Habitat Heterogeneity, Coexistence and Habitat Utilization in Five Backswimmer Species (Notonecta spp.; Hemiptera, Notonectidae)

In this study, we present data on life history, distribution and coexistence among five backswimmer species, Notonecta glauca, N. lutea, N. maculata, N. obliqua and N. reuteri, from 72 waters in a study area on the Swedish west coast. Two temporal life history patterns were found; species reproducing in the autumn (N. reuteri and N. lutea) and those reproducing in the spring (N. glauca N. obliqua and N. maculata). Female backswimmers were generally larger than conspecific males, except for N. lutea, in which the sexes were similar in size. The sex ratio of N. glauca, N. lutea and N. reuteri did not differ from 1/1. The most abundant species was N. glauca (49% of the waters inhabited by backswimmers) and then N. obliqua (19%), N. maculata (14%), N. lutea (10%) and N. reuteri (8%). In all, 972 individuals were recorded. The species were sequenced, with reference to their habitat use (from species occurring in temporal habitats to more stable and complex ones), as follows; N. maculata – N. glauca – N. obliqua – N. reuteri – N. lutea. N. glauca had the widest habitat distribution pattern. Two species combinations in pools were most commonly found and the five species were never found together. Possible competition among adults, according to their habitat distribution, may occur for: N. glauca with all species; N. obliqua mainly with N. glauca; N. lutea mainly with N. reuteri; N. reuteri mainly with N. lutea and N. glauca; N. maculata mainly with N. glauca. If body size is an important factor in the competitive ability between individuals, not merely species but also sex and temporal aspects have to be considered. The most intense competition should then exist between N. lutea and N. reuteri females.