Ecology of Organisms and Populations

Ch. 18

Ecology

Study of interactions between organisms and their environment

Ecology can be divided into four increasingly comprehensive levels: Organismal ecology Population ecology Community ecology Ecosystem ecology

Ecology

Organismal ecology Is concerned with

evolutionary adaptations that enable individual organisms to meet the challenges posed by their abiotic environments. http://www.seabird.org/assets/killer%20whales%20internet%202.jpg

Ecology

Population ecology Is concerned with

populations, groups of individuals of the same species living in the same area.

Concentrates mainly on factors that affect population density and growth.

http://newsimg.bbc.co.uk/media/images/44609000/jpg/_44609350_puffins512.jpg

Ecology

Community ecology Is concerned with

communities, assemblages of populations of different species.

Focuses on how interactions between species affect community structure and organization.

http://www.mass.gov/envir/forest/images/multiLayerForest.jpg

Ecology

Ecosystem ecology Is concerned with ecosystems, which include all the abiotic

factors in addition to the community of species in a certain area.

Focuses on energy flow and the cycling of chemicals among the various abiotic and biotic factors.

http://www.african-books.com/images/Animals/montage.jpg

Components of the Environment The abiotic component

Consists of nonliving chemical and physical factors.

The biotic component Includes the living factors.

Abiotic Factors of the Biosphere On a global scale, ecologists have recognized striking

regional patterns in the distribution of terrestrial and aquatic life.

Global distribution patterns Reflect regional differences in climate and other abiotic factors.

Sunlight

Solar energy powers nearly all ecosystems. Availability of sunlight affects aquatic and

terrestrial environments.

http://artfiles.art.com/images/-/Aflo/Sun-Shining-in-Blue-Sky-Over-Tree-in-Winter-Snow-Biei-Hokkaido-Japan-Photographic-Print-C13062664.jpeg

Water

Aquatic organisms may face problems with water balance.

For terrestrial organisms, the main water problem is drying out.

Temperature

Environmental temperature Is an important

abiotic factor because of its effect on metabolism.

http://www.wildherps.com/images/herps/standard/desert_iguana.jpg

http://www.sciam.com/media/inline/A186A7F7-D8EA-DDDF-0F715313A7DA2A91_1.jpg

Wind Some organisms depend on nutrients

blown to them by wind. Organisms such as plants depend on wind

to disperse pollen and seeds. Can also affect the pattern of a plant’s

growth.

http://www.asdk12.org/staff/vanarsdale_mark/pages/Ecology_Images/wind_tree.jpg

Rocks and Soil

Soil variation contributes to the patchiness we see in terrestrial landscapes.

In streams and rivers, the composition of the soil can affect water chemistry.

Periodic Disturbances

Catastrophic disturbances Can devastate biological communities.

After a disturbance, An area is recolonized by organisms, or repopulated by

survivors. The structure of the community undergoes a succession of

changes during the rebound.

Ecosystems

What biotic and abiotic factors do you see in this picture of the rain forest?

Ecosystems

What biotic and abiotic factors do you see in this picture of a tundra?

Populations• A population is…

Members of the same species… Who live in the same place At the same time.

Populations• The environment where a population

lives: habitat.

Populations Population ecologists study many

things about populations in their habitats:

Population size Population density Population growth

Population Density

Population density Is the number of individuals of a species per unit of area or

volume. In most cases, it is impractical or impossible to count all

individuals in a population. In some cases, population densities are estimated by indirect

indicators, such as number of bird nests or rodent burrows.

Populations Populations are densest where there

are resources available.

Populations

Patterns of Dispersion

The dispersion pattern of a population is the way individuals are spaced within the population’s geographic range.

Clumped Pattern of Dispersion

Individuals aggregate in patches.

Uniform Pattern of Dispersion

Results from interactions among the individuals of a population.

Random Pattern of Dispersion

Individuals are spaced in a patternless, unpredictable way.

Population Growth Models

Two models, the exponential growth model and the logistic growth model, will help us understand population growth.

The growth rate Is the change in population size per time

interval.

The Exponential Growth Model: The Ideal of an Unlimited Environment

The exponential growth model Describes the rate of expansion of a population

under ideal, unregulated conditions.

The Exponential Growth Model: The Ideal of an Unlimited Environment

• A key feature of the exponential growth model is that the rate at which a population grows depends on the number of individuals already in the population.

The Logistic Growth Model: The Reality of a Limited Environment

In nature, a population may grow exponentially for a while, but eventually one or more environmental factors will limit its growth.

Population-limiting factors restrict population growth.

Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings

The Logistic Growth Model: The Reality of a Limited Environment

The logistic growth model Describes growth of an idealized population that is

slowed by limiting factors.

A comparison of the logistic growth model and the exponential growth model

Carrying Capacity

Is the number of individuals in a population that the environment can just maintain with no net increase or decrease.

http://www.abc.net.au/reslib/200710/r189329_709751.jpg

Regulation of Population Growth Density-Dependent Factors

Are population-limiting factors whose effects intensify as the population increases in size.

Increase a population’s death rate and decrease the birth rate.

Regulation of Population Growth Density-independent factors

Are population-limiting factors whose intensity is unrelated to population density.

Include events such as seasonal freezing. In many natural populations, density-independent factors limit

population size before density-dependent factors become important.

Growth Rate Four influences:

Birth rate Death rate Immigration Emigration

Birth + Immigration – Death – Emigration

Population Cycles

Some populations Have regular boom-

and-bust cycles. Boom-and-bust

cycles of the snowshoe hare and one of its predators, the lynx

Communities and Ecosystems

Ch. 19

Key Properties of Communities

Diversity—variety of different kinds of organisms that make it up

Prevalent form of vegetation—determines kinds of organisms that will survive in the area

Stability—ability to resist change and return to its original species composition after being disturbed

Trophic level—feeding relationships among the various species

Diversity

The diversity of a community Is the variety of different

kinds of organisms that make up the community.

Species richness, the total number of different species in the community

Relative abundance of the different species

Which community is more diverse?

Interactions Between Populations of Different Species Interspecific interactions—occur b/w

populations of different species Coevolution—a change in one species

acts as a selective force on another species

Interspecific Competition

Competition occurs when 2 or more populations overlap in their niches Limiting resources

Food Space Mates

Generally, one will out-compete the other

Competition in Nature Two possible Outcomes

1. Weaker competitor becomes extinct

2. One or both species may evolve enough to use a different set of resources (resource partitioning)

Competition cannot operate for long periods of time

Competitive Exclusion Principle Two species cannot

coexist in a community if their niches are identical

Joseph H. Connell Study

Interactions Between Populations of Different Species Predation—consumption of

one organism by another Parasitism—specialized

predator (parasite) lives on/in its host, not killed immediately

Endoparasitism—live inside host (tapeworms/viruses)

Ectoparasitism—live on surface

of host (mosquitoes/aphids)

Herbivory—herbivores consume plants

http://www.dl-digital.com/images/z_oldimages/2002-10-d28-aphid2-fr18.jpg

Predator Adaptations Most predators have acute senses. Many predators

Have adaptations such as claws, teeth, fangs, stingers, or poison to help catch and subdue prey.

Are fast and agile.

http://upload.wikimedia.org/wikipedia/commons/thumb/7/7c/Hawk_eating_prey.jpg/300px-Hawk_eating_prey.jpg

http://images.encarta.msn.com/xrefmedia/sharemed/targets/images/pho/00123/00123ed3.jpg

Plant Defenses Against Hebivores Physical defenses

thorns, hooks/spines on leaves

Chemical defenses Make plant

distasteful or poisonous

Morphine from opium poppy

Nicotine from tobacco

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Poison Ivy

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Animal Defenses Against Predators Behavioral defenses

Alarm cries Distraction displays

Cryptic coloration/shape (camouflage)

Blend in with environment Asposematic coloration

Red/black; yellow/black

Mechanical/chemical defenses Quills, spines, and other

similar structures Toxins—distasteful or

poisonous

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Monarch butterfly on Milkweed

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Stick Insect

Animal Defenses Against Predators

Mimicry—prey resembles species that cannot be eaten Batesian mimicry: Imitate

color patterns or appearance of more dangerous/unpalatable organisms

Müllerian mimicry: 2 unpalatable species that inhabit the same community mimic each other

Animal Defenses Against Predators Mimicry can be used to lure

prey Snapping turtle wriggles

tongue like a worm to attract and capture small fish

Angler Fish attract prey close enough to their mouths to be easily grabbed

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Symbiotic Relationships

Non-Beneficial Parasitism—host harmed

Beneficial Mutualism—both partners benefit

Lichens-association b/w fungus and algae Nitrogen-fixing bacteria and legumes

Community Structure

Predators can moderate competition among its prey species

Keystone species can alter the whole community

Community Structure

Introduction of a species (exotic species) into a community can have drastic affects on the existing community members

Lake Davis, CA

http://www.dfg.ca.gov/lakedavis/

Northern Pike

http://aquanauts_dc.homestead.com/files/northern_pike1.jpg

Disturbances in a Community Storms, fire, floods, droughts, overgrazing,

or detrimental human activities: Remove organisms Alter resource availability

Create opportunities for new species that have not previously occupied the habitat

Humans are the biggest disturbance Logging, agriculture, overgrazing

Ecological Succession Primary succession

Begins in a virtually lifeless area where soil has not formed

Lichens and mosses colonize first Soil gradually forms and small plants and shrubs take

root

Secondary succession Occurs where an existing community has been cleared

by some disturbance that leaves soil in tact Earliest plants to recolonize are often those that grow

from wind-blown or animal-borne seeds

Ecological Succession

Tolerance to abiotic conditions determines early species

Competition among early species shape the succession of an area

Mt. St. Helen 1980 Eruption

http://denali.gsfc.nasa.gov/research/volc2/MSHreflection.gifMSH80_st_helens_spirit_lake_before_may_18_1980.jpg

http://www.jqjacobs.net/photos/volcano/st_helens.html

Mt. St. Helen Secondary Succession

Red alder disperses easily and is capable of rapid growth on the nutrient-poor, volcanic deposits.

A red-legged frog –one of the creatures living in one of the dozens of ponds created after the eruption.

70 species of birds, including hummingbirds, western meadowlarks and Savannah sparrows

http://www.kgw.com/news-local/stories/L_IMAGE.101688cd0b5.93.88.fa.7c.27913b573.jpg

www.kgw.com/news-local/stories/kgw_051505_env...

www.kgw.com/news-local/stories/kgw_051505_env...

An Overview of Ecosystem Dynamics

An ecosystem Is a biological community and the abiotic

factors with which the community interacts.– Energy flow

• Is the passage of energy through the components of the ecosystem.

– Chemical cycling• Is the use and reuse of chemical elements within

the ecosystem.

Energy

Flows through an ecosystem when consumers feed on producers.

Cannot be recycled within an ecosystem, but must flow through continuously.

Ecosystem Dynamics

Energy flow and chemical cycling Depend on the transfer of substances in the

feeding relationships, or trophic structure, of an ecosystem.

Trophic relationships Determine an ecosystem’s routes of energy flow

and chemical cycling.

Trophic levels Divide the species of an ecosystem based on

their main sources of nutrition.

Trophic Relationships Ecosystems divided into trophic levels

(feeding levels) Producers—autotrophs (mostly photosynthetic) Primary consumers—herbivores Secondary consumers—carnivores that eat

herbivores Tertiary consumers—carnivores that eat other

carnivores Detrivores—consumers that eat dead or

decaying matter

Food Chain/Food Web

Energy Flow in Ecosystems

Each level in a food web contains a different quantity of stored chemical energy

When consumers eat producers or 2 consumers eat 1 consumers, some energy is lost in each transfer from one level to the next

Energy pyramid

A diagram that represents the cumulative loss of energy from a food chain.

Chemical Cycling in Ecosystems Ecosystems

Depend on a recycling of chemical elements.

Biogeochemical cycles Are chemical cycles in an ecosystem that

involve both biotic and abiotic components.

Biogeochemical Cycles

Three key points : Each circuit has an

abiotic reservoir. A portion of chemical

cycling can rely completely on geological processes.

Some chemicals require processing before they are available as inorganic nutrients.

Examples of Biogeochemical Cycles

Carbon Nitrogen Phosphorus Water

Carbon Cycle

Human Impacts: Greenhouse Effect

Increase of atmospheric CO2

Combustion of fossil fuels

Burning of wood from deforestation

Increase in global temperature

Nitrogen CycleHuman Impact: Cultivation—turns up soil and ↑

decomposition of organic matter; Releases more nitrogen Harvesting ↓ nitrogen from

ecosystem Adding industrially

synthesized fertilizers to soil has resulted in doubling globe’s supply

Excess nitrogen leeches into soil and into rivers, streams, and lakes and ground water—

– ↑ levels are toxic to aquatic organisms and humans

– Algal blooms in lakes ↑ eutrophication

Phosphorus Cycle

Human Impact: Sewage treatment

facilities and fertilizers ↑ amounts of

phosphates to aquatic systems, causing eutrophication of lakes.

Water Cycle

Human Impact: Destruction of tropical

rain forest Will change the amount

of water vapor in the air. May alter local and global

weather patterns. To irrigate crops,

humans pump large amounts of ground water to the surface.