Population Dynamics

Question 1

List the 4 symbiotic relationships.

Answer 1

1. Parasitism
2. Mutualism
3. Commensalism
4. Ammensalism

Question 2

What is symbiosis by definition?

Answer 2

Symbiosis is a relationship in which two quite different organisms live and function together in close association, to the benefit of at least one of them. Mutualism, commensalism and parasitism are all examples of symbiotic relationships.

Question 3

Describe “parasitism.” Provide an example of this relationship.

Answer 3

One species (parasites) benefits at the expense of another species (host). Lice are parasitic organisms that depend on the body of a living host in order to survive and reproduce. However, the animal host as a result will experience itching and infections.

Question 4

Define what a “vector” is.

Answer 4

A carrier of disease.

Question 5

Define what an ecological niche is.

Answer 5

The role an organism occupies in an ecosystem.

Question 6

What is each organism in a symbiotic relationship referred to as?

Answer 6

Each organism in a relationship is referred to as a symbiont.

Question 7

What are the two types of symbiosis? Define them and provide examples.

Answer 7

1) Obligate symbiosis (necessary for survival)
* Example: many pollination relationships (e.g yucca plants rely exclusively on yucca moths)
2) Facultative symbiosis (beneficial but not necessary for survival, sometimes referred to as proto-cooperation).
* Example: oxpeckers benefit from other large cattle as they can consume fleas present on their bodies.

Question 8

How does competition occur?

Answer 8

Competition occurs when there are two organisms in the same niche, and there is limited access to this resource.

Question 9

What is competitive exclusion principle?

Answer 9

Involves one species being better at obtaining resources, excluding the other from the available resources and sometimes driving them to extinction. Species better adapted survive and outcompete other species.

Question 10

What is a “limiting factor?”

Answer 10

Limiting Factor: refers to the scarcest resource needed by a population. For example, food, water, shelter and light are essential for a population’s growth. If all of these resources are available. except for water, then water is the limiting factor

Question 11

What is environmental resistance?

Answer 11

Environmental Resistance: the factors that limit the growth of populations due to reduction to health, reproduction rate and survival. These factors are either density-independent or density dependent.

Question 12

What is the difference between density-independent and density-dependent factors?

Answer 12

Density independent: Affect a population’s size regardless of the size/density of the population.
Density dependent: Affect the rates of births and deaths in a population; increase as population increases.

Question 13

List examples of density independent factors:

Answer 13

Affect a population’s size regardless of the size/density of the population.
Include:
* Conditions in which the species can survive.
* Tolerance range
Major disturbances (e.g bushfires, droughts) and anthropogenic (human-made) changes (e.g construction and pollution).

Question 14

List examples of density-dependent factors:

Answer 14

• Competition
• Predation
• Crowding
• Parasitism and infectious diseases

Question 15

Explain how competition affects a population.

Answer 15

Two organisms in the same niche, limited access to this resource = competition. Better adapted species will outcompete their competitors and will grow in population, while the competitor will fall in population.

Question 16

Explain how predation affects a population.

Answer 16

Predator-prey relationships have a significant impact on populations.
→ Increase in prey species = more abundant source of food for predators.
→ Predators will increase in population, prey will decrease as more are being eaten.
→ Eventually, there will be a large amount of predators but very few prey = competition for resources.
→ Predator population will begin to decrease, and prey population will slowly start to increase again.
The cycle repeats.

Question 17

Explain how crowding affects a population

Answer 17

High density → stress → fewer offspring being produced
Or, immune systems affected → more prone to disease.

Question 18

Explain how parasitism and the spread of diseases affects a population.

Answer 18

Parasites are more easily able to invade more dense populations, as they become weaker with resources becoming more scarce.
Denser populations = more contact with one another ∴ diseases are more likely to spread.

Question 19

Consider “point sampling” as a sampling technique. Outline its procedure, uses and considerations to be made.

Answer 19

Individual points are selected on a map and organisms are counted at those points.

Used to determine the diversity and abundance of organisms in an area.

Time efficient, minimal disturbance, but rare organisms may be missed.

Question 20

Consider “transect sampling” as a sampling technique. Outline its procedure, uses and considerations to be made.

Answer 20

Lines are drawn across a map. Organisms occurring at the lines are sampled. (typically used for plants).

Used to determine the change in distribution and abundance of communities across areas with different abiotic factors

Time efficient, minimal disturbance, rare organisms may be missed. Only suitable for sampling slow-moving or stationary organisms.

Question 21

Consider “quadrat sampling” as a sampling technique. Outline its procedure, uses and considerations to be made.

Answer 21

Sampling squares called quadrats are placed in a grid pattern on the sample area and the occurrence of organisms in each quadrat is noted.

Estimates the abundance and diversity of immobile organisms in a large area.

Time consuming to do well (more quadrats = more efficient)
Only suitable for sampling slow-moving or stationary organisms. Minimal disturbance to the environment.

Question 22

Consider “mark recapture” as a sampling technique. Outline its procedure, uses and considerations to be made.

Answer 22

Animals are captured, marked, then released. After time progresses, the population is resampled using the same method.

Determining the populations of highly mobile species such as birds and possums, and also tracking the movements of species.

Tracking should not harm species.
Time consuming to do well.
Not suitable for sampling slow-moving or stationary organisms.