Introduction

Humans are terrestrial. Our experience is almost exclusively with that environment, and we should therefore have an intuitive understanding of terrestrial situations that is superior to our grasp of aquatic situations, whether freshwater or marine. For that reason, I have begun this description and criticism of ecological experiments with those performed on land. One of the themes of this book is that many generalizations in ecology are unlikely to hold across environments that differ in major ways. A consideration of the results of observations and experiments suggests that on land, interactions among the elements of the biota will be distinctive for at least the following categories: forest, prairie, desert, and tundra. Further subdivisions may be necessary.

A conventional and logical arrangement of the experiments to be described is to consider them in the context of the trophic level on which they were conducted, starting with the decomposers. It is recognized that it is not always possible to make the assignment cleanly. For example, in taking prey, most predators do not discriminate between herbivores and smaller predators, but for a considerable majority of the experiments, the assignments are reasonable. No attempt is made to describe all of the experiments on any trophic level. Those experiments selected either illustrate the interactions of greatest interest, or are examples of problems that face experimental ecologists, or represent good or bad experimental design.