LECTURE NOTES - Week 2
The Biosphere
Köppen-Geiger System
3 major categories:
Climate
Precipitation
Temperature
5 climate types
Tropical rainy (equatorial)
Dry (arid)
Warm temperate
Cold forested (snow)
Polar
6 precipitation types
8 temperature types
The three categories can be combined (e.g., Csa = (C) warm temperate, (s) summer dry, (a) hot summer = bright green on the map)
Climate Diagrams
Summarizes monthly mean and annual records of temperature & precipitation
Used to characterize the climate for a “typical” locality within a region of interest
Terrestrial Biomes
A large scale terrestrial biological community shaped by the regional climate, soil, and disturbance patterns where it is found, usually classified by the growth form of the dominant plants
How do you regonize a dominant plant form?
Floristically
By taxa
Structurally
By 3-D form
Funtionally
By role
Survey of Biomes
Brief Survey of Major Biomes
Information in the following slides is organized as:
Descriiption and location
Climate features, diagrams
Soils
Major biological features
Human infleunces
Keep in mind:
Very broad generalization
A degree of subjectivity
Tropical Rain forest
High primary productivity
Importance of canopy
Year-round biological activity
Increadible diversity
Many specialists
Rapid decomposition
Climate Diagram:
No frost
Constant warm temperatures
Prolonged operiods of wet conditions; rainfall generally > 100 mm/month
Warm and wet throughout the year
Soils subject ot leaching; nutrient-poor except young volcanic soils
River margin soils are replenished by flooding
Historical use:
Non-intesnive hunting
Gathering
Shifting agriculture
Current uses:
Logging
Mining
Intensive agriculture
Threats to biodiversity
Threats to regional climate patterns
Nutrient losses
Drought in the tropics
Tropical Seasonal Biome
Strong seasonality in precipitation driven by shifts in the ITCZ
Changes in forest structure and drought deciduousness
Dry forest vs. savannah driven by both climate conditions as well as distturbance processes
Tropical Dry Forest:
Marked seasonality in pattern of precipitation, but not in temperature
Marked seasonal contrasts in lushness of the vegetation
Migrations of fauna
Pressues:
Dry tropical forest has the highest human population densities:
Forestry
Ranching
Cereal farming
Cotton farms
Tropical Savanna
Strong seasonality, especially in precipitation
Importance of fire and grazing
“Feast” or “famine”
Grasslands, thorny and scrubby scattered trees
Wet season short and intense
Total precipitation generally lower than for forests
Role of soils
Impermeable subsurface keeps water near surface
Fire, grazing, low precipitation favor grasses over trees
Pressures:
A circle of events:
Conversion of savanna to agricultural land attracts immigrants
Expansion of human population near protected areas leads to yet more conversion of land to agriculture
Pressures are greatest at Reserve and Park boundaries
Ploughing can disrupt the soil causing erosion
Livestock ranching
Climate change coupled with increasing population densities both human and livestock has caused desertification
Deserts
Subtropical desert near ~30 degrees N or S
Continetal deserts
Rain shadow deserts
Coastal deserts
Overall, ~20% of land surface of the Earth
Common features:
Low precipitation
Water loss exceeds precipitation
Bottom line:
Lack of available water during much of the year
Soil often poor, little organic matter, high concentrations of salts
Subtropical:
~30 degrees S; high atmospheric pressure zones, percipitsation < 25 cm/y, mostly in summer
Drought tolerance
Opportunists
Examples:
The Austrialian deserts
The African deserts
Continental:
Continetal climates
Cold winters, little precipitation
E.g., Gobi Deset, Great Basin Desert of USA (also affected by rain shadow)
Rainshadow:
Rainshadow effect
Very little precipitation
The lack of moisture can be quite extreme (e.g., driest part of Judean Desert gets ~100 mm per year)
Costal:
Not restricted to any latitude
Depends on pattern of precipitation; climate and rainshadow Atacama Desert of Chile is an extreme example
Blocked from precipitation because of mountains (to the east) and the prevailing high pressure over the Pacific
Some locations have no recorded precipitation
Human Influences:
Irrigation
Salt build-up
Water over-exploitation
Desertification
Temperate Shrublands and Woodlands
Woodlands and shrublands (chaparral, mayoral, garrigue, fynbos, mallee)
Mediterranean coast of Europe, Middle East, and Africa; California, chile, S. Africa, sw coasr of Austrilia
Scattered evergreen woody shrubs, grasses, aromatic herbs, fire-resistant plants; highly diverse flora and fauna
Climate diagram Chaparral:
Temperatures are warm, hotter in summer
Summers are dry; winter is the rainy season
Vegetation - woodland, shrubbland and grasses
Summer drought; winter rains
Warm annual mean temperatures
Water conservation strategies
Defeses against fire and browsing
Soils often fragile, moderate fertility
Human influences:
High human population densities
Low intensity agriculture promotes sustainable systems
Urbanization
Climate change
Increased risk and intensity of fires
Temperate Grasslands
Natural grasslands (prairies, steppes, veldt, pampas)
Extensively altered for agriculture
Trees and shrubs
Confrined to stream and river margins
Role of fire and grazing
Vertibrate herbivores
Invertibrate herbivores
Most precipitation occurs in the growing season
Cool to cold and dry winters
Subject to droughts, sometimes prolonged
Deep soils, miuch organic matter, slow decomposition
Human influences:
Conversion to agriculture
Resporation efforts recent and small
Loss of soil, loss of soil organic matter
Temperate Forest
Seasonal deciduous forests of Eurasia, eastern N. America
Temoerate coniferous rainforests
Forests of New Zealand, southern Chile
Seasonal deciduous:
Vertical stratification:
Herbs
Shrubs and saplings
Shade tolerant understory (subcanopy, the “sapling bank”)
Canopy
Climate diagram:
Temperature seasonality, long growing season + winter
P > ET, > ~600 mm/y
Trees rather than grasses
Frosts can occur in early and late season
Percipiation supports trees (> ~650 mm/y)
Moist growing season, also more moisture in winter than grasslands
Could but snowy winters
Soils are generally fertile
Temperate Evergreen Forest
Mild winters, heavy winter rain, summer fog and moderate summer drought
Needle-leaved trees (redwoods, firs, Auracaria)
High biomass, low diversity
Fossil evidence goes back to mid-Mesozoic
Human influences:
Settlements
Agriculture
Exploitation
Industry
Urbanization
Reforestation
Taiga/Boreal
Long winters, short growing season
Low mean annual temperature and extreme ranges
Moderate annual rates of precipitation
Thin acidic soils, low fertility
Human influences:
Forest exploitation
Climate change
Drying, lightning
Insect pests
Permafrost thaw
“Drunken forests”
Taiga: 2014 Forest Fires
Wildland - urban interface
Carbon losses
Loss of ecological resilience
Long term impacts on wildlife availability
Tundra
Long cold winters
Permafrost; Thaw depth: 0.5 - 1 m
Poor drainage
Low or dwarf vegetation
Soils are nutrient poor
Migratory birds and mammals; insects
Population cycles
Climate diagram:
Cold (mean < 0 degrees celsius)
Short frost-free season
Precipitation:
Fairly constant, low
Conditons are moist (precipitation > ET)
Short growing season (6-10 weeks)
Total precipitation varies - but, key points:
Levels are low, there is no period of moisture deficit
Vegetation
Human influences:
Airborne pollutants
Oil and mineral exploration, extraction and transport
Global warming, permafrost thawing, landslips and coastal erosion, tundra ‘greening’
Mountains: Several Biomes
From valleys topeaks, serval “biomes” can occur, in unique juxtazpositions
Gradient in altitude can parallel gradients in latitude
Direction of exposure is important
Mountain Biological Zones
Coping with Environmental Variation
How Do Organisms Deal With Environmental Extremes?
Life History Strategies
Avoidance:
A response to stresswful environmental conditions that lessens their effect through some behavioor or physiological activity that minimizes an organism’s exposure to the stress
Tolerance:
The ability to survive stressful environmental conditions
Environmental Tolerance
The Niche
Fundamental niche:
The full range of conditions and resources that allows a species’ popolation to survive and reproduce in the absence of competitors and predators
Realized niche:
The full range of conditions and resources that allows a species’ popu;ation to survive and reproduce in the presence of competitors and predators
Climate Envelopes
The range of climate conditions under which a species occurs (climate niche)
Stress
The condition in which an environmental change results in a descrease in the rate of an important physiological process thereby lowering the potential for an organism’s survival, growth, or reproduction
Acclimation Vs. Adaptation
Acclimation (individual) - the adjustment (plastic response) of physiology, morphology or behavior to lessen the effect of an environmental change and minimize the associated stress
Adaptation (population) - A physiological, morphology, or behavioral trait with an underlying genetic basis that enhances the survival and reproduction in that environment
Temperature
Temperature Response
How do organisms result temperature?
Modifying Energy Balance
Condution - direct transfer of energy from warmer, rapidly moving molecules to cooler, slowly moving molecules
Convection - heat carried away by cool water or air moving across a warm body
Evaporative cooling - latent heat transfer resulting from a change in the state of water from liquid to vapor
Reducing the amount of incident solar radiation
Metabolic heat generation
Transpiration
How Can Plants Modify Incident Solar Radiation?
What Else Would Fuzziness (Pubescence) Modify?
Fur Thickness Can Play A Similar Insulating Role
What Else Do Animals Do?
Endotherms (warm blooded):
Rely primarily on internal heat generation
Ectotherms (cold blooded):
Regulate body temperature primarily through energy exchange with the external environment
Animals Have Some Extra Tricks for Modifying Energy Balance
Muscle contraction
Behavioral changes
Thermoregulation - Metabolic heat generation
Torpor or Adaptive Hypothermia
Allows endotherms to alter their lower critical temperature during cold periods when sufficient food is unavailable
Body temp may drop as much as 20 degrees celsius
Torpor:
A state of lowered body temperature, slow breathing and heart rate and low metabolic activity
Hibernation:
Sustained and prolonged torpor
Water Potential - A Quick Review
Ψ = Ψ0 + Ψp + Ψm
Total water potential in Mpa - Ψ
Osmotic potential (Ψ0) - energy associated with dissolved solutes (negative value)
Pressure potential or turgor (Ψp) - energy associated with exertion of pressure (positive or negative)
Matric potential (Ψm) - energy associated with the attractive forces on the surfaces of large molecules inside cells or on the surface of soil particles (negative value)
Water Moves Down A Water Potential Gradient From High to Low
Solutes, negative pressure (tension) and matric potential all reduce the free energy of water, reducing the water potential
Water Balance in Plants - Turgor Pressure Critical For Plant Structure and Growth
Ψ = Ψo + Ψp + Ψm
Water Potential and Water Loss in Plants
Biomass Allocation Tracks Water Availability
More generally plants will modify biomass allocation to meet resource limitation
Water Exchange Mechanisms in Animals Are More Diverse
Extra Challenges to Living in Aquatic or Saline Environments
Hypersomotic - aquatic environment is more saline than an organism’s cells or blood (lower water potential)
Hypoosmotic - aquatic environment is less saline than an organism’s cells or blood (higher water potential)
Plants face this problem too
Animals Lose Water in Terrestrial Environemtns Too
Balance between gas exchange and water loss
High water loss can be balanced with high water intake but what if water supply fails?
Resistivity of External Coverings Are Key and Vary By Environment
Kangaroo Rats As An Extrme Example of Evolution of Drought Tolerance
Oxidative metabolism
Behavioral changes
Think, oily skin with few sweat glands
Efficient water removal in kidneys and intestines
Unique Challenges of Freezing