Session 3: Practical Ecology

Question 1

What is a population?

Answer 1

all individuals of a given species living in one area at the same time

Question 2

Talk about population sampling: why we do it, what we do.

Answer 2

We take measurements of a population such as its total size or its density for conservation purposes, etc. and is often done repeatedly because populations are dynamic and subject to continual change.

Question 3

Overall: What is the more efficient way to count populations with population sampling? And how do we get higher accuracy?

Answer 3

Populations can be large and impractical to count, so population sampling involves identifying individual numbers in small areas and then extrapolating to estimate population totals. Higher accuracy comes from taking more samples and using larger sampling areas but there is a point where increasing the amount may not actually increase accuracy any further (plateauing graph).

Question 4

What are sampling techniques.

Answer 4

Quadrats, e.g. direct counting, percentage cover, or frequency, are used for sessile (stationary) species.
Capture-recapture method with estimating based on the Lincoln index is used for motile (active) species.

Question 5

Sample counts can be more…

Answer 5

reliable and cost sensitive

Question 6

What are the advantages and disadvantages of counting every individual?

Answer 6

Advantage is that it’s accurate, disadvantage is that its difficult to count rapidly moving species, some live in areas that are difficult to observe (e.g. burrows, tall grass), its time consuming, and there can be too large numbers and too large areas of habitat which make it impractical.

Question 7

Why should we estimate the total population and what is the equation for this?

Answer 7

Estimating is more efficient and cost sensitive, if we know what fraction of the total area was sampled. we can extrapolate to estimate the total number of organisms.

Total number = (number counted x total area) / area sampled

Question 8

How do you estimate population density?

Answer 8

You need the number of organisms and the area or volume.

Density = total number counted / area sampled

Question 9

What are the differences between random and systematic sampling?

Answer 9

All types of sampling can be random or systematic sampling. Random sampling is entirely by chance, each sample has an equal chance of being included, and it avoids bias as long as enough samples are taken. With systematic samples a set interval is selected and consistently applied to all sample sites, it is more consistent than random sampling.

Question 10

Describe quadrat sampling.

Answer 10

Quadrats are small sampling areas placed randomly or in a grid pattern. All organisms within the quadrat are counted. Quadrats can be square, round, or hexagonal, and the size of the quadrat should be appropriate to organisms and habitat. Quadrat sampling is useful for determining community composition and features of population abundance, species density, frequency of occurrence, and biomass.

Question 11

Describe transect sampling.

Answer 11

A line or belt is drawn across a community, everything touching the line is counted, and you can use multiple lines. A belt transect is like a very long quadrat (everything within the belt is counted), or quadrats can be counted at intervals along a transect line (sample points, etc.). Transects can be used to determine changes in community composition (distribution) along an environmental gradient (zonation: e.g. ocean –> splash zone to high tide zone, to mid tide zone, to low tide zone). Transects disadvantages are that low density organisms may not be sampled and larger organisms have a greater chance of being sampled.

Question 12

What is equation for finding abundance?

Answer 12

Abundance (total number) = (number of organisms x total area studied) / (number of quadrats x area of one quadrat)

Question 13

What is the equation for finding estimated average density?

Answer 13

EAD = total number of organisms counted / (number of quadrats x area of one quadrat)

Question 14

Describe the capture-recapture method of sampling.

Answer 14

Used for counting organisms that move rapidly, for calculating population density, monitoring populations over time, and tracking individual organisms. A sample of organisms are captured, marked/tagged, and then released. Then a second sample is captured and the number of marked organisms in this sample is counted.

Question 15

What is the equation for the Lincoln index?

Answer 15

The Lincoln index can be used for the capture-recapture method.

Total population = (number of marked individuals in 1st sample x total number in 2nd sample) / number of marked individuals in 2nd sample.

OR

N = (n1 x n2) / n3

Question 16

What are indirect measurements?

Answer 16

trails, droppings, measurements, camera traps, etc. used to measure populations. Good for species that are difficult to physically count but need lots of background information and is less accurate than other forms of measurement.

Question 17

What are some examples of data analysis?

Answer 17

looking at the number of species and individual organisms, comparing populations, and testing for association between groups.

Question 18

What are species richness, species evenness, and species diversity?

Answer 18

Richness is a measure of the number of different species found in a sample.

Evenness is a measure of the relative abundance of the different species making up the richness of an area.

Diversity is similar to species richness except it takes into account both the numbers of species present and the dominance or evenness of species in relation to one another.

Question 19

What is the Diversity Index?

Answer 19

A measure of the number of different organisms in an ecosystem. It takes into account the number of species present as well as the abundance of each species. A higher diversity index number means it is more diverse, a lower number means it is less diverse.

Question 20

Describe Simpson’s Reciprocal Diversity Index.

Answer 20

It is used to quantify the biodiversity of a habitat, is good from comparisons, and takes into account the number of species present and the abundance of each species.

Question 21

Describe the Chi-squared Analysis.

Answer 21

It is good for testing for association (relationships between species, meaning in patterns, etc.), testing for goodness of fit, and is used to study differences between data sets. It is only used for frequencies/counts and never measurements. It is used to compare an experimental result with an expected theoretical result –> it tests the validity of the null hypothesis: that there is no difference between groups of data. It is not a valid test for small sample sizes, e.g. less than 20.

Question 22

What is a P-value?

Answer 22

The probability that the observed relationship or difference occurred by pure chance, and that in the population from which the sample was drawn, no such relationship or differences exist. If the P-value is small then the difference is quite unlikely to be caused by random chance, meaning it is statistically likely that there is a reason for the difference. P ranges from 0 to 1 and can also be written as a percentage.