Chapter 52: An Introduction to Ecology and the Biosphere

Overview: The Scope of Ecology

The Scope of Ecology Ecology- the scientific study of interactions

between organisms and the environment1. Organismal Ecology2. Population Ecology3. Community Ecology4. Ecosystem Ecology5. Landscape Ecology6. Global Ecology

52.2Interactions between organisms and the environment limit the distribution of species

Ecologists have long recognized global and regional patterns in the distribution of organisms.

They ask: where do species occur and why do they occur there.

To answer they look at two kinds of factors: Biotic – (living factors) all the organisms that are part of

the individual’s environment. Abiotic – (nonliving factors) all the chemical and physical

factors such as temperature, light, water, etc.

Ecologists need to consider multiple factors are at play when trying to explain distribution of species.

Dispersal and Distribution Dispersal – movement of individuals

away from their area of origin or from centers of high population density.

This contributes to the global distribution of organisms.

Dispersal and Distribution: Species Transplants To determine if dispersal is a key factor limiting

the distribution of a species, ecologist may intentionally transplant species to areas where they previously were absent.

For it to be successful, they must survive in the new area and reproduce there.

If successful: the potential range of the species is larger than its actual range (could live in other areas where it doesn’t)

Sometimes this disrupts the communities and ecosystems where they have been introduced.

So… ecologists rarely do these experiments across geographic regions. Instead they look at when this happens accidently or if they were introduced for a purpose (game animals or pest predators).

Behavior and Habitat Selection When individuals seem to avoid certain

habitats (even when they are suitable for living), the organism’s distribution may be limited by habitat selection behavior.

One of the least understood of all ecological processes.

Biotic Factors Interactions with other organisms in the form of

predation, parasitism, or competition contribute to an organism’s inability to survive and reproduce in a new area.

On the other hand, the lack of other species that the organism depends on also limits survival.

Organisms that eat, can limit the distribution of organisms that get eaten. Predators (organisms that kill their prey) and

herbivores (organisms that eat plants or algae) limit distribution of species.

Continued…. The presence or absence of food

resources, parasites, pathogens, and competing organisms can act as biotic limitations on species distribution.

Most striking cases occur when humans accidentally or intentionally introduce exotic predators or pathogens into new areas, wiping out native species.

Abiotic Factors Temperature, water, salinity, sunlight, or

soil. Physical conditions of an area can limit

a specie’s ability to survive there.

Abiotic Factors: Temperature Important because of the effects on

biological processes. Cells may rupture at temperatures below

0°C and proteins of most denature at temperatures above 45°C.

Few organisms can maintain an active metabolism at very low or very high temperatures.

• Most organisms function best within a specific range.

Abiotic Factors: Water The dramatic variation in water

availability among habitats is a factor in species distribution. Species living at the seashore or in tidal

wetlands can desiccate (dry out) as the tide recedes.

• The distribution of terrestrial species reflects their ability to obtain and conserve water.

Abiotic Factors: Salinity The salt concentration of water in the

environment affects the water balance of organisms through osmosis.

Because of their limited ability to osmoregulate, most aquatic organisms are restricted to either freshwater or saltwater habitats.

Many terrestrial organisms can excrete excess salt from specialized glands or feces, however; high-salinity habitats typically have few species of plants and animals.

Abiotic Factors: Sunlight Because sunlight provides the energy that drives most

ecosystems through photosynthesis, too little sunlight can limit distribution of photosynthetic species.

Particularly for seedlings on the ground, shading by forest treetops makes competition for sunlight intense.

In aquatic environments, because every meter of water depth selectively absorbs about 45% of red light and about 2% of blue lights, most photosynthesis occurs relatively close to the surface.

Too much light can also limit survival. At high elevations the atmosphere is thinner and the sun’s

rays are more likely to damage DNA and proteins. Deserts have high light levels which can increase stress if

the organism cannot escape the light or can’t cool down.

Latitudinal Variation in Sunlight Intensisty

Abiotic Factors: Rocks and Soil The pH, mineral composition, and physical structure of

rocks and soil limit the distribution of plants and the animals that feed on them.

The pH of soil and water (through extreme acidic or basic conditions, or through solubility of nutrients and toxins) can limit distribution.

In streams and rivers, composition of the substrate (bottom surface) can affect water chemistry and influence what can reside there.

In freshwater and marine environments, the structure of the substrate determines the organisms that can attach to it or burrow into it.

Climate The long-term prevailing weather conditions in a

particular area. Four abiotic factors: temperature, precipitation,

sunlight, and wind Climate patterns can be described on two scales:

Macroclimate – patterns on the global, regional, and local level

Microclimate – very fine patterns (i.e. community of organisms that live beneath a fallen log)

Climate: Global Climate Patterns Earth’s global climate patterns are

determined largely by the input of solar energy and the plant’s movement in space.

The sun’s warming effect on the atmosphere, land, and water establishes: the temperature variations, cycles of air

movement, and evaporation of water.

Climate: Regional, Local, and Seasonal Effects on Climate

Proximity to bodies of water and topographic features such as mountain ranges create regional climate variations.

Climate: Regional, Local, and Seasonal Effects on Climate (Bodies of Water)

Ocean currents influence climate along the coasts of continents by heating and cooling overlying air masses which pass along land.

Coastal regions, then, are generally moister than inland regions.

Because of the high specific heat of water, oceans and large lakes tend to moderate the climate of nearby land. During a hot day, air over the land heats up and

rises which draws in a cool breeze. At night, the warm air over the water rises and

draws out the land’s cool air to replace it with warmer air.

Climate: Regional, Local, and Seasonal Effects on Climate (Mountains) Mountains affect the amount of sunlight

reaching an area and consequently the local temperature and rainfall.

This affects the types of species able to inhabit the different regions of the mountain.

Climate: Regional, Local, and Seasonal Effects on Climate (Seasonality) Earth’s tilted axis of rotation and its

annual passage around the sun cause strong seasonal cycles in the middle to high latitudes.

Seasonal changes in wind patterns produce variations in ocean currents. Stimulates growth of surface-dwelling phytoplankton and the organisms that feed on them.

Seasonal Variation in Sunlight Intensity

Climate: Microclimate Many features in the environment

influence microclimates by casting shade, affecting evaporation from soil, or changing wind patterns.

Every environment on Earth is similarly characterized by a mosaic of small-scale differences in the abiotic factors that influence the local distributions of organisms.

52.3 Aquatic biomes are diverse and dynamic systems that cover most of the Earth

Biomes- major terrestrial or aquatic life zones Characterized by vegetation, or physical

environment Aquatic= account for largest part of the

biosphere Oceans are the largest biome Figure 52.16 on page 1160

Stratification of Aquatic Biomes Light is absorbed by water and photosynthetic

organisms Intensity decreases with depth of water Photic Zone- sufficient light for photosynthesis Aphotic Zone- little light Benthic Zone- at the bottom of all aquatic

biomes; receives no sunlight Composed of sand, and organic/inorganic

substances

Stratification of Aquatic Biomes Benthos are the community of

organisms that live in the benthic zone Detritus- a major food source for food

many benthic species Abyssal Zone- part of the benthic zone

that lies between 2,000-6,000m below the surface

Stratification of Aquatic Biomes Thermal energy from the sun warms the water, but

it can’t reach down into the deeper water Bottom is always more cold

Thermocline- separates the warm water from the cold water

Summer and winter= layers of temperature in the water

Turnover- when the oxygen rich surface water goes to the bottom while the nutrient rich water from the bottom comes to the surface Happen in autumn and spring

Figure 52.17 on page 1161 Winter: coldest water is just below the ice on

the surface with the “warmest” water at the bottom

Spring: as the ice melts, the water sinks and there is almost a uniform temperature

Summer: surface is the warmest because of the sun’s heat while the bottom is drastically lower

Autumn: the surface cools and drops to the bottom creating an almost uniform temperature again

Affects on Communities Separated by:

Water depth Degree of light penetration Distance from the shore Whether found in open water or on the

bottom

Types of Aquatic Biomes Lakes- standing water Wetlands- standing water but it can dry

out Streams and River- moving water Estuaries- where freshwater and

saltwater meet Intertidal Zones- periodically submerged

by the tide

Types of Aquatic Biomes (cont.) Ocean- large body of moving saltwater Coral Reef- reefs that are made of

calcium carbonate skeletons (living); many fish and coral live there and are in the water

Benthic Zone- receive no sunlight because so deep on the ocean floor

52.4The structure and distribution of terrestrial biomes are controlled by climate and disturbance

Because there are latitudinal patterns of climate over Earth’s surface, there are also latitudinal patterns of biome distribution.

These biome patterns are modified by disturbances ( and even such as a storm, fire, or human activity that changes a community, removing organisms from it and altering resource availability).

Climate and Terrestrial Biomes A climograph (a plot of the temerpature

and precipitation in a particular region) can show the impact of climate on the distribution of organisms.

General Features of Terrestrial Biomes and the Role of Disturbance Most terrestrial biomes are named for major

physical or climatic features and for their predominant vegetation.

Each biome is also characterized by microorganisms, fungi, and animals adapted to that environment.

Although there are boundaries between biomes, terrestrial biomes usually grade into each other.

Ecotone – area of intergradation (may be wide or narrow)

Continued… Vertical layering (largely defined by shapes and sizes

of plants) are important features of terrestrial biomes. Many forests layer from upper canopy, low-tree layer,

shrub understory, ground layer of herbaceous plants, forest floor, and root layer.

Layering of vegetation provides many different habitats for animals and creates well-defined feeding groups.

Disturbances rather than stability keep biomes dynamic. Natural wildfires are important for grasslands, savannas,

and many coniferous forests. Hurricanes create openings for new species in tropical

and temperate forests.• Results in patchiness with several communities of the

area.

Chapter 55: Ecosystems

Overview Ecosystem-all living organisms in a

community as well as the abiotic factors that they interact with

Ecosystems can be of any size Involve energy flow and chemical

cycling Energy flows through the ecosystem,

while matter cycles through it.

55.1Physical laws govern energy flow and chemical cycling in ecosystems

Ecosystem ecologists study the transformations of energy and matter within a system and measure the amounts of both that cross the system’s boundaries.

The movements of chemical elements can be mapped and the transformations of energy in an ecosystem can be followed by grouping the species in a community into trophic levels of feeding relationships.

Conservation of Energy The first law of thermodynamics states that energy

cannot be created or destroyed but only transferred or transformed.

The transfer of energy can be accounted for through input as solar radiation to its release as heat from organisms.

The total amount of energy stored in organic molecules plus the amounts reflected and dissipated as heat must equal the total solar energy intercepted by a plant.

Energy conversions cannot be completely efficient as some energy is always lost as heat.

Conservation of Mass Matter cannot be created or destroyed. Because mass is conserved, it can be determined

how much of a chemical element cycles within an ecosystem or is gained or lost by the at ecosystem over time.

Chemical elements are continually recycled within an ecosystem. (CO₂)

Elements move between ecosystems as inputs and outputs. Ecosystems are open systems that absorb energy and mass and release heat and waste products.

The balance between inputs and outputs determine whether an ecosystem is a source or a sink for a given element.

Energy, Mass, and Trophic Levels

Ecologists assign species to trophic levels on the basis of their main source of nutrition and energy.

Primary producers – the trophic level that ultimately supports all others. (consists of autotrophs)

Most autotrophs are photosynthetic organisms. Plants, algae, and photosynthetic prokaryotes are

the biosphere’s main autotrophs Certain chemosynthetic prokaryotes are primary

producers in certain ecosystems such as deep-sea hydrothermal vents and spring-fed pools in caves

Continued… Organisms in trophic levels above the primary

producers are heterotrophs. Herbivores (eat plants and other primary producers) are

primary consumers. Carnivores (eat herbivores) are secondary consumers. Carnivores (eat carnivores) are tertiary consumers. • Detritivores (decomposers) are consumers that get their

energy from detritus (nonliving organic material such as remains of dead organisms, feces, fallen leaves, etc.) Prokarytoes and fungi secrete enzymes that digest organic

material, absorb the broken down products, and link the consumers and primary producers in an ecosystem.

55.2- Energy and other limiting factors control primary production in ecosystems

Primary Production- the amount of light energy converted to chemical energy by autotrophs in a given time

Photosynthetic product is the main starting point for the energy flow

The energy harnessed from the light is then broken down into ATP

Through food webs, consumer obtain their organic fuels

Ecosystem Energy Amount of sun that hits the earth

determines the photosynthetic output Because of the solar radiation and other

factors, only about 1% is actually turned into photosynthesis

Gross and Net Primary Production Gross primary production (GPP)- total

primary production in an ecosystem Net primary production (NPP) Respiration (R) NPP is usually ½ of GPP in normal

ecosystems

NPP=GPP-R

Gross and Net Primary Production NPP represents the storage of chemical

energy that will be available NPP shouldn’t be confused with total

biomass-really the new biomass added at a

given period of time

Gross and Net Primary Production Tropical rainforests are among the most

productive terrestrial ecosystems Contribute a lot to the NPP

Coral reefs and estuaries have high productivity Put little forth to the global total

Oceans are fairly unproductive Contribute equal amounts global NPP as

terrestrial systems do

Primary Production in Aquatic Ecosystem Light and nutrients are important

controls for primary production Light depth perception is important

About ½ is absorbed in the first 15m

Nutrient Limitation Nutrients are limiting

Nitrogen or phosphorous Limiting nutrient- the element that must

be added for production in increase Windblown dust contributes more of the

iron levels Little often reaches center of ocean

Nutrient Limitation Nutrient available can/will control

marine primary production Common in freshwater lakes as well Eutrophication- growing cyanobacteria

and algae at large and fast rates Reduces clarity and O2 concentrations

Primary Production in Terrestrial Ecosystems Temperature and moisture are large

factors in primary production Warm and wet condition promote plant

growth Contrasts in climate:

Extreme moisture: tropical rain forests Middle: temperate forest and grasslands Extremely dry: dessert Extremely cold: tundra

Primary Production in Terrestrial Ecosystems Actual evapotranspiration- annual amount of

water transpired by plants and evaporated from a landscape Increase with the amount of precipitation, solar

energy Mineral nutrients in soil can limit pp Nitrogen and phosphorus are also limiting

nutrients Adding a new nutrient will not stimulate production Add more limiting nutrient, production is stimulated

55.3- Energy Transfer Between Trophic Levels is Typically Only 10%

Secondary production- amount of chemical energy in consumer’s food that is converted to their own new biomass during a given timer period

Herbivores can’t full digest producers Much primary production is not used by

consumers

Production Efficiency Energy flows through a ecosystem

Doesn’t cycle Secondary consumer food sources is

chemical energy stored by herbivores in the form of biomass

Net secondary production- energy stored in biomass

Assimilation- total energy taken in and used for food

Production Efficiency Production efficiency- the percentage of

energy in assimilated food that is not used for respiration

Tropic Efficiency and Ecological Pyramids Tropic efficiency- percentage of

production transferred from one tropic level to the next Only about 10% from one level to the

next The loss of energy limits the abundance

of top-level carnivores an ecosystem can support

Pyramid of Net Production The width of each tier is proportional to

the net production The net production is represented in

joules (J) Figure 55.11 on page 1229

Pyramid of Net Production Some aquatic have inverted pyramids

Consumers outweigh producers Turnover time- small standing crop

compared to their production

The Green World Hypothesis Green world hypothesis- terrestrial

herbivores are held in check by a variety of factors Plant defenses Abiotic factors (temperature, moisture

extremes) Interspecific/intraspecific competition Parasites/pathogens

55.4 Biological and geochemical processes cycle nutrients and inorganic parts of an ecosystem

Biogeochemical Cycles Chemical elements on earth are limited Recycling of these chemical elements is

essential for life Biogeochemical cycle

Any chemical cycle that involves both biotic and abiotic components of ecosystems

General Model of Nutrient Cycling

Figure 55.13, pg. 1231

Nutrient Cycles 4 major cycles

The water cycle The carbon cycle The terrestrial nitrogen cycle The phosphorous cycle

Figure 55.14, pg. 1232-1233

The Water Cycle Importance:

Water is essential to all organisms and influences the rates of ecosystem processes.

Reservoirs: 97% in the ocean, 2% in glaciers/polar ice caps,

1% in lakes, rivers, and groundwater Key Processes:

Evaporation of water by solar energy is the main process. Transpiration also accounts for a significant amount of water movement into the atmosphere

Precipitationover land

Transportover land

Solar energy

Net movement ofwater vapor by wind

Evaporationfrom ocean

Percolationthroughsoil

Evapotranspirationfrom land

Runoff andgroundwater

Precipitationover ocean

The Carbon Cycle Importance:

Carbon-based organic molecules are essential to all organisms.

Reservoirs: Fossil fuels Soils Sediments of aquatic ecosystems Ocean Plant and animal biomass The atmosphere

Key Processes: Photosynthesis, cellular respiration, and the burning of

fossil fuels all drive the carbon cycle

Higher-levelconsumersPrimary

consumers

Detritus

Burning offossil fuelsand wood

Phyto-plankton

Cellularrespiration

Photo-synthesis

Photosynthesis

Carbon compoundsin water

Decomposition

CO2 in atmosphere

The Nitrogen Cycle Importance:

Nitrogen is part of amino acids, proteins, and nucleic acids. Reservoirs:

The atmosphere (80%) Soils and sediments of lakes, rivers and oceans Surface water and ground water Biomass of living organisms

Key Processes: Nitrogen fixation is the major way for nitrogen to enter an

ecosystem. Ammonification decomposes organic nitrogen to NH4+ Nitrification is when NH4+ is converted to NO3- Denitrification allows for NO3- to convert back to N2

Decomposers

N2 in atmosphere

Nitrification

Nitrifyingbacteria

Nitrifyingbacteria

Denitrifyingbacteria

Assimilation

NH3 NH4 NO2

NO3

+ –

–

Ammonification

Nitrogen-fixingsoil bacteria

Nitrogen-fixingbacteria

The Phosphorous Cycle Importance:

Phosphorus is a major component of nucleic acids, phospholipids, and ATP

Reservoirs: Sedimentary rocks of marine origin Soils The oceans Organisms

Key Processes Weathering of rocks adds PO4

3- to soil.

Leaching

Consumption

Precipitation

Plantuptakeof PO4

3–

Soil

Sedimentation

Uptake

Plankton

Decomposition

Dissolved PO43–

Runoff

Geologicuplift

Weatheringof rocks

Decomposition Controlled by

Temperature Moisture Nutrient availability

Decomposers typically grow faster and decompose at a faster rate in warmer ecosystems Rainforests-few months to a few years Temperate forests-four to six years

55.5 Human activities now dominate most chemical cycles on Earth

Agriculture and Nitrogen Cycling Agriculture removes nutrients, mainly

nitrogen, from ecosystems Nutrients in fertilizer pollute

groundwater and surface water ecosystems Can stimulate eutrophication

Human activities have more than doubled Earth’s supply of fixed nitrogen available to primary producers

Contamination of Aquatic Ecosystems Critical load-the amount of added

nutrient that can be absorbed by plants without damaging ecosystem integrity.

The critical load is exceeded when excess nutrients are added to an ecosystem.

Nutrient runoff can lead to eutrophication, excess algal growth

Mississippi Basin Pollution Mississippi river will carry nitrogen pollution to

the Gulf causing a phytoplankton bloom in the summer.

When the phytoplankton die they will cause a “dead zone” of low oxygen availability

This will cause fish, shrimp, and other marine animals to disappear.

To reduce the size of this “dead zone,” Farmers use fertilizers more efficiently The wetlands in the Mississippi watershed are being

restored.

Winter Summer

Acid Precipitation Burning of fossil fuels is the main cause Acids fall to the earth as precipitation at a

pH of less than 5.2 Regional problem caused by local emissions Freshwater ecosystems are especially

sensitive to acid precipitation Lakes in North America and northern

Europe that have low levels of bicarbonate are the most easily damaged

Toxins in the Environment Biological magnification-the process in

which retrained substances become more concentrated at each higher tropic level in a food chain Ex: DDT used to control insects caused a

decline in various bird species Toxins can stay in the environment for

decades They can also be converted from harmless to

toxic through various reactions.

Greenhouse Gases and Global Warming Atmospheric concentration of CO2 has

been steadily increasing due to the burning of wood and fossil fuels and other human activities

The Greenhouse Effect and Climate Greenhouse effect

the warming of the Earth due to the atmospheric accumulation of carbon dioxide and certain other gases

These gases absorb reflected infrared radiation and reradiate some of it back toward Earth

Increased CO2 concentrations are linked to increased temperatures

Depletion of Atmospheric Ozone Ozone molecules in the atmosphere

protect life on Earth from the harmful effects of UV radiation

The ozone layer has been thinning since 1975

Chlorine-releasing products and other human activities cause the thinning of the ozone layer

(a) September 1979 (b) September 2006

Essay Question #1 Describe the trophic levels in a typical

ecosystem. Discuss the flow of energy through the

ecosystem, the relationship between the different trophic levels, and the factors that limit the number of trophic levels.

Essay Question #2

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