Productivity, niche availability, species richness, and extinction risk: Untangling relationships using individual‐based simulations

Abstract

It has often been suggested that the productivity of an ecosystem affects the number of species that it can support. Despite decades of study, the nature, extent, and underlying mechanisms of this relationship are unclear. One suggested mechanism is the “more individuals” hypothesis (MIH). This proposes that productivity controls the number of individuals in the ecosystem, and that more individuals can be divided into a greater number of species before their population size is sufficiently small for each to be at substantial risk of extinction. Here, we test this hypothesis using REvoSim: an individual‐based eco‐evolutionary system that simulates the evolution and speciation of populations over geological time, allowing phenomena occurring over timescales that cannot be easily observed in the real world to be evaluated. The individual‐based nature of this system allows us to remove assumptions about the nature of speciation and extinction that previous models have had to make. Many of the predictions of the MIH are supported in our simulations: Rare species are more likely to undergo extinction than common species, and species richness scales with productivity. However, we also find support for relationships that contradict the predictions of the strict MIH: species population size scales with productivity, and species extinction risk is better predicted by relative than absolute species population size, apparently due to increased competition when total community abundance is higher. Furthermore, we show that the scaling of species richness with productivity depends upon the ability of species to partition niche space. Consequently, we suggest that the MIH is applicable only to ecosystems in which niche partitioning has not been halted by species saturation. Some hypotheses regarding patterns of biodiversity implicitly or explicitly overlook niche theory in favor of neutral explanations, as has historically been the case with the MIH. Our simulations demonstrate that niche theory exerts a control on the applicability of the MIH and thus needs to be accounted for in macroecology.

Niche-mediated bacterial community composition in continental glacier alluvial valleys under cold and arid environments

“…As found in previous studies, the upstream of the dam could prolong the retention time of the river, resulting in the increase and accumulation of nutrients, such as organic matter (Liu et al, 2018 ). According to the more individual hypothesis (Furness et al, 2021 ), the higher resource availability leads to an increased number of individuals ( Supplementary Figure S6 ), thus supporting higher microbial richness. In contrast, serious sediment erosion and nutrient loss made the downstream of the dam unfavorable for microbial habitat, possibly resulting in lower bacterial abundance ( Supplementary Figure S3 ).…”

Different contributions of plant diversity and soil properties to the community stability in the arid desert ecosystem

“…Moreover, this study only analyzed the changes of community stability with spatial scale and its influencing factors. It is well known that functional traits, niche and species turnover also vary across temporal scales ( Furness et al, 2021 ; Xu et al, 2021 ). For example, ephemeral plants are common in desert communities in early spring.…”

Comparison of assembly process and co-occurrence pattern between planktonic and benthic microbial communities in the Bohai Sea

“…As expected, the diversity of microbial community in different habitats was distinct. According to the “more individuals hypothesis,” higher resource availability would increase the number of individuals and thus sustain higher microbial diversity ( Storch et al, 2018 ; Furness et al, 2021 ). In our study, the microbial alpha diversity was higher in sediment than in waters.…”