Chapter 6Part 1

Species Interactions and Community Ecology

Zebra Mussels Invade the Great Lakes• Polluted waters Great Lakes became cleaner

after the Clean Water Act of 1970 – used again for recreation and fishing

• Zebra mussel arrived, native to western Asia and eastern Europe.

• Larval stage is well adapted for long-distance dispersal, and it encountered none of the predators, competitors, and parasites it was used to

Zebra Mussels (continued)• Zebra mussels can – clog up water intake pipes– damage boat engines, docks, and fishing gear– sink buoys that ships use for navigation

• Zebra mussels also have severe impacts on the ecological systems they invade– take large quantities of food (phytoplankton)

needed by native molluscs for food• It is being displaced by the quagga mussel,

which has a larger niche than even the zebra mussel.

Species Interactions

• Most common interactions–Competition–Predation–Parasitism–Herbivory–Mutualism

Competition• Occurs when resources are limited• Intraspecific competition – between members

of the same species– Limits population growth

• Interspecific competion – among members of at least 2 different species –Affects composition (what is in) of

communities*interstate runs between more than one state

Competitive Exclusion

• One species is a very effective competitor• Excludes another species from a

resource completely• Example: zebra mussel outcompeted

the native mussel in the Great Lakes

Species Coexistence

• When one species does not fully exclude another from resources• State of equilibrium – population size

of each species remains constant• Species that use the same resources

can minimize competition

Minimizing Competition• Use only a portion of the total array of

resources (niche) that they are capable of using

• Full niche of a species is called its fundamental niche

• An individual that plays only part of its role because of competition or other species interactions - displaying a realized niche. (page 143, Fig. 6.2)

Minimizing Competition (continued)

• Resource partitioning - competing species may evolve to use slightly different resources or to use their shared resources in different ways.

• Over time, character displacement may occur as they evolve physical characteristics that reflect their use of a specific portion of the resource

• Natural Selection!

Exploitative Interactions

• Exploitation occurs when one member of an interaction exploits or uses another for its own gain.

• Examples: –Predation–Parasitism–Herbivory

Predation

• Predation - an individual of one species hunts, captures, kills, and consumes an individual of another species, its prey.

• Predation can sometimes drive population dynamics, causing cycles in population sizes.

• Better predators will leave more and healthier offspring – making them better hunters.

• Prey species - evolve defense mechanisms

Parasitism• Parasitism - the parasite, depends on the

host, for nourishment or some other benefit while doing the host harm.

• Many parasites live in close contact with their hosts, such as tapeworms, ticks, and lamprey.

• Other types of parasites are free-living and come into contact with their hosts only infrequently (e.g., nest parasites such as cuckoos and cowbirds).

Parasitism (contiued)

• Some parasites cause little harm, but others may kill their hosts

• Examples:– Parasitic wasps• Lay eggs on caterpillars• Larvae burrow into and eat caterpillar’s tissue• Larvae turn into wasps that fly out of dead

cateripillar– Sea lampreys (see handout)

Herbivory

• Herbivores exploit (use) plants.• Herbivory occurs when animals feed on the

tissues of plants• Plant defenses:

–Production of toxic chemicals–Thorns, spines, irritating hairs–Other insects working with plant to

attack the predators (ants protect some plants)

Mutualism

• Mutualists help one another.• Mutualism - two or more species benefit from

interaction with one another.• Many mutualistic relationships occur between

organisms that live in close physical contact; this is called symbiosis.

• Bees and flowers engage in mutualism in the process of pollination.

Use Your Book!

• Use your text to list examples of mutualism – you have 5 minutes.

Commensalism

• Some interactions have no effect on some participants.

• Commensalism occurs when one organism benefits and the other is unaffected.

• Barnacles – barnacles attach to skin of whales and can be transported to new sources of food

• Remora sharks – have an adhesive (sticky) disk on their head and can attach to whales. After the whale eats, the shark detaches and eats the leftovers!

Book Work!

• Page 171, Testing Your Comprehension, numbers 1 – 3

• SAVE THIS PAPER! YOU WILL BE ADDING MORE TO IT!

Ecological Communities

• Energy passes among trophic levels.• As organisms feed on one another - energy

moves through the community from one trophic level to another.

• Producers are the first trophic level.• Examples:– Grasses, algae, chemosynthetic bacteria

Consumers• Second trophic level - primary consumers–Most of them consume plants and are

called herbivores (deer or grasshoppers eat grass)

• Third trophic level - secondary consumers–prey on primary consumers (rodents eat

grasshoppers that eat grass)

Consumers (continued)

• Higher trophic levels –tertiary consumers –hawks eat rodents that eat

grasshoppers that eat grass

* Secondary and tertiary consumers are carnivores because they eat animals

Consumers (continued)• Animals that eat both plant and animal food

are omnivores.• Detritivores (scavengers) and decomposers

(break down) consume nonliving organic – These “eat” the dead material from all

other trophic levels• Look at page 149, Fig. 6.10• The arrow points to what is doing the “eating”

Rule of 10

• Think back to our Rule of 10 pyramid! • Only 10% of the usable energy is passed on.• The producers start with the most energy, and

it decreases with every step up.• Being a vegetarian, rather than a meat-eater,

decreases a person’s ecological footprint. Why?

• Page 150, Weighing the Issues

Biomass• Biomass – organic material that makes up

living organisms• Biomass energy – energy harnessed from

plant and animal matter • The Rule of 10 applies to – Energy– amount of biomass/biomass energy– and number of organisms

Food Webs

• Show feeding relationships and energy flow• Visual map• Shows the many paths by which energy passes

among organisms as they consume one another.

• Page 151, Fig. 6.12

With a Partner: 20 Minutes• Draw a food web that could be found in TN– Use colored pencils – Do not have to have elaborate drawings

• Stick drawings (like Mrs. Alred’s drawings) are fine

• Must include– Producer (10 points)– Primary consumer (10 points)– Secondary consumer (10 points)– Tertiary consumer (10 points)– Decomposer/Detritivore (10 points)

Keystone Species

• Some organisms play bigger roles in communities than others.

• keystone species - has a particularly strong or far-reaching impact

• Examples: Large-bodied secondary or tertiary consumers (hawks, wolves, sharks)

• Some keystone species physically modify the environment (beavers, prairie dogs, fungi)

Communities Respond to Disturbances

• A community that resists change and remains stable is said to show resistance to the disturbance.

• A community may show resilience, meaning that it changes in response to disturbance but later returns to its original state.

Succession Follows Severe Disturbance

• If a disturbance eliminates all/most of the species in a community, the site will undergo a series of changes called succession.–Primary succession–Secondary succession

Primary Succession

• Primary succession - a biotic community is built from scratch

• 1) Pioneer species, such as lichens (fungi and algae), are the first to arrive.

• 2) Lichens secrete acid, starting the process of soil formation.

• 3) New, larger organisms arrive and pave the way for more new species, - a community becomes established.

Secondary Succession

• Secondary succession -a disturbance dramatically alters an existing community but does not destroy all living things or all organic matter in the soil– Grasses– Shrubs– Saplings– Pines– Hardwoods Look at Page 155, Fig. 6.15

Book Work

• Add this to your original paper of #s 1-3• Page 170, TYC #s 4-6• Due on Wednesday!

Invasive Species

• a non-native organism that spreads, becomes dominant, and has potential to substantially alter a community.

• controlling and eradicating invasive species are so difficult and expensive that preventive measures represent a much better investment.

Impact of Invasive Species

• most cases - overall negative impacts on ecosystems

• rare cases, non-native species like the honeybee provide important economic benefits to agriculture and ornamental crops

Ecological Restoration

• Efforts to restore areas to a more pristine habitat

• Restoration ecologists research the history of an area to understand its “presettlement” condition (before it was altered)

• Time consuming and expensive , so it is better to protect natural landscapes from degradation

Ecological Restoration Projects• Great Plains and Midwest prairie restoration• Florida Everglades– 30 years, $7.8 billion– Provides drinking water, tourism, ecosystem services

• Mesopotamian marshes– New effort – no access of funds allowed yet– Between Tigris and Euphrates Rivers in Iraq– Restore traditional lifestyles to former minorities

forced out by Saddam Hussein