Does risk of intraspecific interactions induce shifts in prey-size preference in aquatic predators? |
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Authors: | P A Nilsson Kristian Nilsson Per Nyström |
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Institution: | (1) Department of Animal Ecology, Ecology Building, 22362 Lund, Sweden e-mail: anders.nilsson@zooekol.lu.se Tel.: +46-46-2223704, Fax: +46-46-2224716, SE |
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Abstract: | Interactions between foragers may seriously affect individual foraging efficiency. In a laboratory study of handling time,
prey value and prey-size preference in northern pike and signal crayfish, we show that risk of intraspecific interactions
between predators does not affect handling time or value of prey. However, the presence of agonistic intraspecific interactors
shifts prey-size preference in these predators. Neither northern pike nor signal crayfish foraging alone show a prey-size
preference, while pike foraging among conspecifics prefer small prey, and crayfish foraging in groups prefer large prey. We
ascribe the different outcomes in prey preference to differences in susceptibility to interactions: northern pike under risk
avoid large prey to avoid long handling times and the associated risk of interactions, while signal crayfish foraging among
conspecifics may defend themselves and their prey during handling, and thus select prey to maximise investment. In addition,
the value of pike prey (roach) is low for very small prey, maximises for small prey, and then decreases monotonically for
larger prey, while crayfish prey (pond snail) value is low for very small prey, has a maximum at small prey, but does not
decrease as much for larger prey. Therefore, a large and easily detected snail prey provides a crayfish with as much value
as a small prey. We conclude that interaction risk and predator density affect prey-size preference differently in these aquatic
predators, and therefore has different potential effects on prey-size structure and population and community dynamics.
Received: 4 October 1999 / Revised: 20 March 2000 / Accepted: 27 May 2000 |
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Keywords: | Optimal foraging Intraspecific interactions Prey preference Northern pike Signal crayfish |
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