Dr. Douglas Fraser

Douglas F. Fraser

B.S. University of Michigan (1963)
M.S., Ph.D. University of Maryland (1970, 1974)

Courses: Ecology, Biology of the Vertebrates, Conservation Biology

We are engaged in a long term study of the ecology and behavior of fish that live in the jungle streams of Trinidad. Our studies, which take me and several of my students to Trinidad 3 or 4 times a year, are centered around the question of how fish survive and make their living in streams that also contain predator fish. We have found that the predator fish can have a very strong effect on the small, prey fish, not only by eating them, but also by intimidating them.

For example, a little minnow-like fish, the jumping guabine, refuses to occupy the same water as its predator and uses its ability to breath air to flip out and seek nearby flood pools, or to swim up tiny rivulets that the predator cannot negotiate. The behaviors of individual fish have important consequences for populations. We study these behaviors and their consequences in laboratory tanks at Siena, where we simulate certain natural conditions. We also study them in the tropical streams of Trinidad where we test out our laboratory findings.

Siena students have made significant contributions to this work and have been co-authors of papers resulting from these studies. Paige MacGowan (class of ‘96) studied how the jumping guabine manages to court and reproduce when dangerous predators are also present in the stream. Because the jumping guabine can breath air through its skin, we knew that they could easily survive in very shallow water of stream margins, where we often find them, but could they also court, and lay their eggs in such places? Paige answered this question by observing the mating behavior of these fish in aquaria containing water of different depths. She found that jumping guabines can lay eggs in water that scarcely covers their backs. Last summer Paige was a member of our summer Trinidad expedition, where we stayed at the William Beebe Tropical Research Station, founded by the famous naturalist, Beebe, in the 1950's. She tested her findings in a natural stream. She concluded that the jumping guabine is a very flexible species that can lay eggs in water of any depth.

What is the importance of Paige's research? The tropical forests of Trinidad's Northern Range Mountains are rapidly disappearing, and its streams and rivers are being affected by this deforestation. To be able to predict the impact of such disturbances on river animals, we need to understand how species, like the jumping guabine, relate to their habitat. Paige's work has filled in many details about how this important river fish uses its environment.

Recently, we completed a large survey of the entire fish community in a major river drainage in Trinidad. Our studies are helping us to understand not only the biology of the jumping guabines, interesting in its own right, but also some basic principles concerning the factors that govern the distribution of stream fish. We can apply this knowledge to identifying potential conservation problems associated with stream alterations. Our laboratory work and travels to Trinidad have been financed by grants from the National Science Foundation. We have been very successful in winning grants that are specifically targeted towards students, paying them summer stipends, travel expenses to Trinidad and buying them equipment needed for their experiments. Over a dozen students like Paige have benefited from these awards.

Representative Publications

Fraser, D.F., J.F. Gilliam and T. Yip-Hoi. 1995. Predation as a agent of population fragmentation in a tropical watershed. Ecology 76:1461-1472.

Fraser, D.F., J.F. Gilliam, M.P. MacGowan, C.A. Arcaro. 1997. Habitat quality in a tropical river corridor. Submitted to Ecology, July 1996

Fraser, D.F. and J.F. Gilliam. 1992. Nonlethal predator effects in a patchy environment: habitat shifts and suppression of reproduction and growth. Ecology 73:959-970

Gilliam, J.F., D.F. Fraser and M.E. Alkins-Koo. 1993. Structure of a tropical fish community: tests for biotic interactions. Ecology 74:1856-1870.