BIOL208 Lecture Notes - Lecture 21: Species Evenness, Species Richness, Mycorrhiza
1 May 2018
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The Benefits of Mycorrhizae for Plants
1. Water Absorption
a. Increases root surface, in turn increases contact with moisture and surface area
for absorption of water
2. Inorganic nutrients
a. Fixes nitrogen, phosphorus, and micronutrients, necessary for growth (and often
limiting)
The Benefits to Fungi
• Source of carbohydrates
How did these relationships evolve?
• The evolution of mutualism
o Evolutionary theories predict that mutualism will evolve when the benefits of
the mutualism exceed the costs IE. BENEFITS > COSTS
▪ Eg. Ants and plants with extra floral nectaries
• Attract insects that will help keep away herbivores
• The energetic cost of producing nectar is less than the energetic
cost of recovering from herbivory
How communities are described
• Community Structure: Attributes of a community, such as the number of species or the
distribution of individuals among species within the community
o Species Diversity: A measure of diversity that increases with species evenness
and species richness
▪ Three types
• Gamma: Diversity within a region or landscape
• Alpha: Diversity within a locality within a region or landscape
• Beta: Difference between the diversity of a region or landscape,
and a locality within the region or landscape
o Beta (ex. Compare species richness of Edmonton vs. the
entire province of Alberta)
o Species Richness (s): The number of species in a community
o Species Evenness: The relative abundance of species in a community
• Guilds: Group of similarly functioning organisms
• Species dominance
o More samples = more accurate
• Niche spots will be lost in non-stable communities. Diverse communities will allow
niches to always stay filled.
• Shannon-Wiener diversity index
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