Environmental Controls of species distributions

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Environmental Controls of species distributions

• The law of the minimum- the factor in shortest
  supply will limit growth the most
• Water, light, nutrients, micronutrients
• Problems with this idea
• Excess supply of a factor can be toxic
• Factors may be substitutable

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Environmental Controls of species distributions

• Physiological Tolerance Model
• The range of habitats for a given species is the
  sum of tolerance limits for each environmental
  factor.

Soil nitrogen
Soil pH
Light intensity
Frost free
Potential habitat
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Environmental Controls of species distributions

• Problems with this model
• Assumes that environmental factors limit plant
  distribution and ignores biotic factors such as
  competition
• Physiological tolerances may change when plants
  are grown together and are competing

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Relative growth
pH
pH
Pure culture
Mixed culture
Physiological tolerance can shift when plants are
grown in competition
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Environmental Controls of species distributions

• Physiological range-potential range of a species
• Physiological optimum-optimal conditions for a
  species
• Ecological range- observed range when grown under
  natural conditions
• Ecological optimum-observed optimum when grown
  under ideal conditions

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What is a species?

• Definition of species
• (A) Typological species-defined through reference
  to a type specimen
• (B) Morphological species-defined through shared
  traits
• Flower structure,leaf shape, chromosome number,
  biochemical pathways, similarity of DNA sequences
• (C) Biological species-members of a group of
  populations that interbreed or potentially
  interbreed with each other and produce viable
  offspring

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We typically use the Biological species concept
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Observation The morphology of a species may be
very variable
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So what causes that variation?
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• Central Questions in Ecology
• Is the variation seen in nature environmentally
  or genetically determined or both?

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Before we answer that question

• Phenotype- the observed characteristics of an
  individual, resulting from the interaction
  between the genotype and the environment in which
  development occurs
• Genotype-the sum total of the genetic information
  contained in an organismthe genetic constitution
  of an organism

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Last time we discussed

• Phenotypic plasticity-an individual that changes
  its phenotype in response to the environment
• Example plants allocate more biomass to roots
  when grown under low nutrient conditions,
• plants produce more chlorophyll when grown in
  the shade than when grown in the sun
• leaves are larger in the sun than in the shade

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How do we determine if the variation we see is
the result of differences among GENOTYPES or
PHENOTYPIC VARIATION (PHENOTYPIC PLASTICITY)
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Grow individuals taken from different
environments in a Common Garden
Turreson 1920s Hawkweed (Hieracium
umbellatum) Herbaceous perennial weed Southern
Sweden Found on sand dunes, rocky headlands,
fields and woodlands
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What Turesson did? Collected hawkweed plants
from different environments Grew them in a test
garden Any differences in morphology when grown
in test garden must be genetically based
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Were these different species?
Turesson made all the crosses and found they
could interbreed
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Genetically and morphologically distinct
individuals Ecotypes
Interfertile Yet morphologically/physiologically
distinct Prevented from interbreeding by
ecological barriers
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Hawkweed ecotypes in common garden
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Criteria for Ecotypes

• 1. Genetically based
• 2. Distinctive morphological, physiological,
  phenological or some combination
• 3. Occurred in distinct habitats
• 4. Genetic differences were adaptations
• 5. Potentially interfertile
• 6. Discrete entities, with clear differences

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• Claussen, Kieck and Hiesey 1920s
• California in the Sierra Nevada
• Multiple species
• Each species was collected at a variety of sites
• maritime, coastal, valley,foothill, subalpine,
  alpine, great basin
• Species were cloned in greenhouse

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Claussen, Kieck and Hiesey
Clones of each individual were planted out in 3
test gardens Near sea levelStanford mid-elevation
Mather High Elevation Timberline
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Environments of three transplant gardens
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Claussen, Kieck and Hiesey Results
Potentilla glandulosa (cinquefoil) Four
EcotypesA coastal range ecotype Two
mid-elevation ecotypes Alpine and subalpine
ecotype
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Figure 3.6 from book