Pollination, breeding system and seed abortion in some African acacias

Abstract

TYBIRK, K., 1993. Pollination, breeding system and seed abortion in some African acacias. Studies of the flower visitors and pollination ecology of Acacia albida Del., A . nilotica (L.) Willd. ex Del. A . tortilis (Forssk.) Hayne and A . senegal (L.) Willd. in Senegal and Kenya showed a high diversity of floral foragers. One hundred and eighteen taxa of insects mainly from Hymenoptera, Lepidoptera, Coleoptera and Diptera were collected. The most important pollen vectors were bees from the families Megachilidae and Halictidae, and wasps from the families Scoliidae and Eumenidae. Beetles, flies and butterflies were secondary pollen vectors. Diversity and frequency of flower visitors of species with floral nectar ( A . senegal and A . albida) were not clearly different from species without floral nectar ( A . tortilis, A . nilotica). Acacia tortilic was almost exclusively outcrossed (Index of Self Incompatibility = 0.2), with 5.5% of the inflorescences (0.13% of the flowers) developing fruits. The number of seeds per pod was positively correlated with dispersal type. Wind dispersed species had fewer seeds per pod than animal dispersed species. About 5% of the seeds were aborted in A . fortilis and A . nilotica, while 2211.8% of the seeds were aborted in A . senegal, A . ataxacantha DC. and A . polyacantha Willd. Most abortions in the latter three species occur in the proximal end of the pods, indicating selective seed abortion.

Partitioning of Pollinators during Flowering in an African Acacia Community

“…The flowers of both subgenera are typically protandrous, and last for a single day (Tybirk 1989, Stone et al 1996, Willmer and Stone 1997. The flowers of both subgenera are typically protandrous, and last for a single day (Tybirk 1989, Stone et al 1996, Willmer and Stone 1997.…”

“…Predictions based on competitive explanations for phenological divergence in flowering seasons (Rathcke and Lacey 1985) can also be applied to daily partitioning. Acacia nilotica, A. senegal, and A. tortilis are widely distributed through Africa to Arabia and (for the first two species) India (Khan 1970, Ross 1981, Milton 1987, Coe and Beentje 1991, and form part of a wide diversity of Acacia assemblages with different pollinator guilds (Tybirk 1993). With the possible exception of A. Senegal, we found little evidence of spatial variation in the timing of pollen release by the Acacia species in the community studied on a 20 X 50 km spatial scale.…”

“…Three factors may predispose Acacia species to the exploitation of the daily time resource axis. Second, the scented and showy inflorescences of Acacia species are visited by a wide diversity of flower visitors, at least some of which are shared by more than one Acacia species (Bernhardt 1987, Tybirk 1989, Stone et al 1996. Second, the scented and showy inflorescences of Acacia species are visited by a wide diversity of flower visitors, at least some of which are shared by more than one Acacia species (Bernhardt 1987, Tybirk 1989, Stone et al 1996.…”

Tree Spacing and Coexistence in Semiarid Savannas

“…The average number of seeds produced annually by an African Acacia varies between 13 000 and 24 000 (Tybirk 1993) of which 3% are germinable under optimal conditions (Miller 1994). The average number of seeds produced annually by an African Acacia varies between 13 000 and 24 000 (Tybirk 1993) of which 3% are germinable under optimal conditions (Miller 1994).…”

Plant–pollinator interactions in a Mexican Acacia community

“…First, multispecies acacia assemblages commonly coflower in highly seasonal tropical habitats (Ross 1981;Stone et al 1998Stone et al , 2003. Second, their scented and showy flowers are visited by a wide diversity of flower visitors, some of which are shared (Bernhardt 1987;Tybirk 1993;Stone et al 1998Stone et al , 2003. Third, the common, open 'pom-pom' structure of acacia flowers allows pollen transfer between coflowering species.…”