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Biology Unit 4 > Populations > Flashcards

Populations Flashcards

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1
Q

Define ‘ecology’

A

The study of inter-relationships between organisms and thier enironment (inc. biotic and abiotic factors)

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2
Q

Define ‘biosphere’

A

The part of the planet where life occurs - layer of land, air and water

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3
Q

Define ‘ecosystem’

A

A self-contained area together with all of its organisms - there are two major processes within an ecosystem; the flow of energy and the cycling of elements

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4
Q

Define ‘habitat’

A

The physical/abiotic part of an ecosystem where a community of organisms live - most ecosystems have many habitats

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5
Q

Define ‘microhabitat’

A

A localised specific habitat within a larger habitat

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6
Q

Define ‘biotic’

A

A living or biological factor

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7
Q

Define ‘abiotic’

A

A non-living or physical factor

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8
Q

Define ‘population’

A

The members of the same species living in one habitat at the same time - often the boundaries of a population are difficult to define

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9
Q

Define ‘community’

A

The organisms of all species that live in the same area at the same time

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10
Q

Define ‘species’

A

A group of organisms that can successfully reproduce to produce fertile offspring

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11
Q

Define ‘niche’

A

How an organism fits into the environment (where it lives and what it does there) - no two species occupy the same niche

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12
Q

Define ‘abundance’

A

The number of individuals of a species within a given space

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13
Q

Why are samples taken?

A

Counting every organism is time consuming and damaging to habitat

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14
Q

Define a method of random sampling

A
  • Lay out two tape measures at right angles along two sides of the study area
  • Obtain a series of coordinates from a random number generator
  • Place a quadrat at the intersection of each set of coordinates and record the spieces wihtin it
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15
Q

What factors need to be considered when using quadrats?

A
  • The size of the quadrats used
    The number of the sample quadrats to record
  • The position of each quadrat eg, random sampling produces statistically significant results
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16
Q

Define ‘distribution’

A

Where a particular species is within the area being investigated

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17
Q

What is a line transect?

A

Comprises a string/tape stretched across the ground in a straight line and any organism which touches the string/tape is recorded - quick method but can be unrepresentative

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18
Q

What is a belt transect?

A

A strip - usually 1 metre wide - which is marked by putting a second line parallel to the first. The species occuring within the belt between the two lines are recorded

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19
Q

What is a point quadrat?

A

A horizontal bar supported by two legs. At set intervals along the horizontal bar are ten holes which a pin can be dropped through. Each species that the pin touches is then recorded.

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20
Q

What is a frame quadrat?

A

A square frame divided equally into subdivisions by string/wire. The quadrat is places in different locations within the area being studied and the abundance of each species within the quadrat is recorded.

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21
Q

State two methods of measuring abundance

A
  • Frequency (liklihood of a particular species occuring in a quadrat)
  • Percentage cover (an estimate of the area within the quadrat that a particular species covers)
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22
Q

When is systematic sampling used?

A

If you are investigating a specific pattern within an ecosysten then systematic sampling would be used as you can choose where to take samples from

23
Q

Describe 2 techniques used to sample animals

A
  • Sweep nets (used to capture insects above grass land by using a large net)
  • Beating trays (collect organsisms in a tray after shaking canpoy such as a tree)
24
Q

Outline the mark-release-recapture method

A
  • Capture a known number of animals using a trap technique
  • Mark the animals and release them back into their original community
  • Some time later, a given number of individuals are collected randomly and the number of marked individuals is recorded
25
Q

How would you calculate the size of a population from the mark-release-recapture method?

A

Estimated population size = (total number of individuals in 1st sample x total number of individuals in 2nd sample) / number of marked individuals recaptured

26
Q

Assumptions of the mark-release-recapture method

A
  • Proportion of mark to unmarked individuals in 2nd sample is the same as in the whole population
  • Marked individuals from 1st sample have enough time to redistibute themselevs evenly
  • Population has definite boundaries (no immigration/emigration)
  • Marking mehtod is not toxic and will not make individuals more liable to predation
  • Mark does not rub off
27
Q

What is the usual pattern of growth for a natural population?

A
  • Period of slow growth as the initially small number of individuals reproduce slowly and build numbers
  • Period of rapid growth where individuals continue to reproduce
  • Period when the population growth fluctuates due to food supply and population size of predator but stays more or less stable
28
Q

Define ‘population density’

A

A measure of the number of organisms that make up a population in a defined area

29
Q

How can data be analysed?

A
  • Present data in table/graph to compare easily
  • Calculate SD to give range of values around the mean
  • Spot correlations (not causations as many factors contribute towards differences)
  • Statistically analyse data to reduce effect of chance and calculate strength/direction of any correlation eg, Spearman rank correlation
30
Q

Explain some abiotic factors

A
  • Temperature - enzymes/denature/optimum temperature
    Warm-blooded animals can maintain relatively constant body temperatures but the further the outside temperature gets from their optimum temperature, the more energy they use to maintain their normal body temperature, the less energy for individual growth and reproduction
  • Light - ultimate source of energy
    (higher intensity > increased rate of photosynthesis > faster plant growth/more seeds and spores produced thus increasing plant population and growth > population of animals feeding on plants increases
  • pH - affects enzymes
  • Water/humidity - little water means small populations mainly organisms adapted to living in dry conditions
    Humidity affects transpiration and evaporation of water from bodies of animals thus more populations of species which are adapted to tolerate low humidity (dry air conditions) are present
31
Q

Advantages of measuring abiotic factors

A
  • Quick
  • Quantitative
  • Accurate
  • Can be automatically recorded at regular time intervals over a period of time
  • Data can be transferred to computers for storage
32
Q

State some biotic factors

A
  • Predation
  • Competition - intra/interspecific
  • Migration - immigration/emigration
33
Q

Describe interspecific competition

A

Usually one species will out-compete another within the same niche as one species will have an advantage over the other and will increase in size while the other will be reduced and can be completely removed - COMPETITIVE EXCLUSION PRINCIPLE

34
Q

Describe intraspecific competition

A

Members have the same niche so will compete for the same resources
Intraspecific competition increases if the population gets too big and decreases if the population gets too small

35
Q

Why is it difficult to prove that competition is the reason for variations in populations?

A
  • Other factors influencing the population size eg, abiotic factors
  • A casual link has to be established to show correlation
  • Often a time lag so population change may be due to competition years earlier
  • Data on natural population sizes are hard to obtain and not always reliable
36
Q

What is a predator?

A

An organism that feeds on another organism (known as prey)

37
Q

Why is it a good thing that predators and prey have evolved together?

A

To prevent extinction

38
Q

Define ‘selection pressure’

A

Individuals able to withstand disease/escape predators will survive and reproduce so the population will evolve and become better adapted

39
Q

What two major events have led to an explosion in the human population?

A
  • The development of agriculture

- The development of manufacturing and trade that created the industrial revolution

40
Q

What have temporarily reversed this upward trend?

A

Wars, disease and famine

41
Q

What four factors does the increase in population/population rate depend on?

A

Immigration, emigration, birth rates and death rates

42
Q

What is the equation for calculating growth rate?

A

Growth rate = (birth rate - death rate) + (immigration rate - emigration rate)

43
Q

What is the equation for calculating the percentage population growth in a given period?

A

(population change during the period / population at the start of the period) x 100

44
Q

Define ‘demographic transition’

A

A change in society from short life expectancy and high birth rates to long life expectancy and low birth rates
It leads to the levelling-off of the population and the establishment of the typical sigmoid population growth curve

45
Q

What are factors affecting birth rates?

A
  • Economic conditions
  • Cultural/religious backgrounds
  • Social pressures/conditions
  • Birth control
  • Political factors (education/taxation policies)
46
Q

What is the equation to calculate birth rate?

A

Birth rate = (no. of births per year / total population in the same year) x 1000

47
Q

What are factors affecting death rates?

A
  • Age profile (higher proportion of elderly = higher death rates)
  • Life expectancy (LEDC/MEDC)
  • Food supply (balanced diet)
  • Safe drinking water/effective sanitation (cholera)
  • Medical care
  • Natural disasters
  • War (immediate drop in population and longer term fall due to less fertile adults)
48
Q

What is the equation to calculate death rate?

A

Death rate = (no. of deaths per year / total population in the same year) x 1000

49
Q

What does the future size of the population depend upon?

A

The number of females of child-bearing age

Therefore it is useful t know the age and gender profile of a population

50
Q

What is a population pyramid?

A

Gives information about the future growth of the population and about life expectancy
The wider the base, the faster the population growth, a narrow base shows a falling population

51
Q

Three main pyramids

A

Stable population - birth/death rates are in balance so no increase/decrease in population
Increasing population - high birth rate and fewer older people (often LEDC)
Decreasing population - lower birth rate and a lower mortality rate (often MEDC)

52
Q

Define a ‘survival curve’

A

Plots the number of people alive as a function of time - typically plots the percentage of a population still alive at different ages but can be used to plot the percentage of population still alive following a particular event eg, onset of disease

53
Q

Define ‘average life expectancy’

A

The age at which 50% of the individuals in a particular population are still alive - can be calculated from a survival curve

Biology Unit 4 (5 decks)

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