In the pursuit of survival, many organisms physically change the environment around them. While some of these changes are modest, with limited impact, others have a large influence on other species and the functioning of entire ecosystems. Named "ecosystem engineers" by Institute ecologist Dr. Clive Jones, these organisms play a major role in creating, modifying, maintaining, and destroying the habitats that other species depend upon. By controlling energy and material flows, they can profoundly affect the way ecosystems function.

Ecosystem engineers come in myriad forms, including plants, animals and tiny microorganisms. For example, beaver build dams, trees cast shade, the empty shells of dead mollusks provide shelter, and earthworms burrowing in soil alter drainage. Depending on the magnitude and type of physical environmental changes they cause, engineer effects on ecosystem processes, communities and species populations range from subtle to extreme. Understanding why some engineers have large effects, while others do not, is a central focus of the research conducted by Dr. Jones and colleagues. This work includes investigations of the engineering roles played by many species, from rock-eating snails in Israel's Negev desert to cushion plants in the Andes Mountains of Chile.

There are two types of ecosystem engineers: those that change the physical environment by their own biological structures (autogenic engineers) and those that modify the environment by transforming living or non-living materials (allogenic engineers). Mollusks are a good example of autogenic engineers; long after they have died their shell structures persist in the environment. Other aquatic and shoreline-dwelling animals use the structures provided by their empty shells as refuge from predators and environmental stresses, such as the force of water currents.

The beaver is the classic allogenic engineer; they are the only North American animals, besides humans, capable of felling mature trees. Their clear-cutting and stream damming activities turn streamside environments into wetlands. Beaver dams alter stream flow, transforming running water into slow moving or standing water. Dragonflies, frogs, and vascular plants thrive in this beaver-created habitat. Other species, such as salamanders, do not. Institute research has shown that by increasing habitat diversity, beaver dramatically enhance plant biodiversity in the riparian zone of New York's Adirondacks.

By studying these and many other engineers— including digging porcupines, leaf-tying insects, and microbial crusts that generate runoff water— Dr. Jones and his colleagues are increasing our understanding of Nature's engineers. When assessing how ecosystems function, the affects exerted by these species are often an important part of the ecological puzzle.