Fragmentation of habitats used by neotropical migratory birds in Southern Appalachians and the neotropics (original) (raw)
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PLoS ONE, 2013
Habitat loss and attendant fragmentation threaten the existence of many species. Conserving these species requires a straightforward and objective method that quantifies how these factors affect their survival. Therefore, we compared a variety of metrics that assess habitat fragmentation in bird ranges, using the geographical ranges of 127 forest endemic passerine birds inhabiting the Atlantic Forest of Brazil. A common, non-biological metric -cumulative area of size-ranked fragments within a species range -was misleading, as the least threatened species had the most habitat fragmentation. Instead, we recommend a modified version of metapopulation capacity. The metric links detailed spatial information on fragment sizes and spatial configuration to the birds' abilities to occupy and disperse across large areas (100,000+ km 2 ). In the Atlantic Forest, metapopulation capacities were largely bimodal, in that most species' ranges had either low capacity (high risk of extinction) or high capacity (very small risk of extinction). This pattern persisted within taxonomically and ecologically homogenous groups, indicating that it is driven by fragmentation patterns and not differences in species ecology. Worryingly, we found IUCN considers some 28 of 58 species in the low metapopulation capacity cluster to not be threatened. We propose that assessing the effect of fragmentation will separate species more clearly into distinct risk categories than does a simple assessment of remaining habitat.
Demographic Responses by Birds to Forest Fragmentation
Conservation Biology, 2005
Despite intensive recent research on the effects of habitat loss and fragmentation on bird populations, our understanding of underlying demographic causes of population declines is limited. We reviewed avian demography in relation to habitat fragmentation. Then, through a meta-analysis, we compared specific demographic responses by forest birds to habitat fragmentation, providing a general perspective of factors that make some species and populations more vulnerable to fragmentation than others. We obtained data from the scientific literature on dispersal, survival, fecundity, and nesting success of birds. Birds were divided into subgroups on the basis of region, nest site, biogeographical history, and migration strategy. Species most sensitive to fragmentation were ground-or open-nesters nesting in shrubs or trees. Residents were equally sensitive to fragmentation in the Nearctic and Palearctic regions, but Nearctic migrants were more sensitive than Palearctic migrants. Old World species were less sensitive than New World species, which was predicted based on the history of forest fragmentation on these two continents. Pairing success was the variable most associated with fragmentation, suggesting an important role of dispersal. Fledgling number or condition, timing of nesting, and clutch size were not associated with sensitivity to fragmentation, suggesting that negative fragmentation effects on birds do not generally result from diminished food resources with increasing level of fragmentation. Future studies on demographic responses of birds to habitat fragmentation would be more effective if based on a combination of measures that can distinguish among the demographic mechanisms underlying population changes related to habitat fragmentation.
Many insectivorous birds of the tropical rainforest understory, particularly terrestrial species, are prone to local extinctions in fragmented forests. We evaluated the hypothesis that vegetation structural changes in rainforest fragments reduce the availability of microhabitats used by terrestrial insectivores. Near Manaus, Brazil, we compared the vegetation in forest fragments to the vegetation in a continuous forest site where nine species of terrestrial insectivores were observed foraging. Our focal species included those that are extinction prone in fragments (Myrmornis torquata [Wing-banded Antbird], Grallaria varia [Variegated Antbird], Hylopezus macularius [Spotted Antpitta]), a fragmentation-tolerant species (Myrmothera campanisona [Thrush-like Antpitta]), and species that have and intermediate response (Myrmeciza ferruginea [Ferruginous-backed Antbird], Formicarius colma [Rufous-capped Anttrush], Formicarius analis [Black-faced Antthrush], Conopophaga aurita [Chestnut-belted Gnateater], and Corythopis torquata [Ringed Antpipit]). To quantify vegetation, we measured sixteen habitat variables in 8-m radius plots where birds were observed foraging as well as random points in continuous forest and forest fragments of 1-, 10-, and 100-ha. Four principal components were produced from a principal component analysis and we selected a variable (leaf litter depth, plant cover 3–10 m, density of plants 1–2 m, and plant cover >20 m) from each principal component for our fragment vs continuous forest comparisons. Using Markov chain Monte Carlo (MCMC) simulation, we estimated the probabilities that the density of plants 1–2 m, proportion of plant cover 3–10 m, and leaf litter depth increased with decreasing fragment area and also exceeded the values associated with fragmentation-sensitive species. We also tested the prediction that plant cover >20 m decreased in forest fragments and that those sites became more open than typical sites used by our focal species. Our predictions were strongly supported: decreasing fragment size was correlated with increasing density of tall plants, increasing mid-story vegetation cover, decreased canopy cover, and increasing leaf litter depth. Even if our focal species are able to disperse to small forest fragments, our results suggest that they may not find enough appropriate habitat.
Biological Conservation, 2011
Developing a predictive theory for species responses to habitat fragmentation is a large, complex challenge in conservation biology, and meeting this challenge likely requires tailoring predictions to specific habitats and taxa. We evaluate the effects of fragmentation on forest birds living in three distinct forest ecosystems found in Brazilian Atlantic forest: seasonal semi-deciduous forest (SF), mixed rain forest (MF), and dense rain forest (DF). We test the hypotheses that (1) bird species most prevalent in SF (relative to other habitat types) will be least vulnerable to population declines in fragmented SF, and (2) species with stronger affiliations with DF or MF will be relatively more sensitive to fragmentation in SF. Using an exploratory statistical technique called ''Rank Occupancy-Abundance Profiles (ROAPs),'' we compared distribution and abundance of birds among large ''continuous'' areas of each forest type, then compared abundances in continuous SF forests with patterns of abundance in small fragments of SF, where edge effects could play a marked role in population dynamics. Overall, 39 species showed substantially lower local abundance, occupancy, or both in SF fragments versus continuous SF. As predicted, a higher proportion of bird species associated with DF appeared sensitive to fragmentation in SF; by contrast, species most abundant in SF and MF were similarly abundant in fragmented SF. Our study demonstrates how quantifying distribution and abundance in diverse habitats may enhance managers' ability to incorporate species-specific responses to human disturbances in their conservation plans, and points out ways that even small reserves may have significant conservation value.
Independent Effects of Forest Cover and Fragmentation on the Distribution of Forest Breeding Birds
Ecological Applications, 1999
The aims o f this study were (1) to determine the relative importance o f the independent effects o f forest cover and fragmentation on the distribution o f forest breeding birds, and (2) to test the hypothesis that the negative effect o f forest fragmentation on species distribution increases with decreasing forest cover, i.e., the negative interaction effect o f forest cover and fragmentation on distribution. The independent effects o f forest cover and forest fragmentation on the distribution o f forest breeding birds were studied in 94 landscapes, 10 X 10 k m each, ranging in forest cover from 2.5% to 55.8%. For each landscape, percent forest cover was measured, and a fragmentation index (independent o f forest cover) was generated using PCA from the measures o f mean forest patch size, number o f forest patches, and total forest edge. Presence o f 3 1 forest breeding bird species in each landscape was determined using Breeding Bird Atlas data. The effects o f forest cover and forest fragmentation on species presence were analyzed using multiple logistic regression. All responses o f individual species to forest cover were positive. Responses to forest fragmentation were weak and variable. There were only two species for which the interaction between cover and fragmentation was significant (one positive, one negative). W e found no evidence for the hypothesized negative interaction effect between forest cover and forest fragmentation on species distribution. W e conclude that (1) forest cover at the 10 X 10 k m (Universal Transverse Mercator [ U T M ]) scale has a positive effect on the distribution o f forest breeding birds, (2) forest fragmentation does not have a consistent negative effect on the distribution o f forest breeding birds, (3) the effect o f forest cover is greater than that o f forest fragmentation, (4) responses to forest fragmentation are generally weak and highly variable among species, and (5) the effect o f forest fragmentation on species distribution does not increase with decreasing forest cover. These results suggest that conservationists' primary focus should be on preventing a decrease in forest cover. They should not be misled by recent discussions o f "fragmentation effects" to think that the negative effects o f forest loss can somehow be countered by careful consideration o f the spatial pattern o f remaining forest. Our results indicate that they cannot.
Habitat loss and fragmentation are considered the main causes of species extinctions, particularly in tropical ecosystems. The objective of this work was to evaluate the temporal dynamics of tropical bird communities in landscapes with different levels of fragmentation in eastern Guatemala. We evaluated five bird community dynamic parameters for forest specialists and generalists: (1) species extinction, (2) species turnover, (3) number of colonizing species, (4) relative species richness, and (5) a homogeneity index. For each of 24 landscapes, community dynamic parameters were estimated from bird point count data, for the 1998-1999 and 2008-2009 periods, accounting for species' detection probability. Forest specialists had higher extinction rates and a smaller number of colonizing species in landscapes with higher fragmentation, thus having lower species richness in both time periods. Alternatively, forest generalists elicited a completely different pattern, showing a curvilinear association to forest fragmentation for most parameters. Thus, greater community dynamism for forest generalists was shown in landscapes with intermediate levels of fragmentation. Our study supports general theory regarding the expected negative effects of habitat loss and fragmentation on the temporal dynamics of biotic communities, particularly for forest specialists, providing strong evidence from understudied tropical bird communities.
Land cover and land use surrounding fragmented habitat can greatly impact species persistence by altering resource availability, edge effects, or the movement of individuals throughout a landscape. Despite the potential importance of the landscape matrix, ecologists still have limited understanding of the relative effects of different types of land cover and land uses on species patterns and processes in natural systems. Here we investigated whether Neotropical resident bird communities in limestone forest patches differed if they were embedded in three different human-dominated matrix types (agriculture, peri-urban development, and bauxite mining) relative to sites in continuous forest in central Jamaica. We found that species richness, community composition, and abundances were matrix-dependent, with agricultural landscapes supporting greater avian diversity and more intact community assemblages than either peri-urban or bauxite landscapes. Abundance of almost 70% of species differed in forest embedded in the different landscape matrix types. Traits related to resource use best predicted species responses, including diet guild, nest height, habitat association, and foraging strata. Insectivores, frugivores, canopy nesters, understory and canopy foragers, and forest-restricted species rarely observed in matrix habitats had lower abundances in forest fragments embedded in human-dominated matrix types than in continuous forest. In contrast, nectarivores, omnivores, granivores, ground and multi-strata nesters, ground foragers, and species regularly in matrix habitats were least sensitive to forest fragmentation. Results suggest that structure, composition, and land use disturbance regimes in matrix areas impact overall habitat quality in landscapes by potentially mediating resource availability inside as well as outside forest habitat. This study reinforces the importance of differentiating among land cover and land uses in fragmentation research and lends support to the hypothesis that resource availability may be a primary factor driving Neotropical bird responses to fragmentation.
Journal of Tropical Ecology, 2008
In this paper, we report on range use patterns of birds in relation to tropical forest fragmentation. Between 2003 and 2005, three understorey passerine species were radio-tracked in five locations of a fragmented and in two locations of a contiguous forest landscape on the Atlantic Plateau of São Paulo in south-eastern Brazil. Standardized ten-day home ranges of 55 individuals were used to determine influences of landscape pattern, season, species, sex and age. In addition, total observed home ranges of 76 individuals were reported as minimum measures of spatial requirements of the species. Further, seasonal home ranges of recaptured individuals were compared to examine site fidelity. Chiroxiphia caudata, but not Pyriglena leucoptera or Sclerurus scansor, used home ranges more than twice as large in the fragmented versus contiguous forest. Home range sizes of C. caudata differed in relation to sex, age, breeding status and season. Seasonal home ranges greatly overlapped in both C. caudata and in S. scansor. Our results suggest that one response by some forest bird species to habitat fragmentation entails enlarging their home ranges to include several habitat fragments, whereas more habitat-sensitive species remain restricted to larger forest patches.