Population Ecology

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Ecology• Study of the interactions between organisms and

the environment• Study of the physical and biological variables

governing the distribution & growth of living things

Population • Individuals of a given species occurring at

one place at one time

• Population ecology– Study of population growth & interactions

Population Size

• (births + immigrants) – (deaths + emmigrants) = Population change

• Immigration – movement into a population

• Emigration – movement out of a population

Growth Rate

• Subtract death rate from birth rate

• r = b – d– r is growth rate– b is birth rate– d is death rate

• Population growth = rN– N = initial population size

Exponential Growth

• Rate of increase remains constant

• Population size soon increases greatly

• Can only occur under ideal conditions

• This type of growth cannot continue forever

Exponential Growth of a Bacteria

Carrying Capacity• Indefinite exponential growth is limited• Shortages of growth factors will limit population

growth• Carrying capacity = maximum number that can

be supported in a particular environment

Sigmoid Growth Curve• Initial exponential growth and subsequent

stabilization at carrying capacity

Boom & Bust Cycle

• Sometimes populations do not level off

• Exponential growth with a sudden die-off

Population Size & Ability to Survive

• Very small populations are less able to survive than large populations

– Random events can wipe out small populations

– Small populations have less genetic variability

Population Density• Number of organisms per unit area

• Density influences survival

Dispersion

• Way that individuals are arranged

• Three patterns– Uniform– Random – Clumped

Uniform Distribution

• Individuals evenly spaced

• Often results from territoriality

• Also plants with allelopathy

Random Distribution• Lacking definite order

• Individuals do not influence others growth

Clumped Distribution

• Individuals form clusters

• Clumping due to interaction of individuals

Density Dependent Factors

• Factors that affect a population only if its density changes

• Types of density dependent factors– Competition – Predation – Parasitism

Competition

• Interaction among organisms for the same resources– Food– Living space

• Regulates population size & is a driving force of evolutionary change

Competition Types

• Intraspecific – among the same species

• Interspecific – between species

Predation

• One species will kill & eat another

• Interactions maintain natural populations

• More prey results in more predators

• Less prey reduces predator numbers

Parasitism• One species living at the expense of another• Regulates populations by weakening or killing

Density-Dependent Factors & Boom & Bust Cycles

• Example:– Lemmings have large increases & declines– Lemming populations increase, then

predators increase– Then, lemming populations are mostly

eliminated causing predator populations to decrease because of lack of food

– Then, lemming populations can increase….

Density-Independent Factors

• Operates regardless of population density

• Includes factors such as weather & physical disruptions

• A certain percentage of the population will die due to the event

Survivorship• Age distribution

– Proportion of individuals that survive to an age category

– Differs greatly from species to species

Mortality vs. Survivorship• Mortality – death rate

• Survivorship – proportion of an original population that survives to a certain age

Type I Survivorship• Low infant mortality

• Small number of offspring, parental care

• Most survive to an old age

Type II Survivorship• Often reproduce asexually

• Mortality is constant over lifespan

Type III Survivorship• High infant mortality• Those that survive are likely to live to old age• No parental care, high reproductive rate

Demography

• Statistical study of human population

• Human population is in exponential growth

Human Population Growth has Different Patterns

• Stable population– Remains the same– Same number entering reproductive age

as at end of reproductive age

• Population pyramid– Graphic representation of population age– Shows patterns in population change

Population Growth in Developed Countries

Population Growth in Developing Countries

World Population distribution

Share of the World Population

Interactions Within Communities

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Community

• Grouping of populations living together in a particular area at a particular time

Abiotic Factors

• Nonliving factors within the environment– Air– Water– Rocks

• Abiotic factors affect living (biotic) factors

Ecosystem• Biotic & abiotic factors in a certain area

• Community along with abiotic factors

Habitat

• Space within an area where an organism lives

• Each organism plays a certain role

Niche• Two ways of defining

– An organism’s role in the environment– Organism’s use of biotic & abiotic resources

Competition

• Organisms that live near one another strive to obtain the same limited resource

• Competitive exclusion principal– If 2 species are competing with one another

for the same limited resource , the species able to use the resource most efficiently will eventually eliminate the other species

Competition in Nature• Sage & grass both need the same soil nutrients• Sage out competes grass by secreting toxic

chemicals

Barnacle Competition• Balanus & chthamalus

– Both live in the intertidal zone– This intertidal zone is their niche

Fundamental Niche• Chthamalus can live out of

water longer than Balanus• Fundamental niche

– Everywhere a species can inhabit

Realized Niche• When both species are present

– Each actually lives where it competes best– This defines their realized niche

Predation

• Predator – kills & eats another species

• Prey – eaten by another species

• Predator-prey relationships affect each other’s populations

• Several outcomes are possible

Predator-Prey Example• Didnium – the predator• Paramecium – the prey• Predator & prey

introduced into new environment

Outcome 1

• Predator exterminates prey

• Predator then dies due to lack of food

Outcome 2• Some prey hide in sediment• Predator eats those in clear fluid• Predator dies because it cannot find more food

Outcome 3• Prey is introduced in successive intervals

• Predator-prey follow cyclical pattern

Plant –Herbivore Coevolutioin• Plants develop defenses against being eaten• Natural selection chooses animals able to feed

on plants with new defenses

Protective Adaptation• Some animals have adapted to eating plants

that are toxic• Some (like monarch butterfly) are able to store

toxins from food• Stored toxin protects the animal from predation

Protective Coloration• Some highly poisonous organisms

advertise with bright colors• Warning coloration is effective defense

Mimicry

• Unprotected species have come to resemble harmful or distasteful species

– Batesian mimicry

– Example: grasshopper that looks like a tiger beetle

Mimicry• Protective coloration of different animals

come to resemble each other• Both posses similar defenses

– Mullerian mimicry– Example: Monarch & Viceroy butterflies

Camouflage

• Animal blends into its surroundings

• Not seen by predators

• Example: cabbage butterfly caterpillar

Camouflage

Symbiosis

• One organism lives with another

• Three types– Commensalism– Mutualism – Parasitism

Termite Gut Symbiosis

Commensalism• One species benefits• The other species neither benefits or is harmed• Examples: barnacles living on whales

Mutualism• Both species benefit from relationship

• Example: clownfish & anemones

Mutualism• Red billed oxpeckers & impala

Parasitism• One species benefits

• One species is harmed

• Example: humans & hookworms

Plant Parasitism

Succession

• Change in communities over time

• Generally linked to disturbance

Primary Succession

• Starts on surfaces not previously supporting organisms

• Soil must accumulate

• Pioneer community becomes established– Usually plants able to grow under harsh

conditions

Primary Succession

• Pioneer community paves way for growth & development of native vegetation

• Plant community changes through time

• Eventually a climax community establishes

Primary Succession Mount St. Hellens

Succession of a Pond

Secondary Succession

• Areas with soil have been disturbed

• Community does not start from no soil stage

• Common due to human activity

Ecosystems

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Ecosystem

• Includes abiotic environment & community

• Types of organisms of an ecosystem– Producers– Consumers– Decomposers

Producers • Make their own food

• Base of the food chain

• Plants & photosynthetic protists

Consumers• Heterotrophs – feed on other organisms

• Kill & eat their food

Decomposers • Special group of consumers

• Nourishment from dead matter

• Recyclers

An Ecosystem

Ecosystem Boundaries• May or may not be distinct

Transfer of Nutrients

• Ultimate source of most energy is the sun

• Green plants capture energy from the sun

• Consumers eat producers & other consumers

• Detritivores convert organic materials to nutrients usable by plants

Trophic Levels

• Feeding levels & transfer of energy

– Producer

– Primary consumer – feed on producer

– Secondary consumer – eat primary consumer

– Tertiary consumer – eat secondary consumer

Food Chain

Food Web

• Many species do not strictly feed on one trophic level

• Interactions become more complicated

• Food web – group of interwoven food chains

Energy Flow Through Ecosystems

• Most energy is lost & does not transfer to the next trophic level

• Higher trophic levels must have fewer individuals– Next highest trophic level has about 1/10th the

number of individuals, biomass & energy

Flow of Energy

Numbers in Trophic Levels

Biomass in Trophic Levels

Energy in Trophic Levels

Obtaining Substances for Life

• Materials cycle through ecosystems

• Reservoir –area with most of a material

• Examples of ecosystem cycles– Water (hydrologic cycle)– Nitrogen– Phosphorus– Oxygen– Carbon

Water Cycle

• Most living things are primarily water

• Life’s chemical reactions require water

• 90% of water that reaches atmosphere comes from plant transpiration

• Atmospheric water condenses

Water Cycle

• Plants take up about 1000 kg of water to produce 1 kg of biomass

• Groundwater provides ¼ of water used by humans in U.S.

• 2% of U.S. groundwater is polluted– Industry – Pesticides

Carbon Cycle

• CO2 found in atmosphere & oceans

• Producers & some consumers incorporate carbon into organic molecules

• Animals & combustion return carbon to atmosphere

Oxygen Cycling

• Plants use CO2, release O2

• Consumers use O2, release CO2

• Some CO2 is liberated by decomposition

Nitrogen Cycle

• Important plant nutrient

• Atmosphere is reservoir

• Nitrogen fixing bacteria convert N2 to ammonia

Phosphorus Cycle

• Required plant nutrient

• Soil has only small amounts

• Animals obtain phosphorus by eating plants

End chapter 40

Biomes & LifeLife Zones Biomes & LifeLife Zones

Food for ThoughtIn The News

Biomes• Large ecosystems occurring over wide areas of

land within specific climatic regions• Support communities of characteristic organisms

Patterns that Determine Biomes

• Amount of solar radiation

• Global atmospheric circulation

• Features of the earth (topography)

Solar Energy• Some parts of earth receive more energy

• Greater latitude, colder climate

Circulation Patterns• Differential heating creates six coils

of rising & falling air• Rotation of earth deflects winds

– Trade winds of equator– Westerlies of middle latitudes

Precipitation• Warm air rises & is cooled

• Cool air holds less moisture

• Warm air absorbs available moisture

Shadow Effect

• Air traveling up a mountain is cooled– Precipitation forms– Windward side is moist– Leeward side is arid

Ocean Circulation

• Ocean moves in great spiral patterns

• These surface currents affect climate– Redistribute heat

Climatic Regions Classify Biomes

• Tropical rain forest

• Savannas

• Deserts

• Temperate grasslands

• Temperate deciduous forests

• Taiga

• Tundra

Elevation & Biomes

Tropical Rain forests• High temperature & rainfall

– 200 – 450cm/yr (80 – 175 in/yr)– Average 25º C (77º F)

• Found on both sides of the equator

Rain Forests

• Extensive canopy of plants– 2% of light reaches forest floor– Plants do not grow well on forest floor

• Epiphytes grow on trees

• Giant diversity of life

• Poor soils, do not support agriculture

Savannas

• Areas near the equator

• High temperature, moderate rainfall– 90 – 150 cm/yr (35 – 60 in/yr)

Savannas

• Open grasslands, scattered shrubs & trees

• Supports large number of grazing herbivores

• Large number of plant eating invertebrates

Termite Mounds of Australia

Deserts

• Low precipitation– 25 cm/yr (10 in/yr) or less

• 20 to 30 degrees north & south of equator

Deserts

• Organisms with adaptations

• High diversity, small populations

• Many nocturnal animals

Temperate Deciduous Forests

• Distinct seasons

• Trees are deciduous

• Precipitation moderate– 75 – 150 cm/yr (30 – 60 in/yr)

Temperate Deciduous Forests

• Upper canopy of dominant trees

• Animal life abundant in trees & forest floor

• Includes many human population centers

Temperate Grasslands

• Includes prairies & steppes• 25 – 75 cm/yr (10 – 30 in/yr) of precipitation

Temperate Grasslands

• Large quantities of perennial grass

• No trees

• Grazing animals & burrowing rodents

• Rich soils

• Many areas converted to agriculture

Taiga• Long cold winters

• Little precipitation– Most is in summer– Plants go through life cycle in

short amount of time

Taiga

• Cone bearing trees common

• Many large mammals

Tundra

• Found at the top of the world

• Permanent ice

• Low precipitation like deserts

Tundra

• Life is apparent in short summer

• Grasses & sedges

Fresh-water Ecosystems

• Intertwined with terrestrial ecosystems

• Includes only 2% of earth

• Ponds & lakes, rivers & Streams

• Different water depths have different communities

Life Zones of a Lake

Rivers & Streams

• Characterized as an open ecosystem

• Nutrients washed into water– Feeds heterotrophs– Autotrophs rare

Estuaries

• Freshwater meets saltwater

• Producers are mostly algae & phytoplankton

• Nutrients abundant

• High diversity of organisms

Oceans

• Covers nearly ¾ of Earth

• Variety of habitats– Intertidal zone– Neritic zone– Open sea zone

Intertidal Zone

• Harsh environment for life

• Tide rolls in & out

• Abundant light for photosynthesis– Variety of producers

• Different habitats based on substrate– Rocky shore– Sandy shore

Rocky Shore

Sandy Shore

Neritic Zone

• On continental shelf

• Abundant plant & animal life

• Includes coral reefs

Open-sea Zone

• Beyond continental shelf

• Many diverse forms of life

Regions of Open-sea

• Photic – Light penetrates– Supports phytoplankton

• Mesopelagic – No photosynthetic organisms– Water pressure increases

Regions of Open-sea

• Abyssal – Deep water

• Benthos – Sea floor bottom

The Biosphere

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The Biosphere

• The global ecosystem

• Includes all life on Earth

Nonrenewable Resources

• Formed at a rate more slowly than they are consumed

• Examples:– Coal– Oil – Copper– Iron

Fuel Resources

• Fossil fuels (nonrenewable)– Coal– Oil – Natural gas

• Currently 77% of worlds energy supply– Coal 20%– Oil 36%– Natural gas 21%

Nuclear Power

• Nonrenewable, but large supplies

• 2.2 lbs. produces as much electricity as 2200 tons of coal

• Problems– Cost of building power plants– Disposal of radioactive waste

Mineral Resources

• Inorganic

• Occur naturally

• Present in fixed amounts

• Supplies will eventually be used

Municipal Solid Waste

• Many things thrown away– Paper– Food waste– Plastics– Metals– Rubber– Leather– Textiles– Glass – Wood

Municipal Solid Waste

Strategies to Conserve

• Reduce consumption

• Reuse some items

• Recycling

• Buying recycled goods

Renewable Resources

• Replace themselves over time

• Renewable energy sources– Solar power– Water power– Wind power– Geothermal energy– Bioenergy

Solar Power• Use of sun for heating or to produce

electricity• Solar cells convert energy into

electricity• May be major source of energy by

2030

Water Power• Falling water drives turbines to produce

electricity• Wave power uses energy in sea waves• Tidal power• Problems: high cost & unsteady rate

Wind Power• Wind to generate electricity• U.S. may generate 10-20% of energy by 2030

Geothermal Energy

• Hot water or steam from within Earth

• Uses– Directly for heating– Converted to electricity

Bioenergy

• Using living plants to produce energy

• Types of bioenergy– Burning of wood– Decomposition of animal waste

• Produce methane-rich gas• Produce electricity

– Ethanol production from plants

Pollution

• Threatens the biosphere• Substances that physically or chemically

change water• Types of contaminants

– Infections agents– Runoff, drainage & hazardous waste dumps– Toxic substances– Thermal pollution– Solid waste

Dumping Pollutants into Water

• Point source – where they enter water

• Non-point source – enter in various places– Sediments in runoff

• Often from agriculture

– Mine drainings– Poisons leaching from hazardous dumps– Pesticides, herbicides, & fertilizers

Toxic Dump Threatening Groundwater

Toxic Substances

• Come from many sources

• Most do not degrade

• Biological concentration– Toxins accumulate in fatty tissues

• Biological magnification– Amounts increase in food chain

Biological Magnification of DDT

Pollution from Organic Nutrients

• Common sources– Sewage treatment plants– Paper mills– Meat packing plants

• Food for bacteria that grow in water

• Decreases oxygen in waters

Pollution from Inorganics

• Common sources– Croplands– Laundry detergents

• Can lead to eutrophication– Heavy plant growth– Plants die– Bacteria decompose plants, use oxygen

Mismanagement of Solid Waste

• Sanitary landfills help, but problems still exist– Space is running out– Groundwater contamination is possible

Air Pollution Sources

Burning Fossil Fuels• Major source of air pollution

• Causes smog or grey air

Secondary Pollutants• Sun causes reactions with chemicals in air• New pollutants are created• Ozone is principal secondary pollutant

– Irritating to eyes & respiratory system

Ground Level Ozone in U.S. Cities

Acid Rain• Caused by precipitation in polluted air

• pH of waters are lowered

Acid Rain Effects

• Acidifies lakes– Kills aquatic life

• Leaching of metals

• Eats away stone

• Kills plants

Acid Rain Effects

Damage to Ozone Level• Ozone in stratosphere shields UV rays• Main source of damage is chlorofluorocarbons

Deforestation

• 2% of Earth (rainforests) has 50% of plants & animals

– Contribute to 25% of medicines

• Plays important role in worlds climates

Deforestation• Population & poverty is high• Logging & farming efforts reduce forests

– Poor soils do not support agriculture for long

Forest Conservation

• Reserves are a partial answer

Global Warming

• High CO2 levels block outward heat radiation– Creates greenhouse effects

• Other gases contribute– Methane– Nitrogen oxides

Species Extinction

• Factors threatening species– Habitat destruction– Pollution– Illegal trade

• Results in reduction of biological diversity

Value of Biological Diversity • Elimination of species affects other species• Sources of food, medicine, …• Less diversity in crops means more vulnerability