Seed Predation by Animals

Many plants suffer very heavy preand/or post-dispersal seed predation by animals. A few exemplary studies (2,18,38,52,74,87, 106, 110, 111, 124, 140, 161, 162, 171, 181, 187, 196, 197, 203, 205, 207, 217, 220, 227) and a variety of shorter reports scattered through the agricultural, botanical, and zoological literature suggest a large and important, yet unexploited, field of study. It is clear that the pattern of seed predation is highly structured and that it co evolved at, the chemical, spatial, and temporal level. It involves all levels of animal-plant interaction from the internal energy budget of indi­ viduals to the entire community (203 ) . Owing to parental and sibling com­ petition, successful development of a seedling may depend on the seed's dis­ persal (101). Equally important, thc seed must escape from the predators at the seed crop and in the parent plant's habitat before and after dispersal (111 ) . The game is played by mobile predators in search of sessile prey; escape is through a single dispersal move, seed chemistry, parental morphol­ ogy and behavior, and evolutionary change. The processes and patterns are:ideal candidates for ecological and evolu­ tionary analyses (83, 111 ) of the typcs traditionally conducted by zoologi­ cally oriented biologists (37, 51,73, 141, 155,156, 182) or applied to plants in general ( 40,116,208,209,241) . Seed predators and leaf eaters are often lumped together in ecological discussions, but they differ in ways especially important in the coevolution of seed predators and seeds: (a) Like leaves, seeds are highly subdivided and small, but unlike leaves and other vegetative parts, they have very high nutrient values per unit volume. ( b) While obvious in large quantities, they may be extremely inconspicuous once dispersed. ( c) Being comparatively dormant, seeds have low self-repair abilities but can contain high concentra­ tions of toxic compounds (secondary substances) with less sophisticated ad­ aptations against self-intoxication than can leaves and meristematic tissues. ( d ) Seed production is not continually required for direct survival of the parent plant; seed timing, quantity, and quality can therefore be manipu­ lated more freely by natural selection than can these traits of leaves and other vegetative parts. (e ) Seeds are not directly replaced· when killed or germinated; once removed, seeds may be absent far longer than edible vege­ tative parts and thus a common plant species may be rare in time,toa seed