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Biomes, zonation and succession 2.4 (Succession (Secondary (It occurs at…
Biomes, zonation and succession 2.4
Zonation
Changes in communities along an environmental factor gradient due to factors such as changes in altitude, latitude, tidal level or distance from shore
Succession
Primary
e.g. Rocks exposed by landslide, sand dunes, glacial deposits or volcanic lava flows
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Secondary
It occurs at sites where that have previously supported a community after a major environmental disturbance disrupts a previous succession.
e.g. Fires, ploughing, road building, floods
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The orderly process of change in structure and species composition of a community over time. It is directional as one community is replaced by another
- Hydrosere = a succession on water
- Psammosere = a succession on sand dunes
- Xerosere = a succession on bare rock
- Halosere = a succession on salt marshes
It starts with a pioneer community then the vegetation transitions through various intermediate communities to the final climax community. Each stage is a SERE
Bare, inorganic surface → stage 1 colonisation → stage 2 establishment → stage 3 competition → stage 4 stabilisation → climax community
The climax community is a stable sere that can only be disturbed by:
- The soil
- The range of random events (natural disasters)
- The climatic factors
It is the moment where the community has reached a balance with natural conditions
Humans can impact succession = deflected succession to an alternative state = by modifying the ecosystem = agriculture, grazing, resource use = if sheep constantly graze a field, the field will be in a plagioclimax stage. This can be purposeful or not.
The resilience of the ecosystem is a measure of how well an ecosystem can tolerate drastic changes without collapsing into a different state governed by different processes. It is the cycle of disturbance followed by recovery.
Biomes
A collection of ecosystems sharing similar climatic conditions
- Tundra = Arctic and alpine
- Desert = Hot, coastal and cold
- Grassland = Savana and Temperate
- Aquatic = Marine and freshwater
- Forest = Tropical rainforest, temperate forests and taiga
The distribution is determined by:
- Temperature = e.g. tundra is cold whereas, tropical rainforest is mostly dry and warm. - determined by earths tilt and seasons
- Precipitation = the cycle, sun warms water, evaporation = hot moist air rises and cools = cool air holds lss moisture so falls as precipitation - different regions have different amounts due to this.
- Insolation = measured by the amount of solar energy received per square cm/min. As the earth rotates around the sun, the position of land will change resulting in various concentrations of solar radiation over the land. This amount of energy received will be measured to find the insolation of the land
They cross borders, distribution around the world defines the biome.
The tricellular model
This results in the precipitation and climate of all biomes. It is the warmest at the equator where the northern and southern hemisphere trade winds meet (30º -Hadley and 60º - Ferrel from the equator)
There are 3 air masses in the model, the Polar, Hadley and Ferrel cell
There is also the ITCZ (Inter-tropical convergence zone) = meeting place of the trade winds from both the northern hemisphere and the southern hemisphere. It is a low-pressure area where the trade winds, which have collected heat from the oceans, are forced to rise by convection currents. These rising convection currents are then cooled which forms cumulonimbus clouds.
Climate change impact
It is altering the distribution of biomes (as they are majorly determined by climate) which causes BIOME SHIFTS
If significant climate change occurs, natural populations of wild organisms will be unable to exist within their original ranges. Changes in temperature and precipitation, and thus, changes in vegetation and habitat, will affect the ecosystems causing plants and animals to be unadapted for the conditions. Thus, they move, run away.
- Towards the poles where it is cooler
- Higher up mountains where it is cooler
- Towards the equator where it is wetter.
R-strategists
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Soil starts to form as weathering begins to break down the rocks and plants contribute organic matter to the debris.
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○ Population size is very unstable, Low Parental care
K-strategist
○ Larger, slow reproduction, long lifespan, high parental care, population is stable
○ Elephants, Humans, Tigers
Greater biodiversity in ecosystems and individuals leads to greater stability. e.g. species with high genetic diversity and many populations that are adapted to a wide variety of conditions are more likely to be able to survive disturbances, disease, and climate change. It also enriches humans with medicine.
Eventually, the r-strategists will be replaced by the k-strategists as the k strategists are more adapted to competition, living longer etc.
The more complex an ecosystem the more stability as if there if e.g. two organisms that convert nitrates to ammonium and a disturbance causes one of them to be wiped out, the other will continue the process and stability will be maintained despite the event.
In the early stages, the GPP is low due to conditions and low density of producers. The energy lost through respiration is low too = NPP is high (the system is growing along with biomass).
In the later stages, produces, consumers and decomposers increase so GPP also increases. Until a max in the cimlax community. This is balanced by equally high rates of respiration so NPP approaches 0 and the production:respiration ratio (P:R) approaches 1.