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BILD 3 - Lecture 23

BILD 3 - Lecture 23 - In some cases ecological succession...

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In some cases, ecological succession may take a very long time. When a tropical rainforest is logged, the exposed land is quickly leached of nutrients. If the soil is an iron-rich lateritic soil such as is common in the tropics, it bakes into a hard brick-like crust. This makes it difficult for the forest to be replaced. But the tropics are remarkably resilient. The picture below shows a Costa Rican cloud rainforest at about 5,000 feet altitude that had been a farmer’s field only 18 years earlier. Ecological Niches Selective pressures acting on organisms are made up of abiotic (non- living) and biotic (living) factors. The former are physical factors, such as moisture, light and temperature, that determine whether the environment can support particular kinds of life. The latter are of three types: (1) competitive interactions with other species that share resources of the environment such as water and light, (2) antagonistic (“enmity”) interactions such as those between predator and prey, and (3) cooperative or mutualistic interactions with other organisms that aid an organism’s survival. Together, these abiotic and biotic interactions contribute to the unique ecological niche that is occupied by, and shaped by, each species.
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Ecologists recognized early in the last century that different species must occupy distinct ecological niches. The term niche was originally derived from the niches in medieval cathedrals that hold statues of saints and angels — just as a niche in a cathedral provides a place for a statue, an ecological niche provides a place for a species! The pioneering ecologist Charles Elton thought of a niche as being like a human profession, and defined a niche as the function performed by the species in the community of which it is a member . Later, G. Evelyn Hutchinson took a different approach. He defined a niche as the set of factors that influenced the organism. He called a niche a region in a “multidimensional space” made up of environmental factors that affect the welfare of a species . Ecologists today combine these definitions. The abiotic and biotic characteristics of the immediate environment influence organisms’ survival and reproduction. At the same time, organisms can influence the nature of the niches that surround them.
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