To investigate the impact of Trichocorixa verticalis on pool and pond communities en the Doñana area. We have three complementary objectives: 1) To establish the present distribution of T. verticalis and look for biotic and abiotic factors that may explain its distribution. Special attention will go to distribution overlap with autochthonous Corixidae. 2) In its home range, Trichocorixa is known as a quick and abundant disperser, which may prevent colonization and establishment of other fauna (priority effects). We will investigate what the colonization rate of Trichocorixa is in newly flooded pools and how this may affect colonization by other fauna (with special attention to other Corixidae). For this objective, we can join and build further on an ongoing monitoring of colonization by invertebrates in newly dug pools in the Doñana park in cooperation with Dr. A. J. Green. Trichocorixa verticalis has been observed to commonly colonize these ponds (per. Comm. A. J. Green). 3) Test the competitive ability of Trichocorixa with respect to other corixidae (Sigara lateralis, S. selecta, S. stagnalis possibly other species) that are found in the same habitats.