Trends in Ecology & Evolution
The role of propagule pressure in explaining species invasions
Introduction
Propagule pressure (also termed ‘introduction effort’ [1]) is a composite measure of the number of individuals released into a region to which they are not native [2]. 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 and/or the number of individuals released increases, propagule pressure also increases. Here, we concentrate on the role of propagule pressure in determining the establishment success or failure of non-native populations (Figure 1). However, increasing propagule pressure might be equally important in understanding the rate of geographical spread of non-native populations (e.g. [3]) (Box 1). Determining the role of propagule pressure within these different invasion contexts should lead to broader ecological and management insights into invasive species biology.
Section snippets
Variation in invasion success
Propagule pressure is an ‘event-level’ characteristic 1, 4: that is, it can differ for each introduced population. This is in contrast to location- and species-level traits, which are constant across repeated introductions (e.g. [5]). For example, rainbow trout Oncorhynchus mykiss have been purposefully introduced into Africa, Australia, New Zealand, Europe and many other locations worldwide [6]. We can explain the success of rainbow trout using its life history or ecological traits (e.g.
The idiosyncrasy of the invasion process
The importance of propagule pressure to establishment success can also explain why the invasion process often appears so idiosyncratic. In a recent exploration of the role of propagule pressure in the establishment of non-native bird populations, Cassey and colleagues [16] identify two reasons for this importance. First, this research showed that most variation in propagule size was clustered among release events [16]. Thus, a single species that has been introduced to several islands or
Understanding the role of propagule pressure
The strength of the relationship between propagule pressure and establishment success does not, however, negate roles for location and species 20, 21, although it is the interaction of these factors with propagule pressure that might be the more important element to furthering our understanding of invasions. In that regard, we highlight four research agendas that can promote our understanding of the role of propagule pressure within invasions beyond recognizing the importance of large numbers.
Conclusions
Elucidating the factors that determine introduction success involves disentangling the influence of characteristics of the species and environment, and the idiosyncrasies of specific introduction events [4]. From the array of possibilities available, propagule pressure is emerging as a single consistent correlate of establishment success. Propagule pressure can explain not only why some introductions succeed when others fail, but also why introduction success is so idiosyncratic. However,
References (52)
Pattern, process, and prediction in marine invasion ecology
Biol. Conserv.
(1996)- et al.
Predicting the impact of introduced species: lessons from the multiple invasions of the European green crab
Biol. Conserv.
(1996) Metapopulation dynamics: does it help to have more of the same?
Trends Ecol. Evol.
(1989)- et al.
Progress in invasion biology: predicting invaders
Trends Ecol. Evol.
(2001) - et al.
Determinants of establishment success in introduced birds
Nature
(2001) - et al.
Inferring process from pattern in plant invasions: a semimechanistic model incorporating propagule pressure and environmental factors
Am. Nat.
(2003) The ecology of avian invaders
Annu. Rev. Ecol. Syst.
(2003)Life history and ecology influences establishment success of introduced land birds
Biol. J. Linn. Soc.
(2002)Naturalized Fishes of the World
(1996)- et al.
A neutral terminology to define ‘invasive’ species
Div. Dist.
(2004)
Which insect introductions succeed and which fail?
Biological Invasions
Applied Population Ecology
Turnover rates in insular biogeography: effect of immigration on extinction
Ecology
Founder population size and number of source populations enhance colonization success in waterstriders
Oecologia
Global patterns of introduction effort and establishment success in birds
Biol. Lett.
The time to extinction of a colonizing propagule of lizards increases with island area
Nature
Which animal will invade?
Lessons from the establishment of exotic species: a meta-analytical case study using birds
J. Anim. Ecol.
Ecosystem resistance to invasion and the role of propagule supply: a California perspective
J. Med. Ecol.
Invasion vectors: a conceptual framework for management
Translocation as a species conservation tool. Status and strategy
Science
The Balance of Nature?
Global hotspots of biological invasions: evaluating options for ballast-water management
Proc. R. Soc. Lond. Ser. B
Rapid genetic differentiation and founder effect in colonizing populations of common mynas (Acridotheres tristis)
Evolution
Cited by (1959)
Priorities for improving predictions of vessel-mediated marine invasions
2024, Science of the Total EnvironmentA global synthesis of the patterns of genetic diversity in endangered and invasive plants
2024, Biological ConservationThe wild cost of invasive feral animals worldwide
2024, Science of the Total EnvironmentGenomic and phenotypic signatures provide insights into the wide adaptation of a global plant invader
2024, Plant Communications