Food Limitation of Larval Dragonflies: A Field Test of Spacing Behaviour

Density-dependent growth and survival of larval odonates may result from some larvae excluding others from profitable hunting sites. This hypothesis predicts that both degree and variation in food limitation should increase with population density; it also suggests that large larvae should show less food limitation than small larvae. I tested these predictions by analyzing food limitation, determined by mass of fecal pellets, and population density of larval Ischnura verticalis and Enallagma ebrium from a pond in southern Ontario. When data from all sampling days were combined, population densities of both species were negatively correlated with gut fullness but there was no correspondence between population density and gut fullness measured at different sites on any given day. Also, there was no correlation between population density and variation in food limitation and there was no evidence that small larvae suffered a greater degree of food limitation than larger larvae. A lack of discrete and persistent prey patches and/or low larval population densities may account for the lack of evidence that larvae are excluded from patches of prey.