Large Species Shifts Triggered by Small Forces

Abstract

Changes in species composition of communities seem to proceed gradually at first sight, but remarkably rapid shifts are known to occur. Although disrupting disturbances seem an obvious explanation for such shifts, evidence for large disturbances is not always apparent. Here we show that complex communities tend to move through occasional catastrophic shifts in response to gradual environmental change or evolution. This tendency is caused by multiple attractors that may exist in such systems. We show that alternative attractors arise robustly in randomly generated multispecies models, especially if competition is symmetrical and if interspecific competition is allowed to exceed intraspecific competition. Inclusion of predators as a second trophic level did not alter the results greatly, although it reduced the probability of alternative attractors somewhat. These results suggest that alternative attractors may commonly arise from interactions between large numbers of species. Consequently, the response of complex communities to environmental change is expected to be characterized by hysteresis and sudden shifts. Some unexplained regime shifts observed in ecosystems could be related to alternative attractors arising from complex species interactions. Additionally, our results support the idea that ancient mass extinctions may partly be due to an intrinsic loss of stability of species configurations.

Interannual variability in species composition explained as seasonally entrained chaos

“…The model is based on a straightforward multi-species version of the classic Rosenzweig-MacArthur predator-prey model (Rosenzweig & MacArthur 1963;Vandermeer 1993;van Nes & Scheffer 2004), extended with seasonal forcing Scheffer et al 1997). In our interpretation, the model represents a plankton community, although our findings can probably be generalized to other multi-species communities in which organisms have fast growth rates and short generation times compared with the length of the growing season (e.g.…”

“…The phytoplankton species are consumed by zooplankton species, as described by a multi-species functional response (of Holling type II) with a fixed half-saturation constant H k and maximum grazing rate g k . Selective predation (Chesson 1978) is introduced through the selectivity coefficient S ik of zooplankton species k for phytoplankton species i and it can take values between 0 and 1, indicating the preference of the predator for its prey (van Nes & Scheffer 2004). The factor u accounts for small levels of immigration and is introduced to reduce the probability of heteroclinic cycles.…”

Seed banks trigger ecological resilience in subalpine meadows abandoned after arable farming on the Tibetan Plateau

“…Disturbance by agricultural activities may reduce the resilience of a high-diversity stable state, increasing the likelihood that the system will cross a critical threshold into a low-diversity self-reinforcing stable state (van Nes and Scheffer 2004, Downing et al 2012, T€ or€ ok et al 2018. Some research has shown how the recovery of abandoned fields may be possible (Meiners et al 2002, Hermy andVerheyen 2007).…”

Sustainability of Human Ecological Niche Construction

“…Simple ecological models have offered unique insights and general rules regarding the long-term dynamics of many complex systems (May 1976, Tilman 1982, Leibold 1996, Holt and Polis 1997, van Nes and Scheffer 2004, Loreau 2010, Kylafis and Loreau 2011. We build on previous ecological theory considering omnivory (Holt and Polis 1997) and niches (Leibold 1996, Kylafis andLoreau 2011) to explore the cascading effects, long-term consequences, and limits of human niche construction.…”