Ecophylogenetic studies often make the assumption that if competition is the dominant driver of assembly a species that has close relatives in an environment will have a difficult time invading. This approach ignores the evolutionary context that the invader is coming from. The Evolutionary Imbalance Hypothesis (EIH) predicts that species evolving in regions containing close relatives will have higher fitness than species in regions containing distant relatives. Therefore, it should be easier for an introduced species to succeed if 1) they come from a region containing close relatives; and 2) are introduced into a region containing distantly-related species. Although the key variable of this hypothesis is the difference in phylogenetic structure between native and introduced regions, tests of this hypothesis looking at the differences between native and introduced region phylogenetic structures are currently lacking.
We utilized a series of natural experiments (bird introductions) to test the Evolutionary Imbalance Hypothesis and to evaluate which phylogenetic metrics and regions (native region vs. introduced region) have the best ability to predict successful establishment. We calculated both native region and introduced region mean phylogenetic distant (MPD) and asked whether 1) native region MPD, 2) introduced region MPD or 3) the inclusion of both native and introduced region was a stronger predictor of introduction success.
Our results support models containing both native and introduced region MPD as predictor variables (delta AIC >8). Our results also show that including native region MPD reverses the effect of introduced region MPD: models including only introduced region MPD indicate that species MORE closely-related to the introduced community are more likely to succeed, whereas the models including both native and introduced region MPD indicate that species are more likely to succeed if they 1) come from a region containing close relatives; and 2) move into a region containing distant relatives. This work provides support for the EIH, suggesting that relative ecophylogenetic structure may be more important than absolute ecophylogenetic structure in community assembly processes. It may be worth revisiting previous studies examining the ecophylogenetic patterns in biological invasions in light of this evidence.