Ch. 53 Warm-Up (Review) Sketch an exponential population growth curve and a logistic population growth curve. What is an ecological footprint? What are ways that you can reduce your ecological footprint? Define: Demography Semelparity Iteroparity Carrying capacity Exponential growth curve Logistic growth curve K-selection r-selection Ecological footprint
Chapter 53 Population Ecology
Introduction Population = group of individuals of a single species living in same general area Density: # individuals / area Dispersion: pattern of spacing between individuals
Determining population size and density: Count every individual Random sampling Mark-recapture method
Patterns of Dispersal: Clumped – most common; near required resource Uniform – usually antagonistic interactions Random – not common in nature
Demography: the study of vital statistics that affect population size Additions occur through birth, and subtractions occur through death. Life table : age-specific summary of the survival pattern of a population Represent data with a survivorship curve. Plot # of individuals in a cohort still alive at each age.
Life Table
Survivorship Curves: Type I curve: low death rate early in life (humans) Type II curve: constant death rate over lifespan (squirrels) Type III curve: high death rate early in life (oysters)
Life History: traits that affect an organism’s schedule of reproduction and survival 3 Variables: Age of sexual maturation How often organism reproduces # offspring during each event Note: These traits are evolutionary outcomes, not conscious decisions by organisms
Semelparity Big-bang reproduction Many offspring produced at once Individual often dies afterwards Less stable environments Agave Plant
Iteroparity Repeated reproduction Few, but large offspring More stable environments Lizard Critical factors: survival rate of offspring and repeated reproduction when resources are limited
Change in Population Size N/t = B-D N = population size t = time Change in population size during time interval Births during time interval Deaths during time interval = -
Zero population growth: B = D Exponential population growth: ideal conditions, population grows rapidly
Unlimited resources are rare Logistic model: incorporates carrying capacity (K) K = maximum stable population which can be sustained by environment dN/dt = rmax((K-N)/K) S-shaped curve
Laboratory Populations
Factors that limit population growth: Density-Dependent factors: population matters i.e. Predation, disease, competition, territoriality, waste accumulation, physiological factors Density-Independent factors: population not a factor i.e. Natural disasters: fire, flood, weather
K-selection r-selection K-selection: pop. close to carrying capacity r-selection: maximize reproductive success K-selection r-selection Live around K Exponential growth High prenatal care Little or no care Low birth numbers High birth numbers Good survival of young Poor survival of young Density-dependent Density independent ie. Humans ie. cockroaches
Populations fluctuate due to biotic and abiotic factors 1975-1980: peak in wolf numbers 1995: harsh winter weather (deep snow)
What do you notice about the population cycles of the showshoe hare and lynx?
Boom-and-bust cycles Predator-prey interactions Eg. lynx and snowshoe hare on 10-year cycle
Human Population Growth 2 configurations for a stable human population (zero population growth): High birth / high death Low birth / low death Demographic transition: occurs when population goes from A B
Age-Structure Diagrams
Global Carrying Capacity UN predicts: 7.8 to 10.8 billion people by the year 2050 2012 = 7 billion Estimated carrying capacity = 10-15 billion? Ecological footprint: total land + water area needed for all the resources a person consumes in a pop. 1.7 hectares (ha)/person is sustainable U.S.: 10 ha/person over K?? Limitations? Consequences? Solutions?
Map of ecological footprint of countries in the world (proportional sizes shown)