4.1 Ecological Succession and Interactions in Marine Organisms

Question 1

In this distribution, members of a population are relatively evenly spaced out. This distribution is not very common in nature. It is thought to arise in animals that show territorial behavior. Territorial marine birds, such as penguins, exhibit regular distribution.

Answer 1

Regular distribution.

Question 2

This is the most common distribution form. Organisms group together in clumps, with few or no members scattered in between the clumps. This happens either because of distribution of resources in scattered areas or for group protection. This is a type of social distribution with members of a family or pack forming clumps or groups. Various species of fish, such as the bluestripe snapper in the image, are found in clumped distributions called schools.

Answer 2

Clumped distribution.

Question 3

This form of distribution does not show any regularity and positions of members are unrelated. This is a rare distribution pattern. Oyster larvae have a random distribution due to random sea currents.

Answer 3

Random distribution.

Question 4

This pyramid indicates a declining population. The birth rate is low, and the population is characterized by a low percentage of young organisms.

Answer 4

Urn-shaped structure.

Question 5

This pyramid represents a stable population. It is characterized by an equal number of young and middle-aged organisms.

Answer 5

Bell-shaped polygon.

Question 6

The pyramid forms a typical triangle. In this age structure, the percentage of young organisms (pre-reproduction) is high. This is because of a high birth rate and low death rate. Each generation is more in number than the preceding generation. Such populations are also called young populations.

Answer 6

Triangular shape.

Question 7

Secondary succession: This refers to a form of ecological succession that takes place in an area with an already established ecosystem community. The community is reduced or destroyed by some means, ranging from a volcano to extreme weather. This allows a secondary succession to occur. These successions are more common and occur faster than primary successions. For example, a marine habitat like a swamp may be devastated by hurricanes. However, plant species eventually grow back and make the area suitable to sustain animal life.

Answer 7

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Question 8

Seasonal succession: A seasonal or cyclic succession occurs regularly after a period of time, due to cyclic changes in the environment. In this succession, a small number of species is replaced at a time. Thus, there is no large-scale disturbance in the community. For example, lakes and ponds may freeze over during winter. Surface species may migrate to warmer areas, while species at lower levels survive in the deep water. When the lakes thaw out again, migratory species return to them.

Answer 8

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Question 9

Primary succession: Primary succession, as the name suggests, refers to the development of an ecosystem for the first time. Some areas that are devoid of any life may suddenly see a succession of plants and animals. Areas that experience extreme factors, such as lava flow, glacial activity, and so on, may not be able to sustain a community. Changes in such conditions that facilitates ecological succession is called a primary succession. From a marine perspective, primary successions can take place due to shifting of water currents, extreme weather phenomena, and so on. For example, an underwater earthquake may open up a thermal vent that provides nutrients in a deep sea area. This makes an otherwise dead zone habitable to deep sea creatures.

Answer 9

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Question 10

Ecosystems are dynamic in nature and changing all the time. However, some communities may remain unchanged for long observable periods of time. These are called ____________.

Answer 10

Climax Community.

Question 11

These types of parasites live on the host. They usually live on much larger animals and feed on the host’s skin cells or blood, or on prey caught by the host. An example is the sea louse that feeds on the blood of many species of fish.

Answer 11

Ectoparasites.

Question 12

These parasites live within their host. This category includes parasitic worms and bacteria. An example is that of parasitic worms, which reside in the livers of fish.

Answer 12

Endoparasites.

Question 13

In this relationship, one organism provides a service (such as cleaning skin or teeth), while the other provides a resource (mostly food). For example, cleaner fish eat food particles lodged in the teeth of larger fish.

Answer 13

Service-resource

Question 14

Here, both organisms provide some service to the other. For example, sea anemones protect clownfish using their stings. The clownfish protect the anemones from butterfish, which are impervious to their stings.

Answer 14

Service-service

Question 15

This occurs when one organism uses another as a mean of transport. For example, a suckerfish attaches itself to a host, such as a shark or stingray.

Answer 15

Phoresy.

Question 16

This occurs when one organism uses another for permanent shelter. For example, eels may live in cracks and holes found in coral.

Answer 16

Inquilinism.

Question 17

This form of commensalism occurs when one organism indirectly benefits from another. For example, hermit crabs use seashells discarded by other creatures for protection.

Answer 17

Metabiosis.

Question 18

In this form, one organism directly influences another organism and prevents it from obtaining the resource. For example, two fish of the same species often confront each other over a suitable mate.

Answer 18

Interference competition

Question 19

This occurs when organisms compete for limited resources. If one organism gets the resource and the other doesn’t, there is no direct confrontation. For example, when a barnacle attaches itself to a hard surface, other barnacles are not able to grow on that spot and need to find another area. This becomes competitive if space is limited.

Answer 19

Exploitative competition.

Question 20

This occurs indirectly, when two species are exploited by a third species. If one of the species develops a method to avoid being exploited, then the other species might be more exploited. For example, a species of shark may prey on seals and a large fish species. If the fish start swimming in larger schools, it might dissuade the sharks from attacking. In turn, the sharks would hunt more seals.

Answer 20

Apparent competition.

Question 21

This result from a combination of direct and indirect effects. One change in a species can cause a chain reaction, which in turn will affect many other species. For example, changes in the population of producers (such as plankton) will affect the population of herbivores (such as crabs). In turn, this will affect the population of secondary consumers (carnivores) that prey on the herbivores, such as octopuses. Cascading effects can take place from the bottom up, or from producers to primary consumers to secondary consumers. It can also take place as a top-bottom process, or from secondary consumers to primary consumers to producers.

Answer 21

Cascading effects.

Question 22

These effects happen when a change in the population of a certain species affects another species through an intermediate species. If the population of a carnivore decreases, it will cause an increase in the population of its prey. The prey (usually an herbivore or omnivore), in turn, may feed on another species (plants or smaller animals). This species will see a drop in population. For example, if there are not enough starfish to keep mussels in check, the mussels will grow abundantly in the area. This will result in a decreased population of plankton, on which the mussels feed.

Answer 22

Indirect effects.