The prey perspective - behaviour and appearance in a world of predators
Abstract: The varieties of prey phenotypes that have been revealed in nature are vast and many of these phenotypes are the result of the selective force that predators have had on prey traits in the past. Even within species and populations we see variations due to both differences in the selection forces they live under but also due to individual trait variation. In this thesis I investigate both the direct and indirect effects that predators have on two freshwater prey species, focusing especially on prey defence traits. In addition, the unexplained variation around average trait values in my and other studies led me to also study the effects of animal personalities on anti-predator adaptations. I found evidence for indirect effects on the adaptations to the dominant predator regime in Gammarus pulex. Individuals adapted to a life in the presence of predatory fish spent more time in refuges and had a higher non-consumptive mortality. Males seem to be the most affected sex as they had higher mortality than females, but also because they had to trade-off their mate-guarding behaviour due to an increased risk of fish predation. The freshwater snail Radix balthica showed plasticity in their mantle pigmentation when exposed to both predatory fish and ultraviolet radiation (UVR). In the presence of fish they got more complex pigment patterns. When exposed to UVR and UVR combined with fish, snails responded with increasing their pigmentation even further, which led to a loss in pattern complexity, suggesting a trade-off between photoprotection and camouflage. These snails also showed a trade-off when exposed to fish and leech predators simultaneously. The presence of leeches in refuges force snails out in the open, facilitating fish predation. Since these indirect effects of leeches are only present when leeches are combined with fish, they have earlier been overlooked as a fish effect. When zooming in on individual snails, they showed consistence in a personality trait associated with risk taking (boldness). This means that some snails are shy and others are bold across contexts. In fish-free ponds, dominated by invertebrate predators like leeches, I could not find any selection for either bold or shy snails. On the other hand I found, both in the lab and in the field, that in fish ponds, bold snails survived to a greater extent than shy snails. One explanation for this is that bold snails also had a shell with a rounder shape and bigger aperture, providing better protection from shell crushing predators like fish. My work reveals some new insights in how predators have shaped prey phenotypes through years of selective predation. In addition to the non-consumptive effects that predators have on prey phenotypes its clear that phenotypes that are badly adapted will quickly be removed from the population. Intriguingly, I also found that predators can shape the distribution of animal personalities and give rise to phenotypic compensation, where bold individuals compensate their risky life style with more pronounced defence traits.
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