ENVIRONMENTAL LITERACY UNDERSTANDING THE ISSUE

1

What is community ecology, and how is it studied? How do matter and energy move through ecological communities?

INFOGRAPHIC 10.1 AND INFOGRAPHIC 10.2

Question 10.1

Community ecologists study:

  • the relationships between species in a given area.

  • the way species interact with their environment.

  • the things that increase or decrease the number of species in an area.

  • all of the above.

D

Question 10.2

In ecological terms, a consumer is:

  • any plant.

  • any animal.

  • any organism that eats other organisms.

  • any animal that eats other animals.

C

Question 10.3

Draw a simple food web for a natural area near you. Include producers and at least three levels of consumers, as well as detritivores and decomposers.

Answers will vary

2

How do biotic and abiotic factors affect community composition, structure, and function?

INFOGRAPHIC 10.3, INFOGRAPHIC 10.4, AND INFOGRAPHIC 10.5

Question 10.4

Edge effects:

  • apply only to the largest and smallest members of a community.

  • occur in the areas where two or more habitats meet.

  • are beneficial for nearly all organisms.

  • are harmful for nearly all organisms.

B

Question 10.5

True or False: Ecosystem complexity increases as the variety of habitat and the number of species increases.

TRUE

Question 10.6

Cowbirds lay their eggs in the nests of smaller forest birds such as bluebirds. The bluebirds then spend the next several weeks caring for a huge baby cowbird, which quickly kills the bluebirds’ own young. Cowbirds prefer open, disturbed areas near a forest and seldom venture far into the forest for any reason, even to lay eggs. Use the concept of edge effect to explain what happens to the populations of bluebirds when humans build roads, recreation areas, homes, and businesses in a large forest.

In an undisturbed forest cowbirds only parasitize the bluebird nests around the edges of the forest. As humans open up the area by removing trees and replacing them with open areas the cowbirds move into those open spaces. The cowbirds can then parasitize all nests around the edge of each smaller portion, leaving fewer and fewer bluebirds untouched in the much smaller central areas of the forest.

3

How do species interactions contribute to the overall viability of the community?

INFOGRAPHIC 10.6 AND INFOGRAPHIC 10.7

Question 10.7

An example of mutualism is:

  • a dog and a flea.

  • an ant and a grasshopper.

  • a butterfly and a flowering plant.

  • a deer and a wolf.

C

Question 10.8

How do mangrove forests fit the definition of a keystone species?

Keystone species have an effect far beyond simply being present in an ecosystem and providing food for a few species. Mangrove forests provide shelter for many species of fish and other sea life that grow in the shallow waters among the tangled mangrove roots. They also provide many ecosystem services such as protection of the shoreline from erosion and the interwoven branches give many species of birds a place to nest.

Question 10.9

Explain why both species richness and species evenness are important for a healthy ecosystem.

Species richness is a measure of the number of different species within an ecosystem. More species means that an area will likely be more stable and less prone to disturbance should something happen to one or two of the species. Having a healthy species richness contributes to the resilience and stability of the ecosystem. Species evenness means that, at a given trophic level, there will be approximately the same number of individuals within each population. This is important to preserve the balance of populations within the ecosystem, and reduce the chance of a rare population becoming extinct.

4

In general, how do human actions affect the diversity of ecosystems? Why might this change in diversity make it difficult to restore damaged ecosystems?

INFOGRAPHIC 10.8

Question 10.10

True or False: The construction of canals and levees to drain parts of the Everglades increased its ecosystem complexity.

FALSE

Question 10.11

It might be hard to restore damaged ecosystems like the Everglades because:

  • there are no economic benefits to restoring the places like the Everglades.

  • there is no early warning system in place to alert us that the area is being damaged.

  • some important species might no longer be present.

  • All of these are correct.

C

Question 10.12

What happens to the net primary productivity and to the species diversity when humans disrupt wetlands by adding more nutrients, as in the example of agriculture in the Everglades?

Net primary productivity is the amount of energy left after producers have used what they needed to survive; it’s the energy left for all the consumers. As synthetic nutrients run off agricultural fields they create algal blooms, which chokes off other species. Species diversity drops because many organisms cannot survive because of the competition with algae or lack of open space. [The details of eutrophication and hypoxia from algal blooms are discussed in Chapter 16.]

5

How do ecosystems change over time through ecological succession? How can we use this knowledge to assist in ecosystem restoration?

INFOGRAPHIC 10.9

Question 10.13

Ecological succession is important because it:

  • allows ecosystems to respond to environmental changes.

  • promotes competition and fair use of resources.

  • eliminates K species.

  • is a natural way to get rid of invasive species and replace them with native species.

A

Question 10.14

An example of when secondary succession would occur in a particular area would be after:

  • lichens have started to grow on a bare rock surface.

  • a flood has removed much of the vegetation.

  • hot ash from a volcano has completely burned and buried the area.

  • a disease has reduced the top predator’s population.

B

Question 10.15

How might a restoration ecologist use an understanding of ecological succession to help repair a damaged area?

An ecologist who understands which species are present at any given stage of succession can use this knowledge to identify what successional stage a damaged community is currently in and then bring in the appropriate species to help succession proceed. Taking other steps to physically alter the area (remove invasives, restore natural water flow, etc.) may also make it easier for the next successional stage to take root and grow.

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