|
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, P.E. and Benkman, C.W. (2002) Granivory. In Plant-animal Interactions: An Evolutionary Approach, ed. C.M. Herrera and O. Pellmyr. Oxford: Blackwell.〕 in many cases leaving the seeds damaged and not viable. Granivores are found across many families of vertebrates (especially mammals and birds) as well as invertebrates (mainly insects);〔Janzen, D.H. (1971) Seed predation by animals. Annual Review of Ecology and Systematics, 2, 465-492.〕 thus, seed predation occurs in virtually all terrestrial ecosystems. 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. 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. 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. == Seeds and their defenses == 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 are 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. Seeds, especially in arid areas, may have a mucilaginous seed coat that can glue soil to seed hiding it from granivores. 〔https://smartech.gatech.edu/jspui/bitstream/1853/36772/1/sch_biol_hay_0164.pdf〕 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-glycosides, 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. Plants may reduce the severity of seed predation by making seeds spatially or temporally scarce to granivores. Seed dispersal away from the parent plant is hypothesized to reduce the severity of seed predation.〔Janzen, D.H. (1970) Herbivores and the number of tree species in tropical forests. American Naturalist, 102, 592-595.〕〔Connell, J.H. (1971) On the role of natural enemies in preventing competitive excusion in some marine animals and in rainforest trees. In Dynamics of Populations, ed. P.J. den Boer and G.R. Gradwell. Wageningen: Center for Agricultural Publishing and Documentation, pp. 298-312..〕 Seed masting is an example of how plant populations are able to temporally regulate the severity of seed predation. Masting refers to a concerted abundance of seed production followed by a period of paucity. This strategy has the potential to regulate the size of the population of seed predators. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「seed predation」の詳細全文を読む スポンサード リンク
|