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Key Concept Review (Answers to in-text “Concept Checks”)
Chapter 16
1. A community is comprised of the many populations of organisms that interact at a
particular location.
2. A population is a group of organisms of the same species occupying a specific area.
3. The largest marine community (in volume) is probably the open ocean itself, but with
the discovery of vast extremophile communities in and beneath seabeds and
continents, this view may change.
4. A habitat is an organism’s “address” within its community, its physical location. Each
habitat has a degree of environmental uniformity. An organism’s niche is its
“occupation” within that habitat, its relationship to food and enemies, an expression
of what the organism is doing.
5. Physical factors such as temperature, pressure, and salinity affect the success of an
organism. Biological factors include crowding, predation, grazing, parasitism,
shading from light, generation of waste substances, and competition for limited
oxygen.
6. Environmental resistance is the sum of the effects of limiting factors in the
environment. An unfettered population will reproduce in a “J” shaped growth curve
until a limiting factor intervenes.
7. Random distribution is most rare.
8. A climax community is a stable, long-established community. This self-perpetuating
aggregation of species tends not to change with time.
9. The rocky intertidal zone supports rich communities because of the large quantity of
food available. Organisms have evolved defenses against the rigors of the area, and
often have solid substrate on which to cling.
10. Sand and cobble beaches don’t offer a firm substrate. Burrowing animals can quickly
be dislodged and into unfavorable places. Only a few organisms (burrowing clams,
for example) have evolved adaptations permitting them to succeed in shifting
sediment.
11. Estuaries serve as marine nurseries, protecting oceanic species for a few weeks or
months before they venture to sea. Birds also nest in these areas. Development
would disrupt the life cycles of these organisms.
12. Coral reefs are the most biodiverse communities. Less diverse communities include
sand beaches and the open ocean below about 200 meters (660 feet).
13. The largest marine community may be the open ocean below about 200 meters (660
feet), but deep rock extremophile communities (as noted above) may greatly exceed
the open ocean in total volume.
14. Primary production in deep vent communities is accomplished by chemosynthesis.
15. Whale fall communities may act as “stepping stones” for sulfur-oxidizing
chemosynthetic bacteria, allowing generations of them to cross the seabed to colonize
newly formed vents.
16. Symbiosis describes the co-occurrence of two species in which the life of one is
closely interwoven with the life of the other.
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17. Mutualism (in which both partners appear to benefit), commensalisms (in which one
partner benefits and the other neither benefit nor is harmed), and parasitism (in which
one partner benefits at the expense of another) are symbiotic relationships. These
three categories form a continuum in nature.
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