Communities

1
Communities Ecosystems

• Chapters 53-54

2
Communities

• A community is an assemblage of populations in an
  area or habitat.
• Are species in a community independent of one
  another?
• Are some species locked in association?
• Species in a community do interact.

3
Populations May Be Linked In Several Ways

• Ecological Niche The sum total of a species
  use of the biotic and abiotic resources in its
  environment.
• Competitive Exclusion Principle (Gauses
  Exclusion Principle, 1934). Two species that
  compete for the same resources (or occupy the
  same niche) cannot stably coexist. One will
  become extinct.
• Resource partitioning Species occupy slightly
  different niches. Extinction didnt occur.
• Character Displacement (niche shift) may occur
  over time.

4
Resource Partitioning by 7 Species of Anole
Lizards
Direct competition is avoided when each species
occupies a different micro-habitat
La Palma, Dominican Republic
5
One species seeks sunny places
Another species seeks shady branches
6
Character Displacement
Beak sizes have become different on the same
island and they now eat different size seeds
The two species have similar beak size when on
different islands
7
Niches

• Fundamental niche Niche that an organism
  occupies in the absence of competing species.
• Realized niche That part of their existence
  where niche overlap doesnt occur and
  competition is avoided.

8
Fundamental vs. Realized Niche
9
Three Forms of Symbiosis
Mutualism between Clown fish and anemones
Mutualism between the ants and acacia trees - The
ants and trees both benefit
Commensalism between Remora and shark
10
ParasitismThe host is harmed
Tapeworm parasitic flatworm
Mosquito
Ascaris lumbricoides parasitic round worm
11
Coevolution may explain why two species seem to
be reciprocally adapted.

• A change in one species acts as a selective force
  on another species, and vice versa.
• Examples Mimicry secondary compounds in plants
  (tannins, nicotine, latex

12
Animal Defenses Against Predators
Camouflage or cryptic coloration
13
Protective Coloration Schemes
Aposematic (warning) Coloration
Batesian Mimicry A palatable species mimics an
unpalatable one
Poison Dart Frogs
Hawkmoth larva
Snake
Mullerian Mimicry Two unpalatable species
resemble one another
14
Trophic Levels in Ecosystems
Marine
Terrestrial
15
Food Webs
16
Dominant vs. Keystone Species

• Dominant Species Highest abundance - Oak,
  Hickory forests
• Keystone Species exert control by niche not by
  abundance

17
Disturbances of the Community
Fires may be part of the ecology
18
Disturbances by Human Activity

• Destruction of habitats
• Extinction of species
• Salinization of streams
• Toxic Wastes
• Fires that are not part of the natural order
• Lack of fires where needed
• Etc., etc., etc.
• TOO MUCH CHANGE TOO FAST

19
Primary Succession
Occurs on substrates that never previously
supported living things. For example, on
volcanic islands, on lava, and on rock left
behind by retreating glaciers
20
Succession on Rock or Lava

• Begins with establishment of lichens
• Lichens hold moisture and break down rock into
  soil
• Bacteria, protists, mosses and fungi appear and
  soil continues to improve
• Insects and arthropods become established
• r-selected species become established
• K-selected species may replace r-selected ones

21
Succession on Sand Dunes(A very long process)

• Organic matter washes ashore and decays at tide
  line adding nutrients
• Grasses stabilize the fore-dune sand and hold
  moisture. They also add nutrients
• Shrubs colonize stabile sand
• Cottonwood trees become established
• Pines and black oaks further develop soil
• Beech-maple climax forest develops

22
Primary Succession at the Indiana Dunes
23
Dune Succession
Changes in the amounts of soil nutrients,
moisture, and the creation of new microclimates,
encourages new species to replace old ones.
24
Primary Succession in the Arctic
Bare rock
Lichens
Mosses
Shrubs and stunted trees
Climax boreal forest
Fir and pines
25
Lake Succession

• Eutrophication
• A slow process taking thousands of years.
• A continuous process of change.
• What will be the end stage of succession?

26
Secondary Succession of Farmland
Established soil nutrients and organisms make
colonization easier
27
Secondary Succession in a Cornfield
5th year Mature grasses and sedges
1st year Stubble
10th year Prairie plants and shrubs, few juniper
2nd year Wild grasses invade
20th year Mature juniper, birch and maple
http//www.micro.utexas.edu/courses/levin/bio304/e
cosystems/succession.2.gif
28
Generalized Secondary Succession to Forest
2yr. 5yr. 10yr. 20yr. 50yr. or more
29
Summary of Succession

• Slow process taking many years (100s or
  1,000s).
• Primary succession begins on bare ground or rock.
• Physical and chemical processes break down the
  substrate to provide basic living conditions.
• Organisms colonize the substrate and enrich the
  substrate with humus (decayed matter).
• Soil and microclimates develop allowing new
  species to colonize and replace the old ones.
• A stable climax community eventually develops
  depending upon climate.
• Secondary succession begins with a fertile
  substrate.

30
Ecosystems Approach To Ecology

• Ecosystem ecologists study the flow of energy and
  nutrients in an ecosystem
• Species are grouped by trophic levels
• All ecosystems are dependent upon the primary
  producers for energy
• Nutrients can be recycled by decomposers, but
  energy is eventually lost as heat

31
Ecosystem Dynamics
32
Primary Production

• The amount of light energy converted to chemical
  energy (organic compounds) by autotrophs in a
  given time period
• 1 of light striking plants is stored
• Producers create 170 billion tons of organic
  matter per year (mostly cellulose)
• Gross Primary Production (GPP)
• Net Primary Production (NPP)GPP - R

33
Comparing Ecosystems
34
Aquatic Ecosystems

• Light and nutrients limit aquatic systems
• Nitrogen limits phytoplankton growth in
  enrichment experiments with algae
• Fertilizer run-off can cause algal blooms
• Iron may limit production in some oceanic systems

35
Terrestrial Ecosystems

• Temperature and moisture are the key factors
  controlling primary production here
• Locally, soil minerals may control GPP
• Primary production removes soil nutrients
• Decomposition restores nutrients
• Farming may deplete the soil of nutrients

36
Secondary Production

• is amount of chemical energy in consumers food
  converted to biomass in a given amount of time.
• Only small amounts of primary production by
  plants are converted to biomass in animals.
• Production Efficiency the fraction of food
  energy that is used for growth and reproduction
  not respiration.
• 1-40

37
Trophic Efficiency

• Also know as ecological efficiency.
• Proportion of energy at one trophic level that is
  passed on to the next level.
• Averages around 10.
• Limits the number of possible trophic levels in a
  food chain to about 3.

38
Pyramid of Energy
39
Pyramid of Biomass
40
Pyramid of Numbers
41
The Cycling of Chemical Elements in Ecosystems

• Consider the reservoirs, assimilation, and
  release of nutrients in each cycle

42
A General Model of Nutrient Cycling
43
Water Cycle
44
The Carbon Cycle
Huge amounts of carbon are locked up in limestone
and peat deposits
45
http//www.eia.doe.gov/oiaf/1605/ggccebro/chapter1
.html
46
The Nitrogen Cycle
47
Hubbard-Brook Forest Experiment
48
The Phosphorus Cycle
49
Human Impact

• Deforestation results in mineral and water loss
• Slash and burn agriculture releases CO2 and
  removes nutrients as crop harvest
• Accelerated eutrophication of bodies of water
• Toxic chemicals concentrate in the food chain
• Loss of biodiversity destroys ecosystems
• Disruption of natural cycles

50
Acid Rain From Burning Fossil Fuels
51
Global Warming
http//www.whrc.org/carbon/index.htm
52
Ozone Layer Depletion by CFCs
Ozone layer hole