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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
Scoring Guidelines: http://apcentral.collegeboard.com/apc/public/repository/ap07_biology_q3.pdf