[분수대] 에코시스템(ecosystem)

The clown fish is a fish shy orange with white stripes that have become familiar after a species featuring the main character in "Finding Nemo". Clownfish often swim around the sea anemones, hiding in the tentacles when danger threatens. Anemones' tentacles toxic avert the danger and the reader away clowns anemones natural enemies. Therefore, the clown fish is also called the "anemone fish." It is typical of the symbiotic relationship of mutualism in the ecosystem. However, not all of these relationships are mutually beneficial. In a commensalist relationship, one organism benefits but the other is neither harmed nor benefitted such as when mites ride on insects as a means of transportation. Parasitism is a relationship in which one organism benefits while the other is harmed. A parasite lives at the expense of its host. In any case, both commensalism and parasitism are symbiotic relationships, taking advantage of and helping one another. The ecosystem plays host to a series of threats and even a peaceful meadow teems with life and death. A lion may be at the top of the food chain, but it is not easy being a lion either. A lion’s rate of hunting success is about 30 percent. If a lion gets injured in the course of hunting, it could die of starvation. Or, if the zebra population declines and a draught hits the meadow, even the lions may go the way of mutual destruction. 오렌지색 몸체에 흰 띠를 두른 겁쟁이 물고기가 흰동가리다. 영화 ‘니모를 찾아서’의 주인공이다. 광대처럼 생겼다고 서양에서는 ‘클라운 피시(Clown Fish)’로 부른다. 주로 말미잘 주위를 배회하다 덩치 큰 녀석이 다가오면 쏜살같이 말미잘 촉수 속으로 숨는다. 촉수에는 독성이 있어 ‘아가리’도 멈칫한다. 대신 말미잘의 천적들을 흰동가리가 쫓아낸다. 말미잘 이름을 붙여 ‘아네모네 피시(Anemone Fish)’로도 부르는 배경이다. 전형적인 ‘공생(共生)’ 관계이다. 약육강식의 자연계엔 필연적으로 ‘공생의 거미줄’이 촘촘하다. 악어와 악어새, 고비물고기와 새우, 감자와 뿌리혹박테리아가 대표적이다. 그러나 항상 누이 좋고 매부 좋은 ‘상리(相利) 공생’만 있는 것은 아니다. 이동 수단으로 곤충을 이용하는 진드기, 포유류를 활용하는 의갈류, 조류에 달라붙는 노래기가 있다.

Kickass Mutualisms: Lycaenids+Ants « Teaching Biology

Anyway, on to the topic of this post: the best example of a mutualism I know of. It’s the mutualism between the lycaenid caterpillar and ants: the ants, being top predators, protect the defenceless herbivorous caterpillar in exchange for a nutritive reward.

This reward consists of carbohydrates (Maschwitz, 1975) secreted from an exocrine gland, the dorsal nectary organ . When a caterpillar feels threatened, it will release a signal, most likely pheromonal, which attracts ants; once they arrive, it pumps out the secretion (Agrawal & Fordyce, 2000), making it attractive for the ants to stay and protect this easy source of valuable nutrients (Cushman et al. , 1994). It’s my personal favourite example of a mutualism, and one I use in every lecture I give on the subject.

Those who have been to one of those lectures will know how much I stress the fluid nature of such associations, and how they can easily lapse into cases of parasitism (and vice versa; it’s all on a spectrum, both on ecological and evolutionary timescales). This can also be seen here: several of these lycaenid caterpillars have secondarily become entomophagous – they use the same attractants to gather ants, and eat them before they realise there’s no reward (Akino et al.