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Community Structure – spatial arrangement of its individuals and populations. Chapter 8. Community Characteristics. Physical Appearance – relative size, stratification and distribution of its populations and species Species Diversity – number of species

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Chapter 8

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Chapter 8 l.jpg

Community Structure – spatial arrangement of its individuals and populations

Chapter 8


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Community Characteristics

  • Physical Appearance – relative size, stratification and distribution of its populations and species

  • Species Diversity – number of species

  • Species Abundance – numbers of each species

  • Niche Structure – number of ecological niches and how they interact


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Biodiversity

  • Species Diversity – variety of different species

  • Genetic Diversity – variability among individuals within a species

  • Ecological Diversity – variability of ecosystems


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Most Biodiversity

  • Tropical Rain Forests

  • Coral Reefs

  • Deep Sea

  • Large Tropical Lakes


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Factors Affecting Species Diversity

  • Latitude

  • Depth (in aquatic) – species diversity increases from surface to about 2,000 m


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© 2004 Brooks/Cole – Thomson Learning

25

25

Snails

Tube worms

20

20

15

15

Species diversity

10

10

5

5

Coast

Deep Sea

Coast

Deep Sea

0

0

0

2,000

4,000

6,000

0

2,000

4,000

6,000

Depth (meters)

Depth (meters)


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Factors Affecting Species Diversity

  • Pollution (in aquatic) – decrease in diversity and abundance because pollution


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Species diversity increases with….

  • Increasing solar radiation

  • Increasing precipitation

  • Decreasing elevation

  • Pronounced seasonal variations


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Species Equilibrium Model

  • The number of species found on an island depends on:

  • The rate at which new species immigrate to the island

  • The rate at which species become extinct on the island

  • At some point they reach an equilibrium that determines the island’s average number of different species


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© 2004 Brooks/Cole – Thomson Learning

High

Rate of immigration

or extinction

Low

Equilibrium number

Number of species on island

(a)

Immigration and extinction rates


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Rates are affected by:

  • Size

  • Distance


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Smaller island has lower diversity because…

  • Smaller target for potential colonizers

  • Smaller islands have higher extinction rates because they have fewer resources and less diverse habitats for colonizing species


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  • For islands of equal size – the island closest to the mainland will have the higher immigration rate and thus higher diversity


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© 2004 Brooks/Cole – Thomson Learning

High

Rate of immigration

or extinction

Low

Small island

Large island

Number of species on island

(b)

Effect of island size


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© 2004 Brooks/Cole – Thomson Learning

High

Rate of immigration

or extinction

Low

Far island

Near island

Number of species on island

(c)

Effect of distance from mainland


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Types of Species

  • Native Species – species that normally live and thrive in a particular ecosystem

  • Nonnative Species – (invasive species or alien species) species that migrate into an ecosystem or are deliberately or accidentally introduced

  • Indicator Species – species that serve as early warnings of damage to a community or ecosystem


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Types - continued

  • Keystone Species – species that play a pivotal role in the structure and function of an ecosystem because of their strong interactions with other species and the fact that they process material out of proportion to their numbers or biomass.


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How Do Species Interact?

  • Intraspecific competition – competition between members of the same species

  • Interspecific competition – competition between members of two or more different species for food, space or any other limited resource.


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Interspecific Competition

  • Interference competition – a species limits another’s access to some resource.

  • Exploitation competition – species have roughly equal access to a specific resource but differ in how fast or efficiently they exploit it


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Competitive Exclusion Principle

  • Species cannot occupy the same ecological niche indefinitely.


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High

Relative population density

Low

0

2

4

6

8

10

12

14

16

18

Days

Each species grown alone

Paramecium

aurelia

Paramecium

caudatum


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High

Paramecium

aurelia

Relative population density

Paramecium

caudatum

Low

0

2

4

6

8

10

12

14

16

18

Days

Both species grown together


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Resource Partitioning

  • Species that compete for the same resources evolve adaptations that reduce or avoid competition or an overlap of their fundamental niches.


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Predator - Prey Interactions

  • Predation – members of one species (predator) feed directly on all or part of a living organism of another species (prey)


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Bombardier beetle

Span worm

Wandering leaf insect

Foul-tasting monarch

butterfly

When touched, the

snake caterpillar

changes shape to look

like the head of a snake

Poison dart frog

Viceroy butterfly mimics

monarch butterfly

Hind wings of io moth

resemble eyes of a

much larger animal


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Symbiosis

  • A relationship in which species live together in an intimate association. There are three types of symbiosis


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Three types of symbiosis

  • Parasitism – one species (the parasite) feeds on part of another organism (the host) by living on or in the host. Examples include: tapeworms, fleas, ticks, mosquitoes, mistletoe plants and fungi


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  • Mutualism – two species involved in a relationship interact in ways that benefit both.

  • Benefits include: having pollen and seeds spread; being supplied with food, or receiving protection

  • Examples include: mycorrhizae that live in plant roots; bacteria in the digestive tracts of animals; birds on the backs of black rhinos that remove insects


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Mutualism


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  • Commensalism – a relationship in which one species benefits but the other is neither harmed nor helped.

  • Examples include: redwood sorrel which grows in the shade of redwood trees; epiphytes which attach themselves to the branches of large trees.


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Ecological Succession

  • The gradual change in species composition in response to changing environmental conditions.

  • Two types: primary and secondary

  • Primary is the gradual establishment of biotic communities on bare rock

  • Secondary is the reestablishment of biotic communities


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Pioneer Species

  • Before a community of plants can become established there must be soil present

  • Depending on the climate, it can take several hundred to several thousand years to produce fertile soil

  • Soil formation begins when pioneer species attach themselves to rock (lichens and mosses)


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  • Pioneer species are replaced by small perennial grasses and herbs (ferns in the tropics)

  • These are early successional plant species

  • These grow close to the ground, have short lives and can establish large populations quickly


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  • Mid successional plant species – herbs, grasses and low shrubs.

  • These are replaced by trees that are adapted to lots of sunlight

  • Late successional plant species – (mostly trees) that can handle shade


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Mature oak-hickory forest

Young pine forest

Shrubs

Perennial

weeds and

grasses

Annual

weeds

Time


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Secondary Succession

  • Begins in an area where the natural community has been disturbed, removed or destroyed

  • Examples include abandoned farms, burned forests, polluted streams, flooded land


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Factors Affecting Succession

  • Facilitation – one set of species makes an area suitable for species with different niche requirements

  • Inhibition – an early species hinders the establishment and growth of other species

  • Tolerance – late successional plants are unaffected by plants at earlier stages of succession


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  • A disturbance to an ecosystem can convert a particular stage of succession to an earlier stage

  • Types of disturbances: habitat destruction, fire, flooding, drought, landslide, stream alteration, etc…


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  • Ecosystems are continually changing

  • Cannot predict the course of a given succession

  • Cannot view it as preordained progress toward an ideally adapted climax community


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Stability

  • All living systems contain feedback loops (positive and negative) that interact to provide some stability over each system’s expected life span

  • This stability is maintained by constant dynamic change in response to changing environmental conditions


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Ecosystem Stability

  • Inertia or persistence – the ability of a living system to resist being disturbed or altered

  • Constancy – ability of a living system to keep its numbers within the limits imposed by the available resources

  • Resilience – ability of a system to bounce back after a disturbance (not drastic)


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