Using soundscapes to investigate homogenization of tropical forest diversity in selectively logged forests

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.

Human-driven land-use changes increasingly threaten biodiversity, particularly in tropical forests where both species diversity and human pressures on natural environments are high. The rapid conversion of tropical forests for agriculture, timber production and other uses has generated vast, human-dominated landscapes with potentially dire consequences for tropical biodiversity. Today, few truly undisturbed tropical forests exist, whereas those degraded by repeated logging and fires, as well as secondary and plantation forests, are rapidly expanding. Here we provide a global assessment of the impact of disturbance and land conversion on biodiversity in tropical forests using a meta-analysis of 138 studies. We analysed 2,220 pairwise comparisons of biodiversity values in primary forests (with little or no human disturbance) and disturbed forests. We found that biodiversity values were substantially lower in degraded forests, but that this varied considerably by geographic region, taxonomic group, ecological metric and disturbance type. Even after partly accounting for confounding colonization and succession effects due to the composition of surrounding habitats, isolation and time since disturbance, we find that most forms of forest degradation have an overwhelmingly detrimental effect on tropical biodiversity. Our results clearly indicate that when it comes to maintaining tropical biodiversity, there is no substitute for primary forests.

To design robust protected area networks, accurately measure species losses, or understand the processes that maintain species diversity, conservation science must consider the organization of biodiversity in space. Central is beta-diversity--the component of regional diversity that accumulates from compositional differences between local species assemblages. We review how beta-diversity is impacted by human activities, including farming, selective logging, urbanization, species invasions, overhunting, and climate change. Beta-diversity increases, decreases, or remains unchanged by these impacts, depending on the balance of processes that cause species composition to become more different (biotic heterogenization) or more similar (biotic homogenization) between sites. While maintaining high beta-diversity is not always a desirable conservation outcome, understanding beta-diversity is essential for protecting regional diversity and can directly assist conservation planning.