Factors Influencing Mussel Abundances across Southwest USA Rivers: A Test of an Underlying Assumption of the More-Individuals Hypothesis

The More-Individuals Hypothesis (MIH) predicts that productivity regulates organismal abundances, such that more productive systems support a greater number of individuals, and therefore species richness. Previous assessments of the underlying assumption of MIH (i.e., positive relationship between productivity and animal abundances) have yielded mixed results with lack of detectable relationships between productivity and numbers of individuals attributed to several confounding factors including assessments with narrow ranges in productivity or high trophic diversity among tested assemblages. The purpose of this study was to test a mechanistic process to describe the general pattern of greater numbers of freshwater mussels (Unionidae; with similar feeding behaviors) along a large productivity gradient from west to east Texas. I compiled published and unpublished surveys from 2000 to 2024 across nine Texas river drainages, spanning 61 reaches and 744 mussel beds (76,649 individuals, 47 species). Reach-level estimates of productivity were obtained from the National Commodity Crop Productivity Index (i.e., soil fertility). Water quality and hydrology are known factors affecting mussel abundances, therefore, I obtained water quality and hydrological data at the reach level from publicly available data. Estimates of productivity, as a categorical variable and as a continuous variable, were positively related to the number of mussels across Texas drainages. Numbers of mussels generally were not related to water quality, except for total organic carbon (a measure of aquatic productivity) or hydrological variables (e.g., median flow, percent zero flow days). Study results supported the MIH concept and its applicability to aquatic systems. Additionally, study findings contributed to the growing body of knowledge regarding factors influencing population viabilities of freshwater mussels and provided expectations for mussel abundances by reach and drainage, which can be incorporated into a monitoring program (e.g., index of biotic integrity) for assessing health of mussel populations statewide.

Author dc:creator

• Laughrey, Colt M.

Contributors dc:contributor

• Bonner, Timothy H.
• Dutton, Jessica
• Martin, Noland
• Randklev, Charles
• Littrell, Bradley

• more-individuals hypothesis
• mussel populations

Language dc:language

en

Identifier

Laughrey, C. M. (2025). Factors influencing mussel abundances across southwest USA rivers: A test of an underlying assumption of the more-individuals hypothesis. [Master's thesis, Texas State University].

OAI identifier oai:identifier

oai:tdl-ir.tdl.org:10877/23415