Study design concepts for inferring functional roles of mammalian top predators

Abstract

The roles and functions of top predators have in recent years been an important yet controversial field of biodiversity conservation research. Interrelationships between sympatric species within complex systems can pose enormous challenges for designing studies that gain clear understanding of specific relationships and processes. Teasing out the nature of the relationships is made far more difficult, if not impossible, if the experimental design of the studies is flawed or too limited for the desired inferences, and/or if the observational methods are inappropriate or too unwieldy to obtain the necessary data validly. The most powerful observation methods for understanding the interrelationships among sympatric species require standardized and repeated observations of populations over time, seasons, habitats and geographic space. Yet, the most powerful experimental designs underpinning the observation methods actually rest in fairly straight-forward design concepts. The two general components for collecting such data are the design structure for the study (possible population manipulation, and where and when observations are to be made) and the procedures for making observations (population assessments) in each location at each time. Here, we discuss these and other experimental design concepts which, if followed, will assist in clarifying the ecological roles of top predators and resolving debates about these roles.