05 05 2011 LECTURE 21 Ecology and Plant Succession Ecology from the Greek oikos house logy study Ecology is the study of the effects of the environment on living organisms the effect of living organisms on the environment the effects of living organisms on each other Ecology deals with studies of organisms populations communities ecosystems and the biosphere Ecological Hierarchy Organisms Populations Communities Ecosystems Biosphere Plant Ecology the interaction among plants and between plants and the environment Population are all the members of a single species living together Habitat the location where the population is found the address of an organism Niche the functional role an organism plays in the ecosystem it encompasses habitat plus relationships with other organisms in the ecosystem Plant Community different populations of plants living together in the same geographical area Dominant species the most influential species in the community for example Redwood forest They control structure and species composition of the community through Physical factors o Light provide shade o Wind wind screen o Humidity higher than in open areas Chemical factors o nutrients o pH Ecosystem is the functional unit of study in the environment A community with all its living organisms biotic and non living organisms abiotic Biotic there are many organisms that live in a community organisms interact in food chains Producers 1st order consumers 2nd order consumers photosynth herbivores carnivores Each step in the food chain is called a Trophic level energy is lost at each level Biomass and fungi are decomposers of dead material Food Chain vs Food Web A food web is more realistic o Multiple interactions between several food chains o There s usually more than one producer more than one primary consumer o Consumers have alternative food sources Abiotic non living components of the environment climate light soil inorganic substances Biogeochemical cycles o Carbon cycle o Water cycle o Nitrogen cycle Carbon Cycle o CO2 enters plants through Photosynthesis Carbon is released back to the air through Respiration or combustion of fuels Fossil fuels oil coal gas were formed from remains of ancient organisms SLIDE 9 o Water enters the atmosphere as vapor from the land and Transpiration from plants Vapor condenses rainfall into rivers streams oceans SLIDE 10 Water Cycle Nitrogen Cycle o Nitrogen gas is fixed by bacteria in plant root nodules Plants assimilate N and incorporate it into organic nitrogen compounds Animals assimilate N by ingesting plants Animal waste and organic nitrogen compounds are broken down SLIDE 11 Biosphere areas on Earth in which organisms are found all of the communities on Earth Ecosphere interactions among Earth s biosphere atmosphere water and land Greenhouse Effect Humans upset the balance of the Carbon Cycle 1 Global Deforestation 2 More CO2 released due to burning fuels Result a 25 increase in global CO2 Carbon dioxide acts as a heat trap capturing sunlight Consequence global warming Earth s temperature has increased 1o F more expected Less agricultural areas shifting north Diseases such as malaria affecting more people Ocean levels would increase floods hurricanes Carbon dioxide and other gases trap solar energy reradiating it back to the Earth as heat therefore warming the atmosphere The 1997 Kyoto Protocol Plant Succession a series of predictable changes over time in the kinds of plants growing in an Global Warming area Ecosystems mature and change with time o Ecosystems are determined by the physical parameters in the environment As ecosystems age the kinds of organisms change until a stable type of community forms o Initial stages unstable high rate of replacement o Later stages more stable low rate of change Climax community relatively stable community at the end of succession 1 in equilibrium with the environment 2 permanent until some major change 3 varies depending on conditions Kinds of succession o Primary succession o Secondary succession Primary succession when plants become established on land completely devoid of soil and vegetation Ecosystems are not static they change over time Soil portion of Earth s surface of disintegrated rock and organic materials humus Possible primary succession on Forest Habitats Lichens mosses grasses shrubs trees pioneer species ferns o Primary succession begins as pioneer species lichens and mosses invade bare rock Climax community is spruce fir and birch forest Each stage prepares the way for the next invasion of species Pioneer species first inhabitants forms the soil Soil is formed and thickens Eventually community is mature climax Soil Soil provides essential nutrients to all plants Water and mineral nutrients Soil is the product of the living environment and is influenced by o Climate o Topography o Parent material o Time 4 5 bya Earth was mixture of rocks Characteristics o Parent material soil particles of naturally occurring inorganic material o Soil texture all soils contain 3 kinds of particles Sand Silt Clay most important it holds nutrients for plants o Organic matter humus is decomposing organic matter in the soil o Soil pH acid low pH or basic high pH soil influences soil fertility and nutrient availability o Best soil is neutral or slightly acidic pH Secondary succession natural forces or human intervention destroy the existing vegetation fire flooding logging agriculture When the disturbance stops community begins secondary succession back to climax community Speed of secondary succession o Since soil is already in place secondary succession can take place 5 to 10 times faster than primary succession o Abiotic factors affect the nature of the plant community Weather Temperature Humidity An example of Secondary succession on barren rock or lava is Mount St Helens in Washington State 1980 eruption o Mt St Helens recovery after the eruption Also community affects these factors o For example in the tropical rain forests the vegetation creates the rainfall through plant transpiration o When trees are removed rainfall stops and land becomes arid o The resulting new climax community is often desert shrubs Why is it important to know about succession Understand that natural systems maintain themselves whereas disturbed systems cannot Human influence on succession they usually knock out climax community Example of human interference with succession o Maintaining a green weed free lawn a constant battle with nature plant