Download Statistical Analysis of Stream Data

Hypothesis development
 Environmental quality of the Poudre River
 Urban impact from Fort Collins
 Influence assessed through physical, chemical and
biological characteristics
Data sampling
 Environmental data
 Physical data

Watershed-scale


Urbanization, road
density, etc.
Reach-scale

Stream width, slope, etc.
 Chemistry data
 Nitrate, conductivity, etc.
 Biological data
 Invertebrate metrics

Taxonomic, biotic index,
species traits
 Epilithon
 AFDM, Chl a
 Benthic organic matter
 AFDM
Taxonomic community structure
 Richness (how many taxa)
 Abundance (how many individuals per taxa)
 Specific taxonomic groups
 Based on knowledge of group tolerance levels


% Chironomids
% Ephemeroptera, Plecoptera and Trichoptera (EPT)
Biotic index
 A score that represents the species’ tolerance to
disturbance
 Based on observation and expert opinion, not
ecological theory
Abundance
Chironomidae
Tolerance
Total
30
×
8
=
240
Lepidostomatidae
10
×
1
=
10
Baetidae
20
×
4
=
80
60
330
=
5.5
Species traits
 Traits are morphological, behavioral, ecological, or
physiological characteristics of species
 Traits link the environment to species distribution
 Convert community metric (e.g., richness, abundance,
biomass) into proportion of taxa with each trait state
Rhithrogena
Rhyacophila
Small Size
Large Size
60%
40%
Pteronarcys
Hydropsyche
Baetis
% Chironomids
35
30
Max
25
20
Range
Descriptive statistics
% Chironomids
% Chironomids
30
25
20
# Samples
 Central tendency
15
 Mean or median
3510
30 5
 Variance
250
 Standard deviation or error20
15
 Range
10
 Minimum and maximum 5
0
 Distribution
 Histogram of data
15
10
5
0
Min
Mean
3.5
3
2.5
2
1.5
1
0.5
0
Standard
deviation
Standard
errors
Urbanized
Natural
% Chironomids
Hypothesis testing
 For every hypothesis, there is a null
 For example
 You observe that shredders eat leaf material, which is a
significant portion of benthic organic matter (BOM)
 Hypothesis: Shredder distribution is dependent on the
quantity of BOM

Null: Shredder distribution is NOT dependent on BOM quantity
 Alternative hypothesis: Small streams have more leaf litter
per unit area, so shredder abundance is related to the width of
streams

Null: Shredder abundance is NOT related to stream width
Null hypothesis testing
 Statistics test the null hypothesis
 P-value is the probability that the null hypothesis is
true
 Or, if the data were randomly generated, P-value is the
probability that you would find the same result
ANOVA
35
35
30
30
% Chironomids
% Chironomids
 Tests the means and variances of categorical data
 Two or more samples per category required to calculate
variance
 T-test equivalent to ANOVA with only two categories
25
20
15
10
5
0
25
20
15
10
5
0
Urbanized
Natural
Urbanized
Mixed
Natural
Regression
 Tests the variances between two sets of continuous
variables
 May explain relationship (positive or negative)
 Can compute P-value
% Chironomids
 Will test strength of relationship (R2)
50
40
30
20
10
0
y = 0.5577x + 13.462
R² = 0.8512
0
20
40
% Urbanization
60