Residence Time, Biogeographical Origin, and Climate as Predictors for Range Size and Species Richness of Exotic Plants in Great Britain

The spread potential of exotic species depends on several factors in the new environment. De Albuquerque et al.(2011) researched some of these factors to see which most affected range size and species richness of exotic plants in Great Britain. The factors they observed on 1,406 exotic species were the amount of time since the plant had been introduced to the new habitat, the origin of the plant, climate of the new habitat, and the human footprint. De Albuquerque et al. grouped the plants into four residence time categories and three biogeographical origins. They found that range increased with residence time and region of origin did not have a strong effect. The results also showed that the human footprint played a small role in determining species richness, while climate was the predominant factor. —Isabelle Heilman
De Albuquerque, F.S., Castro-Díez, P., Rueda, M., Hawkins, B.A., Rodríguez, M.Á., 2011. Relationships of climate, residence time, and biogeographical origin with the range sizes and species richness patterns of exotic plants in Great Britain. Plant Ecology 212, 1901-1911.

In the study of invasive ecology there is a hypothesis which predicts that the more time an invasive species has been in a certain area, the greater the chance that the species will be widespread. De Albuquerque et al. tested this hypothesis in their study of exotic species in Great Britain. Using data from the New Atlas of British and Irish Flora, they explored the various factors that determine species richness and range size of exotic species. The goals of the study were to find the relationship between range size and biogeographical origins and mean residence time of the species, how climate and human footprint affect species richness, and whether species richness grouped by origin and mean residence time have overlapping distributional patterns.
To begin the study, the authors grouped the plant species into four categories determined by their residence time. The oldest species group was the archaeaphytes, which first inhabited Great Britain before 1500, then the older neophytes from 1550–1800, the intermediate neophytes from 1800–1900, and the recent neophytes from 1900–2011. All of the species were also categorized according to their biogeographical origin, either Northern Holarctic, Mediterranean, or Tropical/subtropical. Range sizes of the different categories of species were determined using the Atlas of British and Irish Flora divided into 10×10 km cells, excluding islands and coastal areas with less than 50% land in the cell. The researchers also considered species richness variables in the groups of energy, water, combined water-energy, topography, and human footprint. 
Analysis of the relationship between residence time and range expansion of the exotic species was performed using ANOVA tests and a Tukey’s unequal-N-HSD test to also compare the mean number of grid cells occupied by all groups and the mean residence time for the three neophyte groups, because the year of introduction of archaeaphytes is unknown. An ANCOVA test was used to find the relationship between the plant’s origin and its range expansion. To test the effects of climate and human footprint, OLS multiple regression and partial regressions were used. The effects of environmental factors, such as water and energy were determined by a Varimax-rotated principal component analysis, which showed that the mean annual temperature and annual precipitation were the strongest environmental factors, and were then used in the multiple regressions for climate and human footprint.
The results of the study showed that residence time was the greatest indicator of exotic species range size. Archaeaphytes were the species that had occupied the area the longest and had the largest species ranges, while the youngest group, the new neophytes, had the smallest species range size. Biogeographical origin was not significant; however species that came from the Northern Holarctic and the Mediterranean had larger species ranges than those from the Tropics/subtropics. The researchers also found that temperature had the greatest effect on exotic species richness patterns. Species richness increased in Great Britain going from north to south, and mean annual temperature was the largest correlate of environmental factors.
Although mean residence time was the strongest predictor variable, temperature also played a large role in the expansion of exotic species and their species richness across Great Britain. Exotic species can invade habitats and drain the resources from native plants, killing them. Even though the full effects of climate change are yet to be seen, temperature increases could play a large role in the future expansion of exotic species, causing the death of many native plants. 

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