Testing the role of body size and litter depth on invertebrate diversity across six forests in North America

Authors: Roeder, Karl; BENSON, BRITTANY - University Of Oklahoma; WEISER, MICHAEL - University Of Oklahoma; KASPARI, MICHAEL - University Of Oklahoma

Submitted to: Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2021
Publication Date: 11/25/2021
Citation: Roeder, K.A., Benson, B.F., Weiser, M.D., Kaspari, M. 2021. Testing the role of body size and litter depth on invertebrate diversity across six forests in North America. Ecology. 103(2). Article e03601. https://doi.org/10.1002/ecy.3601.
DOI: https://doi.org/10.1002/ecy.3601

Interpretive Summary: Species diversity varies across space and through time. In this paper, we focus on two potential drivers of invertebrate diversity in brown food webs—body size and litter depth—and test hypotheses on how these drivers shape patterns of abundance and richness in mites, springtails, and spiders across six forests in North America. Despite a large amount of variation, the predicted negative relationship between mean body size and abundance occurred in only 18% of cases. We likewise found only 18% of tests supported our prediction that increasing litter depth allows for more individuals. In contrast, invertebrate abundance was linked to species richness 76% of the time and often mediated any effect that body size and litter depth may have had on species richness. Our results suggest that body and habitat size are weak predictors of invertebrate abundance, but that variation in the number of species can generally be predicted by abundance.

Technical Abstract: Ecologists search for rules by which traits dictate the abundance and distribution of species. Here we search for rules that apply across three common taxa of litter invertebrates in six North American forests from Panama to Oregon. We use image analysis to quantify the abundance and body size distributions of mites, springtails, and spiders in 21-m2 plots per forest. We contrast three hypotheses: two of which focus on trait-abundance relationships and a third linking abundance to species richness. Despite three orders of magnitude variation in size, the predicted negative relationship between mean body size and abundance per m2 occurred in only 18% of cases—never for large bodied taxa like spiders. We likewise found only 18% of tests supported our prediction that increasing litter depth allows for high abundance; 2/3 of which occurred at a single deciduous forest in Massachusetts. In contrast, invertebrate abundance constrained species richness 76% of the time, often mediating any effect that body size and litter depth may have had on species richness. Our results suggest that body size and habitat volume in brown food webs are rarely good predictors of patchiness in abundance, but that patchiness in diversity is generally well predicted by abundance.