Biomes & Zonation

definition of succession

how the species composition of an ecosystem changes in time

comparable characteristics of succession

• dynamic

• temporal - long time periods

• progressive changes over time

definition of zonation

how an ecosystem changes along an environmental gradient (e.g. altitude)

comparable characteristic of zonation

• spacial

• static

• caused by an abiotic gradient

seral stage: bare, inorganic surface

• soil = mineral particles

• nutrient poor

• erratic water supply

• e.g. eruptions, sand dunes

seral stage 1 - colonisation

• pioneer species adapt to extreme conditions

• usually r species

• soil starts from dust/windblown particles

seral stage 2 - establishment

• species diversity increases

• invertebrates visit

• humus increases

• weathering of rock increases nutrients

seral stage 3 - competition

• microclimate changes as new species colonise

  • larger plants provide shade

• shelter enables K species to establish

• abiotic factors start to stabilise

• pioneer species are out-competed

seral stage 4 - stabilisation

• arrival rate of new species decreases

• narrowing niches

• more complex food webs

seral stage 5 - climax community

• stable, self-perpeptuating

• dynamic equilibrium

• maximum possible development under abiotic factors

human impacts on succession

• can divert succession to plagioclimax community through

  • burning

  • agriculture

  • grazing pressure

  • resource extraction

• direct & indirect impacts

• change abiotic & biotic components

• impact depends on ecosystem’s reslience

definition of resilience

ability of an ecosystem to recover from a disturbance & return to its natural state

biotic changes during succession

• size of organisms increases

• biodiversity increases

• niches appear

• species diversity increases then falls

• NPP & GPP rise then fall

• productivity & respiration ratio falls

• energy flow becomes more complex

abiotic changes during succession

following increase:

• soil depth

• humus

• water capacity

• mineral content & cycling

hydrosere

• succession in water

• continuous sediment input from streams/lakes

• build allows rooted plants to invade

secondary succession

• occurs when established community is destroyed

  • e.g. natural disasters, plowing

• shortened number of seral stages as components already established

5 major types of biome

1. aquatic

2. forest

3. grassland

4. desert

5. tundra

definition of biomes

large-scale ecological communities that are characterised by their dominant vegetation, climate, and other abiotic factors that shape their biotic communitie

description of the Hadley Cell

• largest

• equator → 40° north and south

• trade winds blow easterly

• trade winds meet at equator, hot air rises

• tropical storms are formed

• air flows from the stop of the storms to higher latitudes

• it becomes cooler & sinks over subtropical regions

• this = dry, cloudless air, warmed by the sun as it descends

description of Ferrel Cell

• middle cell

• edge of Hadley → 70° north and south

• joins sinking air of Hadley cell which travels close to earth until it rises at border of polar cell

• accounts for frequent, unsettled weather

description of Polar Cell

• smallest & weakest

• edge of Ferrel → poles

• cold air sinks = high pressure

• cold air flows towards lower latitudes

• warms & returns at altitude to poles

role of global atmospheric circulation model

• Air moves from high → low pressure, generating wind

• Wind = large scale movements of air due to air pressure difference

• This pressure is due to uneven insolation

  • hot air rises

  • cool air sinks

• this creates pressure cells