NECTAR IS AN IMPORTANT BIOLOGICAL RESOURCE that is utilized by a wide variety of animals. Insects are the most abundant floral visitors, but some vertebrates also regularly take nectar. These include flying animals such as birds and bats as well as nonflying animals (e.g., primates, marsupials, and reptiles). Along with pollen, nectar can be regarded as a reward to the floral visitor in return for the pollinating service. Although composition of nectar is dominated by sugars, being in the range of 10 to 40 percent w/v, amino acids form a ubiquitous and substantial component of floral nectar, occurring at millimolar concentrations (Baker & Baker 1973). This discovery initiated a series of investigations into the concentration and composition of amino acids in nectar, and provoked debate concerning their ecological role as a resource (Baker & Baker 1975, 1982, 1983, 1986; Baker 1977; Gottsberger et aI. 1984, 1989). To date the role of nectar amino acids as a resource for pollinators has not been satisfactorily resolved, but the consensus view is that plants that are adapted to pollination by butterflies show high concentrations of amino acids. Plants pollinated by birds exhibit low concentrations of amino acids. The ecological rationale behind this is that butterflies are specialized liquid feeders as adults and nectar is their only source of nitrogen. Birds, however, are able to capture insects and so gain nitrogen in the form of protein (Brice & Grau 1991, Brice 1992). Bees are able to eat and digest pollen; plants that they pollinate form an intermediate group.
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