Deck 53: Ecosystems

Question 1

Five processes can foster microevolutionary change: gene flow, genetic drift, mutation, natural selection, and nonrandom mating (see SectioN₂1.3)Which of those processes might contribute to the evolution of Batesian mimicry in two butterfly species? Would the same processes affect both the mimic and the model similarly? Which processes might have contributed to the evolution of the mutualistic relationship between ants and acacia trees, and how would their action on the two mutualists differ?

Answer 1

Species exist in an environment by adapting its ecological conditions. They adapt to its physical as well as the biological conditions. They thrive and increase its richness. They interact with other species and survive. However, the environmental conditions are not always the same, they keep on changing. Thus, the species has to evolve in order to survive.
Mimicry is a technique applied by organisms to resemble other organisms in order to escape predation. In Batesian mimicry, the mimic who is harmless and palatable, mimics the poisonous and unpalatable model. This helps in avoiding the prey. Mimicry is natural selection. The mimic and the model both are protected.
Those organisms which do not mimic the model are subjected to harmful actions by the predators. On the other hand, those able to mimic survive. The process of natural selection benefits the mimic as it is able to survive in drastic conditions. The model is not subjected to any change, so the natural selection may not have much effect on it.
Mutualism is a type if symbiosis in which both the organisms are benefited. Ants and Acacia trees have a mutualistic relationship. The tree provides the ants with food and shelter in the form of nectar and thorns. The ants in return protect the trees from herbivores and microbial pathogens.
The relation between acacia trees and ants is co-evolutionary. Both the organisms evolve in relation to the other. This leads to evolution of special structures. This relationship has evolved over time. Multiple successive mutations have led to this relation.

Question 2

After reading about the two potential biases in the scientific literature on competition, describe how future studies of competition might avoid such biases.

Answer 2

Species always co-exist in ecology. They interact and compete to survive. The study of these interactions and competition gives a strong overview of the species survival tactics. The ecologists and scientific literature, both have their own favorites, when it comes to discussion.
The ecologists and the scientific literature are both biased towards competition and interaction, respectively. The ecologists are more inclined towards competition existing between species. On the other hand, the scientific literature is more biased towards the interactions occurring between the species. The ecologists give more importance to the study of competition between species and publish papers on them.
The scientific literature underestimates the competition. According to them, if strong competition does not persist for a long time, populations competing strongly in nature are difficult to find. However, this scientific bias on the competitions is problematic. The exact information, on the type of competition existing, is hard to find.
Inter-specific competition is a competition of survival existing between two different species. These types of competition usually involve the same niche and resources. The scientific literature does not give much importance to competition.
However, it is necessary to study it. For this bias to eliminate, the literature needs to have more patient records. They have to deal with competition, which is both short lived and stretched over a longer period. A longer study may even lead to a new species establishment.

Question 3

Chaparral, a community of woody shrubs that is fairly common in California, often grows adjacent to grassland.The two communities are consistently separated by a "bare zone," usually less than 1 m wide, where no vegetation of either type grows.Ecologists have proposed two possible explanations for this strip of bare soil: (1) that the leaves of chaparral shrubs release harmful, water-soluble chemicals that keep the grass seeds from germinating in the adjacent soil; and (2) that small mammals living in the dense cover provided by chaparral consume the grass seeds before they germinate; the animals don't venture very far from the shrubs because they would be easy targets for predatory hawks.Design a set of field experiments to test the two hypotheses.

Answer 3

Species of a community co-exist. They maintain their living by surviving all the odds. They usually maintain their own territories, thereby preventing foreign entries. If a foreign species try to invade, a fight for survival occurs. The fittest survives. Thus, organisms survive on their abilities.
Woody shrubs and the grasslands exist adjacently to one another. However, there is barren land between the species. The zone is known as the "bare zone". Here, neither the grassland nor the shrubs exist. There can be more than one explanation for such type of phenomenon to exist. The limiting factor can come either from shrubs or from the grasslands.
The first hypothesis states that the leaves of the shrubs release toxins which prevent the grassland germination in the adjacent soils. This can hold true only if the toxins released are not destructive for the shrubs themselves. The chemicals which seep into the soil are either too slow or less volatile. The region to which they spread is limited to adjacent soil only.
The other hypothesis states that the tiny organisms growing in the shade provided by the shrubs, eats the grass seeds before their germination. This prevents the grassland formation in the adjacent soil. This could be true, as the organisms always look for food in the vicinity. They avoid predation by eating food available nearest. Hence, this could be a potential reason for not growing of grasslands.

Question 4

The Mediterranean shrub Hormathophylla spinosa loses as much as 80% of its flowers and fruits to herbivorous mammals each year, and biologists interpret the spines on its flowering stems as an antiherbivore adaptation.Jose M.Gomez and Regino Zamora of the University of Granada, Spain, conducted an exclosure experiment in which they used fences to protect some shrubs from feeding by herbivores and left other shrubs unprotected as controls.The accompanying graph illustrates the density of thorns on the experimental and control groups over a period of two years.How did the protected shrubs respond to the experimental reduction of feeding on the flowers and fruits? How did the unprotected shrubs respond to the control treatment? What benefits would unprotected shrubs derive from their response? 11eb5caa_28c6_b98a_9f04_c567c479f162

Question 5

According to optimal foraging theory, predators:

A)always feed on the largest prey possible.
B)always feed on the prey that are easiest to catch.
C)choose prey based on the costs of capturing and consuming it compared to the energy it provides.
D)feed on plants when animal prey are scarce.
E)have coevolved mechanisms to overcome prey defenses.

Question 6

How do human activities disrupt the process of succession in terrestrial communities? Would you describe most of our activities as mild disturbances, moderate disturbances, or severe disturbances?

Question 7

The use of the same limiting resource by two species is called:

A)brood parasitism.
B)interference competition.
C)exploitative competition.
D)mutualism.
E)optimal foraging.

Question 8

Humans are destroying natural communities at an everincreasing pace.Using the predictions of the theory of island biogeography, develop hypotheses about what might happen as patches of natural habitats get smaller and smaller.How would you test these hypotheses?

Question 9

The range of resources that a population can possibly use is called:

A)its fundamental niche.
B)its realized niche.
C)character displacement.
D)resource partitioning.
E)its relative abundance.

Question 10

Differences in the bill sizes of finch species living on the same island in the Galapagos may be caused by:

A)predation.
B)character displacement.
C)mimicry.
D)interference competition.
E)cryptic coloration.

Question 11

Bacteria that live in the human intestine assist digestion and feed on nutrients the human consumed.This relationship might best be described as:

A)commensalism.
B)mutualism.
C)endoparasitism.
D)ectoparasitism.
E)predation.

Question 12

The table below shows how many individuals were recorded for each of five species in five separate communities (a-e)Which community has the highest species diversity? 11eb5caa_28c8_b560_9f04_0594769d6c82

Question 13

A keystone species:

A)is usually a primary producer.
B)has a critically important role in determining the species composition of its community.
C)is always a predator.
D)usually reduces the species diversity in a community.
E)usually exhibits aposematic coloration.

Question 14

Species richness is often highest in communities where disturbances are:

A)very frequent and severe.
B)very frequent and of moderate intensity.
C)very rare and severe.
D)of intermediate frequency and moderate intensity.
E)very rare and mild.

Question 15

The change in the species composition of a community from bare and lifeless rock to climax vegetation is called:

A)disturbance.
B)competition.
C)secondary succession.
D)primary succession.
E)facilitation.

Question 16

The equilibrium theory of island biogeography predicts that the number of species found on an island:

A)increases steadily until it equals the number in the mainland species pool.
B)is greater on large islands than on small ones.
C)is smaller on islands near the mainland than on distant islands.
D)can never reach an equilibrium number.
E)is greater for islands near the equator than for islands near the poles.