Confronting the paradox of enrichment to the metacommunity perspective

Role of limiting dispersal on metacommunity stability and persistence

The role of dispersal on the stability and synchrony of a metacommunity is a topic of considerable interest in theoretical ecology. Dispersal is known to promote both synchrony, which enhances the likelihood of extinction, and spatial heterogeneity, which favors the persistence of the population. Several efforts have been made to understand the effect of diverse variants of dispersal in the spatially distributed ecological community. Despite that environmental change strongly affects the dispersal, the effects of controlled dispersal on the metacommunity stability and their persistence remain unknown. We study the influence of limiting the immigration using two-patch prey-predator metacommunity at both local and spatial scales. We find that the spread of the inhomogeneous stable steady states (asynchronous states) decreases monotonically upon limiting the predator dispersal. Nevertheless, at the local scale, the spread of the inhomogeneous steady states increases up to a critical value of the limiting factor, favoring the metacommunity persistence, and then starts decreasing for a further decrease in the limiting factor with varying local interaction. Interestingly, limiting the prey dispersal promotes inhomogeneous steady states in a large region of the parameter space, thereby increasing the metacommunity persistence at both spatial and local scales. Further, we show similar qualitative dynamics in an entire class of complex networks consisting of a large number of patches. We also deduce various bifurcation curves and stability conditions for the inhomogeneous steady states, which we find to agree well with the simulation results. Thus, our findings on the effect of the limiting dispersal can help to develop conservation measures for ecological communities.

Metacommunity persistence to environmental change: Stabilizing and destabilizing effects of individual species dispersal

Ecological communities face a high risk of extinction to climate change which can destabilize ecological systems. In the face of accelerating environmental change, understanding the factors and the mechanisms that stabilize the ecological communities is a central focus in ecology. Although dispersal has been widely used as an important stabilizing process, it remains unclear how individual species dispersal affects the stability and persistence of an ecological community. In this study, using a spatially coupled predator-prey community, we address the effects of individual species dispersal and nutrient enrichment on metacommunity stability in constant and varying environments. We show two contrasting effects of dispersal on metacommunity persistence in temporally constant and varying environments. Specifically, predator dispersal in constant environments shows stronger stability through inhomogeneous (asynchronized) states, whereas prey dispersal shows an increasing extinction risk through a homogeneous (synchronized) state. On the contrary, the metacommunity dynamics in temporally varying environments reveal that predator dispersal causes a local extinction through tracking unstable states and also a delayed shift between dynamical states. Moreover, our results emphasize that metacommunity persistence depends on individual species dispersal and environmental variations. Thus, our findings of the individual species dispersal can help to develop conservation measures that are tailored to varying environmental conditions.

Resource-dependent antagonistic coevolution leads to a new paradox of enrichment

The classical, ecological, paradox of enrichment describes a phenomenon that resource enrichment destabilizes predator-prey systems by exacerbating population oscillations. Here we suggest a new, evolutionary, paradox of enrichment. Resource enrichment can lead to more asymmetrical predator-prey coevolution (i.e., extremely high levels of prey defenses against predators) that decreases predator abundances and increases predator extinction risk. A major reason for this is that high resource availability can reduce fitness costs associated with prey defenses. In our experiments with a bacterium and its lytic phage, nutrient-balanced resource enrichment led to patterns in population demography and coevolutionary dynamics consistent with this coevolution-based paradox of enrichment; in particular, phage population extinction events were observed under nutrient-rich, not nutrient-poor, conditions. Consistent with ecological studies, carbon-biased resource enrichment (with carbon availability disproportionately increased relative to other nutrients) did not destabilize dynamics, and the asymmetry of coevolution was not altered in this context. Our work highlights the importance of integrating ecological and evolutionary thinking for studies of the consequences of nutrient pollution and other types of environmental changes.