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Title: Predators vs. prey : the information ecology of warning signals
Author: Hämäläinen, Liisa Lotta
ISNI:       0000 0004 8501 2536
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2020
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Explaining the origin and maintenance of aposematism has remained a challenge for evolutionary biologists because conspicuous warning signals are predicted to have a high initial predation cost before predators learn to avoid them. Most previous work has assumed that predators need to sample prey individually (personal information) to learn about these defences, however recent research suggests that observing predation events of others (social information) may also shape selection for prey defences and help resolve this puzzle. Here I use great tits and blue tits as model predators to investigate what influences predators' decisions to use different types of information when encountering novel prey, how information use varies across predator species, and whether this can operate in a predator community in the wild. First, I investigated if previous experience with toxins increases great tits' reliance on social information about novel aposematic prey, but found that toxin load had no effect: socially-educated birds consumed fewer aposematic prey, regardless. This indicates that social information can reduce predation pressure on novel aposematic prey even when a predator's risk of increasing their toxin load is low. Social interactions among predators might, however, also increase predation on aposematic prey if predators gather social information about the presence of palatable mimics. Therefore, I next investigated if educated great tits became more likely to consume mimics after observing warning signals being palatable but found that the birds were hesitant to sample palatable mimics, regardless of social information. These results suggest that while social information about models is potent in increasing predator avoidance, model-mimic dynamics are unlikely to be affected when predators have recent personal experience of the model's unpalatability. Because predator communities are often complex and consist of multiple species, I next extended my work to blue tits that typically form mixed-species flocks with great tits. I first tested whether video playback is a suitable method for providing social information for blue tits. I then investigated conspecific and heterospecific information use in blue tits and great tits, and found that both species used social information about aposematic prey, including information from heterospecifics. Finally, I tested the ecological relevance of my results with a field experiment where blue tits and great tits were presented with novel palatable and unpalatable food. I conducted the experiment in the summer when naïve juveniles are abundant and aposematic prey suffer high predation. Consistent with my work with birds in captivity, I found that both species used social information in their food choices also in the wild. Together, my findings demonstrate that social transmission of knowledge about prey defences shapes predator-prey communities, and an information ecology approach can therefore help us to understand the evolution and maintenance of prey warning signals.
Supervisor: Kilner, Rebecca ; Thorogood, Rose Sponsor: Finnish Cultural Foundation ; Emil Aaltonen Foundation
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: aposematism ; blue tits ; chemical defence ; great tits ; predator-prey interactions ; social information use ; warning signals