Predicting biodiversity change and averting collapse in agricultural landscapes

Abstract

The equilibrium theory of island biogeography is the basis for estimating extinction rates and a pillar of conservation science. The default strategy for conserving biodiversity is the designation of nature reserves, treated as islands in an inhospitable sea of human activity. Despite the profound influence of islands on conservation theory and practice, their mainland analogues, forest fragments in human-dominated landscapes, consistently defy expected biodiversity patterns based on island biogeography theory. Countryside biogeography is an alternative framework, which recognizes that the fate of the world's wildlife will be decided largely by the hospitality of agricultural or countryside ecosystems. Here we directly test these biogeographic theories by comparing a Neotropical countryside ecosystem with a nearby island ecosystem, and show that each supports similar bat biodiversity in fundamentally different ways. The island ecosystem conforms to island biogeographic predictions of bat species loss, in which the water matrix is not habitat. In contrast, the countryside ecosystem has high species richness and evenness across forest reserves and smaller forest fragments. Relative to forest reserves and fragments, deforested countryside habitat supports a less species-rich, yet equally even, bat assemblage. Moreover, the bat assemblage associated with deforested habitat is compositionally novel because of predictable changes in abundances by many species using human-made habitat. Finally, we perform a global meta-analysis of bat biogeographic studies, spanning more than 700 species. It generalizes our findings, showing that separate biogeographic theories for countryside and island ecosystems are necessary. A theory of countryside biogeography is essential to conservation strategy in the agricultural ecosystems that comprise roughly half of the global land surface and are likely to increase even further.

Quantifying and sustaining biodiversity in tropical agricultural landscapes

“…Moreover, we start our approach by identifying tree cover at the finest spatial scales feasible using satellite images, for two reasons. First, previous studies of bats and birds suggest that biodiversity responds to changes in small areas, such as the area inside a circle with a 50-to 70-m radius (3,19). Second, resampling or aggregating tree cover from smaller to larger scales is simple with spatial data.…”

“…We focused on remotely sensing tree cover because it is a good predictor of biodiversity in deforested tropical regions (3,19). Moreover, we start our approach by identifying tree cover at the finest spatial scales feasible using satellite images, for two reasons.…”

“…Specifically, our models predicting the number of species at a site (α-diversity; Tables S2-S4) coupled with results that describe the kinds of species at a site (β-diversity) support arguments that increasing tree cover around existing forest reserves will lead to small gains in the number of species, but the species gained tend to be rare, unique, and at risk for extinction because of deforestation (2,3,41,42) Our results also suggest that conservation efforts to diversify farmland by increasing tree cover in and around crop fields and pastures leads to large gains in the number of species, but the species gained tend to be common. Our results provide a theoretical basis for aligning conservation strategies to slow extinctions and for boosting some ecosystem services by buffering remaining forests with wildlife-friendly farmland and regenerating forests where politically feasible, given demands to farm the planet (43).…”

“…1B). These forest elements, together with the agricultural land in which they are embedded, support significant dimensions of biodiversity, whereas the adjacent crop fields and pastures support a different community (2,3).…”

Bats in the Anthropogenic Matrix: Challenges and Opportunities for the Conservation of Chiroptera and Their Ecosystem Services in Agricultural Landscapes

“…Although one study has suggested that landscapes dominated by crops and open fields have a stronger negative influence on bats than water (Ekman and de Jong 1996), a recent analysis of bat responses to isolation on islands versus in forest fragments embedded in agricultural matrix suggests that the anthropogenic matrix is more permeable than water matrix (Mendenhall et al 2014). Thus, agricultural intensification at the landscape level should make the matrix less permeable due to the reduction of natural resources and structural elements such as trees, affecting not only the persistence of bats in fragmented landscapes, but also the degree to which bat assemblages show a negative response to agriculture.…”