A Critique of Interspecific Territoriality and Character Convergence

Abstract

Cody (1969) suggested that species may converge in appearance or voice because similarities increase interspecific aggressiveness, which leads to the individuals of two species maintaining mutually exclusive territories in a common habitat. The advantage of such behavior is that it results in the exclusion of food competitors within the individuals' territories. Thus, according to Cody, interspecific territoriality is adaptive. In 1971 I published an interpretation of observed cases of interspecific territoriality, in which I assumed that interspecific territoriality was aggression that evolved in intraspecific contexts but was misdirected toward individuals of other species which possessed similar features that normally stimulated intraspecific territorial aggression (Murray 1971). I argued that mutual interspecific territoriality is maladaptive for at least one of the species because the subordinate species would eventually be excluded from otherwise optimal habitat, but I did not exclude the possibility of the existence of cases of adaptive interspecific territoriality. The two hypotheses, then, seem contradictory. The first assumes that cases of mutual interspecific territoriality are adaptive, while the second assumes that they are not. Some authors studying birds (Barlow et al. 1970, Brown and Orians 1970, Cheke 1971, Rohwer 1972, 1973, Kroodsma 1973, Emlen et al. 1975), fishes (Myrberg and Thresher 1974), hermit crabs (Hazlett 1972 a, b), and flowers (Levin and Schaal 1970) have found Cody's hypothesis reasonable. It has appeared as an annual review article (Cody 1973) and as a portion of a book (Cody 1974), and has been described in at least two ecology textbooks (Ricklefs 1973, Smith 1974). Because Cody's hypothesis is widely accepted and is contradictory to my own, I wish to examine it and the evidence for it in some detail.