Populations and Sustainability

Question 1

What is carrying capacity?

Answer 1

The maximum population size that can be maintained over a period of time in a particular habitat.

Question 2

What are the features of a standard population growth curve?

Answer 2

• Lag phase: Individuals are acclimatising to environment and there are few individuals in the environment, so rate of reproduction (and population growth) is slow.
• Log (exponential) phase: Conditions are optimum and there are lots of resources to go around, so rate of reproduction (and population growth) is fast.
• Stationary phase: Carrying capacity of the environment reached. Mortality rates increase due to lack of food, space; and increase in competition. Birth and mortality rates are equal, so size of population is constant.

Question 3

What are the abiotic limiting factors of a population?

Answer 3

• Availability of space.
• Water availability.
• Light availability.
• Temperature.
• Shelter availability.

Question 4

What are the biotic limiting factors of populations?

Answer 4

• Disease.
• Food availability.
• Mating.
• Predation.
• Intraspecific and interspecific competition.

Question 5

How do abiotic factors affect population size?

Answer 5

The less favourable the conditions in a habitat are for an organism, the less efficient its metabolism. This results in rate of their growth and reproduction being slow. The further away external conditions are compared to internal conditions, the more energy and nutrients are wasted by and organism in maintaining constant internal environment. They require more food, so amount of food available can only support smaller population.

Question 6

What is the general trend seen between predator and prey population?

Answer 6

1. As predator population size increases, more prey are eaten.
2. Prey population decreases, which in turn results in less food for the predator.
3. Reduced availability of food results in more predators dying of starvation, so predator population decreases.
4. Fewer predators means fewer prey are eaten and more survive, so prey population increases.
5. This is followed by the predator population also increasing due to more food.
6. Cycle repeats.
7. The result of this relationship is regular fluctuations in prey population over time, followed closely by predator population.

Question 7

How do limiting factors work in terms of determining maximum population size?

Answer 7

After the population size exceeds a certain limit, the factor in question , e.g. Shelter becomes insufficient. This results in the mortality rate increasing, rapidly decreasing population size back to limit. This maintains constant population size at carrying capacity of environment.

Question 8

What is intraspecific competition?

Answer 8

Competition between members of the same species.

Question 9

What is interspecific competition?

Answer 9

Competition between members of different species.

Question 10

How does intraspecific competition help maintain maximum constant population size?

Answer 10

Once carrying capacity of environment is reached, the population size stays relatively stationary with few minor fluctuations because:

• If population size increases above carrying capacity, competition increases, resulting in less resources being available to individuals. Mortality exceeds birth and population size drops.
• If population size decreases below carrying capacity, competition decreases, resulting in more resources being available to individuals. Birth exceeds mortality and population size rises.

Question 11

How does interspecific competition occur?

Answer 11

• Interspecific competition occurs when 2 or more species have overlapping niches.
• One species is usually better adapted than the other.

Question 12

What effect does interspecific competition have on the populations involved?

Answer 12

• Competitive exclusion: Competition occurs between the 2 species of paramecium aurelia and caudatum. P. aurelia is better adapted than P. caudatum so are more successful at obtaining food and other resources. This resulted in little/ no food and resources being available to P. caudatum. Over time, P. aurelia population grew and P. caudatum population shrank until all P. caudatum had died out. This is called competitive exclusion.
• As opposed to dying out, other factors may result in simply result in less resources being available to less well adapted species, but not necessarily none. This simply means the maximum population size for worse adapted population remains constant, well below that of better adapted population, but does not result in extinction.

Question 12

Why was sustainability not a problem in the past?

Answer 12

• Populations were small, so demand for natural resources was not great enough for exploitation of ecosystems to be damaging and unsustainable.
• Machinery did not exist to allow for mor intensive and destructive exploitation mechanisms, e.g. Bulldozing forests, netting fish on a large scale.

Question 13

What methods are there for sustainable timbre production?

Answer 13

• Coppicing.
• Pollarding.
• Rotational harvesting/coppicing.

Question 14

What is coppicing?

Answer 14

Cutting a deciduous tree trunk close to the ground and letting new shoots develop from the cut trunk. The shoots mature into stems and are narrow so can be used for fencing firewood, furniture… This method keeps trees alive and ensures they still continue to contribute to ecosystem and so is sustainable.

Question 15

What is pollarding?

Answer 15

Same principle as coppicing, but the trunk is cut much higher to prevent new shoots developing from being eaten by local wildlife (e.g. Deers).

Question 16

What is rotational harvesting/coppicing?

Answer 16

Sectioning a woodland and harvesting a different section each year either by coppicing section or cutting down tree and replanting. This ensures that a cycle can be set up whereby the first section matures when the last section is harvested, allowing cycle to repeat. This method ensures the woodland ecosystems are not lost as a result of clear-felling and the habitats of local wildlife are not destroyed, which is sustainable. In fact, this process can even be beneficial in encouraging biodiversity by halting succession. Although sections cannot be too large as to avoid large amounts of soil erosion.

Question 17

How can large-scale timbre production be managed sustainably?

Answer 17

• Replanting another tree in place of every tree cut down.
• The forest must maintain ecological function (e.g. By rotational harvesting).
• Selective cutting involving cutting down only most valuable trees and leaving other wildlife alone.
• Local people should be allowed to benefit from the forest.
• Ensure trees grow to give higher yield so less need to be cut down.

Question 18

How can replanting trees be carried out efficiently to give higher yield?

Answer 18

• Only native tree species should be planted as they are the best adapted to the climate.
• Young trees are attached to posts for support and are protected by plastic tubing to prevent new shoots from being eaten by local wildlife, increasing chance of survival.
• Trees need to be well spaced out to ensure they have enough room to grow as well as not being in competition with each other for soil nutrients and water.
• Control pests and diseases.