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Population Dynamics Quickie vocab review Population group of individuals of the same species living in the same geographic area Carrying capacity maximum number of individuals of a species that the ecosystem can support Limiting Factors Factors that regulate population using multiple criteria (internal vs. external, abiotic vs. biotic, density-dependent vs. density independent) Density-dependent factors: factors that inhibit the overgrowth of a pop’n when numbers of the pop’n are large Density-independent factors: factors that affect population growth but have nothing to do with density DD Factor, or DI Factor? food Water supply parasitism temperature predation floods storms fires earthquakes amount of sunlight disease weather competition space Examples In most freshwater lakes algal productivity is limited by the availability of inorganic phosphorus in the form of the ion phosphate. The production of grass in a field can be limited by nutrients even if there is enough sunlight. Population Growth Curves Nearly all populations will grow exponentially as long as there are resources available http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookpopecol.html The J-curve occurs when there is no limit to population size Population Growth Curves The S-curve, or logistic curve, shows the effects of a limiting factor on population http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookpopecol.html Biozone p. 58 points for biozone: /10 Add axes to this sketched population curve, and identify and give a definition for the lag phase Laptops ready? 1. Use Excel to plot the data shown on p. 59 of Biozone, and then answer the questions in your book. Show me your Excel plot (with a title, and labeled axis) for credit. 2. You may consult with a partner for the questions, but you must do the Excel graph on your own. You should create the Excel data by using a formula. 3. Be ready to discuss your answers to the questions when finished. Visualizing Effects of Birth Rate on Population Growth Predict: What type of growth would a population show if it has a constant birth rate and is not limited by food or disease? _____________________ Sketch a graph of what you would predict for the above situation, and label your axes Go to http://www.otherwise.com/population/exponent.html and click on “run applet” under the exponential growth section 1. 2. 3. 4. 5. Set the birth rate to 1.2 and press “run,” and “stop” the simulation when the 25th generation has been born. Sketch the graph on both sets of axes on the next slide (give minimums and maximums but no scale needed), and label it. LABEL AXES FIRST. On the set of axes for Chart 1, draw a prediction of how the graph would look if you changed the birth rate to 1.5, and label your prediction clearly. Change the rate to 1.5 and click “reset,” and then “run” the simulation for 25 generations. Observe graph and then sketch it on the axes for Chart 2. Label your plot clearly. On the same axis as before, predict what the graph might look like if the birth rate fell to 0.8 and draw your prediction. (label) Now test out your prediction. Draw the actual graph on Chart 2. Chart 1. Set of graph sketches for predictions at birth rate = 1.5, 1.2, and 0.8 Chart 2. Actual sketches at birth rate = 1.5, 1.2, and 0.8 Points: / 15 Adding carrying capacity to the simulation Scroll down to logistic growth, then “run applet” 1.Before running the applet, sketch a prediction of the expected shape of this graph on Chart 3. 2.Run the applet for 30-40 generations at each of the following sets of parameters, hitting reset in between: b. rate: 1.8 carrying cap.: 1000 b. rate: 2.0 carrying cap.: 1000 b. rate: 3.0 carrying cap.:1000 Sketch all three of the situations on Chart 4. Label all axes appropriately before moving on. ALS1 Slide 13 ALS1 Stop in between here! Alyssa Schultheis, 2/4/2009 Chart 3. Sketch of overall expected shape when carrying capacity introduced Chart 4. Actual sketches at birth rate = 1.8, 2.0, 3.0, and carrying capacity constant at 1000 Points: / 10 Choose one of the birth rates used previously, and run for three different carrying capacities. Sketch results and label clearly. Points: /8 Quiz Review R-strategists vs. K-strategists NOTE: these are idealized categories and many organisms occupy a place on the continuum between these two types R-strategists prefer survival at low population density, near the lag phase of the curve where biotic potential (r) is high can develop rapidly and produce a large # of offspring (adapted to exp. Increases) Ex: American oyster, house mouse, pioneer species– wide dispersal in disturbed habitats R-strategists vs. K-strategists K-strategists survive well at or near carrying capacity (K) usually found in stable habitats long life spans (ex: elephant and tortoise) take good care of young and infant mortality tends to be low Survivorship Curves I: high survivorship of young, live to old age II: relatively constant death rate (due to hunting/disease) III: high birth rates, young die early Carrying Capacity Scenarios Determining Carrying Capacity of Non-humans Maximum population of a species that can survive indefinitely in a given environment Depends on: -conditions and resources available -consumption habits of species Issues with calculating Human K Human K and the IPAT equation “If there are too many people, even the most wisely managed technology will not keep the environment from becoming overstressed.” Environmentalists Paul Ehrlich and John Holdren (1972)- Journal of Industrial Ecology, 2001 http://www.buddycom.com/ecol/Brainfood/EcoLaws.html http://belfercenter.ksg.harvard.edu/files/ John%20Holdren%20headshot%20300 %20dpi.jpg The IPAT equation: I = PAT I = environmental impact P = population, A = affluence, T = technology •I can be expressed in terms of resource depletion or waste accumulation •A refers to level of consumption of a population • T refers to processes used to obtain resources and turn them into useful goods and wastes Estimates of K for humans range from ½ billion to 300 billion! If the variables are considered separately… I = PAT What would happen to I if P, A, T decrease? What would happen to I if P, A, T increase? If impact and population held constant, how does A change with P? Even though the IPAT equation assumes independence of the variables… Not so in the real world! For ex., in the 1980s, slower pop’n growth appeared to facilitate faster consumption growth in developing countries Also, higher income levels tend to improve environmental technology Ehrlich used the IPAT formula to show that population growth was the dominant factor in environmental damage. That darn exponential population growth!! In reality, different elements have been most important at different historical times Examples of Applications of IPAT equation Increase in arable land in many parts of Africa up to ~1980 and deforestation that went with it was due mainly to pop’n growth (there was little rise in consumption of agricultural products/person and little improvements in yield) By contrast, the dramatic rise in human output of CFCs from the 1940s on was due to introduction of a new technology Many economists argue… …that human carrying capacity can be expanded continuously through technological innovation. Ex: if we learn to use energy and material 2x as effic., we can doub. the pop’n or use of E w/o necess. increasing load on env. To compensate for future population growth deemed necessary, though, it is suggested that efficiency would have to be raised by a factor of 4 to 10 to remain within global carrying capacity Questions to Ponder with a Partner Why do you agree/disagree with the statement that human carrying capacity can be expanded continuously through technological innovation? Estimates of human carrying capacity vary from 2.5 bill. to 40 billion. Why do the estimates vary so widely? Identify at least 4 variables that can be considered when using models to determine human carrying capacity, and explain how these variables can affect K. What value systems are involved in the consideration of the variables you mentioned for the previous question?