Unit 3 Human Population and Carrying Capacity

Population Dynamicsis the study of how populations change in size, density and age distribution.

Size- total number of individualsDensity- number of individuals in a certain space( spatial distribution)Age distribution- the proportion of individuals of each age in a population

Four Factors affecting Population size?

How do populations increase or decrease?

Immigration: movement of individuals of a species into a country or an area

Emigration: movement of individuals of a species out of a country or area

Natality – birthrate

Mortality- deathrate

Population Change=(Natality+Immigration)-(Mortality+Emigration

Exponential GrowthA population with few or no resource limitations grows exponentially.Rate 1% - 2%Examine the data: starts slowly and gradually increases Invasive speciesWhooping crane p.169

However, this is not true for most populations.

Together biotic potential (essentially how fast they can reproduce without the environment having an impact) and environmental resistance (environmental limits that affect population growth) determine a carrying capacity for a population.

Carrying capacity (K) - the maximum population of a particular species that a given habitat can support.

Fig. 9-4

Logistic Growthinvolves rapid exponential growth followed by a steady decline in population growth until the population size levels off.This occurs because the population encounters environmental resistance and its rate of growth decreases as it approaches the carrying capacity.After leveling off, the population fluctuates slightly above and below the carrying capacity.

Fig. 9-5

Overshoot- when organisms use up their resources and temporarily exceed their carrying capacity

This happens because of a reproductive time lag: the period needed for the birthrate to drop and the deathrate to rise as a result of resource overconsumption.

Fig. 9-6

A dieback or crash occurs unless a switch to an alternate resources or leaves the area.Reindeer introduced on an island in Alaska had no alternate resource and the death of the herd.

Limiting Factor -when a particular condition or factor can be identified as a key component that limits the size of a population.

Air, water, nutrients, food, shelter, etc.

There are four categories of limiting factors:

What limits population growth?

1. Availability of Raw Materials

Plants need nitrogen and magnesium from the soil as raw materials to manufacture chlorophyll.

Adding fertilizer to the soil is a way of preventing nitrogen from being a limiting factor.

2. Availability of Energy

Plants require energy from sunlight.Animals require food energy.

Food webs can be changed.

3. Accumulation of Waste Products

commonly a limiting factor for bacteria and organisms that live in small ecosystems such as puddles, pools and petri dishes.not a limiting factor for most organisms

4. Interactions among Organisms

Since cottontail rabbits and white tailed deer eat the twigs of many species of small trees, they have a limiting effect on the size of some tree populations.

Parasites and predators cause the premature death of individuals thus limiting the size of the populations.

Factors Affecting Population Size

Fig. 9-3

Types of Population Change curves

stable- fluctuates above and below the carrying capacity

irruptive- a stable population which on occasion will explode or irrupt

cyclic- cyclical fluctuations over a defined period of time

irregular- no order the fluctuations- chaos

Natural Population Curves

Fig. 9-7

Where Might the human population be on this growth curve?

Human population

Video clip : http://www.youtube.com/watch?v=4BbkQiQyaYc

See worksheet: Applying Human Populations