Abstract
Species extinctions are accelerating globally, yet the mechanisms that maintain local biodiversity remain poorly understood. The extinction of species that feed on or are fed on by many others (i.e. ‘hubs’) has traditionally been thought to cause the greatest threat of further biodiversity loss. Very little attention has been paid to the strength of those feeding links (i.e. link weight) and the prevalence of indirect interactions. Here, we used a dynamical model based on empirical energy budget data to assess changes in ecosystem stability after simulating the loss of species according to various extinction scenarios. Link weight and/or indirect effects had stronger effects on food‐web stability than the simple removal of ‘hubs’, demonstrating that both quantitative fluxes and species dissipating their effects across many links should be of great concern in biodiversity conservation, and the potential for ‘hubs’ to act as keystone species may have been exaggerated to date.
Highlights
Biodiversity loss is a major threat to Earth’s ecosystems (Barnosky et al 2011) and it is crucial to identify and conserve influential ‘keystone’ species or nodes, whose loss would cause the cascading extinctions of many other species (Dunne et al 2002; Jordan 2009)
In the last few decades, the influence of random loss of nodes (‘error’) and selective loss of the most-connected nodes (‘attack’) has been investigated in many real-world networks, e.g. the Internet (Albert et al 2000). All of these networks exhibit high fragility against the removal of the most-connected nodes (i.e. ‘hubs’), which in an ecological context suggests these nodes would represent keystone species that play an important role in maintaining biodiversity
Memmott et al 2004; Dunne & Williams 2009). This conclusion is drawn based on topological approaches that always underestimate the amount of secondary extinctions (Curtsdotter et al 2011)
Summary
Biodiversity loss is a major threat to Earth’s ecosystems (Barnosky et al 2011) and it is crucial to identify and conserve influential ‘keystone’ species or nodes, whose loss would cause the cascading extinctions of many other species (Dunne et al 2002; Jordan 2009). Selective removal of nodes with the most trophic links in a network typically causes more secondary extinctions than random removal of nodes (Dunne et al 2002; Memmott et al 2004; Dunne & Williams 2009) This index of node importance based on degree centrality ignores two major components of food webs: the strength or weight of the links and indirect effects (Scotti et al 2007). This can lead to an inaccurate ranking of species importance, such that removing the most-connected nodes does not necessarily identify the most destructive extinction sequence (Allesina & Pascual 2009)
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