Ecosystems and Living Organisms

Chapter Overview

I. Evolution

II. Succession

III. Keystone Species

IV. Symbiosis

V. Predation

VI. Competition

VII. Species Richness

The American Alligator

Diversity of Life

Kingdoms of Life

Diversity of Life

Species

Similar organisms

that have the

potential to

produce viable

offspring together.

Evolution

• Genetic changes in a population through time.

• Mechanism for how species changed was explained by Charles Darwin.

– Origin of Species, 1859

– Evolution occurs through natural selection.

• Inherited, favorable traits are “preserved”

• Inherited, UNfavorable traits are “eliminated”

• Adaptation - genetic traits that increases the chances of survival and reproductive success.

Evolution

Survival of the Fittest

species heritable traits most suitable for the

environment are most successful.

fitness – describes the success of an organism at

surviving and reproducing.

The number of fit individuals will increase in the

population, changing the frequency of favorable

traits in the population.

Evolution

• How does evolution cause a species to change

over time?

Overproduction

Variation

Struggle for existence

Differential reproductive success

Causes

allele

frequencies

to change

(=species

change)

Evolution

Evolution• Hardy-Weinberg Equilibrium

• Allele and gene frequencies do NOT change in an ideal population.

• Population must experience the following for HW to apply:

• No mutation

• No selection

• No migration

• No genetic drift

• Random mating

• Population will not evolve if the above factors are true.

Evolution

• Hardy-Weinberg Equilibrium

• Formula:

p2 + 2pq + q2 = 1

• p = frequency of dominant allele

• q = frequency of recessive allele

• The sum of these frequencies is 1 if the population is in

equilibrium.

Evolution

3 Types:

Modes of Action

Natural selection has three modes of action:

1. Stabilizing selection

2. Directional selection

3. Diversifying selection

Number

of

Individuals

Size of individuals

Small Large

1. Stabilizing Selection

Acts upon extremes and

favors the intermediate

Number

of

Individuals

Size of individuals

Small Large

2. Directional

SelectionFavors variants of one

extreme

Number

of

Individuals

Size of individuals

Small Large

3. Diversifying

SelectionFavors variants of opposite

extremes

Number

of

Individuals

Size of individuals

Small Large

Coevolution

CoevolutionOne species acts as a selective force on a

second species Induces adaptations

Example:1. Wolf and Moose2. Acacia ants and Acacia trees3. Lichen

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Speciation

Evolution of new species

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At any given moment (e.g. the

‘present’), all we see is current

diversity…

all extinct forms are gone

(99.9%)

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BiodiversityBiodiversity increases with speciation decreases with extinction

Extinction creates evolutionary opportunities for surviving species

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Richness (number of species)

Relative abundance

Due to:

Evolutionary

history

Climate

Comparison of

Two Communities

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The larger the

geographic

area, the

greater

the number

of species

Species-Area Curve

Fig. 23.25 North American Birds

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Species Richness on Islands

Depends on:

Rate of immigration to island

Rate of extinction on island

These in turn depend on:

Island size

Distance from mainland

Species Richness

Species richness - Number of different species in a

community

Species Richness

Forest Grassland

EC

OT

ON

E

Where edge effect occurs - different

species composition

Typically greater species richness

Ecotone - transition zone where 2+ communities meet

Species Richness

Species Richness and Ecosystem Services

Ecosystem Ecosystem services

Forests,

Grasslands

Purify air / water

Produce / maintain soil

Absorb CO2

Wildlife habitat

Freshwater

systemsModerate water flow

Mitigate flooding

Dilute / remove pollutants

Drinking water

Recreation

Species Richness

Species Richness and Community Stability

Greater the richness = Greater the stability

- community stability

- ability of a community to withstand environmental

disturbance

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Threats to Ecosystem Stability

1. Drop in Primary Productivity

2. Increased Nutrient Losses

3. Decline or extinction of indicator species

4. Increased populations of insect pests or disease organisms

5. Decline in Species diversity

6. Presence of Contaminants

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How do species move? Humans (accidental and intended)

Animals (sticky seeds and scat)

Wind and ocean currents (+ or -)

Land bridges

Stepping stone islands affected by climactic changes (glaciation)

ocean levels

short-term weather patterns

Biological Communities

Rotting Log Community

Keystone Species

• Single species that strongly influences an entire

community.

• Example: figs

frugivores depend upon fruit

usually avoid figs, but during certain times of the year,

figs are only species bearing fruit

if figs were eliminated, many frugivores would die out

Interactions Among

Organisms Symbiosis –

one species living in or on another species

results from coevolution

Symbiosis

1) Mutualism - both partners benefit

Without mycorrhizae With mycorrhizae

Symbiosis

2) Commensalism - one partner benefits

and the other partner is neither harmed

nor helped.

Epiphytes

Symbiosis

3) Parasitism - one partner benefits

and the other partner is harmed

Tracheal mites

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Predator Adaptations Prey detection and recognition

sensory adaptations - distinguish prey

from non-prey

Discuss why each of the following demonstrates

sensory adaptations.

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Predator Adaptations Prey detection and recognition

sensory adaptations - distinguish prey from non-prey

Prey capture

passive vs. active

individuals vs. cooperative

Determine if the following pictures are examples of passive or

active prey capture. Explain why.

Determine if the following pictures are examples of individual or

cooperative prey capture. Explain why.

Discuss the costs and benefits of each strategy.

.

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Predator Adaptations Prey detection and recognition

sensory adaptations - distinguish prey from non-prey

Prey capture

passive vs. active

individuals vs. cooperative

Determine if the following pictures are examples of passive or

active prey capture. Explain why.

Determine if the following pictures are examples of individual or

cooperative prey capture. Explain why.

Discuss the costs and benefits of each strategy.

.

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Predator Adaptations Prey detection and recognition

sensory adaptations - distinguish prey from non-prey

Prey capture

passive vs. active

individuals vs. cooperative

Eating prey

teeth, claws etc.

Describe why each of the following is an adaptation.

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Prey AdaptationsAvoid detection

camouflage, mimics,

diurnal/nocturnal

Explain how natural selection leads to

camouflage and mimicry.

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Prey AdaptationsAvoid detection

camouflage, mimics, warning coloration

diurnal/nocturnal

Avoid capture

Flee, resist, escape

Describe how each of the following examples

demonstrates avoidance of capture.

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Prey Adaptations Avoid detection

camouflage, mimics,

diurnal/nocturnal

Avoid capture

flee

resist

escape

Disrupt handling (prevent being eaten)

struggle?

protection, toxins

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HerbivoryHerbivore needs to find most nutritious food sources.

circumvent plant defenses

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HerbivoryHerbivore needs to find most nutritious

circumvent plant defenses

Herbivory is a strong selective pressure on plants

structural adaptations for defense

chemical adaptations for defense

Explain why the following exemplifies coevolution.

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Predator-Prey Interactions Predator and prey populations are

interdependent.

Interactions Among

Organisms Competition –

individuals attempting to utilize common

resources

Intraspecific competition - between

individuals of same population

Interspecific competition - between

different species

The Ecological Niche

• All of an organism’s adaptations, use of resources,

lifestyle, and habitat.

– Fundamental vs. Realized Niche

• Fundamental Niche - potential, idealized

ecological niche

• Realized Niche - actual, realized ecological

niche

– Limiting Factor

• Environmental resource that restricts an

organism’s niche because of limited availability.

The Ecological Niche

Example: Tale of Two Anoles

Green Anole Brown Anole

The Ecological Niche

Fundamental vs. Realized Niche

Fundamental

Niche of

Green Anole

Fundamental

Niche of

Brown Anole

Overl

ap

Brown anole out-competes

green anole, therefore . . .

COMPETITION

The Ecological Niche

Fundamental vs. Realized Niche

Realized

Niche of

Green Anole

Overl

ap Realized

Niche of

Brown Anole

The Ecological Niche

Limiting Resources

The Ecological Niche

Competitive Exclusion

no 2 species can occupy the same niche indefinitely.

one species is excluded from part of the niche

because of interspecific competition.

The Ecological Niche

Competitive Exclusion

The Ecological Niche

Competitive Exclusion

The Ecological Niche

Resource partitioning

coexisting species’ niches differ from each other in

more than one way.

Biological Communities

Succession:

Process of community development over time

Species in one phase of development are replaced by other species.

earlier species modify the environment

less competition for earlier species

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DisturbanceEvent that disrupts an ecosystem or community

• Natural disturbance

•tree falls, fires, hurricanes, tornadoes,

droughts, & floods

• Human–caused disturbance

•deforestation, erosion, overgrazing, plowing,

pollution, mining

• Disturbance can initiate primary and/or secondary

succession

Succession Two Types:

Primary succession

change in species composition in an environment that had not been established before.

no existing seed bank when development begins

pioneer community - initial community to develop

Secondary succession –

change in species composition after a disturbance destroys existing vegetation

Existing seed bank

Biological Communities

Primary succession –

Lichens

Mosses

Rocks

Biological Communities

Primary succession –

Rocks

Lichens

Mosses

Grasses

Shrubs

Biological Communities

Primary succession –

Rocks

Lichens

Mosses

Grasses

Shrubs

Trees

Biological Communities Secondary Succession

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Ecosystem Stability

Climax community – community that has reached a

“steady state”

Ecosystem stability – ecosystem that is resistant to

change.

Can an ecosystem have a climax community?

Increase biodiversity increase ecosystem stability