2.4. BIOMES, ZONATION AND SUCCESSION
Knowledge and Understanding
climate determines the type of biome in a given area although individual ecosystems may vary due to many local abiotic and biotic factors
Succession leads to climax communities that may vary due to random events and interactions overtime
Ecosystem stability, succession and biodiversity are intrisically linked
Biomes - collection of ecosystems sharing similar climactic conditions
Aquatic
Fresh water - swamp forests, lakes and ponds, streams and rivers, bogs
Marine - rocky shore, mud flats, coral reef, mangrove swamp, continental shelf, deep ocean
Deserts - hot and cold
Forests - tropical, temperate, boreal
Grassland - tropical or savanna, and temperate
Tundra - arctic and alpine
each biome has characteristic limiting factors, productivity and biodiversity, insolation, precipitation, and temperature
Bioosphere - part of earth inhabited by organisms
Why biomes are what they are:
climate
terrain/geography - slope, aspect, altitude
ocean currents and wind
temperature, precipitation
Climate change and biome shift
changes
temperature increase
greater warming at higher latitudes
more warming in winter
some areas becoming drier and others wetter
stronger storms
Moves
towards the poles where it is cooler
higher up mountains where it is cooler
towards the equator where it is wetter
Tricellular model of atmospheric circulation
Succession - how an ecosystem changes over time
Zonation - how an ecosystem changes along an environmental gradient e.g. altitude
the change in community along an environmental gradient due to factors such as changes in altitude, latitude, tidal level or distance from shore / coverage by water
Human activity can alter zonation e.g. road building or deforestation
change in species composition in an ecosystem overtime
primary succession - bare inorganic surface, colonisation of newly created land by organisms soil formation starts the process
secondary succession: occurs where soil already formed but vegetation has been removed e.g. after a fire or flood
Early succession - GPP and respiration are low, NPP is high as biomass accumulates
Later stages - GPP may remain high, respiration increases so NPP may near zero and productivity:respiration ratio approaches 1
End of succession - climax community is reached when species composition stops changing - there may be several states of climax community depending on abiotic factors
The more complex the ecosystem, the more stable it tends to be
In agricultural systems, humans often deliberately stop succession when NPP is high and crops are harvested - humans also disrupt succession by deforestation, grazing with animals or controlled burning
Species diversity in successions : in early stages, only few species within the community, then it increases quickly until most niches are filled
Disturbance: communities are affected by periods of disturbance e.g. from a hurricane, earthquake etc. - these make gaps available that can be colonised by pioneer species - adds to the productivity and diversity of the community
Subclimax community - succession stopped at a certain stage by an abiotic factor e.g. soil conditions or biotic factors e.g. grazing - community will only continue to develop after the limiting factor is removed
Plagioclimax community - a climax community may be affected by either a natural event, e.g. fire or landslide or human activity such as agriculture or habitat destruction - farmers want to maintain their crops at a plagioclimax - higher productivity
K- and r-strategists' reproductive strategies
K and R are two variables that determine the shape of the population growth curve - they are the extremes to the continuum of reproductive strategies and many species show a mixture of these characteristics
K strategists - e.g. humans and other large mammals
small number of offspring
invest large amounts of time and energy in parental care
most offspring survive
good competitors
population sizes are usually close to the carrying capacity
In stable climax ecosystems, K strategists out compete R
R strategists e.g. invertebrates and fish
uses lots of energy in production of large amounts of eggs
no energy used in raising them after hatching
lay their eggs and leave them forever
reproduce quickly
able to colonise new habitats rapidly
because of their fast reproductive and growth rates they may exceed the carrying capacity with a population crash as a result - they predominate in unstable ecosystems
Survivorship curve - shows the fate of a group of individuals