Ecology is a broad biological science and can be divided into many sub-disciplines using various criteria. Many of these fields overlap, complement and inform each other, and few of these disciplines exist in isolation. For example, the population ecology of an organism is a consequence of its behavioral ecology and intimately tied to its community ecology. Methods from molecular ecology might inform the study of the population, and all kinds of data are modeled and analyzed using quantitative ecology techniques.
When discussing the study of a single species, a distinction is usually made between its biology and its ecology. For example, "polar bear biology" might include the study of the polar bear's physiology, morphology, pathology and ontogeny, whereas "polar bear ecology" would include a study of its prey species, its population and metapopulation status, distribution, dependence on environmental conditions, etc. In that sense, there can be as many subdisciplines of ecology as there are species to study.
Ecology can also be classified on the basis of:
the primary kinds of organism under study, e.g. animal ecology, plant ecology, insect ecology;
the biomes principally studied, e.g. forest ecology, grassland ecology, desert ecology, benthic ecology, marine ecology, urban ecology;
the geographic or climatic area, e.g. arctic ecology, tropical ecology
the spatial scale under consideration, e.g. macroecology, landscape ecology;
the philosophical approach, e.g. systems ecology which adopts a holistic approach;
the methods used, e.g. molecular ecology.
Specialized branches of ecology include, among others:
applied ecology, the practice of employing ecological principles and understanding to solve real world problems (includes agroecology and conservation biology);
biogeochemistry, effect of biota on global chemistry, and the cycles of matter and energy that transport the Earth's chemical components in time and space.
biogeography, the study of the geographic distributions of species ;
chemical ecology, which deals with the ecological role of biological chemicals used in a wide range of areas including defense against predators and attraction of mates;
conservation ecology, which studies how to reduce the risk of species extinction;
ecological succession, which focuses on understanding directed vegetation change;
ecophysiology which studies the interaction of physiological traits with the abiotic environment;
ecotoxicology, which looks at the ecological role of toxic chemicals (often pollutants, but also naturally occurring compounds);
evolutionary ecology or ecoevolution which looks at evolutionary changes in the context of the populations and communities in which the organisms exist;
fire ecology, which looks at the role of fire in the environment of plants and animals and its effect on ecological communities;
functional ecology, the study of the roles, or functions, that certain species (or groups thereof) play in an ecosystem;
global ecology, which examines ecological phenomena at the largest possible scale, addressing macroecological questions;
landscape ecology, which studies the interactions between discrete elements of a landscape;
macroecology, the study of large scale phenomena;
marine ecology, and aquatic ecology, where the dominant environmental milieu is water;
microbial ecology, the ecology of micro-organisms;
microecology, the study of small scale phenomena;
paleoecology, which seeks to understand the relationships between species in fossil assemblages;
quantitative ecology, the development of mathematical and statistical tools to interpret and analyze ecological data.
restoration ecology, which attempts to understand the ecological basis needed to restore impaired or damaged ecosystems;
soil ecology, the ecology of the pedosphere;
theoretical ecology, the development of ecological theory, usually with mathematical, statistical and/or computer modeling tools;
urban ecology, the study of ecosystems in urban areas.
Ecology also plays important roles in many inter-disciplinary fields:
ecological design and ecological engineering.
ecological economics.
festive ecology.
human ecology and ecological anthropology.
social ecology, ecological health and environmental psychology.
Ecology has also inspired (and lent its name to) other non-biological disciplines such as
industrial ecology.
media ecology.
software ecology and information ecology.
Finally, ecology is used to describe several philosophies or ideologies, such as
deep ecology
social ecology
