Ecology is a broad biological science and can thus be divided into many sub-disciplines using various criteria. For example, one such categorization, based on overall complexity (from the least complex to the most), is:
Behavioral ecology, which studies the ecological and evolutionary basis for animal behavior, focusing largely at the level of the individual;
Population ecology (or autecology), which deals with the dynamics of populations within species, and the interactions of these populations with environmental factors;
Community ecology (or synecology) which studies the interactions between species within an ecological community;
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;
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;