Ecologists have traditionally explained the distribution and abundance of organisms by such factors as food availability, presence of enemies, competition and climate. It is now apparent, however, that other factors are also important. One of these other factors is "ecosystem engineering." Ecosystem engineers are organisms that create, modify or maintain habitats (or microhabitats) by causing physical state changes in biotic and abiotic materials that, directly or indirectly, modulate the availability of resources to other species. Despite widespread recognition of these often important effects, the ecosystem engineering concept has yet to be widely used in ecological applications.

Types of Ecosystem engineers:
1. Allogenic engineers: They change the environment by transforming living or nonliving materials from one physical state to another, via mechanical or other means.
2. Autogenic engineers: They change the environment via their own physical structures, i.e. their living and dead tissues. As they grow and become larger, their living and dead tissues create habitats for other organisms to live on or in.

Examples of Allogenic Engineering:
The Beaver is an important allogenic engineer of the Northern Hemisphere. It transforms living trees into dead trees by cutting them down, and then uses them to dam streams and create ponds. Beaver engineering alters the distribution and abundance of many different organisms, including birds, reptiles, amphibians, plants, insects; and also increases biodiversity at the landscape scale

The Indian Crested Porcupine digs for its food in the ground, and so creates soil pits that persist for decades. Seeds, water and other organic material accumulate in these pits and create microhabitats that have increased plant abundance and diversity.

When woodpeckers excavate holes in which to nest, they create homes not only for themselves but for many other animals.

Examples of Autogenic Engineering
Trees, corals, and giant kelps are good examples of autogenic engineers. As they grow and become larger, their living and dead tissues create habitats for other organisms to live on them.

Lianas (woody vines) are also autogenic engineers. For example, when lianas grow through a forest canopy, they connect trees together, forming arboreal pathways that monkeys and other animals can use to travel without having to descend to the ground

Significance of Ecosystem Engineers:
By creating, modifying and maintaining habitats, ecosystem engineers disturb the natural environment. This disturbance will usually cause some species to increase in abundance and others to decrease in abundance. These organisms can have a great impact on the species-richness and heterogeneity of the landscape of an area. However, since all organisms contribute to the modification of their environment in one way or the other, ecosystem engineer is only used to describe keystone species which plays a critical role in maintaining the ecological community and affects other organisms in the ecosystem.