Behavioural flexibility in response to environmental change

• Main Author: Kimbell, Helen
• Other Authors: Morrell, Lesley J. ; Chapman, Ben B.
• Published: University of Hull 2015
• Subjects: 363.7; Biological sciences
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.684217

A fundamental challenge in biology is to understand how animals can respond to the unprecedented environmental changes caused by human activities. In aquatic systems, pollution and disturbance from anthropogenic activities often impacts upon the sensory environment, and affects a number of important fitness-related behaviours. This PhD focuses on how a degraded environment impacts the behavioural responses of fish. The first section (chapters 2, 3 and 4) examines whether a degraded visual environment immediately affects the aggregation behaviour of fish as prey, and explores the implications for fish as predators. The second section (chapters 5 and 6) considers the way that previous experiences of a degraded or variable environment shape behavioural responses. Together, the results highlight the importance of considering the relationship between environmental conditions and behaviour over different time spans and during different developmental stages in order to understand how fish may respond to anthropogenic environmental change. The first section offers new evidence on the ways that groups of fish respond to predators in turbid water, and how predators target individuals within those groups. In chapter 2, I investigate how shoals of guppies respond to a simulated aerial predator attack in increasing levels of turbidity. I find that, in turbid water, guppies form looser shoals, and alter their behaviour in response to a simulated attack by showing weaker escape manoeuvres and increasing freezing behaviour as opposed to darting escape manoeuvres. In chapter 3, I explore the ‘selfish herd movement’ rules that guppies use to form shoals in response to a predator attack in clear and turbid water. I find that guppies use more complex rules (moving towards a location determined by the position of multiple individuals) in clear water, resulting in large compact shoals. By comparison, guppies are unable to use these rules when forming groups in turbid water, resulting in smaller, more fragmented shoals. In chapter 4, I consider the effect of turbidity from the perspective of both predator and prey, in the context of the oddity effect. Firstly, I assess the effect of turbidity on how stickleback predators target Daphnia prey individuals of different sizes from within mixed groups. Secondly, I explore how turbidity influences the social choices made by sticklebacks. From the perspective of the predator, sticklebacks selected large bodied Daphnia from mixed groups more than expected by chance in clear water, but not in turbid water. From the perspective of the prey, large individuals lost their preference for size-matched shoalmates in turbid water, whereas small individuals showed no social preference in either clear or turbid water. The oddity effect appears weakened in turbid water, relaxing predation pressure on large odd individuals at the expense of small individuals. Together, these three chapters consider the immediate, flexible responses of both predator and prey to short-term changes in turbidity. The second section of the thesis explores the longer-term impacts of a degraded or variable environment on the behavioural responses of fish. In chapter 5, I investigate how adult guppies respond to different food cues (visual, olfactory, or a combination of both) with increasing levels of experience of a visually poor environment. Previous work rearing guppies under similar conditions found that individuals make a sensory switch from vision to olfaction. I find that, although guppies with more experience of a dark environment increase their foraging success in visually poor environments, they do not make a sensory switch from vision to olfaction as seen in juvenile fish. Finally, in chapter 6, I step away from the visual environment and look at how recent experience of a variable habitat combined with low or high food levels affects boldness and exploratory behaviour in guppies. While some behaviours are modified with experience of low food, for example, the time to attack a food item, I find that exploratory behaviour was not influenced by either energy state or experience of a variable environment, remaining remarkably stable over time. These final two chapters highlight the importance of investigating behavioural responses to the environment over different time spans and during different developmental stages.