Species coexistence and overlapping distributions in a metacommunity are compatible with niche differences and competition at a local scale

Abstract

<jats:p>Niche partitioning is the most studied factor structuring communities of competing species. In fragmented landscapes, however, a paradox can exist: different taxa may competitively dominate different types of habitat patches, resulting in a form of spatial niche partitioning, yet differences in long-term distributions among species can appear surprisingly small. This paradox is illustrated by an emblematic metacommunity - that of Daphnia spp. in rockpools on the Finnish Baltic coast, where three species compete with each other, have distinct ecological preferences, yet largely overlap in long-term distributions. Here we examine how metacommunity models that explicitly estimate species-specific demographic parameters can solve the apparent paradox. Our research confirms previous studies that local extinction rates are influenced by environmental variables in a strong and species-specific way and are considerably increased by interspecific competition. Yet, our simulations show that this situation exists alongside interspecific differences in realized niches that are, overall, small, and identified three main explanations for this compatibility. Our results illustrate how state-space modelling can clarify complex metacommunity dynamics and explain why local competition and niche differentiation do not always scale up to the landscape level.</jats:p>

Genetic drift shapes the evolution of a highly dynamic metapopulation

“…We found IBD both within and between islands, suggesting that gene flow is more likely between geographically closer subpopulations from the same and from different islands. This pattern is consistent with previous findings that subpopulations on the same island are genetically less differentiated than subpopulations on different islands (Roulin et al, 2016) and that dispersal distance exponentially decays, in which case long distance colonization events are rare (Dubart et al, 2020; Pajunen, 1986; Pajunen & Pajunen, 2003). As described for several aquatic organisms, sequential colonization can shape IBD (Montero-Pau et al, 2018).…”

“…By identifying the genomic variation, age, ecology, and geography of individual subpopulations, we investigated the evolution of interconnected populations. Previous research in our focal D. magna metapopulation has found high turnover dynamics, small numbers of subpopulation founders, and the accumulation of deleterious mutations in the mitochondrial genome, all consistent with the propagule model (Altermatt & Ebert, 2010; Dubart et al, 2020; Ebert et al, 2013; Fields et al, 2018; Zumbrunn, 2011). Subpopulations tend to be short-lived, undergoing frequent, strong genetic bottlenecks during the colonization of empty habitat patches and subsequently suffering from inbreeding.…”

“…A subpopulation was considered newly established if animals were observed after three consecutive visits of seeing no animals, i.e., animals not being seen for more than a year. The chance of a subpopulation remaining undetected for three visits in a row was estimated to be below two percent, as the detection probability of D. magna is 0.74 in this survey (Dubart et al, 2020). The subpopulation age was log10(age + 1)-transformed for statistical analyses.…”

“…As previous findings have suggested, this metapopulation follows the propagule model and is highly dynamic, i.e., characterized by small and unstable subpopulations, high extinction–(re)colonization dynamics, and strong colonization bottlenecks. A long-term survey of this metapopulation (Dubart et al, 2020; Ebert et al, 2013; Pajunen & Pajunen, 2003) has revealed high turnover rates: of the 20 % of the rock pools that contain D. magna subpopulations, about 20 % go extinct every year, and about 5 % of the empty ponds are colonized per year. This metapopulation has been shown to be an “inverse mainland-island” type of metapopulation (Altermatt & Ebert, 2010), where the pool of migrants primarily come from small subpopulations.…”

A genomic analysis of parasite-mediated population differentiation in a metapopulation

“…= 5 yrs). Population age was assessed from the longitudinal time series data (Ebert, et al 2001; Dubart et al, 2020; Pajunen & Pajunen, 2003). A population which was not present for two survey periods (and one winter) in a row is considered extinct.…”