Abstract
Tropical forests are undergoing drastic transformations, putting at risk the species that rely on them. On the island of Borneo, between 1973 and 2015, 50% of the forest has been lost, much of this to oil palm and other industries. We explore the impacts of these four decades of forest loss on the functionally connected habitat of 245 forest birds and mammals. First, we map potential suitable habitat in 1973 and 2015 by refining reported ranges by elevation, forest cover and patch size. We find that, on average, these species have lost 28% of habitat within their ranges. Then we use graph-theory connectivity models to calculate the amount of area that is functionally connected for each species, according to their natal dispersal abilities. This analysis shows a mean loss of 35% of their connected habitat and reveals the larger, and often hidden, impacts from deforestation. Losses in functionally connected habitat are largely driven by area of habitat loss, yet maximum elevational range limit also explain some of the differences modelled across species with lowland species being the most affected. We present a vulnerability index of threat arising from functionally connected habitat loss. The spatial aggregation of this vulnerability index serves as a tool for setting conservation priorities for forest remnants on Borneo, given that most of the ranges of these species are not protected. We make recommendations for the use of connectivity models to prioritize resources for research and conservation on Borneo and other biodiversity hotspots.
Highlights
Habitat loss, fragmentation, and degradation due to agricultural expansion are the main threats to tropical ecosystems and biodiversity (Pimm and Jenkins, 2010; Haddad et al, 2015)
In order to understand the changes in functionally connected habitat availability, we modeled the relative connectivity loss (ECA) as a function of maximum elevational range limit, mean dispersal distance, change in area of habitat, and change in mean fractal index using general linear mixedeffects models (GLMMs) (Table 1)
After accounting for remaining forest cover and elevation constraints, we found that the area of habitat within the individual ranges of the 245 forest species (216 birds and 29 mammals) was greatly reduced between 1973 and 2015 (Figure 1)
Summary
Fragmentation, and degradation due to agricultural expansion are the main threats to tropical ecosystems and biodiversity (Pimm and Jenkins, 2010; Haddad et al, 2015). The resulting fragmentation and degradation effects on species and ecosystems are pervasive and far ranging (Clavel et al, 2011; Estes et al, 2011; Schnell et al, 2013; Haddad et al, 2015). This is especially relevant in biodiversity hotspots, where large concentrations of endemic species coincide with alarming rates of habitat loss (Balmford and Long, 1994; Myers et al, 2000; Jenkins et al, 2013). Losses in ecosystem functions can imperil important animal-aided restoration efforts (Corlett, 2001; Strassburg et al, 2016) and species’ adaptability and persistence in future landscapes under climate change scenarios (Scheffers et al, 2016)
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