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18 - `Sept 18th COMMUNITY ECOLOGY Communities groups of...

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`Sept 18 th : COMMUNITY ECOLOGY Communities : groups of species (populations) living together and interacting with one another in space and time. Limits / Ranges of Tolerances: moisture, temp too hot too dry – similar to population limit/range Community complexity → stability Community complexity → symbioses Community boundaries → edges, ecotones Community disturbances → succession Fire ecology Biomes Community limits / Ranges of tolerances: (Similar to population limits/ranges) Physical factors: temperature, moisture, soil profiles/types Indicator species have narrow ranges ≡ species with narrow ranges of tolerance which may indicate economic deposits. e.g.: Certain milk vetch, locoweed-like plants in thewestern US are found where soil- selenium concentrations are high; and selenium is associated w/uranium deposits Redbud trees are associated w/dolomite (MgCO 3 ) Coliform bacteria are associated w/pollution by sewage Some Indicator Species for Economic Deposits* Aluminum – Holly Boron – Russian Thistle Cobalt – Tupelo or Sorghum Copper – several species of moss Lead – some birches, poplars Lithium – Meadow Rue Manganese – Locust Phosphorus – Bindweed Selenium – Prince’s Plume Zinc – some violet species, sweet gum * after H. Cannon. 1971. Taxon , 20:227-256. Communities/Succession/Biomes 9/17/07 1
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Severe physical conditions = simple communities (arctic) Simple communities with few species are found in the arctic/alpine tundra. The loss of a species or two can potentially compromise the availability of energy to a significant part of the next trophic level. These communities are subject to drastic changes when the numbers of a single species fluctuate. A road across the tundra leaves scars for hundreds of years! Mild physical conditions → complex communities Complex communities with many species are found in tropical rainforests and coral reefs. Loss of a few species here would have an insignificant impact on the community. A road through a tropical rainforest is overgrown and gone in a few tens of years – e.g ., forest in Truk Thus, as species richness/diversity increases, so does community stability – think tundra vs. rainforest. Greater diversity promotes tighter niches because of greater competition – think five species of warblers in the same forest. Compare the following: Central America. A 4-acre plot contains 67 species of trees and 30 species of bats. Colorado spruce/fur forest. A 4-acre plot contain a maximum of 5 species of trees and 3 species of bats. Borneo . 200 sp. trees & 800 sp. orchids per acre We have been simplifying our communities since the agricultural revolution. We grow few species of crop plants and animals and drastically reduce their natural pests and predators. These large monocultures run the risk of crop failures due to new plant diseases and pests.
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