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Natural Selection and Species Interactions

“Nature has given women so much power….” - Samuel Johnson

The Great Leap Forward• Starting in 1958, Mao Zedong, leader of the

Communist Party of China, initiated a series of policies to transform the country into a modern, industrialized, communist society.

• One of the first actions taken was known as the Four Pests Campaign. ❖ This campaign sought to eliminate rats,

flies, mosquitoes, and sparrows.

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The Four Pests Campaign ~ Sparrows…

• Masses of people were mobilized to eradicate the Eurasian Tree Sparrow.

• Tactics included: ❖ Banging pots and pans,

preventing the birds from landing, until they were exhausted.

❖ Tearing down nests. ❖ Shooting them from the sky

using guns and sling shots.

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“Everyone come and fight sparrows.”

• The sparrows were hunted because they ate grain seeds; reducing crop yields.

• MILLIONS of sparrows were eradicated.

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In Addition to the Four Pests Campaign

• The government made a series of other poor agricultural decisions at this time, including: ❖ Ordering farmers to increase the density of

their planting by 6 times, believing that the same species of plant would compete with itself.

❖ Deeper plowing of the soil, which brought up sand and rocks instead of more topsoil.

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• By April of 1960, Chinese leaders came to realize that the sparrows also ate a large number of pest insects, including locusts.

• At the same time, peasants and labour were celebrating that they had followed the government’s desires and killed all the birds.

• Unbeknownst to them, they had created one of the worst disasters in history…

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The Great Famine

• The locust plague, overplanting, and overplowing combined with a severe drought.

• The number of victims is unknown, but estimated between 20 - 43 million!!

•Hmmmm…who knows the population of Canada?

•Which of the above contributing factors to this human disaster was natural? Which was due to human actions?

•SOMEbody must have been absent for the ECOSYSTEM unit!!

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Remember the Law of Unintended Consequence?

• The locust plague, overplanting, and overplowing combined with a severe drought.

• Number of Chinese who died of starvation in 4 years is estimated to be between 36 - 45 million!!

•Hmmmm…who knows the population of Canada?

•Which of the above contributing factors to this human disaster was natural? Which was due to human actions?

•SOMEbody making policy must have been absent for the ECOSYSTEM unit!!

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ECOSYSTEMS: EvErYtHiNg is CoNnEcTeD!

• Components of an ecosystem: ❖ Biotic Factors – Living and once

living parts of an ecosystem. - Ex: Plants, animals, dead

matter, waste ❖ Abiotic Factors – Nonliving parts

of an ecosystem. - Ex: Water, rocks, light, climate

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• An ecosystem is all of the organisms living in an area.

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Organization of Life and the Environment• Organism – An individual of a particular species.

• Species – A group of organisms able to breed fertile offspring.

• Population - All members of a species that live in the same area at the same time.

• Biological Community - All populations living and interacting in an area.

• Ecosystem - A biological community (biotic) and its physical environment (abiotic).

• Biome - Large geographic location determined by the climate and soil type.

• Biosphere – All ecosystems in the entire Earth.

Ecosystem Organization

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What lives where, and why?

• Habitat - Set of environmental conditions in which a particular organism lives.

• Critical Factor - Single factor that is the most critical in determining how species are distributed – who lives in what habitat.

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Tolerance Limits

❖Tolerance Limits - Minimum and maximum levels beyond which a particular species cannot survive or reproduce.

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Ecological Niche

• Ecological Niche - Description of role played by a

species in a biological community.

➢Predator/prey ➢Herbivore/omnivore ➢Nocturnal/diural

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Specific Types of Niches

• Opportunistic Species - Quickly appear when any opening in an ecosystem arises. ❖ Many weeds.

• Pioneer Species – Able to quickly colonize new ground where nothing else is growing.

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Types of Niches

• Keystone Species - A species whose impact on its ecosystem is especially large and influential.

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SPECIES INTERACTIONS

• Predator-Prey ❖ Any organism that feeds directly on another

living organism is termed a predator. - The organism that is eaten is the prey.

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Competition

• Intraspecific - Competition among members of the same species. ❖ Dispersal

- Seeds sent far away from parent ❖ Territoriality

- Each individual defends part of ecosystem ❖ Resource Partitioning

- Adults and larvae eat different foods ➢Ex: Caterpillars and butterflies

• Interspecific - Competition between members of different species.

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Resource Partitioning

• -

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Symbiosis

• Symbiosis - Intimate living together of members of two or more species. ❖ Commensalism - One member benefits

while other is neither benefited nor harmed.

❖ Mutualism - Both members benefit.

❖ Parasitism - One member benefits at the expense of other.

Example of Symbiosis

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• Barnacles create homes by attaching themselves to whales. The whales are unaffected.

Example of Symbiosis

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• Clownfish have a mucus coating that allows them to live in sea anemones. Their presence attracts other fish for the anemone to eat.

Example of Symbiosis

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• As bison walk through grass, insects are disturbed and fly away. They are eaten by cowbirds.

Example of Symbiosis

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• Ostriches and gazelles feed next to each other. Ostriches have excellent eyesight, while gazelles have stronger senses of hearing and smell.

Example of Symbiosis

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• Mistletoe extracts water and nutrients from the spruce tree directly.

What Type of Symbiotic Relationship?

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Distribution of Species

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POPULATION DYNAMICS

• Population Growth ❖ Studies of population growth are based on

the idea of biotic potential. ❖ Biotic Potential - Potential of a population

to grow in the absence of limitations.

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Exponential Growth

• Exponential growth is graphed as a J curve. ❖ Carrying Capacity - Number of individuals

that can be indefinitely supported in a given area.

- Overshoot - When a population surpasses the carrying capacity of its environment.

- Dieback – Population experiences a sudden steep drop.

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Population Oscillations

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Growth to a Stable Population

• Logistic Growth - Growth occurs more slowly as the population approaches carrying capacity due to environmental resistance.

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Limiting Factors

• Environmental Resistance ❖ Any factor that slows the growth of a

population. ❖ Density-Dependent Factors – Most likely

to affect dense populations. - Disease, Stress, Predation

❖ Density-Independent Factors – Affects dense and diffuse populations evenly.

- Changes in climate, natural disasters

Population Growth Strategies

• There are two main types of growth strategies: ❖ K-strategists focus on long-term

development and a long life. - Ideal for stable, predictable

environments. ❖ R-strategists focus on reproducing as

much and as quickly as possible. - Ideal for risky, unstable environments.

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(K) Strategies

• Long life • Slower growth • Late maturity • Fewer large offspring • High parental care

and protection • High investment in

individual offspring

• Adapted to stable environment

• Later stages of succession

• Niche specialists • Predators • Regulated mainly by

intrinsic factors • High trophic level

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(R) Strategies

• Short life • Rapid growth • Early maturity • Many small offspring • Little parental care • Little investment in

individual offspring

• Adapted to unstable environment

• Pioneers, colonizers • Niche generalists • Prey • Regulated mainly by

extrinsic factors • Low trophic level

Type of Strategist?

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Type of Strategist?

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Population Distribution

• spacial arrangement of organisms within an area.

• Clumped (most common) ❖ Individuals cluster together for

protection, assistance, or resource access.

• Uniform ❖ Individuals are evenly spaced

due to territoriality • Random

❖ Individuals live wherever resources are available.