Hybridization can facilitate species invasions, even without enhancing local adaptation.
The founding population in most new species introductions, or at the leading edge of an ongoing invasion, is likely to be small. Severe Allee effects-reductions in individual fitness at low population density-may then result in a failure of the species to colonize, even if the habitat could support a much larger population. Using a simulation model for plant populations that incorporates demography, mating systems, quantitative genetics, and pollinators, we show that Allee effects can potentially be overcome by transient hybridization with a resident species or an earlier colonizer. This mechanism does not require the invocation of adaptive changes usually attributed to invasions following hybridization. We verify our result in a case study of sequential invasions by two plant species where the outcrosser Cakile maritima has replaced an earlier, inbreeding, colonizer Cakile edentula (Brassicaceae). Observed historical rates of replacement are consistent with model predictions from hybrid-alleviated Allee effects in outcrossers, although other causes cannot be ruled out.
School of BioSciences, The University of Melbourne, Victoria 3010, Australia;
Mohsen B
MB
Mesgaran
Mathematical and Statistical Sciences, University of Alberta, Edmonton, AB, Canada T6G 2G1;
Mark A
MA
Lewis
School of Ecosystem and Forest Sciences, The University of Melbourne, Victoria 3010, Australia;
Peter K
PK
Ades
Department of Biology, Duke University, Durham, NC 27708.
Kathleen
K
Donohue
School of BioSciences, The University of Melbourne, Victoria 3010, Australia;
Sara
S
Ohadi
School of BioSciences, The University of Melbourne, Victoria 3010, Australia;
Chengjun
C
Li
School of BioSciences, The University of Melbourne, Victoria 3010, Australia; rcousens@unimelb.edu.au.
Roger D
0000-0003-2192-0183
RD
Cousens
D019607:Brassicaceae / Q000235:genetics / Q000254:growth & development; D017753:Ecosystem; D056084:Genetic Fitness; D006824:Hybridization, Genetic; D007178:Inbreeding; D058865:Introduced Species; D008957:Models, Genetic; D054817:Pollination / Q000235:genetics; D011156:Population Density; D011157:Population Dynamics
Cakile; mating system; model; sea-rockets; species colonization