Article

Energetics of Pollination

11/2003; 6:139-170. DOI: 10.1146/annurev.es.06.110175.001035
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    ABSTRACT: AUSTRALIAN PLANTS DIFFER FROM THOSE in the northern hemisphere in the extent to which they are pollinated by birds and mammals (Levin & Kerster, 1974; Armstrong, 1979; Proctor et al., 1996; Menz et al., 2011). The primary pollination vectors in Europe are insects and wind (chapter 7A) and the importance of vertebrates as pollinators of many Australian flowers was slow to be appreciated (Ford et al., 1979). These differing modalities can have far-reaching genetic consequences for plants, and it has often been assumed that mating opportunities are largely restricted to nearest neighbours, because of the forces extrinsic to plants that limit pollen dispersal (Smouse & Sork, 2004). This is the case where wind and insects are the pollination vectors, and a skewed distribution is typical in northern-hemisphere plants with many grains dispersed close to the pollen source and a long tail of fewer, far-dispersed grains (Webb, 1998; Sork et al., 1999). A recent molecular analysis of paternity in a natural population of the Australian plant species, Banksia hookeriana (Proteaceae), however, has demonstrated a significant departure from these assumed patterns of pollen dispersal (He et al., 2004; Krauss et al., 2009), comparing the vertebrate-pollinated Banksia hookeriana with a bee-pollinated species, Persoonia mollis (Krauss, 2000) (Fig. 1). These data from Banksia hookeriana signal hitherto unexpected genetic consequences of pollination by vertebrate vectors and the need for a landscape approach to gene flow in plants (Sork et al., 1999). In the study, 96% of two-seeded fruits were multiply sired, indicating extensive pollen carry-over with promiscuity facilitated by highly-mobile nectar-feeding birds (White-cheeked honeyeater) moving effectively in a random manner (Krauss et al., 2009). In another study of fragmented populations in kwongan of the shrub Calothamnus quadrifidus, pollen was regularly dispersed by honeyeaters between fragments as much as 5 km apart (Byrne et al., 2007). The highly-diverse Southwest Australian Floristic Region (SWAFR) is an internationally-recognised biodiversity hotspot under multiple threats (chapter 8) (Myers et al., 2000; Phillips et al., 2010) and one where vertebrate pollinators are of great significance. Fifteen per cent of some 7380 plant species are considered to be either bird or mammal pollinated, a striking 40% of which are threatened endemics (Hopper & Gioia, 2004). This contrasts with other vertebrate-pollinated regions of South Africa and Central America where only 4% of the flora is bird pollinated (Bawa, 1990). Bird pollination is a prominent feature of the ancient Gondwanan families Proteaceae and Myrtaceae, and 110 species of birds have been recorded visiting the flowers of 1000 species of plants in more than 64 genera and 16 families (Ford et al., 1979; Keighery, 1982; Brown et al., 1997). The 'otherness' of the Australian environment and its plants and animals has long attracted and intrigued biologists, but it is only now that the underlying reasons for this are beginning to be understood (Stafford Smith & Morton, 1990). The immense age of the continent, particularly its western Yilgarn craton with some of the oldest rocks on the planet (Myers, 1995), and the weathering that has depleted
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    ABSTRACT: A major determinant of bumblebees pollination efficiency is the distance of pollen dispersal, which depends on the foraging distance of workers. We employ a transect setting, controlling for both forage and nest location, to assess the foraging distance of Bombus terrestris workers and the influence of environmental factors on foraging frequency over distance. The mean foraging distance of B. terrestris workers was 267.2 m $\pm $ 180.3 m (max. 800 m). Nearly 40% of the workers foraged within 100 m around the nest. B. terrestris workers have thus rather moderate foraging ranges if rewarding forage is available within vicinity of the nests. We found the spatial distribution and the quality of forage plots to be the major determinants for the bees foraging decision-making, explaining over 80% of the foraging frequency. This low foraging range has implications for using B. terrestris colonies as pollinators in agriculture.
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    ABSTRACT: Fluid-feeding Lepidoptera use an elongated proboscis, conventionally modeled as a drinking straw, to feed from pools and films of liquid. Using the monarch butterfly, Danaus plexippus (Linnaeus), we show that the inherent structural features of the lepidopteran proboscis contradict the basic assumptions of the drinking-straw model. By experimentally characterizing permeability and flow in the proboscis, we show that tapering of the food canal in the drinking region increases resistance, significantly hindering the flow of fluid. The calculated pressure differential required for a suction pump to support flow along the entire proboscis is greater than 1 atm (~101 kPa) when the butterfly feeds from a pool of liquid. We suggest that behavioral strategies employed by butterflies and moths can resolve this paradoxical pressure anomaly. Butterflies can alter the taper, the interlegular spacing and the terminal opening of the food canal, thereby controlling fluid entry and flow, by splaying the galeal tips apart, sliding the galeae along one another, pulsing hemolymph into each galeal lumen, and pressing the proboscis against a substrate. Thus, although physical construction of the proboscis limits its mechanical capabilities, its functionality can be modified and enhanced by behavioral strategies.
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