Population Ecology The factors and interactions that affect population size

How do we study populations? Key Terms Demography - study of human populations Density - number of individuals per unit area Dispersion - relative arrangement of individuals within a given amount of space

Population Density of U.S.

Dispersion There are 3 types:

Dispersion

How do we study populations? Growth Rates Growth Rate : change in population over time Positive (+): birth rate > death rate Zero (0): birth rate = death rate Negative (-) = birth rate < death rate Fertility Rate: The average number of offspring a female has in its lifetime Replacement Rate : each mating couple has two offspring that survive to reproduce, replacing their parents.

Reproductive Potential Maximum number of offspring each member of a population can produce Increases when members reproduce often and earlier in their reproductive life Generation time - time it takes for an average member of a population to reproduce. Human Generation time: 20 years E.Coli Generation time: 17 minutes

Population Growth Curves

Exponential Growth Increase in population size due to a constant growth rate Unlimited resources Ideal conditions “J” curve

Logistic Growth Population growth slows or stops following a period of exponential growth Birth rate decreases, Death rate increases OR Both “S curve”

Carrying Capacity (K) The maximum amount of individuals an environment can support What happens to growth rate as it approaches K?

Reaching Carrying Capacity

Logistic Growth- “Overshoot” rewild.info

Limiting Factors Pair and Share (2 min): What factors would cause a population’s size to increase ? What factors would cause a population’s size to decrease ?

Limiting Factors Food Water Sunlight (producers) Space Disease Competition Predation

Limiting Populations Density-Dependent Deaths occur more quickly in a more crowded environment Limited resources Disease Density-Independent Size of population does not matter; Deaths occur independently of population density Ex: natural disasters

If humans have no natural predators, how is our population controlled?

Human Carrying Capacity? Current human population: approx 7.12 billion people Ranges estimated from 4-16 billion people Hard to estimate how many people this world can hold Technological innovations Medical breakthroughs

What sparked our growth? Industrial Revolution (~1750) Modern medicine (20 th century) Death rates DROPPED due to better care Agricultural Advances Transportation Advances

Human Population Growth Population (in billions) Year Years elapsed between milestones Source: U.S. Census Bureau- World POPclock Projection

What takes us out? Pair and Share (2 min): Humans are at the top of any food web resulting in no natural predators to keep our populations in check… 1.What are the limiting factors of the human population? 2.How are we different than other species in regards to population control?

What’s our limiting factor? Disease: Bubonic Plague, AIDS, Flu, Malaria Access to food Access to clean water Competition (a.k.a. War)

EventCasualties American War Deaths, all-time600,000 India Famine ( )3,000,000 AIDS deaths in 20111,700,000 Influenza Epidemic (1918)21,000,000 Indonesian Tsunami/Earthquake (2004) 230,000 Bubonic Plague ( )75,000,000