FRWS-3700
Midterm Exam 2
Fall 2004
Name:
Intro to Exam:
This exam is intended to provide you an opportunity to summarize your understandings
on the concepts of monitoring and inventory from the material presented in class, labs, and
through readings. This exam will be counted as 15% of your grade. In addition to thoughtful
answers, we expect answers to be concise and well-written. Answer with complete sentences
where appropriate.
I. General review questions
Multiple choice, choose the best single answer (2 points each, total of 24 points).
1. Which of the following is NOT a necessary assumption of the Lincoln-Peterson markrecapture population estimator:
a) demographic closure
b) sample methods are the same each sample period
c) all individuals have equal chance of being captured
d) no tags are lost
2. What is the standard error (se) of a complete census:
a) se = 1+ v(standard deviation)
b) se = 0
c) se = vN
d) se can’t be determined with the information given.
3. Which situation is NOT a reason for measuring plant cover instead of plant density:
a) the investigator has a good method for estimating cover
b) cover is the parameter if interest
c) individuals are difficult to discern
d) all of the above are good reasons for measuring plant cover
4. Which of the following is a method for determining whether a boundary plant is
counted to be in a quadrat:
a) include only plants touching two of the four sides
b) randomly select every third plant
c) all boundary plants are excluded
d) all boundary plants are included
5. Which of the following is measure of the precision of an estimate:
a) mean
b) standard deviation
c) standard error
d) bias
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FRWS-3700
Midterm Exam 2
Fall 2004
6. Which definition best describes a 95 % confidence interval:
a) interval of one standard error about the mean
b) interval that contains the true value 95% of the time
c) interval with a 95% probability that it contains the true value
d) interval bounding the bias of the true value
7. Which of the following is a necessary assumption in using population indices in
monitoring studies?
a) the proportion of the population sampled remains the same
b) the metric you are sampling (e.g., tadpole abundance) does not change
c) the population index is from a methods book
d) changes in abundance are linear through time
8. Which of the following in NOT a reason for sampling:
a) complete census is not possible
b) money is limited
c) time is limited
d) you have a good method
9. A species whose effects on other species or ecosystem structure or function are
much greater than would be predicted based simply upon their abundance or biomass:
a) umbrella species
b) endangered species
c) keystone species
d) a poor indicator species
10. Which of the following does NOT apply to a good indicator species:
a) species whose status is believed to reflect the effects of environmental
perturbations
b) species that is easy to count
c) species whose status is believed to reflect habitat quality
d) species whose status changes relatively randomly
11. Which of the following is NOT a method for estimating plant cover:
a) line intercept
b) visual estimates in quadrats
c) mark-recapture
d) point intercept
12. A necessary assumption of estimating population density with distance sampling is:
a) all individuals must be seen
b) distance to center line or point is estimated for an individual when they stop
moving
c) transects or points must be randomly distributed
d) individuals must be clumped in distribution
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FRWS-3700
Midterm Exam 2
Fall 2004
II. Definitions (use only words listed at the end of this section) (30 points):
1. (4 points) ___Geographic___ closure means that there is no movement into or out of
the population. ___Demographic___ closure means that there are no births or deaths
within a population during sampling.
2. (2 points) “A/an __parameter____ is the true population value of interest, expressed
as a number.”
3. (4 points) “A/an _sample statistic_____ is an estimate of a true population value of
interest and a mathematical expression that indicates how to calculate an estimate of a
parameter from the sample data is called a/an _estimator/model__.”
4. (2 points) A complete count of a population is called a/an ____census___.
5. (2 points) Individuals of teasel are counted in a random selection of 10 quadrats from
a population of 1000 quadrats. This is an example of a/an ___sample_______.
6. (4 points) _Standard deviation__ is a measure of the variability of a population
attribute while __standard error___ is a measure of precision of an estimate.
7. (2 points) The __coefficient of variation__ is a measure of the relative variability of
an attribute within a population.
8. (4 points) Two quantities relate how good is an estimate. __Precision__ is relatively
easily measured, but __bias__ is much more difficult to measure because it requires
the true value to be known.
9. (2 points) Determining presence or absence of a species is an example of
__qualitative____ sampling.
10. (4 points) When populations do not meet the assumption that they are __closed_,
the Jolly-Seber population estimation model is appropriate for estimating the size of
these _ open_ populations.
Possible answers to fill-in-the-blank questions (you will not use all but may use some
more than once): accuracy, assessment, bias, biological, census, closed, coefficient of
variation, demographic, emigration, estimate, geographic, idiotic, immigration, indices,
individual, inventory, mark-recapture, macroplot, microplot, model, monitoring, nonsampling, open, parameter, population, precision, quadrat, qualitative, quantitative,
random, rate, sample, sample statistic, sampling, spatial, state, statistical, target,
temporal, threshold, trigger point
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FRWS-3700
Midterm Exam 2
Fall 2004
III. Concepts (24 points)
1. (8 points) You were asked to develop a strategy for monitoring the effect of a
mechanical treatment on weed invasion. The area of interest was from the edge
of a stream to 200 m from the stream, and for a distance of 5 km. Weed density
prior to the treatment decreased rapidly from the stream’s edge and it was
assumed there would be a similar pattern after treatment. If your sampling
objective was to provide the most precise estimates of weed density prior to and
after the treatment, would you obtain a more precise estimate by sampling
perpendicular to the stream or parallel? Why? Assume you used line
transects, the number of which was the same for both sampling scenarios.
Hint: look at the equations for various statistics in Part IV.
a. Perpendicular or parallel? Perpendicular
b. Why?
Precision is improved – or variance reduced- when the
variation AMONG samples (in this case transects) is reduced.
Thus, you want to capture the variation within a transect so
that samples are most similar.
Number of Replicate Studies
2. (8 points)Identify the difference between precision and bias
B
C
A
D
True Value
Estimated Mean Weight of Mule Dear
The weight of mule deer were collected during a large study in 2002 and collected with 4 different
sampling schemes. Imagine that the same study was done over and over again and the weight
of mule deer remained the same for each of the four methods. This would be similar to a
computer simulation. The results in terms of bias and precision were very different for the four
methods.
Match the four methods, A-D, with the following (1 point each for total of 4 points):
1.
2.
3.
4.
Precise but high bias
Precise and low or no bias
Imprecise but high bias
Imprecise but low or no bias
A.
B.
C.
D.
__4
__2
__3
__1
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FRWS-3700
Midterm Exam 2
Fall 2004
3. Mark-Recapture
(4 points) What is the fundamental reason for using mark-recapture methods to
estimate population size?
The fundamental reason for using mark-recapture for estimating population size
with mark-recapture methods is in situations where not all individuals are
counted—when detection probability is <1.0 .
4. Distance sampling
(4 points) What is the basic conceptual idea behind distance estimation methods in
estimating density of a wildlife species?
The basic idea behind estimation of population size or density using
distance-sampling methods is that the observer’s ability to detect animals (or
any object) declines with distance from the observer.
IV. Estimation (30 points)
Use calculators to compute the quantities requested, but use the formulas below (not
those programmed in your calculator)
n
__
Population mean: Mean = X =
∑X
i
i =1
n
n
__
∑(X − X )
i
Standard Deviation: Stdev =
Standard Error: SE =
i =1
2
n −1
Stdev
n
95% Confidence Interval: CI95 = Mean ± 1.96 * SE
Coefficient of Variation: CV = Stdev / Mean
You were contracted by the U.S. Fish and Wildlife Service to monitor the response of
burrowing owl chicks to various grazing regimes used in Utah. Through collaborative
efforts, it was decided that either the mass (weight) of the chicks or the length of the
wing chord (length of longest primary) at 30 days of age would be the metric to use in
the monitoring program. Prior to developing a monitoring plan, you wanted to determine
which trait was relatively more variable in the population and estimate various statistical
properties of the sample. Here are the results of the data from the pilot study:
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FRWS-3700
Midterm Exam 2
Individual
1
2
3
4
5
6
Fall 2004
Mass (g)
40
35
27
39
40
28
wing chord (mm)
99
120
95
100
90
95
(15 points) Compute the mean, standard deviation, standard error, 95% confidence
interval, and the coefficient of variation of each metric for the sample of 6 chicks.
Please show all work.
a.
Mean =
Wing Chord
99.8
Mass
34.8
Stdev
=
5.98
10.48
SE
=
2.44
4.28
95% CI =
30.0-39.6
91.4-108.2
CV
17.2%
10.5%
=
c. (5 points) Which metric is relatively most variable and how did you determine this?
Mass was more variable than wing chord on a relative scale. The
coefficient of variation provides a measure of relative variation.
c. (10 points) Interpret (by definition, do not provide values) the meaning of each of
these in terms of the mass of chicks.
Mode: The most frequent value of mass in the sample
Median: The mass at which half of the samples are below this value, and
half are above.
St. Deviation: A measure of variability of mass of chicks
St. Error: A measure of precision of the estimated mean mass of chicks
95 % confidence interval: The interval that likely (95% of the time) contains
the true mean mass of chicks.
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