Nested species interactions promote feasibility over stability during the assembly of a pollinator community

Abstract

The foundational concepts behind the persistence of ecological communities have been based on two ecological properties: dynamical stability and feasibility. The former is typically regarded as the capacity of a community to return to an original equilibrium state after a perturbation in species abundances and is usually linked to the strength of interspecific interactions. The latter is the capacity to sustain positive abundances on all its constituent species and is linked to both interspecific interactions and species demographic characteristics. Over the last 40 years, theoretical research in ecology has emphasized the search for conditions leading to the dynamical stability of ecological communities, while the conditions leading to feasibility have been overlooked. However, thus far, we have no evidence of whether species interactions are more conditioned by the community's need to be stable or feasible. Here, we introduce novel quantitative methods and use empirical data to investigate the consequences of species interactions on the dynamical stability and feasibility of mutualistic communities. First, we demonstrate that the more nested the species interactions in a community are, the lower the mutualistic strength that the community can tolerate without losing dynamical stability. Second, we show that high feasibility in a community can be reached either with high mutualistic strength or with highly nested species interactions. Third, we find that during the assembly process of a seasonal pollinator community located at The Zackenberg Research Station (northeastern Greenland), a high feasibility is reached through the nested species interactions established between newcomer and resident species. Our findings imply that nested mutualistic communities promote feasibility over stability, which may suggest that the former can be key for community persistence.

Keystoneness, centrality, and the structural controllability of ecological networks

“…First, we found a comparatively small but thought‐provoking negative relationship between the controllability of a network and its nestedness. Previous studies indicate that nestedness promotes species coexistence and confers robustness to extinction (Bastolla et al, ; Memmott et al, ) even at the expense of the dynamic stability of the mutualistic community (Saavedra et al, ). These observations are in agreement with our results, as we would expect the dynamic stability (the ability to return to equilibrium after a perturbation in species abundances) of a community to be correlated to the difficulty to control it.…”

“…To allow comparison across communities, the structural stability values were scaled within each network to have a mean of zero and a standard deviation of one. Here, we assume values of the mutualistic trade-off and mean interspecific competition of δ = 0 and ρ = 0.01 respectively (Saavedra et al, 2016). However, the choice of these parameters does not affect the results (Supporting Information S4) the effects that the other species have in the community.…”

A guideline to study the feasibility domain of multi-trophic and changing ecological communities

“…Yet, ecological communities are dynamic and permanently changing ( Grant and Grant, 2014;Saavedra et al, 2016a;2016b ). Thus, the challenge is to integrate the information given by changes of species interactions under a systematic analysis of the feasibility domain Saavedra et al, 2017a ).…”

“…This normalized solid angle ( A ) can be efficiently computed via a quasi-Monte Carlo method for even relatively large communities ( Genz and Bretz, 2002;Saavedra et al, 2016b ). The code in R to compute this probability is archived on GitHub.…”

“…Analytically, ( A ) can be calculated by the cumulative function of a multivariate Gaussian distribution ( Ribando, 2006;Saavedra et al, 2016b ):…”