1、L1 互利共生要 点互利共生和共生现象互利共生是不同种两个体间一种正的互惠关系，可增加双方的适合度。互利共生可以是共生性的，生物体以一种紧密的物理关系生活在一起。专性 互利共生 有些互利共生者，如地衣，是永久性成对组合，其中一方或双方不能独立生活。大多数共生者是专性共生，还有一些非共生性的互利共生也是专性的，如蘑菇 -耕作蚁之间的互利共生。共生：地衣Mutualism is a positive reciprocal relationship between two individuals of different species which results in increased fitn
2、ess for both parties. Mutualism may be symbiotic,in which the organisms live together in close physical association.Key NotesMutualism and symbiosisL1 MUTUALISMSome mutualisms, such as lichens, are permanent pairings in which one or both partners cannot lead an independent life. Most symbioses are o
3、bligate, as are some nonsymbiotic mutualisms, such as those formed by fungus-farming ants.Obligate mutualism兼性 互利共生 互利共生的多数是非专性和机会性的。这些互利共生可能是散开的，包含有不同的物种混合，如许多传粉者与其传粉植物之间的互利共生。传 粉异型杂交植物需要将其花粉转移到同种植物的柱头上，并接受同种植物的花粉。一些植物种类靠风来传播花粉，如果植物生长在广大的植物种类单一的地方如草地和松林，这种传播方式会很有效。但是大多数开花的双子叶植物，依靠昆虫、鸟、蝙蝠或小型哺乳动物来传播花
4、粉，作为交换，这些动物或以花蜜或以花粉本身为食。传粉The majority of mutualisms are nonobligatory and opportunistic. They may be diffuse, involving a varying mixture of species, as occurs between many pollinators and their plants.Facultative mutualismAn out crossing plant needs to transfer its pollen to the stigma of a conspe
5、cific plant, and receive pollen from a conspecific. Some plant species rely on the wind to achieve this, which can work acceptably well if plants grow in large homogeneous stands of few species, as occurs in grasslands and pine forests, However, in most species of flowering dicotyledonous plants, in
6、sects, birds bats or small mammals are employed to transfer pollen from plant to plant, usually in exchange for either nectar or pollen itself as a foodsource.Pollination种子扩散 大型种子无法有效的被风传布，除非靠水传布（如椰树的种子），或依靠动物来散布。啮齿动物、蝙蝠、鸟和蚂蚁都是重要的种子扩散者。防御性互利共生一些互利共生为其中一方提供对捕食者或者竞争者的防御。这种防御性互利共生的例子见于一些草和产生植物碱的真菌之间，以及
7、许多种植物和蚂蚁之间。浦公英Large seeds cannot be effectively wind-dispersed, and unless dispersal by water (as occurs in the coconut palm) occurs, such plants are dependent on animals for dispersal. Rodents, bats, birds and ants are all important seed dispersers.Seed dispersalA number of animal species rely to s
8、ome extent on mutualisms with mutualists which reside within their bodies. Ruminants (deer and cattle) possess a multi-chambered stomach in which bacterial and protozoan fermentation take place. In some termites, which feed on wood, the necessary breakdown enzymes are provided by bacterial mutualists. Intracellular bacterial symbionts which transform amino acids occur in a number of insect groups, including aphids and cockroaches.Symbiotic mutualists within animal tissues and cells
