Identifying general patterns and trends underlying biological invasion
population dynamics and impacts has proven elusive for scientists.
Recently, the impact curve was proposed as a means to predict impacts
over time from invasive alien species, characterized by a sigmoidal
growth pattern in cumulative abundances. While the impact curve has been
empirically demonstrated with monitoring data of a single invasive alien
species (New Zealand mud snail, Potamopyrgus antipodarum), the
broadscale applicability of this trend remains to be tested for other
taxa. Here, we examined whether the impact curve can adequately describe
the invasion dynamics of 13 other aquatic invasive alien animal species
(spanning over different taxa: Amphipoda, Bivalvia, Gastropoda,
Hirudinea, Isopoda, Mysida, and Platyhelminthes) at the European scale,
employing multi-decadal time series of macroinvertebrate abundances from
regular benthic monitoring efforts. For all except one tested species
(the ‘killer shrimp’, Dikerogammarus villosus), the sigmoid impact curve
was strongly supported (R2 > 0.95), characterized by an
exponential increase in cumulative abundance, followed by a subsequent
decline in the rate of accumulation and eventually approaching a
saturation level in the long term, where impact was maximized. For the
D. villosus exception, the impact had not yet saturated, likely
reflecting the early phase of an ongoing European invasion. The impact
curve further allowed estimation of introduction years and lag phases,
as well as parameterisation of growth rates and carrying capacities,
providing strong support for the boom-bust dynamics typically observed
in several invader populations. These findings suggest that impact can
grow rapidly before saturating at a high level, with timely monitoring
often lacking for the detection of invasive species post-introduction.
We further confirm the applicability of the impact curve to determine
trends in invasion stages, population dynamics, and impacts of pertinent
invaders, ultimately helping inform timing of management interventions.
We hence call for improved monitoring and reporting of invasive alien
species over time to permit further testing of large scale impact
consistencies across various habitat types.