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Research Progress Report
Gaylord Donnelley Environmental Fellowship
January 2001
Testing the effect of state dependent decision making of individual herbivores on food web dynamics.
Submitted by: Dr. Ofer Ovadia
Yale Faculty Sponsor: Professor Oswald Schmitz,
Yale School of Forestry and Environmental Studies
A short description of the project:
Scientific
Background
:
Understanding
the origin and maintenance of global patterns of
biodiversity is one of the monumental problems of
biology (Ricklefs and Schluter 1993).
Ecological studies of the past thirty years tended
to focus on population level processes in order to
explain community structure. However, this
approach failed to explain global biodiversity
patterns (Ricklefs and Schluter 1993). These
studies as many others at the population and
community levels were based only on numerical
effects and did not take into account the possible
behavioral effects. Recently, it has been
shown that individual behavior may stabilize
population dynamic (Mangel and Roitberg 1992),
drive trophic cascades (Schmitz et. al. 1997), and
be critical to persistence of populations in the
landscape (Lima and Zollner 1996; Roitberg and
Mangel 1997). These studies as some others
have led ecologists to the conclusion that one
should not ignore the role of individual behavior when
studying the structure and the function of complex
ecological entities (e.g., Sutherland 1996;
Fryxell and Lundberg 1998).
Dr.
Ovadia’s research aim is to incorporate state
dependent decision making by individual herbivores
into a model of food web dynamics, and to test
this model experimentally in the field.
The
Model:
Dr.
Ovadia uses the Gecko (Booth 1997; Schmitz and
Booth 1997; Schmitz 2000) as a tool for studying
the effect of state dependent decision-making by
individual herbivores on food web dynamics.
The Gecko is a spatially explicit individual based
model developed at the CCE (Center of
Computational Ecology) to explore the effect of
individual behavior on food web dynamic (Booth
1997; Schmitz and Booth 1997; Schmitz 2000).
He has modified the Gecko to include state
dependent foraging decisions by individual
herbivores and ran simulations and used the
results to design and to generate predictions for
the field study.
The
Empirical Study:
The
study is located in an old-field located at the
Yale-Myers Research Forest in northeastern
Connecticut. The food web includes three-trophic
levels, spider predators, grasshopper herbivores
and herbaceous plants.
The
field study is divided into two major parts:
behavioral experiments and food web experiments.
During the behavioral experiments Dr. Ovadia
monitors the foraging behavior of grasshoppers
with different internal Body State exposed to
different levels of predation risk. During
the food web experiments, he tests the effect of
different levels of chronic internal Body State of
grasshoppers on community dynamic.
Research
Plan:
September
1999 – April 2000:
Theoretical
study which includes three parts: 1) Modifying the
Gecko to include state dependent decision making
by herbivores, 2) Running simulations to test the
effect of herbivores state on food web dynamic,
and 3) Using the simulations results to design and
to generate predictions for the field study.
April
2000 – September 2000:
Field
study that includes two major parts: 1) Behavioral
experiments, and 2) Food web experiments.
September
2000 – April 2001:
Analyzing
the results from the empirical study. Using
the first year results to enhance the development
of the theoretical study.
April
2001 – September 2001:
Field
study testing the predictions generated by the
Gecko during the theoretical study of the second
year.
The
progress done since Dr. Ovadia’s arrival at the
Yale University:
1)
Dr. Ovadia is working in collaboration with Ginger
Booth from the CCE. They have modified the
Gecko to include state dependent foraging decision
by the herbivores in the model. He ran
simulations and used the results to design and to
generate predictions for the field study.
2)
Dr. Ovadia did a large field experiment during the
summer and is currently analyzing the data.
3)
Dr. Ovadia is working on his PhD publications and
has submitted two papers, one accepted for
publication in Behavioral Ecology and the other
currently is in review.
Dr.
Ovadia is working on two papers: the first
manuscript is a theoretical state dependent Gecko
paper and the second one is an empirical paper
that is based on the results of field study.
References
1) Booth, G. 1997. Gecko: A continuous 2D world for ecological modeling. Artificial Life. 3: 147-163.
2) Fryxell, J.M. and Lundberg, P. 1998. Individual Behavior and Community Dynamics. Chapman and Hall, London.
3) Lima, S.L. and Zollner, P.A. 1996. Towards a behavioral ecology of ecological landscapes. Trends in Ecology and Evolution. 11(3):131-135.
4) Mangel, M. and Roitberg, B.D. 1992. Behavioral stabilization of host-parasite population dynamics. Theoretical Population Biology. 42:308-320.
5) Ricklefs, R.E. and Schluter, D. 1993. Species Diversity in Ecological Communities, Historical and Geographical Perspectives. The University of Chicago Press, Chicago.
6) Roitberg, B.D. and Mangel, M. 1997. Individuals on the landscape: behavior can mitigate landscape differences among habitats. Oikos. 80:234-240.
7) Schmitz, O.J. 2000. Combining field experiments and individual-based modeling to identify the dynamically-relevant organizational scale in a field system. Oikos. In Press.
8) Schmitz, O.J., Beckerman, A.P. and O’Brien, K.M. 1997. Behaviorally mediated trophic cascades: effects of predation risk on food web interactions. Ecology. 78(5):1388-1399.
9) Schmitz, O.J. and Booth, G. 1997. Modeling food web complexity: The consequences of individual-based, spatially explicit behavioural ecology on trophic interactions. Evolutionary Ecology. 11: 379-398.
10) Sutherland, W.J. 1996. From Individual Behaviour to Population Ecology. Oxford University Press. Oxford.
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