Terrestrial Communities Chapter 4 Ecology: Evolution, Application, Integration Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Jan 20, 2016
Terrestrial Communities
Chapter 4
Ecology: Evolution, Application, Integration
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Concepts
• 4.1 What Determines Species Distributions?
• 4.2 What Are the Fundamental Types of Terrestrial Communities?
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
What Determines Species Distributions?
• Physical environment– Tolerance limits
• Biotic interactions– Food– Predators– Competitors– Parasites– Diseases
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Abiotic Factors Determining the Geographic Range
• Climate as a key component of the physical environment– Temperature– Precipitation
• Soils
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Climate and Weather
• Weather refers to various physical conditions of the lower atmosphere at a specific place over a short period of time.
• Climate refers to the prevailing weather conditions in an area over a relatively long period of time.
• Climate is much more predictable and has a major impact on ecological interactions.
Climate
• The product of weather which is driven by unequal heating of air masses.– Weather is short term pattern
– Climate is long term pattern
• Climate type– Determined by average temperature and
average precipitation
– Depends on adiabatic processes
Adiabatic Processes
• Warm air is less dense and therefore rises
• Cool air is more dense and therefore sinks
• Altitude affects air density and temperature– warm at lower altitudes (compressed gas)
– cool at higher altitudes (expanded gas - adiabatic cooling)
Climate
• Three main factors shape the climate:
– The amount of incoming solar radiation.
– The movement of air and water.
– The major features of the Earth’s surface.
Incoming solar radiation shapes climate
• The angles at which sunlight strikes Earth result in differences in temperature from the polar to the tropic regions.
– Greatest at equator• The sun’s rays are more perpendicular to earth.
– Less at higher latitudes• Sunlight strikes the earth’s surface at a lower angle, and
is spread over a greater area
• It also must pass through more of the earth’s atmosphere.
Latitudinal Variation in Temperature
• Driven by the angle of the sun rays relative to the Earth surface
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Altitudinal Variation in Temperature
• Driven by the adiabatic cooling of the air
• Lapse rate (the rate of T° decrease with altitude) depends on humidity– Dry lapse rate 10°C/km– Wet lapse rate 5.5°C/km– Environmental lapse rate
6.4°C/km
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Rising Air Rains and Dropping Air Dries
Seasonal Variation in Temperature
• Driven by the tilt of the Earth’s axis relative to the SunEcology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
• Earth’s climate is affected by four giant convection cells that are formed by the rising of warm, moist air and the sinking of cool, dry air.
• These cells produce relatively constant and predictable wind patterns known as the prevailing winds
• Ocean currents move large amounts of water and have significant effects on regional climates
The movement of air and water shapes climate
General Patterns of Climate
– Tropical at equator • warm, wet
– Subtropical (about 30o N and S)• warm, arid
– Temperate• moderate temps and humidities
– Polar • cold, dry
Hadley cell - Low latitude air movement toward the equator that with heating, rises vertically, with poleward movement in the upper atmosphere. This forms a convection cell that dominates tropical and sub-tropical climates.
Ferrel cell - A mid-latitude mean atmospheric circulation cell for weather named by Ferrel in the 19th century. In this cell the air flows poleward and eastward near the surface and equatorward and westward at higher levels.
Polar cell - Air rises, diverges, and travels toward the poles. Once over the poles, the air sinks, forming the polar highs. At the surface air diverges outward from the polar highs. Surface winds in the polar cell are easterly (polar easterlies).
Intertropical Convergence
• Lots of rain in the Tropics because water cycles more rapidly through the tropical atmosphere. – heat of the sun warms the air and causes
water to evaporate• warm air rises and cools• moisture condenses forming clouds• as moisture droplets in clouds collide they
aggregate and form droplets• eventually these droplets become too large to
be supported by the rising air and they drop out as precipitation
The Formation of Deserts
• Deserts are characterized by very low precipitation and frequently occur at approximately 30° latitude.
– Dry air descending at this latitude brings little moisture.
– These regions are close to the equator and receive large amounts of solar radiation.
Deserts• Air at the equator now rises
– eventually it stops rising and begins to spread north and south• this high-altitude air is dry because the moisture fell
as tropical rains
– as the air mass flows north and south it cools and sinks back to the earth’s surface at about 30o latitude• this dry air flows north and south and draws moisture
from the land beneath it creating deserts• air moving back towards equator completes one cell
Deserts of the world - roughly 30o north and south of
equator
Temperate and Polar Cells
• Air moving towards the poles becomes part of the circulation cell at the middle latitudes– Warm, moist air flowing from the south rises as it
meets cold polar air from the north. – The air mass now rises, and moisture picked up
as the air crossed the desert areas now condenses to form clouds that will produce abundant precipitation in the temperate regions.
– As the air cool it sinks completing the temperate cell and initiating the high latitude polar cell.
Coriolis Effect
• Winds don’t appear to move directly north and south– northern hemisphere: apparent deflection
to the right– southern hemisphere: apparent deflection
to the left• apparent = relative to someone standing on the
earth’s surface. This is the perspective relevant to ecosystems on earth!
• from space they look north and south• due to the earth’s rotation
Coriolis Effect
The major features of Earth’s surface also shape climate
• By retaining heat, oceans and large lakes moderate the climate of surrounding lands.
• Mountains cause a rain shadow effect.
Effects of Ocean Currents
• Eastern coasts tend to be warmer– warm water tends to move toward
temperate latitudes along the eastern coasts of continents• Gulf Stream
• Western coasts tend to be cooler– cold water tends to move toward the
Tropics along the western coasts of continents• Peru Current
Latitudinal Variation in Precipitation
• Driven by the global air circulation – Atmospheric
circulation cells: Hadley, Ferrel, & Polar cells
• Mid-latitude desertification– World’s largest
deserts are around 30° N & S
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Latitudinal Variations• Between each of these circulation cells are bands of high
and low pressure at the surface. The high pressure band is located about 30° N/S latitude and at each pole. Low pressure bands are found at the equator and 50°-60° N/S.
Usually, fair and dry/hot weather is associated with high pressure, with rainy and stormy weather associated with low pressure. You can see the results of these circulations on a globe. Look at the number of deserts located along the 30°N/S latitude around the world. Now, look at the region between 50°-60° N/S latitude. These areas, especially the west coast of continents, tend to have more precipitation due to more storms moving around the earth at these latitudes.
Local Variation in Precipitation
• Driven by major landscape features– Mountain rain shadow
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Slope effect: east facing slope covered with montaine forest; west facing slope has xeric-adapted community
How do abiotic and biotic factors affect species distribution?
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Ecological Filtering
• Occurs when biotic or abiotic factors limit the membership of species in a local community.
• Abiotic filters:– Environmental conditions– Limiting resources
• Biotic filters:– Competition– Predation– Parasitism
• Disturbance can function as an ecological filter (e.g., by directly removing a species) or as a process that influences the intensity of other ecological filters (e.g., by altering limiting resources).
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Distribution Depends on Evolutionary History
• Geological history– Continental drift– Glaciation (e.g. formation of
the Bering Land Bridge)
• Historical shifts in climate– Range breaks due to
historical local extinctions
• Phylogenetic history– Phylogenetic conservatism
of the species’ range limits– Divergence of the range
limits
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Take Home Points
• A species’ geographic range is determined by the climate, substrate, and local biological interactions.
• Climate (temperature and precipitation patterns) reflects the local combination of geographic features.– Latitude, altitude, aspect, and proximity to large
bodies of water.
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Take Home Points
• Soil and substrate – Product of weathered parent material, external
inputs, and organic matter. • Dispersal and time determine whether the
species reaches a favorable region.
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
The Fundamental Types of Terrestrial Communities: Large Scale
• Biogeographic realms– The boundaries
determined by the evolutionary history, the geological connections among regions, and regional climate
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
The Fundamental Types of Terrestrial Communities: Small Scale
• Biomes– Ecosystems characterized by specific types of vegetation,
the form of the plant life.
• Composition of plant species (the flora) may be different in the same biomes in different geographical regions– E.g., deciduous forests in Europe vs. North America or
rainforests in Asia vs. South America
• Useful descriptive concept
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
The Fundamental Types of Terrestrial Communities: Biomes
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Biomes
• Variations in species present and ecological conditions may exist within a single biome.
• No distinct boundaries
• Plant distribution patterns influenced by climate, topography, and soil
Climate (temperature and precipitation) are the main determinants of biome’s plant life
A climate diagramEcology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Biome 1. Rainforest
Key adaptations:• Leaf morphology to prevent water
accumulation and leaching• Trunk buttresses• Epiphytic habit• Shallow root system• Mycorrhyzae
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Biome 2. Tropical Savanna
Key adaptations:• Deciduous habit to reduce water
loss during the dry season• Grasses regrow from roots• Thorns and spines (protection from
grazers)
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Biome 3. Desert
Key adaptations:• Allelopathy• Reduced leaves• Water storage (trunks)• Hairy leaves• Annual habit
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Biome 4. Mediterranean Shrubland
Key adaptations:• Flammable oils (a few species such
as chamise) promote fires• Resprout from roots• Hard, needle-like (sclerophyllous)
leaves with few stomata
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Biome 5. Temperate Grassland
Key adaptations:• Extensive root systems• Quick regrowth from roots• Growth zone near the base, not
the tip to prevent damage from grazing or fire
• Wind pollination• Narrow leaves to reduce water loss
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Biome 6. Temperate Deciduous Forest
Key adaptations:• Deciduous habit• Broad leaves to capture sunlight• Thick bark to protect from cold• Understory plants flower in the
spring before the canopy develops
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Biome 7. Boreal Forest (Taiga)
Key adaptations:• Evergreen habit• Needle-like leaves to reduce water
loss and snow retention• Waxy coating on needles • Dark color to absorb more heat• Drooping branches to shed excess
snowEcology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Biome 8. Arctic Tundra
Key adaptations:• Small size and low-growing plants• Shallow root system (permafrost)• Dark color to absorb solar heat• Hairy stems and leaves• Growth in clumps for protection
from the wind and cold
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Biomes Are Linked to Climate Patterns
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Human Impacts on Biomes
• Local– Heat dome in the cities– Land use
• Global– Global climate change– No-analog climates (up to
39% of the terrestrial biomes by 2100) → No-analog communities
Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press
Terrestrial Biomes
• Climate and people influence the location, extent, and distribution of biomes.
• The effects of temperature and moisture on species cause particular biomes to be found under consistent conditions