Unit 2.5

Question 1

Sampling strategies

Answer 1

Random Sampling - usually carried out when the area under study is fairly uniform, very large, and or there is limited time available

adv: Unbiased, suitable for large populations

disv: may not have acces to some sample points. Sample points may miss some places

Systematic Sampling (includes line transect and belt transect methods). - when samples are taken at fixed intervals, usually along a line.

adv: easier to apply than random sampling, no need for sampling grid.
Coverage of full area can be achieved

Disv: biases because different chances of selection. Patters may be missed or area exaggerated.

Stratified Sampling. - used to take into account different areas (or strata) which are identified within the main body of a habitat. These strata are sampled separately from the main part of the habitat

adv: Representative as long as all proportions are known.
Flexible (can combine with random and systematic)
Good for comparing subsets

disv: must know the size of the subsets to get an accurate picture

Question 2

What are quadrats used for?

Answer 2

Study plants and non motile animals or ones that dont move very much.

Measure the number of individuals

Percentage frequency (how often a species appears in an area)

Population density. By extrapolating

Question 3

Evaluation of quadrafts for assessing number of individuals, percentage frequency and population density

Answer 3

Advantages
- Quick and easy to measure
- Accurate with large species
- Good for comparisons over time or space

Disadvantages
- Very difficult with small species
- Inaccurate with species like grass, which propagate under-groud
- may miss some species in layered vegetation
- Must be able to identify species accurately
- Species may look different in different stages

Question 4

Transects

Answer 4

Line transects A line is placed according to a sampling strategy and then the vegetation that touches the line can be recorded at intervals, usually every 1 meter.

Stratified sampling – in areas where there are known subsets then the number of lines placed in each area must reflect the proportions seen in the whole area.

Systematic sampling – if the study area is an environmental gradient then transect line must be placed along that gradient

Belt transects These use a quadrat to create a belt of sampling. The placement of the belt can be achieved just the same as for a line transect.

Question 5

Abiotic factors

Answer 5

marine - salinity, PH, temperature, dissolved oxygen, wave action

fresh water - turbidity, flow velocity, ph, temperature

terrestial - temperature, light intensity, wind speed, particle size, slope, soil moisture, drainage, mineral content

Question 6

Instruments to measure abiotic factors

Answer 6

Question 7

Probes evaluation
(salinity, pH, temp, dissolved oxygen, soil moisture)

Answer 7

Adv. Quick, accurate, easy to use, datalogger tan take continous readings over a period

Disv - expensive, can give false readings, not always available

Question 8

Secchi disk to measure turbidity

Answer 8

Adv
- Simple instrument
- easy to make one for yourself
-cheap

disv
- need a boat or dock to get into deep enough water
- different people may have different abilities so see the disk

Question 9

Flow meters evaluation

Answer 9

ad
- accurate
- readings can be taken at varying depths

disv
- can be expensive
- mixig watr and electicity can cause problems

Question 10

Evaluation of pooh sticks to measure flow velocity

Answer 10

ad
- limited equipment
cheap

disv
- not very accurate
- readings only at surface and velocity varies with depth

Question 11

Anemometer to measure wind velocity

Answer 11

ad
- immediate reading with no calculations needed
- quick results
- simple to use

disv
- expensive
not available

Question 12

Soil texture assesment

Answer 12

ad
- simple and cheap
- simple hand identification

dsiv
- not accurate
- people opinions
- slow settling method

Question 13

Dichotomous keys evaluation

Answer 13

ad
- easy to use
- easy to construct

disv
- require previous knowledge
- organisms look different at different stages
- parts can be damaged

Question 14

Measuring biomass in trophic levels

Answer 14

in simple
Harvest all vegetation in a quadrat
Remove soil, insects
wash vegetation
place in overnight oven
weight the sample and return to oven
repeat until weight is constant
find mean dry weight biomass
multiply by the area to measure for the whole area

Question 15

Measuring energy in trophic levels

Answer 15

NPP = GPP – R

method:
three identical quadrants
all same vegetation
all same size
Quadrat B covered in pblack plastic (cannot photosynthesize only respire)

Harvest vegetation in A
Remove soil, insects
Wash vegetation
Dry overnight
Weigh and return to oven until samples are constant
After a month do B and C

NPP= quadrat C - QA
=100

NPP= GPP - R
100= GPP - 50
150 = GPP

Question 16

Lincon Index

Answer 16

Used to estimate population
N= n1 x n2 / m2

N= total population
n1= number of animals marked in first capture
n2= number of animals recaptured
m2= number of animals marked in recapture

Es decir. Tu lo harias así:
Quieres estimar cuantas monedas tienes en tu monedero. En el primer capture (un puñado de monedas) te salio que tenias 10, esas 10 las marcas con un plumón negro (cero racismo) y las vuelves a poner en el monedero. Después vuelves a sacar un puñado y esta vez te salen 11 y de esas 11, 3 estan marcadas con plumón. Entonces puedes hacer tu lincoln de mierda asi:

N = 10 x 11 / 3
N= 36.7 osea 37 porque no puedes tener 36.7 monedas pes.

Question 17

Lincon Index evaluation

Answer 17

Assumptions
- The proportion of marked animals in the second sample is the same as the proportion of marked animals to unmarked animals in the whole population.
Enough time has elapsed to allow full mixing of marked and unmarked animals.
All animals are just as easily caught – that is unlikely as some animals may be more easily caught in both samples giving a biased sample.
The population is closed and that there is no immigration or emigration.

Problems
Capturing the animals may injure them or alter their behaviour.
The mark may be toxic to some animals but not others – you may not know until it is tested on the organism under study.
Marks may rub off between release and recapture.
Marks may make the animal more or less attractive to predators.
Some animals become trap happy (causing an overestimation of numbers) whilst others become trap shy (causing an under-estimation).

Question 18

Species richness vs species diversity

Answer 18

Species richness is a number of species in a community and is useful comparative measure.

Species diversity in communities is a product of two variables. The number of species (richness) and their relative populations (evenness)

Question 19

Simpson diversity index

Answer 19

The higher the D the greater the species diversity. Only useful when comparing two similar habits.

D= N(N-1)/ sum n(n-1)

N= total organisms of all species
n= number of individual of a particular species
D= diversity index