Terrestrial Communities Chapter 4 Ecology: Evolution, Application, Integration Ecology: Evolution,...

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?


What Determines Species Distributions?

• Physical environment– Tolerance limits

• Biotic interactions– Food– Predators– Competitors– Parasites– Diseases


Abiotic Factors Determining the Geographic Range

• Climate as a key component of the physical environment– Temperature– Precipitation

• Soils


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


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


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


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


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?


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).


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


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.


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.


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


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


The Fundamental Types of Terrestrial Communities: Biomes


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


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)


Biome 3. Desert

Key adaptations:• Allelopathy• Reduced leaves• Water storage (trunks)• Hairy leaves• Annual habit


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


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


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


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


Biomes Are Linked to Climate Patterns


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


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

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