4) biogeochemical cycles carbon cycle nitrogen cycle phosphorus cycle sulfur cycle water cycle

‣ 4) Biogeochemical Cycles

Carbon cycle

Nitrogen cycle

Phosphorus cycle

Sulfur cycle

Water cycle

‣ 5) Ecosystem Stability

Environmental change

Key species

Ecological succession

‣ 1) Biomes

Distribution of biomes

Classification of biomes

‣ 2) Components of Ecosystems

Components of ecosystems

Factors affecting ecosystems

Habitats

Adaptations

‣ 3) Energy flow in Ecosystems

Trophic structure

Energy in ecosystems

Ecosystem productivity

Ecological pyramids

Contents

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Ecology‣ Ecology is the study of

the relationships between organisms and their physical and biotic environment:

Relationships involve interactions with the physical world as well as interrelationships with other species and individuals of the same species.

O2

Nutrients

CO2

‣ Living organisms can be studied at different levels of complexity.

‣ From least to most complex, these levels are (in an ecological context):

Individual

Population

Community

Ecosystem

Biome

Biosphere

Biological Complexity

Biosphere

Biome

Ecosystem

Community

Population

Individual

• The biosphere isthe region within which all living things are found on Earth.

• It is the narrow belt around the Earth extending from the bottom of the oceans to the upper atmosphere.

The Biosphere

Image: NASA

• Our knowledge of what constitutes the biosphere continues to develop as scientists continue their exploration of the Earth.

• The biosphere extends into the Earth’s crust, below the oceans and deep into rock fissures; it extends well into the Earth’s upper atmosphere.

Exploring the Biosphere

Life exists in all places, from blind white crabsin lightless environments...

to tube worms in the crushing ocean depths.

• The biosphere encompasses all living things on Earth.It comprises a number of aquatic and terrestrial biomes.

• Biomes are the largest geographically based biotic communities that can be conveniently recognized.

• Biomes within the same category have specific, characteristic features.

Biomes

Desert biome

• Terrestrial biomes are recognized for all the major climatic regions of the world and are classified on the basis of their predominant vegetation type.

The same biome may occur in widely separated regions.

Terrestrial Biomes

• Three air cells circle each hemisphere of the Earth.The interaction of these cells is a major contributor the formation of biomes.Biomes and Weather Cells

Dry air descends at the poles

Polar cell

Air rising at the equator causes the

formation of rain clouds

Rising air allows cloud formation in temperate regions

After losing its moisture, dry air

descends

Hadley cell Ferrel

cell

Polar Temperate Desert Tropical Desert Temperate Polar

• Deserts are arid regions (annual rainfall generally less than 25 cm). The hot desert biome is found in two belts, centered at 30° latitude north and south of the Equator.

• Hot deserts receive most of their rainfall in summer. The driest regions are in central Australia and the middle of the Sahara Desert.

The temperature range is approximately 30°C, and the winter and summer are both very warm.

Hot Deserts

Ayres Rock, Australia Sand dunes, Namibia

Temperature range: 9°CThe winter and summer are both very warm.

Annual total rainfall: 15 cm

Example: Khartoum, Sudan 15.5°N

Physical Factors:Hot Deserts

Khartoum

• The cold desert biome is found in dry regions in the mid to high latitudes, especially in the interiors of large continents. Cold deserts also occur at high altitudes in the rain shadows of mountain ranges.

• Cold deserts receive most of their small amount of rainfall in winter.

Cold Deserts

Arches National Park, USASierra Nevada, USA

Example: Cheyenne, Wyoming 41°N

Temperature range: 23°CThe winters are cold; summers are much warmer.


Physical Factors:Cold Deserts

Cheyenne

‣ Tropical savannas are found in central and eastern Africa, and in tropical and subtropical regions of South America and Australia. Thorn forests are found on the equatorial sides of hot deserts.

• Both have mild, dry winters and mild, wet summers.

Unlike savanna, thorn forests generally lack grasses. This reflects the increased aridity of the climate.

Savanna & Thorn Forests

Temperature range: 10.7°C


Example: Kayes, Mali 14°N

Physical Factors: Savannas

Kayes

• Tropical evergreen forests are found in equatorial regions where total annual rainfall exceeds 250 cm and the dry season lasts for no more than 2-3 months. These forests are species-rich.

• The climate is warm and rainy all year round.

Tropical Rainforests

Rainforest, Central America

Temperature range: 2.2°C


Example: Iquitos, Peru 3°S

Physical Factors: Tropical Rainforests

Iquitos

Temperate Forests• Temperate forests occur

throughout mid latitudes where there is a high annual rainfall.

• Temperate forests are usually deciduous, but where seasonal fluctuations are moderated by proximity to the coast, the forests are evergreen and are termed temperate rainforests.

Temperate rainforests occur in south-eastern Australia, New Zealand, along the Pacific North-West coast of the United States.

Temperate deciduous forest

Temperate rainforest

Physical Factors:Temperate Forests

Temperature range: 31°C The temperature fluctuates dramatically between summer and winter.

Total annual rainfall: 81 cmAmple falls throughout the year.

Example: Madison, Wisconsin 43°N

Madison

Temperate Grasslands• Temperate grasslands

or prairies occur in mid latitudes, in regions that are relatively dry for much of the year. They occur in many parts of the world, and include:

The Pampas of ArgentinaThe South African veldtThe Great Plains of the USA

• Grasslands are highly productive and large regions have been converted to agriculture.

Temperature range: 24°CThe temperature fluctuates widely, with hot summers, cold winters.

In some grasslands, most precipitation occurs in the winter. In others, the majority falls in summer.

Total annual rainfall: 31 cm

Example: Pueblo, Colorado 38°N

Physical Factors:Temperate Grasslands

Pueblo

• The tundra biome is found in the Arctic and high in the mountains at all latitudes. It is dominated by low-growing perennial plants.

The Arctic tundra is very wet even though rainfall is low and this is because the water cannot drain down through the permafrost (permanently frozen ground).

Tundra

Tundra: northern Canada

Arctic tundra

Temperature range: 28°C

Total annual rainfall: 23 cm

Example: Greenland 73°N

Physical Factors:Tundra

Greenland

• Mountainous regions are associated with their own altitude adapted vegetation.

• The icy regions of the polar ice caps (the Arctic and Antarctic) form sheets of ice that extend into and over the sea.

Mountains and Ice

Predicting Biome Distribution 1• Temperature and precipitation are excellent predictors of

biome distribution. Temperature decreases from the equator to the poles.

Arctic region

Subarctic region

Temperate region

Tropical region

Polar

Latit

udin

al re

gion

s

Equatorial

Annual precipitation (mm)

Predicting Biome Distribution 2• Temperature and precipitation act together as limiting factors to determine the type of

desert, grassland, or forest biome in a region.

Components of an Ecosystem

Community

Physical environment

• A biome is a large geographical region comprising natural units called ecosystems.

• An ecosystem encompasses the physical environment and the community.

Physical environment

Community

Biotic factorscompetitors symbionts predators parasites

pathogens

EcosystemAbiotic factors

atmospheresoil

water

wind speed

wind directioncurrent velocity

Ecosystems Light intensity varies

Flow rate varies Rainfall level varies

• An ecosystem includes:

all of the organisms(the community) … and their physical environment.

• There are many different sorts of ecosystems from natural to artificial, and they range in size from large to small.

Still water habitatFast flowing water habitat

Rock habitat Stream bank habitat

• A community is a naturally occurring group of organisms living together as an ecological entity; the biological part of the ecosystem.

Communities

A nudibranch snail feeding on rock

encrusting organisms

Environments

• The physical environment refers to the physical surroundings of any organism, including:

the medium, e.g. watersubstrate, e.g. soil climatic (atmospheric) conditionslight …and other physical properties.

• The type and extent of vegetation in a particular ecosystem is determined by physical factors on both a large scale and on a very localized (microclimate) level.

Vegetation patterns are governed largely by climate (which is broadly related to latitude) and altitude.

Climate and Vegetation

High latitude climate

Temperate climate

‣ Abiotic (physical) factors are the influences of the non-living parts of the ecosystem.

Examples include pH, salinity, temperature, turbidity, wind speed and direction, humidity, precipitation, water pressure, and light intensity and quality.

‣ Biotic factors are the influences of the living parts of the ecosystem. Producers and consumers interact as competitors, parasites, pathogens, symbionts, and predators.

Factors Affecting Ecosystems

• Devices for measuring the physical factors in the field include the following meters:

Quantum light meter

Dissolved oxygen

Oxygen meter

pH meter

Total dissolved solids (TDS) meter

Current meter

Multi-purpose meter

Hygrometer

Wind meter

Other equipment includes:

Secchi discs

Nansen bottles

Monitoring Physical Factors

Pho

to: C

ourte

sy P

AS

CO

sci

entif

ic

Pasco datalogger with attached sensor

‣ Gradients in abiotic factors are found in almost every environment.

They influence habitats and microclimates, and determine patterns of species distribution.

• The effects of these physical (or environmental) gradients are particularly evident where physical conditions change markedly within a short distance, e.g. in deserts, along rocky shores, in lakes and tropical rainforests, and on mountains.

Physical Gradients

‣ Desert environments experience extremes in temperature and humidity, but they are not uniform with respect to these factors.

Physical conditions vary widely within the one general environment. Crevices, burrows, and the presence of rock overhangs and vegetation create microclimates where extremes in physical conditions are reduced compared to the desert surface.

Desert Environments

Desert Factors

1 m above ground

33°C, 20% humidity

300 m altitude27°C, 20% humidity

Desert surface45°C, <20% humidity

Under rock28°C, 60% humidity

Burrow(2 m underground)25°C, 95% humidity

Crack/crevice(1 m underground)27°C, 95% humidity

Hypothetical values for temperature (°C) and percentage humidity at midday in a desert environment.

• Rocky shore environments typically exhibit marked physical gradients as a result of tidal movements. Horizontal and vertical gradients in salinity, temperature, dissolved oxygen, and exposure time are reflected in the communities found at different positions on the shore.

Horizontal: from the low tide to the high tide marks

Vertical: from the bottom to top surfaces of rocks and boulders.

Rocky Shore Environments

Rocky Shore FactorsHypothetical values for physical factors in rock pools at different

places on a rocky shore.

Salin:

42 gl-1

Temp:28° CDO: 20%Exp:12 h

Salin:

39 gl-1

Temp:28° CDO: 30%Exp:10 h

Salin: 38.5 gl-1

Temp: 26° CDO: 42%Exp:8 h

Salin: 37 gl-1


Salin: 36 gl-1


Salin: 35 gl--1


Salin: salinityTemp: temperatureDO: dissolved oxygenExp: exposure time

(per 12 hour tidal cycle)

• The high species diversity of tropical rainforests can be supported because of the wide variety of microhabitats provided by the layered structure of the forest.

• The physical conditions at the uppermost level are quite different to those at the forest floor with respect to light intensity (and quality), wind speed, and humidity.

A Tropical Rainforest

Canopy

Subcanopy

Understorey

Ground layer

Rainforest FactorsLight: 70%Wind: 15 kmh-1

Hum: 67%

Light: 50%Wind: 12 kmh-1

Hum: 75%


Hum: 80%


Hum: 85%


Hum: 90%


Hum: 98%

Light: light intensityWind: wind speedHum: humidity

‣ Oxbow lakes are formed from old river meanders that have been cut off and become isolated from the main channel following the change in the river’s course.

Occasionally they may be deep enough to develop temporary, but relatively stable, gradients in physical factors from the surface to the bottom of the lake.

Oxbow Lakes in Summer

Oxbow Lake Factors

Zone of mixing

Temp: 16°COxy: 5.2 mgl-1

Light: 10%

Temp: 24.6°COxy: 9.2 mgl-1

Light: 100%


Light: 2.5%

Temp: 13°COxy: 3.4 mgl-1

Light: 5%


Light: 25%

Habitat• The ecological niche describes the functional position of an organismin its environment.

• A niche comprises:

the habitat in which the organism lives.the organism’s activity pattern: the periods of time during which it is active.the resources it obtainsfrom the habitat.

Ecological Niche

Adaptations

Activitypatterns

Presence of other organisms

Physicalconditions

• The fundamental niche of an organism is described by the full range of environmental conditions (biological and physical) under which the organism can exist.

• The realized niche of the organism is the niche that is actually occupied. It is narrower than the fundamental niche.

This contraction of the realized niche is a result of pressure from, and interactions with, other organisms.

The Fundamental Niche

• The physical conditions influence the habitat in which an organism lives. These include:

substratehumiditysunlighttemperaturesalinitypH (acidity)exposurealtitudedepth

• Each abiotic (or physical) factor may be well suited to the organism or it may present it with problems to overcome.

Physical Conditions

• The law of tolerance states that “For each abiotic factor, an organism has a range of tolerances within which it can survive.”

Law of Tolerance

Tolerance range

Optimum range

Unavailable niche

Marginal niche

Num

ber o

f org

anis

ms

Preferred niche

Marginal niche

Unavailable niche

Examples of abiotic factors that influence size of the realized niche

Too acidic pH Too alkaline

Too cold Temperature Too hot

• An organism’s habitat is the physical place or environment in which it lives.

• Organisms show a preference for a particular habitat type, but some are more specific in their requirements than others.

Habitat

Lichens are found on rocks, trees, and bare ground.

Most frogs, like this leopard frog, live in or near fresh water, but a few can

survive in arid habitats.

• An organism’s habitat is not always of a single type. Some organisms occupy a range of habitats. There are various reasons why:

Highly adaptable in habitat requirements. Different, but equivalent, resources available in different habitats.Reduced competition for resources in sub-optimal habitats.

• Habitat extremes may influence growth form, especially in plants.

Habitat Range

• Organisms may select particular areas within their general habitat, even in apparently homogeneous environments, such as water.This is termed habitat preference.

Example: Aquatic organisms may show a preference for a particular substrate type, water depth or velocity, water clarity, or degree of vegetation cover or habitat disturbance.

• Knowledge of habitat preference can be used to protect species in their environment.

Habitat Preference

Damselfly nymph

Rainbow trout

• The habitat provides organisms with the following resources:

Food and water sourcesMating sitesNesting sitesPredator avoidanceShelter from climatic extremes

• However, the organism may or may not have the adaptations to exploit all the available resources fully.

Resources in a Habitat

4) biogeochemical cycles carbon cycle nitrogen cycle phosphorus cycle sulfur cycle water cycle

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