Whenever we choose a place in the natural world, various species of living organisms live there together. In ecology, this is considered as a group and is called a community, but the term biological community is used to distinguish it from human communities. The general rule is to include all the plants and animals that live in that place, and it is convenient to use terms such as shellfish communities and bird communities to focus on specific groups of organisms. When a community is divided into a plant part and an animal part, the former is called a plant community and the latter an animal community. The location is basically arbitrary, but places with a cohesive landscape, such as a lake, are often chosen. On land, plants generally form the landscape, and communities are often defined in terms of plant communities, and are expressed as "beech forest communities" and "cogon grassland communities." While the various individual organisms that make up a community have close intraspecific relationships over the resources they need to survive and reproduction, they also live in deep inter-species interactions. For example, animals, which are heterotrophs, live by eating other animals and plants, and cannot imagine their own existence without the existence of other species that serve as their food. Similarly, green plants, which are called autotrophs and appear to live independently of other species, live in competition and cooperation with other animals and plants over light, water in the soil, and nutrients. As for relationships between animals and plants, the cooperative relationship between insects and plants over pollination of insect-pollinated flowers, while somewhat unique, is well known. These things show that a community is not simply a collection of various organisms, but a local group of organisms that live in mutual interaction. The concept of a community, which includes such interactions or relationships between organisms, is of paramount importance in ecology, the "science of living organisms," because all real organisms' lives are carried out within the relationships of communities. When these relationships are viewed as a community as a whole, structures such as food chains and ecological pyramids appear. Furthermore, the overall balance of the relationships can produce dynamic systems such as those seen in the succession of plant communities. For this reason, communities can be viewed as entities with their own unique structures and forms of development, but it is clear that communities do not have clear boundaries with their members that remain constant over time, and it is important to note that this view of communities is merely operational. [Yasuo Esaki] [Reference] |Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend |
自然界のある場所をとると、そこにはかならずいろいろな種の生物が混じり合って生活している。生態学ではこれを一つの集団とみなして群集とよぶが、ヒトの群集と区別する際に生物群集の語を用いる。その場所に生息するあらゆる動植物を含めるのが原則であり、特定の生物群に着目して貝類群集、鳥類群集などと用いるのは便宜的な使用である。群集を植物部分と動物部分に分けるとき、前者を植物群落、後者を動物群集とよぶ。場所のとり方は基本的に任意であるが、景観としてまとまりのある場所、たとえば湖などを選ぶことが多い。陸上では一般に植物が景観を形成しており、植物群落を単位として群集を規定することが多く、「ブナ林の群集」「チガヤ草原の群集」などと表現される。 群集を構成する各種生物個体は、生きるに必要な資源や繁殖などをめぐって密接な種内関係を有している一方で、種間でも深くかかわり合いながら生活している。たとえば、従属栄養生物たる動物は他種の動植物を食うことによって生きており、餌(えさ)となる他種の存在なしにはそれ自身の存在を考ええないものである。また、独立栄養生物とよばれ、一見他種とは無関係に生活しているかにみえる緑色植物も、光や土壌中の水や養分をめぐっての他種動植物との競争・協調のなかで生活しているのである。動物と植物間の関係としては、やや特殊ながら、虫媒花における受粉をめぐっての昆虫と植物との協調的な関係はよく知られている。これらのことは、群集が各種生物の単なる寄せ集めではなく、相互にかかわり合いながら生活している生物の地域集団であることを示している。 群集の概念はこのような生物間の相互作用、もしくは諸関係を含むものであるがゆえに「生物の生活の科学」たる生態学のなかでもっとも重要な位置を占めている。なぜなら、現実の生物の生活はすべて群集の諸関係のなかで営まれているからである。 これらの諸関係を群集全体として眺めるとき、そこには食物連鎖、生態ピラミッドなどの構造が現れてくる。また、諸関係の総決算が植物群落の遷移にみられるような動的な系を生み出すこともある。このため群集は独自の構造と発展形態を有する統一体としてとらえられることもあるが、群集が時系列的に不変の構成員と明確な境界をもたないことは明らかであり、このような群集観があくまで操作的なものにすぎないことは注意を要する。 [江崎保男] [参照項目] |出典 小学館 日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について 情報 | 凡例 |
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