2.4 Biomes, zonation and succession Flashcards
Biome
collections of ecosystems that share distinctive abiotic factors, species and climatic conditions
Types of biome
Terrestrial (forest, desert, grassland, tundra), marine and freshwater (aquatic)
Tricellular model of atmospheric circulation
explains differences in temp + precipitation and how they influence the structure and productivity of different biomes.
Latitude and atmospheric circulation
are the primary factors affecting insolation, temp, and precip.
→ the higher the latitude, the colder the temperatures
→ areas around equator receive the most insolation / unit area of earth
→ polar areas have more atmosphere to pass through, = more loss of energy and cooler temps
Formations
Hot air heated at equator, rises to form Hadley cell.
→ as air rises, it cools and condenses, forming tropical storms (explains tropical rainforest at equator)
→ cooled air spreads and descends - descending creates high pressure and dry areas at 30° (explains desert biome)
→ air travels towards pole as warm winds, when met with cooler polar air at 60° it rises, condenses and forms precipitation (explains temperate forest biome)
Tropical rainforests
distribution: band around equator, within tropics of cancer and capricorn
→ temperature: high and consistent yearly (~26°C)
→ precipitation: high
→ insolation: high, little to no seasonal variation. Provides year round growing season.
→ productivity: comprises ~ 40% of NPP for terrestrial ecosystems. High photosynthesis and NPP caused by low latitude and ample direct sunlight.
→ biodiversity: high, up to estimated half of world’s species in rainforest canopy. High diversity due to high climate factors year round.
→ structure: stratified tree canopy, many niches. Only ~1% of light on canopy reaches forest floor, canopy has highest NPP.
→ soil low in nutrients, majority stored in trees. High rates of decay maintain rates of growth.
→ heavy rains can result in nutrients being washed away, which limits PP.
→ canopy usually protects soils from rainfall, but logging causes soils to be eroded rapidly
Temperate forest
distribution: between 40° - 60°N of equator
→ temperature: cold winters, warm summers
→ precipitation:determines whether temperate forests or grasslands develop
→ insolation: varies according to tilt of Earth, limits growing season
→ productivity: lower compared to rainforests due to power temps and rainfall. Second highest NPP in all biomes.
→ biodiversity: lower than rainforests, forests usually dominated by one species
→ structure: less stratification and layering, less dense canopy, reduces species diversity and complexity of niches
→ two types of trees (evergreen, deciduous - deciduous lose their leaves in winter)
→ forest floor leaf layer increases insulation and nutrients when it decays in warm temperatures
Deserts
distribution: 30° N and S
→ temperature: high during day (45-49°C), low at night (10-0°C)
→ precipitation: low - often very uneven
→ insolation: high (air is dry after leaving tropics)
→ productivity: lack of water limits photosynthesis and NPP, results in sparse vegetation
→ biodiversity: xerophytic species (adapted to fluctuations in temp and scarcity of water), reptiles most common vertebrates due to cold-blooded metabolism, cacti reduce surface area for transpiration via spines
→ structure: soil can be rich in nutrients as there is no leaching, decomposition is low due to lack of water
Tundra
→ distribution: high altitudes, the north polar region
→ temperature: low for majority of year, -50°C, warmer during 6 week period.
→ precipitation: low, water mainly stored in ice
→ insolation: short days, limited sunlight; almost 24h of sunlight during summer. Life increases during summer.
→ productivity: very low due to variable light intensity, rainfall and temperatures affecting race of photosynthesis
→ biodiversity: low, very few species adapted to cold conditions - large animals to reduce heat loss
→ structure: low temperatures lead to low cycling of minerals → peat bogs form in carbon sinks
Effects of climate change on biome distribution
→ increases in CO2 and other GHG increases mean global temperature, affecting rainfall patterns
→ climate change alters biome distribution
Spatial and temporal changes in communities
→ spatial changes occur along environmental gradients due to changes in altitude, latitude, distance from sea
→ temporal changes occur as a community develops from early to later stages
Zonation
→ the arrangement or pattern of communities in bands in response to a change in environmental factors over distance (eg. altitude, latitude, distance from shore)
Rock shores
organisms high on shore exposed to air for long periods of time, have adapted to withstand changes in salt concentration and temperature
→ organisms low on shore are covered by seawater, experience less variation in temperature and salt concentration, with greater wave stress
Succession
→ change over time in an ecosystem involving pioneer / intermediate / climax communities
→ each distinct community in the succession is a seral stage
→ succession explains how ecosystems develop from a bare substrate over time
→ lithosere (bare rock)
→ fresh water (hydrosere)
→ dry habitat (xerosere)
Pioneers
first stage of ecological succession - species able to withstand difficult conditions
Climax community
final stage of succession, more stable than earlier stages, in equilibrium
Primary succession
occurs on previously uncolonised substrate (eg. rock)
Secondary succession
occurs in places where a previous community has been destroyed. Faster than primary succession due to soil and seed bank.
Primary succession on shingle ridge
→ lichens and mosses pioneer species that photosynthesise and trap water on nutrient-poor shingle
→ pioneer species trap particles blowing by and weather the rock
→ decomposition of pioneers results in a thin layer of soil
→ red fescue colonise area, roots trap soil and prevent erosion, pioneers begin to be outcompeted
→ xerophytic plants eg. sea kale prevent water loss, nitrogen-fixing plants eg. rest harrow increase soil nutrients
→ decomposition continues and allows growth of larger plants eg. shrub community of bramble
→ climax community of temperate forest (oak/sycamore) develops, shrubs are replaced by shade-adapted species like ferns
Secondary succession in yellowstone
Fires in Yellowstone National Park wiped out many aspects of the park’s forest - some fires burned soil and ground biomass, some burned the canopy. Fires burned for several months.
→ recovery began almost immediately with herbaceous fireweed as a pioneer species
→ lodgepole pines, though a climax species, are serotinous, allowing fast regeneration in burned areas
→ comprising 80% of park’s forests, they only release seeds when high temperatures eg. fires create favourable open canopies for seedling establishment
→ aspen, wildflowers had an increase in productivity as nutrients were released from forest litter during burning
→ soil depth only charred to 14mm, leaving diverse root systems unharmed
→ minimal overall loss of wildlife from fires, only browsers eg. moose populations declining
→ other k-strategists eg. elk, bison, deer rebounded due to rapid plant growth, birds able to find ants and worms easily in newly uncovered soil
changes through succession
GPP → pioneer communities have low GPP because of the low density in producers. Climax communities have high GPP as there is an increased consumer community.
NPP → high in pioneer communities as community respiration is low (low # organisms). High NPP means biomass is continuing to accumulate. Approaches zero in climax community as GPP is balanced by increased respiration
Climax communities
community of organisms that is in steady-state equilibrium with natural environmental conditions. It is the endpoint of ecological succession.
→ greater biomass, high species, habitat and genetic diversity
→ favourable soil conditions and structure (deeper, greater water retention/aeration)
→ more k-strategist organisms (taller plants etc)
→ greater community complexity, resilience and stability
R strategists
Colonisers
Highly adaptable
Rapid growth/development
Short lifespans
Small size, many offspring
Early, high reproduction
Type III survivorship
Suited to pioneer communities
Continuous J-curve population
K strategist
Dominant species
Specialist, susceptible to change
Slow growth/development
Long lifespans
Large size, few offspring
Delayed reproduction
Type I or II survivorship
Suited to climax communities
S-population curve
