Deck 54: The Biosphere

Question 1

The dramatic loss of energy as it is transferred upward through a food web produces pyramids of energy, biomass, and numbers that are very narrow at the top.Which agent of evolution (SectioN₂1.3) would you expect to influence allele frequencies in the relatively small populations that are typical of top predators? What are the long-term evolutionary effects of small population size?

Answer 1

In nature, there are five agents of evolution that bring about an evolutionary change in the organisms. These are a mutation, non-random mating, gene flow, genetic drift, and natural selection.
A mutation is a change in the DNA (deoxyribonucleic acid) sequence of an organism and is caused due to the different factors. A mutation can either cause a change in a single base of DNA or shift the entire reading frame of the DNA.
Gene flow is the transfer of the genes or the alleles from one population to another. Gene flow is usually the result of migration of the organisms into or out of an existing population. The gene flow causes a change in the allele frequencies.
Non-random mating means, in a population, the probability of two individuals, who will mate together, will not be the same for every pair of individuals. Genetic drift is the condition, in which there is a variation in the relative frequencies of the different genotypes in a population.
This occurs because of the disappearance of certain genes by chance, because there is no death or reproduction in certain individuals of the population. Natural selection, is the selection of organisms, which are better suited to live in an environment. Organisms having adaptive features that make them fit for survival are selected by nature.
The pyramids of energy, biomass, and numbers are very narrow at the top, since there is a huge energy loss, as the energy is transferred from a lower layer of the pyramid to its next higher layer. The agent of evolution that influences the allele frequencies in the relatively small populations of top predators is the gene flow.
This is due to the fact that the animals of the two different trophic levels will be different from each other and there will be the transfer of the allele frequencies if new organisms of a particular type migrate in the population that occupies the top level of the pyramid.
In a small population, the evolutionary changes over a very long period of time may give rise to the new species of organisms, with a completely different genetic makeup as compared to the existing population.

Question 2

A lake near your home became overgrown with algae and pondweeds a few months after a new housing development was built nearby.What data would you collect to determine whether the housing development might be responsible for the changes in the lake?

Answer 2

The phenomenon of aging of a lake is termed as eutrophication. It can be natural or human-induced. Natural eutrophication generally takes couple of years by natural means depending upon the length and depth of a lake.
When eutrophication is influenced by the human activities in the surroundings of lake, then this type of eutrophication is known as human-induced eutrophication. A lake near a house became overgrown with algae and pond-weeds a few months after a new housing development was built nearby.
The housing development causes the release of domestic wastes or garbage, which includes minerals and nutrient that can initiate aging of lake.
Hence in such condition, it is best to examine the quality of water of the lake for analysing the availability and quantity of the nutrients such as phosphorous and nitrogen, which increase the growth of algae and weeds in the ponds or lakes.
These nutrients are commonly present in the domestic wastes, and thus, the waste should be also analysed that is dumped in the lake directly or indirectly. If the nutrients responsible for the algal growth and development of weeds are found to be present in the domestic waste of the residents then, it can be concluded that eutrophication has been induced by the humans living nearby the lake.

Question 3

Design an experiment to test the hypothesis that predators in an aquatic ecosystem regulate the ecosystem's primary productivity.Establish as many experimental ponds as you wish, and imagine stocking them with organisms at different trophic levels.If the hypothesis is correct, describe the results you would expect to record from each of your experimental treatments.

Answer 3

Predators in any ecosystem will regulate the ecosystem's primary productivity. The situation will be quite similar for an aquatic ecosystem. The components of an aquatic ecosystem can be mentioned as follows:
1. Producers: These include the phytoplanktons and the submerged and the floating plants.
2. Primary consumers: These include the zooplanktons, mollusks, Cyclops, and many others, which eat the primary producers.
3. Secondary consumers: These include the insects, fishes, frogs, crab, and the other animals, which depend upon the primary consumers for food.
4. Tertiary consumers: These include the large fishes and frogs, and they can eat plants as well as animals of the aquatic ecosystem.
5. Top consumers: These are the predators, which eat the primary, secondary, and the tertiary consumers. The examples include the water snakes and the water birds Experimental design: The experiment can be designed as follows:
1. Consider 10 ponds, each having phytoplanktons, zooplanktons, insects, small fishes, frogs, large fishes, and water snakes
2. The ponds can be labeled from A-J.
3. In each pond, let the organisms of one trophic level can be removed. As an example, in pond A, the small fishes are removed; in pond E the frogs can be removed, and so on.
4. Imagine what would happen in each of the ponds with the removal of organisms of particular trophic levels
Result: The result of the experiment can be mentioned as follows:
It is obvious from the model as suggested above that removing the organisms in any one of the trophic level will result in the disruption of the whole pond ecosystem. For example, if the zooplanktons are removed completely, then the primary consumers will not have anything to eat.
Moreover, they will be eaten up by the secondary consumers. A time will come, when there will be no more of the primary consumers. As a result of this, the secondary consumers will not have anything to eat and, in turn, will be eaten up by the tertiary consumers.
A time will come, when there will be no more of the secondary consumers. Similarly, after some time, the tertiary consumers will, also, not be able to survive. Finally, the top predators will be there, since they cannot be eaten by any other higher order animals.
However, during this whole process, the primary producers will increase in the profuse amounts to fill up the entire pond, since there are no more consumers to eat those phytoplanktons and the top predators cannot eat plants.
Conclusion: The conclusion of the experiment can be made as follows:
From the above model, we can see that every trophic level is dependent on each other for their food, and this maintains a balance in any ecosystem. It is the top predator that maintains the population of tertiary consumers.
This, in turn, regulates the secondary consumers population, that controls the population of primary consumers, which finally result in maintaining the number of the primary producers. This proves the hypothesis that the predators in an aquatic ecosystem regulate the ecosystem's primary productivity.

Question 4

Amy Rosemond of Vanderbilt University and two colleagues at the Oak Ridge National Laboratory conducted a study of primary productivity in the algal community of Walker Branch, a stream in eastern Tennessee.In their experiment, they compared the productivity of algae that were eaten by snails (grazed) to the productivity of algae that were protected from herbivores (ungrazed) under three experimental treatments: (1) the addition of nitrogen to the stream; (2) the addition of phosphorus to the stream; and (3) the addition of both nitrogen and phosphorus to the stream.They compared the results of these treatments to control treatments of both grazed and ungrazed algae that received no nutrient enrichment.How would you interpret their results, presented in the accompanying graph? Was algal productivity controlled by the presence of herbivores, the addition of nutrients, or a combination of the two factors? 11eb5caa_28cb_4d77_9f04_bf65603e97a4

Question 5

Which of the following events would move energy and material from a detrital food web into a grazing food web?

A)beetle eats the leaves of a living plant.
B)An earthworm eats dead leaves on the forest floor.
C)robin catches and eats an earthworm.
D)falcon eats a robin.
E)bacterium decomposes the feces of an earthworm.

Question 6

Some politicians question whether the recent increase in atmospheric temperature results from our release of greenhouse gases into the atmosphere.They argue that atmospheric temperature has fluctuated widely over Earth's history, and the changing temperature is just part of a historical trend.What information would allow you to refute or confirm their hypothesis? In addition, describe the pros and cons of reducing greenhouse gases as soon as possible versus taking a "wait and see" approach to this question.

Question 7

The total dry weight of plant material in a forest is a measure of the forest's:

A)gross primary productivity.
B)net primary productivity.
C)cellular respiration.
D)standing crop biomass.
E)ecological efficiency.

Question 8

If you could design the ideal farm animal-one that was grown as food for humans-from scratch, what characteristics would it have?

Question 9

Which of the following ecosystems has the highest rate of net primary productivity?
a.open ocean
b.temperate deciduous forest
c.tropical rainforest
d.desert and thornwoods
e.cultivated land

Question 10

If you were growing a vegetable garden, identify the factors that might affect its primary productivity.How would you increase productivity? Identify some possible consequences of your gardening activities to nearby ecosystems.

Question 11

Endothermic animals exhibit a lower ecological efficiency than ectothermic animals because:

A)endotherms are less successful hunters than ectotherms.
B)endotherms eat more plant material than ectotherms.
C)endotherms are larger than ectotherms.
D)endotherms produce fewer offspring than ectotherms.
E)endotherms use more energy to maintain body temperature than ectotherms.

Question 12

The amount of energy available at the highest trophic level in an ecosystem is determined by:

A)only the gross primary productivity of the ecosystem.
B)only the net primary productivity of the ecosystem.
C)the gross primary productivity and the standing crop biomass.
D)the net primary productivity and the ecological efficiencies of herbivores.
E)the net primary productivity and the ecological efficiencies at all lower trophic levels.

Question 13

Some freshwater and marine ecosystems exhibit an inverted pyramid of:

A)biomass.
B)energy.
C)numbers.
D)turnover.
E)ecological efficiency.

Question 14

Which process moves nutrients from the available organic compartment to the available inorganic compartment?

A)respiration
B)erosion
C)assimilation
D)sedimentation
E)photosynthesis

Question 15

Which of the following materials has a sedimentary cycle?

A)water
B)oxygen
C)nitrogen
D)phosphorus
E)carbon

Question 16

Which of the following statements is supported by the results of studies at the Hubbard Brook Experimental Forest?

A)Most of the energy captured by primary producers is lost before it reaches the highest trophic level in an ecosystem.
B)Deforested watersheds experience significantly less runoff than undisturbed watersheds.
C)Deforested watersheds lose more calcium and nitrogen in runoff than undisturbed watersheds.
D)Nutrients generally move through biogeochemical cycles very quickly.
E)Deforested watersheds generally receive more rainfall than undisturbed watersheds.

Question 17

Nitrogen fixation converts:

A)atmospheric molecular nitrogen to ammonia.
B)nitrates to nitrites.
C)ammonia to molecular nitrogen.
D)ammonia to nitrates.
E)nitrites to nitrates.