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 – unpredictable spacing, 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

Survivorship Curve: represent # individuals alive at each age Type I: low death rate early in life (humans) Type II: constant death rate over lifespan (squirrels) Type III: high death rate early in life (oysters)

POPULATION PROBLEMS

NO … not that problem … these problems

Components needed know B = number of births I = number of immingrants D = number of deaths E = number of emmigrants b = birth rate d = death rate N = population size r = population growth rate

Change in Population Size dN/dt = B-D t = time Change in population size during time interval Births during time interval Deaths during time interval = -

Calculate population growth rate (r) With emigration and immigration r = (B + I) – (D +E) N0 Without emigration and immigration r = B – D = b - d

Zero Population Growth …

Population Growth Models

Exponential population growth: ideal conditions, population grows rapidly

Exponential Growth Equation

Exponential Growth Problem Sample Problem: A certain population of mice is growing exponentially. The growth rate of the population (r) is 1.3 and the current population size (N) is 2,500 individuals. How many mice are added to the population each year?

Calculating Population of Next Generation(s) … Exponential Growth N1 = N0r + N0 ... repeat until you reach generation of choice Or Nt = N0 (1.00 + r)t ... Where subscript and superscripts = time

Doubling Time – only applies to exponential growth When r is in % form, 70% r When r is in decimal form, 0.7

What is the current population density of Transylvania? SAMPLE PROBLEM: The country of Transylvania contains 2.3 million people (not including vampires) and covers 800,000 square miles. In the year after that last census, there were 111,000 new children born and 109,000 people died. What is the current population density of Transylvania? What is the population growth rate (r)? What will be the population of Transylvania in 25 years? What is the doubling time of Transylvania? Density = 2.9 people/mi2 r = 0.00087 = 0.087% N25 = 2,350,551 doubling time = 805 years

Logistic Model Unlimited resources are rare Incorporates carrying capacity (K) = maximum stable population which can be sustained by environment

Logistic Growth Equation dN/dt = change in population

Calculation of next generation population size - Logistic Growth N1 = N0 + r N0[(K- N0)/K]

Logistic Growth Problem Sample Problem: If a population has a carrying capacity (K) of 900, and the growth rate (r) is 1.1, what will be the population size in generation 1 when the population (N0) is 425? 672

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

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

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

Biotic & abiotic factors  Population fluctuations 1975-1980: peak in wolf numbers 1995: harsh winter weather (deep snow)

Boom-and-bust cycles Predator-prey interactions What do you notice about the lynx and snow hare relationship?

Boom-and-bust cycles Predator-prey interactions Eg. lynx and snowshoe hare on 10-year cycle

Human Population Growth Age-Structure Diagrams

Global Carrying Capacity Current world population = http://www.worldometers.info/ 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 Typical person in U.S. = 10 ha footprint Limitations? Consequences? Solutions?

Map of ecological footprint of countries in the world (proportional sizes shown)