Populations

Question 1

Draw, label, and annotate with explanations, a generalised growth curve for natural populations.

Answer 1

Draw out curve on paper.

1) Phase 1 - slow growth. The small number of individuals that are there are reproduce, increasing the population size. Birth rate is higher than death rate.
2) Phase 2 - period of rapid growth. As the number of reproducing individuals increases, the total population multiplies exponentially. No constraints are limiting the population explosion.
3) Phase 3 - stable state. Further population growth is limited by external constraints. Over this time, the population size fluctuates but generally remains stables because the birth and death rates are relatively equal. Slight increases and decreases can be explained by the fluctuation of limiting factors, such as presence of predators.

Question 2

Define the term “abiotic factor”

Answer 2

non-living factor

Question 3

Define the term “biotic factor”.

Answer 3

living factor

Question 4

Define the term ‘carrying capacity’

Answer 4

The maximum population size that an environment can support.

Question 5

Give 3 examples of limiting factors for population size and explain how each affects population size.

Answer 5

• availability of water or oxygen (abiotic): availability of resources makes survival more likely.
• temperature (abiotic): If the temperature is the optimum for an organisms enzymes, it will be more likley to thrive and reproduce.
• competition between organisms (biotic): some organisms will outcompete others for resources, causing the weaker to die out.
• presence of predators (biotic): predators will reduce size of prey population.
• disease (biotic): epidemics of disease can significantly reduce population size.

Question 6

Define the term “density dependent factors” and give 3 examples.

Answer 6

Factor limiting the size of a population whose effect is dependent on the number of individuals in the population.
Most commonly biotic.
- disease: disease can spread more quickly through dense populations because the organisms are in closer proximity.
- competition for food and resources: competition for resources will become more intense as the population of organisms requiring resources increases.
- predation: a higher prey population will attract more predators.

Question 7

Define the term “density independent factors” and give 3 examples.

Answer 7

Factors that have an effect on the whole population regardless of its size.
Most commonly abiotic.
- earthquakes (natural disasters in general)
- temperature
- human activities

Question 8

Define the term “migration”.

Answer 8

Seasonal movement of organisms into one region or place of habitat to another. Effects population size in either place.

Question 9

Define the term “immigration”.

Answer 9

The movement of organism into a particular place. Increases population size in that place.

Question 10

Define the term “emigration”.

Answer 10

The movement of organisms out of a particular place. This reduces the population size of that place.

Question 11

Define the term “interspecific competition”.

Answer 11

Competition between different species.

Question 12

Define the terms “intraspecific competition”.

Answer 12

Competition between members of the same species.

Question 13

Give 4 examples of what organisms might compete for.

Answer 13

• food (i.e. prey, or in plants mineral ions such as nitrates)
• sunlight
• shelter
• space

Question 14

Describe and explain the “competitive exclusion principle”.

Answer 14

If two species are competing for the same resources, but one is better-adapted, the less-well adapted species is likely to be outcompeted. If conditions remain the same, the less well-adapted species will decline in number until it can no longer exist alongside the better-adapted species. This is known as the competitive exclusion principle.

Question 15

Explain why intraspecific competition is an example of a density dependent biotic factor, and why it may result in fluctuations in population size over time.

Answer 15

• It is density dependant because as the population size increases, the more organisms there will be competing one another for the same resources, and therefore the competition will be more intense.
• The availability of resource determines the population size; the greater the availability the larger the population that can be supported. This results in fluctuations in population size at a particular time.
• When there is an abundance of resources, organism reproduce and population size increases.
• As the population size increases, so does the competition for resources. This causes the population size to decrease.
  (Draw out intraspecific competition graph - pg 636 - and label stages)

Question 16

Define the term ‘prey’

Answer 16

1. Organisms that are killed and eaten by other organisms

2. Prey have evolved to avoid capture- camouflage, mimicry or defence mechanisms (spines).

Question 17

Define the term ‘predator’

Answer 17

1. Organisms that kill and eat another organism
2. Predators have evolved to become highly efficient at capturing prey e.g. sudden bursts of speed, stealth and fast reactions

Question 18

Describe and explain the general pattern shown in predator-prey relationships.

Answer 18

1. Peaks and troughs in the size of prey population are mirrored by peaks and troughs of predator population after a time delay.
2. Stage 1- An increase in prey populatio provides more food for predators, allowing more to survive and reproduce- increase in predator population
3. Stage 2- Increased predator poplation eats more prey organisms, causing a deline in prey population Death rate of prey> birth rate
4. Stage 3- Reduced prey population can no longer support the large predator population. Intraspecific competition for food increases , resulting in decrease in size of predator population.
5. Stage 4- Reduced predator numbers result in less of the prey population being killed. More prey organisms survive and reproduce, increasing prey population.
6. Cycle continues