PARENT SESSION
Oral Session # 9: Invasive Species I: Theory and Modeling.
Presiding: E Rykiel
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 201.

What determines invasion success?

Colautti, Robert, Grigorovich, Igor, MacIsaac, Hugh,

ABSTRACT- Several recent attempts to predict invasions have focused on the ability of species to invade novel habitats (i.e., 'invasiveness') and the susceptibility of habitats to invasion (i.e., 'invasibility'). We conducted a meta-analysis of the recent (1991-2002) invasion literature to search for putative correlates of invasion success, but a lack of explicitly defined terms made generalizations difficult. In particular, the terms 'introduced', 'invasive' and 'naturalized' and their derivatives contained implicit differences between studies. Nevertheless, we found seven species-specific characteristics that were always positively associated with 'invasiveness': 'invasion history', 'germination success or rate', 'reproductive output', 'consumption efficiency', 'hermaphroditic/asexual reproduction', 'brain size', and small 'seed size'. Conversely, only one of five habitat-specific characteristics was concordant among all studies of 'invasibility': 'nutrient levels'. Of particular interest, studies examining resident species diversity found positive relationships with invasion success in ten cases, and negative relationships in thirteen cases. Of 128 total studies, only seventeen examined 'propagule pressure' (i.e., variation in introduction effort) hypotheses, yet this factor was a consistent predictor of invasion success for studies of both 'invasiveness' and 'invasibility'. Furthermore, correlations between 'propagule pressure' and other species- or habitat-specific characteristics implicate a potential for 'propagule biases' (artificial patterns of invasion success owing to non-random patterns in introduction effort). Since 'propagule pressure'-hypotheses remain poorly explored, we introduce a novel framework for the study of invasions that could aid in future attempts to predict invasions, and act as a basis for operational terms and concepts.

Key words: invasibility, invasiveness, propagule pressure, nonindigenous species