2.4 Biomes, zonation and succession

Question 1

Biome

Answer 1

collections of ecosystems that share distinctive abiotic factors, species and climatic conditions

Question 2

Types of biome

Answer 2

Terrestrial (forest, desert, grassland, tundra), marine and freshwater (aquatic)

Question 3

Tricellular model of atmospheric circulation

Answer 3

explains differences in temp + precipitation and how they influence the structure and productivity of different biomes.

Question 4

Latitude and atmospheric circulation

Answer 4

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

Question 5

Formations

Answer 5

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)

Question 6

Tropical rainforests

Answer 6

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

Question 7

Temperate forest

Answer 7

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

Question 8

Deserts

Answer 8

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

Question 9

Tundra

Answer 9

→ 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

Question 10

Effects of climate change on biome distribution

Answer 10

→ increases in CO2 and other GHG increases mean global temperature, affecting rainfall patterns
→ climate change alters biome distribution

Question 11

Spatial and temporal changes in communities

Answer 11

→ 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

Question 12

Zonation

Answer 12

→ the arrangement or pattern of communities in bands in response to a change in environmental factors over distance (eg. altitude, latitude, distance from shore)

Question 13

Rock shores

Answer 13

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

Question 14

Succession

Answer 14

→ 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)

Question 15

Pioneers

Answer 15

first stage of ecological succession - species able to withstand difficult conditions

Question 16

Climax community

Answer 16

final stage of succession, more stable than earlier stages, in equilibrium

Question 17

Primary succession

Answer 17

occurs on previously uncolonised substrate (eg. rock)

Question 18

Secondary succession

Answer 18

occurs in places where a previous community has been destroyed. Faster than primary succession due to soil and seed bank.

Question 19

Primary succession on shingle ridge

Answer 19

→ 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

Question 20

Secondary succession in yellowstone

Answer 20

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

Question 21

changes through succession

Answer 21

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

Question 22

Climax communities

Answer 22

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

Question 23

R strategists

Answer 23

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

Question 24

K strategist

Answer 24

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

Question 25

Human impact on succession

Answer 25

Human disturbance halts process of succession and divert it so a different stable state other than a climax community is reached.
→ activity modifies the ecosystem (eg. use of fire, grazing, agriculture, deforestation, overfishing); depending on the resilience of an ecosystem changes may be more or less permanent.
Eg. deforestation of tropical rainforest biome
→ increased demand for meat demands land for cattle ranching and agriculture, 90% of the reason why land is deforested in the Amazon. Results in habitat destruction and loss of climax community.
→ replacement with agricultural system affects global biodiversity, weather, sedimentation patterns
→ CO2 released returns to atmosphere