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)