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BIOLOGY PAPER 2 > populations in ecosystems > Flashcards

populations in ecosystems Flashcards

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1
Q

Define ecology

A

study of inter-relationships between organisms and their environment

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2
Q

Define the term abiotic factor

A

Non living factors in an environment eg temperature or rainfall

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3
Q

Non living factors in an environment eg temperature or rainfall

A

living factors in an environment eg competition and predation

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4
Q

Define ecosystem

A

dynamic system made up of a community and all of the non living factors of its environment

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5
Q

Name two major process that occur within an ecosystem

A

-flow of energy
-cycling of elements

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6
Q

Define population

A

group of individuals of the same species occupying the same habitat at the same time and can interbreed

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7
Q

Define community

A

the populations of different species in a particular place at the same time

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8
Q

Define habitat

A

the place where an organism normally lives

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9
Q

Define microhabitat

A

a smaller unit within a habitat with its own microclimate

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10
Q

Define niche

A

how an organism fits into its environment (where the organism lives and what it does there)

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11
Q

Why do we describe populations as dynamic?

A

they vary in size and composition over time

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12
Q

Why is it necessary to use a logarithmic scale to plot growth curves for rapidly reproducing organisms?

A

So that all of the data can be represented on the same axis

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13
Q

Define limiting factor

A

factor that limits the growth of a population

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14
Q

State the factors that affect the size of a population

A

abiotic and biotic factors affect rate of growth and size of a population

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15
Q

Define carrying capacity

A

the size of population of a species that can be supported by the ecosystem

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16
Q

Describe how temperature affects a population size

A

-different species have different optimum temperatures.
-Temperatures above or below these may slow/denature enzymes in cold blooded animals or require excessive energy use to maintain in warm blooded animals

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17
Q

Describe how light affects population size

A

-Light is required for photosynthesis.
-More light, more photosynthesis, more biomass both for plant survival and for animals to feed on

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18
Q

Describe how pH affects population size

A

-pH affects action of enzymes.
-Organisms have an optimum pH and will not survive well in pH away from optimum

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19
Q

Describe how water affects population size

A

-In scarce water conditions only well adapted organisms survive.

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20
Q

Describe how humidity affects population size

A

-in low humidity transpiration and water loss increase.
-Plants and animals well adapted to tolerate low humidity will have larger population size

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21
Q

Why is it necessary to use a logarithmic scale to plot growth curves for rapidly reproducing organisms?

A

So that all of the data can be represented on the same axis

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22
Q

Describe competition

A

when 2 or more species share a resource that is insufficient to satisfy their requirements fully

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23
Q

Describe intraspecific competition

A

competition between members of the same species

24
Q

Describe interspecific competition

A

competition between individuals of different species

25
Q

Outline how the availability of resources affects a population

A

less resources - more competition - lower population size

26
Q

Explain how competition causes smaller numbers of large trees in a forest rather than larger numbers of small trees

A

trees compete for resources - a few grow larger -this restricts resources for the others - which die

27
Q

How does interspecific competition affect population size?

A

the population with the competitive advantage will increase in size while the other will decrease.

28
Q

What is the competitive exclusion principle?

A

one species has the competitive advantage over another - population of less competitive species will decrease - until it becomes extinct

29
Q

Describe the competitive exclusion principle in terms of niches

A

when resources are limiting no two species can occupy the same niche

30
Q

Suggest how an increased food supply may result in a population increase

A

More food - more individuals survive - increased reproduction - increase in population

31
Q

Define predator

A

organism that eats another organism

32
Q

Define prey

A

organism that is eaten by another organism

33
Q

Comment on the evolution of predators and their prey if extinction has not occurred

A

predators evolved to be more effective at catching prey - prey evolved simultaneously to be more effective at avoiding predators

34
Q

Explain why it is difficult to obtain data on predator and prey populations in natural environments

A

it is not possible to count all individuals

35
Q

Describe the predator prey relationship

A

-predator eats prey and reduces prey population -fewer prey means greater competition for food amongst predators
-predator population decreases due to lack of food
-less predators so less prey eaten and more survive and reproduce
-prey population increases
-repeat

36
Q

Suggest why fluctuations in natural predator prey populations is not generally severe

A

a range of food is available to the predators

37
Q

Why is sampling done in ecology?

A

-To find the abundance of organisms in an area when it is not possible to count every one individually, too time-consuming and is likely to cause damage.

38
Q

Describe two types of quadrats and describe the suitable conditions for their use.

A

-A point quadrat > horizontal frame with long vertical pins > Any plant touching the pin is counted > Useful for small areas and plants which grow low to the ground.
-A frame quadrat > organisms within the frame are counted > They vary in size and an appropriate size should be chosen depending on area of the survey and size of the organisms.

39
Q

Explain the use of random sampling

A

-Random sampling is used to get estimates of population size within a study area.
-It can also be used to investigate the effects of an abiotic factor if that factor is also recorded at each quadrat location.
-Random sampling avoids bias. It can be used to compare species composition in two or more different areas.

40
Q

Explain the use of systematic sampling

A

-This is used to assess abundance and distribution, -particularly where there are gradual changes in an abiotic factor and subsequently the communities present.
-A transect can be used to document changes in communities over a distance.

41
Q

Define abundance

A

Abundance is the number of individuals of a species within a given area.

42
Q

Describe two measures of abundance

A
  • Frequency- the likelihood of a particular species occurring in a quadrat. E.g. if a species occurs in 10 out of 20 quadrats its frequency would be 50%.
    -Percentage cover is an estimate of the area within a quadrat that a particular plant species covers. Individual plants do not need to be counted.
43
Q

Explain the use of Mark-release-recapture

A

-This is a method of measuring abundance of motile species which could not be counted using a quadrat
-they run away, they are hidden, and are therefore difficult to catch.
-A known number of animals are caught, marked in a non-harmful way and then released .
-At a later time a given number of individuals are caught in the same area and the number of marked individuals is recorded.
-A calculation is carried out- total number in first sample x total number in second sample/number of marked individuals recaptured- gives an estimate of population size

44
Q

Explain why Mark-release recapture is not always reliable

A

-A number of assumptions are made:
-the proportion of marked to unmarked in the second sample is representative of the population as a whole.
-The marked individuals in the first sample spread out into the population.
-The population remains stable between surveys, i.e. there is no immigration or emigration, or no deaths or births.
-The marking does not hamper the survival of the individuals.
-The marking will not be removed between surveys.

45
Q

Suggest what is meant by the statement ‘ecosystems are dynamic’

A

they change on a daily basis as populations fluctuate

46
Q

Define succession

A

the changes over time in the species that occupy a particular area

47
Q

Describe what happens at each stage of succession

A

new species colonise an area - the new species changes the environment

48
Q

Describe two effects of a new species (B) altering an environment during succession

A
  • environment becomes less suitable for existing species (A) which is outcompeted
  • environment becomes more suitable for another species (C) which then outcompetes species B”
49
Q

How can successional changes affect biodiversity?

A

-new species alter abiotic environment
-making it less hostile for other species, which survive
-new communities are formed
-biodiversity changes

50
Q

Describe a pioneer species

A

organisms that colonise inhospitable environments

51
Q

Describe the features of a pioneer species

A

-asexual reproduction (fast)
-large quantities of wind dispersed seeds/spores (reach isolated environments)
-rapid germination of seeds (fast)
-photosynthetic (light tends to always be available)
-nitrogen fixing (poor soil)
-tolerant to extreme condition”

52
Q

Describe how a pioneer species might change abiotic factors in the environment

A

weathering of rock produces ‘soil’ decomposition of pioneer species adds nutrients to the soil

53
Q

Define climax community

A

Balanced equilibrium of species, few/no new species replacing established, high biodiversity

54
Q

What determines succession in animals?

A

the plant species available for them to feed on and live in

55
Q

State 5 common features of succession

A

-abiotic environment becomes less hostile
-greater variety of habitats and niches
-increased biodiversity
-more complex food webs
-increased biomass

56
Q

Describe secondary succession

A

succession that occurs on land that has previously sustained life but has been altered (eg by fire)

57
Q

Describe primary succession

A

succession from bare rock or barren land

BIOLOGY PAPER 2 (15 decks)

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