國防大學生命科學研究所生態學特論上課講義
生態圈範疇、不同群落介紹及群落自 然演化
龍世俊 副研 究員 中央研 究院環 境變 遷研究 中心 Research Center for Environmental Changes 1.
Ecology
The study of how organisms interact with each other and their physical environment Nowadays, ecology has taken on new meanings in social rather than scientific contexts “environmentalist” vs. “ecologist”
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Galaxies Stars Planets Earth Biosphere Ecosystems Communities
Biological entities
Populations Organisms Organ systems Organs Tissues Cells Molecules Atoms Subatomic particles
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Population
a group of individuals of the same species living in the same area there is no limit on the size of the area All populations undergo three distinct phases during their existence:
Growth, stability and decline
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Definitions
Intrinsic rate of increase = birth ratedeath rate Carry capacity: maximum population size that can be sustained by an environment for a long time, the carrying capacity is usually briefly exceeded by an “overshoot” phase before the population levels off in the stability phase 5.
Four Basic Abundance Controls
Physical environment
Physical limitations
Biological environment
Competition Predation Symbiosis: mutualism, parasitism, commensalism, amensalism
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Population decline
Density-independent regulation vs. density-dependent regulation Interaction of the factors Law of the minimum: growth is limited by the resource in the shortest supply
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Population range
Population maximum occurs where the physical and biological factors that control abundance are the most favorable Endemic species: localized and may have just one population that inhabits only a small area; this pattern is especially common in tropical organisms and in organisms that are highly specialized to live on resources with limited distribution or that have narrow environmental tolerances 10.
Community
A community consists of all population that inhabit a certain area An ecosystem is that community plus its physical environment Community structure: open vs. closed A closed community was a discrete unit with sharp boundaries called ecotones; an open community has populations distributed randomly 11.
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Community structure
Most communities are open and most species are rare in communities Terrestrial: tundra, grassland, desert, taiga, temperate forest, tropical forest Aquatic: marine, freshwater
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Community diversity
Latitudinal diversity gradient describes how species richness in most groups steadily decreases going away from the equator Depth diversity gradient shows how species richness increases with water depth, down to about 2000m Four interrelated factors: environmental stability, community age, length of growing season, nutrients 16.
Community change through time
Community succession is the sequential replacement of species in a community by immigration of new species and the local extinction of old ones Biomass, the total weight of living tissue in a community, increases in later stages because living tissue accumulates 17.
Community change through time (2)
Pioneering plants tend to be smaller in size and exhibit rapid growth that maximizes productivity; in later stages, as more specialized, slower-growing species begin to migrate in, productivity declines In later stages, diversity increases with more species with larger size and longer life cycles 18.
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