Introduced Alien Plant Species in the Neotropics: the Panama Case

Non-insular tropical biomes appear relatively resistant to invasive alien species (IAS). While some argue fewer IAS in continental tropical communities is the result of the complexity of species-rich communities (e.g., Elton's biological resistance hypothesis), others suggest lack of IAS might reflect fewer invasion opportunities, which could change with time. In effect, deforestation may lead to the simplification of tropical habitats, thus reducing biological resistance. Little is known about the current status of alien plants species, factors contributing to their spread and IAS in non-insular tropical systems. Here I report on the status of alien plant species in relation to area, number of native and endemics species, population, forest cover and cultivated area across provinces of Panama. Alien plant species comprise nearly 4 percent of the flora and was positively correlated with the number of native plant species (r = 0.84, P < 0.001) and while this pattern runs counter to Elton's premise, it is consistent with other landscape-scale studies. In Panama, the number of alien plant species is explained by population density (r= 0.91, P < 0.01) and potentially linked to disturbance, albeit coarsely, as the proportion of aliens negatively correlates with forest cover (r = 0.69, P < 0.05). Thus, despite high diversity, these results portray disturbed tropical forests becoming dotted with introduced alien species. While few species seem to become invasive in the continental tropics, rapid land use change could promote the success of IAS representing serious consequences for tropical countries' economies and biodiversity.