Revista Chilena de Historia Natural 81 (1): 111-121, 2008
RESEARCH ARTICLE
Patterns of turnover and floristic similarity show a non-random distribution of naturalized flora
in Chile, South America
The current geographical distribution of alien species could be informative of processes
involved in the biological invasions facilitated by humans. Because environmental and anthropic factors affect the geographic
distribution of alien plants, we hypothesize that naturalized plants have a non-random distribution along extensive geographical ranges.
On the basis of a complete and updated database of naturalized plants in Chile, we analyzed their turnover and floristic similarities
among regions that encompass a wide latitudinal gradient in South America. Using Moran’s index and Mantel’s test we characterized
the spatial auto-correlation (regional aggregation) and the effect of geographical distance on the index values. Additionally, we used
clustering methods and resampling procedures to detect plant assemblages at regional level. Whittaker’s index displayed a positive tilt,
increasing according to geographical distance and reaching a plateau; conversely, Jaccard’s index was negatively associated with
geographical distance. Removing the effect of distance, both Whittaker’s and Jaccard’s values showed no significant trends.
Multivariate analysis combined with resampling procedures revealed the existence of three distinctive plant clusters: Northernmost
Chile, Central-southern Chile, and Southernmost Chile. These clusters are characterized by naturalized plants that are not present in
the others. Based on this evidence, we conclude that the set of naturalized plants in Chile exhibits a non-random geographical
distribution, displaying an ordered geographical pattern across regions (latitude). We discuss the role of the environmental variables
(climate, latitude) and land use post-European colonization as factors in the distributional patterns here documented.
Key words:
Jaccard’s index,
Whittaker’s index, plant invasions, naturalized plants, similarity, turnover
