13.1 Ecologists Study Relationships

KEY CONCEPT Ecology is the study of the relationships amongorganisms and their environment.

13.1 Ecologists Study Relationships

Ecologists study environments at different levels oforganization.

• Ecology is the study of the interactions among livingthings, and between living things and their surroundings.

13.1 Ecologists Study Relationships

OrganismOrganism

• An organism is an individual livingthing, such as an alligator.

13.1 Ecologists Study Relationships

OrganismOrganism

Population

Population

• A population is a group of the samespecies that lives in one area.

13.1 Ecologists Study Relationships

OrganismOrganism

Population

Population

Community

Community

• A community is a group of differentspecies that live together in one area.

13.1 Ecologists Study Relationships

OrganismOrganism

Population

Population

Community

Community

Ecosystem

Ecosystem

• An ecosystem includes all of theorganisms as well as the climate, soil,water, rocks and other nonliving thingsin a given area.

13.1 Ecologists Study Relationships

OrganismOrganism

Population

Population

Community

Community

Ecosystem

Ecosystem

Biome• A biome is a major regional or globalcommunity of organisms characterizedby the climate conditions and plantcommunities that thrive there.

13.1 Ecologists Study Relationships

Ecological research methods include observation,experimentation, and modeling.

• Observation is the act of carefully watching somethingover time.

• Observations of populations can be done by visualsurveys.– Direct surveys for easy to spot

species employ binoculars orscopes.

– Indirect surveys are used forspecies that are difficult totrack and include looking forother signs of their presence.

13.1 Ecologists Study Relationships

• Experiments are performed in the lab or in the field.– Lab experiments give researchers more control. – Lab experiments are not reflective of the complex

interactions in nature.– Field experiments give a

more accurate picture ofnatural interactions.

– Field experiments maynot help determineactual cause and effect.

13.1 Ecologists Study Relationships

• Computer and mathematical models can be used todescribe and model nature.

• Modeling allows scientists to learn about organisms orecosystems in ways that would not be possible in anatural or lab setting.

Ecologists use data transmittedby GPS receivers worn by

elephants to develop computermodels of the animal’s

movements.

13.2 Biotic and Abiotic Factors

KEY CONCEPT Every ecosystem includes both living and nonlivingfactors.

13.2 Biotic and Abiotic Factors

An ecosystem includes both biotic and abiotic factors.

• Biotic factors are living things.– plants– animals– fungi

– bacteria

plants

13.2 Biotic and Abiotic Factors

• Abiotic factors are nonliving things. – moisture– temperature

– wind

– sunlight – soil

moisture

sunlight

13.2 Biotic and Abiotic Factors

Changing one factor in an ecosystem can affect manyother factors.

• Biodiversity is the assortment, or variety, of living things inan ecosystem.

• Rain forests have more biodiversity than other locations inthe world, but are threatened by human activities.

13.2 Biotic and Abiotic Factors

• A keystone species is a species that has an unusually largeeffect on its ecosystem.

keystone

13.2 Biotic and Abiotic Factors

• Keystone species form and maintain a complex web of life.

creation ofwetlandecosystem

increased waterfowlPopulation

increasedfishpopulation

nesting sitesfor birds

keystone species

13.3 Energy in Ecosystems

KEY CONCEPT Life in an ecosystem requires a source of energy.

13.3 Energy in Ecosystems

Producers provide energy for other organisms in anecosystem.

• Producers get their energy from non-living resources.

• Producers are also called autotrophs because they maketheir own food.

13.3 Energy in Ecosystems

Producers provide energy for other organisms in anecosystem.

• Consumers are organisms that get their energy by eatingother living or once-living resources.

• Consumers are also called heterotrophs because they feedoff of different things.

13.3 Energy in Ecosystems

Almost all producers obtain energy from sunlight.

• Photosynthesis in most producers uses sunlight as anenergy source.

• Chemosynthesis in prokaryote producers uses chemicalsas an energy source.

carbon dioxide + water +hydrogen sulfide + oxygen

sugar + sulfuric acid

13.4 Food Chains And Food Webs

KEY CONCEPT Food chains and food webs model the flow of energyin an ecosystem.

13.4 Food Chains And Food Webs

A food chain is a model that shows a sequence of feedingrelationships.

• A food chain links species by their feeding relationships.

• A food chain follows the connection between one producerand a single chain of consumers within an ecosystem.

DESERT COTTONTAILGRAMA GRASS HARRIS’S HAWK

13.4 Food Chains And Food Webs

• Consumers are not all alike.– Herbivores eat only plants.– Carnivores eat only animals.

– Omnivores eat both plants and animals.

– Detritivores eat dead organic matter.

– Decomposers are detritivores that break down organicmatter into simpler compounds.

carnivore decomposer

13.4 Food Chains And Food Webs

• Specialists are consumers that primarily eat one specificorganism or a very small number of organisms.

• Generalists are consumers that have a varying diet.

13.4 Food Chains And Food Webs

• Trophic levels are the nourishment levels in a food chain.– Primary consumers are herbivores that eat producers. – Secondary consumers are carnivores that eat

herbivores.– Tertiary consumers are carnivores that eat secondary

consumers.

– Omnivores, such as humans that eat both plants andanimals, may be listed at different trophic levels indifferent food chains.

13.4 Food Chains And Food Webs

A food web shows a complex network of feedingrelationships. • An organism may have multiple feeding relationships in an

ecosystem.

• A food web emphasizes complicated feeding relationshipsand energy flow in an ecosystem.

13.5 Cycling of Matter

KEY CONCEPT Matter cycles in and out of an ecosystem.

13.5 Cycling of Matter

Water cycles through the environment.

• The hydrologic, or water, cycle is the circular pathway ofwater on Earth.

• Organisms all have bodies made mostly of water.

precipitation condensation

transpiration

evaporation

water storagein ocean

surfacerunoff

lake

groundwater

seepage

13.5 Cycling of Matter

Elements essential for life also cycle throughecosystems. • A biogeochemical cycle is the movement of a particular

chemical through the biological and geological parts of anecosystem.

• The main processes involved in the oxygen cycle arephotosynthesis and respiration.

13.5 Cycling of Matter

• Oxygen cycles indirectly through an ecosystem by thecycling of other nutrients.

oxygen

respiration

carbondioxide

photosynthesis

13.5 Cycling of Matter

fossil fuels

photosynthesis

carbon dioxidedissolved in water

decompositionof organisms

respiration

carbondioxide

in air

photosynthesis

combustionrespiration

• Carbon is the building block of life.– The carbon cycle moves carbon from the atmosphere,

through the food web, and returns to the atmosphere.– Carbon is emitted by the burning of fossil fuels.

– Some carbon is stored for long periods of time in areascalled carbon sinks.

13.5 Cycling of Matter

nitrogen inatmosphere

animals

denitrifyingbacteria

nitrifyingbacteria

nitrifyingbacteria

ammonium

ammonification

decomposers

plant

nitrogen-fixingbacteria in soil

nitrogen-fixingbacteria in

roots

nitrates

nitrites

• The nitrogen cycle mostly takes place underground.– Some bacteria convert gaseous nitrogen into ammonia

through a process called nitrogen fixation.– Some nitrogen-fixing bacteria live in

nodules on theroots of plants;others livefreely inthe soil.

13.5 Cycling of Matter

– Ammonia released into the soil is transformed intoammonium.

nitrogen inatmosphere

animals

denitrifyingbacteria

nitrifyingbacteria

nitrifyingbacteria

ammonium

ammonification

decomposers

plant

nitrogen-fixingbacteria in soil

nitrogen-fixingbacteria in

roots

nitrates

nitrites

– Nitrifying bacteria change the ammonium into nitrate.

– Nitrogen moves through the foodweb and returnsto the soil duringdecomposition.

13.5 Cycling of Matter

geologic upliftingrain

weathering ofphosphate from rocks

runoff

sedimentationforms new rocks

leaching

phosphate in solutionanimals

plants

decomposers

phosphatein soil

• The phosphorus cycle takes place at and below groundlevel.– Phosphate is released by the weathering of rocks.

– Phosphorus moves through the food web and returns tothe soil duringdecomposition.

– Phosphorus leaches into groundwater from the soil and is locked in sediments.

– Both mining and agriculture add phosphorus into the environment.