The pollination success of Agave palmeri is strongly dependent on nectar—feeding bats. In areas with very low or nonexistent bat populations, Agave seed set is <5% of its maximum potential. A 30 yr trend of declining seed set parallels a decline in bat numbers during that period. We speculate that habitat destruction and an increase in human use of Agave are causal factors. Over half of the measurable energy in the plant biomass is allocated to advertising and reproduction. We discuss the costs and risks involved in the semelparous strategy when pollinators decline. Where bats remain, agaves in dense patches show higher seed set than do outlying plants, suggesting that the pollinators favor grouped plants. This behavior may reinforce the plants' colonial tendencies.
Scales on the hairs of pollinating bats spread out at an angle to the main hair shaft. In contrast, the hairs of most bats not associated with plants are relatively smooth. Both megachiropteran and microchiropteran flower-feeding bats show this divaricate scale structure which may aid in the collection of a heavy coating of pollen. Some of the pollen is transferred to subsequent flowers, but most is groomed from the fur and ingested as the only reliable nitrogen source for the bat. The tongues of nectar-feeding bats also show structural modifications which allow efficient uptake of the carbohydrate fraction of the diet. Structural specializations of the hiars and tongue are analogous to those seen in other nectar-feeding animals.
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