Male contesis for territories and females in the fly Dryomyza Anilis

Dryomyza anilis males defend the small carcasses on which females oviposit as well as the females themselves during copulation and oviposition. Contests over territories and females, were compared to assess the way different asymmetries affect the outcome of a struggle. In contests over females with a lot of eggs the rate of take-over was lower than in contests over immature females, but the size of the female or her size relative to the owner did not affect the outcome. In territorial disputes and territories was the size difference between the opponents. Fifty-three per cent of the contests over females and 39% of territorial struggles resulted in a take-over. In take-overs, owners were smaller than copulating males or territory owners on average. Take-overs are part of a process in which resource owners continue to change until one is strong enough to defend the resource successfully. Contests over females lasted significantly longer than those over territories, which suggests that for males females are more valuable than territories. This is to be expected as territories are of value because they ultimately increase the probability of obtaining females. A positional advantage or the higher payoff of the owner in disputes over females may be the reason for the lower rate of take-over in female defence than in territorial struggles between opponents of similar size.