Spatial covariation of competing species in a fluctuating environment

Abstract

Understanding how stochastic fluctuations in the environment influence population dynamics is crucial for sustainable management of biological diversity. However, because species do not live in isolation, this requires knowledge of how species interactions influence population dynamics. In addition, spatial processes play an important role in shaping population dynamics. It is therefore important to improve our understanding of how these different factors act together to shape patterns of abundance across space within and among species. Here, we present a new analytical model for understanding patterns of covariation in space between interacting species in a stochastic environment. We show that the correlation between two species in how they experience the same environmental conditions determines how correlated fluctuations in their densities would be in the absence of competition. In other words, without competition, synchrony between the species is driven by the environment, similar to the Moran effect within a species. Competition between the two species causes their abundances to become less positively or more negatively correlated. The same strength of competition has a greater negative effect on the correlation between species when one of them has a more variable growth rate than the other. In addition, dispersal or other movement weakens the effect of competition on the interspecific correlation. Finally, we show that movement increases the distance over which the species are (positively or negatively) correlated, an effect that is stronger when the species are competitors, and that there is a close connection between the spatial scaling of population synchrony within a species and between species. Our results show that the relationships between the different factors influencing interspecific correlations in abundance are not simple linear ones, but this model allows us to disentangle them and predict how they will affect population fluctuations in different situations.

Micro‐scale geography of synchrony in a serpentine plant community

“…There is a growing recognition of the importance of spatial heterogeneity in community stability (Wang et al., 2019; Wang & Loreau, 2014; Wilcox et al., 2017); exploring factors that structure geographies of synchrony may provide insights into the mechanisms that underlie these patterns. We also found empirical evidence supporting a role of competition in determining site‐wide synchrony and its spatial structure, which is generally consistent with recent theory on population and interspecific synchrony among competitors (Jarillo, Saether, Engen, & Cao, 2018; Lee, Saether, & Engen, 2019). Studies of synchrony offer a natural approach given the recognized importance of synchrony in population and community ecology, and that many statistical approaches are applicable to both cases.…”

General statistical scaling laws for stability in ecological systems

“…Indeed, there are usually many potential mechanisms that could explain patterns equally well. For example, although a concave‐up relationship between var( x ) and ecological scale implies negative average correlations in interspecific abundances, these correlations could result from many different mechanisms, including competition, species differences in their response to disturbances, or observation error (Clark et al, 2019; Lee et al, 2020).…”

“…Our first model of a single species and patch describes a linear stochastic dynamical system near equilibrium (Arnoldi et al, 2018, 2019; Lande et al, 1999; Lee et al, 2020). We consider dynamics of standardised abundance x ( t ) = N ( t ) − K , where N ( t ) is species abundance at time t , and K is carrying capacity.…”

Spatial synchrony is related to environmental change in Finnish moth communities

“…Taking a bottom-up perspective, synchrony in the emergence or abundance of a resource may drive synchronous dynamics in the predator species [48]. Relatedly, numerically dominant outbreaking species may drive synchrony by disrupting community dynamics and promoting synchrony in other species through competitive interactions [49,50]. Both of these are potential explanations for the latitudinal variation observed in the importance of each site to the synchrony network, as resource availability and community composition changes with latitude in Finland [51].…”