@article {33471, title = {The imbalance of nature: revisiting a Darwinian framework for invasion biology}, journal = {Global Ecology and Biogeography}, year = {2014}, month = {Jan-10-2014}, pages = {n/a - n/a}, abstract = {

Aim

A major implication of natural selection is that species from different parts of the world will vary in their efficiency in converting resources into offspring for a given type of environment. This insight, articulated by Darwin, is usually overlooked in more recent studies of invasion biology that are often based on the more modern Eltonian perspective of imbalanced ecosystems. We formulate a renewed Darwinian framework for invasion biology, the evolutionary imbalance hypothesis (EIH), based only on the action of natural selection in historically isolated populations operating within a global network of repeated environments. This framework predicts that successful invaders are more likely to come from biotic regions of high genetic potential (with independent lineages of large population size), experiencing a given environment for many generations and under strong competition from other lineages.

Location

Global.

Methods

We test the predictive power of this framework by examining disparities in recent species exchanges between global biotic regions, including patterns of plant invasions across temperate regions and exchanges of aquatic fauna as a result of modern canal building.

Results

Our framework successfully predicts global invasion patterns using phylogenetic diversity of the world\&$\#$39;s biotic regions as a proxy that reflects their genetic potential, historical stability and competitive intensity, in line with the Darwinian expectation. Floristic regions of higher phylogenetic diversity are more likely to be source areas of invasive plants, and regions of lower phylogenetic diversity are more likely to be invaded. Similar patterns are evident for formerly isolated marine or freshwater assemblages that have been connected via canals.

Main conclusions

We advocate an approach to understanding modern species invasions that recognizes the potential significance of both the original Darwinian explanation and the more modern view that emphasizes novel ecological or evolutionary mechanisms arising in the introduced range. Moreover, if biological invasions are a natural outcome of Darwinian evolution in an increasingly connected world, then invasive species should continue to displace native species and drive widespread shifts in the functioning of ecosystems.

}, keywords = {Biotic resistance, Darwin, Elton, empty niche, floristic regions, natural selection, phylogenetic diversity, pre-adaptation, species invasions}, doi = {10.1111/geb.12221}, url = {http://doi.wiley.com/10.1111/geb.12221}, author = {Fridley, Jason D. and Sax, Dov F.} } @article {33463, title = {Resource competition assays between the African big-headed ant, Pheidole megacephala (Fabricius) and the invasive Argentine ant, Linepithema humile (Mayr): mechanisms of inter-specific displacement}, journal = {Ecological Entomology}, year = {2014}, month = {Jan-05-2014}, pages = {n/a - n/a}, abstract = {

1. The spread of Argentine ants,\ Linepithema humile\ (Mayr), in introduced areas is mainly through the displacement of native ant species owing to high inter-specific competition. In South Africa,\ L. humile\ has not established in the climatically suitable eastern and northern escarpments dominated by the African big headed ant,\ Pheidole megacephala\ (Fabricius), probably owing to local biotic resistance.

2. Inter-specific aggression, at the individual and colony level, and competition for a shared resource were evaluated in the laboratory.

3. Aggression between the two ant species was very high in all of the assays. Both species suffered similar mortality rates during one-on-one aggression assays, however, during symmetrical group confrontations,\ L. humile\ workers showed significantly higher mortality rates than\ P. megacephala\ workers. During asymmetrical group confrontations both species killed more of the other ant species when they had numeric advantage. Both ant species located the shared resource at the same time; however, once\ P. megacephala\ discovered the bait, they displaced\ L. humile\ from the bait through high inter-specific aggression, thereafter dominating the bait for the remainder of the trial.

4. The results demonstrate the potential of\ P. megacephala\ to prevent the establishment and survival of incipient\ L. humile\ colonies through enhanced resource competition and high inter-specific aggression. This is the first study to indicate potential biotic resistance to the spread of\ L. humile\ in South Africa.

}, keywords = {Argentine ant, big-headed ant, Biotic resistance, foraging efficiency, inter-specific competition, Linepithema humile, Pheidole megacephala}, doi = {10.1111/een.12126}, url = {http://doi.wiley.com/10.1111/een.12126}, author = {Mothapo, Natasha P and Wossler, Theresa C} }