Where do floaters settle? An experimental approach in odonates

Abstract

According to classic ecological models, nonterritorial males should settle in low-quality habitats as a result of losing competition over reproductive sites (‘defeated male’ hypothesis). Alternatively, according to evolutionary game theory models, nonterritorial males should settle in the vicinity of high-quality sites and ‘choose’ to delay breeding until these habitats are vacant for them (‘male player’ hypothesis). However, nonterritorial male spatial distribution has not been experimentally tested. If the defeated male hypothesis is true (1) deterioration of high-quality sites should increase the number of nonterritorial males in a population and (2) vacated low-quality territories should be taken over by new territorial males. If the male player hypothesis is true, a similar manipulation should (1) decrease the number of nonterritorial males and (2) vacated low-quality territories should not be taken over. We performed two types of field experiment to test these hypotheses: male removal and patch quality manipulation. Our study species was the territorial damselfly Calopteryx splendens; males of this species exhibit both territorial and nonterritorial behaviour. Our results suggest that deterioration of high-quality habitats significantly reduced the number of nonterritorial males. The proportion of take-overs of the high-quality territories was significantly higher than that of low-quality territories. Our study supports the assumptions of the male player hypothesis and indicates that nonterritorial damselflies are more sensitive to habitat quality changes than territorial ones. Because nonterritorial individuals exist in most populations of territorial taxa, a better understanding of their settlement rules may be relevant for population dynamics and modelling.