Habitat segregation of Banksia shrubs at Gibraltar Range National Park

Abstract

Events during seedling recruitment affect species' distributions, causing habitat segregation of congeneric species within the same area. We documented the segregation of Banksia marginata and B. spinulosa var. neoanglica in adjacent swamp and woodland habitats at two sites by surveying adult and seedling distributions. We also examined seed banks and seed characters as factors contributing to segregation. Habitat segregation was pronounced, with 92% of B. marginata adults located in swamps and 98% of B. spinulosa adults located in woodlands. After fire, 84% of B. marginata seedlings were in swamps, but 10 months later this increased to 93%, indicating that although seeds dispersed to and germinated in adjacent woodlands, most seedlings failed to establish. Seedlings of B. spinulosa were confined to woodlands, indicating that seeds did not disperse into swamps or that, if they did, seeds failed to germinate or seedlings suffered early mortality. Canopy seed banks of both species were large (> 280 seeds/plant) and seeds of both species possess membranous wings, allowing dispersal between habitats. Overall, neither limited numbers of seeds nor limited seed dispersal are likely to cause habitat segregation. Instead, processes occurring during early seedling growth are probably more influential.