Comparative population ecology of the dragonflies Libellula lydia and Libellula luctuosa (Odonata: Libellulidae)

Abstract

Temporal and spatial patterns of habitat use, population size structure, and survivorship were compared over three generations of Libellula lydia and Libellula luctuosa in a small pond in Indiana. The two species were univoltine, had similar phenologies, and converged on the same within-pond habitats. There was little evidence for any spatial and (or) temporal habitat partitioning that might be expected between such morphologically and ecologically similar species. Larval populations of each species were highly size structured because oviposition and hatching were extended over 3 months in summer. Intraspecific size differences were greater than those frequently reported to accommodate interspecific coexistence. Thus, intraspecific resource partitioning and cannibalism should have an important effect on population dynamics. Both similar and disparate interspecific size combinations frequently co-occurred in time and space so that competition and predation should simultaneously affect coexistence. Larval mortality was high in late summer and fall, negligible in winter, and high again in spring. Fewer than 10% of either species survived to emerge from the pond. Interodonate predation is a likely source of much of this larval mortality, given that other odonates are among the most abundant large predators in fishless ponds.