Orange-breasted Sunbird Anthobaphes Violacea Research Articles

Post-pollination barriers enable coexistence of pollinator-sharing ornithophilous Erica species.

Some evolutionary radiations produce a number of closely-related species that continue to coexist. In such plant systems, when pre-pollination barriers are weak, relatively strong post-pollination reproductive barriers are required to maintain species boundaries. Even when post-pollination barriers are in place, however, reproductive interference and pollinator dependence may strengthen selection for pre-pollination barriers. We assessed whether coexistence of species from the unusually speciose Erica genus in the fynbos biome, South Africa, is enabled through pre-pollination or post-pollination barriers. We also tested for reproductive interference and pollinator dependence. We investigated this in natural populations of three bird-pollinated Erica species (Erica plukenetii, E. curviflora and E. coccinea), which form part of a large guild of congeneric species that co-flower and share a single pollinator species (Orange-breasted Sunbird Anthobaphes violacea). At least two of the three pre-pollination barriers assessed (distribution ranges, flowering phenology and flower morphology) were weak in each species pair. Hand-pollination experiments revealed that seed set from heterospecific pollination (average 8%) was significantly lower than seed set from outcross pollination (average 50%), supporting the hypothesis that species boundaries are maintained through post-pollination barriers. Reproductive interference, assessed in one population by applying outcross pollen three hours after applying heterospecific pollen, significantly reduced seed set compared to outcross pollen alone. This may drive selection for traits that enhance pre-pollination barriers, particularly given that two of the three species were self-sterile, and therefore pollinator dependent. This study suggests that post-pollination reproductive barriers could facilitate the coexistence of congeneric species, in a recent radiation with weak pre-pollination reproductive barriers.

Nesting success and within-season breeding dispersal in the Orange-breasted Sunbird Anthobaphes violacea

Nest predation is a primary cause of nesting mortality for many bird species, particularly passerines. Nest location can affect predation, and it has also been demonstrated that predation risk can alter nest site selection. Birds can limit predation risk by selecting specific habitat characteristics; by changing nest site characteristics between attempts; and by dispersing between nesting events. Here we report breeding data from a population of Orange-breasted Sunbirds Anthobaphes violacea (L.), for a single breeding season in the Jonkershoek Nature Reserve, South Africa. Neither shrub type nor nest height was found to affect the outcome of a nest. For subsequent breeding attempts, birds were not more likely to change the type of shrub in which they nested after a predation event than when the attempt was successful, nor did they change the height of their nest. However, we found that the distance between a nest and the subsequent one was significantly shorter after a successful nest than after an unsuccessful one. We interpret this as an adaptive strategy to avoid predation.