Ch. 14 Interactions in Ecosystems

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14.1 Habitat vs. Niche

Habitat – all biotic and abiotic factors where an organism lives

– WHERE a species lives

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Ecological Niche

All physical, chemical, and biological factors needed to:

– Stay alive

– Stay healthy

– Reproduce

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Ecological Niche

Can be described in terms of:

– Space utilization

– Food consumption

– Where it fits in the food web

– When it’s active

– Temperature range

– Moisture requirements

– Mating requirements

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Ecological Niche

Role of particular species in ecosystem – Its “job”

The impact of its presence

How an organism lives within its habitat

NOT WHERE it lives 5

Resources to Survive

Organisms must have:

– Food

– Shelter

– Water

Birds of Paradise

5 min

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Competition

When two species must use same resources

– Food

– Living space

– Light

– Water

– Mates

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Competitive Exclusion

If two species are competing, the one that uses the resource(s) most efficiently will eventually eliminate the other

– One eliminated:

New niche

Become extinct

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Niche Partitioning

When a niche is divided

– Animals stay in only part of area even though they could live in any of it

– Avoids competition

Ex: Bees and butterflies Both use flowers for food

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Warbler Niche Partitioning

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Ecological Equivalents

Species that occupy similar niches but live in different areas

– Ex: Poison dart frog of South America and mantella frog of Madagascar

– Both:

Bright, poisonous, live in similar habitats, eat similar insects

DON’T compete bc live in different areas of world

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14.2 Community Interactions

Competition Two species use same resources

Predation – one organism captures and feeds on another

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Predator – Prey Relationships

Predator

– Organism that kills for food

Prey

– Organism eaten

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Competition

1) interspecific – between 2 different species

– Ex: dandelions and grass

2) intraspecific – within same species

– Ex: male birds

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Symbiotic Relationships

Symbiosis

– Different organisms living in close, long term relationship

Types:

– Mutualism

– Commensalism

– Parasitism

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Mutualism

Both benefit

Animal partnerships 4:20

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Mutualism

Ex: Ants and aphids

– Aphids suck fluid (honeydew) from plants

– Ants “milk” aphids; use honeydew as food

– Ants protect aphids

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Commensalism

One benefits , one unaffected

Ex:

– Demodicids (mites) in eyelashes

– The Unknown Micro World 7 min

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Commensalism

Ex:

– Sea anemone

Tentacles are poisonous

– Clown fish

Protection; not bothered by poison

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Parasitism

One benefits = parasite

One loses = host

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Parasitism

Most parasites do not kill their host

– Why not?

Ex: wasp and caterpillar

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Parasitism

2 types:

– Ectoparasite – live on outside of host

Ex: leeches, ticks, fleas

– Endoparasite – lives on inside of host

Ex: tapeworms, hookworms

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14.3 Population Density

Number of individuals in a defined space

= # of individuals

area (units2)

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Population Dispersion

How individuals within a population are spread in an area

3 types:

– 1) clumped

– 2) uniform

– 3) random

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1) Clumped

Live close together

– Helps with:

Mating

Protection

Food resources

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2) Uniform

Live at specific distances

Due to competition:

– for territory

– Between species

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3) Random

Spread out with no clear pattern

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Survivorship Curve

Diagram that shows # of survivors of a group over time

Ex: All the people born in 1920

– Track until all die

– Plot data

3 Types:

– I

– II

– III

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Type I

Large mammals

– Humans

Most survive until old age

Need parental care

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Type II

All ages survive at ~ equal rate

Ex:

– Birds

– Small mammals

– Some reptiles

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Type III

High birth rate and infant mortality rate

– Few survive until adulthood

Ex:

– Invertebrates

– Fish

– Amphibians

– Plants

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14.4 Demography

Statistical study of populations

Demographer

– Studies composition of a population

– Predicts changes in size

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Demography

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Demographics

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Population Growth Rate

Growth

– More born than die

Decline

– More die or leave than born

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Population Changes

Immigration – individuals move into an area

Emigration – individuals move out of an area

Birth

Death 36

Population Growth Curves Graph – Change in population over time

Y-axis = Population

X-axis = Time (generations)

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Exponential Growth

Population increases dramatically in short time – Resembles “J”

shape

– Ex: rabbits in Australia 24 brought for sport

hunting

Now over 200 million

Australian Rabbits 2:46 38

Carrying Capacity

Max population an environment can support

– Cannot grow unchecked

Limited by:

– Predators

– Disease

– Resources

– Population density

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Logistic Growth

Population held in check: – Resembles “S”

shape

– Carrying capacity represented

Takes into account declining resources

How most populations grow

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Logistic Growth

Carrying Capacity:

– If Below

rate is rapid

– If Near

rate slows

– If above

rate falls

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Population Crash

Dramatic decline in short time

Ex. of Causes:

– Food

– Disease

– War

Ex: Reindeer on St. Matthew Island, AK

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Limiting Factor

Factor w greatest effect of keeping population down

2 types:

– Density-dependent

– Density-independent

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Invasive Species

Do not belong

– Not native

– Exotics

– Have not developed relationships over long periods of time

Problems!

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Density-dependent

Affected by # of individuals in area

– More crowded can lead to more problems

Ex:

– Competition

– Predation

– Parasitism

– Disease 45

Density-independent

Parts that limit population growth regardless of population density

Ex:

– Unusual weather

– Natural disasters

– Human activities

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14.5 Succession

Sequence of biotic changes

– Regenerate damaged community

– Creates new community in a previously uninhabited area Ex: Hawaii

– Regular progression of species replacement

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Succession

Forms new habitats

Occurs after:

– Forest fires

– Volcano eruptions

– Glacier recedes

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Primary Succession

Primary succession

– Occurs in habitat previously uninhabited

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Primary Succession

Pioneer Species

– First organisms to live in a previously uninhabited area

“Colonizers”

– Small fast growing plants

– Change the soil over time

Ex: lichens and some mosses

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Secondary Succession

Reestablishment of a damaged ecosystem where soil was left intact – Ex: abandoned field

or forest clearing

Always occurring

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Example of Succession

Glacier Bay, Alaska

Primary succession

– Receding glacier left piles of rocks and gravel

– Pioneer species

Lichens

Moss

Fireweed

Willows

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Glacier Bay Succession

10 years later

– Dead leaves of plants enriched soil

– Alders enter by seed

Nitrogen fixing nodules add nitrogen to the soil

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Glacier Bay Succession

30 years later:

– Willows

– Alders

– Cottonwoods

– Thickets of trees and shrubs

Kill smaller pioneer species

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Glacier Bay Succession

80 years later:

– Sitka spruce invade

Use nitrogen

Form dense forest

Alder dies out (little sunlight)

– Next, Hemlock enter

Shade tolerant

– Stable community formed 55