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AQA A Level Biology > 3.3.1 The Effect of Biotic and Abiotic Factors on Populations > Flashcards

3.3.1 The Effect of Biotic and Abiotic Factors on Populations Flashcards

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1
Q

Define Habitat

A

Place where an organism lives

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2
Q

Define Population

A

All the organisms of one species in a habitat

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3
Q

Define Community

A

All populations of different species in a habitat = community

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4
Q

Define Ecosystem

A

A community + all abiotic & biotic factors in the area

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5
Q

Define Abiotic conditions

A

Non-living features of ecosystem

e.g. temperature, availability of water

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6
Q

Define Biotic conditions

A

Living features of ecosystem

e.g. predators, food

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7
Q

Define Niche

A

Role of a species within its habitat

e.g. what it eats, where and when it feeds

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8
Q

Define Adaptation

A

Feature that member of a species have that increases their chance of survival and reproduction

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9
Q

The niche of a species occupies within its habitat includes…

A
  • Its biotic interactions
    • e.g. the organisms it eats, and those it’s eaten by
  • Its abiotic interactions
    • e.g. oxygen an organism breathes in & CO2 it breathes out
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10
Q

If 2 species try to occupy same niche, there’ll be ______

A

competition

(One species will be more successful & it’ll be one its own)

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11
Q

Organisms are adapted to both ____ conditions (e.g. water availability) and _____ conditions (e.g. predators) in their ecosystem

A

Organisms are adapted to both abiotic conditions (e.g. water availability) and biotic conditions (e.g. predators) in their ecosystem

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12
Q

What is meant by carrying capacity?

A

Maximum stable population size of a species that an ecosystem can support

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13
Q

What does population size vary due to? (2x)

A
  • Abiotic Factors
  • Biotic Factors
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14
Q

Name 3 examples of abiotic factors

A

light, water, space available, temperature, chemical composition of surroundings, pH, etc.

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15
Q

Explain how when a mammal’s surroundings is the ideal temperature (e.g. abiotic factor), it can lead variations in population size

A
  • e.g. when temperature of a mammal’s surroundings is the ideal temp. for metabolic reactions to take place = don’t have to use up as much energy maintaining their body temperature
  • ∴ more energy can be used for growth and reproduction & population size will increase
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16
Q

Name 3 biotic factors that affect population size

A
  • Intraspecific Competition
  • Interspecific Competition
  • Predation
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17
Q

What is interspecific competition?

A

When organisms of different species compete for same resources

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18
Q

Explain how interspecific competition can cause a change in population size

A
  • Results in reducing the resources available to both populations
    • e.g. if share same food source = less available for both of them
    • Both populations limited by lower amount of food
    • Less energy for growth and reproduction
    • ∴ populations sizes lower for both species
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19
Q

What happens when 2 species are competing but one is better adapted to surroundings?

A

Less adapted species = out-competed (won’t exist with other species)

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20
Q

Define Intraspecific Competition

A

When organisms of the same species compete for same resources

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21
Q

Explain how intraspecific competition leads to variation in population size

A
  1. Population of species increases when resources plentiful
    • Population ↑ = more organisms competing for same amount of space + food
  2. Resources become limiting (not enough for all organisms)
    • Population ↓
  3. Smaller population = less competition = better for growth and reproduction
    • Population ↑
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22
Q

Explain how predation leads to variation in population size

A
  1. Predator population peaks after prey population
  2. Prey population ↑ (due to less preadators/more food available)
  3. More food available = predator population ↑
  4. As predator population ↑, ↑ predation ∴ prey population ↓
  5. Less food for predators = predator population ↓
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23
Q

Predator and Prey Population Cycle

Why does the prey population initially decline?

A

∵ there’s too many of them for amount of food available

(This is then accelerated by predation)

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24
Q

Describe how to take a random sample from an area you’re investigating

A
  1. Choose an area to sample
  2. Samples should be random to avoid bias
    • e.g. divide field into grid and use random number generator to select coordinates
  3. Use appropriate technique to take sample
  4. Repeat processes many times to reduce likelihood that results are due to chance
  5. No. of individuals for whole area can be estimated by taking mean of data collected in each sample & multiplying it by size of whole area
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25
Q

Name 2 methods of investigating non-motile organisms

A
  • Transects
  • Quadrats
26
Q

What is recorded in each quadrat?

A

Species frequency or no. of individuals of each species

27
Q

How can the percentage cover of a species be measured?

A

By counting how much of quadrat is covered by species

Count a square if it’s more than half-covered

28
Q

What is the benefit of measuring percentage cover?

A

Quick way of investigating populations & don’t have to count all individual organisms

29
Q

What are transects used for?

A

Used to find out how organisms (e.g. plants) are distributed across an area

30
Q

Describe how you would conduct a belt transect

A

Place quadrats are next to each other along a transect to work out the species frequency & percentage cover along transect

31
Q

What’s an interrupted belt transect?

A

(It’s for larger distances) quadrates placed at intervals along the line

32
Q

Name the method you would use for investigating motile species

A

Mark-Release-Recapture

33
Q

What is the mark-release-recapture method used for?

A

To measure abundance of motile species

34
Q

Describe how you would conduct a Mark-Release-Recapture

A
  1. Capture a sample of a species using appropriate technique & count them
  2. Mark them in harmless way
  3. Release them back into habitat and allow time to re-integrate with rest of population
  4. (Wait a week) Take 2nd sample from same population
  5. Count how many of the second sample are marked
  6. Use an equation to estimate total population size
35
Q

Mark-Release-Recapture

State the equation you use to estimate the total population size

A
36
Q

Name 3 assumptions made when using the Mark-Release-Recapture method

A
  1. Marked sample has had enough time and opportunity to mix back in with population
  2. Marking hasn’t affected individuals’ chances of survival & marking is still visible
  3. No changes in population size due to births, deaths and migration during period of study
37
Q

What is succession?

A

The process by which an ecosystem changes over time

(Biotic + abiotic conditions change)

38
Q

Where does primary succession happen?

A

Happens on newly formed/exposed land

There’s no soil or organic material to start with e.g. just bare rock

39
Q

Give an example where primary succession may occur

A

Where volcano has erupted to form new rock surface or where sea level dropped and exposed new land

40
Q

Where does secondary succession happen?

A

Happens on land that’s been cleared of all plants but soil remains

41
Q

Give an example where secondary succession may occur

A

e.g. after forest fire or deforestation

42
Q

What happens at the start of primary succession?

A

Pioneer species colonise new land surface

e.g. Seeds and spores blown by wind & begin to grow

43
Q

Primary Succession

Why is it at first only the pioneer species grow?

A

Abiotic conditions are hostile (e.g. no soil to retain water) & only pioneer species = specially adapted to cope with harsh conditions

44
Q

Primary Succession

Describe how the pioneer species change the abiotic conditions

A
  • Change in environment
    • They die and micro-organism decompose dead organic material (humus)
    • Forms basic soil
45
Q

Primary Succession

What is the result after a basic, thin soil has formed?

A
  1. Makes conditions less hostile (e.g. basic soil retains water) ∴ new species with different adaptations can grow
  2. Then die and decomposed adding more humus = makes soil deeper and richer in minerals
  3. ∴ larger plants (shrubs) can grow & more water retained
46
Q

Primary Succession

What happens at each stage (competition wise)?

A

Different plants and animals that are better adapted for improved conditions move in & out-compete plants and animals already there & become dominant species in ecosystem

47
Q

Primary Succession

As succession goes on, ______ increases

A

biodiversity

48
Q

Primary Succession

Name and describe the final stage

A
  • Climax community
    • Ecosystem is supporting the largest and most complex community of plants and animals it can
    • Won’t change much = in steady state
49
Q

Secondary succession happens in same way but at a ___ stage

A

later

Pioneer species are larger plants e.g. shrubs

50
Q

What is meant by plagioclimax?

A

When succession is stopped artificially (e.g. by humans), climax community its called plagioclimax

51
Q

How are ecosystems conserved?

A

Succession is prevented to preserve an ecosystem in its current stage of succession

52
Q

Name 2 ways to manage succession to conserve moorland ecosystem

A
  • Animals are allowed to graze on land
  • Managed fires
53
Q

Describe how allowing animals to graze on land can manage succession

A

(Similar to mowing) = growing points of shrubs and trees eaten = stops them establishing themselves & keeps vegetation low

54
Q

Describe how having managed fires can manage succession

A
  • After fires = secondary succession will occur
  • & species that grow back first (pioneer species) are being conserved
  • Larger species will take longer to grow back & will be removed when moor is burnt
55
Q

Define Conservation

A

Protection and management of species and habitats in sustainable way

56
Q

Name and describe 4 examples of conservation techniques

A
  • Protected areas (e.g national parks & nature reserves) protects habitats
    • Restrict urban development, industrial development & farming
  • Using seedbanks to conserve plants
    • They’re stores of lots of seeds from lots of different plant species
    • If they become extinct = can be replanted
  • Fishing quotas
    • Limits to amount of a fish species fishermen can catch
    • Reduces no. caught & killed
  • Endangered species can be bred in captivity
    • to increase their numbers & then returned to wild
57
Q

Describe how you would investigate the effect of competition on seedling growth

A
  1. Divide base of Petri dish into 8 equal segments. Do this for 5 dishes.
  2. Place filter paper in each Petri dish & same amount of water (just enough so the paper is wet)
  3. In 1st Petri dish, place 1 seed in the middle of each segment
    • Continue placing seeds in the rest of the Petri dishes, increasing the number of seeds in each segment each time by 1
  4. Place lids on Petri dishes
    • Put all dishes together in dark cupboard
  5. Observe the seeds at same time each day & count how many seeds have germinated
  6. After 3 days, remove seedlings & measure the growth of shoot and root
  7. Record results in table & carry out statistical test to see if there’s a significant difference in germination and initial growth in the seedlings at different densities of sowing
58
Q

When investigating the effect of competition on seedling growth, name 4 precautions you should take

A
  • Wash hands
  • Use boiled water
  • Don’t handle seeds and there should be minimal handling of the inside of Petri dishes and filter papers
  • Petri dishes should be clean/sterile

All to destroy/prevent the spread of micro-organisms

59
Q

When using the mark-release-recapture method, why is it important that the samples contain as many organisms as possible? (2)

A
  • More organisms in sample = improve accuracy of estimate
  • ∵ calculation assumes a constant ratio between total number of marked and unmarked individuals
60
Q

What is meant by uniformly distributed (1)?

A

Same number (of organisms) in each region / (organisms) equally spread

61
Q

The pioneer plants had seeds that germinate better when the temperature fluctuates. Explain the advantage of this to these pioneer plants. (2)

A
  • Bare soil temperatures fluctuate
  • More bare soil, early / at start of succession / when few plants

AQA A Level Biology (41 decks)

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