The Consequences of Anti-Predator Strategies for Population Dynamics: A Case Study with Daphnia pulex.

Predator-prey relationships are among the most common species interactions in nature. By consuming prey, predators influence the composition, structure and dynamics of populations, communities and ecosystems. Moreover, the effect of predators on prey extends beyond that of direct consumption. When prey detect the risk of predation, via predator kairomones, prey alarms cues or elevated encounter rates, they can induce an array of plastic traits aimed at decreasing predation mortality, but that also result in changes in reproductive output. Defence strategies also often include simultaneous changes in several behavioural, morphological and life-history traits. Despite much theoretical and empirical effort, some major questions remain unanswered in this area. Firstly, why is there so much variability in the combinations and magnitudes of anti-predator defences induced within a single prey species? One theory is that multiple trait combinations provide similar survival, reproductive, and thus dynamic effects. To test this idea requires us to investigate how different anti-predator strategies affect each of these factors. The second question asks of the relative importance of consumptive and non-consumptive effects of predators on prey, and whether these are also affected by differences in anti-predator strategies. In this thesis, I make use of the model organism system of Daphnia pulex and its predators to address these questions. Using multivariate techniques I characterise the anti-predator strategies of Daphnia pulex genotypes in response to the phantom midge (Chaoborus flavicans) and three spine stickleback (Gasterosteus aculeatus). I then test the theory that phenotypically distinct anti-predator strategies result in similar reproduction, survival and population dynamics for D. pulex genotypes. Finally, I test if they affect the relative importance of consumptive and non-consumptive effects of Chaoborus on Daphnia. I found that different genotypes expressed different multivariate anti-predator strategies, and that these strategies affected the relative consumptive and non-consumptive effects of Chaoborus on Daphnia populations. However, I also found that the different strategies resulted in similar overall population effects for each of the genotypes tested, supporting the idea that there are multiple possible anti-predator strategies for dealing with the same predator. This work contributes to our understanding of the effects of variation in anti-predator defences on predator-prey interactions.