Insects are the major agents of pollination, seed predation, or seed dispersal in many ecosystems. Although few studies have evaluated the effects of pollinators, seed predators, and seed dispersers on ecosystem processes, these organisms often are critical to seedling recruitment and vegetation dynamics that affect other ecosystem processes.
Pollination is an important means of increasing genetic heterogeneity and improving plant fitness. Pollination can be accomplished by abiotic (wind) or biotic (insects, birds, and bats) agents. Wind pollination is inefficient but sufficiently effective for species that dominate temperate ecosystems. However, animal agents increase pollination efficiency for more isolated plants and are critical to survival of many plant species that usually occur as widely scattered individuals, especially in deserts and tropical forests. Pollinator functional groups can be distinguished on the basis of their degree of specialization on particular floral resources.
Seed predators often consume the entire reproductive effort of host plants. Predispersal seed predators usually focus on concentrated seed resources on the parent plants, whereas postdispersal seed predators must locate more scattered seed resources on the ground. Insects are more important predispersal seed predators, but vertebrates are more important postdispersal seed predators in most ecosystems.
Seed dispersal is critical to plant species survival both because new habitats can be colonized and because seed relocation often improves seed and seedling survival. Seeds can be dispersed by abiotic (wind and water) or biotic (insect and vertebrate) agents. Animals can increase dispersal efficiency by moving seeds to more suitable germination sites, especially if seeds are buried. Ants, in particular, can increase seed survival and seedling growth by relocating seeds to nests, where seeds are protected from further predation, from suboptimal surface conditions, and from competition with parent plants. Ant nests also may provide more suitable soil conditions for germination and growth. Some seeds require scarification of hard seed coats and must pass through vertebrate digestive systems before germination can occur.
Both pollination and seed dispersal affect plant population and community dynamics. Differential pollination, seed predation, and seed dispersal efficiencies among plant species affect seedling recruitment and growth. Survival of some plant species depends on sufficient abundance of pollinators, seed dispersers, or both. However, research should address the extent to which pollinators, seed predators, and seed dispersers affect ecosystem processes.
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