Intraspecific competition in ant-lion (Macroleon quinquemaculatus) larvae in the field.

The number of larvae of the pit-digging ant-lion Macroleon quinquemaculatus at a food-poor site in Tanzania increased between May and October 1983 and then remained at high density until the following rainy season in March. Food availability was low and small larvae were most likely to suffer food shortage. Hunger level varied within and between instars: hunger was greatest after moults and only third-instar larvae weighing more than 100 mg were well fed. A simple model showed that exploitation competition was asymmetric and most likely to affect small larvae, by removing small prey. Exploitation was estimated to reduce food intake by 30-60%. Within-site differences in growth rate and size were associated with differences in larval density. Small larvae were much more likely to move than large larvae; the latter tended to occupy the periphery of the habitat. The reduction in food intake experienced by small larvae was a consequence of interference competition, which was the main factor operating at this site.