Chapter 5 Populations

5.1 How Populations Grow Describing Population Geographic Range: area inhabited Density and Distribution: Population Density - # of individuals per unit area Distribution – individual spacing in a population (random, uniformly, clumping Wild Flowers King Penguin Striped Catfish Growth Rate: size of population over time (increase, decrease, stay the same) Age Structure: # and age of males/females

Population Growth Birthrate & Death Rate: influence whether pop grows, stay the same or decreases Immigration: moving into range (increased good supply) Emigration: moving out of range (food shortage)

Exponential Growth: occurs with unlimited resources; # of offspring increases with each new generation Organisms that reproduce rapidly : (bacteria reproduce very 20 minutes) J–curve: slow growth first then faster Organisms that reproduce slowly: Organisms in new environment: (invasive species: no natural predators)

Logistic Growth Phases of Growth: Phase1: Exponential w/initial unlimited resources (few die; many reproducing) Phase 2. Slows: pop. grows at slower rate Phase 3. Stops: zero growth rate (curve levels off; pop. can remain here indefinitely)

Logistic Growth Curve: S-shaped curve Exponential growth slows, then stops Decreased birthrate; increased death rate Decreased immigration; increased emigration

Carrying Capacity: Max # of species individuals environment can support Birthrate = death rate; immigration = emigration Slight pop. change over time; stabilizes at that approx #

5.2 Limits to Growth Limiting Factors: (ie: limiting nutrient controls productivity) Control the growth of populations Determines carrying capacity of envirnmt for species Shaped history of life on earth (Darwin)

Density Dependent Limiting Factors Operate when # of org/unit area reach certain level Competition: for limited essential resources w/ pop Within species: some thrive/reproduce; some starve (can lower birthrate/increase death rate) Between diff species: can drive evolutionary change

Predation and Herbivory: Predator-prey Relationships Pop. cycle up or down (or fluctuate) over time Isle Royal: Wolves and moose Herbivore Effects: herbivores/plants pop. also fluctuate Isle Royale: Moose and Balsam Fir (overgrazing) Humans as Predators Cod birthrate can’t keep up w/Hi death rate Biologists use birthrate/age structure data est. limits

Parasitism and Disease: Both weaken/kill host; spread easier w/high population Isle Royale Canine Parvovirus left 3 breeding females Stress from overcrowding: Too much fighting: ↓ birthrates, ↑ death/emigration CPV is life threatening and can affect the heart or intestinal tract with symptoms of vomiting/ diarrhea

Density-Independent Limiting Factors: Unusual weather/natl disasters affect all pops similarly Hurricanes, floods/wildfires Can cause pop to “crash” (be decimated) then rebound True Density Independence? Moose pop exploded after CPV – pop crashed with harsh winter=effects greater w/unnaturally dense pop Controlling Introduced Species Artificial measures (removal) temporary/expensive Best to find/introduce natural predator=sterilize for minimal adverse effects

5.3 Human Population Growth Historical Overview: Slow past growth w/limiting factors: scarce food/predators/disease=↑ death rate=multiple offspring w/few surviving Exponential Human Population Growth Industrial revolution improved nutrition/medicine = ↓ death rates w/birthrates remaining hi The Prediction of Malthus Exponential growth can’t last Growth limited by competition-war; scarce resources-famine; parasitism-disease Density Dependent Limiting Factors World Population Growth Slows Exponential Growth through mid-sixties; then slowed

Patterns of Human Population Growth Demography: study of human growth (birth/death rates and age structure) The Demographic Transition Shift from High birth/death rates (Phase 1) to low birth/death rates (Phase 3) = U.S, Japan, Europe; J to S curve Age Structure and Population Growth A higher % of young people = growing population; equal age group # = slower, steady growth Future Population Growth Approx. 9 billion by 2050; but grow more slowly than last 50 years