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AP Biology, Chapter 53 Population Ecology Counting Sheep 53.1 Dynamic biological processes influence population density, dispersion, and demographics Intro Density and Dispersion Intro 1. Define and distinguish between density and dispersion. Density = number per unit of area Not static; birth, death, immigration, and emigration Dispersion = pattern of spacing between individuals Dispersion shows finer detail Density: A Dynamic Perspective 2. How are animal population sizes estimated by the mark-recapture method? Some(s) are marked, released, and allowed time to mix in Second sample: # marked (x) and total (n) are counted Pop. Size (N) = sn/x Patterns of Dispersion 3. Describe conditions that may result in the clumped, uniform, and random dispersion of populations. Clumped From heterogeneous resources Most common Uniform From interactions among individuals like territoriality For example, plants avoiding one another's shade Random From lack of interaction and homogeneous environment For example, trees in a rainforest Demographics Intro Life Tables Survivorship Curves 4. Describe the characteristics of populations that exhibit Type I, Type II, and Type III survivorship curves. Type I High survivorship until late in lifespan (elephants) Large size, few offspring, good care Type II: constant proportion dies at each age gray squirrel) Type III Very high death rates for the young (invertebrates) Small size, many offspring, little or no care Reproductive Rates 53.2 The exponential model describes population growth in an idealized, unlimited environment Intro Per Capita Rate of Increase 5. How are the most basic demographic statistics combined to calculate the change in population size? In a fixed interval Change = Births + Immigrants – Deaths - Emigrants Exponential Growth 6. Describe the exponential model of population growth. dN/dt = rmaxN dN/dt is the instantaneous growth rate rmax is the intrinsic rate of increase, = birth rate - death rate N is the population size Ever steeper; not sustainable 53.3 The logistic model describes how a population grows more slowly ast it nears its carrying capacity Intro The Logistic Growth Model 7. Describe the exponential model of population growth. dN/dt = rmaxN((K-N)/K) K is the carrying capacity As N approaches K, dN/dt approaches zero S-shaped curve; levels off at the carrying capacity The Logistic Model and Real Populations 8. Explain how an environment's carrying capacity affects the intrinsic rate of increase of a population. Real populations rarely have infinite resources The closer to the carrying capacity, the slower the growth There may be overshoot and fluctuation at K 9. How does the Allee effect counter an assumption built into the logistic model? Assumption each new individual has a negative effect on growth Allee effect: populations can be too small Sparse populations may make finding a mate difficult Smaller groups may not be able to defend 53.4 Life history traits are products of natural selection Intro 10. What main traits make up an organism’s life history? Age at first reproduction Frequency of reproduction # of offspring per episode Evolution and Life History Diversity 11. Define and distinguish between semelparity and iteroparity. Semelparous species breed once in their lifetimes Called "big-bang" Salmon and agave Iteroparous species breed repeatedly 12. How may resource availability affect the evolution of life histories. Variable, unpredictable environments Large numbers of offspring Ex.: desert plants germinate, produce many seeds, and die in a rainy month Dependable environments More intense competition; fewer, larger young Ex.: tropical species like Brazil nut trees “Trade-offs” and Life Histories 13. Give examples of the trade-off between reproduction and survival. Fecundity is inversely proportional to probability of death in birds Restriction of reproduction in beetles lengthens life Flycatchers burdened with many eggs produce fewer the following year 14. Distinguish between r-selected populations and K-selected populations. r-selected: adapted for high growth when possible Early mauturation, short life, small size, high death rate, many offspring, no parental care Ex.: bacteria, insects, weeds K-selected: adapted for equilibrium at carrying capacity Late mauturation, long life, large size, low death rate, few offspring, much parental care Humans, elephants 53.5 Many factors that regulate population growth are density dependent Intro Population Change and Population Density 15. Explain how density-dependent factors affect population growth. Usually more intense when populations are more dense Competition, predation, disease, stress, waste accumulation 16. Explain how density-independent factors affect population growth. Not affected by density Natural disasters and habitat destruction by humans Mechanisms of Density-Dependent Population Regulation Intro 17. How may feedback mediate density-dependent population regulation? Competition for Resources Predation Denser population uses up resources faster Fewer resources means less reproduction, greater mortality Lower density allows resources to recover Toxic Wastes Intrinsic factors As population density increases, stress increases, fertility drops As population growth slows density drops Lower density eases stress and increases fertility Territoriality Disease Denser populations allow easier transmission Easier transmission means more disease/mortality Lowered density lowers the incidence of disease Population Dynamics Intro Stability and Fluctuation 18. Describe several boom-and-bust population cycles, noting possible causes and consequences of the fluctuations. Cicada 13 and 17 year life cycles: evade predation Snowshoe hare and lynx: carrying capacity overshoot Population Cycles: Scientific Inquiry Immigration, Emigration, and Metapopulations 19. How are immigration and emigration affected by changing densities in metapopulations? Metapopulation= linked local populations Higher density in one part increases emigration 53.6 The human population is no longer growing exponentially but is still increasing rapidly Intro The Global Human Population Intro 20. Describe the history of human population growth. Exponential growth since the Industrial Revolution Birth rate steady, death rate down from medicine, sanitation, etc. Greatest pressure on the global environment Regional patterns of Population Change 21. Define the demographic transition. Transition from high birth and death rates to low First death rates drop There is a period of rapid growth Then birth rates drop and population size stabilizes Age Structure 22. Compare the age structures of Italy, Kenya, and the United States. Describe the possible consequences for each country. Italy has a smaller fraction of pre-reproductive and reproductive; no growth Kenya has a high fraction of pre-reproductive and reproductive; high growth Us is in between, moderate growth Infant Mortality and Life Expectancy Global carrying Capacity Intro 23. When is the global human population projected to reach ZPG and what is the projected peak size? 2075? 8-12 billion? Estimates of Carrying Capacity 24. What methods have been used to estimate our carrying capacity? Logistic growth curves “Maximum” population density time habitable area Combine amount of farmland, yield, diet Limits on Human Population Size 25. How is the ecological footprint concept applied to the calculation of Earth’s carrying capacity? Ecological footprint All of the land and water area required per person Includes production of resources and absorption of wastes Application 1.7 hectares/person = sustainability U.S. uses 10 ha/person