Density dependence in a larval salamander: The effects of interference and food limitation
I examined the roles of food limitation and aggressive interference in density-dependent growth and survival in larvae of the spotted salmander, Ambystoma,rta maculatum. In a laboratory experiment, I raised larvae at a low density, low food level; high density, low food level; and high density high food level. An increased density of larvae fed low food levels significantly decreased mean body size yet increased the size ratio of the largest:smallest larva (a factor that may promote cannibalism), nigh density also significantly decreased production of metamorphs, although time to metamorphosis did not differ among the three treatments. Food supplementation did not ameliorate the effects of increased density on these variables. Survival was significantly reduced due to an increase in the proportion of larvae cannibalized at the high density. Food supplementation reduced the incidence of cannibalism and improved survival, although it was inadequate to enhance growth significantly. Behavioral trials revealed no difference in aggression across the three treatments, suggesting that it was not a major factor in the observed responses. Rather, density-dependent survival was more a consequence of cannibalism resulting from food limitation. These results provide experimental evidence that, for this species, food limitation may be of greater importance than interference as a mechanism of density dependence.