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LECTURE 21 – Ecology and Plant SuccessionEcology = 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 otherEcology deals with studies of organisms, populations, communities, ecosystems and the biosphereEcological HierarchyOrganisms  Populations  Communities  Ecosystems  BiospherePlant Ecology: the interaction among plants, and between plants and the environmentPopulation are all the members of a single species living togetherHabitat – 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 ecosystemPlant Community– different populations of plants living together in the same geographical areaDominant species – the most influential species in the community; for example: Redwood forestThey control structure and species composition of the community throughPhysical factorsLight (provide shade)Wind (wind screen)Humidity (higher than in open areas)Chemical factorsnutrientspHEcosystem – 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 à 1st order consumers à 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 materialFood Chain vs. Food WebA food web is more realistic:Multiple interactions between several food chainsThere’s usually more than one producer, more than one primary consumerConsumers have alternative food sourcesAbiotic – non-living components of the environment: climate, light, soil, inorganic substancesBiogeochemical cycles:Carbon cycleWater cycleNitrogen cycleCarbon CycleCO2 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)Water CycleWater enters the atmosphere as vapor from the land and Transpiration from plants. Vapor condenses à rainfall, into rivers, streams, oceans. (SLIDE 10)Nitrogen CycleNitrogen 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 EarthEcosphere – interactions among Earth’s biosphere, atmosphere, water and landGreenhouse EffectHumans upset the balance of the Carbon Cycle:1. Global Deforestation2. More CO2 released due to burning fuelsResult: a 25% increase in global CO2Carbon dioxide acts as a heat trap, capturing sunlightConsequence: global warming; Earth’s temperature has increased 1o F, more expectedLess agricultural areas, shifting northDiseases such as malaria – affecting more peopleOcean levels would increase, floods, hurricanesGlobal WarmingCarbon dioxide and other gases trap solar energy, reradiating it back to the Earth as heat – therefore warming the atmosphere. The 1997 Kyoto ProtocolPlant Succession – a series of predictable changes over time in the kinds of plants growing in an areaEcosystems mature and change with timeEcosystems are determined by the physical parameters in the environmentAs ecosystems age, the kinds of organisms change à until a stable type of community formsInitial stages – unstable, high rate of replacementLater stages – more stable, low rate of changeClimax community – relatively stable community at the end of succession1. in equilibrium with the environment2. permanent (until some major change)3. varies depending on conditionsKinds of succession:Primary successionSecondary successionPrimary succession – when plants become established on land completely devoid of soil and vegetationEcosystems are not static, they change over timeSoil – portion of Earth’s surface of disintegrated rock and organic materials (humus).Possible primary succession on Forest HabitatsLichens à mosses & à grasses à shrubs à trees (pioneer species) fernsPrimary succession begins as pioneer species (lichens and mosses) invade bare rock. Climax community is spruce-fir and birch forestEach stage prepares the way for the next invasion of speciesPioneer species: first inhabitants; forms the soilSoil is formed and thickensEventually, community is mature (climax)SoilSoil provides essential nutrients to all plantsWater and mineral nutrientsSoil is the product of the living environment, and is influenced byClimateTopographyParent materialTime (4.5 bya, Earth was mixture of rocks)CharacteristicsParent material – soil particles of naturally occurring inorganic materialSoil texture– all soils contain 3 kinds of particles:SandSiltClay– most important: it holds nutrients for plantsOrganic matter – humus is decomposing organic matter in the soilSoil pH– acid (low pH) or basic (high pH) soil influences soil fertility and nutrient availabilityBest soil is neutral or slightly acidic pHSecondary succession –natural forces or human intervention destroy the existing vegetation (fire, flooding, logging, agriculture)When the disturbance stops, community begins secondary succession à back to climax communitySpeed of secondary successionSince soil is already in place, secondary succession can take place 5 to 10 times faster than primary successionAbiotic factors affect the nature of the plant communityWeatherTemperatureHumidityAn example of Secondary succession on barren rock or lava is Mount St. Helens in Washington State (1980 eruption)Mt. St. Helens recovery after the eruptionAlso, _________ community affects these ____________ factorsFor example, in the tropical rain forests, the vegetation “creates” the rainfall through plant transpiration.When trees are removed, rainfall stops and land becomes aridThe resulting new climax community is often desert shrubsWhy is it important to know about succession?Understand that natural systems maintain themselves, whereas disturbed systems cannotHuman influence on succession: they usually knock out


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UMD BSCI 124 - LECTURE 21 – Ecology and Plant Succession

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