8.5 Community Ecology

• Community

  A group of different species living together in the same location, and they interact with one another
• Species diversity

  • The variety of different types of species and the quantity of individuals included in each species
• Species composition

  • The identity of each species in the community
• Simpson's diversity index

  A measurement tool used to measure the biodiversity of a habitat, the higher the index value the more diverse the community
• Calculating Simpson's diversity index

  Take random samples, count individuals of each species, divide each species count by total, square those values, sum the squared values, subtract that sum from 1
• Organisms cannot create their own energy, they have to access it from the environment
• Competition

  Can shift the dynamics of a community and how populations access energy and matter
• Types of interactions

  • Positive (mutualism, commensalism)
  • Negative (predation, parasitism)
  • Neutral
• Positive interaction: Mutualism

  • Bird picking parasites off mammal, both benefit
• Negative interaction: Parasitism

  • Shelf fungus absorbing nutrients from tree bark, weakening tree
• Removal of key species

  Can cause exponential growth or death in other populations, interrupt energy flow through ecosystem
• Niche partitioning

  Decrease in competition over limited resources between two similar species by accessing resources differently
• No statistical difference between sample means if error bars overlap
• Intermittent stream type had statistically lower macroscopic invertebrate species diversity compared to seasonal streams