lecture note 12 for BGYB50

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Department
Biological Sciences
Course
BIOC50H3
Professor
Herbert Kronzucker
Semester
Winter

Description
LECTURE 12: - An examination of atmospheric CO2 levels over the Phanerozoic reveals that current CO2 levels are exceptionally low, even considering the projected increases due to anthropogenic emissions; current levels near 360 ppm are contrasted by 1,000-2,000 ppm during the reign of the dinosaurs, and levels as high as 7,000 ppm during the Cambrian species explosion; this parameter, too, has experienced constant change throughout the history of life - Mount St. Helens: much has been learned about the ecological responses to drastic disturbances from the eruption of this volcanic peak of the Northern Cascade mountain range; the mountain erupted on May 18, 1980, with the largest debris avalanche in documented geologic history (~2.9 km3), creating some 600 km2 of denuded forest land, and some 20 km2 of near complete devastation in the immediate blast zone, knows as the ‘pumice plains’ - Life was found to return very quickly in the areas near the crater, including plants, such as fireweed (Epilobium angustifolium), whose seeds blew into the pumice plains from the surrounding areas within a season of the eruption - Over longer time scales, the recolonization of species following glacial retreat gives an excellent example of ecological response to disturbance (examples: maple and hemlock trees gradually re-conquered more northerly reaches from their southern refugia [Florida and Mississippi Valley, respectively] after the pinnacle of the last major ice age in North America ended ~10,000 years ago; this process is still ongoing!) - In general, following a disturbance, vegetation, microorganisms, and animals recolonize the affected site, often with significant predictability, in a process known as succession www.notesolution.com - Ecological succession is defined as a continuous, unidirectional, and sequential change in the species composition of a natural community; any such sequence is termed a sere, and it begins with a pioneer community (dominated by early-successional species, such as lichens and mosses) and culminates in a climax community (dominated by late-successional species, such as grass or tree species, depending on the biome) - 10 (primary) succession: the colonization of lifeless ground, and the gradual community change over time, e.g. following volcanic eruptions (e.g. Mt. St. Helens’ immediate blast zone) or glacial retreat - 10 succession typically includes early pioneer phases dominated by lichens, which aid in the breaking down of rock substrates and in the production of topsoil (this can take 1,000 to 2,000 years!) www.notesolution.comLECTURE 12: - An examination of atmospheric CO leve2s over the Phanerozoic reveals that current CO l2vels are exceptionally low, even considering the projected increases due to anthropogenic emissions; current levels near 360 ppm are contrasted by 1,000-2,000 ppm during the reign of the dinosaurs, and levels as high as 7,000 ppm during the Cambrian species explosion; this parameter, too, has experienced constant change throughout the history of life - Mount St. Helens: much has been learned about the ecological responses to drastic disturbances from the eruption of this volcanic peak of the Northern Cascade mountain range; the mountain erupted on May 18, 1980, with the largest debris avalanche in 3 2 documented geologic history (~2.9 km ), creating some 600 km of denuded forest land, and some 20 km of near complete devastation in the immediate blast zo
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