Behavior and Interactions among Microorganisms and Invertebrates - Freshwater Ecology: Concepts and Environmental Applications - page 387

SUMMARY
1. The behavior of microorganisms is based primarily on factors that
control motility. The ability to sense changes in the environment,
coupled with control of movement, allows microorganisms to move
to more favorable habitats.
2. Chemotaxis is movement toward high or low chemical
concentrations, phototaxis is movement toward light, and geotaxis is
movement in response to gravity. Different microbes have evolved
the ability to use some or several of these taxes. Phobic responses are
movements away from stimuli.
3. All the basic interaction types among macroscopic species are also
found in microbial species (exploitation, competition, mutualism,
commensalism, amensalism, and neutralism).
4. Viruses are important parasites of microbes.
5. The rate of feeding on small cells can depend on their concentration
and food quality. Functional feeding descriptions have been
developed to describe these relationships.
6. Microbial adaptations to avoid predation include indigestibility, low
nutrient content, and chemical, behavioral, and mechanical defenses.
7. Parasitism by microbial species is an important ecological interaction
for aquatic organisms.
8. Competition can influence many microbial species in various ways,
including changes in successional sequences and determination of
what species will dominate under specific nutrient regimes.
9. Mutualism occurs in aquatic habitats, with syntrophic assemblages
of anoxic microbes and nutrient remineralization likely the most
common mutualistic interactions.
10. Chemicals excreted into the water mediate many microbial
interactions. Examples include successional sequences of
phytoplankton and excretion of inhibitory compounds to decrease
competition.
QUESTIONS FOR THOUGHT
1. Why do obligate mutualisms appear to be a more important type of
interaction in coral reefs than in the benthos of lakes and streams?
2. How might shredders and scrapers alter microbial activity on leaves
in streams?
3. Is it possible that interactions among organisms can change over
time or with changes in biotic conditions?
4. Why is it less likely that individual diatom species found in
periphyton assemblages would produce chemicals to deter scrapers
than would macrophytes?
5. Planktonic bacterial populations may respond in a complex manner
to temperature. Can you predict if lower growth or decreases in
predation rates related to increased viscosity should be more
important controls of biomass?