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Transcript
Ecology Populations, Communities, Ecosystems Population Growth Population: all indiv. of the same species that live together in the same place at the same time Demography: statistical study of populations 3 Key features of population: Population size Population density Tend to grow in size, b/c indiv. Have more than 1 offspring Very small populations likely to become extinct Number of indiv in a given area Widely spaced are less likely to reproduce Dispersion Clumped (most common) Even Random Population Models Models: hypothetical pop. w/key characteristics of pop being studied Growth – more indiv. are born than die Number of indiv added to pop as it grows (ΔN) r (rate of growth) = birth rate – death rate Exponential growth curve (ΔN vs. time) Carrying capacity (K) – the pop size that an environment can sustain Logistic model – accounts for declining resources as pop grows As N approaches K the population ceases to grow (birth rate = death rate) Limiting Factors Density dependent Density independent Strategies of Pop Growth r-strategists K-strategists Exponential growth than pop size crashes Reproduce early in life, quick gestation Have many offspring at one time Offspring mature rapidly with little parental care Live in changing environments Ex. Small pop size and slow growth Reproduce later in life, few offspring Offspring mature slowly and receive parental care Live in stable environments Ex. Human population Humans expanded carrying capacity of environment Nearly 94 million people are added to the population each year How populations evolve In order to understand how populations change in response to evolutionary forces, you need to understand how they evolve in the absence of these forces Hardy-Weinberg Principle Early 1900’s scientists wondered if dominant alleles would replace recessive alleles Mathematician GH hardy and physician Wilhelm Weinberg independently demonstrated that dominant alleles DO NOT replace recessive alleles, frequency of alleles remains constant from one generation to the next unless evolutionary forces act upon them Hardy-Weinberg Principle Populations do not change unless evolutionary forces act upon them Allele frequency: proportion of the group with a specific allele p: dominant allele q: recessive allele Easily predict the freq of each genotype in a large, randomly mating populations Calculate freq of recessive allele Calculate the freq of dominant allele Determine the freq of heterozygotes P2+2pq+q2 = 1 (AA)2 + 2(Aa) + (aa)2 = 1 5 Forces that cause Populations to Evolve Mutation: ultimate source of genetic variation that makes evolution possible Migration (Gene Flow): movement of alleles into or out of a pop Nonrandom mating (Inbreeding): increases the proportion of homozygotes, deceases heterozygotes Genetic Drift: in small isolated populations, allele frequencies are drastically affected by natural disasters Natural Selection: directly changes freq of alleles Patterns of Natural Selection Only characteristics that are expressed can be selected for or against Directional Selection – eliminates one extreme from a range of phenotypes and favors the other extreme Stabilizing Selection – eliminates extremes at both ends of a range of phenotypes Disruptive Selection – eliminates the intermediate phenotype…aids in speciation Ecosystems Ecology: study of the interactions of living organisms with one an other and their physical environment Habitat: the place where a particular pop of species live Community: many different species living together in a habitat Ecosystem: community and physical aspects of habitat Biotic – living organisms Abiotic – physical aspects (non-living) Biodiversity – variety of organism, genetic differences and the communities and ecosystems in which they occur No distinct boundaries of an ecosystem Changes in an ecosystem Physical Environment Succession – progression of species replacement Changes sets of colonization Volcano – creates an island Glacier recedes – new soil Eventually, organisms colonize new habitat 10 succession: occurs on land where nothing has grown before (pioneer species) 20 succession: occurs in a n area with previous growth (forest clearing, abandoned fields) No 2 successions are alike! Energy Flow Energy flows thru Earth’s ecosystems in one direction Producers, consumers, decomposers Heterotrophs and autotrophs Herbivore, carnivore, omnivore, detrivore Food chain & food web Only 10% of energy moves to the next trophic level Biogeochemical cycles: Water cycle Biogeochemical cycles: substance enters living organisms, then returns to the non-living environment Water Cycle – driven by the sun Nonliving (aquatic ecosystems) Water vapor in atm. Condenses and precipitates to earths surface Some water seeps into soil and becomes ground water retained by earth Remaining water collects in lakes, rivers, and oceans where it is heated by the sun and evaporates into the atm Living (terrestrial ecosystems) Water is taken up by plant roots Transpiration – sun heats earth and creates wind currents which draw moisture out of leaves Carbon Cycle 0.035% CO2 in air and dissolved in water CO2 used by plants, algae, bacteria to build organic molecules (photosynthesis) CO2 returns to atm by 3 ways Cellular respiration Combustion/ burning Carbon in wood Fossil fuels – remains of organisms buried in sediments for thousandsmillions of years (coal, oil, natural gas) Erosion Marine organisms use dissolved CO2 to build shells (CaCO3) Shells covered with sediment – form limestone, then erode when exposed Nitrogen Cycle Atm 78% N2 Organisms are unable to use N2 Nitrogen Fixation: break the N2 triple bond and combines w/H to form ammonia (NH3) Assimilation: absorption and incorporation of nitrogen into plant and animal compounds (proteins, nuc. acids) Ammonification: production of ammonia by bacteria during the decay of nitrogen containing organic matter Occurs only in the absence of O2 Nitrogen fixing bacteria live in soil and nodules underground Urea Dead organisms Nitrification: production of nitrate (NO3-)by bacteria from ammonia Denitrification: bacteria converts nitrates into nitrogen gas Phosphorus Cycle PO4-3 found in rock and soil Dissolves in water and is absorbed by plants Plants use PO4-3 to build ATP and DNA Animals eat these plants and reuse phosphorus When plants and animals die, bacteria in the soil convert phosphorus in organic molecules back to PO4-3 Phosphorus can move to other ecosystems Trapped in sediments form rock If rock is exposed, weathering releases phosphorus Phosphorus level in freshwater is low Prevents growth of photosynthetic algae If added by humans (fertilizers/detergents), so much algae forms that fish and other invertebrates suffocate Communities: How organisms interact Coevolution: back-and-forth evolutionary adjustments between interacting members of an ecosystem Coevolving in opposition Predation: one organism feeds on another Parasitism: one organism feeds on and usually lives on or in host (usually don’t kill host) Defense Overcoming defense Competition: 2 spp use the same resource (s) in short supply Coevolving in Cooperation Symbiosis: 2 or more spp living together in a close, long term association Mutualism: both spp benefit Commensialism: one spp benefits, the other is neither helped nor harmed Niche Niche: the functional role a particular spp performs in an ecosystem… multidimensional Fundamental niche: the total niche an organism is potentially able to occupy within an ecosystem, the entire range of conditions it can tolerate Realized niche: the part of the niche that the spp actually occupies Ex. Cape May Warbler & character displacement Principle of competitive exclusion: if 2 spp are competing, the spp that uses the resource more efficiently will eventually eliminate the other locally – no 2 spp can occupy the same niche Predation can lesson competition among prey – promote biodiversity Ex. Sea stars eat bivalves The Physical Environment Climate depends on… The amount of E from the sun that reaches diff parts of earth and seasonal variation in that E Equator – sun’s rays are perpendicular Poles – rays spread out over grater s.a. (less E) Earth’s daily rotation – prevents build up of extreme temps 23.50 tilt – seasons further from the equator Global pattern of atmospheric and oceanic circulation created by unequal global distribution of solar energy Latitude Distance from ocean Elevation Position relative to mountain ranges Major Biological Communities Marine Fresh Water Strongly connected w/ terrestrial habitat Wetlands Shallow water Open Sea Deep Sea Lots plant growth Biomes: terrestrial communities w/similar climate Tropical Rainforest Savanna Desert Temperate Grassland Temperate Deciduous Forest Temperate Evergreen Forest Taiga Tundra Biome Project You are to select a biome and research its biotic and abiotic characteristics. List and describe types of organisms you would expect to find there. Where in the world would you find this biome. And then select one of the following: Create a 3-D shoebox model of the biome and create a new organism that is well adapted (in at least 4 ways) to its biome Write a paper comparing and contrasting 2 biomes Human Impact on the Environment Acid Rain Coal burning power plants release smoke high in sulfur Sulfur combines w/water vapor sulfuric acid Rain & snow precipitate H2S back to earth’s surface Northeast US has pH 3.8 Destruction of Ozone 1985 – discovered low conc of ozone over Anatartica, now hole over the Artic too More UV radiation to reach Earth’s surface, increase in skin cancer, cataracts, and retina cancer Chlorofluorocarbons (CFC’s) are major cause of ozone depletion CFC’s found in refrigerator coolant, air conditioners, aerosol propellant, foaming agents CFS’s are banned in US Global Warming Excess CO2 released in atmosphere from burning fossil fuels CO2 bonds absorb solar energy trapping heat, methane, and nitrous oxide Greenhouse Effect: the warming of atmosphere as a result of greenhouse gases Studies indicate direct correlation between amt of CO2 in atmosphere and temp increase over the last 130 years Problem: rising sea level (already rose >5cm), if polar ice caps melt, sea levels would rise 150m flooding entire Atlantic Coast of N. America