2.4: biomes, zonation and succession Flashcards
biomes:
collections of ecosystems sharing similar climatic conditions that can be grouped into five major classes: aquatic, forest, grassland, desert and tundra.
each have characteristic limiting factors, productivity & biodiversity. insolation, precipitation & temperature are the main factors governing the distribution of biomes.
types of terrestrial & aquatic biomes -
terrestrial biomes: tundra, grassland, desert, taiga, temperate forest, tropical forest.
aquatic biomes: marine, freshwater, tropical coral reefs, hydrothermal vents
deserts:
- cover 20-30 percent of the land surface
- dry air
- high temperatures (45-49 C in day)
- low precipitation (250 mm yr-1)
- low rates of photosynthesis
- low NPP rates
- vegetation scarce
- soil rich in nutrients and can support plants that can survive there
tundra:
- found in high latitudes
- days are short
limited levels of sunlight - water may be locked up in ice, limiting water resources
- photosynthesis and productivity rates are low
- low temperatures
- soil may be permanently frozen
- nutrients in soil are limited
tropical rainforest:
- high temperatures (average 26 C )
- high rainfall (over 2500 mm yr -1)
- near the equator
- high light levels throughout the year
- all-year round growing season
- high levels of photosynthesis
- high rates of NPP throughout the year
- high diversity of animals and plants
- low levels of nutrients in the soil
temperate forest:
- seasonal weather (hot summers/cold winters)
- 2 types of tree types in forests; Evergreen + deciduous could be in one forest or contain both trees
- rainfall average between 500-1500 mm yr-1
- productivity lower than rainforest
- mild climate, lower average temperature / lower rainfall
effects of global warming -
- biome shifts
either towards the poles and higher up mountains where it is cooler or towards the equator where it is wetter.
low lying biomes like mangroves may be lost completely. - climate changes are happening very fast, within decades, and organisms change slowly, over many generations through evolutionary adaptation. all they can do to adapt to fast change is to move.
- increased temperature may lead to spread of pests and tropical disease vectors
P / E ratio -
precipitation - evaporation ratio
P > E -> increased leaching and loss of nutrients
P = E -> soil is rich & fertile
P < E -> increase in salinity
zonation:
refers to changes in community along an environmental gradient due to factors such as changes in altitude, latitude, tidal level or distance from shore (coverage by water)
more ab zonation -
the arrangement or patterning of plant communities or ecosystems into bands in response to change, over a distance, in some environmental factor.
the main biomes display zonation with altitude on a mountain, or around the edge of a pond in relation to soil moisture.
the distinct vertical layers experience particular abiotic conditions.
succession:
the process of change over time in an ecosystem involving pioneer, intermediate and climax communities
involves the processes of colonization, establishment, and extinction which act on the participating plant species.
succession begins when an area is made partially or completely devoid of vegetation because of a disturbance. some common mechanisms of disturbance are fires, wind storms, volcanic eruptions, logging, climate change, severe flooding, disease, and pest infestation. succession stops when species composition changes no longer occur with time, and this community is said to be a climax community.
more ab succession -
primary succession - colonisation of newly created land by organisms (rock).
secondary succession - occurs in places where a previous community has been destroyed (forest fire). it is faster than primary succession because of the presence of soil and a seed bank.
pioneer - earliest community of the succession.
climax community - the last and final community.
the change from pioneer to climax is called a sere.
diff b/w primary & secondary succession -
primary:
- begins with no life
- no soil present
- new area (eg. volcanic island)
- lichen & moss come first
- biomass is low
secondary:
- follows removal of existing biota
- soil already present
- old area (eg. following a bush fire)
- seeds & roots already present
- biomass is higher
during succession, the patterns of energy flow, gross and net productivity, diversity, and mineral cycling change over time…
initial stage, new abiotic environment more-or-less devoid of life.
stage 1: colonisation by pioneer community; specialised plants (typically r selected species) adapted to extreme environment;low density of producers, low productivity,low diversity,little nutrient circulationapart from some nitrogen-fixation
stage 2: establishment; species diversity increases. invertebrates begin to visit & live in soil thus increasing organic matter content & water-holding capacity. weathering enriches soil w/ nutrients
stage 3: competition; microclimate continues to change as new species colonise. larger plants increase cover & shelter, allowing k selected species to become established. temperature, sun, & wind are less extreme. earlier r-species r unable to compete with k-species for space, nutrients or light and are lost from the community.
stage 4: stablilization; seral communities become increasingly complex; gross and net productivity increasebut gross productivity increases more rapidly as biomass builds up,nutrient circulation increases in volume and complexity asfood-webs develop. fewer new species colonise.
climax community: represents high level of complexity and diversitygross productivity high and biomass at maximum but many consumers, so respiration also hightherefore net productivity approaches zero (NPP is a measure of the increment of new organic material to the ecosystem from photosynthesis). steady-state dynamic equilibrium.nutrient capital in biomass rather than soilnutrient turnover through death and decay of organisms high. maximum possible development reached under prevailing environmental conditions.
changes during succession -
- species diversity increases toward the later stage (because there is an increase in habitats as new species move or are transported into the area)
- NPP & GPP rise then fall
- energy flow becomes more complex as simple food chains become complex food webs
- soil depth, organic matter, water-holding capacity, mineral content and nutrient cycling all increase
- size of organisms increases with trees creating a more hospitable environment
- biodiversity increases because more niches (lifestyle opportunities) appear and then falls as the climax community is reached
- productivity: respiration ratio falls
