The question whether changes in community composition are gradual or rather abrupt along spatial environmental gradients has been the subject of a long-standing debate in ecology. In terrestrial as well as in marine ecosystems, numerous empirical studies were carried out to assess the rate of spatial species turnover, with diverging results. It seems that both continuous and discontinuous changes are possible but few studies identified the ecological and environmental conditions leading to the observed patterns. In this work, we investigate the role of two ecological processes in the emergence of various community patterns, using spatially explicit multispecies models. We first focus on the influence of interspecific competition in the emergence of various community organisations along environmental gradients. We then study how ecological niche construction - i.e the modification of the abiotic environment by species and to their own benefits – can give rise to rapid changes in community composition in space.
Results/Conclusions
In this work, we show that abrupt and gradual changes in community composition are two limiting cases along a continuum of outcomes. In competitive communities, we show that a high variance of competition strength leads to abrupt changes in community composition due to the presence of alternative stable states. In contrast, weak and uniform interactions induce gradual changes in species composition. In the presence of ecological niche construction, we observe the emergence of indirect interactions through the modification of species’ shared environment. These interactions, which can be either competitive or mutualistic, can lead to the emergence of discrete communities in space, separated by sharp ecotones where a high species turnover is observed. We also show that species dispersal can play a confounding role in these patterns.
Our work highlights the critical importance of considering interspecific competition and species-environment interactions to understand and predict the responses of species and communities to environmental changes in space, but also in time.