Explaining why there are more species than limiting resources in natural systems constitutes a long-standing challenge among ecologists. Recently, this apparent paradox was resolved theoretically by showing that species can coexist in clumps along niche gradients. However, models demonstrating this effect have failed to account for a ubiquitous feature of nature, namely variability in environmental conditions. This leaves open the question of whether the proposed mechanisms underpinning “lumpy coexistence” apply in nature or arise as a coincidence of modeling frameworks. Here, we demonstrate the emergence of lumpy coexistence in assemblages self-organizing under fluctuating resource supplies. We show that clumps form predictably as the result of the dynamic pattern in ambient resources driven by the most competitive species in the assemblage.

Abstract

The effect of life-history traits on resource competition outcomes is well understood in the context of a constant resource supply. However, almost all natural systems are subject to fluctuations of resources driven by cyclical processes such as seasonality and tidal hydrology. To understand community composition, it is therefore imperative to study the impact of resource fluctuations on interspecies competition. We adapted a well-established resource-competition model to show that fluctuations in inflow concentrations of two limiting resources lead to the survival of species in clumps along the trait axis, consistent with observations of “lumpy coexistence” [Scheffer M, van Nes EH (2006) Proc Natl Acad Sci USA 103:6230–6235]. A complex dynamic pattern in the available ambient resources arose very early in the self-organization process and dictated the locations of clumps along the trait axis by creating niches that promoted the growth of species with specific traits. This dynamic pattern emerged as the combined result of fluctuations in the inflow of resources and their consumption by the most competitive species that accumulated the bulk of biomass early in assemblage organization. Clumps emerged robustly across a range of periodicities, phase differences, and amplitudes. Given the ubiquity in the real world of asynchronous fluctuations of limiting resources, our findings imply that assemblage organization in clumps should be a common feature in nature.