Species‐rich ecosystems are vulnerable to cascading extinctions in an increasingly variable world

Abstract

Global warming leads to increased intensity and frequency of weather extremes. Such increased environmental variability might in turn result in increased variation in the demographic rates of interacting species with potentially important consequences for the dynamics of food webs. Using a theoretical approach, we here explore the response of food webs to a highly variable environment. We investigate how species richness and correlation in the responses of species to environmental fluctuations affect the risk of extinction cascades. We find that the risk of extinction cascades increases with increasing species richness, especially when correlation among species is low. Initial extinctions of primary producer species unleash bottom-up extinction cascades, especially in webs with specialist consumers. In this sense, species-rich ecosystems are less robust to increasing levels of environmental variability than species-poor ones. Our study thus suggests that highly species-rich ecosystems such as coral reefs and tropical rainforests might be particularly vulnerable to increased climate variability.

Adaptive rewiring aggravates the effects of species loss in ecosystems

“…22. We explore two scenarios: high (r ¼ 0.75) and low (r ¼ 0.25) correlation among species in their response to environmental variation.…”

“…However, in antagonistic networks like food webs and parasite-host networks, rewiring and reallocation of feeding efforts following prey (host) species loss could lead to increased predation pressure (parasite load) on the remaining prey (host) species in the network. High grazing (predation) pressure have been found to reduce diversity of resource species in natural ecosystems 20,21 and to increase extinction risk of primary producers in model food webs 22 . It is also well-known that high densities of herbivores released from predation can result in destructive overgrazing of primary producers in both terrestrial and aquatic ecosystems 9,23 .…”

Extinctions in Ecological Communities : direct and indirect effects of perturbation on biodiversity

“…As species loss goes on, it is accompanied by the erosion of diversity-related mechanisms stabilizing ecosystem function, e.g. redundancy, response diversity and compensation , Elmqvist et al 2003, Folke et al 2004, Gonzalez and Loreau 2009, Laliberté et al 2010, Kaneryd et al 2012). However, not only the number of species going extinct but their identity and traits will be important for the system's continued stability.…”

“…In Papers IV & V a simple algorithm generating pyramidal food webs of 6-24 species was used (Kaneryd et al 2012). In Paper IV connectance is set to 0.14, and in Paper V it ranges from 0.05-30.…”

“…Indeed, I find it interesting to speculate whether unacknowledged differences in interaction patterns might be behind some part of the controversy regarding the effect of diversity on stability (see for example Kokkoris et al 2002, Neutel and Thorne 2014, Tang et al 2014. It is clear at least that differences in the type, strength and variation of inter-and intra-specific competition has implications for how extinction risk relates to diversity (Hughes and Roughgarden 2000, Kokkoris et al 2002, Thebault et al 2007, Kaneryd et al 2012 …”