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Size-selective predation by the threespine stickleback

University of British Columbia

This thesis examines some factors that limit and define size-selective predation by the threespine stickleback, Gasterosteus aculeatus. Behavioural? physical and energetic factors were considered. Enclosure studies in a shallow oligotrophic lake and in a small creek were used to determine the actual size limits for different prey taxa over a range of stickleback sizes. The prey organisms were the amphipods Hyallela azteca and Crangonyx richmondensis, the isopod Asellus occidentalism chironomid larvae and the cladoceran Sida crvstallina. The major question of the thesis is what determines the largest prey organism a stickleback can handle? The hypothesis that physical factors, particularly mouth size, are limiting was tested. The observed linear relationship between maximum prey size (Hyallela and Asellus) and fish size support this hypothesis. Further evidence for mouth size as the limiting factor, is provided by a laboratory experiment using Asellus as prey. Artemia salina nauplii were fed to large and small sticklebacks in an attempt to determine the importance of relative prey and predator size on feeding performance. Large fish did relatively poorly, but the effects of prey size changes were inconclusive due to confounding factors. The role of energetics in size-selective predation was examined via a model which gave minimum capture rates necessary to sustain fish at maintenance levels for a given prey size, predator size and temperature. The model can be used to explain various observations in the feeding ecology literature. The role of vision in size-selective predation was briefly considered. Evidence from the literature indicated that non-linear relationships exist between: 1) reactive distance and prey size5 and 2) prey risk and predator' distance. These non-linearities point to the importance of prey size in predator-prey interactions.

Text

2010-02-01

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http://hdl.handle.net/2429/19484

Zoology

University of British Columbia

Graduate