5.1 Communities and ecosystems
5.1.1 Define species, habitat, population, community, ecosystem, and ecology.
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Species - group or organisms that can interbreed and produce fertile offspring. Members of same species
have a common gene pool
Habitat – the environment in which a species normally lives or the location of a living organism (a tree
branch, a cliff face, seashore, etc.)
Population – a group of organisms of the same species which live in the same area at the same time
Community - a group of populations living and interacting with each other in an area
Ecosystem – a community and its abiotic environment. Refers to where a group of interacting populations
live.
o Consists of abiotic (non-living) components and biotic (living components)
o Biotic Examples: plants, fungi, animals, protists, and bacteria
o Abiotic Examples: light, heat, minerals, oxygen, and humidity
Ecology – the study of relationships between living organisms and between organisms and their
environments
5.1.2 Distinguish between autotroph and heterotroph
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Autotrophs – organisms capable of making their own organic molecules as a food source.
o Synthesize organic molecules from inorganic substances (photosynthesis)
o Autotrophs are producers (plants, algae, cyanobacteria, etc.)
Heterotrophs – organisms that must obtain organic molecules from other organisms (autotrophs or
heterotrophs).
o Ingest organic matter that is living or has been killed
o Referred to as consumers (zooplankton, fish, sheep, etc.)
5.1.3 Distinguish between consumers, detritivores, and saprotrophs
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Consumers – obtain energy by eating/consuming other organisms
o Herbivores
 Obtain energy by eating only plants
 Cows and deer
o Carnivores
 Obtain energy by eating animals
 Snakes, dogs, owls
o Omnivores
 Obtain energy by eating both plants and animals
 Humans, bears, crows
Detritivores, and Saprotrophs - Recycle waste and nutrients in the soil
o Detritivores – organisms that eat non-organic matter (dead leaves, feces, carcasses). Such as
earthworms, woodlice, and dung beetles
o Saprotrophs - live on or in non-living organic matter, secreting digestive enzymes and absorbing
the products of digestion. Fungi and bacteria are saprotrophs, aka decomposers
5.1.4 Describe what is meant by a food chain, giving three examples, each with at least three linkages
(four organisms)
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Food Chain – sequence showing the feeding relationships and energy flow between species
o Grass  Grasshoppers  Toad  hognose snake  Hawk
o Algae  mayfly larva  juvenile toad  kingfisher
o Diatoms  copepods  herring  seal  great white shark
5.1.5 Describe what is meant by a food web
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Interconnecting series of food chains
5.1.6 Define trophic level
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Trophic level – refers to an organisms position in a food chain
o T1- Producer
o T2- Primary Consumer;
o T3- Secondary Consumer;
o T4- Tertiary Consumer
o T5 – Quaternary Consumer
Large number of producers and fewer and fewer members of each subsequent level
Constructing a food web
o Start with producer and add each trophic level until reaching top predator
o Problems
 Some organisms occupy more than one trophic level
 Many ecosystems are not fully understood
 Food webs do not show change over time as populations change
5.1.7 Deduce the trophic level or organisms in a food chain, and a food web & 5.1.8 Construct a food
web containing up to 10 organisms, using appropriate information
5.1.9 State that light is the initial source of energy for almost all communities & 5.1.10 Explain the
energy flow in a food chain
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Sunlight is initial energy source for almost all communities.
Energy flow occurs as energy is photosynthesized by plants, then transferred to the next level when carbs,
proteins, or lipids are eaten and digested by primary consumers, then transferred up the trophic levels
All energy is eventually lost from the ecosystem
5.1.11 State that energy transformations are never 100% efficient
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Only 5-20% of energy is used from previous step in food chain
Reasons include
o Not all of the organism is swallowed as a food source (some parts decay)
o Not all ingested food can be absorbed and used in the body
o Some organisms dies before being eaten by an organism from the next trophic level
o Majority of energy is lost as heat due to cellular respiration, and maintenance of organisms
5.1.12 Explain reasons for the shape of pyramids of energy
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Pyramid of Energy - Shows how much and how fast energy transfers from one trophic level to the next in
a community
o Measured in kJ * m-2 * yr-1
o Each trophic level will be smaller than the one before because less energy is available as you
move up the food chains.
5.1.13 Explain that energy enters and leaves ecosystems, but nutrients must be recycled
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Sunlight is converted to chemical energy by producers and transferred to consumers.
Most of it is lost as heat, and cannot be recycled
Organisms must recycle nutrients such as carbon, nitrogen, and other elements and compounds
necessary for organisms to survive
5.1.14 State that saprotrophic bacteria and fungi (decomposers) recycle nutrients
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Decomposers - Organisms that unlock nutrients stored in plant and animal cells through decay
Saprotrophs and Detritivores
o Recycle nutrients so they are available and not locked in bodies or wastes of other organisms
o Play a major role in the formation of soil
Community Interactions
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Niche - The physical and biological conditions in which an organism lives and how they use them
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This includes –
 The type of food they eat
 What hunts them
 How they obtain the food
 When they reproduce
Competition - Organisms of the same or different species attempt to use an ecological resource in the
same place at the same time
o No two species can occupy the same niche in the same habitat at the same time
Predation - An interaction in which one organism captures and feeds on another organism
o Predator is the organism that does the killing and eating, the prey is the food organism
o Predator/Prey Model - as predators increase, prey decrease and vice versa until a balance is
found
Symbiosis - Any relationship in which two species live closely together
o Three main types:
o Mutualism - Both species benefit from the relationship
 Ex. Flowers depend on insects to pollinate them, where insects get food from the
flowers
o Commensalism - One member of the association benefits and the other is neither helped nor
harmed
 Ex. Barnacles on whales – barnacles benefit from by the whales moving through the
water – brings food to them
o Parasitism - One organism lives on or inside another organisms and harms it
 Parasite obtains all or part of its nutritional needs from the host
 Ex. Tapeworms, Fleas, Ticks
Ecological Succession
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Changes that occur in a community over time is called ecological succession
o Older inhabitants gradually die out and new organisms move in, causing further changes in the
community
o Can be caused by natural and human disturbances
Primary Succession
o Occurs on surfaces where no soil exists
o First species that appear are called pioneer species
o Pioneer species add organic material to help form soil in which plants can grow
Secondary Succession
o Occurs after wildfires burn woodlands and when land cleared for farming is abandoned
o When the disturbance is over community interactions tend to restore the ecosystem to its
original condition
5.3 Populations
Important Characteristics of Populations
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Geographic Distribution (range) - the area inhabited by the population
Density - the number of individuals per unit area
Growth rate - how fast, slow, or steady a population is in terms of numbers of individuals
5.3.1 Outline how population size is affected by natality, immigration, mortality, and emigration.
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Growth Rate
o Three factors affect population size & growth rate:
 Number of births (natality)
 Number of deaths (mortality)
 Number of individuals that enter or leave the population (immigrate/emigrate)
o Types of Growth
 Exponential Growth –
 When a population have abundant space and food, and is protected from
predators and disease, they will multiply rapidly
 A population will reproduce at a constant rate
 Logistic Growth
 Eventually resources become less available and the growth of a population
slows or stops, called logistic growth
 The population will reach their carrying capacity – the largest number of
individuals an environment can hold
5.3.2 Draw and label a graph showing a sigmoid (S-shaped) population growth curve
5.3.3 Explain the reasons for the exponential growth phase, the plateau phase, and the transitional
phase between these two phases.
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Exponential Growth Phase (logarithmic phase) – number of individuals increase at a fast pace. Caused by
plentiful resources, little competition, favorable abiotic factors, & little predation/disease
Transitional phase - growth rate slows b/c Increased competition, increased predation, spread of disease
Plateau Phase (stationary phase) – number of individuals is stabilized. No more growth
5.3.4 List three factors that set limits to population increase.
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Carrying Capacity - Maximum number of individuals that a particular habitat can support
Occurs because of limiting factors that influence the habitat, including:
o Availability of resources (food, water, sunlight, shelter, space)
o Build-up of waste (excrement, CO2)
o Predation
o Disease
A limiting factor is a factor that causes population growth to decrease
Two types of limiting factors:
o Density-dependent
 Factors that are limiting only when the population density reaches a certain level
 Includes competition, predation, parasitism, and disease
 Ex. Predator – Prey Relationships
o Density-independent
 Unusual weather, natural disasters, seasonal cycles, and certain human activities – such
as damming rivers and clear cutting forests – are all examples of limiting factors
Birthrates, death rates, and the age structure of a population help predict population growth
o Age Structure diagrams can be used to determine the growth rate of a given area
Genetic and Biodiversity
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Variety is Diversity
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Biodiversity is the sum total of the genetically based variety of all organisms in the biosphere
Genetic diversity refers to the sum total of all the different forms of genetic information carried
by all organisms living on Earth today
Biodiversity has supplied us with foods, industrial products, and medicines
Threats to Biodiversity
o Extinction: organisms no longer exist in the biosphere
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 Habitat alteration
Fragmentation – spatial separation of habitat units from previous state of greater community
Pollution
 Biological magnification – increasing concentration of toxic substances w/in each link of
a food chain
Invasive Species
 Species that are introduced into new habitats
 Survive because there are no predators to limit their numbers and they often reduce the
number of available resources to the native species
5.2 The Greenhouse Effect
Biogeochemical Cycles
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Unlike energy, matter is recycled within and between the ecosystem
These include the:
o Water cycle
 Water moves between the ocean, atmosphere, and land
 Water enters the atmosphere through evaporation (liquid to gas) from oceans or
through transpiration (evaporation off plant leaves)
 Moist air rises and condenses into droplets to form clouds
 When the droplets are large enough they return to Earth in the form of precipitation –
rain, snow, sleet, or hail
 Precipitation on land usually ends as runoff in bodies of water or is taken up by plants
o Carbon cycle
 Carbon is has many roles
 Calcium carbonate (CaCO3) found in animal skeletons (rocks as well)
 Carbon Dioxide (CO2) important component of the atmosphere (given off during
respiration of organisms)
 4 main processes during Carbon Cycle:
 Biological, such as photosynthesis, respiration, and decomposition
 Geochemical, such as erosion and volcanic activity
 Mixed biogeochemical processes, such as burial and decomposition of dead
organisms (into coal and petroleum, or fossil fuels)
 Human activities, such as mining, cutting and burning of forests and fossil fuels
o Nitrogen cycle
 Nitrogen is needed for amino acids, which help build protein
 Nitrogen fixation converts nitrogen gas into ammonia (used by producers)
 Denitrification converts nitrates into nitrogen gas
o Phosphorous cycle
 Phosphorous is needed for DNA and RNA
 Found in rock and soil minerals and ocean sediment
 Through erosion, phosphorous makes it way to organisms in the ecosystem
5.2.1 Draw and label a diagram of the carbon cycle to show the processes involved. & 5.2.2 Analyze
the changes in concentration of atmospheric carbon dioxide using historical records
5.2.3 Explain the relationship between rises in concentrations of atmospheric carbon dioxide,
methane, and oxides of nitrogen and the enhanced greenhouse effect
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Caused by atmosphere’s ability to retain heat.
o Sunlight enters Earth’s atmosphere b/c gases are transparent to light
o Most Sunlight reflects off surface and travels back out of atmosphere
o Some light energy is transformed into heat energy and warms the planet, which in turn, radiates
heat back into atmosphere
o Greenhouse gases retain some of the heat and trap in in atmosphere
o Results in atmosphere being warmer than space
Earth is undergoing global warming because of an enhanced greenhouse effect
As human population increases, so do the demands for resources and disposals
Occurs b/c of increasing levels of greenhouse gases
o Carbon Dioxide (CO2)
 Human pollution has caused a 25% increase in CO2 levels since industrial revolution
o Methane (CH4)
 Cattle ranching, waste disposal in landfills, production and distribution of natural gas
o Nitrous Oxide (NO2)
 Burning fossil fuels, Using Organic fertilizers, and industrial processes
o Water Vapor
A rise in global temperatures b/c of enhanced greenhouse effect, will likely result in:
o Increase in photosynthetic rates
o Changes in climate w/ varying effect on ecosystems
o Extinction of certain species
o Melting glaciers
o Rise in sea levels and flooding of coastal areas
Ozone Depletion - Ozone layer lays about 20-50 km above the Earth and consists of ozone gas
o It absorbs UV rays and serves as a global sunscreen
o Since the 1970’s the ozone has been depleting
o Gap, or hole, in the ozone was found over Antarctica
o Cause – CFC’s found in aerosol cans, coolants in refrigerators, freezers, and air conditioners
o By banning CFC’s, the amount in the atmosphere will decrease and within 50 years the ozone
holes should shrink and disappear
5.2.4 Outline the precautionary principle
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Intergovernmental Panel on Climate Change (IPCC) came to several conclusions in 2007
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Global temps are increasing (confirmed reality, no longer hypothesis)
90% chances the cause is due to production of greenhouse gases by daily human activity. Less
than 5% chance this occurred naturally
o Sea levels expected to rise 18-59 cm this coming century
o Severe weather events (heat waves, drought, heavy rains) will increase
Ethical theory that believes action should be taken to prevent future harm to environment
If people wish to engage in activity that may cause damage, must first prove it will not do any harm
Prevention is better than cure
o Spend money now on preventative measures will be less expensive than fixing a problem later
5.2.5 Evaluate the precautionary principle as a justification for strong action in response to the threats
posed by the enhanced greenhouse effect
5.2.6 Outline the consequences of a global temperature rise on arctic ecosystems
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More ice is melting every year
Less snow, more frozen rain
Some regions now populated w/ mosquitoes
Woody shrubs are proliferating on warming soils, where only lichens and mosses were before
Bird species, such as robins are moving into areas, where they have no name for them
Decrease in algae
Polar bears decreases habitat and hunting
New species brings new pathogens
Frozen tundra will thaw and release more CO2 into atmosphere
Consequences of global warming in Arctic is that ecosystems are changing