The species-area relationship (SAR) gives a quantitative description of the increasing number of species in a community with increasing area of habitat. In conservation, SARs have been used to predict the number of extinctions when the area of habitat is reduced. Such predictions are most needed for landscapes rather than for individual habitat fragments, but SAR-based predictions of extinctions for landscapes with highly fragmented habitat are likely to be biased because SAR assumes contiguous habitat. In reality, habitat loss is typically accompanied by habitat fragmentation. To quantify the effect of fragmentation in addition to the effect of habitat loss on the number of species, we extend the power-law SAR to the species-fragmented area relationship. This model unites the single-species metapopulation theory with the multispecies SAR for communities. We demonstrate with a realistic simulation model and with empirical data for forest-inhabiting subtropical birds that the species-fragmented area relationship gives a far superior prediction than SAR of the number of species in fragmented landscapes. The results demonstrate that for communities of species that are not well adapted to live in fragmented landscapes, the conventional SAR underestimates the number of extinctions for landscapes in which little habitat remains and it is highly fragmented.extinction threshold | habitat conversion | metapopulation capacity | Atlantic forest | Nagoya biodiversity agreement T he species-area relationship (SAR) describes a very general pattern in the occurrence of species, which is fundamental to community ecology (1), biogeography (2), and macroecology (3). Since the 1920s (4, 5), SARs have been applied to describe the occurrence of a wide range of organisms on true islands (6-8), in fragments of distinct habitat (9, 10), and in parts of more arbitrarily delimited contiguous landscapes (1, 3). In the past decades, SAR has become an important concept and a tool also in conservation biology, where it has been used to make broad assessments of species extinctions from habitat loss (11-18). These calculations have been criticized for various reasons (17,(19)(20)(21), but minimally SAR provides a valuable point of reference for the threat that habitat loss poses to biodiversity.SARs are typically applied to a set of habitat fragments within a single landscape, but in conservation, in contrast, the essential question is how many species will persist in different landscapes (regions) with dissimilar amounts of habitat rather than in different fragments within a single landscape. This creates a problem: Habitat loss is virtually always accompanied by fragmentation (22-24), and hence the remaining habitat is not contiguous, unlike assumed by SAR, at the landscape level. In other words, SAR does not account for any adverse effects of fragmentation on the occurrence of species (25, 26). Fragmentation matters whenever individual habitat fragments are small enough to reduce the viability of the respective local populations (27, 28). ...

No abstract

No abstract

No abstract

Studies dealing with community similarity are necessary to understand large scale ecological processes causing biodiversity loss and to improve landscape and regional planning. Here, we study landscape variables influencing patterns of community similarity in fragmented and continuous forest landscapes in the Atlantic forest of South America, isolating the effects of forest loss, fragmentation and patterns of land use. Using a grid design, we surveyed birds in 41 square cells of 100 km 2 using the point count method. We used multivariate, regression analyses and lagged predictor autoregressive models to examine the relative influence of landscape variables on community similarity. Forest cover was the primary variable explaining patterns of bird community similarity. Similarity showed a sudden decline between 20 and 40% of forest cover. Patterns of land use had a second order effect; native bird communities were less affected by forest loss in landscapes dominated by tree plantations (the most suitable habitat for native species) than in landscapes dominated by annual crops or cattle pastures. The effects of fragmentation were inconclusive. The trade-off between local extinctions and the invasion of extra-regional species using recently created habitats is probably the mechanism generating the observed patterns of community similarity. Limiting forest loss to 30-40% of the landscape cover and improving the suitability of human-modified habitats will contribute to maintain the structure and composition of the native forest bird community in the Atlantic forest.

Summary1. The suitability of human-modified habitats for native species and the response of species to habitat edges are two important ecological processes that affect species and communities in fragmented landscapes. However, field studies generally analyse these two processes separately. We extended a recently proposed continuous approach to link these two processes, using empirical data from birds of the Atlantic forest in Argentina, Paraguay and Brazil. 2. We tested different models for describing the responses of birds (both forest and open-habitat species) to the interior-exterior gradient within different edge types (ecotones). We used two types of data: the first originated from a large data set collected at regional scale using the point-count method and the second originated from a detailed local telemetry study of three bird species. 3. For both data sets, these models successfully described the responses to edges of the majority of species and assemblages and significantly influenced the calculated habitat suitability in both native and anthropogenic habitats. Edge effects were seen in the majority of species; however, the magnitude of these effects was influenced by the ecotone type. At the assemblage level, more species avoided edges in the ecotone with tree plantations compared with open habitats. 4. The effect of edges on the calculated habitat suitability was either positive or negative, depending on the function that best described the response of the species to edges and whether they avoided edges or penetrated into the less-preferred habitat. In general, forest species penetrated deeper into tree plantations but moved only short distances into open habitats. 5. Synthesis and applications. Our results demonstrate the impact of edge effects on bird species and communities in fragmented landscapes. Furthermore, the differential penetration capacity of the native forest birds into anthropogenic habitats shows the importance of using a continuous approach to calculate habitat suitability; classic calculation (without considering the distance to the preferred habitat) is likely to bias the calculated suitability and permeability of the hostile matrix and affect our estimations of connectivity.

1. The degradation and replacement of natural ecosystems affect species abundance, diversity and interspecific interaction through the modification of resource availability and environmental conditions. Land uses preserving the forest canopy show higher species richness and similarity to the native forest.2. In this study, we explored changes in the trophic niche overlap of dung beetles between the native forest and different land uses in the semideciduous Atlantic forest, under the hypothesis that trophic niche overlap increases with species richness.3. We sampled dung beetles in protected native forests and four land uses (pine plantations, agroforestry parklands, silvo-pastoral systems and open pastures), using seven potential food sources (monkey, feline, tapir and deer dung, decomposing fruit, decomposing fungi and carrion). The species richness of each habitat, the trophic niche overlap and the relation between both measures were analysed. Also, we explored species trophic preferences in each habitat to explain and discuss the results obtained in trophic niche overlap measures.4. As expected, our results showed a positive relation between species richness and trophic niche overlap. Moreover, the addition of different resources in open habitats did not increase species richness, suggesting that resource availability may not be the main mechanism explaining the empoverished dung beetle community observed in open habitats. Other mechanisms, such as physiological restrictions, may play a role in limiting the use of these habitats. Studies on the mechanisms leading to the patterns of species abundance and diversity observed in land uses are necessary to propose management recommendations that increase the sustainability of open habitats.

No abstract