determining population size Flashcards

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1
Q
A
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2
Q

What are the principles of ecology are based on? Where is the data obtained?

A

qualitative and quantitative data

data obtained from studies carried out on animals, plants and the
abiotic environment.

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3
Q

What are the three types of distribution in a population? Explain each one

A

Regular distribution
- normal and even distribution throughout
the area. The animals mark out a small area around themselves, defend this area territorially

Random distribution
- distribution pattern where the location of
an individual is not affected by the locations of other individuals. No territoriality is evident.

Cluster distribution
- distribution where individuals group together
in clusters across a defined area. This is a trend with social animals such as a pride of lions or herd of elephants.

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4
Q

What are the requirements to use a direct method?

A
  • organisms are large enough to count accurately
  • not move around too much
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5
Q

What are the direct technique method(s)?

A

A Census

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6
Q

When are censuses used?

A

• the animals are large
• they inhabit a fixed area
• they can be counted quickly and easily
• the organisms are relatively sessile

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7
Q

List 3 advantages and 3 disadvantages of using a census

A

+ accurate and reliable, original data is collected.
+ data for sub-populations/ categories may be available e.g. gender, age etc
+ detailed cross-tabulations of the population categories may be possible.

  • it is an expensive process because every parameter of the population is checked and recorded.
  • it is time-consuming, requires manpower to collect original data.
  • it does not take into account births and deaths which occur in already surveyed place
  • lack of preciseness of the definition of statistical units
  • personal bias of the investigators.
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8
Q

What are the requirements to use an indirect method?

A
  • when needing to estimate the population size.
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9
Q

What are the indirect technique methods?

A
  • Quadrat methods
  • Mark and recapture
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10
Q

What is the quadrat method used to determine? How is it performed?

A

determine the species density and the
species frequency of more than one species at a time.

it involves counting the individuals found in a number of squares that are randomly spaced over the total area.

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11
Q

Define ‘Species Density’

A

number of individuals of a species found in a given area

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12
Q

Define ‘Species Frequency’

A

number of individuals of a species found in each
quadrat. It is the distribution of the species,

(If the species is found in every tenth quadrat, then the frequency is 10% of the total area)

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13
Q

Estimated population formula

A

numbers in sample size x total size of area
——————————————
size of quadrat

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14
Q

Avg number of all quadrats formula

A

1+2 +6+8+ 4+3+2+1+2+4
——————————
Number of quadrats
= 33/ 10
= 3

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15
Q

List 4 factors that will affect the reliability of the quadrat method

A
  • must be selected at random (the quadrat samples are representative of the study area as a whole).
  • Each individual inside each quadrant must be accurately counted.
  • must cover at least 10% of the total area.
  • size of the quadrats is known.
  • total area must be known.
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16
Q

List 4 Advantages and 4 disadvantages of quadrat sampling

A

+ sampling is easy to use, inexpensive
+ suitable for studying plants, slow-moving animals and faster-moving animals with a small range.
+ requires the researcher to perform the work in the field and, without care.
+ measures abundance and needed cheap equipment.

  • not useful for studying very fast-moving animals which don’t stay within the quadrat boundaries
  • biasness in favour of slow moving taxa
  • Collect only taxa that are present in the sampling time and not buried deep in sediment.
  • it is a low estimate of taxonomic richness and assemblage composition
  • It is also a low detectability of among-site differences in assemblage composition
  • Some animals may experience harm if the scientist collects the population within the quadrat rather than studying it in the field.
17
Q

How would one apply/use quadrat sampling?

A
  • broadly used in plant studies
  • applied in ecology especially in biodiversity
  • used to find the taxonomic richness of slow moving taxa in a certain area
  • used to evaluate the impact of weathering, trampling or erosion in an ecosystem or at a cliff or rock face.
18
Q

Define a ‘Transect’

A

A line across a habitat or part of a habitat; string or rope placed in a line on the ground.

19
Q

What is the purpose of a transect?

A

It is used to investigate a gradual change in a habitat rather than to simply estimate the number of organisms within it.

20
Q

What is a disadvantage of using a transect and why?

A

Any species not touching the transect line would not be recorded

A line transect only provides information about the number and distribution of species along an environmental gradient- fixed line

21
Q

Define ‘Mark and Recapture Method (M&R)’

A

Method used to establish the estimated population size of animals that do not remain in the same area permanently or animals that are not always visible.

22
Q

What are the 4 steps of the M&R method

A
  1. We catch, mark and release the animals.
  2. The animals are allowed time to mix with the rest of the population.
  3. After a time, we capture a second sample and count the individuals where marked and unmarked animals will be in the second sample.
  4. We can use the following formula to calculate the estimated population
    size
23
Q

What is the formula for estimated population size?

A

N = CxM/ R

N= Estimated population size
C= Total in 2nd catch
M= Total in 1st catch
R= marked individuals in 2nd catch

24
Q

What are safe marking/ tagging methods to use?

A
  • paint that is non-toxic and waterproof.
  • rubber rings on the legs of birds
  • plastic tags through the ears of buck
  • branding an emblem on the animal’s rump
  • shaving hair in a distinctive pattern
  • aluminium discs on the operculum of fish.
25
Q

List advantages and disadvantages of the M&R method

A

+ allows an estimate of a population to be made when a direct count is impossible
+ Accuracy does not depend on an assessment of the amount of habitat

  • Marked animals may be more easily spotted by a predator.
  • Births, deaths, immigration and emigration may still occur during the period between the first capture and the recapture.
  • Some animals may avoid the trap after being trapped the first time.
  • The animal usually needs to be captured to be marked, which may injure it, or alter its behaviour pattern.
  • Accuracy does depend on capturing a large proportion of the population.
  • Capturing and marking animals can be cost prohibitive and affect animal behaviours, which can bias population estimates.
  • The mark used may harm the animal (for example a dot of a particular paint
    may turn out to be toxic to the animal)
26
Q

List 3 assumptions of the M&R method

A
  • population is physically and demographically closed (i.e., no immigration
    or emigration, no birth or mortality so that the population is constant over the
    time of sampling).
  • Marks or tags are neither lost nor missed
  • Marked individuals returned to the population and mixed randomly with
    unmarked individuals.
  • All individuals within a sample have an equal probability of capture.
  • Individual behaviour or vulnerability does not change after being marked. The marking technique must not harm the individual or affect its survival by predation.
  • The individuals have a lifespan which is long enough for you to capture, mark, release and recapture.
  • The proportion of marked individuals recaptured in the second sample represents the proportion of marked individuals in the population as a whole.