Succession

IB Syllabus: 2.3.5 – 2.3.7

Ch. 8

Syllabus Statements

• 2.1.6: Define the terms species, population, habitat, niche, community, ecosystem with reference to a named example

• 2.6.5 – Describe the concept and process of succession in a named habitat

• 2.6.6 – Explain the changes in energy flow, gross and net productivity, diversity and mineral cycling in different stages of succession

• 2.6.7 – Describe the factors affecting the nature of climax communities

Vocabulary

• Climax Community

• Community

• Evolution

• K strategists

• R strategists

• Sere

• Succession

• Zonation

Community

• A group of populations interacting in a particular area

• The fish community of Ponce Inlet

• The plant community of the scrub habitat

Communities Change

• Ecological Succession: the gradual change in species composition of a given area over time

• Species do change spatially within an area at a certain point in time, this is zonation not succession

• 2 Types depending on start point– Primary succession: gradual establishment of

biological communities on lifeless ground– Secondary succession: reestablishment of biotic

communities in an area where they already existed

Zonation II

• Horizontal bands or zones of animals and organisms– Vertical layers in a rainforest– Differing plant communities as you go up a

mountain

• Created by physical and biological factors• Change in these factors is called an

environmental gradient• In a rocky intertidal zone these would be

– Drying (tides), salinity, competition, grazing

http://upload.wikimedia.org/wikipedia/commons/e/e9/Nerr0878.jpg

So how could you measure changes in biota along an environmental gradient?

• Biota = living organisms• Change in benthic (bottom) community of

rocky intertidal with increased depth• Gradient in moisture or drying• Use modified quadrat method

– run transect into deeper water– At set depths place quadrat and sample

organisms– Do repeated transects along your sample

area– Calculate differences in communities with

depth

Primary Succession

• Begins in area with no soil on land, no sediment in water– Cooled lava, bare rock from erosion, new

ponds, roads

• Must be soil present before producers consumers and decomposers can exist

Time

Small herbsand shrubs

Heath mat

Jack pine,black spruce,

and aspen

Balsam fir,paper birch, and

white spruceclimax community

Exposedrocks

Lichensand mosses

Pioneer Communities

• Lichens and Mosses• Survive on nutrients in

dust and rock• Start soil formation1. Trap small particles2. Produce organic

material - photosynthesis

3. Chemically weather the rock

4. Patches of soil form

Seral Stages: Early Successional Plant Species

• Small perennial grasses and herbs colonize, wind blown seeds

1. Grow close to the ground

2. Est. large pop. quickly in harsh conditions

3. Short lived

4. Break down rock

Seral Stages: Mid to Late Successional Species

• After 100’s of years soil deep enough

• Moisture & nutrients• Also called Seral

Community1. Shrubs then trees

colonize2. Trees create shade3. Shade tolerant

species establish

Seral stages

• A seral community (or sere) is an intermediate stage found in ecological succession in an ecosystem advancing towards its climax community.

• An example of seral communities in secondary succession is a recently logged coniferous forest; – during the first two years, grasses, heaths and herbaceous

plants such as fireweed will be abundant, – after a few more years shrubs will start to appear– about six to eight years after clearing, the area is likely to be

crowded with young birches.

• Each of these stages can be referred to as a seral community.

Climax community

• Characterized by K-selected species

• Determined by – climate in the area – temperature, weather patterns– Edaphic factors – saturated wet, mesic, arid

• Climax community structure is in stable equilibrium for each area

• Humans & other factors may maintain an equilibrium below climax– E.g. current warming trends make climax rainforest

communities w/ softer wood, faster growing species

End Result = Complex Community

• Complex community mix of well established trees shrubs and a few grasses

• Disturbance may change the structure– Fire, Flood, Severe erosion, Tree

cutting, Climate change, Grazing, habitat destruction

– Natural or Human processes– Specific successional stage is

dependent on the frequency of disturbance

Disturbance and Diversity

• Disturbance = any change in conditions which disrupts ecosystem or community structure

• Catastrophic or Gradual

• Disturbance eliminates strong competitors allowing others a chance

• Promotes diversity

• Intermediate disturbance greatest diversity

1000Percentage disturbance

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sity

The intermediate disturbance hypothesis

Townsend et al, cited in Begon Harper & Townsend,  Ecology

Secondary Succession

• Begins when natural community is disturbed BUT soil & sediment remains– Abandoned farms, burned forests, polluted

streams

• New vegetation can germinate from the seed bank

• In both cases succession focuses on vegetation changes

Time

Annualweeds

Perennialweeds and

grasses

ShrubsYoung pine forest

Mature oak-hickory forest

Succession of Abandoned Farmland

Heliconia Bracts

Tropical Rainforest flower

Newer flowers form at the bottom

As flowers form they fill with waterSupport aquatic communities

Newly formed bracts early succession

Nutrients and organics build up

Over time succession occurs Higher bracts have climax

communities

What changes occur through Succession?

1. Diversity• Starts very low in harsh conditions few species

tolerate – r selected species types• Middle succession mix of various species

types – most diverse (role of disturbance)• Climax – k selected species strong competitors

dominate

2. Mineral Cycling• Pioneer, physical breakdown & make

organic, Later processing increase – cycles expand

3. Gross productivity changes (total photosynthesis)

• Pioneer = Low density of producers at first• Middle & climax = high lots of producers and

consumers

4. Net Productivity (G – R = N)• Pioneer = little respiration so Net is large

system is growing, biomass accumulating• Middle & climax = respiration increases

dramatically N approaches zero (P:R = 1)

5. Energy flow• # of trophic levels increases over time• Energy lost as heat increases with more transfers

MidsuccessionalSpecies

ElkMooseDeerRuffled grouseSnowshoe hareBluebird

Late SuccessionalSpecies

TurkeyMartinHammond’s flycatcherGray squirrel

WildernessSpecies

Grizzly bearWolfCaribouBighorn sheepCalifornia condorGreat horned owl

Early SuccessionalSpecies

RabbitQuailRingneck pheasantDoveBobolinkPocket gopher

Ecological succession

© 2004 Brooks/Cole – Thomson Learning

Overview of Successional Changes

Factors in Succession1. Facilitation

• One species makes an area suitable for another in a different niche

• Legumes add nitrogen so other plants thrive

2. Inhibition• Early species hinder establishment and growth of later

species more disturbance needed to continue• Allelopathy by plants is an example

3. Tolerance• Late successors not affected by earlier ones• Explains mixture of species in Climax Communities

Predictability of Succession

• Generally predictable end of succession is a Climax community

• Only real rules are Continuous change, Instability, and unpredictability

• Ever changing mosaic of patches in different successional stages

• No real progression to an end, rather we see a reflection of an ongoing battle for resources and reproductive advantage

Aquatic Succession

Ecological Stability & Sustainability

• Maintained by constant dynamic change• Positive and Negative feedback systems• Community may change but you will still

recognize it as a particular type of community– Inertia = The ability of a living system to resist

disturbance– Constancy = the ability of a system or population to

keep its numbers within limits imposed by resources– Resilience = the ability of a system to bounce back

after a disturbance

Diversity vs. Stability

• Once thought that higher diversity = more stability for a community or ecosystem

• Recent studies by D. Tilman on grasslands suggest– More species higher NPP more stable– Population #’s for individual species in diverse

ecosystems fluctuate more widely

• Some level of diversity does provide insurance against disasters

• Nature is in a continual state of change

The Precautionary Principle

• Human disturbances are disrupting ecosystem processes

• Our ignorance of long term effects means we should be cautious

• Thus, “When there is considerable evidence that and activity threatens human and ecosystem health, we should take precautions to minimize harm, even if the effects are not fully known.”

• Better safe than sorry…

Grizzlybear

NORTHAMERICA

Spottedowl

Black-footedferret

Kemp’sridleyturtle

Californiacondor

Goldentoad

Columbia haslost one-third ofits forest

Black liontamarin

SOUTHAMERICA

More than 60% of thePacific Northwestcoastal forest hasbeen cut down

40% of North America’srange and croplandhas lost productivity

Hawaiianmonk seal

Half of the forestin Honduras andNicaragua hasdisappeared

Mangrovesclearedin Equador for shrimp ponds

SouthernChile’s rainforest isthreatened

Little of Brazil’sAtlantic forestremains

Every year 14,000square kilometers ofrain forest is destroyedin the Amazon Basin

Coral reef destruction

Much of Everglades National Park has dried outand lost 90% of its wading birds

ATLANTICOCEAN

PACIFICOCEAN

Manatee

Chesapeake Bay is overfished and polluted

Fish catch in the north-west Atlantic has fallen42% since its peak in 1973

Humpbackwhale

St. Lawrencebeluga whaleEastern

cougar

Floridapanther

Environmental degradation

Vanishing biodiversity

Endangered species

6.0 or more childrenper woman

EUROPE

Mediterranean

Liberia

AFRICA

Imperial eagle

640,000 square kilometerssouth of the Sahara haveturned to desert since 1940

Mali

BurkinaFaso

SierraLeone Togo

Sao Tome68% of theCongo’srain forestis slatedfor cleaning

Fish catches inSoutheast Atlantichave dropped by morethan 50% since 1973

Blackrhinoceros

Zambia

Angola

CongoRwandaBurundi

UgandaSomalia

Nigeria

ChadNigerBenin Golden

tamarin

Ethiopia

Eritrea

Madagascar haslost 66% of itstropical forest

Aye-aye

YemenOman

SaudiArabia

Poland is one ofthe world’s mostpolluted countries

Many parts offormer Soviet Unionare polluted withindustrial and radio-active waste

Area ofAral Sea hasShrunk 46%

Central Asia from theMiddle East to Chinahas lost 72% of rangeand cropland

ASIA

Asianelephant

India andSri Lankahave almostno rainforest left

In peninsular Malaysiaalmost all forests havebeen cut

INDIAN OCEAN

Indonesia’scoral reefs arethreatenedandmangroveforestshave beencut in half

Giantpanda

Kouprey

Queen Alexandra’sBirdwing butterfly

Nail-tailedwallaby

AUSTALIA

Much ofAustralia’srange andcroplandhave turnedto desert

90% of the coral reefsare threatened in thePhilippines. All virginforest will be goneby 2010

Deforestation in the Himalayacauses flooding in Bangladesh

Japanese timber importsare responsible for muchof the world’s tropicaldeforestation

Blue whale

ANTARCTICA

A thinning of the ozone layer occursover Antarctica during summer

Snow leopard

Hydrosere• A hydrosere is simply a succession which starts in water.

A wetland, which is a transitional area between open freshwater and dry land, provides a good example of this and is an excellent place to see several stages of a hydrosere at the same time.

• In time, an area of open freshwater such as a lake, will naturally dry out, ultimately becoming woodland. During this process, a range of different habitats such as swamp and marsh will succeed each other.

• This succession from open water to climax woodland is likely to take at least two hundred years (probably much longer). Some intermediate stages will last a shorter time than others. For instance, swamp may change to marsh within a decade or less. How long it takes will depend largely on the amount of siltation occurring.

• http://www.countrysideinfo.co.uk/successn/hydro.htm

Hydrosere

Halosere• The term Halosere is an ecological term which describes succession in a

saline environment. An example of a halosere would be a salt marsh.• In river estuaries, large amounts of silt are deposited by the ebbing tides

and inflowing rivers.• The earliest plant colonizers are algae and eel grass which can tolerate

submergence by the tide for most of the 12-hour cycle and which trap mud, causing it to accumulate. Two other colonisers are salicornia and spartina which are halophytes -i.e. plants that can tolerate saline conditions. They grow on the inter-tidal mudflats with a maximum of 4 hours' and exposure to air every 12 hours.

• Spartina has long roots enabling it to trap more mud than the initial conlonizing plants and salicornia, and so on. In most places this becomes dominant vegetation. The initial tidal flats receive new sediments daily, are waterlogged to the exclusion of oxygen, and have a high pH value.

• The sward zone, in contrast, is inhabited by plants that can only tolerate a maximum of 4 hours submergence everyday (24 hours). The dominant species here are sea lavender and other numerous types of grasses.

Halosere

Xerosere

• Xerosere is a plant succession which occurs in conditions limited by water availability or the different stages in a xerarch succession.

• Xerarch succession of ecological communities originated in extremely dry situation such as sand deserts, sand dunes, salt deserts, rock deserts etc.

• A xerosere may include lithoseres and psammoseres.

Psammoseres

• In geography, a psammosere is a sand sere - an environment of sand substratum on which ecological succession occurs.

• In a typical succession on a sea-coast psammosere, the organisms closest to the sea will be salt tolerant species such as littoral algae and glasswort. Progressing inland the succession is likely to include meadow grass, sea purslane, and sea lavender eventually grading into a typical non-maritime terrestrial eco-system.

• www.sanddunes.20m.com/Evolution%20.htm•