Charles Janson

Charles Janson

Professor Emeritus

Office: HS 105
Fax: 406 243-4184

Research Interests

Charles Janson"s research spans two distinct topic in evolutionary ecology: (1) ecological pressures on socical behavior in primates, and (2) ecological and evolutionary consequences of seed dispersal in plants.

He has spent over 80 months observing the ecology and social behavior of several primate species. He is studying how an individual"s social behavior interacts with external aspects of the environment to affect a variety of proximate correlates of fitness such as energy intake, predation risk, and mate choice. For instance, he analyzed how food productivity in patches interacts with group size and individual social status to affect an individual"s food intake in brown capuchin monkeys. He then tested these patterxns experimentally using spatial arrays of artificial food patches in a wild capuchin monkey population in Argentina. Extending the analysis across species, he found that the greater the degree of food competition within groups, the smaller the mean group size of fruit-eating primate species. Recent grant-supported work intends to understand the rules used by primates to decide which of many resources available to visit, and in what order. Understanding the cognitive processes underlying spatial foraging decisions may be crucial to explaining the link between food availability and primate social behavior. An ongoing research interest has been the direct and indirect effects of predation and infanticide on primate social structure.  The main focus of his current field work is to determine how monkeys detect predators and thereby assess the potential anti-predator benefit of social living.  From such studies, he hopes to build realistic models of the evolution of primate social behavior.

Janson also is interested in the evolution of seed dispersal by animals, in particular the relative roles of adaptation and phylogeny in producing the patterns of fruit traits observed among plants now. His approach combines studies of selection on fruit traits in temperate communities, comparisons among fruit traits of species in the biodiverse tropics, and analysis of reflectance characteristics of temperate fruits. His favorite current puzzle is understanding why most bird-dispersed plants have either red or black fruits, when these colors seem to differ markedly in their ability to attract foraging animals.

Field of Study

Primate ecology and behavior;  Evolution of seed dispersal;  Tropical ecology

Selected Publications

Janson, C.H. 2007. Experimental evidence for route integration and strategic planning in wild capuchin monkeys. Animal Cognition 10: 341-356

Janson, C. H. and Vogel, E. R. 2006. Hunger and aggression in capuchin monkeys. In: Feeding Ecology in Apes and other Primates (ed. Hohmann, G., Boesch, C. and Nebel, C.)., pp. 285-312. Cambridge: Cambridge Univ. Press.

Janson, C. H. 2003. Puzzles, predation, and primates: using life history to understand selection pressures. In: Primate Life Histories and Socioecology (ed. P. Kappeler and M. Pereira), pp. 103-131. Chicago: University of Chicago Press.

Di Bitetti, M. D. and Janson, C. H. 2001. The finder"s share in foraging groups of brown capuchin monkeys (Cebus apella). Animal Behaviour.

van Schaik, C. P. and Janson, C. H. 2000. Infanticide by Males and its Implications. Cambridge Univ. Press, Cambridge, England.

Janson, C. H. 1998a. Experimental evidence for spatial memory in wild brown capuchin monkeys (Cebus apella). Animal Behaviour 55: 1229-1243.

Janson, C. H. and Goldsmith, M. 1995. Predicting group size in primates: foraging costs and predation risks. Behavioral Ecology 6: 326-336.

Janson, C.H. 1992. Measuring evolutionary constraints: a Markov model for phylogenetic transitions in seed dispersal syndromes. Evolution 46: 136-158.

Janson, C.H. 1990. Ecological consequences of individual spatial choice in foraging brown capuchin monkeys (Cebus apella). Anim. Beh. 38: 922-934.

Foster, S., and C.H. Janson. 1985. The relationship between seed size and establishment conditions in tropical woody plants. Ecology 66: 773-780.

Terborgh, J.W. and C.H. Janson. 1986. The socioecology of primate groups. Ann. Rev. Ecol. Syst. 17: 111-135.

Chair Director Departments

Division of Biological Sciences

International Experience

Extensive past experience in various countries in Latin America: Peru, Costa Rica, Venezuela, Argentina.  Current active research program in Argentina near Iguazu Falls, Misiones