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Population Ecology Ecology - Study of interactions among organisms and their environment Conservation biology, environmentalism: preservation of natural world • • • • • Biosphere Ecosystems Community Population Organism ECOSYSTEM LEVEL Eucalyptus forest COMMUNITY LEVEL All organisms in eucalyptus forest POPULATION LEVEL Group of flying foxes ORGANISM LEVEL Flying fox Brain ORGAN SYSTEM LEVEL Nervous system ORGAN LEVEL Brain Spinal cord Nerve TISSUE LEVEL Nervous tissue CELLULAR LEVEL Nerve cell MOLECULAR LEVEL Molecule of DNA Figure 1.1 Population Ecology • • • • Population- how to measure? Growth rates: J shaped, S shaped K, r, and reproductive strategies Human population How are populations measured? • Population density = number of individuals in a given area or volume • count all the individuals in a population • estimate by sampling • mark-recapture method depends on likelihood of recapturing the same individual • The dispersion pattern of a population refers to the way individuals are spaced within their area – Clumped – Uniform: – Random: no pattern Figure 35.2C How do populations grow? • Idealized models describe two kinds of population growth 1. exponential growth 2. logistic growth • A J-shaped growth curve, described by the equation G = rN, is typical of exponential growth – G = the population growth rate – r = the intrinsic rate of increase, or an organism's maximum capacity to reproduce – N = the population size Figure 35.3A high intrinsic rate of increase 1500 Population size 1000 low intrinsic rate of increase 500 r=0 zero population growth negative intrinsic rate of increase r = -0.05 0 0 5 10 Time (years) 15 20 2. Logistic growth is slowed by populationlimiting factors K = Carrying capacity is the maximum population size that an environment can support Figure 35.3B • logistic growth curve – K = carrying capacity – The term (K - N)/K accounts for the leveling off of the curve Figure 35.3C Multiple factors may limit population growth declining birth rate or increasing death rate • The regulation of growth in a natural population is determined by several factors – – – – limited food supply the buildup of toxic wastes increased disease predation Density Dependent Factors • • • • Competition Predation Parasitism disease Density Independent Factors • • • • Natural disasters Weather Seasonal cycles Human activities – About every 10 years, both hare and lynx populations have a rapid increase (a "boom") followed by a sharp decline (a "bust") Figure 35.5 • Survivorship curves plot the proportion of individuals alive at each age • Three types of survivorship curves reflect important species differences in life history Figure 35.6 Evolution shapes life histories • An organism's life history is the series of events from birth through reproduction to death • Life history traits include – the age at which reproduction first occurs – the frequency of reproduction – the number of offspring – the amount of parental care given – the energy cost of reproduction • Principles of population ecology may be used to – manage wildlife, fisheries, and forests for sustainable yield – reverse the decline of threatened or endangered species – reduce pest populations The Spread of Shakespeare's Starlings • In 1890, a group of Shakespeare enthusiasts released about 120 starlings in New York's Central Park • Today: over 100 million starlings, spread over N. Amer. Current 1955 Current 1955 1945 1935 1925 1945 1905 1915 1935 1925 1925 1935 • The starling population in North America has some features in common with the global human population – Both are expanding and are virtually uncontrolled – Both are harming other species Why We Live in Interesting Times… Pre 2000 A.D. 1. More youth than elderly 2. More rural than urban Post 2010 A.D. 1. More elderly than youth 2. More urban than rural People alive 1950-2050 A.D. have seen: 1. Highest growth rate (2.1%/year) 2. Population double during their lifetime More people have lived in the last 100 years, than in all of human history before 1900! Thomas Malthus (1798) “An Essay on the Principle of Population” • • Populations grow geometrically while supporting resources grow arithmetically Population, if not purposefully checked (“preventative checks”), would outpace resources and lead to unplanned “positive checks” that would return population to sustainable levels HUMAN POPULATION GROWTH Earth's population: 6 billion (Oct 12, 1999) Every second, five people are born and two people die, a net gain of three people. Every day, +250,000 = 2 x Champaign-Urbana This year, +87,000,000 = Mexico This decade +1,000,000,000 = China THE HUMAN POPULATION • doubled three times in the last three centuries • about 6.1 billion and may reach 9.3 billion by the year 2050 • improved health and technology have lowered death rates • The history of human population growth Figure 35.8A • The age structure of a population is the proportion of individuals in different age-groups RAPID GROWTH SLOW GROWTH ZERO GROWTH/DECREASE Kenya United States Italy Male Female Male Female Ages 45+ Ages 45+ Ages 15–44 Ages 15–44 Under 15 Percent of population Male Female Under 15 Percent of population Percent of population Also reveals social conditions, status of women Figure 35.9B • The ecological footprint represents the amount of productive land needed to support a nation’s resource needs • The ecological capacity of the world may already be smaller than its ecological footprint • Ecological footprint in relation to ecological capacity Figure 35.8B Per capita CO2 emissions (metric tons of carbon) 0 1 2 3 U.S. China 5 6 5.48 2.65 Japan 2.51 0.29 0 0.5 1 U.S. Russia Japan India 1.5 1.49 China 0.75 Russia India 4 Total CO2 emissions (billion metric tons of carbon) 0.91 0.39 0.32 0.28 • What next? Figure 2.10x