Community size affects the signals of ecological drift and niche selection on biodiversity

Abstract

Keywords: aquatic insects; beta diversity deviation; community assembly; demographic 19 stochasticity; dispersal; metacommunities; null models 20 21 22 23 24 25 26 in the relative abundances of genera among large communities in both regions. Habitat destruction, 46 overexploitation, pollution, and reductions in connectivity have been reducing the size of biological 47communities. These environmental pressures will make smaller communities more vulnerable to 48 novel conditions and render community dynamics more unpredictable, as random demographic 49 processes should prevail under these conditions. Incorporation of community size into ecological 50 models should provide conceptual, empirical and applied insights into a better understanding of the 51 processes driving changes in biodiversity. 52Recent syntheses in community ecology propose that four main processes drive the 54 dynamics of metacommunities -deterministic niche selection, ecological drift, dispersal and 55 speciation (Vellend 2010, 2016, Leibold and Chase 2018. At broad spatial scales, dispersal, 56 colonization history, and spatial heterogeneity are thought to produce major biodiversity patterns 57 (Leibold and Chase 2018), while speciation also plays a role by altering the composition of regional 58 species pools at longer time frames (Vellend 2010). Within localities, niche selection determines 59 community structure mainly through species interactions, differential use of resources and species 60 responses to environmental gradients (Leibold and Chase 2018). However, stochasticity may also 61 play a major role in driving local community dynamics, for example, when demographic events 62 occur at random with respect to species identities (Vellend et al. 2014). Indeed, mechanistic models 63 (Orrock and Fletcher 2005, Orrock and Watling 2010) and recent empirical evidence (Gilbert and 64Levine 2017) suggest that ecological drift can even override the effects of niche selection under 65

Latitudinal biodiversity gradients at three levels: Linking species richness, population richness and genetic diversity

“…A species’ range size could also reflect levels of genetic diversity, where small ranges may have lower genetic diversity per species (GenPerSpp) (Fine, ). Small population size or density, typical of tropical species, can lead to increased levels of ecological or genetic drift (Fine, ; Mittelbach et al, ; Siqueira et al, ). While genetic drift has not received much empirical support as an explanation for the species richness gradient, it could be more relevant for intraspecific diversity.…”

“…where small ranges may have lower genetic diversity per species (GenPerSpp) (Fine, 2015). Small population size or density, typical of tropical species, can lead to increased levels of ecological or genetic drift (Fine, 2015;Mittelbach et al, 2007;Siqueira et al, 2019).…”

Spatial heterogeneity in temporal dynamics of Alpine bird communities along an elevational gradient

“…taxa with narrow ecological tolerance) increases as environmental conditions become increasingly demanding (Devictor et al., 2010), this may contribute to a larger influence of deterministic mechanisms (mainly selection) in shaping assemblages at harsh, high‐mountain environments. These factors may counterbalance the effect of community size, as it has been recently suggested that ecological drift drives variation in small communities and that they deviate less from null expectations in comparison with larger communities (Siqueira et al., 2019).…”