Ecological communities are vulnerable to realistic extinction sequences

Abstract

Loss of species will directly change the structure and potentially the dynamics of ecological communities, which in turn may lead to additional species loss (secondary extinctions) due to direct and/or indirect effects (e.g. loss of resources or altered population dynamics). Furthermore, the vulnerability of food webs to repeated species loss is expected to be affected by food web topology, species interactions, as well as the order in which species go extinct. Species traits such as body size, abundance and connectivity might determine a species’ vulnerability to extinction and, thus, the order in which species go primarily extinct. Yet, the sequence of primary extinctions, and their effects on the vulnerability of food webs to secondary extinctions, when species abundances are allowed to respond dynamically, has only recently become the focus of attention. Here, we analyse and compare topological and dynamical robustness to secondary extinctions of model food webs, in the face of 34 extinction sequences based on species traits. Although secondary extinctions are frequent in the dynamical approach and rare in the topological approach, topological and dynamical robustness tends to be correlated for many bottom–up directed, but not for top–down directed deletion sequences. Furthermore, removing species based on traits that are strongly positively correlated to the trophic position of species (such as large body size, low abundance, high net effect) is, under the dynamical approach, found to be as destructive as removing primary producers. Such top–down oriented removal of species are often considered to correspond to realistic extinction scenarios, but earlier studies, based on topological approaches, have found such extinction sequences to have only moderate effects on the remaining community. Thus, our result suggests that the structure of ecological communities, and therefore the integrity of important ecosystem processes could be more vulnerable to realistic extinction sequences than previously believed.

Biodiversity and Resilience of Ecosystem Functions

“…This could result in poor management advice and 70 undervaluation of the importance of biodiversity, because whilst relatively low levels of 71 biodiversity can be adequate to provide current function [12], higher levels might be needed 72 to support similar levels of function under environmental change [2,[13][14][15][16][17][18]. Therefore, 73 there is a need to identify the characteristics of resilient ecosystem functions and capture 74 these in both predictive models and management guidance. 75 76 Defining and applying the resilience concept 77 Resilience is a concept with numerous definitions in ecological [19], social [20] and other 78 sciences [21].…”

The use of DNA barcodes in food web construction—terrestrial and aquatic ecologists unite!

“…Food webs have been described as the defining objects of community ecology (Kitching 2004)-since if we want to understand fundamental issues such as (i) the extent to which populations of different taxa depend on each other, and how a change in the abundance of one species is likely to reflect into a change in the abundance of another (Polis and Winemiller 1996); (ii) how the extinction of one species may result in the extinction of another (Dunne et al 2002;Byrnes et al 2007;Srinivasan et al 2007;Pearse and Altermatt 2013;Berg et al 2015); (iii) how new species may infiltrate community structure and functioning (e.g., Henneman and Memmott 2001;Sheppard et al 2004;Byrnes et al 2007); or (iv) how community organization varies between different parts of the world (Lewinsohn and Roslin 2008;Forister et al 2015), among different feeding guilds (van Veen et al 2008;Novotny et al 2010) or with different levels of environmental change (Tylianakis et al 2007(Tylianakis et al , 2008; Tylianakis and Binzer 2014;Kaartinen and Roslin 2011), then we most certainly need to know who feeds on whom. Likewise, if we are interested in restoring a oncedisturbed habitat, then we should be asking whether we can restore not only what species are there, but also how they interact with each other (Montoya et al 2012).…”

The reliability of R50 as a measure of vulnerability of food webs to sequential species deletions

“…Using a dynamical approach and R 50 as a measure of food web robustness, Berg et al () showed, contrary to most previous studies (all using a topological approach, with one exception; Curtsdotter et al ), that top–down oriented primary species deletions (targeting species with high trophic position, large body size or low numerical abundance) can be as devastating as bottom–up oriented deletion sequences. This is of great relevance since much evidence (Lande , Cardillo et al ) suggests that species with high trophic position, large body size and/or low numerical abundance have disproportionally high extinction risks.…”