Academic journal article The American Biology Teacher

Teaching Principles of Experimental Design While Testing Optimal Foraging Theory

Academic journal article The American Biology Teacher

Teaching Principles of Experimental Design While Testing Optimal Foraging Theory

Article excerpt


We describe a simple field study that we have found useful in introducing students to experimental design. Students manipulate the nutritive gain available from flowers to test the hypothesis that the foraging behavior of nectarivorous insects maximizes energy gain rate. They add sucrose solution to some flowers and water to others; additional flowers are left unmanipulated. Visit durations of foraging butterflies are then measured to test the prediction that individuals will forage longer at patches that offer higher energy gains. The project encourages students to consider how a study's design influences the results obtained, and helps to develop scientific reasoning skills.

Key Words: Adaptation; evolution; experimental design; optimal foraging; coevolution; animal behavior.


The concept of adaptation via natural selection can be demonstrated beautifully to students by investigations of animal morphology or physiology, but studies of the behavior of organisms can be equally valuable. Animal behavior is especially amenable to experimental testing of hypotheses about adaptation and, thus, provides an opportunity for students to learn basic principles of experimental design.

Here, we describe a simple study that we have found useful in introducing students to fundamental properties of well-designed experiments in the context of testing hypotheses about adaptation. We use the experiment as the first of a series of projects conducted in an undergraduate animal behavior laboratory class. The course is for upper-division students, and in addition to collecting data, our students also find and read relevant primary literature, enter and analyze the data, and prepare a lab report in journal-style format. These components of student participation could easily be adjusted so that the study could be conducted in introductory biology labs or advanced placement high school biology courses. The project addresses the content category "Science as Inquiry" of the National Science Education Standards, as well as the "Life Sciences" (Behavior of Organisms, Biological Evolution) and "History and Nature of Science" (Nature of Scientific Knowledge) categories (National Research Council, 1996).

* Background

Virtually any behavior can be used for testing hypotheses about adaptation, but foraging is especially convenient because animals do it frequently and because the costs and benefits of various options that a foraging animal might have can be quantified. The cost/benefit approach to the study of foraging behavior, known as "optimal foraging theory," was devised in the late 1960s through mid-1970s, and it has served to explain multiple aspects of the food-acquisition behavior of animals (for a thorough review, see Stephens & Krebs, 1986; for a discussion of the role of optimality models in studies of adaptation, see Parker & Maynard Smith, 1990). One general use of the theory is the generation of predictions about which types of food animals should include in their diets versus which should be ignored. One might ask, "If I offer an animal a choice of prey items, will it prefer those that are of highest nutritive value?" or "If I offer prey items that are time-consuming to handle (e.g., nuts in shells) and also prey items that can be readily consumed (nuts without shells), will the animals prefer the prey with lower time costs?" An alternative application of the theory is to predict how long an individual should remain in a patch of food before leaving it to search elsewhere. If, for example, food patches are widely spaced (and so require a long time to get to), then one would generally predict that the amount of time spent foraging in each patch will be longer than if travel time between patches is very short. Or if environments vary from rich to poor, such that some habitats offer patches yielding high prey density and others have patches containing few prey, one would predict that animals in the rich environments should stay longer in each patch they visit. …

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