Seed predation, often referred to as
granivory, is a type of plant-animal interaction in which granivores (seed predators) feed on the seeds of plants as a main or exclusive food source (Hulme and Benkman 2002), in many cases leaving the seeds damaged and not viable. Granivores are found across many families of vertebrates and invertebrates (especially mammals, birds and insects) (Janzen 1971); thus, seed predation occurs in virtually all ecosystems (see further readings). Seed predation is commonly divided into two distinctive temporal categories, pre-dispersal and post-dispersal predation, which may involve different strategies and requirements and have different implications at the individual and population level. Nevertheless, regardless of timing, seed predation has great implications for plant population dynamics (see below). To counterbalance effects of predation, plants have evolved defenses such as seed morphology (size, shape, toughness) and chemical defenses (
secondary compounds such as
tannins and
alkaloids) to defend against their seed predators (see below). However, as plants have adapted defenses to seed predation (e.g., chemical compounds), so have seed predators adapted to plant defenses (e.g., ability to detoxify chemical compounds). Thus, many interesting examples of
coevolution arise from this dynamic relationship.
Plant seeds are important sources of nutrition for animals across most ecosystems. Seeds contain food storage organs (e.g., endosperm) that provide nutrients to the developing plant embryo (cotyledon). This makes seeds an attractive food source for animals because they a highly concentrated and localized nutrient source in relation to other plant parts.
Seeds of many plants have evolved a variety of defenses to deter predation from seed predators. Plants may allocate resources toward physical or chemical defenses. Seeds are often contained inside protective structures or fruit pulp that encapsulate seeds until they are ripe. Other physical defenses include spines, hairs, fibrous seed coats and hard endosperm.
Some seeds have evolved strong anti-herbivore chemical compounds. In contrast to physical defenses, chemical defenses in seeds to deter consumption by seed predators by using chemicals that are toxic to granivores or inhibit the digestibility of the seed. These chemicals include non-protein amino acids, cyanogenic-gycosides, protease and amylase inhibitors, Phytohaemaglutinins (Herrera and Pellmyr 2002). Seeds face trade-offs between allocation toward defenses and the size and number of seeds produced. Additionally plants have trade-offs in seed defense allocation between deterring seed predators and attracting seed dispersers.
