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.

A priority for community ecology is to understand the mechanisms determining species composition (Agrawal et al., 2007; Vellend, 2010) and unravel the interplay between ecology, biogeography and evolution. One theoretical approach is to generate biodiversity patterns using theoretical models and compare the patterns to empirical data. The models incorporate processes deemed important from real-world observations or prior theoretical studies. This interplay of theoretical and empirical work helps reveal the elusive links between ecological patterns and their mechanisms. Theoretical models can be studied mathematically or via computer simulations. In this paper, we focus on the latter. Neutral theory represents one notable branch of ecological theory (Hubbell, 2001; Rosindell, Hubbell, & Etienne, 2011). It captures three key mechanisms (dispersal, drift and speciation; Vellend, 2010) in a species-agnostic manner, meaning that species identities do not influence the dynamics. Numerous neutral models have been used

Both niche and stochastic dispersal processes structure the extraordinary diversity of tropical plants, but determining their relative contributions has proven challenging. We address this question using airborne imaging spectroscopy to estimate canopy β‐diversity for an extensive region of a Bornean rainforest and challenge these data with models incorporating niches and dispersal. We show that remotely sensed and field‐derived estimates of pairwise dissimilarity in community composition are closely matched, proving the applicability of imaging spectroscopy to provide β‐diversity data for entire landscapes of over 1000 ha containing contrasting forest types. Our model reproduces the empirical data well and shows that the ecological processes maintaining tropical forest diversity are scale dependent. Patterns of β‐diversity are shaped by stochastic dispersal processes acting locally whilst environmental processes act over a wider range of scales.