Population studies of invasive species allow us to understand how invaders react to new biotic and abiotic conditions, and how native species react to invasion. We evaluated the colonisation efficiency of the invader Zaprionus indianus (Gupta), in the urban area of Porto Alegre city, southern of Brazil. Samples of flies were taken from three urban parks, and ecological indexes were used based on the frequency of the sampled species. The indexes were calculated for breeding and feeding sites separately. The highest frequencies of Z. indianus compared to the other drosophilids were registered during seasons of highest mean temperatures, both for the feeding and the breeding sites. The highest values for the dominance index (D) and the lowest values for diversity (H') were found at the same seasons and for both components. An analysis of the values for Morisita similarity index shows that the Botanical Garden and Farroupilha Park had higher similarity in terms of diversity of the breeding sites. For the feeding sites the highest similarity was between Farroupilha Park and Gabriel Knijnik Park. Despite the three parks have some particularities, the ease with which Z. indianus became established at these places seem to be the same. The arrival of this invader seems to be promoting adjustments in the survival strategies of the resident species, at least at certain periods when the frequency of the populations of the invader increases significantly. However, most of species seem to be able to coexist with the invader.
Biological invasion; ecological index; urban park
