Propagule Pressure

Propagule pressure (also termed introduction effort) is a composite measure of the number of individuals of a species released into a region to which they are not native. It incorporates estimates of the absolute number of individuals involved in any one release event (propagule size) and the number of discrete release events (propagule number). As the number of releases or the number of individuals released increases, propagule pressure also increases. Propagule pressure can be defined as the quality, quantity and frequency of invading organisms (Groom, 2006). Propagule pressure is a key element to why some introduced species persist while others do not (Lockwood, 2005). Species introduced in large quantities and consistent quantities prove more likely to survive, whereas species introduced in small numbers with only a few release events are more likely to go extinct (Lockwood, 2005). Propagule pressure is a composite measure to the number of individuals released into a non-native region (Lockwood, 2005). Three approaches are used to study and measure propagule pressure. One approach introduces a specific amount of propagules into controlled plots. A second approach allows introduced species to mature and colonize naturally while observing native and non-native species during the colonization. The final approach used to study and measure propagule pressure utilizes past records of the numbers of individuals introduced, including natural introductions and intentional introductions (Colautti et al., 2003).