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10
1.
Review: What is a habitat?
A habitat is the natural environment where an organism
lives. Every habitat has distinctive physical, geologic, and chemical
characteristics (such as light levels or water temperature) that help
determine which organisms live there and which do not.
2. What are two important influences on how many and what kinds
of organisms live in any particular place?
The physical, geologic, and chemical characteristics of the habitat
are an important influence on how many and what kinds of organisms are
found in any particular place. Equally important are biological interactions—the
ways that organisms affect one another, such as competition, predation,
and even cooperation.
3. What is ecology?
Ecology is the study of the interactions between organisms
and their environment and how these interactions affect the abundance
and distribution of organisms.
4. What does the term “abiotic” mean?
The term “abiotic” refers to the non-living
part of the environment or the physical, geologic, and chemical characteristics
of the environment.
5. What does the term “biotic” mean?
The term “biotic” refers to the living
part of the environment; that is, all of the living organisms and their
interactions.
6. Review: What is a population? A community?
A population is a group of individuals of the same
species that live together. A community is all the
different populations of organisms that live in the same place.
7. What are physiological adaptations?
Physiological adaptations are changes that an organism
can make to its body, behavior, or metabolism to be more efficient or
productive in its habitat. For example, shivering when it is cold is
a physiological adaptation to raise body temperature. Physiological
adaptations are NOT inheritable; they are NOT passed on to offspring.
[They may be taught to offspring, however.]
8. Review: What is natural selection?
Natural selection is the production of more offspring
by those individuals in a population that are best adapted to the environment.
9. What is evolutionary adaptation?
Natural selection over time involves passing on to offspring the genetic
differences that confer increased success in the environment. For example,
intertidal barnacles that are better able to withstand drying out during
low tides due to an inheritable trait will pass this trait on to their
offspring, who in term will be more successful in their environment.
This is evolutionary adaptation.
10. What are two abiotic factors that may limit how populations
grow over time?
Many factors control or regulate population growth so that no particular
species experiences an unchecked population explosion for an unlimited
period of time. These factors include changes in the abiotic environment
that limit survival (such as cold weather in winter limits plant growth)
and using up all the available resources (so that starvation and death
follow).
11. What are four biotic factors that may limit how populations
grow over time?
Biotic factors that limit population growth include responding to overcrowding
by slowing down or stopping reproduction, competition for space, predation,
and diseases.
12. What are resources?
Resources are the biotic and abiotic factors that populations
need to live and reproduce, such as food, nutrients, and living space.
13. Review: What are nutrients?
Nutrients are the raw materials (other than carbon
dioxide and water) that are needed by primary producers for primary
production.
14. What is the carrying capacity?
The carrying capacity is the largest population size
that can be sustained by the available resources. If the carrying capacity
is exceeded, resources are used up and the population experiences a
dramatic decrease or even extinction.
15. What is a limiting resource?
A limiting resource is one whose short supply limits
population growth. For example, a population of seaweeds may live in
a place with the right temperature and salinity conditions, the right
kind of bottom substrate, all the “right” factors for growth
and reproduction but be limited by the availability of one resource:
light for photosynthesis.
16. What is competition?
Competition is the interaction between organisms that
results when a resource is in short supply and one organism uses the
resource at the expense of the other. These resources may be abiotic
(such as space) or biotic (such as food).
17. Compare intraspecific and interspecific competition.
When members of the same species compete for a resource it is called
intraspecific competition. When members of different
species compete for a resource it is called interspecific competition.
18. What is biodiversity? What is the current status of biodiversity
on earth?
Biodiversity is the richness and variety of life on
earth—the number of species or different kinds of organisms on
earth. The earth’s biodiversity is decreasing as more and more
species become extinct due to pollution, habitat destruction, overexploitation,
and other, mostly human-caused, problems.
19. What are three general ways that species interact?
Species may compete for resources with one another, they may eat one
another, or they may live together.
20. What is competitive exclusion?
Competitive exclusion occurs when one species eliminates
another by outcompeting it for resources in the environment.
21. What are some factors that may impede competitive exclusion?
Periodic disturbances (such as storms) or changes (such as seasonal
temperature changes) may keep a competitively superior species from
dominating in an environment. For example, in the northern Gulf of California,
bubble gum algae dominate in the rocky intertidal during warm seasons
but are outcompeted by other algae during cooler conditions.
22. What is resource partitioning?
Resource partitioning is the sharing of a common resource
by different species and avoiding direct competition. For example, one
species may only feed at night; the other during the day.
23. What is an ecological niche?
The ecological niche is the role that a species plays
in its community. It includes feeding habits, habitat use, behavior,
and all the other aspects of the species’ life style.
24. What is predation?
Predation is the act of one organism eating another.
The organism that does the eating is the predator, and the one that
is eaten is the prey.
25. What is the difference between carnivores and herbivores?
Are they both predators?
Carnivores are organisms that eat other organisms,
and herbivores are organisms that eat primary producers
(plants, algae, bacteria). Both technically are predators.
26. What is the relationship between predation and the prey
population?
Predation affects more than just the individual that is eaten. The prey
population is reduced as a result. If predation levels are not too high,
reproduction by the prey population replaces the eaten individuals.
If other factors (such as storms or overfishing) reduce the prey population,
the predator population suffers as well from lack of food.
27. What are indirect interactions? Give an example.
Predator-prey interactions often affect more than just the prey and
predator populations. Other species are indirectly affected—these
are indirect interactions. For example, sea stars on
rocky shorelines selectively prey on mussels. The space left behind
by the mussels may be filled by barnacles, which would otherwise be
competitively excluded by the mussels.
28. What are three predation strategies?
Some predators, such as sharks and tunas, are highly efficient, fast,
and powerful killing machines. Others, such as octopuses, employ “sneaky”
strategies and use stealth and camouflage to catch their prey. Still
others, such as anglerfishes, may actually lure their prey to its demise.
29. What are three strategies for avoiding predation?
Organisms have many ways to escape predators. Some are fast and able
to escape. Some use camouflage to avoid predators. Others have defensive
mechanisms, such as spines and poisons, to deter predators.
30. What are inducible defenses? Give an example.
Inducible defenses are defense mechanisms that are
used only in response to the presence of predators. For example, the
barnacle Cthamalus anisopoma in the Gulf of California normally grows
upright. When the predatory snail Acanthina angelica is present, the
barnacle grows bent over, which makes it difficult for the snail to
prey on the barnacle.
31. What is coevolution? Give an example.
Coevolution occurs when species evolve in response
to one another. One example is the evolutionary escalation between predator
and prey species, with the predator getting better at catching the prey
and the prey getting better at escaping.
32. What is symbiosis?
Symbiosis is the close association between different
species; this relationship is usually the result of co-evolution. The
smaller partner species in the symbiotic relationship is the symbiont
and the larger one, the host.
33. What are the three types of symbiosis?
The three types of symbiosis are commensalism, parasitism, and mutualism.
34. Describe commensalism and give an example.
In commensal relationships, one species benefits from
the relationship (by obtaining a home or food, for example) while the
other species is unaffected. An example of commensalism is the barnacles
that live only on whales. The barnacles benefit by getting food and
a free ride, whereas the whale is seemingly unaffected by the presence
of the barnacles.
35. Describe parasitism and give an example.
Parasitism occurs when the symbiont species benefits
from the association at the expense of the host species. An example
of a parasite is the giant tapeworms that live in the guts of whales
and derive food and shelter from them. They weaken their hosts (the
whales) and are considered parasites. [Note: parasites normally do not
kill their hosts and eat them (predation).]
36. Describe mutualism and give an example.
In mutualistic relationships, both
species benefit from the association. An example of mutualism is the
zooxanthellae that live in the tissues of corals. The zooxanthellae
benefit by receiving shelter and food from the corals; the corals benefit
by receiving food and oxygen from the zooxanthellae.
37. Review: What are zooxanthellae?
Zooxanthellae are a group of round, golden-brown, photosynthetic
dinoflagellates (unicellular algae in the Kingdom Protista).
38. Describe cleaning associations. What type of symbiosis do
they represent?
Cleaning associations is a type of mutualism that is
common in some marine habitats. Small fishes and shrimp pick the parasites
and dead or diseased tissue off of larger “client” fishes.
Both benefit from the association. Often the client fish could prey
on the cleaning animals but does not in the cleaning association.
39. Define and compare facultative and obligate symbioses.
In facultative symbiosis both partners can get by without
one another. Cleaning associations are an example of facultative symbiosis.
In obligate symbiosis, the two organisms depend on
one another and cannot live without one another.
40. What are some factors that affect the larval ecology of
marine organisms?
Marine organisms often have larval forms that have very different forms
and/or live in very different habitats compared to the adults of the
species. The larvae must be adapted to the biotic and abiotic factors
in its environment, which may be very different from those faced by
the adults. Temperature, salinity, currents, predators, and food may
all be factors affecting larvae.
41. What is ecological zonation?
Ecological zonation is the categorization of communities
according to where and how organisms live.
42. What are benthic organisms?
Benthic organisms are those that live on or buried
in the bottom of the ocean.
43. What are sessile benthic organisms?
Sessile benthic organisms are those that live attached
to one place and don’t move around.
44. What are pelagic organisms?
Pelagic organisms are those that live in the water
column, either actively swimming (nektonic) or passively floating with
the currents (planktonic).
45. What are phytoplankton and zooplankton? How are they different
from the nekton?
Phytoplankton are the autotrophic portion of the plankton,
and zooplankton are the heterotrophic portion of the
plankton. Planktonic organisms swim weakly or not at all and are moved
primarily by ocean currents. The nekton, in contrast,
are the swimming organisms of the ocean—those that can swim against
currents.
46. Describe the zonation in the benthic ocean by depth.
The shallowest part of the continental shelf, right where the land meets
the sea, is the intertidal or littoral zone. This is
the area that is exposed to the air at low tide and covered by water
at high tide. Benthic organisms that live below the intertidal zone
and on the continental shelf live in the subtidal or sublittoral
zone. Deeper in the ocean, past the continental shelf, are
the bathyal, abyssal, and hadal zones. Let’s just call those the
deep-sea floor to make things a bit easier!
47. Describe horizontal zonation in the pelagic ocean.
The pelagic environment that lies over the continental shelf is called
the neritic zone. Pelagic waters beyond the continental
shelf make up the oceanic zone.
48. Describe the vertical zonation in the pelagic ocean by depth.
The shallowest vertical zone in the pelagic ocean is the epipelagic
zone. The epipelagic zone receives plenty of light for photosynthesis.
It usually extends from the surface to about 350 to 650 feet, depending
on the water clarity. Because most of the continental shelf is shallower
than this, nearly all neritic waters lie in the epipelagic zone. Below
the epipelagic zone lies the mesopelagic zone, which
is a “twilight” zone. There is limited light but not enough
to support photosynthesis. The mesopelagic usually extends down to about
3,300 feet. Below the mesopelagic zone are the deepest, darkest waters
of the ocean—the bathypelagic, abyssopelagic, and hadopelagic
zones.
49. Generally describe the flow of energy and materials in an
ecosystem.
Energy and chemical substances flow from the non-living (abiotic) part
of the ecosystem to organisms (biotic) and from organism to organism.
Energy is ultimately lost to the ecosystem as heat; whereas, chemical
substances are returned to the abiotic part of the ecosystem. The pathways
taken by energy and materials tell us a lot about how an ecosystem works.
50. Review: What are autotrophs? What are heterotrophs? What
is primary production?
Autotrophs are organisms that can use energy (usually
solar energy) to make organic matter. Heterotrophs
are organisms that cannot make their own food and must eat the organic
matter produced by autotrophs. Primary production is
the conversion of carbon dioxide into organic matter by autotrophs during
photosynthesis; that is, the production of food.
51. What are trophic relationships?
Trophic relationships are feeding relationships—between
those who make the food and those who eat it. There are two broad components:
the primary producers (autotrophs) who make the food and the consumers
(heterotrophs) who eat it.
52. What is a food chain? How is it involved in the flow of
energy and materials in an ecosystem? What is a trophic level?
A food chain is the progression of who eats whom in
an ecosystem. The transfer of energy and material takes place in several
steps in the food chain; each step is known as a trophic level.
For example, the three-step food chain that is typical of Antarctic
waters goes as follows: Diatoms (autotrophs) are eaten by krill (heterotrophs
and herbivores) and krill are eaten by whales (heterotrophs and carnivores).
53. What is a food web?
Food chains rarely (if ever!) fully describe who eats whom in an ecosystem
because most organisms eat more than one type of food. Food
webs are the complex, interwoven food chains that try to fully
describe all of the trophic or feeding relationships within an ecosystem.
54. What are primary, secondary, and tertiary consumers?
Consumers that feed directly on producers are primary consumers.
Herbivores are primary consumers. Predators that eat the primary consumers
are secondary consumers, and those that feed on the
secondary consumers are the tertiary consumers. Secondary
and tertiary consumers are carnivores. These three levels of consumers
help ecologists describe how energy and materials flow through ecosystems.
55. Describe how the flow of energy in an ecosystem can be modeled
using a pyramid of energy.
Much of the energy contained in a particular trophic level is NOT
passed on to the next level during predation. For example, only 5 to
20% of the energy contained in diatoms and dinoflagellates and other
members of the phytoplankton is passed on to the zooplankton that consume
them. The 80 to 95% of the energy that is lost to the organisms is usually
lost as heat energy to the environment. As a rule of thumb, the average
amount of energy lost between trophic levels is 90%. The trophic structure
of an ecosystem can be represented by a pyramid of energy, with less
energy contained in each succeeding level.
56. What is the relationship of the pyramid of energy to the
pyramid of numbers of organisms in an ecosystem?
Because there is less energy available at each higher level in the pyramid
of energy, there are also fewer individuals in each higher level. The
pyramid of numbers shows the decreasing number of individuals at higher
trophic levels in an ecosystem.
57. What is the relationship of the pyramid of energy to the
pyramid of biomass in an ecosystem?
The energy relationships among trophic levels in an ecosystem also can
be examined by looking at the total weight of living tissue (or biomass)
produced by organisms at each trophic level. As in the pyramid of energy
and the pyramid of numbers, the pyramid of biomass shows decreasing
biomass at higher trophic levels in an ecosystem.
58. What are decomposers? How do they recycle materials in an
ecosystem?
Decomposers are decay bacteria, fungi, and other organisms
that break down non-living organic material (dead and decaying matter
and waste products) into their original components: carbon dioxide,
water, and nutrients. These materials are then available again as inputs
during primary production. This process is called nutrient
regeneration.
59. What is dissolved organic matter (DOM)? What is detritus?
Dissolved organic matter (DOM) is non-living organic
material that is dissolved in sea water. Detritus is
solid non-living organic material. Both DOM and detritus are food sources
for decomposers.
60. How is primary production measured?
The rate of primary production or productivity is a measure of the amount
of carbon turned into carbohydrates by autotrophs during photosynthesis
per square meter of sea surface in a day or in a year. It is expressed
in units of grams of carbon per square meter per day (or year) or gC/m2/day.
61. What is the gross primary production?
Gross primary production is the total amount of organic
carbon manufactured by primary producers.
62. What is the net primary production?
The net primary production is the gross primary production
MINUS the organic carbon used up by the primary producers during respiration.
63. What areas of the pelagic ocean have the highest productivity?
Coastal upwelling areas, the southern ocean, and the coastal temperate
seas have the highest productivity in the ocean, although this varies
seasonally.
64. What areas of the pelagic ocean have the lowest productivity?
The central ocean gyres have the lowest productivity. They are essentially
the deserts of the ocean.
65. What areas of the benthic ocean have the highest productivity?
Coral reefs and salt marshes have the highest productivity (although,
productivity varies seasonally and with latitude in these environments,
too).
66. What areas of the benthic ocean have the lowest productivity?
Salt marshes and mangrove forests have the lowest productivity (again,
this varies seasonally and with latitude!)
67. Review: What does “pelagic” mean? What does
“benthic” mean?
Pelagic refers to the water column, away from the bottom.
Benthic refers to the bottom.
68. Overall, which has higher productivity, the benthic or pelagic
ocean?
Overall, the benthic ocean has higher productivity.
69. What is the standing stock?
The standing stock or standing crop is the total amount
of phytoplankton in the water. It is related to primary productivity
(because, of course, it is the phytoplankton that are doing the photosynthesizing)
but it is not the same thing.
70. How is standing stock determined?
The standing stock is usually determined by measuring the chlorophyll
concentration of the water, usually by using an instrument called a
fluorometer.
71. What is the ultimate fate of energy in an ecosystem?
New energy is added to the system when solar energy is stored in organic
compounds during photosynthesis. Once the energy stored in organic compounds
is used in metabolism or given off as heat, it is lost to the ecosystem
forever.
72. What is the ultimate fate of materials in an ecosystem?
Materials (such as carbon, nitrogen, phosphorous, and water) are used
over and over again in an ecosystem; they are passed through the ecosystem
and recycled.
73. What are three chemical cycles that are important in ecosystems?
Three important cycles are the carbon cycle, the nitrogen cycle, and
the phosphorous cycle.
74. Briefly describe the carbon cycle.
Carbon is stored in the atmosphere as carbon dioxide. Atmospheric carbon
dioxide dissolves in sea water and is available to autotrophs during
photosynthesis to create organic compounds. Some of the organic compounds
are used to create skeletons. Respiration by autotrophs and heterotrophs
breaks down some of the organic compounds into carbon dioxide. The rest
is stored in the tissues and skeletons of the organisms. When they die,
some of their carbon-containing tissues and skeletons are released as
carbon dioxide back in to the water during decomposition. Some may be
stored in the sediments for a while before being recycled.
75. Briefly describe the role of nitrogen fixation in the nitrogen
cycle.
Atmospheric nitrogen is biologically inert—in other words, it
cannot be used to organisms. Certain types of cyanobacteria, bacteria,
and archaebacteria are able to convert inert atmospheric nitrogen into
forms usable by organisms. This is called nitrogen fixation.
76. Briefly describe the phosphorous cycle.
Phosphorous enters the oceans as phosphate dissolved in river water
or deposited by rain on the ocean. Primary producers incorporate phosphorus
into their tissues and it is cycled through the trophic levels of the
marine ecosystems. Some of the phosphorus is eventually stored in the
bottom sediments or transferred to the land by birds (fish-eating birds
have very nitrogen-rich “poop” or guano).
Critical Thinking Questions
77. Two species of sea urchins live practically side by side on sandy
bottoms. They appear to have the same diet: drifting sea weeds and other
bits of organic matter. They are able to live in the same environment
without competing with each other. How might they be able to share their
habitat and food resources?
Competition may be prevented by being active and feeding at different
times of the day and by feeding at different levels in the sand—we
say that they “appear to have the same diet” but there may
be slight differences due to the possibility that one species picks
up organic materials slightly deeper in the sand than the other, perhaps
because the teeth of the Aristotle’s lantern are longer. Competition
also may be avoided by feeding in different areas—we say that
they “live practically side by side” but one of them may
migrate to nearby rocky bottoms at night to graze on a different type
of food. There are many other slight differences in their environment
or their physiology that may allow them to partition the resources in
their environment.
78. It is not always easy to categorize a particular case of
symbiosis. Suppose a certain species of snail is always found living
on a certain coral. No one has found evidence that the snail harms the
coral, so the relationship is classified as an example of commensalism.
How would you go about testing this hypothesis? What kinds of observations
might lead to the conclusion that the snail is a parasite, or that it
has a mutualistic relationship with the coral?
“Harm” is not always easy to detect. In this hypothetical
case, if the snail is a parasite, drastic damage to the coral colony
due to the presence of the snail may not be evident—the injury
may be slight or not obvious. These subtle responses by the coral may
include abnormal feeding behavior by the coral polyps, a decrease in
growth rate, or a decrease in larval production.
The relationship may be mutualistic if, for example, the coral obtains
nutrients from the mucus produced by the snail or if the snail somehow
protects the coral from predators.
You could test these hypotheses by removing the snail from some of the
corals and not others. You would then need to monitor as many indicators
of the coral’s health as possible to see if it improves or deteriorates.
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