Cannibalism and density-dependent mortality in the wolf spider Pardosa milvina (Araneae: Lycosidae)

Cannibalism is an important regulating mechanism in many terrestrial and aquatic arthropod communities. Spider ecologists have suggested that cannibalism with wolf spiders (Araneae: Lycosidae) in the genera Schizocosa and Pardosa is common and can act in population regulation. This hypothesis was tested with the species Pardosa milvina (Hentz), a small wolf spider that shows high densities in disturbance-driven ecosystems, including agricultural fields, throughout eastern North America. Under laboratory conditions, cannibalism was more common between pairs of P. milvina with the greatest differences in both mass and size. Field studies, in which we stocked natural densities, 2x natural densities, and 4x natural densities of R milvina in enclosures placed in soybean fields, revealed that survival was lowest when conspecific density was highest, and larger individuals prevailed under high-density conditions. Thus, cannibalism likely plays an important role in governing populations of P. milvina, and the generality about the prevalence and importance of cannibalism with wolf spiders is supported.