AUTHOR=Pawar Samraat , Dell Anthony I. , Lin Tianyun , Wieczynski Daniel J. , Savage Van M. 

TITLE=Interaction Dimensionality Scales Up to Generate Bimodal Consumer-Resource Size-Ratio Distributions in Ecological Communities

JOURNAL=Frontiers in Ecology and Evolution

VOLUME=7

YEAR=2019

URL=https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2019.00202

DOI=10.3389/fevo.2019.00202

ISSN=2296-701X

ABSTRACT=<p>Understanding constraints on consumer-resource body size-ratios is fundamentally important from both ecological and evolutionary perspectives. By analyzing data on 4,685 consumer-resource interactions from nine ecological communities, we show that in spatially complex environments—where consumers can forage in both two (2<italic>D</italic>, e.g., benthic zones) and three (3<italic>D</italic>, e.g., pelagic zones) spatial dimensions—the resource-to-consumer body size-ratio distribution tends toward bimodality, with different median 2<italic>D</italic> and 3<italic>D</italic> peaks. Specifically, we find that median size-ratio in 3<italic>D</italic> is consistently smaller than in 2<italic>D</italic> both within and across communities. Furthermore, 2<italic>D</italic> and 3<italic>D</italic> size (not size-ratio) distributions within any community are generally indistinguishable statistically, indicating that the bimodality in size-ratios is not driven simply by <italic>a priori</italic> size-segregation of species (and therefore, interactions) by dimensionality, but due to other factors. We develop theory that correctly predicts the direction and magnitude of these differences between 2<italic>D</italic> and 3<italic>D</italic> size-ratio distributions. Our theory suggests that community-level size-ratio bimodality emerges from the stronger scaling of consumption rate with size in 3<italic>D</italic> interactions than in 2<italic>D</italic> which both, maximizes consumer fitness, and allows coexistence, across a larger range of size-ratios in 3<italic>D</italic>. We also find that consumer gape-limitation can amplify differences between 2<italic>D</italic> and 3<italic>D</italic> size-ratios, and that for either dimensionality, higher carrying capacity allows coexistence of a wider range of size-ratios. Our results reveal new and general insights into the size structure of ecological communities, and show that spatial complexity of the environment can have far reaching effects on community structure and dynamics across scales of organization.</p>