Memory Capacity

Memory imposes costs on an animal--both the size of the brain and the energy used in metabolism support memory can be important (Dukas 1999). The ability to discard unneeded memory is important in keeping this cost down. While even relatively small-brained animals, such as the honey bee, can have impressive capacity for memory (Menzel and Mueller 1996), selectivity in what is stored leads to efficient use of neural capacity. Honey bees are very good at learning landmarks, which are essential for finding their way home, but rather less adept in learning experiments which lack relevance to their natural setting.

Animals foraging on flowers learn how to "handle" the flower to get at the nectar or pollen. Many plants present complicated flowers which serve as puzzles for the forager to solve. Lewis' (1986) study of cabbage butterflies, Pieris rapae, showed that these butterflies could learn a limited number of flower types; when presented with novel flowers, they "forgot" previously learned flowers. Subsequent studies have shown some ability of butterflies to generalize handling learned on one flower type to another flower (Kandori and Ohsaki 1996) or to use information used in finding places to lay eggs in choosing flowers (Weiss and Papaj 2003). The ability of many foragers on flowers to learn how to handle multiple flower types helps to insure that fidelity of the foragers to one or a few plant species; this in turn improves pollination, as pollen is carried to flowers of the appropriate species.

Less is known about memory and learning capacities in birds and mammals. While some investigators have postulated that, in a general way, learning capacity may be linked to brain size, this assertion has been controversial (Gould 1981). Recently (Reader and Laland 2002) have shown in an analysis of innovative behavior, social learning, and tool use that, across primate species, the size of the part of the brain devoted to "executive function" (neocortex and striatum) is correlated with these measures of learning and memory. It is probably true that, across a wide range of variation between species, brain size is a meaningful measure of brain capacity. However, as Gould (1981) argued, within species or when making comparisons between brains with relatively small size differences in size, factors other than size have a greater influence on the animal's comparative abilities to learn and remember.

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Menzel R, Mueller U 1996 Learning and memory in honeybees: From behavior to neural substrates. ANNU REV NEUROSCI 19: 379-404
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