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Population Structure. I. Population Characteristics. Population size = the number of individual organisms present at a given time Population density = the number of individuals in a population per unit area Varies by species: Large organisms=low density High isn’t always bad
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I. Population Characteristics • Population size = the number of individual organisms present at a given time • Population density = the number of individuals in a population per unit area • Varies by species: Large organisms=low density • High isn’t always bad • Population Growth • Crude birth (death) rates: number of births (deaths) per 1000 individuals per year • Natural Rate of Increase:(crude birth rate) – (crude death rate)/10 • Fertility Rate: average # of children born per women
I. Population Characteristics Sex Ratio
II. Patterns of Populations 1. Survivorship curves: likelihood of death varies with age Type I: more deaths at older ages Type II: equal number of deaths at all ages Type III: more deaths at young ages
II. Patterns of Populations 2. Exponential Growth • J-Curve • Occurs in nature with: small populations, low competition, ideal (productive) conditions. • Continues until population is limited. • Example: Eurasian collared dove
II. Patterns of Populations Many factors contribute a population’s growth rate and carrying capacity 3. Logistic Growth Carrying capacity = maximum population size an environment can sustain Limiting factors slow and stop exponential growth Create S-shaped logistic growth curve
II. Patterns of Populations 4. Reality does not always fit the curve
III. Reproductive strategies vary among species Think of 4 examples of each species type • K-selected species • Stabilize at or near carrying capacity • Good competitors • Long lived species with few offspring • r-selected species • Often boom and bust – populations fluctuate widely • Little parental care • Often short lived and reproduce quickly • Weedy species
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?
