Bell Ringer Turn in Biome Chart A nearby high school is closing, and all their students will be coming to your high school. What will be different about your school with the addition of all these new students?

Populations

Growing Populations Increases in general populations can put stresses on resources Which resources do we protect and consume? Abundance or scarcity of food sources? Disruption of ecological systems?

Population Ecology A population is a group of members of the same species defined by geographic boundaries Population dynamics help ecologists understand how a population may grow or decline.

Population Dynamics Size - # of organisms Density - # of individuals with a population per unit area 1. High population density 2. Low population density

Population Distribution/Dispersion Spatial arrangement. 1. Random = no pattern. 2. Uniform = Evenly spaced 3. Clumped = In groups

Random Sampling Estimate the size of a population Impossible to count every organism in a given population

Population Dynamics Sex Ratios – Proportion of males to females Age Structure/Age pyramids – relative numbers of organisms of each age within a population a. Pre-reproductive b. Reproductive c. Post-reproductive

Survivorship Curves – Plot the proportion of individuals alive at each age

What limits population growth? Births Deaths Immigration Emigration Population change = (b + i) – (d + e)

Populations (r) = growth rate 2 models of population growth: 1) Exponential growth: assumes ‘r’ stays constant 2) Logistic growth: as popns grow, resources diminish

Exponential population growth Under ideal conditions, a population grows rapidly (J-shaped curve)

Logistic Population Growth Unlimited resources are rare, so populations tend to level out. S-shaped curve

3 Phases in Logistic Growth Carrying Capacity The maximum stable population size a particular environment can support Occurs when Birth rate = Death rate Limited by density-dependent factors

2 Types of Life Histories Strategies 1. K-strategists: organisms live and reproduce around K, and are sensitive to population density 2. R-strategists: organisms exhibit high rates of reproduction and live in unstable environments in which population densities fluctuate

K Selected - Equilibrial R Selected - Opportunistic  Long life span  Long maturation time  Low death rate  Few offspring  Several reproductions per lifetime  Extensive parental care  Usually in stable, predictable environments  Good competitors  Ex: tigers, whales, elephants  Short lifespan  Short maturation time  High death rate  Usually one reproduction/lifetime  Many offspring  No parental care  Temporary large populations followed by crashes  Unpredictable changing environments  Ex: insects, bacteria 2 Types of Life Histories Strategies

Humans: R or K? From beginning to 1350 AD, humans experienced logistic growth But agriculture (food surplus), medicine, and technology expanded carrying capacity Eventually, damage to planet will decrease carrying capacity and slow human growth leading to environmental, health, food & social changes.

Human Population Growth