UNIT 9
ECOLOGY
READING:
Chapter 15
Chapter 16
Chapter 17
Chapter 18
Populations
Ecosystems
Biological Communities
The Environment
OBJECTIVES
At the end of this unit of study the student will be able to:
1.
Define biosphere
2.
Distinguish between population, communities and ecosystems
3.
Distinguish between biotic and abiotic factors and describe how they interact.
4.
Distinguish between habitat and niche.
5.
Describe the various trophic levels.
6.
Describe the flow of energy in a food chain and a food web.
7.
Identify three types of ecological pyramids
8.
Describe the water, nitrogen, and oxygen-carbon dioxide cycles.
9.
Name and describe the characteristics of the various terrestrial biomes
10.
Name and describe the various aquatic biomes.
11.
Define competition and distinguish between intraspecific and interspecific competition.
12.
Define predation and describe the predator-prey relationship.
13.
Define symbiosis and identify and give an example of the three types of symbiosis.
14.
List and give examples of several different time rhythms and cycles of the biotic community.
15.
Distinguish between hibernation and estivation.
16.
Define succession and name and describe the stages of succession.
17.
Distinguish between primary and secondary succession.
18.
Describe the succession process in lakes.
19.
List and define several factors that cause changes in population size.
20.
Define population growth and differentiate between the types of growth curves and explain the
phases of population growth they illustrate.
21.
Define population density and explain the differences between density-dependent and densityindependent limitingfactors.
22.
Summarize human population growth
ASSIGNMENTS:
1.
2.
3.
4.
5.
ECOLOGY
I.
UNIT 9
The biosphere and its units
A. ECOLOGY - The study of the relationships between organisms and their environment.
1. Not just related to pollution
2. Unifying factor of structure, physiology, and behavior of all organisms throughout biosphere is
adaptation.
B. BIOSPHERE
1. Area of earth where life exists
a. Most on or within a few meters of earth's surface.
b. Some plant spores and insects found 8 km high and some organisms (sea urchins and brittle stars)
Found 8 km below ocean surface.
2. Smaller ecological units
a. POPULATION - all members of a species that live in same area and make up a breeding group group of deer in a forest, fish in a lake.
b. COMMUNITY - All populations in an area
C. ECOSYSTEM
1. An ecological unit that includes all interacting parts of an environment in an area.
2. ABIOTIC FACTORS
a. Nonliving components of an ecosystem.
b. Amount of light, precipitation, temperature, slope and drainage of land, and chemistry of soil
and atmosphere.
c. Abiotic factors may interact
1) Heavy rain results in flooding of stream that results in deposition of sediment (soil).
2) Changing of river courses
3) Creation of mountains or islands by volcanoes
4) Landslides removing soil.
3. BIOTIC FACTORS
a. Living components of an ecosystem.
b. Plants, animals, protists, microorganisms - all living things
c. Living things may interact
1) PREDATION - one animal (predator) kills another (prey) for food.
2) SYMBIOSIS - Close relationship between 2 organisms - usually beneficial to one of the
organisms.
4. Abiotic and biotic factors may also interact to affect each other.
a. Climate and soils determine what type of plants will grow; determines animal life of the area.
b. Plants replenish oxygen - photosynthesis
c. Overgrazing by some species can result in loss of soil.
II. Ecosystem Structure
A. HABITAT
1. Place where an organism lives - its "home"
2. Provides food and shelter.
3. Habitats between two organisms may overlap
a. Squirrel looking for nuts among the leaf litter around a tree.
b. Land snail living in moist leaf litter.
c. Little interaction due to the fact that the two species don't compete for the same food.
B. NICHE
1. Role or occupation; everything organism does within its habitat
2. Organisms way of life including habitat, feeding habits, reproductive behavior, and all other biological
aspects of the organism.
3. No two organisms can occupy the same niche - habitats overlap, niches do not.
C. Trophic Levels.
1. Energy enters an ecosystem from the sun.
2. Energy flows between organisms when one organism eats another.
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3. TROPHIC LEVEL is defined by the relationship between what an organism eats and what eats it.
a. The feeding level in an ecosystem.
b. Trophic comes from the Greek word that means "food"
4. PRODUCERS
a. Autotrophic organisms that make their own food using solar or chemical energy.
1) Plants, algae, and photosynthetic bacteria
2) Manufacture all organic nutrients for ecosystem
3) Also called primary producers.
b. Occupy what is called the First Trophic Level
c. PRIMARY PRODUCTIVITY of an ecosystem - rate at which solar energy is converted into
organic compounds
1) GROSS PRIMARY PRODUCTIVITY - total amount of energy produced, including the
energy used by plants for own respiration
2) NET PRIMARY PRODUCTIVITY - rate at which plants store energy that is not used in
plant respiration.
5. CONSUMERS
a. Heterotrophic organisms that feed on producers either directly or indirectly for their energy.
1) PRIMARY CONSUMER - organism that feeds on producers
2) SECONDARY CONSUMER - organism that feed on a primary consumer.
b. Consumers may also be classified on basis of food type
1) HERBIVORE - obtain nutrients by eating primary producers; Ex - cow, deer; "Plant eater"
2) CARNIVORE - obtain nutrients by eating other consumers; Ex - lions, eagles; "meat eater"
3) OMNIVORE - obtain nutrients by eating both primary producers and consumers;
Ex - Grizzly bear, humans
4) SCAVENGER - consumer that feeds on organisms that have recently died.
6. DECOMPOSERS
a. Organisms that breakdown organic material and return it to the environment for use by producers;
heterotrophic organisms.
b. Process is called DECAY
c. Includes bacteria, mold, mushrooms
d. Types
1) SAPROPHYTES - organisms that obtain their food from dead organisms or the waste
products of living organisms; examples - molds, mushrooms
2) PARASITES - organisms that obtain their food from living organisms; Ex - athlete's foot
D. Energy Flow
1. Energy flows in various patterns through ecosystem.
2. Total energy of one trophic level never flows to next level
3. FOOD CHAIN - specific sequence in which organisms obtain energy and organic materials from one
another.
a. Producer ---> Primary Consumer ---> Secondary Consumer ---> Scavenger
b. Grass ---> Deer ---> Puma ---> Vulture
4. FOOD WEB - interconnected food chains that form due to the complex relationships that form
between organisms.
Hawk
Mouse
Rabbit
Snake
Lizard
Bird
Grasshopper
Grass
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a. Many consumers may eat the same type of food
b. Food chains interlink and overlap within the ecosystem
E. Ecological Pyramids
1. Often complexities of an ecosystem are graphed to show the relationship between trophic levels
2. Primary producer at the base of the pyramid with consumer levels above it.
3. Common pyramid models
a. ENERGY PYRAMID
1) Shows that energy is lost at each level
a) Each organism in a given trophic level uses some of energy locked in food to carry on its
own life functions.
b) Always a loss of energy as heat in any system of energy transfer.
2) Never inverted.
b. NUMBERS PYRAMID
1) Shows the number of organisms at each trophic level
2) Usually there is an increase in the size of the organisms with each level
3) Normally producer organisms are most numerous; may be inverted - Single oak tree may
support thousands of caterpillars and other insects and birds.
c. BIOMASS PYRAMID
1) Amount of matter that can be supported at each trophic level.
2) Biomass is the total dry weight of organisms in the ecosystem.
F. BIOGEOCHEMICAL CYCLES
1. Process by which inorganic materials move from the atmosphere or soil into living organisms and
back again
2. Also called NUTRIENT CYCLES.
3. WATER CYCLE
a. Movement of water from atmosphere to the earth and back again.
b. PRECIPITATION - movement of water to earth from atmosphere
c. EVAPORATION - way most water lost from earth's surface to atmosphere.
d. TRANSPIRATION - loss water by green plants through their leaves.
4. NITROGEN CYCLE
a. Process by which nitrogen passes from the atmosphere to organisms and back again
b. Involves four major processes
1) NITROGEN FIXATION - certain bacteria convert nitrogen gas into ammonium compounds;
bacteria live in roots of legumes (beans, peas, clover, alfalfa)
2) AMMONIFICATION - bacteria break down nitrogen-containing amino acids from animal
wastes and dead organisms to form ammonia compounds
3) NITRIFICATION - Bacteria oxidize ammonia compounds to produce nitrates and nitrites
4) DENITRIFICATION - anaerobic bacteria break down nitrate releasing nitrogen gas back
into the atmosphere
5. OXYGEN-CARBON CYCLE
a. Involves the processes of photosynthesis and respiration
b. Photosynthesis removes carbon dioxide from atmosphere and fixes it as glucose and releases
oxygen to atmosphere.
c. During respiration oxygen is removed from atmosphere and carbon dioxide is released.
d. Normally processes of photosynthesis and respiration balance each other. Levels of oxygen and
carbon dioxide remain fairly constant
e. Since about 1850's consumption of fossil fuels have increased
1) Fossil fuels represent stored carbon compounds
2) Combustion of the fuels has increased the carbon dioxide level of the atmosphere.
3) Increased levels of carbon dioxide increase the ability of atmosphere to trap heat.
4) GREENHOUSE EFFECT - an increase in atmospheric temperature due to heat being
trapped
by the atmosphere. Can change climates and habitats
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III. Terrestrial Biomes
A. BIOME - large area identified by the presence of characteristic plants and animals.
1. Commonly identified by dominant plant life.
2. Don't have definite boundaries - abiotic factors gradually change.
3. Usually have characteristic rainfall and temperatures.
B. POLAR BIOMES
1. Surround North and South poles
2. Receive very little precipitation - fresh water scarce
3. Soil is sparse, low in nutrients, frozen much of the year
4. Temperature range - -40o C to 4o C
5. Receive virtually no sunlight for half the year.
6. ARCTIC POLAR BIOME
a. Lies over Arctic Ocean
b. Plants - Some flowering plants, mosses, lichens,
c. Animals - Gulls, Walruses, polar bears along Arctic coast.
7. ANTARCTIC POLAR BIOME
a. Lies over landmass of the Antarctic continent.
b. Plants - lichens, mosses, 3 types of flowering plants
c. Animals - small insects, seals, whales, penguins.
C. TUNDRA
1. Treeless biome blanketed by snow in winter that forms continuous belt across northern North
America, Europe, and Asia
2. Tundralike regions may also exist on mountains above treeline - highest point at which trees grow.
3. Characterized by a PERMAFROST - permanently frozen layer of ground
a. Surface soil above permafrost - thawed for only about 8 weeks
b. During thaw landscape is patchwork of shallow pond, bogs, and soggy soil
4. Climate - cold and dry
5. Plants - mosses, lichens, dwarf woody plants - NO TREES
6. Animals - Insects, ducks, geese, predatory birds, musk ox, caribou, lemmings, and weasels
D. CONIFEROUS FOREST
1. Biome dominated by conifers - cone-bearing evergreen trees
2. Long, cold winters and short cool summers.
3. Nutrient poor soils; usually acidic.
4. Animals - moose, bear, lynx
5. Cover northern parts of Europe, Asia, and North America
6. Three subdivisions
a. TAIGA - northernmost band; found in Canada and Alaska; Russian for "swamp forest"; Spruce
and Fir trees
b. CONIFEROUS BELT - south of Taiga; Canada and northern U.S. Called "spruce-moose" belt for
prominent resident species
c. SOUTHERN PINE FORESTS - southeastern U.S.; pitch pines
E. DECIDUOUS FOREST
1. Characterized by trees that lose their leaves in the fall.
2. Have definite seasons; temperate region
3. Stretch across eastern U.S., much of Europe, part of Asia, South America, Africa, and Australia
4. Precipitation evenly distributed over the year;
5. Moderate rainfall - 75 to 125 cm per year; moderately rich soil
6. Dominant trees - birch, beech, maple, oak, hickory, sycamore, elm, willow, and cottonwood.
7. Animals - white-tailed deer, black bear, raccoons, squirrels, hundreds of bird species
F. GRASSLAND
1. Dominated by grasses
2. Cover about one-fourth of earth's land surface
3. Found in variety of temperature ranges
4. Rainfall - 25 to 75 cm per year.
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5. Animals - bison, antelope, elephants, giraffes, kangaroos
6. Soil usually very rich
7. Goes by variety of names
a. PRAIRIE - North America
b. STEPPES - Asia
c. PAMPAS - South America
d. VELDT - Africa
D. DESERT
1. Dry areas where rainfall averages less than 25 cm per year
2. Organisms are adapted to harsh conditions - plants have deep root systems, some store water, thickened
stems and branches.
3. Temperatures may vary greatly - hot days and cold nights
4. Plants - cactus, sagebrush, creosote, some annuals.
5. Animals - camel, jackrabbits, many reptiles, scorpions, Kangaroo rats
E. RAIN FORESTS
1. TROPICAL RAIN FOREST
a. Found near equator
b. Abundant rainfall and sunlight
c. Rainfall - 200 to 225 cm per year.
d. Supports abundance of plant species - growth rate is rapid
e. Soil is thin, moist, very low in nutrients.
f. Removal of vegetation results in loss of soil
g. Animals - insects, parrots, toucans, apes, monkeys, predatory cats
2. TEMPERATE RAIN FOREST
a. Moderate temperatures and high humidity
b. Along west coast of North America from central California to southern Alaska.
c. Plants - redwood, Sitka spruce
d. Animals - deer, elk, rodents
IV. Aquatic Biomes
A. Occupy majority of earth's surface
B. MARINE BIOME
1. Earth's oceans and associated areas
2. Divided into 3 areas - ocean, intertidal zones, and estuaries
3. OCEAN
a. Covers 70% of earth
b. Water contains about 3.5% salt
c. Divided into two zones
1) PELAGIC ZONE - open ocean
a) NERITIC ZONE - extend out over continental shelf
b) OCEANIC ZONE - over deep water of open sea.
2) BENTHIC ZONE - ocean bottom
d. Divided according to light penetration
1) PHOTIC ZONE - where light penetrates
2) APHOTIC ZONE - region where light doesn't penetrate
4. INTERTIDAL ZONES
a. Area between high tide line and low tide line.
b. Organisms adapted to periodic exposure of air
c. Animals - crabs, clams, mussels, shorebirds.
5. ESTUARY
a. Biome that is zone between freshwater biome and marine biome
b. Region where rivers and streams flow into the sea
c. Subject to the oceanic tides - Tidewater regions
d. Organisms subject to changing environment.
e. Animals - shrimp, oysters, clams, crabs, many fish, numerous birds.
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C. FRESHWATER BIOME
1. Characterized by low levels of dissolved salts
2. Separated into 2 categories
a. LAKES and PONDS
1) EUTROPHIC LAKES - rich in organic matter and vegetation
2) OLIGOTROPHIC LAKES - water contains little organic matter.
b. RIVERS and STREAMS
1) Bodies of water that flows down a gradient or slope
2) Gradient is key abiotic factor of rivers
a) Steep gradient - fast flow
b) Low gradient - slow flow.
3. Animals - fish, muskrats, otters, ducks, loons, numerous insects
V. Biotic Relationships
A. COMPETITION
1. Use or defense of a resource by one individual that reduces the availability of that resource to other
individuals
a. May complete for habitat or food
b. Individuals in nature that don't retain access to prime habitat may be less successful in their
struggle to survive and reproduce.
2. Types
a. INTRASPECIFIC COMPETITION
1) Competition between members of the same species - example - lions fighting for social
status to mate
2) Individuals best adapted to survive will pass their genetic material on to offspring at a
greater rate than competitors.
3) One of the driving forces of evolution.
b. INTERSPECIFIC COMPETITION
1) Competition between organisms of different species.
2) Often not as intense because the members aren't competing for exactly the same materials
3) Deer and rabbits grazing in an open meadow
4) COMPETITIVE EXCLUSION PRINCIPLE - idea that when 2 or more species compete for
the very same resource, all but one will eventually fail as a competitor - 2 competitors
cannot coexist on the same limiting resource.
B. PREDATION
1. One consumer hunts and feeds on another consumer.
a. PREDATOR - the hunter
b. PREY - the hunted.
2. Usually results to maintain an ecological balance or natural equilibrium in an ecosystem
a. Graphs of numbers of predators and prey reveal that maximum number of prey is followed by a
maximum number of predators.
b. Studies of snowshoe hares and lynxes show that an increase in the population of snowshoe hares
leads to an increase in the number of lynxes. Increase in lynx population lowers the snowshoe
hare population leading to a drop in the lynx population.
C. SYMBIOSIS
1. Biological relationship in which 2 dissimilar organisms live together in a close relationship - Interact in a
way that affects survival of one or both organisms
2. Types
a. PARASITISM - symbiotic relationship in which one organism obtains nutrition from another
organism; one benefits and the other is harmed
1) PARASITE - organism that benefits from the relationship.
2) HOST - organism that provides the nutrients and is harmed.
3) A good parasite does not kill its host quickly.
4) examples - athlete's foot - fungus on the skin; ticks and mites; tapeworms
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b. COMMENSALISM - form of symbiosis in which one organism benefits and the other neither
benefits nor suffers harm
1) Host is not harmed.
2) EPIPHYTES - type of plant that grows on other plants; example - orchids - orchid roots
absorb moisture from air, tree supplies high place to obtain light.
3) Barnacles growing on whales - barnacle benefits, steady supply of food as whale moves
through open water, whale not harmed.
c. MUTUALISM - form of symbiosis in which both organisms benefit from living together.
1) Bacteria in digestive tract of cattle - bacteria obtain nutrients; cow able to use the cellulose
broken down by the bacteria.
2) Lichens - composed of two organisms; algae - carries on photosynthesis to provide food;
fungus - supplies water, minerals, and physical support
3) Termites - protozoan in digestive tract breaks down cellulose of wood; termites obtains
nutrients from the cellulose, protozoan obtains water and food from termite.
VI. Rhythmic Patterns
A. Activities of many organisms tied to cycles of time.
1. Called rhythmic because they are regular and predictable.
2. Adaptation that often limit competition - allow different species to occupy the same habitat but to
utilize its resources at different times.
a. Owls hunt mice at night
b. Hawks hunt mice during the day.
3. Rhythmic cycles may be linked to variations in:
a. Length of daylight.
b. Temperature
c. Hormone levels
B. CIRCADIAN RHYTHMS
1. Cycles that occur about every 24 hours
2. Name means "about a day"
3. Cycle controlled by a so-called biological clock - scientists not sure where control center is located
a. Have investigated whether human circadian rhythms are controlled by sunlight, by other physical
factors, or by some internal physiological mechanisms
b. Humans maintain regular cycle between 22 and 26 hours when placed darkened rooms.
4. NOCTURNAL - organisms that are active mainly at night
5. DIURNAL - organisms are active during the day
6. Examples
a. Morning Glories - flowers open - morning; close - night
b. Marine zooplankton - move to surface of ocean at end of day and move downward at dawn.
c. Humans - pulse rate, body temperature, blood pressure, cell division, and sleep-wake cycle.
C. ANNUAL RHYTHMS
1. Any physiological or behavioral pattern that recurs in yearly cycles
2. Many reproductive cycles are tied to annual rhythms
a. Female bears give birth during winter in protection of den
b. Nesting of ducks in spring /summer - allows young time to be strong enough for fall migration.
c. Production of flowers and pollen at particular time of year - Usually in the spring
3. Seasonal Changes
a. HIBERNATION - State of severely reduced physiological activity during the winter.
1) Allows active creatures to survive when temperatures extremely cold and food scarce.
2) Breathing slow and irregular, blood pressure drops, and body temperature drops.
3) Animals that hibernate - bats, chipmunks, woodchucks, many reptiles and amphibians.
4) Some animals may go into a deep sleep, not hibernating - bears, opossums, skunks - may
come out during warm periods.
b. ESTIVATION - annual rhythm characterized by severely reduced physiological activity during
the summer.
1) Permits escape from hot temperatures and dry conditions
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D.
E.
VII.
A.
B.
C.
C.
2) May last for days, weeks, or months
3) Animal usually buries self in mud.
4) Animals that estivate - frogs, toads, box turtles, some mice
MIGRATORY RHYTHMS
1. Seasonal movement of some species from one community or biome to another.
2. Movement is called MIGRATION
3. Allows use of nutrients, habitats, and climatic conditions only available during a particular season.
4. Some movements may cover long distances - arctic tern breeds in N. Atlantic; migrates to Antarctic
5. Migration of Monarch Butterflies from Canada and northern U.S. to Mexico
6. Some mountain dwelling animals may migrate vertically - bighorn sheep and elk move up slopes of
Rocky Mountains at beginning of summer and down into valleys during winter.
TIDAL or LUNAR RHYTHMS
1. Tides caused by gravitational pull of moon and to a certain extent the sun on the oceans of the earth.
2. High tides occur about every 12.5 hours.- low tide in between.
3. Activities of many organisms of the intertidal zone affected by the rise and fall of tides.
a. Barnacles - attached mollusks - shell closed during low tide to prevent drying.
b. Many fish feed in tidal pools at high tide and leave as tide recedes
4. Reproduction of grunion - associated with high tides of spring/summer - Male fish come ashore, followed
by females - eggs laid/fertilized/buried in sand - fry carried to sea about 10 days later.
SUCCESSION
Gradual, sequential replacement of populations in an area by other populations.
1. Organisms tend change their environment in ways that make it less favorable to themselves and more
favorable for other organisms
2. Changes in abiotic factors may lead to changes in the ecosystem
Stages of Succession
1. PIONEERING STAGE
a. PIONEER SPECIES - first species to colonize a new habitat
b. Stabilize and enrich soil.
2. SERIAL or DEVELOPMENTAL STAGE
a. Intermediate communities that occupy an area.
b. Crowd out pioneer species, shade out smaller species; further stabilize and enrich soil
3. CLIMAX COMMUNITY
a. Community that will remain stable as long as the area is undisturbed.
b. Abiotic factors usually determine what the climax community will be.
Types of Succession
1. PRIMARY SUCCESSION
a. Sequential replacement of populations in an area that has not previously supported life.
b. Usually occurs in areas where bare rock has been exposed.
c. Lichens are the pioneer organisms - help begin soil formation
d. As soil becomes established larger plants may inhabit the area.
e. Eventually a climax community will be reached.
f. Process is very slow - may require hundreds of years.
2. SECONDARY SUCCESSION
a. Development of a community in an area where a previous community was removed.
b. Usually associated with some type of natural disaster.
c. Soil is usually still present - grasses are usually the pioneer species.
d. Usually re-establishes the original community.
e. Progresses more rapidly than primary succession - usually requires about a hundred years.
f. OLD FIELD SUCCESSION - replacement of populations in abandoned farm fields.
LAKE SUCCESSION
1. Transformation from crystal clear bodies of water to dry land
2. Involves process of EUTROPHICATION - an increase in nutrients in an environment.
3. Young lakes are low in nutrients - called OLIGOTROPHIC - relatively few organisms can survive
in lake.
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4.
5.
6.
7.
8.
As nutrients and silt flows into the lake the water becomes murkier.
Sediment accumulates around roots of cattails and rushes around edge of lake
Biomass of the lake increases - aquatic arthropods and fish populate the lake.
Sediment begins to fill the lake, becoming eutrophic - contains many nutrients.
Eventually lake becomes so filled with rich sediment it becomes a marsh, then a swamp, and finally
dry land - then can proceed through stages to become dense forest.
VIII.Population Changes (Growth)
A. Growth of a population - due to births and immigration
1. IMMIGRATION - movement of new individuals or organism into an area.
2. Population increase in size.
B. Decrease of a population - due to deaths and emigration.
1. EMIGRATION - movement of organisms or individuals from an area.
2. Size of the population decreases.
C. Change in population size can be expressed as mathematical formula:
Change in Population Size = (Births + Immigrants) - (Deaths + Emigrants)
D. In climax communities, birth and death rates remain about the same
E. In developing communities populations may change in size.
IX. POPULATION GROWTH
A. An increase in a population
B. POPULATION GROWTH RATE - change in the number of individuals in a population over time:
Growth Rate = Change in Number of Individuals / time
C. BIOTIC POTENTIAL of a population - rate at which a population will grow if all individuals survive
and reproduce at maximum capacity.
1. Biotic potential usually never reached - limited by certain limiting factors.
a. Food supply
b. Available space
c. Predation
d. Accumulation of wastes
2. CARRYING CAPACITY - size of a population that a particular environment can support.
D. GROWTH CURVES
1. A graph showing the number of individuals in a population over time
2. Types of Growth Curves
a. J - SHAPED CURVE - exhibits lag and exponential phases
1) LAG PHASE - period when there is little or no increase in a population - limited number
of females reproducing
2) EXPONENTIAL PHASE - population increases so rapidly that number of individuals
doubles in a specific time interval; keeps doubling in increasingly shorter periods of time
b. S - SHAPED CURVE - exhibits lag & exponential phases; levels; doesn't increase as rapidly.
1) Leveling off represents a period of relative stability after the lag and exponential phases.
2) Leveling gives an indication of the carrying capacity of the ecosystem.
c. May also get a curve that declines after leveling off - associated with bacterial/fungal cultures.
E. Limits to Growth
1. POPULATION DENSITY - number of individuals per unit of area; Density = Individuals / Area
a. Low population density may result in population dying out.
b. High population density - protects individuals in the population
2. DENSITY-DEPENDENT FACTORS
a. Factors that affect populations in different ways depending on population density
b. Usually biotic
c. Availability of food controls the size of population
d. Factors include availability of space and light, disease, number of predators, and parasitism
3. DENSITY-INDEPENDENT FACTORS
a. Factors that affect populations regardless of population density.
b. Usually abiotic
c. Temperature, rainfall, wind speed, etc.
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X. Human Populations
A. Survival rate of humans has increased due to domestication of crops and animals
1. Provided humans with more constant food supply.
B. Human Population Growth
1. From about 6000 B.C. to A.D. 1800, number of humans in world increased steadily - Lag phase of
J - shaped curve
2. About mid 1800's, dramatic increases - entered exponential phase
a. Increased food production, rise of industry, and better medicine
b. Life expectancy became longer.
3. Eventually will be limited by same density dependent factors that limit other populations.
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