Assemblage structure: an overlooked component of human-mediated species movements among freshwater ecosystems

  • D. Andrew R. Drake Great Lakes Laboratory for Fisheries and Aquatic Sciences, Canada.
  • Farrah T. Chan University of Windsor, Canada.
  • Elizabeta Briski Great Lakes Laboratory for Fisheries and Aquatic Sciences, Canada.
  • Sarah A. Bailey Great Lakes Laboratory for Fisheries and Aquatic Sciences, Canada.
  • Hugh J. MacIsaac | University of Windsor, Canada.


The spread and impact of alien species among freshwater ecosystems has increased with global trade and human movement; therefore, quantifying the role of anthropogenic and ecological factors that increase the risk of invasion is an important conservation goal. Two factors considered as null models when assessing the potential for invasion 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 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 potentially different ecological outcomes. An assemblage exhibiting high PS but low CS (species poor, but highly abundant) may overcome 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) may provide multiple opportunities for one of n arriving species to circumvent environmental barriers, albeit with lower potential to overcome demographic constraints. Species abundance distributions and the corresponding influence of CS and PS are some of many influential factors (e.g., demographic and genetic stochasticity, environmental variability, composition of recipient ecosystems) that will help refine an understanding of establishment risk following the human-mediated movement of species. 



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Author Biographies

Farrah T. Chan, University of Windsor
Great Lakes Institute for Environmental Research
Hugh J. MacIsaac, University of Windsor

NSERC Canadian Aquatic Invasive Species Network II, Great Lakes Institute for Environmental Research

Supporting Agencies
financial support from the CNR (Italy) for a short-term mobility grant to HJM, NSERC Discovery grants to HJM and SAB, NSERC scholarship to FC, and NSERC Visiting Fellow Stipends to DARD and EB from Transport Canada and Fisheries and Oceans Canada.
biological invasion, alien species, invasive species, rank-abundance distribution, colonization pressure, propagule pressure, vector management, risk assessment, model
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How to Cite
Drake DAR, Chan FT, Briski E, Bailey SA, MacIsaac HJ. Assemblage structure: an overlooked component of human-mediated species movements among freshwater ecosystems. J Limnol [Internet]. 2014Apr.8 [cited 2021May18];73(s1). Available from: