1. (in neurophysiology) The activation of extra motor neurons in order to bring about an increased response to a stimulus that is present at an even intensity.

2. (in ecology) The attracting of beneficial organisms, e.g. predatory animals, by plants as a means of defending the plant against attack from pests. Such an attack may, for example, trigger the release of volatile chemicals that attract the attention of beneficial parasitic wasps; these may then mount a counterattack against caterpillars eating the leaves of the plant.