The future of gradient studies in examining plant-plant interactions for the next 100 years
Times are a changing. Global changes are real, dramatic, and prominent in ecological research. Even most fundamental research studies on interactions, gradients, or perturbation invoke global change issues as the validation and implication of the respective work reported. However, integrating individual studies is challenging, and ecology must now very rapidly move beyond context specificity to provide useful, reproducible evidence for many of these global issues. Gradients are a changing too in connectance, length, and severity. Herein, a review and conceptual framework of gradient studies that explore ecological interactions are developed. Experimental field manipulations and syntheses are also presented as a means to advance theory and highlight opportunities for future research.
Gradients are powerful tools that can be used to shape distributed, collaborative studies of interactions provided interaction estimates are coupled with drivers at multiple scales, network dynamics, and trophic levels. Contrasts of the frequency and/or importance of interactions, positive or negative, are only as useful as their capacity to expand the relevance of the local ecological context. None of the reviewed studies explored bidirectional plant-animal interactions, used a network approach to the study facilitation, estimated cost to benefactors, nor contrasted interaction strengths. We propose that multi-trophically integrated sets of experiments incorporating plant facilitation into community dynamics are thus critical in advancing management of high-stress ecosystems and advancing theory development in community ecology more broadly. Shrubs are an excellent foundation species to catalyze this research, and associated animals functioning as consumers or dispersers are also likely to significantly mediate interactions. Environmental gradients and more comprehensive trait sets – particularly for the shrubs - should be incorporated into plant facilitation studies to address community-level responses to perturbation. The frequency of plant-animal interactions and trait-mediated facilitation is a novel extension to existing theory.