Graduation Year


Document Type




Degree Name

Master of Science (M.S.)

Degree Granting Department

Biology (Integrative Biology)

Major Professor

Marc J. Lajeunesse, Ph.D.

Co-Major Professor

Andrew M. Kramer, Ph.D.

Committee Member

Steven M. Deban, Ph.D.


consumptive effects, indirect effects, nonconsumptive effects, trait modifications


Theoretical and empirical considerations of predator-prey dynamics have sought to determine the dominant of two effects exerted by predators onto prey: consumptive effects of predators and non-consumptive, or trait-mediated, effects. Many studies have identified trait-mediated interactions (TMIs) in diverse taxa, and meta-analyses of these studies found that prey population dynamics are as strongly – if not more strongly – affected by TMIs as density-mediated interactions (DMIs). Since then, there is now an expanded primary literature, and given this potential for new insight on the direct and indirect effect of predators on prey, the cost of traits involved in TMIs relative to the cost of consumption in DMIs should be revisited and reanalyzed with state-of-the-science research synthesis practices. Here we use a novel trivariate meta-analysis to jointly synthesize and model the multivariate effects of TMIs and DMIs on prey populations. We found that DMIs have twice the negative effects on prey populations than TMIs, but are more variable then TMIs, and that TMIs have the strongest effects in aquatic systems. Finally, we found that the model of total predator effects is not additive of DMIs and TMIs. Total predator effects were less than DMIs—which is biological intuitive given that prey should not initiate TMIs and therefore trait changes if it did not lessen total predator effects below that of DMIs. Gaps in the literature were detected, specifically that more experiments are needed that simultaneously assess TMIs and DMIs to a common control and that more studies are needed examining the demographic consequences of morphological TMIs. Our findings that DMIs are stronger than TMIs in affecting prey demographics suggests that DMIs are stronger regulators of prey populations. Our findings also suggest that the total predator effect requires measuring the combination of DMIs and TMIs, and that TMIs should be researched within the context of how they reduce the impacts and cost of DMIs from predators.