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Table 1 Four drivers of hybridization and introgression tested within this study and associated prediction for each

From: Patterns of introgression vary within an avian hybrid zone

Driver

Prediction

Demographic processes (relative population density)

Amount/direction of introgression, as well as distribution of genotypic classes will be directly proportional to the relative abundance and mate availability of the two species, with higher rates and more symmetrical patterns of introgression in the center and inland sites vs. southern and coastal sites

Natural selection (exogenous environmental factors)

Distributions of adult and offspring genotypes, including amount and direction of introgression, will reflect the speciesā€™ differential habitat and nesting affinities of Nelsonā€™s Sparrows to inland sites and Saltmarsh Sparrows to coastal sites, regardless of mate availability

Natural selection (endogenous factors)

Selection against hybrid females through genetic incompatibilities will result in male-biased production of hybrid offspring and/or reduced survival of hybrid females from nestling to adult stage

Sexual selection (environmentally independent)

Interspecific mating will be avoided, such that proportion of inter-specific mating events will be less than expected from the availability of interspecific mates