Perceived predation risk and mate defense jointly alter the outcome of territorial fights |
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Authors: | Tsunenori Koga Satoshi Ikeda |
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Institution: | (1) Faculty of Education, Wakayama University, Wakayama 640-8510, Japan |
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Abstract: | Virtually all animal conflicts occur over access to mates or resources that affect survival, the two key components of fitness.
In this paper, we report that predation risk and mate defense jointly affect the outcomes of contests between male sand crabs
(Scopimera globosa) for burrows in which crabs mate and take shelter from predators. We observed the contests under three different conditions:
(1) the natural condition of low predation risk and without the presence of a female; (2) the first experiment in which we
imposed upon only intruding males the perception of predation risk—by digging them from their burrows, capturing and handling
them, and placing them into other males’ burrows—to increase the value of the burrows for the intruders as shelter, and (3)
the second experiment in which we repeated this treatment but increased the resource value of the burrow to the resident by
placing a female in his burrow. The difference in body size between contestants was the main determinant of victory in all
analyses. However, perceived predation risk also partly affected the outcomes of the fights: The motivated intruders were
likely to win even when they were a little smaller than the residents. In addition, defense of a female had a significant
effect on the outcomes of fights: The motivated residents won more fights than the motivated intruders, indicating that these
two treatments caused asymmetric increases of the resource value. This is the first report of two external factors simultaneously
raising resource value, affecting motivation of contestants, and altering the outcome of fights. |
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