Abstract
We evaluate potential warning signals that may aid in identifying the proximity of ecological communities to biodiversity thresholds from habitat loss—often termed “tipping points”—in tropical forests. We used datasets from studies of Neotropical mammal, frog, bird, and insect communities. Our findings provide only limited evidence that an increase in the variance (heteroskedasticity) of biodiversity-related parameters can provide a general warning signal of impending threshold changes in communities, as forest loss increases. However, such an apparent effect was evident for amphibians in the Brazilian Atlantic Forest and Amazonian mammal and bird communities, suggesting that impending changes in some species assemblages might be predictable. We consider the potential of such warning signs to help forecast drastic changes in biodiversity.
Highlights
Our scientific capability to predict abrupt changes in nature—such as from disease epidemics, earthquakes, and insect-plagues—is limited, and this can have serious consequences for human wellbeing[1]
We focused on heteroskedasticity of biodiversity measures as a potential warning signal of collapse (Fig. 1), because heteroskedasticity is related to greater variance in a system and is simple to calculate and extract from all measures of diversity, including richness and incidence
The threshold values provided by authors for Brazilian Atlantic forest birds, and Amazonian mammals and birds were higher than the confidence interval of our thresholds (Af: Authors: 70.61% of habitat loss, our study: 77.58% ± 3.61 s.e.; Am mammals and birds: Authors: 51.58%, our study: 64.17 ± 2.13; Fig. 2a)
Summary
Our scientific capability to predict abrupt changes in nature—such as from disease epidemics, earthquakes, and insect-plagues—is limited, and this can have serious consequences for human wellbeing[1]. The ecological threshold concept is generally defined as a point where even small changes in environmental conditions will lead to large changes in the state of a system—frequently termed a “tipping point”[2,3,4] This concept is useful for guiding decisions made on relatively short timescales and in human-impacted systems. Thresholds may originate from species having synchronous responses to habitat loss and fragmentation, such as shrinking forest patch size and increasing isolation, exacerbating Allee effects or breakdowns in mutualisms[6,7,9] These nonlinear effects of habitat loss and fragmentation on population abundances can cause dramatic shifts in community composition when disturbances surpass a level that the community can no longer tolerate. We might detect anomalies, such as increased autocorrelation and variance, in biodiversity-related metric values prior to reaching thresholds in response to increasing forest loss[15,18]
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