Example to illustrate biological interaction Pollination illustrates mutualism between flowering plants and their animal pollinators.

Humans have always had an interest in the distribution and abundance of other organism.As hunters and gatherers, prehistoric people had to learn where game and edible plants could be found in abundance. With the development of agriculture and the domestication of animals, people learned more about how the environment affects the growth, survival, and reproduction of plants and animals. Later, naturalists from Aristotle to Darwin and beyond observed and described organisms in their natural habitats and systematically recorded their observations. Because extraordinary insight can still be gained through this descriptive approach to discovery science , natural history remains a fundamental part of the science of ecology.

In addition to its long history as a descriptive science, ecology is also a rigorous experimental science. Despite the difficulties of conducting experiments in natural environments, ecologists often test their hypotheses through field of experiments. The long‐term research by Gene Likens and his colleagues in the Hubbard Brook Experimental Forest is one example.

Other examples of field experiments include studies in which researchers measure the impact of herbivory (plant‐eating) on plant species diversity by comparing open control plots to experimental “exclosures” (An exclosure, in an area being used extensively for grazing, is a limited area from which unwanted animals,for example browsing animals, such as domestic cattle or wildlife, such as deer, are excluded by fencing or other means ) designed to keep out certain herbivore species. Perhaps because of ecology's focus on complex systems that challenge the capacity of scientists to produce consistent results, ecologists have been innovators in the areas of experimental design and the application of statistical inference. We will encounter many examples of ecological experiments throughout this unit.