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.
Propagule pressure is a composite measure to the number of individuals released into a non-native region (Lockwood, 2005).
Later, it was suggested that the niche theory and biotic resistance help explain the variation in success or failure of nonnative invasion (Colautti et al., 2006).
More recent studies have shown that particular invasive species characteristics, such as ability to compete for resources, aid in their proliferation in habitats.
One important concept of propagule pressure is how it can be used to predict and or prevent invasions of non-native species in high risk locations.
As invasion rates increase and biodiversity decreases, the probability of non-native establishment needs to be more accurately measured (Leung et al., 2004).
When this is the case detailed information on rates of population introduction and size are difficult to obtain (Leung et al., 2004).
They found that resource availability had to coincide with invasion time and was a limiting factor to seaweed success (Britton-Simmons et al., 2008).
Of the invasiveness characteristics studied, most did not significantly correlate to establishment, spread, abundance or impact of nonindigenous species.
The communities that experienced more disturbances and resource availability achieved higher establishment and abundance of invaders.
On a similar note, propagule pressure also plays a role in unintentional invasions of nonnative species to particular habitats.
Once propagule pressure is considered, more suitable measures can be taken to reverse the unwanted effects of nonnative invasions.
Measures of propagule pressure have been shown to have specific relationships with the probability of establishment (Leung et al. 2004).