Multi-annual cycles in population of Ischnura e. elegans induced by crowding and mediated by sexual aggression (Odonata: Coenagrionidae)
Hinnekint, B.O.N.; Dumont, H.J.
Entomologia Generalis 14(3-4): 161-166
A re-analysis of published female mating frequencies in mature and immature Ischnura e. elegans (Vander Linden 1820) shows that male sexual aggression varies with crowding, young mature .male..male. driving away immature and old .male..male., and .female..female. from the edges of ponds. This effect is more pronounced in .female..female., heteromorphs and immatures, and generates a male-biased sexually active population near the water, where newly matured .male..male. form the dominant fraction. - It is hypothesised that density dependant male aggression is one of the driving forces beyond the existing hyperfine effect causing a pluriannual population cycle. Below a certain population density threshold, there is a constant minimum "basic" sexual aggression. Above the threshold, the sexual harassment that causes the fall of overall mating frequency causes a steep increase of the frequency of matings involving immature .female..female.. At peak population density general aggression disappears, and sexual aggression drops back to its base level.