Invoking life history theory to understand species' responses to human disturbance

Background/Question/Methods

Trade-offs between energetically costly activities are well-established in life history theory. A trade-off between survival and reproduction has been documented in natural populations across several taxonomic groups, yet little is known about how human disturbance might influence this trade-off. Human disturbance confers multiple threats to wildlife populations, including altered food abundance and changes in actual or perceived predation risk, that may influence the cost of reproduction on survival, potentially altering this trade-off from that expected where human disturbance is minimal. Across 24 bird species and 84 locations in the northeastern United States with varying levels of human disturbance (as measured by housing density), we tested for evidence of a trade-off between survival and reproduction. We then determined if the direction of the relationship differed between less disturbed and more disturbed locations (locations with <50 versus >100 housing units/square kilometer). We addressed our question using both phylogenetic regression and mixed effects models to account for species relatedness and repeated measures, and included body metrics in our analysis to control for effects of body size.

Results/Conclusions

We observed a trade-off between survival and reproduction when performing our analysis across all locations and in less disturbed locations, but this trade-off no longer occurred in more disturbed locations. Where a trade-off was present, the negative relationship between survival and reproduction across species was more strongly supported when body metrics were included in models: the relationship between survival and reproduction became more negative, and there was a positive relationship between body size and survival. This relationship was robust across both phylogenetic regressions in which species’ data were aggregated as an average across locations, and mixed effects models in which all locations were included in the analysis. The lack of a trade-off between survival and reproduction across species in more disturbed locations likely reflects a highly variable and non-uniform response to human disturbance across species. Investigating this trade-off across other taxa may aid in determining species’ vulnerabilities, and serve in testing application of concepts in life history theory to human-disturbed regions.