6.3.2 populations and sustainabiltiy

Question 1

What is a population?

Answer 1

all the members of ONE species in a given area

Question 2

what is the carrying capacity?

Answer 2

The carrying capacity is the maximum population size that a given habitat/ecosystem can sustain. The carrying capacity is determined by the limiting factors present.

Question 3

what is a limiting factor

Answer 3

A limiting factor is something which stops a process or population increasing any further

Question 4

what happens if the carrying acapacity is exceeded?

Answer 4

the limiting factors present will tend to bring the population size back down (negative feedback)

Question 5

what does the population size do arround the carrying capacity?

Answer 5

it fluctuates around the carrying capacity

Question 6

Sketch a graph showing how the population of newly‐introduced species may change over time, in a habitat with a fixed carrying capacity

Answer 6

Question 7

what are density-dependenty limiting factors?

Answer 7

limiting factors that have an increasingly significant effect on the population
growth rate as the population size increases

Question 8

give 4 examples of Density‐dependent limiting factors

Answer 8

Limited food availability

Inadequate space

Presence of infectious disease

Intraspecific and/or interspecific competition

Question 9

what are Density‐independent limiting factors?

Answer 9

These are limiting factors that have a consistently significant effect on the population growth rate regardless of the present population size.

Question 10

give 2 examples of Density‐independent limiting factors

Answer 10

Temperature (too high or too low)

Factors that determine photosynthesis rate

Question 11

intraspecific competition definition and example

Answer 11

Intraspecific competition occurs when members of the same species compete for the same resource.

example: Lions in the same habitat are in competition for the same food sources

Question 12

interspecific competition definition and example

Answer 12

Interspecific competition occurs when two (or more) different species compete for the same resource

example: Buzzards and barn owls compete for small mammals

Question 13

what is a Predator–prey relationships, give an exmaple, what does it mean?

Answer 13

when a specific predator has one principal (main) prey species on which it feeds and when that prey species has no/few other predators

example: Lion and gazelle

the population size of each species can strongly affect the population size of the other species: the two populations show a high level of interdependence

Question 14

Sketch a graph showing how the relative sizes of a predator population and its prey population may vary over time

Answer 14

Question 15

explain this graph

Answer 15

1. When predator numbers are low, the prey population increases as few are eaten by predators. Most prey offspring survive to breed themselves. Birth rate of prey is higher than death rate.
2. However, the increasing prey population now means there is more readily available food for predators. If the prey population has increased beyond its carrying capacity, some prey individuals may be weakened by lack of food (as intraspecific competition for limited food may lead to starvation) or by the increased presence of disease or pathogens spreading through the crowded population. These factors plus the high prey density mean that predators can catch prey more easily, with low energy expenditure themselves.
3. Predators therefore now have increased growth rates (enabling them to breed sooner), higher fertility and more offspring that survive to breed themselves. Hence, after a time delay, the previous increase in prey population is now followed by an increase in the predator population. The delay between the two will be longer in species where the predators are slow to reach maturity and have long gestation periods: it could then take several years before an increase in prey actually translates to bigger predator population.
4. Now the predator population is increasing (with their birth rate higher than their death rate), they will be killing and feeding on more prey. This results in the prey population declining. Death rate has now exceeded birth rate in the prey.
5. However, if the prey population is falling, this means food is less readily available to the predators. The predators may have to expend more energy to catch the increasingly scarce prey. The prey may be stronger (less weak) and so better at evading capture as they have less intraspecific competition for their own food sources (hence they are better nourished); they may have fewer diseases and parasites (as these don’t spread readily in a sparse population).
6. The predator population may now fall as the predators struggle to get enough food: they may reach breeding age later due to poor nutrition and fewer offspring may survive to breed themselves. If the predator population has exceeded carrying capacity, its numbers may also be declining due to increased disease or parasite transmission. Death rate of predators now exceeds birth rate.
7. As the predator population falls, there are fewer predators killing prey. Hence the prey population has the opportunity to increase again: the above sequence of events will restart and repeat. Both populations will oscillate over time, but the changes in the predator population always lag behind those in the prey population.

Question 16

what is preservation?

Answer 16

Preservation is the prevention of any human activity in a pristine ecosystem, in order to avoid its damage or modification

Question 17

examples of preservation

Answer 17

keeping humans out

banning tourism, mining, deforestation, hunting, industry, housebuilding

Question 18

why is preservation hard?

Answer 18

Most ecosystems have been subjected to modification or exploitation by humans already, therefore it cannot be preserved

Question 19

what is an example of preservation?

Answer 19

Antarctica

Question 20

what is conservation?

Answer 20

Conservation is the active management of a habitat/ecosystem (by humans)
with the aim of maintaining or increasing its biodiversity

Question 21

what are the aims of conservation?

Answer 21

increase or maintain the diversity of habitats, the species diversity and the genetic diversity of one or more species

Question 22

What are the three catagories for conserving biological resources?

Answer 22

Economic reasons

Social reasons

Ethical reasons

Question 23

what are the economical reasons for conserving biological resources?

Answer 23

high biodiversity = avoid problems relating to soil mineral depletion

avoid large‐scale deforestation = less soil loss via erosion by wind/water

ecotourism

protects jobs

genetic resource for future selective breeding or genetic engineering

new materials for manufacturing or new medicines

Question 24

what are the social reasons for conserving biological resources?

Answer 24

Sustainable fishing helps coastal communities remain viable by protecting jobs

considered beautiful and many people experience a better sense of wellbeing

Question 25

what is the ethical reasons for conserving biological resources?

Answer 25

Humans have a moral responsibility to protect ecosystems and avoid causing extinctions. In particular, given the interdependence of organisms in a food web, keystone species should be identified and conserved (since their presence significantly affects all others in the ecosystem, e.g. via predation or via the modification of the habitat).

Question 26

what does it mean for a resource to be used in a sustainable manner?

Answer 26

the resources we harvest from the ecosystem will continue to be available at predictable levels into the future

the resources are being replenished at (at least) the same rate as they are being harvested.

Question 27

what are the two examples we must learn for sustainable management of ecosystems?

Answer 27

Sustainable timber production

sustainable fishing

Question 28

what are the aims of sustainable timber?

Answer 28

predictable yield of timber can be harvested every year into the future, achieving sustainability

increase the biodiversity

ecotourism

Question 29

what are the three management strategies for sustainable timber?

Answer 29

rotational coppicing, pollarding and selective felling and replanting

Question 30

what are the 5 steps of rotational coppicing?

Answer 30

1. The woodland is divided into (for example) nine sections of equal size;
2. In one section only, suitable trees (e.g. hazel, sweet chestnut) are cut down close to ground level, leaving a coppice stool or stump;
3. Over the next nine years, the stumps will grow new shoots from their remaining meristem tissue;
4. Each year, a different section of the woodland is coppiced, i.e. the scheme is rotational;
5. By the time all nine sections have been coppiced, the trees in the original section have regrown sufficiently that their timber can be harvested again.

Question 31

what are the benefits of rotational coppicing?

Answer 31

The timber from rotational coppicing is a sustainable resource: it will remain available into the future, since the rate of regeneration of the resource (at least) matches its rate of harvest

There is an ongoing economic benefit to the landowner, who has a predictable yield of timber to sell each year: the timber from coppicing (called ‘small wood’ due to the relatively narrow diameter of the logs) is used for making fences, garden furniture, charcoal etc;

Biodiversity is increased due to there effectively being nine different habitats in the ecosystem, each with different light intensities and different stages of tree (re)growth: different species of plants, insects and birds will thrive in the particular conditions present in each section.

The high biodiversity may attract visitors to the woodland (ecotourism): they may psychologically benefit from spending time there, and may provide economic opportunities for the landowner e.g. a pay‐and‐display carpark or a café.

Question 32

what is pollarding?

Answer 32

Pollarding is similar to coppicing but the tree is cut much higher up the trunk (e.g. at least 2m
above ground level). The new shoots which grow from the meristem tissue in the trunk

Question 33

why use pollarding?

Answer 33

Pollarding is used in areas where deer are common. The new shoots which grow from the meristem tissue in the trunk are safely out of reach of deer.

Question 34

what is Selective felling and replanting

Answer 34

the occasional cut down and replanting of trees.

Question 35

benefits of Selective felling and replanting

Answer 35

The timber from a standard (which may be a 200 year old oak tree) will be of very high value, as it provides wide planks that can be used for making high quality furniture; there is a significant economic gain from the felling of a standard;

Felling of only a small number of trees minimises the disruption to the whole woodland, as there is only a limited amount of disturbance by heavy machinery and its noise (that would disturb wildlife);

The ‘gap’ left in the woodland where the standard used to grow will be a new microhabitat: additional light reaches ground level in the gap, hence biodiversity may be increased.

Question 36

what should be considered during Selective felling and replanting?

Answer 36

Plant tree saplings of fast growing native species, as these will immediately play a beneficial role in the ecosystem, supporting insects and birds

Protect saplings with plastic cylinders or wire mesh, so that they are not eaten by herbivores

Avoid a high planting density (i.e. too many trees in a given area) as trees strongly compete for light, water and mineral ions and their growth will be stunted if they’re too close together

Be prepared to carry out pest and disease control if necessary, e.g. use of insecticides.

Question 37

strip felling

Answer 37

cutting down trees in a narrow strip through the forest

Question 38

clear felling

Answer 38

the removal of all trees and other vegetation from a large area of forest

Question 39

why strip felling over clear felling?

Answer 39

Strip felling causes less significant disruption to the ecosystem since it doesn’t involve destroying a large area of the habitat

Strip felling leaves some vegetation (including roots) in place, so avoids significant soil erosion occurring; in contrast, clear felling often leads to loss of topsoil via erosion by wind and water

Since strip felling maintains the topsoil in situ, minerals are retained to support future plant growth

Following strip felling, the habitat often generates quite rapidly because seeds fallinto the area from the surrounding intact woodland (essentially resulting in a secondary succession process); this doesn’t happen if the area was clear felled.

Question 40

how is fishing sustainable?

Answer 40

the rate of removal of fish must not exceed the rate of reproduction in the remaining populations

Question 41

why should fishing be sustainable?

Answer 41

If fish populations remain at a level at which commercial fishing remains viable into the future, jobs in the fishing industry are maintained and fish will continue to be available to humans as widely‐available, affordable, healthy protein source

If a balanced ecosystem is maintained, this helps conserve marine biodiversity. If overfishing occurred and the population of a particular fish species fell sharply in a given area, there would be a knock‐on effect to other species in the marine ecosystem, e.g. a lack of food for that species’ predators.

Question 42

what are the strategies for sustainable fishing?

Answer 42

larger Mesh size of fishing net

fishing Quotas

No take’ zones and Marine Conservation Zones

Seasonal restrictions

large scale Fish farming

Question 43

give an example of an ecosystem where there is a Balancing conflict between conservation and meeting human needs

Answer 43

Peat bog

Question 44

give an example of an ecosystem where the effects of human activities has had an impact on the ecosystems

Answer 44

Antarctica

Question 45

describe Antartica

Answer 45

What happenning:

global warming

hunting of whales and seals

soil contamination

discharging of waste intoi sea

whats being done:ecotourism

protected areas

conservation and preservation

protection of environment

cooperation between governments

Question 46

describe peat bogswet

Answer 46

wet spongy ground cotaining decomposing vegetation

Question 47

what is a niche?

Answer 47

the role an organism plays in a community

Question 48

what happens if two or more species share a niche?

Answer 48

out‐compete the other

The successful species will be the one best adapted to the niche

Question 49

what happens if niches overla[p? example

Answer 49

two different bird species may require some of the same food sources (e.g. specific seeds or insects) and so compete for these, whilst having different nesting requirements and so not competing in that regard

Question 50

what does interspeciofic competition play a key role in?

Answer 50

determining where particular species are found in their ecosystem and the times at which they are active

Question 51

what to remember when reading predator prey realtionship gaphs?

Answer 51

On graphs, to highlight the interdependent relationship between the population sizes, the lines for each species may be drawn on the same axes but using a different numerical scale for each species. Pay close attention in exam questions to check whether this is the case!