Introduction

Some biological sciences, like agronomy, physiology, and the like, share concepts and research methods with the science of ecology, but there are obvious differences regarding the way data are gathered. In the former subjects, designed experiments with the sampling processes carried out under controlled conditions are more often performed. Although the use of experiments in ecology has always been suggested in order to gain a better idea of cause-and-effect relationships (Underwood, 1997), this is often difficult or impossible, and ecologists are compelled to use observational methods of sampling. Moreover, there are multidisciplinary areas combining the ecological component and socioeconomic approaches (e.g., ethnobiology, natural resource management) in which the only sampling strategy available is a nonexperimental, observational approach.