Social organization of mountain lions: Does a land-tenure system regulate population size?

Mountain lions (Puma concolor) are thought to regulate their populations vi a social behavior. The proposed mechanism is a land-tenure system that resu lts in exclusion of individuals from the population through territoriality and temporal avoidance. In the absence of mortality from intraspecific aggr ession, social behavior can regulate a population only by limiting reproduc tion. Successful reproduction among large mammals is related to the availab ility of food. Four states of nature must hold if a population is regulated by social behavior via a land-tenure system in mountain lions: (1) individ uals should not be distributed randomly, but each should have its own disti nct distribution, and those individuals should maintain regions of exclusiv ity; (2) use of food within the distribution of an individual should not be random, but should be clumped as individuals try to exclude each other fro m access to prey; (3) those clumps of prey must not be simply the result of prey distribution, but of social interactions among lions; and (4) social interactions and defense of food should occur in regions where distribution s of individuals overlap; therefore, prey use by individual lions in areas of overlap should be less than expected based on the distribution of prey. We tested hypotheses regarding social regulation for a population of mounta in lions that co-occurred on a winter range with a population of mule deer (Odocoileus hemionus) in the eastern Sierra Nevada, California, from 1991 t o 1997. Individual mountain lions (rt = 10) exhibited distinct distribution s, and deer killed by individuals (n = 112) were not distributed randomly w ithin the distribution of the lion that did the killing. Furthermore, the n onrandom distribution of lion-killed deer could be explained by the distrib ution of live deer alone, but that result was marginally not significant (P = 0.06) and indicated that something else affected the locations of kills made by lions. Results from tests of whether the presence of another mounta in lion affected where individuals chose to kill prey indicated that social interactions had no effect. The distribution of deer killed by individual mountain lions in areas of exclusive use and areas of overlap was identical to that expected based on the distribution of live deer alone. That outcom e indicated social behavior was not regulating the population of mountain l ions via partitioning of prey, and temporal differences in use of space cou ld nor explain the distribution of mountain lions we observed. A system of land-tenure and mutual avoidance did not limit the population of mountain l ions in Round Valley via partitioning of prey. Our results are concordant w ith other studies of large mammalian carnivores, which reported that popula tions were not limited primarily by territoriality but by the supply of foo d.