Populations and ecosystems Flashcards

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1
Q

Define population

A

A group of organisms of the same species, occupying a particular space at a particular time that can potentially interbreed

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2
Q

Define ‘gene pool’

A

All the alleles of all genes in a population

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3
Q

Define Community

A

All the populations of different species living in the same habitat at the same time

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4
Q

What are biotic conditions? Give examples

A

Living factors of an ecosystem.
e.g predation, disease, food supply.

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5
Q

What is a plagioclimax?

A

When human activities prevent succesion and stop a climax community forming. It is usually used for the conservation of a species (as it prevents them being out competed by a new environment)

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6
Q

Define ecosystem

A

The community of biotic and abiotic factors of an area and their interactions. It is said to be dynamic

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7
Q

State 5 features of an ecosystem

A
  • Dynamic
  • Can range in size from very small to very large
  • Can range in complexity (e.g a desert is relatively smple, a tropical rainforest is very complex)
  • Self-contained
  • Flow of energy and nutirents within it
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8
Q

Why are ecosystems described as ‘dynamic’?

A

o Populations constantly rise and fall
o Any small change can have a large effect
o Biotic and abiotic factors may alter the condition of the ecosystem

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9
Q

What 4 factors affect population size and distribution?

A
  • Interspecific Competition
  • Intraspecific Competition
  • Predation
  • Abiotic Factors
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10
Q

What is interspecific competition?
Outline the process

A

When individuals of different species compete for the same resources such as food, light etc.

  • Where populations of the two species share the same niche, one will normally have a competitive advantage over the other.
  • The population of this species will eventually increase in size and the other will diminish.
  • If these conditions continue this will lead to the compete removal of one species. This is known as the local extinction.
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11
Q

What is intraspecific competition? What is eventually reached as a result?

A

When individuals of the same species compete for the same resources such as food, light etc.

  • This is competition for the same resources between individuals from the same species
  • For example: When resources are plentiful, the population of species increases
  • As the population increases, however, there are more individuals competing for these resources (e.g. food and shelter)
  • At one point, the resources become limiting and the population can no longer grow in size – the carrying capacity has been reached
  • The population may then decrease so the cycle starts again
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12
Q

Describe a predator-prey cycle (Lokta-Volterra model)

A

The prey population increases because there are not many predators to eat the prey
The predator population increases because there is plenty of prey for them to eat, so more survive and reproduce.
The prey population decreases because there are many predators eating the prey
The predator population decreases because there isn’t as many prey as animal s, so there is less food available for them to eat, so there is more intraspecific competition between predators.
Each cycle is approx. x years

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13
Q

What is meant by ‘carrying capacity’?

A

The maximum stable population size of a species that an ecosystem can support

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14
Q

Define the term ‘niche’

A

The role that an organism plays in a ecosystem, which is governed by adaptations to abiotic and biotic conditions

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15
Q

What is the competitive exclusion principle?

A
  • A niche can only be occuped by one species, meaning that every individual species has its own unique niche
  • Competition for food / named resource;
  • If two species had identical nichces, one would go extinct
  • The better adapted outcompetes the other species
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16
Q

What causes interspecific competition?

A

Overlap between the niches of different species

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17
Q

Population size and Carrying capacity

Label the graph

A B C K

A

A = lag phase. Few individuals still acclimatising to their habitat. Rate of reproduction is low.

B = 10 log phase/exponential phase.
Plentiful resources and suitable conditions. Reproduction rate is fast and exceeds the mortality rate.

C = stationary phase. Reached carrying capacity of the habitat. Rate of reproduction and mortality are equal. The habitat cannot support a large population.
Population remains stable.

K = carrying capacity. maximum size of a population an ecosystem can support

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18
Q

Why is sampling carried out?

A

To select a sample which is representative of the population

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19
Q

What are the 5 key factors to consider when carrying out an ecological study?

A

Large sample size
Removing bias
Seasonal differences
Choosing appropriate samples
Conclusions shown

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20
Q

Sampling can either be ______or ________

A

Sampling can either be random or systematic

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21
Q

Describe, in detail, how and why we use random sampling in an ecological study

A

1) Choose an area to sample - a small area within the area being investigated.
2) Samples should be random to avoid bias, e.g. if you were investigating a field you could pick random sample sites by dividing the field into a grid and using a random number generator to select coordinates.
3) Use an appropriate technique to take a sample of the population
4) Repeat the process, taking as many samples as possible. This will reduce the likelihood that your results are down to chance. Eliminates bias
5) The number of individuals for the whole area can then be estimated by taking the mean of the data collected in each sample and multiplying it by the size of the whole area.

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22
Q

How is systematic sampling different to random sampling?

A
  • A similar grid is used, however samples are taken at regular intervals.
  • Usually used to investigate environmental gradient.
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23
Q

How can we increase the reliability of data used in an ecological study? 6

A
  • Increase repeats
  • Calculate running mean
  • When enough quadrats used, graph would level off
  • Take enough readings to carry out statistical test
  • Test a large number to make sure results are reliable
  • Need to be sure work can be carried out in designated time
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24
Q

Why do we use random samples? [3]

A
  • Avoids bias
  • Data representative / Choice of X variable not influencing results
  • Allows use of statistical tests
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25
Q

What are the 3 ways we can estimate population size?

A

For non-motile and slow moving
Quadrats (random)
Transects (systematic)

For motile
Mark, Release, Recapture

26
Q

What is meant by distribution of a species?

A

Describes how it is spread throughout the ecosystem

27
Q

What is meant by abundance?

A

The number of individuals of that species

28
Q

Describe the two types of quadrats

A
  • Frame Quadrats (place randomly, count number)
  • Point Quadrat (drop pins randomly, count number of species it touches)
29
Q

What are the 2 ways we can record data on species using quadrats?

A

Percentage Cover
Percentage Frequency

30
Q

What are the advantages/disadvantages of using Percentage Frequency when measuring with quadrats?

A

Advantages:
· Quick to carry out
· Useful for species that are hard to count (e.g. grass)
Disadvantages:
· Doesn’t provide detailed info on distribution of a species

31
Q

What are the advantages/disadvantages of using % cover when investigating with quadrats?

A

Advantages:
· Useful for species that are hard to count (e.g. grass)
· Useful for species that are very abundant in area
· Don’t need to count individual plants
Disadvantages:
· Not useful in areas where organisms occur in overlapping layers (becomes difficult to estimate an exact amount)

31
Q

What’s precentage frequency?

A

The likelihood of a particular species occurring in a quadrat e.g. if you found daises in 15 out of 30 quadrats the frequency would be 50%

32
Q

What’s percentage cover?

A

An estimate of an area within a quadrat
that a particular species covers. It is useful where a species is particularly abundant or difficult to count. Using this method means that data can be collected quickly

33
Q

What are the 3 types of transect and how are they used?

A

o Line Transect
§ Run a tape measure between two points
§ Record all species that touch the tape

o Belt Transect
§ Use quadrats along the length of the transect

o Interrupted Transect
§ Use quadrats at fixed intervals along the length of the transect

34
Q

‘’Describe how you would investigate the distribution of x from one side of an ecosystem to the other’’ MS [3]

A

· Transect from one side of the ecosystem to the other
· Place quadrats at regular intervals along the line
· Count the % cover of the plant in quadrats

35
Q

Why are belt transects used in a non-uniform ecosystem?

A

To investigate the effect of changing physical conditions on species distribution

36
Q

Describe the Mark-Capture-Rerelease Method [5]

A
  1. Capture a known sample and mark them (without causing harm)
  2. Release back into the community
  3. Allow time for re-integration, the community is then revisited and a given number of individuals is caught again
  4. The number of marked individuals is counted
  5. Population size is calculated via the equation
36
Q

Why is more difficult to study animals and insects as opposed to plants?

A

· Mobile
· Stay hidden from the investigator

37
Q

What are the 4 issues surrounding the Mark-Capture-Rerelease method?

A

· Deciding in a large area how many individuals to capture and recapture
· Ensuring to mark them in a harmless way
· Ensure to mark in a way that stays til the second collection
· Deciding time for re-integration

38
Q

Accuracy of mark release recapture depends on 3 things:

A
  • The marked sample has had enough time and opportunity to mix
    back in with the population
  • The marking hasn’t affected the individual’s chances of survival
    (e.g. making them more visible to predators, it is non toxic and
    does not affect the animals chances of reproduction. The marking
    has not rubbed off).
  • There are no changes in population size due to births, death and
    migration during the period of the study.
39
Q

Define ‘succession’

A

The change over time in the species that occupy a particular area

40
Q

Why would a bare, barren rock not be habituated by organisms?

A

Exposed
No Soil
Absorbs + Reflects Heat
Dry
No Nutrients

41
Q

Describe the steps in primary succession. MS [6]

A
  1. Colonisation occurs by a pioneer species
  2. Pioneer species causes a change in environment e.g more food / nutrients / stabilises
  3. Enables other species to colonise once there is a change
  4. Change (increase) in species diversity / biodiversity
  5. Stability increases, environment is less hostile
  6. Climax community is reached
42
Q

What 5 things happen as a result of primary succession?

A
  • Abiotic environment becomes less hostile
  • Greater number/variety of habitats and niches
  • Biodiversity increases
  • More complex food webs emerge
  • Increased biomass
43
Q

What is the role of pioneer species? MS [6]

A
  • Stabilize environment
  • Soil development / increase humus
  • Change soil pH
  • Hold more water
  • Release more nutrients / increase N content
  • Provide shelter
44
Q

What is meant by ‘climax community’?

A
  • The final stage in succession
  • Community in equilibrium with environment
  • Community is stable
45
Q

What are the 3 key features of a climax community?

A
  • Populations are stable around the carrying capacity
  • Abiotic factors constant
  • Same species present / stable community
46
Q

What are two types of succession and what’s the difference?

A
  • Primary succession occurs when plants grow in newly formed/exposed land and is gradually colonised.

-Secondary succession occurs when plants grow where there has previously been a population. These will have been destroyed e.g by fire

47
Q

What do we need to know about animal succession?

A

Animal species present depend on the plant species found in the area
For example, mosses and grasses provide food and habitats for insects and worms. These can then support secondary consumers.

48
Q

What is deflected succession?

A

A community that remains stable on because human activity prevents succession from running its course

49
Q

Describe 5 ways in which deflected succession can be caused MS [5]

A
  • Grazing
  • Burning
  • Mowing
  • Selective Herbicide
  • Exposure to Wind
50
Q

Conservation of habitats frequently involves the…

A

…management of succession.

51
Q

Define ‘conservation of habitats’

A

The management of the natural resources to enable future generations to maximize their use

52
Q

What does conservation of habitats involve?

A

Maintaining ecosystems
Maininting biodiveristy
Management of existing resources
Ensuring damaged resources can be obtained again as well

52
Q

What are the 4 main reasons for conserving habitats?

A
  • Economical - large genetical pool in organisms which could lead to the development of valuable resources in the future
  • Ethical - respecting living things that co-exist with us on Earth
  • Aesthetic Reasons
  • Cultural - people turn to nature for inspiration
53
Q

Many species that previously existed on earth no longer do. Explain why in terms of succession and habitats.

A
  • Habitats have changed or completely disappeared as a result of succession.
  • Some have been out competed by other species, mostly the dominant species in a community.
54
Q

How could we prevent species from dying out due to succession? [MS] 3

A

Through the management of succession. We can ensure that changes to habitats are minimal and that they only occur when needed. Ensuring that any organisms displaced by change are placed into a suitable environment.

55
Q

Grassland management is an example of conservation. Recall this.

A
  • Much of the higher ground in the UK is moorland.
  • Vegetation growth rate slows significantly due to heather burning and sheep grazing
  • Burning maintains plant vigour and removes unwanted vegetation
  • Prevents climax community from being reached as the young tree saplings are destroyed, stopping progression into deciduous woodland
56
Q

What is sustainable foresty? Give two examples.

A

These are techniques that employ a variety of removal and replacement methods that provide timber while reducing the impact of timber removal on the environment.

Coppicing:
- Trees coppiced
- Stems grow from stump
- Stems provide wood from the stump

Selection Logging:
- Trees selected for removal based on height, girth
- Felled individually and directed to fall to minimise damage
- Forest managed to ensure continued growth of young seedlings + provide balance of tree ages

57
Q
A