Extinction–immigration dynamics lag behind environmental filtering in shaping the composition of tropical dry forests within a changing landscape

Abstract

The impact of rapid habitat loss and fragmentation on biodiversity is a major issue. However, we still lack an integrative understanding of how these changes influence biodiversity dynamics over time. In this study, we investigate the effects of these changes in terms of both niche-based and neutral dynamics. We hypothesize that habitat loss has delayed effects on neutral immigration-extinction dynamics, while edge effects and environmental heterogeneity in habitat patches have rapid effects on niche-based dynamics.We analyzed taxonomic and functional composition of 100 tree communities in a tropical dry forest landscape of New-Caledonia subject to habitat loss and fragmentation. We designed an original, process-based simulation framework, and performed Approximate Bayesian Computation to infer the influence of niche-based and neutral processes. Then, we performed partial regressions to evaluate the relationships between inferred parameter values of communities and landscape metrics (distance to edge, patch area, and habitat amount around communities), derived from either recent or past (65 yr ago) aerial photographs, while controlling for the effect of soil and topography.We found that landscape structure influences both environmental filtering and immigration. Immigration rate was positively related to past habitat amount surrounding communities. In contrast, environmental filtering was mostly affected by present landscape structure and mainly influenced by edge vicinity and topography.Our results highlight that landscape changes have contrasting spatio-temporal influences on niche-based and neutral assembly dynamics. First, landscape-level habitat loss and community isolation reduce immigration and increase demographic stochasticity, resulting in slow decline of local species diversity and extinction debt. Second, recent edge creation affects environmental filtering, incurring rapid changes in community composition by favoring species with edge-adapted strategies. Our study brings new insights about temporal impacts of landscape changes on biodiversity dynamics. We stress that landscape history critically influences these dynamics and should be taken into account in conservation policies.

The Internal Structure of Metacommunities

“…For instance, the spatial structure of environmental features among sites almost always changes different explicitly determined landscapes due to spatial contingency (Peres-Neto et al 2012). In contrast with many previous studies (e.g., Blanchard et al 2020, Jabot 2020), we emphasize that different species can be heterogenous in how they contribute to metacommunity level properties and that different sites can also be heterogenous in how they contribute to these patterns (but see Pandit et al 2009, Legendre and De Cáceres 2013). Using this concept as a starting point, we highlight the importance of understanding the ‘internal structure’ of metacommunities, which can help resolve more complex dynamics that could not be resolved without taking this different perspective.…”

“…Finally, it is increasingly clear that temporal dynamics of community change in metacommunities can provide critical insights about the mechanisms that drive metacommunity patterns (e.g. Jabot et al 2020, Blanchard et al 2020, Guzman et al 2021). We imagine future work on the internal structure of metacommunities as being very amenable to incorporating temporal changes (see for example, Ovaiskainen et al 2017 for an initial step in this direction).…”

“…For instance, the spatial structure of environmental features can vary within landscapes (i.e., among sites) which, in turn, can affect the ways species interact and are sorted into local communities (Peres-Neto et al 2012). Thus, in contrast with many previous studies (e.g., Blanchard et al 2020, Jabot et al 2020, we emphasize that species can be heterogeneous in how they contribute to metacommunity level properties and that different sites can also vary in how they contribute to these patterns (as suggested by earlier work by e.g. Pandit et al 2009, Legendre andDe Cáceres 2013).…”

Environmental range per unit space determines a unimodal pattern of species richness along a heterogeneity gradient

“…Reducing either the number of available spaces or the proportion of available spaces decreases the probability that species occur in their respective available spaces (Chave et al 2002, Tilman 2004, Schwilk and Ackerly 2005, Chisholm and Lichstein 2009). Having fewer available spaces overall, lower proportions of available spaces, and/or larger distances between spaces are strong environmental filters that decrease the probability of species dispersing into their respective available spaces (Bar‐Massada 2015, Blanchard et al 2020). According to the niche theory, it is important for coexisting species to grow in their respective available spaces (Gravel et al 2006, Levine and HilleRisLambers 2009, Bar‐Massada 2015).…”

Imprints of Past Habitat Area Reduction on Extant Taxonomic, Functional, and Phylogenetic Composition

“…Changes in the area of available habitat should affect stochastic demographic dynamics, yielding greater abundance variation among species and extinction risk in smaller refugia (Figure 1). Specifically, we expect that the influence of ecological drift be greater in smaller assemblages and thus shape the relative abundances of species (Vellend, 2010;Blanchard et al, 2020). Thus, we expect demographic fluctuations to happen quickly over the timescale of habitat changes, so that extant taxonomic diversity should be more sensitive to recent than to ancient refugia.…”