Topic 4 Ecology: Community Ecology

Question 1

• Community ecology is concerned with the interaction of populations, such as interspecific competition.

Answer 1

Note

Question 2

• When two species compete for exactly the same resources (or occupy the same niche), one is likely to be more successful. The principle states that no two species can sustain coexistence if they occupy the same niche.
• An example of Gause’s principle is when two Paramecium species are mixed to compete for the same food. One population will grow more rapidly and use the resources more efficiently, while the second species is eliminated

Answer 2

Competitive exclusion principle (Gause’s Principle)

Question 3

• When two species occupy the same niche but pursue slightly different resources, individuals can minimize competition and maximize success through resource partitioning. This way, multiple species can survive relatively near each other but in slightly different niches.
• For example, five species of warblers coexist in spruce trees by feeding on insects in different regions of the tree and using different feeding behaviors

Answer 3

Resource Partitioning

Question 4

• As a result of resource partitioning, certain traits allow for more success in obtaining resources in their partitions. This reduces competition and increases the divergence of features. Thus, character displacement occurs where unique differences among species diverge even more when they coexist near each other.
• For example, two species of finches on separate islands have similar beaks suited for the same food supply (seeds). On a third island, the finches can coexist due to evolution since the beaks of each bird species is different. This way, they can minimize competition; each finch species feeds on seeds of a different size depending on their beak size
• Another example is the mating calls of two species of frogs. The calls are different when they occupy the same island. On separate islands, the mating calls are the same

Answer 4

Character Displacement (niche shift)

Question 5

• The niche that an organism occupies in the absence of competing species is its fundamental niche. In other words, the fundamental niche is the area that a species could potentially survive in. The realized niche is the area that the species actually lives in due to factors such as competitors. When competitors are present, the multiple species may be able to coexist by occupying their realized niches. They coexist by occupying areas of the niche that do not overlap, so there is no competition for resources.
• For example, one barnacle species can live on rocks that are exposed to the full range of tides; this is its fundamental niche. In the natural environment, a second species of barnacle outcompetes the first, but only at lower tide levels where desiccation is minimal. The first species then only survives in its realized niche, which is the higher tide levels

Answer 5

Realized and fundamental niches

Question 6

• This is another form of community interaction. A predator is any animal that totally or partly consumes a plant or another animal

Answer 6

Predation

Question 7

1. True Predator
2. Parasite
3. Parasitoid
4. Herbivore

Answer 7

Types of Predation

Question 8

• Kills and eats another animal

Answer 8

1. True Predator

Question 9

• Spends most of its life living on a host and obtaining nourishment by feeding off the host’s tissues. The host usually does not die until the parasite has completed at least one life cycle

Answer 9

2. Parasite

Question 10

• This is an insect that lays its eggs on a host (insect or spider). After the eggs hatch, the larvae obtain nourishment by consuming the host’s tissues. The host eventually dies, but not until the larvae complete development and begin pupation

Answer 10

3. Parasitoid

Question 11

• An animal that eats plants. Granivores are seed eaters and act like predators because they totally consume the organism. Grazers (animals that eat grasses) and browsers (animals that eat leaves) only eat part of the plant and thus weaken it

Answer 11

4. Herbivore

Question 12

• This is an intimate, often permanent association between two organisms. The association may or may not be beneficial, and some associations may be obligatory if one or both organisms cannot survive without the other

Answer 12

Symbiosis

Question 13

1. Commensalism
2. Mutualism
3. Parasitism

Answer 13

Types of Symbiosis

Question 14

• One organism benefits while the other is unaffected. Examples are a remora and a shark, where the remora gets the food that the shark discards. Another example are barnacles and whales, where the barnacle gets wider feeding opportunities by associating with a whale while the whale is unharmed

Answer 14

1. Commensalism

Question 15

• Both organisms benefit in their association. Tick bird and rhinos are in a mutualistic relationship because the bird gets food (ticks) and the rhino loses its ticks. Lichen (fungus and algae) is a mutualistic relationship because algae produces food for itself and the fungus via photosynthesis, while the fungus provides CO2 and nitrogenous wastes. Nitrogen-fixing bacteria and legumes are another example because the legumes provide nutrients for bacteria while the bacteria fixes nitrogen for the legumes. Protozoa and termites are an example too because protozoa digests cellulose for the termites, while termites protect and provide food for protozoa. The last example is intestinal bacteria and humans. The bacteria utilize our food but provide us with vitamin K

Answer 15

2. Mutualism

Question 16

• One organism benefits at the expense of the host. The parasites live with minimum expenditure of energy. Parasites can be ectoparasites (cling to the exterior of the host) or endoparasites (live within the host). All viruses are parasites and infect hosts. Pathogenic bacteria are parasites that infect hosts as well, such as diphtheria infecting humans, anthrax in sheep, or tuberculosis in cows or humans. There are also parasitic fungi that can infect hosts, such as ringworm which infects humans.
• Tapeworms are well-known parasites that infect humans. Tapeworms are less dangerous, meaning the host will be more likely to live and allow the parasite to keep surviving. Thus, it is better for the parasite to not kill the host

Answer 16

3. Parasitism

Question 17

• Some species have positive effects on the survival and reproduction of another species without necessarily living in direct and intimate contact for symbiosis. This is common in plant ecology. E.g., black rush makes soil more hospitable for other plant species in the same zone.

Answer 17

Facilitation

Question 18

• Saprophytes are protists and fungi that decompose dead organic matter externally and absorb nutrients.

Answer 18

Saprophytism

Question 19

• Consume dead animals directly (e.g., vultures, hyenas, bacteria of decay).

Answer 19

Scavengers

Question 20

• Is competition between members of the same species, and it is influenced by disruptive (competition) and cohesive (reproduction and protection from predators and weather) forces.

Answer 20

Intraspecific Interactions

Question 21

• Is between members of different species, and is ultimately negative for both since they are competing against each other for resources.
• Community structure can be altered by pathogens. Zoonotic pathogens are transferred from other animals to humans. Vectors are intermediate species of infections.

Answer 21

Interspecific Competition

Question 22

• Occurs directly between individuals via aggression, etc. Other individuals are directly prevented from physically establishing themselves on the habitat to prevent the sharing of mutual resources. This can be done via the mechanism of allelopathy, which is the production of biochemicals by an organism to influence the growth/survival/reproduction of other organisms.

Answer 22

Interference Competition

Question 23

• Occurs indirectly through the depletion of a common resource.

Answer 23

Exploitation Competition

Question 24

• Occurs between two species preyed upon by the same predator. E.g., species A and B are hunted by C. If the amount of A increases, then this will lead to the survival of more predator C, which in turn hunts more of B, thus decreasing them.

Answer 24

Apparent Competition