Resource availability determines the importance of niche‐based versus stochastic community assembly in grasslands

Abstract

Niche‐based selection and stochastic processes can operate simultaneously to generate spatial and temporal variation in species composition. Yet, the conditions under which ecological dynamics are dominated by niche‐based versus stochastic processes are poorly understood. Using a field experiment in early‐successional temperate grassland and null models of beta diversity, this study investigates the effects of soil nutrient supply on the relative importance of niche‐based selection versus stochastic dynamics for variation in species composition among sites. Nutrient availability was manipulated experimentally, individual seed mixtures with 25 species were sown in each experimental plot, and then stochastic and deterministic niche‐based assembly processes were allowed to happen. We found that compositional variation among grassland plots with low nutrient supply was driven by stochastic immigration and extinctions. In contrast, nutrient enrichment reduced the importance of stochasticity and imposed a deterministic environmental filter that homogenized communities through the selection of few species with greater competitive ability for light. This demonstrates that soil nutrient availability is a critical environmental feature that dictates the degree to which terrestrial plant communities are controlled by niche‐based selection versus stochastic assembly processes. Our study shows further that alternative states of eutrophic grasslands emerge from initial stochastic variation in the composition of a particular functional group of species that can become dominant at high nutrient supply. We discuss potential mechanisms underlying the shift from stochastic to niche‐driven dynamics along soil nutrient gradients.

Nitrogen addition does not reduce the role of spatial asynchrony in stabilising grassland communities

“…Therefore, the fact that additive beta diversity (b a ), but not the other beta diversity measures, declined with N enrichment suggests that the observed b a responses to N enrichment were largely driven by joint absences of species that became increasingly frequent with more N addition. The lack of beta dissimilarity response to N addition, however, contrasts with those of previous studies reporting that N enrichment could either increase (Chalcraft et al 2008;Houseman et al 2008;Chase 2010) or decrease (Inouye & Tilman 1995;Chalcraft et al 2008;Donohue et al 2009;Conradi et al 2017) beta dissimilarity. Whereas the positive effect of N enrichment on beta dissimilarity has been frequently attributed to greater stochasticity in community assembly leading to alternative community states in more productive environments (Steiner & Leibold 2004;Chase 2010), the negative effect of N enrichment on beta dissimilarity has often been explained by reduced abiotic heterogeneity among localities selecting for more similar local communities (Chalcraft et al 2008;Donohue et al 2009).…”

“…; Conradi et al . ) beta dissimilarity. Whereas the positive effect of N enrichment on beta dissimilarity has been frequently attributed to greater stochasticity in community assembly leading to alternative community states in more productive environments (Steiner & Leibold ; Chase ), the negative effect of N enrichment on beta dissimilarity has often been explained by reduced abiotic heterogeneity among localities selecting for more similar local communities (Chalcraft et al .…”

Environmental filtering both indirectly and directly drives the Dry Tropical Forest species composition and functional composition

“…While neutral processes include stochastic mechanisms and dispersion limitation (Conradi, Temperton, & Kollmann, 2017; Hubbell, 2001), deterministic processes are probed by the ecological niche theory approach (Hutchinson, 1957). In this case, inter/intraspecific interactions and functional traits (Conradi et al, 2017) determine species coexistence through processes which include limiting similarity, with greater relevance of biotic interactions in coexistence patterns (Algar, Kerr, & Currie, 2011; Cadotte & Tucker, 2017; De Bello, Price, Münkemüller, et al, 2012), and environmental filtering in which abiotic forces can condition communities with convergence on functional traits and ecological strategies, which may reflect their tolerance to environmental constraints (Cadotte & Tucker, 2017; Delhaye et al, 2019; Weiher et al, 2011). In turn, these traits may or may not be conserved phylogenetically and consequently be dependent or not on the evolutionary history of adaptive traits (Araújo & Santos, 2019; Pillar & Duarte, 2010; Webb, Ackerly, McPeek, & Donoghue, 2002).…”

The role of plant–soil feedbacks in stabilizing a reindeer‐induced vegetation shift in subarctic tundra

“…The higher soil mineral nitrogen (N) concentrations, but lower total N pool in HMG soils in the heath, suggest that positive plant–soil feedbacks are likely important for the maintenance of the HMG vegetation, at least in naturally nutrient‐poor habitats (Egelkraut, Aronsson, et al., ). The higher quality plant litter inputs of plants growing in HMGs result in a higher mineral nutrient availability in that soil, that in turn supports a more productive vegetation (Conradi, Temperton, & Kollmann, ), thus creating a positive feedback loop (Hobbie, ). How these changes in soil characteristics of HMGs contribute to other abiotic and biotic plant–soil feedbacks remains unknown.…”