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    Community Ecology

    The Community as an Ecological UnitCommunity Development

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    Plant Communities

    Communitiesare composed of populations of

    many species living together in the same

    location at the same time.

    Similar communities tend to occur under similarenvironmental conditions.

    Associationshave a consistent species composition and

    habitat

    But, composition can vary considerably from one

    location to another.

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    Examples of Communities

    Chesapeake Bay

    shallow water

    community

    Bog

    Piedmont forest

    Salt marsh

    Alpine community

    Dune community

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    Some Characteristics of Plant Communities

    1. Architecture (for example forest layers)2. Species composition (native , invasive)

    3. Species diversity

    4. Nutrient cycling (demand, storage capacity)

    5. Development over time (succession)

    6. Productivity (Biomass)

    7. Microenvironments

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    Plant Communities:

    The Piedmont Forest

    1. Part of the temperate deciduous biome

    a. Precipitation relatively high

    b. Soils rich in organic matterc. Broad-leaf trees that lose their leaves seasonally

    dominate

    2. The piedmont is defined as the plateau

    between the coastal plain and theAppalachian mountains.

    The foothills of the Appalachian Mountains

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    1. Coastal Plain

    2. Piedmont Province

    a. Upland

    b. Lowland

    3. Ridge/Valley Province:Middle

    4. Appalachian PlateauProvince:

    Allegheny Mountain section

    Maryland Biogeography

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    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: contains 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 20thcentury

    Chestnut-Oak forests until 1930s chestnut blight

    Oak-Pine or Oak-Hickory forests

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    Layers of the Forest

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    Layers of the Forest

    1. Canopy

    2. Understory

    5. Forest Floor

    4. Herbaceous plants

    3.Shrubs

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    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 theinsects

    Squirrels (eastern gray squirrel)

    protection for the forest below

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    Canopy Trees of the

    Piedmont Forest Several

    species of Oak

    BitternutHickory

    Buckeye

    Red Maple

    Beech

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    The Understory

    Smaller trees make up theunderstory

    Young trees (same species ascanopy trees)

    Low-growing trees(dogwoods)

    Many birds and animalsspend most of their lives inthe understory.

    Good for nesting, protectionfrom hawks, owls, andstormy weather

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    Understory Trees of the

    Piedmont Forest

    Dogwood

    Redbud

    Paw-Paw

    Service Berry

    Musclewood

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    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

    Effect of a closed forest canopy/ open forestcanopy on the shrub community

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    Spicebush

    Blueberry

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    Shrub Community

    Protective cover for smallmammals

    shrews

    mice chipmunks

    Nesting sites for Robins (inshrubs)

    Berries and seeds for manymammals and birds

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    Herbaceous Layer

    Emerges during the spring before the canopy isfully 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

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    Spring BeautyClaytonia virginica

    Northern VioletViola sp.

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    Lichens and

    Mosses

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    Forest Floor

    The wastebasket for all thelayers of the forest above

    leaves, petals, fruits, seeds,

    twigs, limbs, whole tree trunks,feathers, fur, feces, animal

    carcasses

    estimated 2000-3000 lbs/acrein the fall

    in various stages of decay

    Yellow coral mushroom

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    a handful of dirt viewed with amagnifying glass reveals

    earthworms, other nematodes

    mites, spiders, black ants, and manyother insects

    many more organisms are

    microscopic The plants and animals on one acre

    may out number the entire humanpopulation by 106to one!

    Decomposers of the forestecosystem break down the organicmatter and release inorganic matter(Nitrogen, O2, etc)

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    Measuring Diversity in

    Plant Communities

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    Levels of Biodiversity

    1. Genetic diversity: the gene pool within a

    population

    2. Species diversity: the number and types of

    species in an area

    3. Higher taxonomic diversity (Families,

    Genera)

    4. Community Diversity

    5. Ecosystem diversity (Habitat diversity)

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    Species diversity

    has two components:

    1. Species richness:how many different species

    are present in a habitat2. Species abundance:total number of

    individuals of each species present. Usually

    expressed as %

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    Defining Biodiversity:

    Old growth forest in the Shenandoah Mountainsof Virginia

    50,000 trees represented by 10 species.

    Managed forest, recently clear cut

    45,000 trees are maple and birch

    Only 1/10thof the forest is represented by theremaining 8 species

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    Species diversityhas two

    components:1. Species richness:how

    many different species

    are present in a habitat

    2. Relative abundance:total

    number of individuals of

    each species present

    3. Which area is morediverse?

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    Defined as the transition in speciescomposition over ecological time

    Plants and animals appear and graduallyalter their environment as they carry ontheir normal activities.

    The accumulation of waste, dead organic

    matter, and abiotic factors such as light andwater availability further alters thecommunity.

    Community Development:

    Ecological succession

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    1. Primary succession

    Occurs in an area not previously inhabited

    Areas that have been completely devastatedby disturbance

    2. Secondary succession

    Occurs where there is a pre-existingcommunity and well-formed soil

    Community Development:

    Ecological succession

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    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.

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    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

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    Primary Succession

    Occurs on essentiallylifeless terrain

    Volcanic eruptions

    Retreat of glaciers

    May take hundreds to

    thousands of years

    The first group oforganisms to appear

    1. Autotrophic bacteria

    2. Lichens

    3. Mosses (organisms thatreproduce by spores)

    4. Grasses, ferns, shrubs,pine trees

    Lichens are a symbioticrelationship between Algae and

    Fungi. They secrete acid thatturns rock into soil. Once thesoil is established, plants cancolonize

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    Primary Succession

    Iceland is a new country emergingfrom both the recent ice age andfrequent volcanic eruptions

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    Primary

    Succession in

    Ponds and Lakes 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 arefilled by precipitation

    Grow smaller every

    year because of

    succession

    Bogs

    Algae carried in by birds andthe wind

    They die and fall to the bottom

    contributing to the organicmatter.

    Duckweeds form at the edges

    When nutrients, oxygen, pH,and temperatures are low

    Peat mosses take over,forming a thick mat.

    Woody shrubs and carnivorousplants grow on this substrate

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    Bogs are an example of

    Primary Succession

    Peat moss

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    Duckweeds occur early in succession

    Under less acidic

    conditions, duckweeds

    are one of the 1stplants to

    grow

    Grass-like sedges become

    established and form a

    mat

    Once a mat is formed,bushes, shrubs and trees

    become established

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    Secondary Succession Existing community has

    been disturbed Soil is intact

    Abandoned Agriculturalfields:

    Old field succession Climax community can

    become established afteronly decades

    Disturbance colonizers:

    weedy plant species1. a high reproductive rate,

    2. good at dispersal

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    1styear

    Horseweed

    Crabgrass

    pigweed

    2ndyear

    Asters

    Crab grass

    3rd-18thyear

    Young

    Pine forest

    19th

    -30th

    yearMature pine

    Forest

    Understory of

    Young hardwoods

    70th-100th

    Pine to

    Hardwood

    transition

    100thyear plusClimax

    Oak-hickory

    forest

    Old Field Succession

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    Disturbance1. Disturbance is a

    natural part of thelife of a community:

    2. Most communitiesare always inrecovery from

    disturbance3. Humans, too, areagents ofdisturbance

    TsunamisHurricanes

    Storms

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    The Nature of Disturbance

    1. Damage communities2. Alter the resources available to organisms

    Disrupt the food chain

    3. Removing organisms!!

    4. Opportunity for secondary succession torebuild community

    5. Examples of Disturbancea. Storms, Hurricanes, Tsunamis

    b. Ice storms

    c. Flooding

    d. Tornados

    e. Fire

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    Fire EcologyYellowstone fires of 1988

    Fire is being used to manage marshes and forests

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