# Intro to Chapter 16 – Human pops

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Intro to Chapter 16 – Human pops
Population Ecology (chapter sect 3 and 4) Intro to Chapter 16 – Human pops Each population has A Density A Dispersion A Reproductive Strategy

Population A group of the same species of organism living in the same place Understand food chains and food webs What might effect the survival of THIS group of dolphins?

Characteristics of Populations
4 Major Characteristics of Populations: Geographic Distribution Density Growth Rate Age Structure

1. Geographic Distribution
Area inhabited by a population *remember, there are also ecological equivalents in similar ecosystems around the planet, but if they are not in the same habitat, they are NOT the same population!

Population dispersion
Way in which individuals of a population are spread in an area or a volume 3 types: Dispersion patterns -- page 437 in textbook Clumped Uniform Random

2. Population Density # of individuals in population per unit area
(# individuals) / (area) Varies depending on species in ecosystem Increase density = increase crowdedness

Example: 150 bullfrogs live in a pond that covers an area of 3 square kilometers. What is the bullfrog’s population density?

Answer: 50 bullfrogs per square kilometer

3. Growth Rate How fast a population is growing/shrinking

Negative & Positive Growth
Positive growth: net increase Total penguin population was 1200 at the beginning of the year, now is 1600. Negative growth: net decrease 250 penguin chicks died during the year.

Biotic Potential The maximum rate at which the population of a given species can increase when there are no limits on its growth. “living” potential It is not possible for a population to increase FOREVER – there are limitations!

Factors affecting population growth
Immigration: movement into an area Emigration: movement out of an area ***approach maturity & move out ***shortage of resources Birth Rate Change in # births Death Rate Change in # deaths ***increase/decrease birth & death rates ***birth = death?

Types of Population Growth
Exponential Growth Logistic Growth

1. Exponential Growth J-shaped curve reproduce at a constant rate
Slowly at first, then larger until approaches infinitely large size. ideal conditions unlimited resources

2. Logistic Growth S-shaped curve Carrying Capacity- How could growth
Slow increase, larger increase when large number of resources, then slows when resources become less available, growth slows/stops, oscillates around carrying capacity. Carrying Capacity- largest # individuals environment can support Tells size of population when average growth rate reaches zero. How could growth slow or stop?

How population growth may slow:
Birth rate decreases Death Rate Increases Both occur at the same rate Reason why these change  Limiting factors

Limiting Factors causes population growth to decrease

1. Density Independent Factors
Do not depend on population size Ex: Unusual weather natural disasters seasonal cycles damming rivers clear-cutting forests

2. Density-Dependent Factors
depends on population size. Competition Predation Parasites Diseases Competition Predation Parasites Diseases larger populations are more affected by density-dependent factors (orgs are closer together)

Application Q1: Think about the black racer snake populations in Georgia. Once a pair of mice start reproducing, what would happen to the black racer snake populations, and why?

Answer They will increase because there will be more mice to feed them. Q2: If the mice population dies off, what would happen to the snake populations, and why?

Answer: The snake populations would decrease, because there would be fewer mice to eat. GRAPH this senario! What is the GENERAL shape and height of each curve shown…

Below is called a TRACKING GRAPH – because the peaks of the predators always follow the peaks of the prey

2a. Competition compete for resources when population becomes overcrowded. I only have 5 bottles left

Types of Competition Interspecific Intraspecific

Interspecific Competition
Competition between different species for the same resources. wildebeast and rhino vultures and hyenas

Intraspecific Competition
Competition between members of same species for similar resources. herons lions Bunchgrass in Mojave Desert – roots compete

1b. Parasitism and Disease
Parasite or disease-causing organism takes nourishment from host, weakens/kills host spreads quicker w/ greater density. Wasp Cocoons This larval sphinx moth has been attacked by a parasitic wasp. The wasp inserted its eggs beneath the moth’s skin. After hatching, the wasp larvae fed on their host internally until they appeared as white cocoons on its back.

1c. Predation Predator-prey interactions
Increase prey, increase predator

Demography Study of human population growth characteristics
Looks at growth rate, age structure, geographic distribution Can tell if pop is growing by looking at the difference between the birth rate and the death rate In US, death rate is declining, life expectancy is increasing, fertility rate is decreasing – WHY?

Age-Structure diagrams or Population Pyramids
Describes how many individuals of different ages make up a population Population Pyramids, or Age-Structure Diagrams, show age structure in a population. Populations with large numbers of young offspring have greater potential for rapid growth

Comparing Human Populations…
Expansive Constrictive Near Stationary

Patterns of Population Growth…
The Demographic transition- A change in a population from high birth and death rates to low birth and death rates.

Human Population on Earth
Thomas Malthus – economist, late 1700’s *wrote an essay that stated that human population was growing faster than the Earth’s resource could support Today’s human population exceeds 6 billion…

Human Population -- predictions

Carrying capacity and humans
Carrying capacity for human pop has changed due to technology Due to improvements in: Agriculture, transportation, medicine, sanitation

Nonrenewable vs. renewable resources
Nonrewable – used faster than they form ex. Coal and oil Renewable – cannot be used up or can replentish themselves over time ex. Wind energy If not used carefully, renewable COULD become nonrenewable Ex. Water – pollution often makes it unusable

U.S. uses more resources and produces more waste….
Than any other country on the planet ex. 230 million tons of garbage/year (4.2 lbs per person per day) Ecological footprint: The amount of land necessary to produce and maintain enough food and water, shelter, energy, and waste Depends on: amount and efficiency of resource use, and the amount and toxicity of waste produced See textbook page 487 for world view