58-12 Interplay of Body Size and Functional Ecology: Overlap and Divergence in Bivalvia

Session: Future Leaders in Paleontology

Presenting Author:

Authors:

Abstract:

Although body size undoubtedly impacts an organism’s interaction with its environment, the relation of size to functional ecological traits often used by paleontologists is unclear. Does function determine size, or is size itself another functional axis upon which organisms differentiate themselves? I addressed this question using marine bivalves, which occupy a wide array of functional groups (as determined by a four-dimension scheme based on their mode of feeding, fixation, attachment, and relationship with their substrate) and have body sizes spanning three orders of magnitude. I tested the relationship between body size and overlap in the aforementioned functional ecological traits both generally, and specifically for multiple pairs of families with overlapping geographic ranges. Because phylogeny might also play a role in size and function, I also analyzed the relationship between size and functional overlap and the divergence times of each pair of families. Extant bivalve species show significant relationships between body size and each of fixation, attachment, and substrate. However, functionally similar families — even groups of species from different families with the same functional assignment across all functional dimensions — still often showed significant contrasts in size distributions, indicating that function only partially determines size. How and what a bivalve feeds on, however, is only related to body size for non-suspension feeders. Suspension feeding, exhibited by two-thirds of all bivalve species, covers nearly the entire range of possible bivalve sizes, indicating that it does not impose size limits. These results indicate that function broadly determines the maximum and minimum viable sizes for a bivalve species with those traits, but these limits are not so restrictive as to prohibit differentiation between functionally similar taxa based on their size. On the contrary, functionally similar families often had distinct body size distributions, illustrating that size may be another key trait allowing organisms to partition their environment effectively. This size partitioning may be particularly important for more recently diverged families, which are likely not only to be functionally similar, but to be similar in other unmeasured traits that are important to their relationship with their environment.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7670

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.