From Encyclopedia of Evolution
Excerpt: "Biogeography is the study of diversity through time and space; the study of where organisms live and how they got there. An understanding of biogeography is inseparable from evolutionary science. In fact, biogeography allowed some initial insights into the fact that evolution had occurred. In Origin of Species, Darwin noted that major groups of animals lived on certain continents, and not on others that had similar climates, because they had evolved on those continents. This insight from biogeography was also valuable to Wallace, who also discovered natural selection. Wallace's discovery that the (primarily placental) mammals of Asia were very different from the (primarily marsupial) mammals of New Guinea and Australia is still one of the best examples of evolutionary biogeography."

from The Encyclopedia of Ecology and Environmental Management
Excerpt: "Community ecology is the study of the interactions between populations of organisms, and between populations and the physical environment, in a particular community, and the effects that those interactions have on the behaviour and structure of that community. A community cannot simply be seen as the sum of its constituent species or populations, but has emergent properties that are not features of the component populations. The term, ‘community’ here encompasses a wide range of scales, and indeed one community can be described within another—thus a rotting tree stump may house a community of microorganisms, higher plants, and insects, whilst that stump might be part of a much larger community—a forest."

From The Princeton Guide to Ecology
Excerpt: "The first use of "ecological niche" appeared in a report on ladybugs written by R. H. Johnson nearly a century ago, although the term was used shortly thereafter by the zoologist Joseph Grinnell, who is generally given credit for its original development. The meaning was very close to figurative usage: the ecological niche of a species is its "role," "place," or more literally "recess" (in the sense of a "nook" or "cubbyhole") in an ecological community. Thus, the California thrasher, one of Grinnell's major examples, is a bird of the chaparral community that feeds mostly on the ground by working over the surface litter and eating both animal and plant items of a suitable size. Escape from predators is similarly terrestrial, with the well-camouflaged bird shuffling off through the underbrush on the rare occasions when it is threatened."

From The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide
Excerpt: "In ecology, a unit consisting of living organisms and the environment that they live in. A simple example of an ecosystem is a pond. The pond ecosystem includes all the pond plants and animals and also the water and other substances that make up the pond itself. Individual organisms interact with each other and with their environment in a variety of relationships, such as two organisms in competition, predator and prey, or as a food source for other organisms in a food chain. These relationships are usually complex and finely balanced, and in natural ecosystems should be self-sustaining."

From The Encyclopedia of Ecology and Environmental Management
Excerpt: "The idea of using energy flow to explain the pyramids of numbers and biomass (see pyramid of biomass; pyramid of numbers) was hailed as a major breakthrough in the understanding of ecological systems when it was first introduced by Lindeman (1942; see Characters in ecology) in his paper ‘The trophic dynamic aspects of ecology’. For the first time the structure of communities, as described by the number and mass of organisms in each trophic level, was given a dynamic perspective by describing the rates at which energy flows through each layer of the trophic structure of a community."

From The Princeton Guide to Ecology
Excerpt: "The role of diversity and structural complexity in the dynamics and stability of ecosystems is a longstanding and unresolved issue in ecology. Here, I review the history of this major ecological problem and highlight three relatively distinct historical periods in thought. The first period was one of mostly intuitive belief that suggests nature's diversity gives rise to stability. This period was followed by a second that arose with the rigorous application of mathematics and dynamic systems theory that, more or less, puts this intuitive belief to the test. This theoretical result ultimately pushed ecologists to look beyond diversity to understand the dynamics of these complex natural entities."

From The Princeton Guide to Ecology
Excerpt: "Interspecific interactions are most commonly classified according to their effects on the two species. The effect of any given interaction on a population attribute (usually either population growth or fitness) of a given species can be positive (+), negative (–), or neutral (0). Thus, there are six possible pairwise outcomes, commonly referred to as mutualism (+,+), competition (-,-), commensalism (+,0), neutralism (0,0), amensalism (-,0), and predation, parasitism, and herbivory (+,-). This classification is based on discrete [+, -, 0] effects on each of the interacting populations. As will be discussed in what follows, however, divisions among different forms of interspecific interactions are not nearly so black and white: effects actually range continuously from positive to negative in interesting and important ways."

From The Princeton Guide to Ecology
Excerpt: "Studies of nutrient cycles involve integrating information from very fine spatial and temporal scales (the dynamics of enzymes in the neighborhood of microbes) to very coarse scales (the global biogeochemical cycles); they involve integrating the dynamics of organisms with those of the environment that they inhabit and help to shape. Some of the finest-scale, most biological of processes (e.g., the growth of microbial populations on chemically recalcitrant plant litter) control important aspects of the Earth system (e.g., the persistence of nitrogen limitation to primary production, as in the example above). Nutrient cycles cannot be studied effectively in isolation, whether that means isolation from a consideration of both biological and geochemical processes or isolation from understanding the substantial and increasing influence of human activity on the Earth system."

From The Dictionary of Physical Geography
Excerpt: "The study of changes in population size, relating not just to humans as studied in human geography but also to other organisms investigated in biogeography and ecology. Population dynamics involves a consideration of those factors that might give rise to population growth, and those that might lead to its decline. Growth may be achieved by an increase in rates of birth relative to death and/or by immigration; and decline normally results from an excess of deaths over births and/or emigration. The structure of a population may also influence its dynamics; for example, a population with a relatively high percentage of females of reproductive age is clearly in a favourable position for growth, whereas one without such a representation may not be."