Deby Cassill

Campus Associate Chair (St Petersburg campus)
& Associate Professor

deby cassill


Department of Integrative Biology, USF
St. Petersburg Campus
Office: URL 108 (research lab; doors locked; knock loudly)
Phone: 727-424-1424
Email: cassill@usf.edu

Specialty Area Recent Publications
Key Research Areas: survival behaviors; reproductive behaviors; maternal investment strategies; ecology & evolution; conservation biology; lifetime replacement fitness. Deby Cassill


Florida State University, Ph.D.; Biology 1996
Florida State University, M.S.; Biology, 1991
Florida State University, B.S.; Biology, 1988 (magna cum laude)
University of West Florida, M.P.A., 1980
Rollins College, Florida Teacher's Certificate; Special Education, 1972
University of Iowa, B.A.; Psychology, 1969


Sociobiology, ZOO 4512, and
Animal Behavior, ZOO 4513.

Both courses introduce students to the history, theory, and application of behavioral research with an emphasis on the evolution of behaviors such as competition, predation, cooperation and altruism by natural selection processes. Those processes include starvation, desiccation, predation, disease, catastrophes and even luck (Cassill and Watkins 2010).


My research is bifurcated into two parallel lines of research: (1) I explore the “triggers” of behavior including survival by foraging, cooperation, sharing, altruism, competition, stealing, murder, and predation as well as reproduction by monogamy-polygamy, oviparity-viviparity, uniparity-multiparity, semelparity-interoparity, and maternal abandonment-extended maternal care. (2) I explore the evolution of behaviors. My goal is to extend Darwin’s theory of natural selection to include not only his theory on the fission of populations into new species by competition for scarce resources, but the fusion of populations into hierarchical societies by cooperation in seasonal environments with high predation. I accomplished that integration with my model of maternal risk-management (Cassill 2019).

Students in my lab are using the maternal risk-management model to test predictions on the natural selection pressures (risk factors) that favor the fusion of populations into hierarchical societies in ants, social spiders, bees, elephants, and whales. Other students are using the model to test predictions on the natural selection pressures that favor the abandonment of eggs by sea turtles versus extended maternal care eggs and hatchlings by crocodiles. Other students are using the model to rank species at risk of extinction based on each species’ population replacement capacity—i.e., lifetime replacement fitness defined as the time it takes for a breeding female and her mates to ensure the survival of one mature breeding daughter and one mature outbreeding son (ω = 2).