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Wildlife Techniques > Exam 2 - Abundance estimation > Flashcards

Exam 2 - Abundance estimation Flashcards

1
Q

Population

A

A group of organisms occupying a defined area for a specified time

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2
Q

Abundance

A

Number of individual animals in the population

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3
Q

Density

A

Number of individuals per unit area

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4
Q

Relative density

A

Ratio of density

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5
Q

Census

A

A complete count of all animals in the population

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6
Q

Abundance or density estimate

A

An approximation of the population value based on sample data

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7
Q

Population closure

A

Absence of any added or subtracted individuals over some time period

  • demographic
  • geographic
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8
Q

Demographic

A

No birth or death over the time period

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9
Q

Geographic

A

No immigrants or emigrants over the time period

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10
Q

Open population

A

A population that is not closed over the sample period

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11
Q

Population index

A

Some statistic (usually not a count of animals) that is related to population size

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12
Q

Detection probability

A

The chance that an individual in a sampled area is counted during surveys

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13
Q

Issues in population estimation

A
  1. Detectability: we generally don’t see all animals in our research area (N=C/B)
  2. Sampling: we generally can’t apply the survey method to the entire area of interest (N=N/a)

(Combine the 2 issues to get one equation for population size estimators) (N=C/aB)

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14
Q

The accuracy of our population estimate is dependent on what?

A

a (alpha) & B (Beta)

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15
Q

The variation with a (alpha) is dependent on what?

A

The distribution of the animals (uniform=low, clumped=high)

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16
Q

The variation with B (beta) is dependent on what?

A

Our sampling methods. We want to either minimize it or get a good estimate of it.

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17
Q

Census methods

A
  1. Complete count of animals present
    -Strip transect (fixed & estimated width)
  2. Drive counts
  3. Territory mapping
  4. Aerial photography
  5. Population reconstruction
  6. Thermal scanners
  7. Incomplete counts
    -Double sampling
    -Marked subsample
    -Multiple observers
    -Distance sampling
    -Capture/Removal
    ~Capture-Mark-Recapture
    ~Change in ratio
    ~ Change per unit effort
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18
Q

N

A

True population size

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19
Q

N’

A

Estimate for our sample area

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20
Q

C

A

Count

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21
Q

a

A

Proportion of total area sampled

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22
Q

B

A

Detection probability

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23
Q

Only under what circumstance do you attempt a complete count of animals present?

A
  1. Conspicuous species on open range
  2. Species in restricted habitat
  3. Small, enclosed area
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24
Q

Under a complete count of all animals present, N=C. Why?

A

Both a (alpha) and B (beta) are equal to 1 in this case.

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25
Q

What are drive counts mostly used for?

A

Ungulates and game birds

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26
Q

What are some limitations of drive counts?

A
  1. Assumes all animals present are seen and this is difficult to verify.
  2. Labor intensive
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27
Q

What is done during territory mapping? & what is the only species this technique is used on?

A

Map all breeding territories, boundaries determined by songbird songs.
Songbirds only.

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28
Q

What are some limitations of territory mapping?

A
  1. Limited application
    • Birds only
    • Breeding season/habitat are factors
  2. Counts only breeding males
    • Polygamous systems
    • Juveniles or floaters can bias data
  3. Time consuming
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29
Q

What is aerial photography?

A

Low altitude photography used to identify and count animals.

30
Q

What is aerial photography mostly used for?

A

Ducks on migration stopovers

31
Q

What are some limitations of aerial photography?

A
  1. Limited application
  2. High cost
  3. Uncertainty
32
Q

How is population reconstruction done?

A

Records of only harvested animals are used to reconstruct a population where all harvest is recorded, in the past.

33
Q

What are some limitations of population reconstruction?

A
  1. Assumes all dead animals are identified at time of death and aged accurately.
  2. Post-hoc
    -Can’t get estimate for year X until all animals alive in
    year X have died.
34
Q

How are thermal scanners used?

A 
Infrared detectors (FLIR) 
   -aircraft or truck mounted
35
Q

What are some limitations of thermal scanners?

A
  1. Detection rate varied from 31-89% of known population.

2. Expensive equipment & aircraft time

36
Q

What is the problem with incomplete count methods?

A

Estimating B (beta) formally to correct our estimates

37
Q

What is the primary count method for double sampling (waterfowl)? & what is done to calculate B (beta) for the primary count method?

A
  • Aerial transect survey of breeding areas.

- Intensive ground counts on selected portions of transects.

38
Q

What is used to find B (beta) in a marked subsample?

A

The presence of marked animals in the population; Lincoln-Peterson Esimator

39
Q

What are some limitations of marked subsample?

A
  1. All marked animals are in the survey area at the time of the survey.
  2. Marked and unmarked animals are equally observable.
40
Q

What is done using the multiple observers method?

A

Independent observers map the precise location of animals or other objects.
(Use the Lincoln-Peterson Estimator.)

41
Q

What are some assumptions made using the multiple observer method?

A
  1. Mapping is perfect (ID animals observed by both)

2. Observations are independent

42
Q

Distance sampling uses a statistical modeling to derive what?

A

“Detectability curve” or detection function.

program DISTANCE

43
Q

What is distance sampling most commonly based on?

A

Random line transects through the area of interest.

44
Q

What must be determined in distance sampling?

A

The perpendicular distance from transect line to animal

45
Q

Distance sampling makes what assumptions?

A
  1. Lines are randomly placed
  2. All animals on the line are detected
  3. Animals are detected at original location
  4. Distances are correctly measured
  5. Observations are independent
46
Q

What occurs during Capture-Mark-Recapture? How many events must there be?

A
  • Animals are marked, then the proportion of marked animals in recapture is observed. (estimate original population by assuming proportion of marked animals in overall population is the same.)
  • 2 or more
47
Q

What are some assumptions made using Capture-Mark-Recapture?

A
  1. Populations is closed
    • Relaxed in the Jolly-Seber Model
  2. All animals are equally likely to be captured
    • Relaxed in some complex models (MARK program)
  3. Marks are not lost or overlooked
48
Q

What are some new methods for CMR?

A
  1. Infrared-triggered cameras
    -“captured” if photographed within the period
  2. Genetic mark-recapture
    -use noninvasive techniques (hair or feces) to get
    tissue sample.
    -Genetic finger printing to ID individuals
    Both analyzed with MARK
49
Q

When is the Change in Ratio method used?

A

Where there is removal biased toward one group of animals. (ex. males)
Ratio of males to females changes from pre- to post- harvest bc only males are removed

50
Q

What are some assumptions made using the Change in Ratio method?

A
  1. Observed proportions of x-type and y-type animals are unbiased(detectability is equal)
  2. Population is closed except for removals
  3. Number of animals removed & their type is known
  4. The proportion of x-types in the removal differs from that in the population
51
Q

What is the Catch Per Unit Effort about?

A

Several successive trapping events where animals are removed.
Can also mark them and consider all marked animals removed.

52
Q

If less animals are available, what happens to the catch per unit effort?

A

Declines

53
Q

What are some assumptions made using Catch Per Unit Effort?

A
  1. Population is closed.
    • Complex models (program CAPTURE) relax this
  2. Catchability (=Detectability) is constant
  3. All removals are known
54
Q

Measures of Relative Density do not do what?

A

Determine the population density but correlate with density.

55
Q

What are measures of relative density used for?

A

To compare among time periods or sites

56
Q

What are measures of relative density termed?

A

Population indices

57
Q

What are some assumptions made by measures of relative density?

A

B (beta), though unknown, is constant & unbiased.

58
Q

Examples of population indices

A
  1. Roadside counts

2. Call counts

59
Q

How is the roadside count index to density determined?

A

Number of animals observed per survey mile on designated routes.

60
Q

What is the potential bias with roadside counts?

A

If the roadside vegetation changes

61
Q

What is the call count index to density?

A

The number of calls heard.

62
Q

What are some well-known, long-term call count surveys?

A
  1. North American Breeding Bird Survey
    • Began by Chandler Robbins
  2. Dove Survey
  3. Woodcock Singing Ground Survey
63
Q

What are some types of animal sign that indices have been based on?

A

Tracks, nests or lodges, feces

64
Q

The need to establish sign is proportional to what?

A

Animal abundance

65
Q

Occupancy modeling estimates what, instead of abundance?

A

Probability of occupancy (occurrence)

66
Q

Occupancy modeling is based on what principles?

A
  1. Detection probability is always <1 & is usually unknown.
  2. With unknown detection probability, survey results are unreliable.
  3. Multiple surveys allow us to estimate detection probability.
  4. Occupancy provides meaningful info
67
Q

What program is associated with occupancy modeling?

A

PRESENCE

68
Q

The 2 key parameters of occupancy modeling?

A
  1. Probability of occupancy

2. Probability of detection (p)

69
Q

What are some occupancy assumptions?

A
  1. Population closure
  2. Detection probability is constant over time
  3. No false detections
70
Q

What are some uses of occupancy modeling?

A
  1. Describe habitat characteristics associated with occupancy by a species.
  2. Quantitatively compare detection probability for various survey methods.
  3. Define species distributions.

Wildlife Techniques (3 decks)

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