2010 Lecture _ 2 Structure & Diversity of Ecosystems

8/7/2019 2010 Lecture _ 2 Structure & Diversity of Ecosystems

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(Physical) Structure&

Diversity(biological structure)

ofEcosystems


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Apopulation :

a group ofindividualsofthesamespecies

inhabiting thesame area atthesametime.

Important characteristics:

Population Size

Population Density Genetic Diversity

Autecology & Population Ecology


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Kirkwood Lake Pr

plantation planted

in 1928 :notebiological &

physical structure

ofmonoculture


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Communities :

populationsofmanyspecies

living & interacting together

inthesame location

atthesametime.

Similar communitiesoccur undersimilarenvironmental conditions; but

Composition & structure canvary

considerablyfromone locationto another.

Ecotones : Transitions between communities.

Community Ecologyor Synecology


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Physical STRUCTURETerrestrial Ecosystems based primarilyongrowth habitofplants

ground layer (bryophytes & herbs +

dead,downedtrees)

shrubby layer understory canopy

(sometrees suppressed)

overstory canopy

(dominanttrees;may bemorethanone) climbing vines & epiphytes

may beonlyone layer (?)


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Rich understory species &

downed logs / coarse woody

debris


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Greenwood Lake White Pine Stand Diversity

Foreststructure & compositionOverstory: 100% Pw (composition)

Lower canopy: white & black spruce, balsam

fir, white & yellow birch,sugarmapleShrub layer:mountainmaple and beakedhazel

Herbaceous layer

Standing snags and downed logs(coarse woody debris)


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Physical STRUCTURE

Aquatic Ecosystems

(standing orflowing water)

based 1 on chemical propertiesofwater:1. salinity(saltwater,freshwater, brackish)

2. temperature

3. dissolvedoxygen4. Clarity(colour & how well sunlightistransmitted)


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FreshwaterAquatic Ecosystem


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Changesoverspace & time

Ecological succession (time)

& zonation (space)

(See E&FBCh.21; SternCh.25)


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Succession

During succession plantspecies (& otherorganisms) graduallychangetheirenvironment

sothatotherspecies are better adaptedtonew environment;

New specieseventually becomethedominant

plantformsinthat area. Species composition (& communitystructure)

has changed.


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Succession

Primary Succession - Soil Formation

Secondary Succession - Disturbed areas

Pioneering, Transitional & Climaxspecies:

seres

Climax Vegetation - Stable plant associations

(structure & diversityinequilibrium)


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Primary Succession

Xerosere :Primarysuccessionthat begins with bare rocks

and lava thathave beenexposedthrough

glacial orvolcanic activity,orthroughlandslides


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Primary Succession

Hydrosere :Successionin wethabitats.

May be accelerated byeutrophication:

duetoenrichmentfromsedimentorother runoffcomponents

(ie. phosphorousfoundin

fertilizers & detergents)


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Secondary Succession:Fire Ecology

Natural fires,started primarily by lightning,have played a roleinecosystemsfor

thousandsofyears

ie. Western US, growth ringsofPonderosaPinesfire cycle wasofevery 6-7years;

aroundhere, 60-120 typical

specieshavespecific adaptationsto regular

fires;trying toeliminatefiresdisruptsnatural

cycles & ecosystems; can leadto

catastrophic fires.


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Fire Ecology

Fires also play a roleinforestspeciescomposition:

Manytreespecies repeatedly replace

themselves afterfires (fire climax) Firesmaintain grasslands by recycling

deadorganic material, and byeliminating

shrubs and woodyspecies.


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EdaphicClimax

Somesiteshavespecific soil typesthat restrictthespeciesthat can grow there:

dry, acidic & nutrient-poor: jack pine

wet, acidic & nutrient-poor: black spruce


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Diversity

Number & proportionofspecies can beassessed atdifferent levels

plant communityor association

eg.foreststand,meadow watershedor landscape

forest region

biome(E&FBCh. 28 & 29; SternCh. 26)


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Tundra

Primarily abovethe arctic circle Abovetreeline

Precipitation averages < 25 cm annually

Permafrostholds water atornearthesurface

Short growing seasonof2-3months

Hightemperatures rangeto about 27oC Veryfragile


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Taiga

NorthernConifer (Boreal)ForestAdjacentto andsouthofarctic tundra

Dominated by Spruce,Fir, and Pine

Disturbance-drivenecosystems (1 fire) ExtremeClimate:

Temperate Range-50oCto30oC

Annual precipitation rangesfrom 25-100cm,mostlyinthesummer


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Temperate DeciduousForest

Composedofmostly broad-leaved (fall)deciduoustreespecies

Mostlyin continental interiorsofNorthern

Hemisphere

Longer growing season:

Temperatures rangefrom4oCto 20oC

Annual precipitation rangesfrom 50-165 cm;mostlyoccursinsummer

During summer,solid canopy keepsdirect

sunlightfrom reaching theforestfloor


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Algonquin Park

Forest

Authority


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Grassland

Foundininteriorofcontinental massesoftendueto rainshadow effect

Broadleaftrees,butonly around water courses

Mostlyone layerto communitystructure


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Grassland

Warmsummertemperaturesincreasesevaporationrates

Annual precipitation rangesfrom 25-100 cm

Temperatures rangefrom-45oCto45oC

NorthAmerican grasslands (prairies) grew onfertilesoilssupporting largeherdsofmigratory grazingbuffalo

Mediterranean climate receivesmost

precipitationinthe winter,thus grassesdonotgrow astall asthoseofMidwestern prairies


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Desert

Manyofthe worldsmajordeserts are located at30o N and30o S latitude

Plant adaptationsincludethick cuticles, water-

storagetissuesinstems and leaves, andthick

leaves and / or reducedinsize Verydry:

Most receive < 12.5 cm annual precipitation

Low humidity Widedailytemperaturefluctuations

15oC- 35oCon a hotsummerday


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WesternCoastal Forest

TemperateConiferous Rainforests Pacific Northwest

w slopeofmountainous spineinNA

orographic precipitation

-10 Cto +10 Ctemperature range

long growing season


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MountainForests

SubalpineForests portionsofthe RockyMountains andthe

Sierra Nevada Mountains

SimilartoBoreal Forest

Conspicuous altitudinal zonationofspecies

Relativelydrysummers Frequentforestfire regime


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Tropical RainForest

Closeto Equator

Verydiverse communitiesdominated by broad-leavedevergreentrees

Densemulti-layered canopy

Shallow rootsystems

Poorsoils;Nutrientseither uptaken by plantsorleached byheavy rainfall

Annual precipitation rangesfrom 200-400 cm.

Nodryordormantseason Humidity usually > 80%.

Temperatures range between 25oC and35oC.


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2010 Lecture _ 2 Structure & Diversity of Ecosystems