Keystoneness, centrality, and the structural controllability of ecological networks

Abstract

An important dimension of a species' role is its ability to alter the state and maintain the diversity of its community. Centrality metrics have often been used to identify these species, which are sometimes referred as “keystone” species. However, the relationship between centrality and keystoneness is largely phenomenological and based mostly on our intuition regarding what constitutes an important species. While centrality is useful when predicting which species' extinctions could cause the largest change in a community, it says little about how these species could be used to attain or preserve a particular community state. Here we introduce structural controllability, an approach that allows us to quantify the extent to which network topology can be harnessed to achieve a desired state. It also allows us to quantify a species' control capacity—its relative importance—and identify the set of species that are critical in this context because they have the largest possible control capacity. We illustrate the application of structural controllability with ten pairs of uninvaded and invaded plant‐pollinator communities. We found that the controllability of a community is not dependent on its invasion status, but on the asymmetric nature of its mutual dependences. While central species were also likely to have a large control capacity, centrality fails to identify species that, despite being less connected, were critical in their communities. Interestingly, this set of critical species was mostly composed of plants and included every invasive species in our dataset. We also found that species with high control capacity, and in particular critical species, contribute the most to the stable coexistence of their community. This result was true, even when controlling for the species' degree, abundance/interaction strength, and the relative dependence of their partners. Synthesis. Structural controllability is strongly related to the stability of a network and measures the difficulty of managing an ecological community. It also identifies species that are critical to sustain biodiversity and to change or maintain the state of their community and are therefore likely to be very relevant for management and conservation.

Anti-Tick Microbiota Vaccine Impacts Ixodes ricinus Performance during Feeding

“…Microorganisms do not exist in isolation but form complex ecological interaction webs, with a positive, negative or no impact on the species involved [ 40 , 41 ]. A particularly important feature of any species is its ability to alter the abundance of other species and shape the whole community, which is referred as a species keystoneness [ 42 ]. Network models provide tools for understanding how the microbiota structure can influence host health [ 41 , 43 , 44 , 45 ].…”

Core–periphery dynamics in a plant–pollinator network

“…The latter finding has important implications for our understanding of the dynamics of ecological communities, as it implies that no species will play a central role in the community all the time; in contrast, species seem to alternate in their positions as core or peripheral, resulting in a highly dynamic community organization. The above finding also has far-reaching practical implications, as the idea of focusing management and conservation efforts on a small subset of species at the network core (Cagua, Wootton, & Stouffer, 2019;Chacoff et al, 2012;Fleishman et al, 2002Fleishman et al, , 2007García-Algarra et al, 2017;Hegland et al, 2010;Maia, Vaughan, & Memmott, 2019) may be difficult to achieve, given that virtually no species plays that role consistently over time in the long run. Our findings do indicate that a small subset of species is likely to be found playing a key role as part of the network core in many subseasons and years, which brings them close to the notion of 'core' species and would make them adequate targets for conservation efforts.…”

Temporal switching of species roles in a plant–pollinator network

“…The latter finding has far-reaching practical implications, as the idea of focusing management and conservation efforts on a small subset of species at the network core (19; 20; 21; 22; 23; 36; 37) may be difficult to achieve, given that virtually no species plays that role consistently over time in the long run. Our findings do indicate that a small subset of species is likely to be found playing a key role as part of the network core in many seasons and years, which brings them close to the notion of “core” species and would make them adequate targets for conservation efforts.…”