Stream Fish
Diversity
Ecological Principles of Diversity
1.
2.
3.
Principle of Limiting Similarity - There is a
limit to the similarity of coexisting
competitors; they cannot occupy the exact
same niche.
Niche Separation / Differentiation Competitors use different resources to coexist.
Environmental heterogeneity - Creates more
niche possibilities; therefore, higher
environmental diversity leads to higher species
diversity.
Purpose, Hypotheses, and Prediction

PURPOSE: Test the idea that increased environmental/physical diversity
(niche space) leads to increased species diversity.

Hypotheses and predictions

H1: Fish diversity is determined by competition for niche space and the principle of
limiting similarity.

Prediction: There will be a significant positive correlation between fish diversity and
physical habitat diversity.
Other Possible Hypotheses
The fish assemblage is structured by:
 Predation or number of trophic levels
 Flooding
 Glacial and geographic history (age of the
stream, and its history of isolation)
 (more are possible…use your knowledge of
ecology to think of a few more)
Habitat Parameters that Could
Influence Species Composition
1. Physical (our focus)
 Water depth
 Current velocity
 Substrate type
1. Physical (extra)
 Temperature
2. Chemical



Dissolved O2
Ions
pH
3. Biological



Other organisms present
Nutrient input
Nutrient cycling
Note: We are not measuring all factors, so this is not a complete
test of the hypothesis (we can support but not falsify).
Background for Calculations

Diversity addresses 1) how many categories exist, and 2)
how evenly the categories are represented.
For example, we may have 2 communities with 7 species
(species richness = 7) and 21 total individuals, but each
species may not be represented evenly.
Less Diverse

More Diverse

Community 2 Species Diversity Histogram
Number of Individuals

12
10
8
6
4
2
0
1
2
3
4
Species
5
6
7
A.
B.
E.
C.
D.
F.
H.
G.
A.
B.
H’= 1.24
H’=
1.38
E.
H’= 0.41
C.
H’ = 1.10
D.
H’ = 1.61
F.
H.
H’= 1.39
G.
H’= 0.69
H’= 1.39
Diversity Calculations

For the fish assemblages and habitat
parameters we calculate diversity using the
following equation:
H’=-∑ pi lnpi
Where pi = # of individuals in a category/total #
of individuals
Is There a Correlation Between Habitat
Diversity and Species Diversity?


Today, we will compile fish diversity and habitat diversity
results from all groups in our lab.
This correlation will only involve two or three data
points, so it will probably not be significant. Therefore,
we also will examine some data from a previous year to
increase sample size (n).