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AQA A Level Biology Paper 2 > Topic 8.4 - Populations in Ecosystems > Flashcards

Topic 8.4 - Populations in Ecosystems Flashcards

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1
Q

What is ecology?

A

The study of inter-relationships between organisms

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2
Q

What are the two main processes to consider within an ecosystem?

A
  • the flow of energy through the system

- the cycling of elements within the system

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3
Q

What is a population?

A

A group of individuals of one species that occupy the same habitat at the same time and are able to interbreed

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4
Q

What is a carrying capacity?

A

The size of population of a species which an ecosystem can support

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5
Q

What can causes population sizes to vary?

A

The effect of abiotic factors

Interacts between organisms, eg intraspecific and interspecific competition

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6
Q

What is a community?

A

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

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7
Q

What is a habitat?

A

The place where an organism normally lives and is characterised by physical conditions and the other types of organisms present

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8
Q

What are microhabitats?

A

Smaller units with their own microclimates within a habitat

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9
Q

What is an ecological niche?

A

It describes how an organism fits into its environment and refers to where an organism lives and what it does there

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10
Q

What does a niche include?

A

All the biotic and abiotic conditions to which an organism is adapted in order to survive, reproduce and maintain a viable population

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11
Q

What is the competitive exclusion principle?

A

No two species occupy exactly the same niche

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12
Q

What is population size?

A

The number of individuals in a population

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13
Q

What are abiotic factors which influence the size of a population?

A

Temperature
Light
pH
Water/humidity

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14
Q

How does temperature affect the size of a population?

A

Each species has an optimum temperature, and the further from the optimum, the fewer individuals survive. Enzymes work more slowly so metabolic rate is reduced and they may denature

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15
Q

How does light affect the size of a population?

A

As the ultimate source of energy for most ecosystems, light is a basic need. The rate of photosynthesis crashes as light intensity increases. This increases growth and carrying capacity for animals that feed on the plants

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16
Q

How does pH affect size of population?

A

It affects the action of enzymes, as each enzyme has an optimum pH at which it operates most efficiently. A population of organisms is larger where the appropriate pH exists

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17
Q

How do water and humidity affect population size?

A

Where water is scarce, populations are small and consist only of well adapted species. Humidity affects transpiration rate in plants and water loss from the bodies of animals

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18
Q

What is immigration?

A

Where individuals join a population from outside

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19
Q

What is emigration?

A

Where individuals leave a population

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20
Q

Population growth =

A

(Births + immigration) - (deaths + emigration)

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21
Q

What is intraspecific competition?

A

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

22
Q

What is interspecific competition?

A

When individuals of different species compete for resources such as food, water, breeding sites etc.

23
Q

How does the availability of resources influence population size?

A

The greater the availability, the larger the population. Availability also influences the level of competition.

24
Q

What are examples of intraspecific competition?

A

Limpets competing for algae, their main food.
Oak trees competing for resources such as light, water, space
Robins competing for breeding space - females only attracted to males with established territories, which provide food for a family

25
Q

What is the competitive exclusion principle?

A

The competitive removal of one species when it is out-competed by another as resources are limited.

26
Q

No two species can indefinitely occupy the same…

A

…niche

27
Q

What is a predator?

A

An organism which feeds on another organism, known as prey

28
Q

How does population size fluctuate with predator prey relationships?

A

Predators eat their prey, thereby reducing the population of prey
With fewer prey available, the predators are in greater competition
The predator population is reduced as some individuals don’t get enough prey to survive or reproduce
With fewer predators, less prey are eaten and more survive
The prey population increases
With more prey available, predator population then increases

29
Q

What is selection pressure?

A

The individuals which survive predation, withstand disease and adverse climate are more likely to survive and produce, so the population evolves to be better adapted to conditions

30
Q

What is abundance?

A

The number of individuals of a species in a given space

31
Q

What are the main sampling methods for habitats?

A

Random sampling using frame quadrats or point quadrats

Systematic sampling along a belt transect

32
Q

What is a point quadrat?

A

A horizontal bar supported by two legs. At set intervals along the horizontal bar are ten hole through each of which a long pin may be dropped. Each species that touches the pin is recorded.

33
Q

What is a frame quadrat?

A

A square frame divided by string or ire into equally sized subdivisions. The quadrat is placed in different locations I thin the area being studied and the abundance of each species is recorded.

34
Q

What are the factors to consider when using quadrats?

A

The size of the quadrat to use
The number of sample quadrats to record within the study
The position of each quadrat within the study area

35
Q

Why should the size of the quadrat be considered?

A

It will depend on the size of the plants or animals being counted and how they are distributed within the area. Where a species is not evenly distributed,a larger number of small quadrats may be used to give more representative results.

36
Q

Why should the number of sample quadrat within the area be considered?

A

The larger the number of sample quadrats, the more reliable the results will be. As the recording of species in a quadrat is time consuming, a balance should be found between reliability and time constraint.

37
Q

Why should the position of each quadrat in the study area be considered?

A

To produce statistically significant results, random sampling must be used

38
Q

How should a point be picked for a quadrat in random sampling?

A

Lay out two long tape measures at right angles, along two sides of the study area
Obtain a series of coordinates by using random numbers generated from a table or by a computer
Place a quadrat at the intersection of each pair of coordinates and record the species within them.

39
Q

How can abundance be measured?

A

Frequency

Percentage cover

40
Q

In what other way can sessile or slow moving organisms be measured?

A

Using mark-release-recapture techniques

41
Q

How can estimated population size be calculated from mark-release-recapture?

A

Total no. Of individuals in the first sample x total no. Of individuals in the second sample / no. Of marked individuals recaptured

42
Q

What assumptions does mark-release-recapture rely on?

A

The proportion of marked to unmarked individuals in the 2nd sample is the same as the proportion of marked to unmarked individuals in the population as a whole
The marked individuals from the 1st sample distribute themselves evenly among the population
The population has a definite boundary so that there is no immigration or emigration
There are few, if any, deaths and births within the population
The mark or label is not rubbed of during the investigation

43
Q

What is succession?

A

The term used to describe changes over time to the species that occupy a particular area

44
Q

How can new species alter the environment that they colonise during succession?

A

They can make it less suitable for existing species, as a result the new species may out-compete the existing one and so take over the area
They can make it more suitable for other species with different adaptions, as a result this species may be out-competed by the better adapted new species

45
Q

What are pioneer species??

A

One which are able to colonise an inhospitable environment

46
Q

What feature do pioneer species have that make them suited to colonisation?

A

Asexual reproduction so that a single organism can rapidly multiply to build up a population
The production of vast quantities of wind dispersed seeds or spores, so they can easily reach isolated situations such as volcanic islands
Rapid germination of seeds on arrival as they do not require a period of dormancy
The ability to photosynthesise, as light is normally available but other food is not.
Tolerance to extreme conditions

47
Q

What is a climax community?

A

A stable state of a balanced equilibrium where many species flourish and there is much biodiversity

48
Q

What are the common features in succession?

A

The non-living abiotic environment becomes less hostile
A greater number and variety of habitats and niches
Increased biodiversity
More complex food webs
Increased biomass

49
Q

What is secondary succession?

A

Succession a second time after the land has been altered in some way, for example by fire, and some of the species in he climax community are different

50
Q

What are the main reasons for conservation?

A

Personal
Ethical
Economic
Cultural and aesthetic

51
Q

What is conservation?

A

Management of the Earth’s natural resources by humans in such a an tht maximum use of them can be made in the future

52
Q

What can be maintained by conservation?

A

Ecosystems and biodiversity

AQA A Level Biology Paper 2 (16 decks)

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