I. Population Characteristics 1.Population size = the number of individual organisms present at a given time 2.Population density = the number of individuals in a population per unit area a.Varies by species: Large organisms=low density b.High isn’t always bad 3.Population Growth a.Crude birth (death) rates: number of births (deaths) per 1000 individuals per year b.Natural Rate of Increase:(crude birth rate) – (crude death rate)/10 c.Fertility Rate: average # of children born per women

I. Population Characteristics Sex Ratio

II. Patterns of Populations a.Type I: more deaths at older ages b.Type II: equal number of deaths at all ages c.Type III: more deaths at young ages 1. Survivorship curves: likelihood of death varies with age

II. Patterns of Populations 2. Exponential Growth a.J-Curve b.Occurs in nature with: small populations, low competition, ideal (productive) conditions. c.Continues until population is limited. d.Example: Eurasian collared dove

II. Patterns of Populations 3. Logistic Growth a.Carrying capacity = maximum population size an environment can sustain b.Limiting factors slow and stop exponential growth c.Create S-shaped logistic growth curve Many factors contribute a population’s growth rate and carrying capacity

II. Patterns of Populations 4. Reality does not always fit the curve

Visualize Bust & Boom

III. Reproductive strategies vary among species 1)K-selected species a.Stabilize at or near carrying capacity b.Good competitors c.Long lived species with few offspring 2)r-selected species a.Often boom and bust – populations fluctuate widely b.Little parental care c.Often short lived and reproduce quickly d.Weedy species Think of 4 examples of each species type

Human Populations  Are we too large or have we reached our carrying capacity?  What lessons are there for us in ecosystems?  What are the consequences of such a large human population?

Record your impressions after the clips…