Associations of Forest Cover, Fragment Area, and Connectivity with Neotropical Understory Bird Species Richness and Abundance

Abstract

Theoretical and empirical studies demonstrate that the total amount of forest and the size and connectivity of fragments have nonlinear effects on species survival. We tested how habitat amount and configuration affect understory bird species richness and abundance. We used mist nets (almost 34,000 net hours) to sample birds in 53 Atlantic Forest fragments in southeastern Brazil. Fragments were distributed among 3 10,800-ha landscapes. The remaining forest in these landscapes was below (10% forest cover), similar to (30%), and above (50%) the theoretical fragmentation threshold (approximately 30%) below which the effects of fragmentation should be intensified. Species-richness estimates were significantly higher (F= 3715, p = 0.00) where 50% of the forest remained, which suggests a species occurrence threshold of 30-50% forest, which is higher than usually occurs (<30%). Relations between forest cover and species richness differed depending on species sensitivity to forest conversion and fragmentation. For less sensitive species, species richness decreased as forest cover increased, whereas for highly sensitive species the opposite occurred. For sensitive species, species richness and the amount of forest cover were positively related, particularly when forest cover was 30-50%. Fragment size and connectivity were related to species richness and abundance in all landscapes, not just below the 30% threshold. Where 10% of the forest remained, fragment size was more related to species richness and abundance than connectivity. However, the relation between connectivity and species richness and abundance was stronger where 30% of the landscape was forested. Where 50% of the landscape was forested, fragment size and connectivity were both related to species richness and abundance. Our results demonstrated a rapid loss of species at relatively high levels of forest cover (30-50%). Highly sensitive species were 3-4 times more common above the 30-50% threshold than below it; however, our results do not support a unique fragmentation threshold.

Historical knowledge, richness and relative representativeness of the avifauna of the largest native urban rainforest in the world

“…Despite differences in sampling effort, we found that the avifauna composition of CSP and that of the inner slope patches are similar (Appendix 1), corroborating the hypothesis that even fragmented landscapes with high levels of forest cover can maintain similar species richness to areas of continuous forest (Martensen et al 2012, Morante-Filho et al 2015. This supports the idea that forest patches surrounding Serra da Cantareira should be protected, since they can act as corridors between our study area and other large AF remnants, such as those in Serra da Mantiqueira and Serra do Mar (Fig.…”

“…Habitat disturbance is one of the main drivers of functional extinctions of sensitive guilds, such as understory insectivorous and large-bodied frugivorous (Martensen et al 2012, Galetti et al 2013, Morante-Filho et al 2015. It is very possible that, of the currently rarest species in our study area -e.g.…”

Contemporary and historic factors influence differently genetic differentiation and diversity in a tropical palm

“…Matrix resistance has been pinpointed as an important factor affecting the mobility of individuals and also abundance, occurrence and genetic variability (Eycott et al, 2012;Lange et al, 2012). The change in forest cover may also change the abundance and richness of seed dispersers and pollinators (e.g., González-Varo et al, 2009;Martensen et al, 2012). Most fragments in the studied region of the Atlantic forest are too small (o50 ha; Ribeiro et al, 2009) to support populations of large forest-dwelling frugivorous birds that can move over large distances, such as toucans and cotingas (Galetti et al, 2013).…”

The effects of forest-savanna-grassland gradients on bird communities of Chiquitano Dry Forests domain, in western Brazil

“…The understory insectivorous birds are sensitive to forest loss and fragmentation because they are generally more selective in the habitat use, with small body size and restricted ability to cross open areas and move between forest fragments, making them dependent on large and well connected patches of forests in order to maintain their populations (Martensen et al 2012).…”