Tracking unstable states: ecosystem dynamics in a changing world

Abstract

Ecological systems can show complex and sometimes abrupt responses to environmental change, with important implications for their resilience. Theories of alternate stable states have been used to predict regime shifts of ecosystems as equilibrium responses to sufficiently slow environmental change. The actual rate of environmental change is a key factor affecting the response, yet we are still lacking a non-equilibrium theory that explicitly considers the influence of this rate of environmental change. We present a metacommunity model of predator-prey interactions displaying multiple stable states, and we impose an explicit rate of environmental change in habitat quality (carrying capacity) and connectivity (dispersal rate). We study how regime shifts depend on the rate of environmental change and compare the outcome with a stability analysis in the corresponding constant environment. Our results reveal that in a changing environment, the community can track states that are unstable in the constant environment. This tracking can lead to regime shifts, including local extinctions, that are not predicted by alternative stable state theory. In our metacommunity, tracking unstable states also controls the maintenance of spatial heterogeneity and spatial synchrony. Tracking unstable states can also lead to regime shifts that may be reversible or irreversible. Our study extends current regime shift theories to integrate rate-dependent responses to environmental change. It reveals the key role of unstable states for predicting transient dynamics and long-term resilience of ecological systems to climate change.

Persistence and extinction dynamics driven by the rate of environmental change in a predator–prey metacommunity

“…In ecological theory, unstable states of ecological models are often ignored. Recently, it has been understood that the tracking of unstable states results in dynamical regimes that greatly differ from corresponding stable states, and that can alter long-term community dynamics (Arumugam et al 2020). Our study further broadens the ecological literature of extinction debt through unstable states.…”

“…In this section, we present an example that the combination of a changing environment and a weak Allee effect can lead to extinction. The mechanism here is the tracking of unstable states that we had already seen in the previous section and that was originally explored by Arumugam et al (2020) in the absence of an Allee effect.…”

“…The new phenomenon in this scenario arises when k crosses into region IV, where we expect extinction, and yet the metacommunity continues to persist as it "tracks" the now unstable steady state. This phenomenon of tracking unstable states has been recently explored in more detail in Arumugam et al (2020). It is known that systems typically have long transients near bifurcation points.…”

“…Siteur et al (2016) found R-tipping in a Rosenzweig-MacArthur model with an assumption of separation of time scales. A more decent discovery is that of tracking unstable (quasi-)states (Arumugam et al 2020): as model parameters change, a population may remain close to a state that would be unstable if model parameters were fixed. Of course, the literature on regime shifts is much broader, but most of these studies do not explicitly consider the rate of environmental change as a parameter in the model.…”

Two classes of functional connectivity in dynamical processes in networks

“…Ecological applications of dynamical approaches, like the ones mentioned above, and the classification of the two types of FC addressed in this paper bring new perspectives to assess functional connectivity in freshwater ecology. Additionally, evaluating the SC/FC relationships can highlight the importance of specific nodes in facilitating the overall colonization processes, which can help to estimate a number of effective reserves necessary to achieve a particular conservation goal [103,[122][123][124][125][126].…”