The Energetic Costs of Fighting

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SYNOPSIS. Current evolutionary theory predicts that energy expenditure will be adjusted in contest situations to the value of the disputed resource and the relative probability of winningit. Estimates of energy expended in contest situations support this prediction. I report on theenergetic costs of display relative to other contest costs to individual fitness ( e.g ., risk ofpredation, losses in feeding time, injury and mortality) in territorial disputes of the spider Agelenopsis aperta . Cost estimates obtained in terms of decrements to milligrams wet-weight of future egg production resulting from single contests indicatethat actual energy expenditure inthese territorial disputes represent insignificant costs. Thesecosts are, in fact, 5–6 orders of magnitude smaller than the costs associated with injury, potential predation and even loss infood as a result of time spent in the interactions. Review of the literature indicates that in most instances, energy expenditure may be correlated with some other factor upon which selection is acting ( e.g ., short contests wherepredation risk is high, variation in levels of escalation exhibited). Two exceptions include the tremendous losses of workers to reproductives in ant, termite, and bee colony territorial disputes and the production of specializedagonistic organsexhibited by some corals, sea anemones and corallimopharians when encountering neighbors within“territorial” boundaries.