COS 59-7 - Testing the relationship between intraspecific competition and individual specialization across both behavior and diet

Wednesday, August 14, 2019: 3:40 PM
M112, Kentucky International Convention Center
Amaryllis K. Adey, Natural Resources and Environmental Sciences, University of Illinois Urbana - Champaign, Urbana, IL and Eric R. Larson, Natural Resources and Environmental Science, University of Illinois at Urbana-Champaign, Urbana, IL
Background/Question/Methods

Intraspecific variation is a key component of ecology and a driver of evolutionary processes. As population densities increase, individuals may diversify their strategies to reduce competitive pressure with conspecifics. Theoretical studies support a direct relationship between population density and individual specialization. However, empirical studies have not always supported these theoretical predictions, sometimes suggesting a unimodal relationship, with the greatest individual specialization at moderate densities and decreasing specialization at both high and low densities. One reason for this divergence between theoretical predictions and empirical evidence may be the specific metrics of specialization considered. In this study, we tested the role of intraspecific competition on individual specialization through analysis of both behavior and diet. We conducted this study in Vilas County, Wisconsin using rusty crayfish Faxonius rusticus collected from six lakes across a gradient of relative abundance. We conducted six behavioral assays to measure behavioral diversity between populations and used stable isotope analysis to measure dietary diversity or breadth. We then related both measures of specialization to relative abundance of F. rusticus in our study lakes using linear and quadratic models to represent either increasing or unimodal relationships between individual specialization and intraspecific competition.

Results/Conclusions

We found that a unimodal relationship (AICc=24.51, R2=0.82) was more supported than a linear relationship (AICc=32.69, R2=0.04) between dietary diversity and F. rusticus relative abundance. This indicates that our lakes with intermediate crayfish densities had the most dietary specialization or within-population breadth, and our lakes with low or high densities had less dietary specialization. Decreased dietary specialization at high relative abundance may be due to depletion of preferred food resources that limits opportunity for diet diversification. By contrast, we found equivalent support for linear (AICc=169.17, R2=0.25) and unimodal (AICc=167.41, R2=0.22) relationships between behavioral diversity and relative abundance of F. rusticus, but both models explained relatively little variation in behavioral specialization between lakes. Our question related to behavioral diversity might require more power or replication to resolve than the six lakes considered here. However, our results do show that the specific measure of specialization can influence outcomes of comparisons between intraspecific competition and individual specialization, and illustrates a method of testing for behavioral and dietary specialization within the same individuals.