Comparing process-based and constraint-based approaches for modeling macroecological patterns

TL;DR

This study compares process-based and constraint-based ecological models, finding that process-based models better capture community structure details across diverse forest systems, aiding understanding of ecological pattern formation.

Contribution

It introduces a methodology to directly compare process- and constraint-based ecological models using multiple community patterns across many systems.

Findings

Process-based models have higher likelihoods.

Process models better capture size-abundance relationships.

Constraint models are less detailed in community structure.

Abstract

Ecological patterns arise from the interplay of many different processes, and yet the emergence of consistent phenomena across a diverse range of ecological systems suggests that many patterns may in part be determined by statistical or numerical constraints. Differentiating the extent to which patterns in a given system are determined statistically, and where it requires explicit ecological processes, has been difficult. We tackled this challenge by directly comparing models from a constraint-based theory, the Maximum Entropy Theory of Ecology (METE) and models from a process-based theory, the size-structured neutral theory (SSNT). Models from both theories were capable of characterizing the distribution of individuals among species and the distribution of body size among individuals across 76 forest communities. However, the SSNT models consistently yielded higher overall likelihood, as well as more realistic characterizations of the relationship between species abundance and average body size of conspecific individuals. This suggests that the details of the biological processes contain additional information for understanding community structure that are not fully captured by the METE constraints in these systems. Our approach provides a first step towards differentiating between process- and constraint-based models of ecological systems and a general methodology for comparing ecological models that make predictions for multiple patterns.