Abstract
The number of invaders and the timing of invasion are recognized as key determinants of successful invasions. Despite the recognized importance of "propagule pressure," invasion ecology has largely focused on how characteristics of the native community confer invasion resistance. We simultaneously manipulated community composition and invader propagule pressure in microcosm communities of freshwater bacteria. We show that high propagule pressures can be necessary to establish an invader population, but that the influence of propagule pressure depends on the composition of the resident species. In particular, the number of individuals invading was most important to invasion success when one of the species in a resident community is a strong competitor against other species. By contrast, the timing of invasion was most important when communities had lower growth rates. The results suggest that the importance of propagule pressure varies both between communities and within the same community over time, and therefore have implications for the way we understand the relationship between biotic resistance and invasion success.
Highlights
Invasive species have evolved a great variety of specialized ways to outcompete resident species, and there has been much work to characterize the traits of successful invasive species (Davis 2006, van Kleunen et al 2010)
If it is assumed that a species has the traits that are sufficient for maintaining a population in a new environment, propagule pressure can be important because invasive species that arrive at a high initial abundance are less susceptible to local extinction due to demographic or Manuscript received 30 November 2016; revised 24 March 2017; accepted 31 March 2017
Our results show that the effect of propagule pressure on invasion success strongly depends on the resident community being invaded
Summary
Invasive species have evolved a great variety of specialized ways to outcompete resident species, and there has been much work to characterize the traits of successful invasive species (Davis 2006, van Kleunen et al 2010). Invasive species can be successful irrespective of their traits, through the introduction of sufficient numbers of individuals or through repeated introductions (Johnston et al 2009, Simberloff 2009). While the traits of an invader are undoubtedly important, recent work has shown that the success of an invader can in some instances depend on the propagule pressure of the invasive species. If it is assumed that a species has the traits that are sufficient for maintaining a population in a new environment, propagule pressure can be important because invasive species that arrive at a high initial abundance are less susceptible to local extinction due to demographic or Manuscript received 30 November 2016; revised 24 March 2017; accepted 31 March 2017.
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