Are insects flower constant because they use search images to find flowers?

  • Goulson D
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Abstract

Goulson, D. 2000. Are insects flower constant because they use search images to find flowers? – Oikos 88: 547 – 552. Many insects which gather nectar or pollen exhibit flower constancy, a learned fidelity to a particular species of plant. Recent studies suggest that foraging insects may use a perceptual mechanism akin to a search image to detect flowers, in a manner analogous to the way that predators search for prey. This has emerged as an alternative (but not mutually exclusive) explanation for flower constancy to that proposed by Darwin, who suggested that it may result from a limited ability to learning or remember the handling skills appropriate for particular flowers. However, search images are thought to be a mechanism for locating cryptic prey. Plants which are pollinated by animals have evolved brightly coloured flowers to attract the attention of their pollinators. It thus seems implausible to argue that flowers may actually be cryptic. One possible explanation for this apparent contradiction is that flowers are effectively cryptic when viewed against a background which contains many other flowers of similar colour. I present experimental evidence which suggests that a background of flowers of similar colour does reduce foraging efficiency of bumblebees, but that a background of dissimilarly coloured flowers has no effect. This I interpret as evidence that flowers may be cryptic, suggesting that pollinators may indeed use a search image in location of flowers. However, the relative importance of constraints on foragers' abilities to locate flowers versus their abilities to handle them as causes of flower constancy remain to be elucidated. Many of the most familiar insect groups, including most bees, butterflies and moths, and also some flies and beetles, depend for their sustenance upon pollen or nectar rewards provided by flowers. It is generally only adult, winged insects that specialise in visiting flowers; immature stages do not have the mobility necessary to gather such sparsely scattered resources. Even for flighted insects, efficient collection of floral rewards is problematic. The distribution of rewards is unpre-dictable in time and space; individual plants and plant species open their flowers at different times of the day and flower at different times of the year. Flowers are erratically depleted of their rewards by other insects and take varying amounts of time to replace them, so that at any one time many flowers may be empty. To add to the difficulties, many plant species hide their floral rewards within complex flowers so that only insects with an appropriate morphology can enter them, and learning to handle such flowers takes time. It is perhaps not surprising that the foraging behaviours which have evolved to combat these problems have been the focus of numerous studies. One characteristic strategy of insects visiting flowers is known as flower constancy.

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