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Biology A2 UNIT 4 > Populations > Flashcards

Populations Flashcards

1
Q

Ecosystem

A

More or less self-contained functional unit it ecology made up of all the interacting biotic (living) and abiotic (non-living) features in a specific area.

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2
Q

What are the two major processes to consider in an ecosystem?

A
  • Flow of energy through the system

- The cycling of elements within the system

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3
Q

Population

A

A group of interbreeding organisms of one species in a habitat.

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4
Q

Biosphere

A

Land, air and water surrounding earth.

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5
Q

Why are the boundaries of a population often difficult to define?

A

The same species may live too far away to breed so are separate populations, however others that are equally far away may find it more easy to breed as they can travel further so are one population.

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6
Q

Community

A

The organisms of all species that live in the same area.

All the populations of different organisms living and interacting in a particular place at the same time.

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7
Q

Habitat

A

The place where a community of organisms live.

Many habitats within an ecosystem.

The place where an organism normally lives, which is
characterised by physical conditions and the species of other organisms present.

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8
Q

Microhabitats

A

Smaller units within a habitat.

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9
Q

Ecological niche

A

All conditions and resources required for an organism to survive, reproduce and maintain a viable population.

A niche describes how an organism fits into an environment, refers to where an organism lives and what it does there.

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10
Q

Why do no two species occupy the same niche?

A

Nesting habits or other aspects of behavior.

Different levels of tolerance to environmental factors, such as a pollutant or a shortage of oxygen or nitrates.

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11
Q

Abundance of species

A

The number of individuals of a species in a given space.

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12
Q

3 factors to consider when using quadrats.

A
  1. Size of quadrat to use- depends on size of plants or animals being counted and how they are distributed within the area. Larger species require larger quadrats. Where a species occurs in a series of groups rather than being evenly distributed, a large number of small quadrats will give more representative results.
  2. the number of sample quadrats to record within the study area- Larger number more reliable results. Balance time and validity. The greater the number of species in area, the greater the number of quadrats required.
  3. The position of each quadrat within study area- To produce statistically significant results a technique called random sampling used.
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13
Q

Why is random sampling important? And what does it ensure?

A

To avoid bias in collecting data. Ensures data is valid .

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14
Q

How do you make samples random? (EXAMPLE)

A
  1. Lay out two long tape measures at right angles, along two sides of study area.
  2. Obtain series of coordinates by using random numbers taken from table or generated by computer.
  3. PLace quadrat at the intersection of each pair of coordinates and record species within.
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15
Q

When is systematic sampling better than random sampling?

A

TRANSITION IN COMMUNITIES OF PLANTS AND ANIMALS TAKES PLACE.

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16
Q

What is a line transects?

A

String or tape stretched across the ground in a straight line. Any organism over which the line passes is recorded.

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17
Q

What is a belt transect?

A

A strip, usually a meter wide, marked by putting a second line parallel to the first. Species occuring within belt are recorded.

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18
Q

What is frequency?

A

The likelihood of a particular species occurring in a quadrat. Eg. species occurs in 15 out of 30 quadrats its frequency s 50%.

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19
Q

When is frequency useful?

A

When a species, such as grass, is hard to count. It gives a quick idea of the species present and their general distribution.

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20
Q

What does frequency not show?

A

Does not provide info on the density and detailed distribution of a species.

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21
Q

What is percentage cover?

A

An estimate of the area within a quadrat that a particular plant species covers.

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22
Q

When is percentage cover useful? Why

A

Where a species is particularly abundant or is difficult to count. Data collected quickly and individual plants do not need to be counted.

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23
Q

When is percentage cover less useful?

A

Where organisms occur in several overlapping layers.

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24
Q

How do you obtain reliable results?

A

Make sure sample size is large (many quadrats used). The more used, the more representative it will be of community as a whole.

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25
Q

Why are quadrat not useful for most animals?

A

They are mobile, move away when approached. HIdden

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26
Q

Describe mark release recapture.

A

Known number of animals caught, marked and released back into community. Some time later, a given number of individuals are collected randomly and number of marked recorded.

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27
Q

From mark release recapture how do you estimate pop. size?

A

tot. no. indiv. in 1st sample X to. number of indiv. in 2nd sample/ no. marked individual recaptured.

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28
Q

What does mark release recapture assume? (6)

A
  • The proportion of marked to unmarked individuals in 2nd sample is same as proportion marked to unmarked individuals in the population as a whole.
  • The marked individuals released from the first sample distribute themselves evenly among the remainder of the population and have sufficient time to do so.
  • The population has a definite boundary so that there is no migration.
  • There are few, if any deaths and births within pop.
  • The method of marking is not toxic nor make it more conspicuous to predators.
  • Mark or label not lost or rubbed off.
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29
Q

What can statistical test be used for?

A

To calculate the strength and direction of a correlation.

Difference between data due to chance.

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30
Q

How to keep fieldwork ethical.

A
  • Where possible, the organisms should be studied in situ. If it is necessary to remove them, numbers taken kept to minimum.
  • Organisms removed should be replaced to original habitat asap. Even if dead.
  • A sufficient period of time should elapse before site is used for future studies.
  • Disturbance and damage to habitat avoided
31
Q

Describe the 3 phases of the usual pattern of growth for a natural population.

A
  1. Period of slow growth as initial small number of individuals reproduce too slowly to build up numbers.
  2. Period of rapid growth where the ever increasing number of individuals continue to reproduce. Pop. size doubles during each interval of time.
  3. Period when pop. growth declines until its size remains more or less stable. Decline may be due to food supply limiting numbers or increased predation. Graph levels out with only cyclic fluctuations due to variations in factors such as food supply and pop. size of predators.
32
Q

What do biotic and abiotic factors influence?

A

The rate of growth and final size of a population.

33
Q

ABIOTIC FACTORS

A

Concerned with non-living part of environment.

34
Q

BIOTIC FACTORS

A

Concerned with activities of living organisms

35
Q

What conditions influence the size of a population? (4)

A
  1. Temperature- Each species has a different optimum temperature at which it is best able to survive. The further away from this temp. the smaller the population that can be supported.
  2. Light- Ultimate source of energy for an ecosystem. Rate of photosynthesis increase as light intensity increases. Greater rate of photosynthesis the faster plants grow and more spores or seeds they produce. Pop. size and growth potentially greater.
  3. pH- Affects action of enzymes. Each enzyme has an optimum pH. A population of organisms is larger where the appropriate pH exists and smaller, or non- existent, where pH is different from optimum.
  4. Water and humidity- Where water is scarce, pops. are small and consist only of species that are well adapted to living in dry conditions . Humidity affects transpiration rates in plants and the evaporation of water from the bodes of animals .
36
Q

How does a fall in temperature from optimum affect cold blooded animals, and plants?

A

Enzymes work more slowly so metabolic rate is reduced. Population grows more slowly.

37
Q

What happens when temperature exceeds optimum?

A

Enzymes work less efficiently as they gradually denature . Pop. grows more slowly.

38
Q

How does temperature change from optimum affect warm blooded animals?

A

Warm blooded animals can regulate their temperature, so stays relatively constant , however the further temp gets from optimum the more energy they expend on temp. regulation. Leaves less energy for individual growth so mature more slowly and reproductive rate slows.

39
Q

INTRASPECIFIC COMPETITION

A

When individuals of the SAME species compete with one another for resources such as food, water, breeding sites, etc.

40
Q

EXAMPLES of intraspecific competition.

A
  • Limpets competing for algae
  • oak trees competing for resources- light, water and minerals. Dominant survive.
  • robins competing for breeding territory. Female bird usually only attracted to males with established territory.
41
Q

INTERSPECIFIC COMPETITION

A

When individual of DIFFERENT species compete for resources. When two species initially occupy the same niche, one will normally have a competitive advantage over the other. Pop. of this species gradually increase while other diminishes. If conditions remain the same, it will lead to complete removal of one species. COMPETITIVE EXPULSION PRINCIPLE.

42
Q

What is the competitive expulsion principle?

A

Two species competing for limited resources, the one that uses these resources most effectively will ultimately eliminate the other. No two species can occupy the same niche indefinitely when resources are limiting.

43
Q

How do you show that a factor influences the size of a population?

A

Necessary to link it to birth rate and death rate of individuals in population. Say how it increases/ decrease population.

44
Q

PREDATOR

A

An organism that feeds on another organism- their prey.

45
Q

PREDATION

A

Occurs when one organism is eaten by another.

46
Q

Why do populations of prey rarely become extinct?

A

The area over which the population can travel is large and diverse environment. More potential refuges. Some prey can escape predation.

47
Q

What is wrong/ good with evidence collected on prey and predator populations in a lab?

A

Not necessarily reflective to wild.

Difficult to obtain reliable data on natural populations because can;t count all individuals.

48
Q

Describe the relationship between predators and prey and effect on populations size.

A
  • Predators eat prey, thereby reducing the pop. of prey.
  • With fewer prey available predators are in greater competition with each other for prey that are left.
  • The predator population is reduced as some individuals are unable to obtain enough prey for survival.
  • Fewer predators so fewer prey eaten.
  • Pop. of prey increases
  • More prey now available so predator population increases.
49
Q

Why are periodic crashes in population important in evolution?

A

Creates a selection pressure whereby those individuals who are able to escape predators, or withstand disease or an adverse climate, will survive to reproduce. Population therefore evolves to be better adapted to prevailing conditions.

50
Q

What two things have led to massive recent massive increase in human population?

A
  • Agricultural revolution.

- Development of manufacturing and trade that created the industrial revolution.

51
Q

What is different about the human population growth curve to that of other organisms?

A

Does not stabilise, continues to grow.

52
Q

Factors affecting growth and size of human population.

A

-Birth rate
-Death rate
Balance between these two that determines where population increase, decreases or stays the same.
-Migration
– Immigration- individuals join a pop.
– Emigration- individuals leave pop.

53
Q

How do you work out human population growth?

A

(Births + Immigration)-(Deaths + Migration)

54
Q

How do you work out human percentage population growth(in given period)?

A

pop. change during period/pop. at start of period X 100

55
Q

What is human birth rate affected by? (5)

A
  • Economic conditions- LECs tend to have higher birth rates.
  • Cultural and religious backgrounds- Some cultures encourage larger families and some religions are opposed to birth control.
  • Social pressures and conditions- n some countries a large family improves social standing.
  • Birth control- The extent to which contraceptives and abortion are used.
  • Political factors- Governments influence birth rates through education and taxation policies.
56
Q

How do you work out human birth rate?

A

number of births per year/total population in same year X 100

57
Q

Factors affecting death rate. (7)`

A

Age profile- the greater the proportion of elderly in a po. the higher the death rate.

  • Life expectancy at birth- HICs have higher life expectancy.
  • Food supply- An adequate and balanced diet reduces death rate.
  • Safe drinking water and effective sanitation= reduce death rate by reducing risk of contracting water-borne diseases such as cholera.
  • Medical care- Access to healthcare and education reduces death rate.
  • Natural disasters- The more prone a region the higher the death rate.
  • War- Death during wars produce and immediate drop in population and a longer term fall as a result of fewer fertile adults.
58
Q

What is demographic transition?

A

Change in societies, from those where life expectancy is short and birth rate high to those whose life expectancy is long and birth rate low.

59
Q

What does demographic transition lead to ?

A

Levelling off of the population and the re-establishment of the typical sigmoid pop. growth curve.

60
Q

Describe a stable population.

A

Birth rate and death rate are in balance and so no increase or decrease in population size.

61
Q

Describe an increasing population. (age pop. pyramid)

A

High birth rate so wide base (compared to stable) and fewer old people (low life expectancy) so narrower apex. Typical of LICs

62
Q

AVERAGE LIFE EXPECTANCY

A

The age at which 50% of the individuals in a particular population are still alive.

63
Q

Give an example of how two organisms occupy a different niche (bats)

A

Common pipistrelle bat:
This bat lives throughout Britain on farmland, open woodland, hedgerows and urban areas. It feeds by flying and catching insects using echolocation at a frequency of around 45kHz.

Soprano pipistrelle bat:
This bat lives in woodland areas, close to lakes or rivers. It feeds by flying and catching insects using echolocation, at a frequency of 55kHz.

64
Q

ADAPTATION

A

A feature that members of a species have that increases their chances of survival and reproduction.

65
Q

Examples of adaptations to abiotic conditions.

A
  • Otters have webbed paws- walk on land and swim effectively. Live and hunt on land and water.
  • Whales have a thick layer of blubber- warm in cold sea.
  • Brown bears hibernate- Lower their metabolism over winter. Conserve energy during cold months.
66
Q

Examples of adaptations to biotic conditions.

A
  • Sea otters use rocks to smash open shellfish and clams. Access to another food source.
  • Scorpions dance before mating. Makes sure they attract a mate of the same species. Successful reproduction.
  • Some bacteria produce antibiotics.these kill other species of bacteria in the same area. Less competition.
67
Q

BIRTH RATE

A

The number of live births each year for every 1000 people in the population

68
Q

DEATH RATE

A

The number of people that die each year for every 1000 people in the population.

69
Q

Describe and explain stage 1 of the demographic transition model.

A

Birth and death rate fluctuate at a high level. The population stays low.
Birth rate is high because there’s no birth control or family planning and education is poor.
High infant mortality , so parents have more children so enough survive to work on farms, as well as look after them in later life.

Death rate is high because there’s poor health care, sanitation and diet, leading to disease and starvation.

70
Q

Describe and explain stage 2 of the demographic transition.

A

Death rate falls, birth rate remains high. The population increases rapidly.
Death rate falls because health care, sanitation and diet improve.
Birth rate remains high because there is still little birth control or family planning.

71
Q

Describe and explain stage 3 of the demographic transition.

A

Birth rate falls rapidly, death rate falls more slowly. Population increases at slower rate.
Birth rate falls rapidly because the increased use of birth control and family planning.
Also, the economy becomes more heavily based on manufacturing rather than agriculture, so fewer children need to work on farms.

72
Q

Describe and explain stage 4 of the demographic transition.

A

Birth rate and death rate fluctuate at a low level. The population remains stable but high.
Birth rate stays low because there’s an increased demand for luxuries and material possessions, so less money available to raise children.
They do not need to work to provide income, so parents have fewer children.

73
Q

Describe and explain stage 5 of the demographic transition.

A

Birth rate begins to fall, death rate remains stable. Population begins to decrease. Birth rate falls because children are expensive to raise and people often have dependent elderly relatives.
Death rate remains steady despite continued health care advances as larger generations of elderly people die.

74
Q

What does a survival curve show?

A

The percentage of all the individuals that were born in a population that are still alive at any given age.

Biology A2 UNIT 4 (8 decks)

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