Territoriality of Northern Crayfish (Orconectes virilis) in Itasca State Park

Abstract

In general, it has been shown that large crayfish will tend to win aggressive, territorial conflicts against small conspecific opponents (Figler et al. 1999). Size is not the only factor that can affect the outcomes of territorial interactions however. The “prior residency effect” suggests that the initial resident in a given area will have a dominance advantage over intruders (Peeke et al. 1995). This investigation explores the effects of territorial residency and size on the outcomes of territorial conflicts. We hypothesized that interactions between crayfish with large percent size asymmetries would result in higher eviction rates of the smaller resident by the larger intruder than interactions between crayfish with small size asymmetries. We tested this hypothesis by observing the outcomes of territorial conflicts between crayfish of various sizes in controlled environments. We found that average percent size asymmetries of interactions resulting in evictions of residents were statistically greater than the average percent size asymmetries of interactions resulting in non-evictions of residents by larger intruders. We determined that the level of percent size asymmetry with the highest likelihood of eviction ranged from 67 to 109%. These data support the proposed trend where the likelihood of successful evictions of smaller prior residents by larger intruders increases as the size differences between the two individuals increases.