Stream Fish Diversity
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Stream Fish Diversity. Ecological Principles of Diversity . 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.

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Ecological principles of diversity
Ecological Principles of Diversity

  • 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, Hypotheses, and Prediction

  • PURPOSE: Test the idea that increased environmental/physical diversity leads to increased species diversity.

  • Hypotheses and predictions

  • H1: Fish diversity increases with habitat diversity in the physical environment, due to competition for niche space and the principle of limiting similarity.

  • Prediction: There will be a significant positive correlation between fish diversity and habitat diversity.

Other possible hypotheses
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)


2. Chemical

Dissolved O2



3. Biological

Other organisms present

Nutrient input

Nutrient cycling

Habitat Parameters that Could Influence Species Composition

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
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

Stream fish diversity









Stream fish diversity



H’= 1.24

H’= 1.38


H’= 0.41



H’ = 1.10

H’ = 1.61



H’= 1.39

H’= 0.69


H’= 1.39

Diversity calculations
Diversity Calculations

  • For the fish assemblages and habitat parameters we calculate diversity using the following equation:

    H’=-∑ pilnpi

    Where pi = # of individuals in a category/total # of individuals

Is there a correlation between habitat diversity and species diversity
Is There a Correlation Between Habitat Diversity and Species Diversity?

  • Today, we will compile fish diversity and habitat evenness 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).