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

Abstract

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 (2D, e.g., benthic zones) and three (3D, e.g., pelagic zones) spatial dimensions-the resource-to-consumer body size-ratio distribution tends toward bimodality, with different median 2D and 3D peaks. Specifically, we find that median size-ratio in 3D is consistently smaller than in 2D both within and across communities. Furthermore, 2D and 3D size (not size-ratio) distributions within any community are generally indistinguishable statistically, indicating that the bimodality in size-ratios is not driven simply by a priori 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 2D and 3D size-ratio distributions. Our theory suggests that community-level size-ratio bimodality emerges from the stronger scaling of consumption rate with size in 3D interactions than in 2D which both, maximizes consumer fitness, and allows coexistence, across a larger range of size-ratios in 3D. We also find that consumer gape-limitation can amplify differences between 2D and 3D 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.

Interplay between the paradox of enrichment and nutrient cycling in food webs

“…For instance, the scaling of the attack rate with predator and prey body masses strongly determines the occurrence of limit cycles (Pawar et al, 2019) and varies a lot between studies (Rall et al, 2008;Pawar et al, 2012). However, such differences do not change our main results as the C and SC models respond similarly whatever the values of our scaling constants ( Fig.…”

Methods and approaches to advance soil macroecology

“…For such applications, it may useful to turn to the marine literature where development of SDM techniques for 3‐D systems is already underway (e.g., Duffy & Chown, 2017; Pérez‐Costas et al, 2019). Similarly, investigations into the scaling of interaction strengths within species networks can differ between 2‐ and 3‐D systems in terrestrial and marine realms, where advanced nonlinear statistical approaches, 3‐D statistical point pattern models and 3‐D agent‐based modelling have been successfully applied (see Barrios‐O’Neill et al, 2016; Pawar, Dell, Lin, Wieczynski, & Savage, 2019; Raynaud & Nunan, 2014).…”

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