Ecology

Ecology has long been recognized as complex. One discouraged ecologist suggested, "ecology is not only more complex than we think, it is more complex than we can think." Ecology has assembled an extended body of information about the earth's ecosystems, but consensus on a general theoretical foundation remains elusive and some question its likelihood.

A notable effort to provide a theory of ecology was G. E. Hutchinson's formalization of the niche concept. A species niche is its response to all variables, biological and physical. Hutchinson influenced Robert MacArthur (1969), who pursued a theory of ecology predicated on competition that was widely accepted but subsequently questioned, as other factors such as predation and disturbance were shown to influence species relations.

An early consensus on "dynamic" ecology, focusing on the ubiquitous process of succession or change in ecosystems, regarded succession as "primary" if beginning on a previously unoccupied area, or "secondary" if following disturbance. This remains a factor in complex ecology. Disturbance by biotic or abiotic factors at varied intervals, intensities, or different area sizes is common and some disturbances (e.g., fire) are integrated into the development of an ecosystem, adding to its complexity.

One of the difficulties of assessing regularities in ecology is that ecological entities exist, and functions occur, at different scales of size, time, and rate, and the perspective of history is essential. Consideration of scale is widely evident in recent ecology, increasing its inherent complexity. The traditional ecological entities, population and community, are now expanded to metapopulations, populations of a species connected by migrations among them, and landscape ecology, an extended area including diverse communities. Taxonomic populations are also considered as guilds, species with similar functions apart from their systematic relations. At an extreme the biosphere, the whole-earth system, may be considered, and has been transformed into the GAIA hypothesis, treating the earth as an integrated superorganism transcending conventional ecology.

Another approach to ecological complexity is offered in hierarchy, an effort to deal with the scale problem in ecology. Ecological systems are considered as hierarchies in which processes at higher levels are predictable in some degree based on processes at lower levels. Some properties of the whole are said to be emergent and must be considered at the appropriate hierarchical level.