Residence time and potential range: crucial considerations in modelling plant invasions

Abstract

A prime aim of invasion biology is to predict which species will become invasive, but retrospective analyses have so far failed to develop robust generalizations. This is because many biological, environmental, and anthropogenic factors interact to determine the distribution of invasive species. However, in this paper we also argue that many analyses of invasiveness have been flawed by not considering several fundamental issues: (1) the range size of an invasive species depends on how much time it has had to spread (its residence time); (2) the range size and spread rate are mediated by the total extent of suitable (i.e. potentially invasible) habitat; and (3) the range size and spread rate depend on the frequency and intensity of introductions (propagule pressure), the position of founder populations in relation to the potential range, and the spatial distribution of the potential range. We explored these considerations using a large set of invasive alien plant species in South Africa for which accurate distribution data and other relevant information were available. Species introduced earlier and those with larger potential ranges had larger current range sizes, but we found no significant effect of the spatial distribution of potential ranges on current range sizes, and data on propagule pressure were largely unavailable. However, crucially, we showed that: (1) including residence time and potential range always significantly increases the explanatory power of the models; and (2) residence time and potential range can affect which factors emerge as significant determinants of invasiveness. Therefore, analyses not including potential range and residence time can come to misleading conclusions. When these factors were taken into account, we found that nitrogen‐fixing plants and plants invading arid regions have spread faster than other species, but these results were phylogenetically constrained. We also show that, when analysed in the context of residence time and potential range, variation in range size among invasive species is implicitly due to variation in spread rates, and, that by explicitly assuming a particular model of spread, it is possible to estimate changes in the rates of plant invasions through time. We believe that invasion biology can develop generalizations that are useful for management, but only in the context of a suitable null model.

Fronts, jumps and secondary introductions suggested as different invasion patterns in marine species, with an increase in spread rates over time

“…Apparent increases in invasion frequency or rate have been previously shown to be potential artefacts of the means of estimation. For example, Wilson et al (2007) used two points in time and therefore constrained earlier introductions to a narrower range of potential rates than later introductions. This constraint does not apply to the current study.…”

A Compendium of Essential Concepts and Terminology in Invasion Ecology

“…Residence time -The time since the introduction of a species to a region; because the introduction date is usually derived from post -hoc records and is likely inaccurate, the term minimum residence time has been suggested (Rejm á nek 2000 ). The extent of invasion of alien species generally increases with increasing residence time as species have more time to fi ll their potential ranges (Wilson et al 2007 ;Williamson et al 2009 ). Resident biota/organisms -Species that are present in a community, habitat or region at the time of introduction of an alien species .…”

Is Rapid Adaptive Evolution Important in Successful Invasions?

“…Other theories concentrate on the unique interactions that can arise between environment and invader, such as enemy release (reviewed in Liu & Stiling 2006 ) and novel weapons (see, for example, Thorpe et al 2009 ). Introduction dynamics such as propagule pressure (Simberloff 2009 ), residence time (Wilson et al 2007 ) and human use (Thuiller et al 2006 ), have also been identifi ed as important ecological factors facilitating successful invasions. The possible evolutionary determinants of invasion success have received much less attention (Callaway & Maron 2006 ), but the past few years have seen a surge in interest, with publications considering evolutionary processes now more common than those with a purely ecological perspective ( Fig.…”