Publication Date:
2014-05-10
Description:
Spread of alien species has increased with global trade and human movement, especially over the past century. Some alien species significantly alter the freshwater ecosystems they invade, thus there has been a growing tendency for governments to develop management programs to prevent invasions and their undesirable consequences. Two factors considered as null models when assessing the potential for biological invasions are colonization pressure ( i.e ., the number of species introduced) and propagule pressure [ i.e ., the number (propagule size), and frequency (propagule number), of individuals of each species introduced]. We translate the terminology of species abundance distributions to the invasion terminology of propagule size and colonization size (PS and CS, respectively). We conduct hypothesis testing to determine the underlying statistical species abundance distribution for zooplankton assemblages transported between freshwater ecosystems; and, on the basis of a lognormal statistical distribution, construct four hypothetical assemblages spanning assemblage structure, rank-abundance gradient ( e.g ., even vs uneven), total abundance (of all species combined), and relative contribution of PS vs CS. For a given CS, many combinations of PS and total abundance can occur when transported assemblages conform to a lognormal species abundance distribution; therefore, for a given transportation event, many combinations of CS and PS are possible with differing invasion outcomes. An assemblage exhibiting high PS but low CS (species poor, but highly abundant) easily overcomes demographic barriers to establishment, but with lower certainty of amenable environmental conditions in the recipient region; whereas, the opposite extreme, high CS and low PS (species rich, but low abundance per species) provides multiple opportunities for one of n arriving species to circumvent environmental barriers, albeit with lower potential to overcome demographic constraints. Species abundance distributions of transported assemblages and the corresponding influence of CS and PS are some of many factors ( e.g ., demographic and genetic stochasticity, environmental variability of recipient ecosystems) that will help refine our understanding of establishment risk following human-mediated movements of species assemblages between freshwater ecosystems.
Print ISSN:
1129-5767
Electronic ISSN:
1723-8633
Topics:
Biology
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