Importance of biotic niches versus drift in a plant‐inhabiting arthropod community depends on rarity and trophic group

Abstract

Communities are mostly composed of rare species; yet, the factors that determine their patterns of occurrence remain obscure. Theory predicts that, in contrast with common species, the occurrence of rare species will be poorly correlated with environmental variables (niches) and more affected by stochasticity (ecological drift), but how this pattern varies across different trophic groups is still poorly understood. Here, we compared the ability of environmental variables (bottomup biotic niches) to predict the occurrence of plant-dwelling arthropods across different abundance classes in the Cape Floristic Region of South Africa. We compared three trophic groups, including 104 herbivorous hemipteran, 171 parasitoid wasp and 84 spider species, totalling 4511 individuals in 48 quadrats. To quantify bottom-up biotic niches, we studied the influences of species composition of plants on hemipterans, and of plants and hemipterans on spiders and wasps. We compared the observed strength of the correlation between rare species and their niches with expectations that were generated by repeatedly rarefying abundant species. A large proportion of arthropod species were very rare, i.e. with only one or two individuals (49-55%). Although rarefying abundant species greatly decreased the correlation with bottom-up biotic niches, bottom-up biotic niches generally better predicted the occurrence of rarefied abundant species than very rare ones, suggesting a greater influence of drift on very rare arthropods. That is, (very) rare arthropods are distributed more randomly than rarefied abundant species. Nevertheless, trophic groups differed in the details of their response to bottom-up biotic niches. Plant species composition was a better predictor of rarefied abundant than truly rare hemipterans. In contrast, the importance of bottom-up biotic niches among abundance classes varied less visibly in spiders and wasps. Our study thus suggests that the importance of niches in structuring arthropod communities depends on species rarity and trophic group.

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

“…The role of stochastic community assembly processes in arranging species within and among communities has gained support from theoretical models (Mouquet and Loreau 2003, Orrock and Fletcher 2005, Durães et al 2016 and empirical data (Cottenie 2005, Germain et al 2017, Lancaster and Downes 2017, Swan and Brown 2017, Valente-Neto et al 2017, Bosc et al 2019. Here, we provide empirical observational evidence that community size, a simple characteristic of communities, can mediate the interplay between niche selection and ecological drift as drivers of b-diversity in tropical and boreal stream metacommunities.…”

“…However, stochasticity may also play a role in driving local community dynamics, for example, when demographic events occur at random with respect to species identities (Vellend et al 2014). Indeed, mechanistic models (Orrock and Fletcher 2005, Orrock and Watling 2010), observational studies (Bosc et al 2019), and controlled experiments (Gilbert and Levine 2017) suggest that ecological drift can even override the effects of niche selection under certain circumstances, such as when species’ populations in local communities are small and isolated from other populations. However, the extent to which these findings apply to natural situations is still uncertain, as tests based on field data in regions where community size differs naturally are scarce (Liu et al 2018).…”

Local stochastics and ecoclimatic situation shape phytophagous chafer assemblage composition

“…Investigated macrohabitats were quite different (e.g., forest, grassland, and abandoned plantations). They are known to provide multiple niches (Bosc et al, 2019) for chafer species; however, only a few species were recorded that were specific to these habitats. Most species and resulting assemblages sorted by locality rather than by macrohabitat.…”

Local stochastics and ecoclimatic situation shape phytophagous chafer assemblage composition

“…Investigated macrohabitats were quite different (e.g., forest, grassland, abandoned plantations). They are known to provide multiple niches (Bosc et al 2019) for chafer species, however, only a few species were recorded that were specific to these habitats. Most species and resulting assemblages sorted rather by locality rather than by macrohabitat.…”