Macroscale spatiotemporal distribution patterns show commonalities among notorious invaders

Background/Question/Methods

Exotic plants have become a widespread part of our landscape, and their continual immigration and spread will homogenize the world’s biota if left unchecked.  Increases in invasives disrupts the balance of species assemblages which in turn creates concerns of alteration of large scale system dynamics.  With escalation of this and other multifaceted drivers of global change, there are apprehensions that we are approaching a global tipping point for biodiversity.  To study and predict invasive species dynamics and spread velocity, many models and theories have been developed and investigated which incorporate functional and evolutionary traits, along with landscape heterogeneity.  Although many individual species and dispersal patterns have been examined deeply, there exist a paucity of studies covering larger groupings of species which cover wide scales and incorporate temporal components.  We hypothesized there were macroscale spatiotemporal expansion patterns which repeated, and these patterns were associated with the mode or timing of species introductions.  Motivated by the need for a broad geographical distribution and long term analysis of species expansion patterns, we collected historical specimen records for over 30 listed invasive and noxious species spanning two centuries covering the eastern United States. 

Results/Conclusions

Most invasive species have been introduced via the horticultural chain, with many others brought for reclamation, forage and accidentally through agricultural seeds.  Our primary question of pattern analysis lead to initial visual investigations which showed emerging spatial forms through time and across species.  Population spread patterns are generally distinguished in three modes (1) radial expansion, (2) jump or long distance dispersal, and (3) range infilling.  As yet, geospatial shape analysis has not provided a single adequate index or procedure to define form or measure shape.  Many highly utilized measures designed for landscape ecology, political boundary delineation, and urban expansion studies are highly collinear and have untenable connections to our question.  To be able to quantify and partition repetitive distributional patterns into discrete groupings led us to develop and utilize a specialized set of metrics particular to our questions.  We employed model designs of vector and raster based GIS techniques using kernel densities and multiple landscape metrics, and utilized non-linear regression to aid quantification and segregation of the patterns.  Results show that while specific dynamics of expansion remain challenging to predict, historical distribution analysis confirms repeated and correlated shape patterns and velocity of invasion.