Logistical issues

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Logistical issues

• .
• Independent project.
• You make an observation.
• You state a hypothesis
• You decide the methods,
• collect the data,
• analyze it,
• summarize it.

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Two parts today

• Part 1 What is diversity and how is it measured?
• Part 2 What is biodiversity and how is it
  measured?

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BIODIVERSITY

• SPECIES NUMBER (SPECIES RICHNESS)
• DEGREE OF DIFFERENCE BETWEEN SPECIES 5 Plants lt
  2 plants 3 animals
• Biodiversity was originally intended to convey
  something more than species number
• BUT, Diversity also does not equal sp.

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Species Richness

• How do you sample for species number?

species
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2
3
5
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Sample area
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Diversity

• Loosely used to signify the NUMBER of SPECIES
• Species Richness Species number
• Evenness Species richness Diversity
• So, what is evenness?
• 1 dominance
• A measure of equitability

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Dominance
Virtually all biotic systems are characterized by
VERY strong dominance among a few taxa and
numerous considerably rarer taxa.
Geology 2002
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Models of dominance
Geometric series-generally species poor, early
successional communities Log-normal-generally
mature communities Broken stick-narrowly defined
similar taxa (passerine birds, minnows)
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Measures of diversity

• Simpsons Index
• C ?( pi)2
• pi the proportion of abundance of species i in
  the sample.
• Monospecific stand (n1) C 1
• 100 individuals, 100 species C 0.01
• More diverse stands have lower C
• So, D 1 C Diversity

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Two communities
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Measures of diversity

• Shannon-Weiner Index
• H - ?(pi)(ln pi)
• Monospecific stand H 0
• 100 individuals,
• 100 species
• H 4.61

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Models of dominance
Assessing patterns of dominance can be
statistically difficult (goodness of fit testing
among different models). Assessing changes in
dominance can be an indicator of environmental
health or quality. (British grasslands
study) Temporal change in presence / absence
further muddies the water (is something rarely
encountered, rare, or mostly not there, does it
matter)
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How to compare sites using species?

• Presence / Absence Measures
• Jaccards Index
• J c / (a b c)
• Co-occurrences / total occurrences
• Sorensons Index
• CC 2c / (A B) or CC 2c/(a b 2c)
• Co-oc/arithmetic mean occ at 2 sites

Where a and b are species unique to each site a
and b are species unique to each site, c is
species shared among sites, A and B are all
species in each site.
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Sorensons index

• Has been assailed because it just uses
  presence/absence and
• Varies with species richness, making it invalid
  in comparing sites with really different species
  numbers

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Lots more

• Simple matching coefficient
• Ochiai
• Mozley Margalef
• Mountford
• Jaccard (1901)
• Sorenson (1948)

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Quantitative alternatives

• Euclidean distance
• D2ij ? (xik xjk)2
• D2ij 1/p ? (xik xjk)2 ----average
  distance
• Where I and j are sites, k are the individual
  species p number of species.

Species A
Species B
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Lots more

• City Block
• Mahalanobis
• Bray-Curtis
• Canberra
• Correlation coefficient complement

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Why so many?

• Different indices weight rare species differently
• Different indices place differential importance
  on presence
• Different numbers of species result in different
  ranges of values

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Diversity (species richness) at different scales

• Alpha local diversity species richness
• Beta turnover, diversity difference from one
  location to the next
• Gamma alpha beta diversity, or regional
  diversity

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Other Approaches

• Ecological Quality approaches
• Index of Biotic Integrity
• Coefficient of Conservatism
• Value species within sites by the ecological
  value that they indicate
• Disturbance sensitive species found in only high
  quality sites count more than weeds

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Other Approaches

• Indicators of diversity
• Rapid approaches to assess or predict diversity
  attributes
• Rapid biodiversity assessments (Gentry, Venez.)
• Indicator species analysis
• Site quality assessments

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Underlying patterns of diversity
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Underlying patterns of diversity

• Geographical
• Diversity increases toward the equator
• Biogeographical
• Isolation leads to divergence and reduced
  diversity (islands)

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Underlying patterns of diversity

• Productivity
• Diversity is maximized at moderate levels of
  productivity
• Productivity / Geographical
• Diversity increases with increasing energy supply
• Sampling
• Species-area sampling

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Underlying patterns of diversity

• Ecological
• Intermediate disturbance hypothesis

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Maintenance of Diversity

• Ecological Processes
• Disturbance
• Spatial heterogeneity in resources
• Temporal heterogeneity in resources

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Importance of diversity

• Stability
• Resilience
• Resistance
• Persistence
• Invasibility
• Ecosystem Function