Development of size structure in tiger salamanders: the role of intraspecific interference

Cannibalism affects patterns of density-dependent mortality and may regulat e population size. In many cases, rates of cannibalism depend on size struc ture, the frequency distribution of body sizes in the population, because c annibals can often only capture and consume smaller individuals. Size diffe rences within single-age groups can be caused by a variety of factors. In t his research we tested the hypothesis that size variation among larval tige r salamanders is due, in part, to interference interactions among individua ls of different sizes. We found that size variation was greater when we rai sed larvae in groups rather than in isolation. This increase in size variat ion was due more to a relative deceleration of growth among smaller individ uals rather than acceleration among larger individuals. We also found that smaller larvae had lower feeding rates than larger larvae when in groups, b ut not when isolated. Including spatial structure to limit physical interac tions did not affect the size specificity of feeding rate, although it redu ced feeding rates overall. We argue that these results are consistent with the hypothesis that larger larvae interfere, probably indirectly, with the feeding behavior of small individuals and this contributes to increases in size variation over time. We hypothesize that this indirect interference is caused by a behavioral response of smaller larvae to the risk of predation (cannibalism) by larger individuals.