Chapter 27

Community Characteristics

Why do organisms compete?

• Food, resources and reproduction

27.1 27.1 Biotic FactorsBiotic FactorsNutritional RelationshipsNutritional Relationships

*Predator-prey *Predator-prey relationshiprelationship

*Interspecies Competition*Interspecies Competition

*Intraspecies Competition*Intraspecies Competition

Symbiotic RelationshipsSymbiotic Relationships

*Mutualism (+,+)*Mutualism (+,+)

*Parasitism (+, -)*Parasitism (+, -)

*Commensalism (+,0)*Commensalism (+,0)

SPECIES ASPECIES

BPositive Negative Neutral

Positive

Negative

Neutral

SPECIES A

SPECIES B

Positive Negative Neutral

Positive mutualism Predation (Species A is prey)

Parasitism (Species A is host)

Competitive exclusion of Species A

commensalism

Negative Predation (Species A is predator)

Parasitism (Species A is parasite)

CompetitionLimiting

resources

--

Neutral commensalism -- Resource partitioning

2. Symbiotic Relationships• Different organisms may live together in a

close association.• This is known as symbiosis.• There are three types: 1. Commensalism 2. Mutualism 3.

Parasitism• KEY:

+ = benefits - = harmed

o = not affected

Commensalism• (+ , o)

• In this relationship, one organism benefits and the other is not affected.

• Ex: barnacles on a whale

Commensalism

(+ , o)

• Epiphytes (mosses, orchids, ferns, bromeliad ) attach themselves to tree bark and obtain their nutrients without harm to

the trees.

Mutualism

• (+ , +)• In this relationship both organisms

benefit from each other.• Ex: protozoan living in the digestive

tract of termites.• Wood eaten by termites is digested by

the protozoan. The nutrients released supply both organisms.

Mutualism• (+ , +)

• In this relationship both organisms benefit from each other.

• Ex:

Mycorrhizae (+ , +)

In this relationship both organisms benefit from each other.

• Ex: Red Cedar and mycorrhizal fungi.

Parasitism

• (+ , - )

• In this relationship, the parasite benefits at the expense of the host.

• Ex: athlete’s foot fungus on humans

tapeworm and heartworm in dogs.

Parasitism• (+ , - )

• Pathogens (disease causing agents) are parasites that often

cause the death of its host.• Crown gall disease in plants.

Parasite/Host RelationshipParasite/Host RelationshipGuinea worm/HumanGuinea worm/Human

Parasite/Host RelationshipParasite/Host RelationshipSea Lamprey/FishSea Lamprey/Fish

Parasitism

• Parasite/Host Relationship

• Varroa mite/Honeybee

Tracheal mitesTracheal mites

Do Now:

• Define keystone species and discuss two examples of organisms that are keystone species.

Keystone species

• These determine the nature and structure of an entire ecosystem. Usually found in small numbers but have a key influence.

• Examples: Wolves, Fig Trees

27.4 Predator/Prey Relationships!

27.4 Predator-Prey Cycles

27.7 Predator/Prey Relationships Data collected from fur pelts from the Hudson Bay Company

Studies have shown that Endocrine changes in populations may produce

behavioral changes which tend to limit population growth. Therefore all

population changes may not be due to predator/prey relationships alone.

Case Study "The Effects of Coyote

Removal in Texas:A Case Study in

Conservation Biology"by

Margaret CarrollDepartment of Biology

Framingham State College

Case Study The Wolf, the Moose, and the Fir

Tree:Who Controls Whom on Isle

Royale?A case study of trophic interactions

byGary M. Fortier

Department of Small Animal Science Delaware Valley College

The Data

The Data• Fig. 1. Population parameters of the

Isle Royale ecosystem from 1958-1994. Shaded areas signify periods of forage suppression that may be connected to interactions between herbivores and carnivores.

• Population size of wolves each winter (based on aerial counts).

• Population size of moose each winter (based on aerial counts and skeletal remains).

• Ring-widths from the west end of Isle Royale, N=8.

• Ring-widths from the east end of Isle Royale, N=8.

• Actual evapotranspiration rates (AET), annual calculations based on data from April-October at a weather station 20 km from Isle Royale. AET is an approximation of primary productivity, it represents water availability as a function of temperature and rainfall.

Energy Flow Relationships• For an ecosystem to be self-

sustaining, there must be a flow of energy between organisms.

• The pathway of energy flow through the living components of an ecosystem are represented by food chains and food webs.

          

Nutritional Relationships

• Involves the transfer of nutrients from one organism to another within an ecosystem.

• In terms of nutrition, organisms are either autotrophs or heterotrophs

Energy Flow through a food Chain

Energy Losses The mouse receives energy from the food it eats.

Cells extract the food's energy for growth, acquiring food,

escaping enemies lost as heat. Some lost in the mouse's waste

(feces).

The remaining energy is stored in the mouse's body and is

available to the organism that preys on it.

About 90% of the energy is used or lost, only 10% is available to

predators.

Energy Flow

Biological Magnification• A nondegradable or slowly degradable

substance • That becomes more and more concentrated

in the tissues of organisms at higher trophic levels of a food web.– * Dichloro-Diphenyl-Trichloroethane (DDT)– * Polychlorinated biphenyls (PCBs)

DDT in Food Webs

DDT

PCBs in Food Webs• PCB concentrations in animal

tissue can be magnified up to 25 million times.

• Microscopic organisms pick up chemicals from sediments

• Consumed in large numbers by filter feeding zooplankton.

• Mysid shrimp then consume zooplankton

• fish eat the mysid

• and so on up the food web to the herring gull.

• (Figure and caption from Our Stolen Future, p. 27)

Fig. 41-7, p.736

DDT residues

• Why was there never a concern for the Ring-billed gulls?

DDT Detection

• In 1962, Rachel Carson, a former U.S. Fish and Wildlife Service (USFWS) scientist and writer, published Silent Spring, outlining the dangers of DDT

Fig. 41-8, p.736

DDT in Food Webs• Heinz Meng

• Responsible for the reintroduction of the Peregrine Falcon.

27.3 Competitive Interactions

• Exploitative competition: species do not interact directly but compete for resources

• Competitive exclusion: both species require same resource

27.3 Competitive InteractionsWAYS TO AVOID COMPETITION ???

• Over abundance or resources

• Resource Partitioning

27.3 Natural selection can favor Resource Partitioning: differences in

resource use among species.

• The diagram represents a tree containing three different species of warbler, A, B, and C. Each species occupies a different niche. A fourth species, D, which has the same environmental requirements as species B, enters the tree at point X. Members of species B will most likely 

(1.) live in harmony with species D  (2.) move to a different level and live with species A or species C  (3.) stay at that level but change their diet  (4.) compete with species D

Effect of community complexity onEffect of community complexity on Species richness Species richness

41.8 Ecological Succession• Succession is a process of ecological change in which a series of

natural communities are established and then replaced over time. • Two kinds of succession: .

– Primary succession takes place on an area that is originally completely empty of life.

• flow of lava has, for a time, no life at all on it. • Over a period of time, however, various kinds of organisms begin to grow in the area.

Over time, the variety of life-forms changes as succession continues. – Secondary succession is far more common. It occurs in an area where life

once existed but has then been destroyed. – a forest that has been destroyed by a wildfire. – For a period of time, no living organisms may exist in the area. Before long,

however, certain types of plants begin to reappear. And, as with primary succession, the nature of the plant communities gradually change over time.

http://www.tvcc.edu/depts/biology/Native%20Habitat/ecological_succession.htm

41.8 Ecological SuccessionPioneers

Organisms -lichen

-grasses

Climax Community

United streaming video

• Biologix: Interactions and Relationships among Organisms

• http://player.discoveryeducation.com/index.cfm?guidAssetId=9442E194-317A-4EFD-8410-2392E05F2A25&blnFromSearch=1&productcode=US#