propagule pressure

a measure of introduction intensity, including release from captivity or cultivation, comprising both the number of individuals of a species introduced per introduction (propagule size) and the frequency of introductions

The quantity, quality and frequency of propagules (such as spores, eggs, larvae, or adults) released in a given location. This term can be seen as the introduction effort, i.e. the pool of individuals introduced in a new ecosystem/area/region and the number of times it is released.