Population structure in Ischnura denticollis (Burmeister) (Zygoptera: Coenagrionidae)

A mark-recapture study in I. denticollis was carried out in a large pond in Mexico, with a high population density. Manly & Parr method was used to measure population size, survivorship and increment rate. There were several daily maxima and minima in population size throughout the study. Minima were attributed to the detrimental effect of strong rains. Survivorship had an average of 0.7053 for both sexes, which converted to days gave 2.86, one of the lowest rates in the Odonata. Maximum longevity was 42 days for males as well as for androchromatic and heterochromatic females. As in other studies males had more constant recapture indices, followed by androchromatic and heterochromatic females. Primary sources of observed mortality were spider predation and falls into the water. The Morisita and variance-to-mean indices suggest an aggregated dispersion pattern for both sexes. Vagility appears to be low. Sex ratios were approximately equal. Maturation time, measured from emergence, was 6-9 days for males and androchromatic females. Comparisons are made with other Ischnura spp., but especially with the closely allied I. gemina.