Data from: the two faces of secondary contact on islands: introgressive hybridization between endemics and reproductive interference between endemics and introduced species

Aim: Hybridization is thought to have played an important role in
shaping the evolutionary history of diverse island taxa. Here, we propose
an ecological and evolutionary framework for understanding the causes and
consequences of heterospecific mating on islands – with and without
introgressive hybridization. We use this framework to support our main
contention that cases of secondary contact among endemic species should
commonly result in introgressive hybridization whereas cases of contact
between endemic and introduced species should commonly result in
reproductive interference – resulting in two qualitatively different faces
of secondary contact on islands. Location: Canary Islands,
Galapagos, New Zealand, Caribbean, and Hawaii. Taxa: 705
vertebrate, invertebrate, and plant species spanning 167 genera and 99
families. Methods: Using a quantitative analysis of empirical
research on secondary contact on islands, we weigh evidence for the
drivers of secondary contact and heterospecific mating on islands. In
particular, we compare cases of secondary contact between endemic species
versus secondary contact between endemic and introduced species.
Results: We find that three main drivers of secondary contact and
heterospecific mating on islands most frequently reported in the
literature are disturbance, long-distance (e.g. inter-island) dispersal,
and compromised assortative mating. We find support for the hypothesis
that introgression is a more common outcome between endemic species while
reproductive interference is a more common outcome between endemic and
introduced species. Main conclusions: We conclude that there are
biological reasons to predict secondary contact and heterospecific mating
to be common on islands for all taxa, but that the consequence of
secondary contact is categorically different for contact between endemic
species and contact between endemic and introduced species. We conclude
that the former likely explains the apparent frequency of hybridization on
islands, while the latter presents a cryptic and underappreciated
conservation threat.