators in agroecosystems.

Fragments are not islands: patch vs landscape perspectives on songbird presence and abundance in a harvested boreal forest

Abstract: The boreal mixed-wood forest of northern Alberta. Canada is characterized by a mosaic of deciduous and coniferous forest patches. Recently, the deciduous portion of the forest was allocated for industrial logging. Widespread habitat loss and fragmentation may negatively affect birds and other wildlife. Most research on the effects of habitat loss on bird abundance has focussed on the forest as a patch or island in a matrix of non-habitat, but some species of songbird may use both the forest patch and the matrix. We hypothesized that some species of songbird might be able to compensate for a loss of deciduous forest by moving into other habitat types (termed “habitat compensation”). We report on a replicated field investigation in which we assessed the response of songbirds to commercial timber harvest by first examining their abundance within deciduous forest only, and then adding the clearcuts and coniferous forest in the surrounding areas to the analysis for a broader, landscape view of the system. Bird communities in deciduous and coniferous habitats had significant overlap in species composition: there was less overlap between forest and clearcuts. The shift from patch-centred to landscape sampling altered our interpretation of over half of the most common species' responses to logging in at least one year, suggesting that habitat compensation may have been occurring. However, significant variation in responses of species was observed between the two study areas. Our past reliance on island biogeographic and other single habitat approaches may be inappropriate for this system, and we stress that a broad, landscape view is required to properly assess and interpret species' responses to habitat loss and fragmentation.

Determinants of plant extinction and rarity 145 years after european settlement of auckland, new zealand

Abstract: We analyze a 114-year historical record (1871–1985) of the change in abundance of 373 native plant species in Auckland, New Zealand, with the aim of identifying the attributes that predisposed some species to local extinction and rarity following European settlement. The 1871 survey records the relative abundance of native plants in the Auckland area just 31 years after Europeans began clearing the native vegetation for settlement, whereas the 1985 survey records the relative abundance of the same species 114 years later, when the area had been transformed into an urban landscape. Four attributes were significantly and independently related to the probability that a species was locally extinct or rare in 1985: (1) compared with species that were common in 1871, initially rare species were more likely to be extinct or rare in 1985; (2) compared with tall species, short species were more likely to be extinct or rare in 1985; (3) gymnosperms and dicotyledons were more likely to be extinct or rare in 1985 tha...

Habitat Loss and Changes in the Species-Area Relationship

Abstract: The species-area relationship (SAR) has been used successfully to predict extinction from extent of habitat reduction. These extinction estimates assume that species have uniformly distributed range require- ments and a minimum abundance level required for persistence; how many species are lost depends solely on how much habitat is removed, not on where it is removed. We consider another limiting case in which range requirements, rather than abundances, determine extinctions. We used a new method for constructing SARs based on assumptions about geographic ranges of species. Our results show that habitat destruction can change the SAR and consequently the number of species predicted to be lost due to habitat destruction. Our method generates SARs that vary in shape according to the specific distributions of geographic range and oc- cupancy but that have the common feature of being described by a power law with an exponent of , 1. When the geographic range of species was included in the SAR, the way habitat was lost became important. Al- though the SAR before habitat destruction is often used to predict species loss after habitat destruction, as- sumptions must be clearly stated. To predict the damage caused by habitat loss with our model, it is necessary to know the fraction of aggregated species, the distribution of geographic ranges, the form of habitat destruc- tion, and the sampling protocol. The remaining theoretical challenge is to develop a full theory that links abundance and range.

Community relaxation in fragmented landscapes: the relation between species richness, area and age

Abstract: Estimates of species loss due to habitat destruction are normally based on calculations employing the species–area relation, S = cAz. The validity of this approach is based on the assumption that the value of the exponent (z) defining the slope of the species–area relation in nonfragmented communities is at a steady state and that z is thus a constant. However, departure from such an assumption renders this approach unreliable. Here I report the results from a natural field experiment using “model” bryophyte-based microlandscapes designed to follow the species richness dynamics of microarthropod communities postfragmentation. Community isolation due to fragmentation initiated a delayed community relaxation process and resulted in substantial local extinction. Over the period of the experiment z declined in the control communities and yet remained fairly stable in the fragmented communities. I conclude that predictions of species loss due to habitat fragmentation that do not take into account the fact that often z may not be a constant may lead to error-prone predictions of future species loss.

Behavioral mechanisms and habitat use by birds in a fragmented agricultural landscape

Abstract: Effective conservation and habitat restoration strategies in human-dominated landscapes must be based on an understanding of the ways that habitat loss and fragmen- tation affect native species. We studied avian foraging behavior and patterns of occurrence in the highly fragmented agricultural landscape of the Kellerberrin district of Western Australia to better understand the factors underlying species declines and losses. We con- ducted three surveys of 30 wandoo woodland patches that ranged in size from 1.3 to 101.3 ha. Some patches were part of larger remnants of native vegetation, ranging in size from 3.5 to 1204.8 ha and including other habitat types. We examined the extent to which patterns of species richness, the occurrence and composition of foraging guilds, and the occurrence of individual species varied with features of woodland patches, remnants, and the sur- rounding landscape. Using multiple regression analyses, the best model for species richness included terms for the log of remnant area, the patch diversity of each remnant, and woodland patch condition. We delineated eight foraging guilds based on similarities in the substrate/method dimension and also using multidimensional scaling analyses. The best model for the number of foraging guilds present in a patch included a single variable representing shrub density. Analyses of nestedness based on guilds and on individual species were both significant; and for the latter, 11 of 13 species made a significant contribution to the overall pattern. We derived separate models for the occurrence of each of eight species and one guild using multiple logistic regression. Significant models included, either separately or in combi- nation, the following variables: the log of remnant area, patch area, the total area of wood- land in a remnant, and the distance to other woodland patches. For four species that had sufficient records to examine shifts in foraging behavior, we observed significant differences in both foraging methods and substrates with changes in remnant size and/or the presence of other species or guilds. Our analyses indicated that remnant area was the best single variable for measures of community structure, in part because it was strongly correlated with other variables, such as total woodland area, patch area, remnant patch diversity, number of corridor connections, and measures of isolation. For foraging guilds and for individual species, variables other than remnant area assumed greater importance. The strong patterns of nestedness for for- aging guilds by remnant area may reflect the diminished availability of certain prey items in small, degraded remnants. This notion is reinforced by the relatively high species and guild richness recorded in small patches that were either fenced from grazing or embedded in large remnants. The nested pattern of species within some foraging guilds, however, indicates the importance of additional aspects of their ecology. A focus on richness alone may mask the unique responses of bird species to fragmentation and may divert attention from important considerations in the development of land-use policy and reserve acquisition.

How can maladaptive habitat choice generate source‐sink population dynamics?

Abstract: Several theoretical models have been proposed to describe population dynamics in a spatially heterogeneous environment. The source-sink model is among the most popular. Diffendorfer recently summarized its assumptions and predictions. Given the model reviewed, he argued that source-sink population dynamics arises if dispersal is somehow constrained. I offer an additional mechanism by suggesting that source-sink population dynamics can be generated by anthropogenic changes in landscapes that occur so quickly that organisms no longer make optimal habitat selection decisions. Individuals select the same habitats as their ancestors but these decisions no longer provide high fitness because of human-induced changes in habitat quality, such as increased rates of predation and/or parasitism. Provided that some of the habitats selected are turned by human-induced changes into sink habitats, source-sink population dynamics can emerge.