Thursday Sept 12/Friday Sept 13

AGENDA• Stamp and review homework• Activity: Interactions Among Organisms• Notes: Populations in EcosystemsHOMEWORK• Read pg 119-127• Complete Population Growth Activity• Begin Test Review. Complete #1-24

Populations in Ecosystems•Growth of Populations

•Long-Term Survival of Species•Impact of Environmental Change

•Populations Respond to External Factors

A group of the same kind of organism that lives in the same

place is called a ….

POPULATION

CHARACTERISTICS OF POPULATIONSThree important characteristics of a population

are its:• Geographic distribution or range.

• Population density – the number of individuals per unit area.

• Growth rate

Density• Number of individuals __per unit area_____• Varies depending on species and its ecosystem US Population Density 1990

High or Low Density?

High or Low Density?

POPULATION GROWTH

Three factors can affect population size:• The number of ___births___• The number of deaths.• The number of individuals that enter or leave

the population.

A population can grow when its birthrate is greater than its __death rate_____.

Exponential Growth• Under ideal conditions with unlimited resources, a population will grow exponentially_____.

• Exponential growth occurs when the individuals in a population reproduce at a constant rate.

• The population becomes LARGER and LARGER until it approaches an infinitely large size.

Turn to the person next to you and explain how the two graphs are similar OR different?

Exponential Growth

Do populations really grow EXPONENTIALLY??

Can populations continue to grow exponentially forever?

What do you think?

Answer…..is….NO!!

• As resources become less available, the growth of a population slows or __stops__.

• The result looks more like the S-Shaped graph

Logistic Growth

Carrying Capacity

• The environment can only HOLD or __CARRY__so many individuals

• Largest number of individuals that a given environment can support =

__Carrying Capacity__

What Limits Growth of a Population?

LIMITING FACTORS

Factor that causes population growth to DECREASE

Density Dependent Limiting Factors

• Density-dependent factors operate only when a population is large and dense.

• Examples:• competition• predation• parasitism• disease

Density Independent Limiting Factors

• Density-independent affect all populations in a given area in similar ways, regardless of the _____population size_________.

• Examples:• unusual weather like droughts• natural disasters like hurricanes, forest fire• seasonal cycles• certain human activities

What is Environmental Stability?

How do ecosystems maintain stability despite constant limiting

factors?

What is ecosystem stability?• The vast majority of natural ecosystems

experience regular environmental change, or disturbances.

• Most ecologists describe ecosystem stability as the ability of an ecosystem to maintain its structure and function over long periods of time despite disturbances.

How do Ecosystems maintain stability with all of these limiting

factors?

BiodiversityBiodiversity

• The sum total of the genetically based variety of all the organisms in the biosphere is called biodiversity.

• Biodiversity______ is one of our greatest

natural resources. Species of many kinds have provided us with many foods, industrial products, and medicines.

• Populations have become __adapted__ to live in specific conditions as a result of their environment.

• For Example:– Desert cacti– Palm trees– Snow Owls

Environmental AdaptationsEnvironmental Adaptations

What threatens BIODIVERSITY and ECOSYSTEM STABILITY?

Threats to BiodiversityThreats to Biodiversity

• __Human activities____ can cause decreases in the amount of biodiversity by:– Habitat alteration -- Pollution– Improper hunting --Introduced species

Introduced SpeciesIntroduced Species• Throughout history humans have

transported apparently harmless plants or animals which have become invasive in a

new habitat_______

• Invasive species (also called exotic species or nonnative species) are those that rapidly increase their populations due to lack of natural predators and/or parasites thereby giving it an advantage over native species.

ASIAN CARP INVASION!!!!!!

http://abcnews.go.com/Nightline/video/beware-asian-carp-invasion-12329740

• Changing environmental conditions can cause the decline of local __biodiversity___.

• Ecosystems that are ___less stable__

may not be able to respond to a normal environmental disturbance.

How does environmental change affect ecosystem stability?

How does natural environmental change affect ecosystem stability?

• Fires, heavy storms, and natural climate change can cause major changes in local populations of plants and animals.

• A decline in natural biodiversity can make an ecosystem less stable.

• How will the Earth’s increasing average temperatures affect ecosystem structures and functions?

• Scientists are not yet sure how predicted changes in global climate within the next several decades will affect ecosystem stability worldwide.

Something to think about for the future….