Characterising extinction debt following habitat fragmentation using neutral theory

Abstract

Habitat loss leads to species extinctions, both immediately and over the long term as ‘extinction debt’ is repaid. The same quantity of habitat can be lost in different spatial patterns with varying habitat fragmentation. How this translates to species loss remains an open problem requiring an understanding of the interplay between community dynamics and habitat structure across temporal and spatial scales. Here we develop formulas that characterise extinction debt in a spatial neutral model after habitat loss and fragmentation. Central to our formulas are two new metrics, which depend on properties of the taxa and landscape: ‘effective area’, measuring the remaining number of individuals and ‘effective connectivity’, measuring individuals’ ability to disperse through fragmented habitat. This formalises the conventional wisdom that habitat area and habitat connectivity are the two critical requirements for long‐term preservation of biodiversity. Our approach suggests that mechanistic fragmentation metrics help resolve debates about fragmentation and species loss.

Habitat Fragmentation Increases Overall Richness, but Not of Habitat-Dependent Species

“…This study helps to inform the debate on the effects of FPS on biodiversity (Fahrig, 2017;Fletcher et al, 2018a;Fahrig et al, 2019;Thompson et al, 2019). FPS had no effect or a positive effect on overall gamma-diversity of the focal-habitat across the patches in a landscape, but the gamma-diversity of species for which the habitat had high suitability could decline with FPS depending on species characteristics with respect to specialization and competitive ability.…”

“…Theoretical modeling is a useful way to address contested issues where field data are difficult to collect and are subject to confounding variables. To this end, simulation models have been used to study FPS, which represent individual organisms moving across simulated landscapes (Gunton et al, 2017;Rybicki et al, 2019;Thompson et al, 2019). However, these studies are conducted on binary landscapes with the space between the focal-habitat patches (the habitat type of interest), the matrix, being a single, usually highly unsuitable, habitat type.…”

pycoalescence and rcoalescence: Packages for simulating spatially explicit neutral models of biodiversity

“…A common scenario for neutral modelling is simulating a fully spatially explicit landscape, possibly with changes to the structure and proportion of habitat over time (e.g. Bongalov et al., 2019; Chisholm et al., 2018; Thompson, Chisholm, & Rosindell, 2019). As an example, consider a scenario where an area outside a hypothetical national park will be deforested.…”

“…We have included a diverse feature set, including spatially and temporally varying density, sampling from subsets of the landscape and different modes of dispersal that we believe will cater for the vast majority of studies requiring spatially explicit neutral models. Published applications using these packages include exploring the effects of habitat fragmentation on extinction debt (Thompson, Chisholm, & Rosindell, 2019) and investigating the contribution of niche and neutral processes in a tropical rainforest (Bongalov et al., 2019).…”

Neutral theory exposes the challenge of bending the curve of biodiversity loss for the post-2020 Global Biodiversity Framework

“…Furthermore, even though the model presented here was purposely simplistic, simulations can be made more sophisticated by adding dispersal and speciation. Adjusting these parameters have, for example, already been be used to predict extinction debt following habitat fragmentation (Thompson et al 2019) or whether restoration can mitigate human impacts (Buschke & Sinclair 2019).…”