Abstract
This study was conducted to investigate the structuring of two sympatric and coflowering acacia species - Acacia ehrenbergiana (Hayne) and Acacia tortilis (Forsk.) - in relation to their flowering period distribution, floral reward partitioning, nectar secretion dynamics, and visitor assemblages. This research was performed in an arid climatic zone of the Arabian Peninsula (Saudi Arabia). To determine if there is partitioning of pollinators between the two species their peak flowering periods were monitored and the peak time of pollen release through the day was quantified as the ratio of polyads to anthers. The nectar sugar secretion dynamics were estimated following nectar sugar washing techniques. The types and frequency of visitors were recorded and correlated. The two species varied in their peak flowering time within a season and peak pollen release time within a day. Moreover, both species secreted significant amounts of nectar sugar. The sharing of pollinators and the partial monopoly of certain visitors were observed. The two sympatric acacia species are structured into a partial temporal separation of their peak flowering and pollen release times, which appears to be an adaptation to minimize pollinator competition.