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Revista chilena de historia natural

Print version ISSN 0716-078X


RAPOPORT, EDUARDO H.. Remarks on the biogeography of land invasions. Rev. chil. hist. nat. [online]. 2000, vol.73, n.2, pp.367-380. ISSN 0716-078X.

The percentage of exotic plant species (PES) at large geographic scales is presented in form of political maps (Texas and North America) and of isoline maps (Great Britain). In the latter case it is possible to visualize that higher proportions of alien invaders are present in urban and industrial areas as well as in maritime ports rather than in agricultural lands. Consequently, it is possible to predict that the ratio of urban to agricultural species will continue to increase in the future. Based on a survey of 200 world floras, a multiple regression analysis is presented in order to determine the importance of different factors in the yield of PES values. The contribution to the total variance was: disturbance degree 55 %; total species richness 14%; insularity 9%, and latitude 2%. Neither the mean annual precipitation nor the mean annual temperature showed a significant contribution to the total variance. The predominance of Europe as the main deliverer of weeds to other temperate regions in the world has been attributed to the aggressive or imperialistic geopolitics of this region, and to the construction of the first international oceanic fleet. There are reasons to believe, however, that the great size of Eurasia also played a role in the success of its weedy invasive flora. Since several authors found a weak positive correlation between the radial rate of dispersal and the invading success in plants, a table collecting 153 data allowed a first, tentative comparison among different taxa. The mean dispersal rates were 64.2 for microorganisms; 48.5 for invertebrates, 17.2 for vertebrates, 6.9 for plants, and 0.19 km/yr for palynological registers. A discussion about the significance of these results is included. An alternative way to compare invasive ability, especially among agricultural pests, is by means of an index of cosmopolitanism (C*) which varied as follows: 0.642 for phytopathogens, 0.439 for insects and 0.259 for weeds. Weeds are 15 times, agricultural insects 26 times and phytopathogens 37 times more cosmopolitan than, say, common mammals, taken as an example for comparison. Finally, although animals (invertebrates plus vertebrates) show a higher mean dispersal rate than plants (field observations plus ancient pollen registers), it seems that animals are better colonizers of pristine or scarcely disturbed communities, while plants are more successful in anthropic habitats

Keywords : invasions; dispersal rates; cosmopolitanism; Great Britain; North America; Texas.

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