Lecture 5 Estimating population Size

Question 1

What are the four measures of abundance?

Answer 1

Present/ Not detected
Relative abundance
Density
Total Abundance

Question 2

What is present / not detected measurement?

Answer 2

Whether or not a species is present in a given area. but conveys little useful information.

Question 3

What is relative abundance measurement?

Answer 3

The number or proportion of individuals without specifying the size of the sampling area
ex. 7% cover of blackberry

Question 4

What is Density abundance measurement?

Answer 4

The number of individuals per unit area or volume

Question 5

What is total abundance measurement?

Answer 5

The total number of individuals in a specified area`

Question 6

What is accuracy?

Answer 6

How close an estimate is to the ACTUAL value. accuracy is reduced by bias which ususally results from systemic errors in the measuring procedure or flaws in study design

Question 7

What is precision?

Answer 7

How close measured values are to eachother. precision is affected by random errors, like poor measuring instruments

Question 8

What are some examples of Bias?

Answer 8

Weather bias- greater accuracy is acheived by conducting surveys in standardized conditions
Season Bias- visibility of species varies by season
Observer Bias- results vary by observer. greater accuracy is achieved by calibrating observers in smaller groups

Question 9

What characteristics of organisms may cause you to adjust your survey place and time?

Answer 9

Seasonal distribution

• coloration
• behaviour
• timing of reproduction/ death
• feeding habits

Question 10

what usually ends up being the main controling factor os surveys?

Answer 10

Resource availability

Question 11

What are the 4 general approaches to estimating population size?

Answer 11

1. Complete Count
2. Incomplete Counts
3. Indirect Counts
4. Mark-Recapture Methods.

Question 12

What are Complete Count methods?

Answer 12

Entails counting every member of a population, yielding estimates of density or total abundance.

• Feasible with highly visible species that are aggregated together.
• usually expensive, impractical or impossible.
• may be needed for endangered/ sensitive species

Question 13

What are incomplete Counts?

Answer 13

Counting part of the population, and then extrapolating those counts to the entire population.

• counting individuals within sampling units
• plots, quadrats and transects

Question 14

What are 3 conditions which sampling unit type is dependant on?

Answer 14

1. Size of sampling unit should increase as abundance of target variable decreases
2. rectangular quadrats are more efficient at sampling items when there are clumped distributions
3. Transects are more efficient and convenient when sampling along linear features.

Question 15

What are 3 main types of transect?

Answer 15

1. Encounter– Used for presence/not detected. Transect along which the target variable is counted continuously or at fixed points
2. Strip– Transect along which the target variable is counted within a fixed distance from the center
3. Line– Individuals observed at any distance are counted, together with an estimate fo thier distance from the transect.

Question 16

What are the benefits of Line transects that include the distances from the observers path of travel?

Answer 16

Determines detection functions, helps account for variation in detectability due to distance, observer, weather and other potential biases. Improves accuracy of density estimates

Question 17

What are indirect counts?

Answer 17

Surveying indirect signs of animal presence: Scat, burrows, dens, nests, browsing patters, tracks.

• do not provide actual estimates of abundance.
• these indicies observered can be useful in assessing relative differences in abundance of a target variable amoung sites or time periods

Question 18

What are Mark-Recapture methods

Answer 18

CApturing a number of animals, marking them, returnign them to that population, and then using the proportion of marked individuals in subsequent capture efforsts as a basis for estimating pop size.

Question 19

What are other names for mark-recapture?

Answer 19

CApture-recapture, capture-mark-recapture, sight-resight, mark-release-capture, band recovery

Question 20

What principle is mark recapture based on?

Answer 20

Proportion of animals marked in the total pop is the same as the proportion of animals marked in any subsequent capture effort
M/N=R/C

Question 21

What is the derived formula for population size?

Answer 21

N=(MxC)/R

Question 22

What are the 5 assumptions of mark-recapture model?

Answer 22

1. No change in ratio of marked to unmarked individuals (B/D/I/E)
2. Equal Catchability. marked individuals must not ebcome easier or more difficult to catch
3. sufficient time for marked individual to disperse randomly into the greater population
4. animals are not affected by thier marks
5. Animals must not lose their marks