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AQA A Level Biology > 3.7- Chapter 19- Populations in Ecosystems > Flashcards

3.7- Chapter 19- Populations in Ecosystems Flashcards

1
Q

What factors affect populations and communities?

A
  • Competition for survival occurs between and within populations.
  • Populations within communities are affected by biotic (competition, predation) and abiotic (temperature, rainfall) factors in an ecosystem.
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2
Q

What are ecosystems?

A

Dynamic systems made up of a community and non-living factors. e.g. a pond.

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3
Q

Describe the features of ecosystems?

A
  • There is little to no net loss or gain between natural ecosystems- most substances are recycled.
  • Can be very large to very small
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4
Q

What major process occur in ecosystems?

A
  • The flow of energy through the system- energy is transferred.
  • The recycling of elements within the system.
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5
Q

What is a community?

A
  • Populations of different species form a community.
  • All the populations of different species living together and interacting at a particular place at the same time.
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6
Q

What is a population?

A

A group of individuals of one species that occupy the same habitat at the same time and can potentially interbreed.

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7
Q

Why is a population often difficult to measure or define?

A
  • The boundaries of a population are often difficult to define.
  • Populations are dynamic and vary in size and composition over time.
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8
Q

What is the carrying capacity?

A
  • The size of population of a species an ecosystem supports.
  • This size in population can be sustained over a relatively long period.
  • Determined by limiting factors.
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9
Q

Why do population sizes vary?

A
  • Due to the effect of abiotic factors
  • Due to interactions between organisms- interspecific and intraspecific competition and predation.
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10
Q

What is a habitat?

A
  • The place where an organism normally lives.
  • Characterised by physical conditions and other types of organisms present.
  • Within an ecosystem there are many habitats.
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11
Q

What are microhabitats?

A
  • Smaller units within habitats with their own microclimate.
  • e.g. mud at the bottom of the stream- microhabitats for bloodworms.
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12
Q

What is an ecological niche?

A
  • Within a habitat, a species occupies a niche governed by adaptation to both abiotic and biotic conditions.
  • The niche describes how the organism is adapted to its environment to survive reproduce, and maintain a viable population..
  • The niche includes where an organism lives and what it does there.
  • Some species may appear very similar but their behaviour may be different due to different levels of tolerence to environmental factors.
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13
Q

What is the competitive exclusion principle?

A

No two species can occupy the same niche- the competition means one will not be able to outcompete the other and will die out.

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14
Q

When is it possible/ not possible to plot a population growth curve?

A
  • Where a population grows in size slowly- can plot a graph of population against time.
  • Rapid population in short period of time- hard to plot growth curve e.g. micro-organisms.
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15
Q

How can we mitigate the large population size differences in the population growth of bacteria?

A

Use a logarithimic scale- easier to see patterns.

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16
Q

What is the population size?

A

The number of individuals in a population.

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17
Q

How does population size vary in a population growth curve of photosynthetic bacteria.

A
  1. Initially when there are good conditions, the population increases rapidly because all the factors needed for growth are persent and there is no limiting factors.
  2. Over time, more nutrients are consumed as the population becomes larger, the population becomes so large the bacteria prevent light reaching those at lower levels, other species may be introduced and compete for the same resources as the bacteria or predate on bacteria, and wintery conditions may bring lower light intensity, making conditions tought.
  3. The growth of hte population slows and then stops.
  4. The population size sometimes then decreases
  5. The population then reaches a constant size until conditions change and factors improve to increase growth again.
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18
Q

What affects population size?

A
  • Many biotic and abiotic factors.
  • Changes in these factors influence the rate of growth and size of the population.
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19
Q

Why does no population grow indefinitely?

A
  • Factors limit growth- e.g. food, water etc.
  • Accumulation of toxic wastes, disease and predators limit growth.
  • The population stays within the carrying capacity of its ecosystem.
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20
Q

Name the main abiotic factors that can affect population growth.

A
  • Temperature
  • Light
  • pH
  • Water and humidity
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21
Q

How does temperature affect population size?

A
  • Each species has a different optimum temperature where it survives best
  • Further from optimum= few individuals are able to survie= smaller population.
  • Especially affects plants and cold-blooded animals- if fall below optimum- enzymes work more slowly- metablic rate reduced- smaller carrying capacity.
  • Above optimum- enzymes work less efficiently and denature- carrying capacity and population size reduced.
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22
Q

How do changes in temperature affect warm-blooded animals?

A
  • Warm blooded animals- birds and mammals- maintain constant body temperature regardless of external temperature.
  • Extreme temperature changes from the optimum- mean more energy expended trying to maintain normal body temperature.
  • Less energy for individual growth- mature more slowly and reproductive rate slows.
  • Carrying capacity and population size reduced.
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23
Q

How does light impact population size?

A
  • Light is the main source of energy for most ecosystems- basic necessity of life.
  • Rate of photosynthesis increases as light intensity increases.
  • Faster photosynthesis= faster plant growth and more seeds.
  • Carrying capacity greater and carrying capacity of animals that feed on the plants greater.
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24
Q

How does pH impact population size?

A
  • Affects the action of enzymes.
  • Enzymes- have optimum pH where work most effectively.
  • Population of organisms larger where the right pH exists and smaller where pH is different from the optumum.
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25
Q

How does water and humidity impact population size?

A
  • Low water= small population- only species adapted to dry conditions
  • Humidity- affects transpiration rates of plants and evaporation rates of water from animals.
  • Dry condidtions- populations adapted to tolerate low humidity large than those with no adaptions.
  • Carrying capacity of adapted populations greater.
26
Q

What is the general rule for how abiotic factors affect population?

A
  • When abiotic factors are below the optimum- fewer individuals are able to survive- adaptions not suited to conditions.
  • If no individuals have adaptions to survive- the population becomes extinct.
27
Q

What biotic factors mostly affects the population size and carrying capacity and describe it.

A
  • Interspecific and Intraspecific competition
  • Predation
  • Pathogens
28
Q

What is competition?

A

Two or more individuals share a resource that is in insufficient quantity to satisfy their needs.

29
Q

What are the two types of competition and describe them.

A
  • Intraspecific competition- competition between members of the same species
  • Interspecific competition- competition between members of different species.
30
Q

Describe intraspecific competition?

A
  • Individuals of the same species compete for resources.
  • The availablity of resources determines population size- more= larger population and v.v.
  • Availabilty of resources affects the degree of competition of individuals- larger results in smaller population.
  • This competition can also lead to evolution of the speices and adaptions.
31
Q

Describe interspecific competion.

A
  • Different species compete for resources.
  • One species usually has a competitive advantage- this population increases while the other population decreases
32
Q

Describe the competitive exclusion principle.

A
  • In interspecific competition, species usually has a competitive advantage- this population increases while the other population decreases.
  • If conditions remain the same- this will lead to the complete removal of one species.
  • In competition for limited resources- the species that uses these resources most effectively will ultimately eliminate the other.
  • This only occurs when two species occupy the same niche- habitat, food etc.
  • If species occupy different niches e.g. similar but eat different foods- competitive exclusion can’t happen.
  • No two species can occupy the same niche for a long time without one species eliminationg the other.
33
Q

How must you describe factors in relation to the the population size?

A
  • Link the birth and death rates of individuals in a population.
  • e.g. increase in food- doesn’t mean more individuals just bigger individuals- so have to show what it means e.g. more food= more likely to survive and reproduce so population increases.
  • This means effects usually take longer to influence the population size- there is a time lag.
34
Q

Describe the predator- prey relationship

A
  • Interspecific relationship
  • Predation occurs when one organism is consumed by another.
  • Predator- feeds on another organism
  • Prey- fed on by another organism.
35
Q

Why is evolution important for predators and prey?

A
  • As predators have become more evolveed and better adapted at catching prey, prey have evolved to become better at escaping predators.
  • Predators and prey evolve together.
  • If predators and prey do not adapt one may become extinct, which may lead to the extinction of the other.
36
Q

Why are habitats important for predator- prey relationships?

A
  • If prey and predator are brought together in a lab, they prey exterminates the predator- demonstrating habitats are important for survival of prey.
  • In habitats, the area a population can travel is greater and the variety of environment is more diverse- more potential refuges- prey can escape predation because they are harder to find and catch and rarely become extinct.
37
Q

Why is it hard to study predator-prey relationships?

A
  • Can’t be studied in a lab as doesn’t reflect what happens in the wild.
  • Not possible to count all individuals in a population- population can only be estimated- no guarantee of accuracy- data must be treated with caution.
38
Q

How does the predator-prey relationship affect population size cyclically?

A
  1. Predators eat prey, reducing prey population
  2. With fewer prey, the predators have greater competition.
  3. The predator population is reduced as some are unable to obtain enough prey to survive and reproduce.
  4. With few predators left, fewer prey are eatern and more survive and reproduce so the prey population increases.
  5. With more prey for food, the predator population increases.
39
Q

Why is it hard to reflect predator-prey relationships with data?

A
  • Other factors, such as the prey’s food supply, disease and climatic factors may be affecting results
  • Predators eat a range of foods so the predator and prey aren’t directly linked
40
Q

Describe how the predator prey population changes graphically?

A

Predator and prey populations cyclically fluctuate

41
Q

How does the predator prey relationship influence evolution?

A
  • Population crashes are important for evolution
  • Fluxuations create selection pressues- individuals who escape predators,, catch prey, or withstand disease/ bad climate- more likely to survive and reproduce.
  • The population becomes better adapted to conditions
42
Q

What is the number of individuals of a species in a given space known as?

A

Abundance

43
Q

Why is abundance hard to measure.

A
  • It’s impossible to count every organism
  • Counting organisms is time-consuming an dcan damage habitats.
44
Q

How is abundance usually measured?

A
  • Small samples are studied in detail.
  • Samples should be representative of the wholoe habitat so conclusions are reliable.
45
Q

What sampling techniques can be used to study habitats?

A
  • Random sampling using frame/ point quadrats
  • Systematic sampling along a belt transect.
46
Q

Describe the different types of quadrats.

A
  • Frame quadrat- square frame- divided into equally sized subdivisions. Placed in different locations in the area and the abundance of each species is recorded- sometimes individually or sometimes as percentage cover.
  • A point quadrat- horizontal bar with two legs- holes at set interviews where pins dropped- what pin touches is recorded.
47
Q

What factors must be considered when using quadrats?

A
  • Size of quadrat- depends on size of plant/ animals counted and distribution- larger= larger quadrats. If species not evently distributed- large number of small quadrats- more representative than small number of large quadrats.
  • Number of quadrats- more= more reliable. Balance needs to be reached iwth time constraints. GGreater number of species- greater number of quadrats for reliable results.
  • Position of quadrats- must be random.
48
Q

Why is random sampling important?

A

Avoids bias which ensures the adata is reliable.

49
Q

How do you obtain a random sample with quadrats?

A
  1. Use two long tape measures at random.
  2. Obtain random coordinates randomly generated
  3. Place a quadrat at the coordinates and record the species.
50
Q

Why is sytematic sampling sometimes better than random?

A

Good to measure gradual changes throughout a habitat and the effects of them- especially along lines of succession.

51
Q

How is systematic sampling achieved in habitats.

A
  • Transects- used to show stages of sucession.
  • Achieved by laying a tape measure straight across the ground.
  • A quadrat is laid along the line at equal intervals adn the species within it is recorded.
52
Q

What is abundance?

A

Number of individuals within a species within a given area.

53
Q

How do measurements of abundance vary?

A

Depends on whether species move around.

54
Q

How can abundance be measured (numerically)?

A
  • Frequency- whether a species is encountered in a quadrat and how many it occurs in- then put over the total amount of quadrats e.g. 5/10 is 50%. Useful if species are hard to count. Quick and easy. Doesn’t provide detailed information on distribution and density.
  • Percentage cover- estimate of area in a quadrat that a plant species covers- useful when a species is abundant. Data can be collected rapidly and individual plants don’t need to be counted but less useful when organisms overlap.
55
Q

How are reliable results obtained?

A
  • Large sample size- many quadrats used- mean of all samples obtained.
  • Larger the number of samples= more representative of the community.
56
Q

Why can quadrats and transects not be used to measure the abundance of all organisms?

A
  • Quadrats and transects are good to measure plants and non-moving or slow moving animals.
  • Can’t measure motile organisms as move away when approached, are often hidden adn are difficult to find and identify.
57
Q

What method is used to measure the abundance of motile organisms?

A

Mark-release-recapture

58
Q

How does mark release recapture work?

A
  • A known number of animals are caught.
  • The animals are marked
  • The animals are relased back into the community.
  • Later, a given number of indiiduals is collected randomly and the number of marked individuals is recorded.
59
Q

What is the equation for mark-release-recapture?

A

Estimated population size= No. individuals in 1st sample x no. individuals in the 2nd sample/ No. individuals recaptured.

60
Q

What assumptions are made in mark- release- recapture?

A
  • The proportion of marked to unmarked individuals in the 2nd sample is hte same as the proportion of marked to unmarked individuals in the population as a whole.
  • The marked individuals distribute themselves evenly amongst the rest of the population.
  • The population does not immagrate or emigrate.
  • There are few deaths.
  • The method of marking isn’t toxic or doesn’t make the individual less camoflaged.
  • The mark isn’t rubbed off during investigation.

AQA A Level Biology (7 decks)

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