【文章內(nèi)容簡(jiǎn)介】 te relationship or association between members of two or more species. Usually, one species lives in or on another species. The partners of a symbiotic relationship, called symbionts共生體 , may benefit from, be unaffected by, or be harmed by the relationship. ? Mutualism互利共生 : A symbiotic relationship in which both partners benefit. ? Commensalism偏利共生 : A symbiotic relationship in which one partner benefits and the other partner is unaffected. ? Parasitism寄生 : A symbiotic relationship in which one partnerthe parasiteobtains nutrients at the expense of the otherthe host. ? Coevolution共同進(jìn)化 : the interdependent evolution of two interacting species. 蜜旋木雀 ,半邊蓮 共同進(jìn)化 紅雪松 菌根真菌 互利共生 附生植 偏利共生 寄生 Predation 捕食 ? Predation is the consumption of one species, the prey獵物 , by another, the predator捕食者 . Predation includes both animals eating other animals and animals eating plants. Predation has resulted in and ‘a(chǎn)rms race’, with the coevolution of predator strategiesmore efficient wary to catch preyand prey strategiesbetter ways to escape the predator. ? A predator that is more efficient at catching prey exerts a strong selective force on its prey, and over time the prey reduces the probability of being captured. The countermeasure acquired by the prey in turn may act as a strong selective force on the predator. Competition 競(jìng)爭(zhēng) ? Competition occurs when two or more individuals attempt to use an essential mon resource such as food, water, shelter, living space, or sunlight. Because resources are often in limited supply in the environment, their use by on individual decreases the amount available to others. If a tree in a dense forest grows taller than surrounding trees, it is able to absorb more of the ining sunlight. Less sunlight is therefore available for nearby trees that are shaded by the taller tree. ? Competition can occur among individuals within a population(intraspecific petition) or between different species(interspecific petition) The Ecological Niche 生態(tài)小生境 (生態(tài)位 ) ? 兩個(gè)近緣種不能生活在相同地方的例子很多，這從達(dá)爾文時(shí)代起就引起了人們的注意。與此同時(shí)，達(dá)爾文認(rèn)為，在某個(gè)種占有的生活場(chǎng)所內(nèi)，有近緣種侵入時(shí)，則往往都是前者滅亡，并且認(rèn)為這兩個(gè)現(xiàn)象之間，有共同的機(jī)制在起作用。所謂共同機(jī)制，就是 生存競(jìng)爭(zhēng)在同一種內(nèi)最激烈，其次是在同一屬的近緣種之間近緣種圍繞著共同的資源 (食餌、空間等 )而斗爭(zhēng)，其結(jié)果是一方或雙方種群的生長、生存、分布和增殖受到不良影響，稱為種間競(jìng)爭(zhēng) 。 ? 在進(jìn)化過程中，兩個(gè)近緣種 (有時(shí)為兩個(gè)生態(tài)上接近的種類 )的激烈競(jìng)爭(zhēng)，從理論上講有兩個(gè)可能的發(fā)展方向， 其一是一個(gè)種完全排擠掉另一個(gè)種；其二是其中一個(gè)種占有不同的空間 (地理上分隔 )，捕食不同的食物 (食性上的特化 )，或其他生態(tài)習(xí)性上的分隔 (如活動(dòng)時(shí)間分離 )，通稱為生態(tài)隔離 ，從而使兩個(gè)種之間形成平衡而共存。 生態(tài)位理論 ? 在生物群落中，若無任何競(jìng)爭(zhēng)者和捕食者存在時(shí)，該物種所占據(jù)的全部空間的最大值，稱為該物種的基礎(chǔ)生態(tài)位 ， ? 當(dāng)有競(jìng)爭(zhēng)者時(shí)，必然使該物種只占據(jù)基礎(chǔ)生態(tài)位的一部分。這一部分實(shí)有的生態(tài)位空間，稱之為實(shí)際生態(tài)位 。 ? 由于竟?fàn)幍呐懦庾饔?，生態(tài)位相似的兩種生物不能在同一地方永久共存；否則，其生態(tài)位相似性必定是有限的，它們肯定在食性、棲息地或活動(dòng)時(shí)間等某些方面有所不同，這就是競(jìng)爭(zhēng)排斥原理。 ? 競(jìng)爭(zhēng)排斥原理說明，物種之間的生態(tài)位越接近，相互之間的競(jìng)爭(zhēng)就越劇烈。分類上屬于同一屬的物種之間由于親緣關(guān)系較接近因而具有較為相似的生態(tài)位，可以分布在不同的區(qū)域。如果它們分布在同一區(qū)域，必然由于競(jìng)爭(zhēng)而逐漸導(dǎo)致其生態(tài)位的分離，即競(jìng)爭(zhēng)排斥導(dǎo)致親緣種的生態(tài)分離。大多數(shù)生態(tài)系統(tǒng)具有許多不同生態(tài)位的物種，這些生態(tài)位不同的物種避免了相互之間的競(jìng)爭(zhēng)，同時(shí)由于提供了多條的能量流動(dòng)和物質(zhì)循環(huán)途徑而有助于生態(tài)系統(tǒng)的穩(wěn)定性。但是，在許多動(dòng)物之間，卻存在著生態(tài)位重疊因而具有部分競(jìng)爭(zhēng)。 ? 對(duì)于自然種群，符合競(jìng)爭(zhēng)排斥原理的例子也很多。在太平洋的許多島嶼上都曾分布有緬鼠。后來，隨著交通運(yùn)輸事業(yè)的發(fā)展，黑家鼠和褐家鼠也常隨船只來到這些島嶼。由于“外來客”與“老住戶”食性相近，彼此之間便出現(xiàn)激烈的競(jìng)爭(zhēng)，結(jié)果，競(jìng)爭(zhēng)能力較差的緬鼠被排擠而發(fā)生滅絕。還有另一個(gè)著名的例子。當(dāng)東美灰松鼠進(jìn)入到英國后，原產(chǎn)在大不列顛島及其周圍大部分地區(qū)的栗松鼠由于競(jìng)爭(zhēng)而滅絕。這些例子說明外來種進(jìn)入某地時(shí)，可能與當(dāng)?shù)厣鷳B(tài)位相似的物種發(fā)生競(jìng)爭(zhēng)，這是引種工作所應(yīng)重視的問題。競(jìng)爭(zhēng)排斥原理對(duì)于養(yǎng)殖業(yè)也有指導(dǎo)意義。例如，青、草、鰱、鳙四大家魚由于相互之間的空間或食物生態(tài)位具有差別，因此可以混合養(yǎng)殖在同一水域，不會(huì)發(fā)生競(jìng)爭(zhēng)導(dǎo)致抑制產(chǎn)量和降低經(jīng)濟(jì)效益。 Gaia hypothesis地球女神假說 ? Almost pletely isolated from everything in the universe but sunlight, Earth has often been pared to a vast spaceship with a lifesupport system consisting of the anisms that inhabit it. These living things modify the position of gases in the atmosphere, transfer energy, and recycle waste products with great efficiency. ? Broadly speaking, Earth is capable of selfmaintenance of its plex biologicalphysical systems. Organisms interact with the abiotic environment to produce and maintain the chemical position of the atmosphere, the global temperature, the ocean’s salinity, and other characteristics. Thus, Earth’s environment and anisms are intimately linked to one another and work together as a homeostatic (Biological systems have homeostatic mechanisms such as feedback loops to help maintain a steady state or constant environment.) ? The series of hypotheses that Earth’s anisms adjust the environment to keep it habitable for life has been called, collectively, the Gaia hypothesis. (Gaia is derived from the Greek Gaea, who is Earth personified as a goddess.) James Lovelock, a British chemist, and Lynn Margulis, a . biologist, first proposed the Gaia hypothesis in the early 1970s. Since then, the original hypothesisthat pla Earth behaves like a living anismhas been modified to emphasize that substantial interactions between anisms and the physical environment can lead to global selfregulation. The hypothesis requires no foresight or planning on the part of living anisms. The field of study based on the Gaia hypothesis is called ? As an example of the Gaia hypothesis, consider Earth’s temperature. It is generally accepted that the temperature has remained relatively constant at a level suitable for life over the to 4 billion years that life has existed. Yet there is evidence that the sun has been heating up during that time. Wh