2.1 Species and populations

Question 1

What is the definition of “population”?

Answer 1

Group of organisms of the same species living in the same area at the same time and capable of interbreeding

Question 2

What is the definition of “Carrying capacity”?

Answer 2

The maximum number of a species that can be sustainably supported by a given environment

Question 3

What are “Symbiotic relationships”?

Answer 3

Close, long-term relationships between two different species

Question 4

What are examples of symbiotic relationships?

Answer 4

• Predation
• Herbivory
• Parasitism
• Mutualism
• Disease
• Competition

Question 5

What is predation?

Answer 5

One animal, the predator, eats another animal, the prey

Question 6

What is herbivory?

Answer 6

An animal (herbivore) eats a green plant. The carrying capacity of the herbivore is affected by the availability of the plants they feed on.

Question 7

What is parasitism?

Answer 7

Parasitism is a relationship between two species in which one species (the parasite) lives in or on another (the host), gaining its food from it. The parasite benefits at the expense of the host.

Endoparasites - Lives inside the host, eg. Tapeworm
Ectoparasites - Live on the host

Question 8

What is mutualism?

Answer 8

Mutualism is a relationship between two or more species in which both or all benefit and none suffer. Mutualism can increase the carrying capacity of both species in the relationship.
Example: Lichens and green algae

Question 9

What is a disease?

Answer 9

Caused by pathogens. This may reduce the carrying capacity of the organism it infects.

Question 10

What is competition relationship?

Answer 10

A common demand by two or more organisms over a limited supply of a resource

Question 11

What are the types of competition?

Answer 11

Intraspecific: Competition between individuals of the same species.

Interspecific: Competition between individuals of a different species

Question 12

What is the principle of competitive exclusion?

Answer 12

The principle of competitive exclusion states that when two species are competing with each other for the same limited resource, then one species will be able to use that resource more efficiently that the other and will eventually eliminate that species.

Question 13

What do the s and J population curves describe?

Answer 13

S and J population curves describe a generalised response of populations to a particular set of conditions (abiotic and biotic factors).

Question 14

What are “limiting factors”?

Answer 14

Limiting factors will slow population growth as it approaches the carrying capacity of the system.

Question 15

What is “population size”?

Answer 15

Number of individuals in a population

Question 16

What is “population density”?

Answer 16

Number of individuals per unit area or volume at a given time

Question 17

What is “population growth”?

Answer 17

Change in number of individuals

Question 18

What is “population growth rate”?

Answer 18

Change in number of individuals per unit time

Question 19

If populations were in the presences of unlimited resources, how would their populations grow?

Answer 19

Exponentially

Question 20

What are the three main factors that affect population growth?

Answer 20

1. Biotic potential - maximum rate at which a population can reproduce given all the resources it needs
2. Limiting factors or environmental resistance - all the factors that may limit the growth of a population (eg. adverse climate conditions)
3. Carrying capacity - maximum population size that can be sustained over a relatively long period of time by a particular environment

Question 21

What is the “Biotic potential”?

Answer 21

maximum rate at which a population can reproduce given all the resources it needs

Question 22

What causes increases and decreases in population size?

Answer 22

+ birth, immigration
- death, emmigration

Question 23

What are the two types of growth?

Answer 23

Logistic growth and Exponential growth

Question 24

What shape does the logistic growth graph have?

Answer 24

S-Shaped

Question 25

What shape does the exponential growth graph have?

Answer 25

J-Shaped

Question 26

What species often show a logistic growth graph?

Answer 26

Longer lived species with few predators

Question 27

What species often show a exponential growth graph?

Answer 27

Fast reproducing, short lived species at lower trophic levels (eg. rodents, insects..)

Question 28

What are the four phases of the S-shaped (logistic) growth curve, and explain them:

Answer 28

1. Lag phase: Slow growth: Birth > Death, little reproducing individuals
2. Exponential (Log) phase: Rapid increase in growth rate, max rate (grows at biotic potential), Birth >> Death
3. Transitional phase: Limiting factors begin to affect population and restrict its growth. Increased competition for resources
4. Population stabilizes and fluctuates around the carrying capacity due to limiting factors, Birth = Death

Question 29

Explain the shape of a J-shaped (exponential) growth curve?

Answer 29

1. Population increases so rapidly during exponential growth phase that it overshoots the carrying capacity
2. The environment cannot support the population and a population crash usually follows
3. Overpopulation can damage the environment leading to a new lower carrying capacity
4. Numbers are mainly regulated by external causes such as predation, available nutrition or climatic conditions

Question 30

How can humans cause population growth?

Answer 30

• Increase available resources
• Reduce competition
• Reduce pressure from predators
• Introduce animals to new areas

Question 31

How can humans decrease population growth?

Answer 31

• Change physical environment (habitat disruption)
• Change biological environment (introducing new species)
• Cause secondary extinctions (when one species goes extinct, other extinctions also occur)
• Overkill (elimination or drastic reduction in an animal population by hunting or killing)