Sympatric speciation in Erica mammosa (Ericaceae): Resprouters versus seeders and the roles of pollinators, moisture availability and fire

Abstract

The Cape Floristic Region (CFR) genus Erica is hyperdiverse with approximately 800 taxa in an area roughly the size of Austria. To date no studies have systematically investigated the biotic and abiotic differences between sympatric Erica variants with a view to helping explain patently explosive speciation within the genus in the region. Erica mammosa L. has four distinct resprouting and seeding variants occurring over a wide geographic area within the south-western CFR. Here we focus upon two sympatric variants of this taxon, a resprouting pink-flowered variant and a seeding yellow-flowered variant, on the Cape Peninsula. Results show that considerable differences exist between the two variants in fine scale geographic distribution, the populations being homogeneous and not intermixed; in fire survival strategies and responses, in that the seeder variant is killed by fire and the resprouter variant requires fire when moribund and to recruit occasional seedlings; in seed set, the seeder variant having more ovules and producing more seeds than the resprouter variant; in population proportions, the seeder variant vastly outnumbering the resprouter variant; in water stress responses, the seeder variant being significantly more drought stressed; and in and in flowering phenologies, the resprouter variant flowering from November to May and the YS variant from January to March; The variants share two sunbird pollinator species although are not significantly cross-compatible in terms of seed set, suggesting that pollinators may not be primary drivers of speciation in this instance, but rather other selective pressures such as fire, edaphic habitat and soil-moisture availability.