Populations and Sustainability

Question 1

What is population dynamics?

Answer 1

The study of population growth and the factors responsible for influencing their growth rate.

Question 2

What is population density?

Answer 2

The number of individuals per unit area/volume.

Question 3

What is the name of the shape of the curve delineated by a natural population increase?

Answer 3

Sigmoid curve

Question 4

What are the three main stages of the natural growth of a population?

Answer 4

Lag phase
Log phase
Stationary phase

Question 5

Describe the lag phase of natural population growth.

Answer 5

Few individuals, still acclimatising to the habitat.

Reproductive rate is low so the population growth is slow.

Question 6

Describe the log phase of natural population growth.

Answer 6

Conditions are favourable, so reproductive rate far exceeds mortality rate, resulting in exponential population increase.

Question 7

Describe the stationary phase of natural population growth.

Answer 7

The population size has stabilised at the carrying capacity of the habitat, but still fluctuates around an equilibrium value.
The reproductive rate is roughly equal to the mortality rate.

Question 8

What are limiting factors for population growth?

Answer 8

Factors that prevent exponential growth in natural populations.
Factors become limiting, providing environmental resistance to exponential growth.

Question 9

What are some examples of abiotic limiting factors?

Answer 9

Temperature, light intensity, pH of soil, availability of water, oxygen.

Question 10

What are some examples of biotic limiting factors?

Answer 10

Predation, disease, competition (interspecific and intraspecific)

Question 11

What is carrying capacity?

Answer 11

The maximum population size that can be maintained over a period of time in a particular habitat.
The population still fluctuates around an equilibrium level.

Question 12

What are the two types of factors influencing mortality rates?

Answer 12

Density dependent.

Density independent.

Question 13

What are density dependent factors?

Answer 13

Limit the growth of the population in proportion to the size of the population (population density). Mainly biotic factors.

Question 14

What are density independent factors?

Answer 14

Limit the growth of the population independently of population density. Mainly abiotic factors (natural disasters such as earthquakes or floods)

Question 15

What are the two types of migration?

Answer 15

Immigration

Emigration

Question 16

Describe immigration and give an example.

Answer 16

Movement of organisms into an area, increasing population size.
Christmas island red crabs (from forest to coastal areas)

Question 17

Describe emigration and give an example.

Answer 17

Movement of organisms out of an area, decreasing population size.
Norway lemmings (away from high population density)

Question 18

What are the two types of competition?

Answer 18

Interspecific and intraspecific

Question 19

What is interspecific competition?

Answer 19

Competition between different species for the same resource.

Question 20

What is the competitive exclusion principle and when does it apply?

Answer 20

Interspecific competition.
If one species is less well adapted (uses the limited resource less effectively), it is outcompeted and will eventually be eliminated.
This is called competitive exclusion, where species have overlapping niches.

Question 21

What is an example of interspecific competition?

Answer 21

Red and grey squirrels in the UK.

Question 22

What is intraspecific competition?

Answer 22

Competition between members of the same species due to limiting factors.

Question 23

What is the relationship between predator and prey populations?

Answer 23

Predation can act as a limiting factor on a population of prey, which can in turn affect the predators population size (interdependence).

Question 24

Describe the 4 stages of a predator-prey relationship.

Answer 24

1. When the predator population increases, more prey are eaten.
2. Prey population decreases, meaning less food for predators.
3. Predator population decreases.
4. Prey population increases due to decrease in predation.

Cycle repeats

Question 25

What is conservation?

Answer 25

The maintenance of biodiversity through the active management of an ecosystem.
Conservation is a dynamic process involving management and reclamation.

Question 26

What is preservation?

Answer 26

A form of conservation, but leaves ecosystems undisturbed, attempting to keep things the way they are.

Question 27

What are some conservation/preservation techniques?

Answer 27

Provide extra food (raise carrying capacity).
Restrict dispersal by fencing.
Control predators and poachers.
Vaccinate individuals against disease.
Prevent pollution/disruption of habitats.
Increase habitat size.
Remove non-indigenous species.
Irrigate/drain dry/swamp land.

Question 28

Why is sustainable management so important?

Answer 28

The increase of the human population results in the need to intensely exploit the environment for resources. This leads to the destruction of habitats, reduced biodiversity and the eventual complete depletion of resources.

Question 29

What are 3 sustainable management techniques for small scale timber harvest?

Answer 29

Coppicing, Pollarding, Rotational coppicing

Question 30

What is coppicing?

Answer 30

Cutting deciduous tree trunks close to the ground to encourage new growth from the merismatic tissue.

Question 31

Why is coppicing good?

Answer 31

The tree recovers much more quickly than a newly planted tree.
The root system is still intact, so the soil is not disrupted.

Question 32

What is pollarding and why is it useful?

Answer 32

Similar to coppicing, but the tree is cut higher up.

Pollarding prevents herbivory by animals such as deer.

Question 33

What is rotational coppicing?

Answer 33

Foresters divide a wood into sections and only cut one section each year, rotating once all have been cut.

Question 34

In rotational coppicing, what determines the period of the rotation?

Answer 34

The species of tree.

The dimensions of the wood required.

Question 35

Why is rotational coppicing good?

Answer 35

Maintains biodiversity, as the trees do not block out all the light, so succession cannot occur and more species can survive.

Question 36

What are the dangers of large scale timber harvest?

Answer 36

Often involves clear-felling of all the trees in an area, so:
destroys habitats.
leads to water pollution due to the destruction of root networks.
reduces soil nutrient levels.

Question 37

What is reforestation?

Answer 37

Areas of destroyed forest can be replanted.

Question 38

What is afforestation?

Answer 38

New forest planted in areas where there previously was no forest.

Question 39

What are some sustainable planting strategies (large scale).

Answer 39

Trees not planted too closely together (limits competition).
Young trees protected from grazing.
Only native plant species planted.
Fast-growing trees planted (e.g: conifers).
Control pests and pathogens.

Question 40

What are some sustainable felling strategies? (2)

Answer 40

Selective felling (only mature trees removed).
Strip felling (trees cut in strips to maintain biodiversity).

Question 41

What are 5 sustainable fishing practices?

Answer 41

EU common fisheries policy (quota and species allowed for fishing).
Minimum netting mesh size (allows juvenile fish to escape).
Fishing seasons (helps allow time for repopulation).
Fishing licences.
Dedicated fish farms.

Question 42

What are the problems with fish farms?

Answer 42

Ethical issues.
Easy spread of disease.
Can harm biodiversity in the area.

Question 43

Why is it important to maintain ‘wild types’ of crop species?

Answer 43

Can be a source of useful alleles.
Can be cross bred with crops to increase genetic variation.
Allow the introduction of different traits that may be required in future, particularly due to changing climates.
Promotion of hybrid vigour.
Source of replacement of crop populations if the cultivated population is in danger.