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The role of body size in the habitat choice and foraging behaviour of juvenile coho salmon under predation risk Reinhardt, Ulrich Georg
Abstract
Models of behaviour in trade-off situations between foraging and predator avoidance predict that an animal's decision should depend on dynamic internal states, such as energy or hormonal levels. For example, it is predicted that willingness to risk mortality decreases with increasing assets of the forager. In this thesis, I used a combination of experimental manipulation and computer modeling to examine the influence of various dynamic states, particularly body size, on the risk taking behaviour of coho salmon (Oncorhynchus kisutch) fry. I showed that fry in semi-natural stream channels used protective cover opportunistically, associating with it only when it protected them from predators. In the laboratory, I observed habitat choice and agonistic behaviour of groups of coho fry under simulated predation risk. Bigger coho used a risky habitat less than smaller individuals. Bigger fry aggressively monopolized access to food in the absence of predation risk, but in the presence of risk, the size-dependent territorial hierarchy broke down and risk-prone small fish achieved relatively higher growth rates. Using a dynamic optimization computer model with parameters representative of coho foraging, I explored the relationship between body size and optimal foraging effort over the first feeding season. Like earlier dynamic optimization models, my model showed that the willingness to risk predation should decrease with size. In contrast to earlier models, my coho-specific model predicted that risk taking should be highest in the spring. In a final experiment, I examined the influence of feeding conditions, body size, and season on the willingness of individual coho fry to feed under simulated predation risk. As expected, bigger fish were more risk averse than small fish in the summer. This was not the case in the fall when the overall willingness to risk exposure to the predator was lower. I suggest that juvenile salmonids integrate information on their internal state and the environment into their foraging behaviour to a greater extent than previously thought. If increased risk aversion with size is common in nature, it may have important ecological consequences, for example, it may help to explain the widely reported lower mortality rate of bigger juvenile fish.
Item Metadata
Title |
The role of body size in the habitat choice and foraging behaviour of juvenile coho salmon under predation risk
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1998
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Description |
Models of behaviour in trade-off situations between foraging and predator avoidance predict that an
animal's decision should depend on dynamic internal states, such as energy or hormonal levels. For
example, it is predicted that willingness to risk mortality decreases with increasing assets of the forager.
In this thesis, I used a combination of experimental manipulation and computer modeling to examine the
influence of various dynamic states, particularly body size, on the risk taking behaviour of coho salmon
(Oncorhynchus kisutch) fry. I showed that fry in semi-natural stream channels used protective cover
opportunistically, associating with it only when it protected them from predators. In the laboratory, I
observed habitat choice and agonistic behaviour of groups of coho fry under simulated predation risk.
Bigger coho used a risky habitat less than smaller individuals. Bigger fry aggressively monopolized
access to food in the absence of predation risk, but in the presence of risk, the size-dependent territorial
hierarchy broke down and risk-prone small fish achieved relatively higher growth rates. Using a
dynamic optimization computer model with parameters representative of coho foraging, I explored the
relationship between body size and optimal foraging effort over the first feeding season. Like earlier
dynamic optimization models, my model showed that the willingness to risk predation should decrease
with size. In contrast to earlier models, my coho-specific model predicted that risk taking should be
highest in the spring. In a final experiment, I examined the influence of feeding conditions, body size,
and season on the willingness of individual coho fry to feed under simulated predation risk. As expected,
bigger fish were more risk averse than small fish in the summer. This was not the case in the fall when
the overall willingness to risk exposure to the predator was lower. I suggest that juvenile salmonids
integrate information on their internal state and the environment into their foraging behaviour to a
greater extent than previously thought. If increased risk aversion with size is common in nature, it may
have important ecological consequences, for example, it may help to explain the widely reported lower
mortality rate of bigger juvenile fish.
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Extent |
5344176 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-06-02
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0074823
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1998-05
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.