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Community Ecology

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Title: Community Ecology


1
Community Ecology
  • The Community as an Ecological Unit
  • Community Development

2
Plant Communities
  • Communities are composed of populations of many
    species living together in the same location at
    the same time.
  • Similar communities tend to occur under similar
    environmental conditions.
  • Associations have a consistent species
    composition and habitat
  • But, composition can vary considerably from one
    location to another.

3
Examples of Communities
  • Dune plant community includes beach grass,
    seaside golden rod, beach heather, sea rocket,
    beach plum, pine trees, (and many other species).

4
Some Characteristics of Plant Communities
  • Architecture (forest layers)
  • Species diversity
  • Density how many individuals, regardless of
    species occupy a given area
  • Nutrient cycling (demand, storage capacity)
  • Development over time (succession)
  • Productivity (Biomass)
  • Microenvironments

5
Plant Communities The Piedmont Forest
  • Part of the temperate deciduous biome
  • Precipitation relatively high
  • Soils rich in organic matter
  • Broad-leaf trees that lose their leaves
    seasonally dominate
  • The piedmont is defined as the plateau between
    the coastal plain and the Appalachian mountains.
  • The foothills of the Appalachian Mountains

6
Maryland Biogeography
  • Coastal Plain
  • Piedmont Province
  • Upland
  • Lowland
  • Ridge/Valley Province Middle
  • Appalachian Plateau Province
  • Allegheny Mountain section

7
The Piedmont Forest
  • How old is the Piedmont region?
  • Underlying geology dates billions of years old.
  • Granite, gneiss, mica-schist, gabbro, marble, and
    serpentine
  • Soil types loams and clay
  • Loamy soils contain sand, silt, and clay
  • Holds water, but also drains well
  • Good aeration
  • Clay packs tightly, little water retention,
    little aeration
  • Land-use history
  • Deforestation beginning in the colonial period
  • Primarily agricultural until the late 20th
    century
  • Chestnut-Oak forests until 1930s chestnut blight
  • Oak-Pine or Oak-Hickory forests

8
Layers of the Forest
9
Layers of the Forest
1. Canopy
2. Understory
3.Shrubs
4. Herbaceous plants
5. Forest Floor
10
The Forest Community
  • The Canopy
  • the leafy crowns of the trees
  • most of the forests food is made here
    (photosynthesis)
  • feeding ground for many animals
  • just below the surface of the upper most layer of
    leaves
  • leaf eaters beetles, bugs and caterpillars, leaf
    hoppers, aphids etc.
  • Song birds and predatory insects (spiders) feed
    on the insects
  • Squirrels (eastern gray squirrel)
  • protection for the forest below

11
Canopy Trees of the Piedmont Forest
  • Several species of Oak
  • Bitternut Hickory
  • Buckeye
  • Red Maple
  • Beech

12
The Understory
  • Smaller trees make up the understory
  • Young trees (same species as canopy trees)
  • Low-growing trees (dogwoods)
  • Many birds and animals spend most of their lives
    in the understory.
  • Good for nesting, protection from hawks, owls,
    and stormy weather

13
Understory Trees of the Piedmont Forest
  • Dogwood
  • Redbud
  • Paw-Paw
  • Service Berry
  • Musclewood

14
Shrub Community
  • Shrubs are woody plants with many stems
  • A characteristic canopy will harbor a
    characteristic shrub community
  • Oak-Hickory forest
  • Spicebush
  • Blueberry
  • Witchhazel
  • Huckleberry (Dangle berry)
  • Rarely greater than 7 feet in height

15
Blueberry
16
Shrub Community
  • Protective cover for small mammals
  • shrews
  • mice
  • chipmunks
  • Nesting sites for Robins (in shrubs)
  • Berries and seeds for many mammals and birds

17
Herbaceous Layer
  • Emerges during the spring before the canopy is
    fully leafed-out
  • Ferns and mosses
  • Lichens
  • Wild flowers
  • Spring Beauties
  • Violets
  • Orchids
  • Lilies
  • The herbaceous layer dies out by mid-summer,
    existing underground as bulbs rhizomes

18
Northern VioletViola sp.
Spring BeautyClaytonia virginica
19
Lichens and Mosses
20
Forest Floor
  • The wastebasket for all the layers of the forest
    above
  • Leaves, petals, fruits, seeds, twigs, limbs,
    whole tree trunks, feathers, fur, feces, animal
    carcasses
  • estimated 2000-3000 lbs/acre in the fall
  • in various stages of decay

Yellow coral mushroom
21
  • A handful of dirt viewed with a magnifying glass
    reveals
  • earthworms, other nematodes
  • mites, spiders, black ants, and many other
    insects
  • Many more organisms are microscopic
  • The plants and animals on one acre may out number
    the entire human population by 106 to one!
  • Decomposers of the forest ecosystem break down
    the organic matter and release inorganic matter
    (Nitrogen, O2, etc)

22
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23
Forest Dynamics
  • How does the canopy affect the other layers of
    the forest?
  • The amount of sunlight entering the lower layers,
    which controls photosynthesis temperature.
  • Influences shading and temperature,
  • Important sources of organic material for
    decomposers, invertebrates and aquatic (stream)
    organisms.

24
Assessing Forest Communities
  • Density how many individuals, regardless of
    species occupy a given area
  • Age class
  • Basal Area
  • Canopy cover
  • Species Diversity

25
Measuring the size of trees
  • Diameter breast height (dbh)
  • Measures the girth of a tree
  • Estimates age of the tree
  • Saplings vs. Mature
  • The larger trees (older trees) have the greatest
    impact on the other trees in the forest

26
Estimating Tree Basal Area
  • Basal area measures the area occupied by a tree.
  • It is reported in ft2 per acre or
    meters2/hectare
  • Measure of biomass and productivity and

27
Dynamics of the tree community in an area of
tropical semi-deciduous forest.
28
Measuring Canopy Closure
  • How much light is hitting the forest floor?
  • The amount of shading influences the temperature
    of habitats under the canopy
  • Using a densitometer

29
Measuring Diversity in Plant Communities
30
Levels of Biodiversity
  • Genetic diversity the gene pool within a
    population
  • Species diversity the number and types of
    species in an area
  • Higher taxonomic diversity (Families, Genera)
  • Community Diversity
  • Ecosystem diversity (Habitat diversity)

31
Species diversity has two components
  • Species richness how many different species are
    present in a habitat
  • Species abundance total number of individuals of
    each species present. Usually expressed as

32
Defining Biodiversity
  • Old growth forest in the Shenandoah Mountains of
    Virginia
  • 50,000 trees represented by 10 species.
  • Managed forest, recently clear cut
  • 45,000 trees are maple and birch
  • Only 1/10th of the forest is represented by the
    remaining 8 species

33
  • Species diversity has two components
  • Species richness how many different species are
    present in a habitat
  • Relative abundance total number of individuals
    of each species present
  • Which area is more diverse?
  • There are many diversity indices used by
    ecologists
  • Shannon-Weiner Diversity Index

34
Community DevelopmentEcological succession
  • Defined as the transition in species composition
    over ecological time
  • Plants and animals appear and gradually alter
    their environment as they carry on their normal
    activities.
  • The accumulation of waste, dead organic matter,
    and abiotic factors such as light and water
    availability further alters the community.

35
Community DevelopmentEcological succession
  • Primary succession
  • Occurs in an area not previously inhabited
  • Areas that have been completely devastated by
    disturbance
  • Secondary succession
  • Occurs where there is a pre-existing community
    and well-formed soil

36
Mount St. Helens Eruption in 1980
  • Five explosive eruptions of Mount St Helens in
    1980 sent pumice and ash 6-10 miles into the air.

37
The Aftermath of Mount St. Helens Eruption
  • These trees were blown down by a lateral blast.
    This is an example of where the process of
    primary succession will begin to bring new life

38
Primary Succession
  • Occurs on essentially lifeless terrain
  • Volcanic eruptions
  • Retreat of glaciers
  • May take hundreds to thousands of years
  • The first group of organisms to appear
  • Autotrophic bacteria
  • Lichens
  • Mosses (organisms that reproduce by spores)
  • Grasses, ferns, shrubs, pine trees
  • Lichens are a symbiotic relationship between
    Algae and Fungi. They secrete acid that turns
    rock into soil. Once the soil is established,
    plants can colonize

39
Primary Succession
  • Iceland is a new country emerging from both the
    recent ice age and frequent volcanic eruptions

40
Primary Succession in Ponds and Lakes
  • Bogs
  • Algae carried in by birds and the wind
  • They die and fall to the bottom contributing to
    the organic matter.
  • Duckweeds form at the edges
  • When nutrients, oxygen, pH, and temperatures are
    low
  • Peat mosses take over, forming a thick mat.
  • Woody shrubs and carnivorous plants grow on this
    substrate
  • In the Northern US, many ponds and lakes are were
    left behind by the receding glaciers (10,000ybp)
  • Many ponds become bogs.
  • have no streams drainage, so they are filled by
    precipitation
  • Grow smaller every year because of succession

41
Bogs are an example of Primary Succession
  • Peat moss

42
Duckweeds occur early in succession
  • Under less acidic conditions, duckweeds are one
    of the 1st plants to grow
  • Grass-like sedges become established and form a
    mat
  • Once a mat is formed, bushes, shrubs and trees
    become established

43
Secondary Succession
  • Existing community has been disturbed
  • Soil is intact
  • Abandoned Agricultural fields
  • Old field succession
  • Climax community can become established after
    only decades
  • Disturbance colonizers weedy plant species
  • a high reproductive rate,
  • good at dispersal

44
Old Field Succession
70th-100th Pine to Hardwood transition
3rd-18th year Young Pine forest
1st year Horseweed Crabgrass pigweed
19th-30th year Mature pine Forest Understory of
Young hardwoods
100th year plus Climax Oak-hickory forest
2nd year Asters Crab grass
45
Disturbance
  • Disturbance is a natural part of the life of a
    community
  • Most communities are always in recovery from
    disturbance
  • Humans, too, are agents of disturbance

Tsunamis Hurricanes Storms
46
The Nature of Disturbance
  • Damage communities
  • Alter the resources available to organisms
  • Disrupt the food chain
  • Removing organisms!!
  • Opportunity for secondary succession to rebuild
    community
  • Examples of Disturbance
  • Storms, Hurricanes, Tsunamis
  • Ice storms
  • Flooding
  • Tornados
  • Fire

47
Fire Ecology Yellowstone fires of 1988 Fire is
being used to manage marshes and forests
48
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