Month Day Topic

Nov. 8 Individuals to populations

10 Holiday!

13 Populations to communities

15 Community patterns

17 Ecosystems

20 Film-1st showing

22 Film-2nd showing

24 Holiday!

27 Ecosystem services

A population is:

A population is:

A group of individuals of the same species living in a given area at a given

time.

What controls where a population lives?

What controls where a population lives?

• It has to get there– Evolution– Dispersal

What controls where a population lives?

• It has to get there– Evolution– Dispersal

• Its ecological niche

Key concept in ecology: the niche

Key concept in ecology: the niche

• Fundamental niche– Abiotic conditions that the species can live

within

Key concept in ecology: the niche

• Fundamental niche– Abiotic conditions that the species can live

within

• Realized niche– Biotic interactions that reduce or enhance

the fundamental niche

Barnacle story

Balanus’ fundamental niche: upper, middle and lower zone

Balanus’ realized niche: middle zone, limited from upper by competition, lower by predation

Interactions among populations determine a species’ realized niche...

A community is:

A community is:

Populations of different species that live

together in a given area at a given time.

Communities are...

• Defined by abiotic factors– Populations in a community have similar

fundamental niches

Communities are...

• Defined by abiotic factors– Populations in a community have similar

fundamental niches

• Defined by biotic interactions– Some are weak– Some are strong

Types of community interactions

POP. 2

Harm No effect Benefit

Harm Competition Amensalism Predation or Parasitism

POP. 1 No effect Amensalism Commensalism

Benefit Predation or Parasitism

Commensalism Mutualism

Types of community interactions

POP. 2

Harm No effect Benefit

Harm Competition Amensalism Predation or Parasitism

POP. 1 No effect Amensalism Commensalism

Benefit Predation or Parasitism

Commensalism Mutualism

Types of community interactions

POP. 2

Harm No effect Benefit

Harm Competition Amensalism Predation or Parasitism

POP. 1 No effect Amensalism Commensalism

Benefit Predation or Parasitism

Commensalism Mutualism

Keys to competition(-/-)

• Organisms compete for limited resources

• Organisms compete for limited resources

• Can be:– Intraspecific

Keys to competition(-/-)

Time

Pop

ulat

ion

size

• Organisms compete for limited resources

• Can be:– Intraspecific– Interspecific

Keys to competition(-/-)

Competition can:

• Restrict species ranges

Competition can:

• Restrict species ranges

• Reduce species abundances

Competition can:

• Restrict species ranges

• Reduce species abundances

• Cause the local extinction or competitive exclusion of species from an area

The ghost of competition past...

Predator-prey interactions(+/-)

• Predators are generally larger than their prey (but many exceptions...)

Predator-prey interactions(+/-)

• Predators are generally larger than their prey (but many exceptions...)

• Predators live outside of the body of their prey

Predator-prey interactions(+/-)

• Predators are generally larger than their prey (but many exceptions...)

• Predators live outside of the body of their prey

• Predators generally kill their prey

Predator-prey interactions

• Dynamics of predator and prey populations may be:

Predator-prey interactions

• Dynamics of predator and prey populations may be:

• Loosely coupled– predator “switches” when prey is scarce

• Tightly coupled– predator starves when prey is scarce

Tightly coupled predator-prey interactions change over time

• An evolutionary “arms race”

• An evolutionary “arms race”

• Mimicry

Tightly coupled predator-prey interactions change over time

Batesian mimicry

Batesian mimicry

Predator-prey interactions change over time

• An evolutionary “arms race”

• Mimicry

• Plant defenses against herbivores

Host-parasite interactions(+/-)

• Parasites are generally smaller than their hosts

• Parasites live inside or on the body of their host

• Parasites generally kill their hosts more slowly than predators

Amensalism(0/-)

Commensalism(0/+)

Mutualisms(+/+)

Mutualisms can be loose or tight

Acacia with ants Acacia without ants

Communities are...

• Defined by abiotic factors– Populations in a community have similar

fundamental niches

• Defined by biotic interactions– Weak and strong interactions determine a

population’s realized niche

• Dynamic– Vary in time and in space

Why do communities vary in time?

Communities are...

Comprised of populations that respond individualistically to change

Communities vary in time

Ecological succession:

a sequence of change in the species composition of a community

Succession

1. Primary– establishment of communities on new

sites that previously had no organisms

1949

2001

Succession

1. Primary– establishment of communities on new

sites that previously had no organisms

2. Secondary– re-establishment of communities

following disturbance

Why do communities vary in space?

Communities vary in space

• Time

• Relief/aspect

• Parent material

• Climate

• Organisms

Terrestrial biome

Terrestrial biome

• A major community type that differs from other types in the structure of its dominant vegetation.

Terrestrial biome

• A major community type that differs from other types in the structure of its dominant vegetation.

• Primarily controlled by climate.– Relationship between rainfall and

temperature

• The vegetation of a biome has a similar appearance wherever on Earth that biome is found.

• In many cases, this is due to convergent evolution.

Biomes

Euphorbiaceae Cactaceae

Tundra

-severe winters

-short growing season,cool summer

-arctic or alpine

Tundra

Tundra

Temperate Forest

Temperate forest

-distinct winter season, frost a defining feature

-summer season usually moist

Temperate Forest

Temperate Forest

Desert

Desert-hot or cold deserts exist

-low precipitation

Desert

-found near the equator

-temperature varies little from approximately 23°C

-Over 2 m of rainfall

Tropical Rain Forest

Tropical Rain Forest

Tropical Rain Forest

-canopy trees up to 55 m tall

-largest biome, on an area basis

-soils are generally unfertile

-nutrients and carbon stored in plant biomass, not soils