Box 1 | Glossary and contextualization of community processes used in the approach  
Dispersal:  The movement of organisms among sites (Stevens  et al. 2014) and the process by which species can be added to a local site from a regional species pool via immigration, or removed from a local site via emigration. Along with speciation, dispersal is one of the two processes that can add species to communities (MacArthur & Wilson 1967; Vellend 2016).             
Speciation:  The process describing species splitting into two more or less reproductively isolated populations, either due to geographic barriers (allopatry) or in situ divergence (sympatry, Coyne & Orr 2004; Hernández-Hernández et al. 2021). Speciation has not traditionally been a focus in community ecology. However, this process is now recognized as an important mechanism influencing the size of regional species pools and the assembly of communities from them (Ricklefs 1987; Mittelbach & Schemske 2015). Speciation is one of two processes that can add species to a local community, along with immigration via dispersal. Allopatric speciation of geographically isolated populations in particular may increase the size of the regional species pool, and thus the number of species arriving at local sites.   
Ecological selection: Species differ in their population growth rates. These differences emerge from the sum of the absolute fitness of all individuals in a population. Such species-level differences can cause variation in their relative abundance over time, which defines a selection process operating at the level of species that shapes community structure (Vellend 2010, 2016). Ecological selection is the best-studied of the four fundamental processes (Cottenie 2005), and is the most diverse with respect to ecological mechanisms it encompasses. It includes i) the impact of the environment in filtering and sorting species from the species pool (e.g. “constant” selection, Leibold et al. 2004; Vellend 2010; Soininen 2014), ii) density and frequency-dependent effects of interactions (e.g. competition, predation and mutualisms), and iii) impacts of environmental heterogeneity over space or time (variable selection).    
Ecological drift: The change in relative abundances of species over time due to random variation in births and deaths of individuals (Hubbell 2001; Vellend 2010; Gilbert & Levine 2017), leading to stochasticity in species’ abundances over time. Drift can ultimately only erode local biodiversity due to random losses of species from communities because it does not generate or introduce new species (Vellend 2016). Drift is likely the least well-studied of the four community processes, despite the fact that it can play an important role in community assembly even when other more deterministic processes are operating and species are not ecologically equivalent (Gilbert & Levine 2017; Svensson et al. 2018). One signature of drift is that its influence is greater when population sizes are small, such as on islands, isolated lakes, and in small habitat patches (Hubbell 2001; Melbourne & Hastings 2008; Orrock & Watling 2010).    
Note: Ecological selection and drift refer to community-level processes shaping diversity in mixed-species assemblages (see Vellend 2016), not changes in allele frequencies or abundances within populations of single species as in evolutionary biology and population genetics.