Week 6

• Interaction chain - a donor species affects the abundance of a transmitter and has an effect on a recipient
• Interaction modification - the donor species alters some other attribute of the transmitter, such as behavior.
• Indirect Interactions:

  • Keystone predation
  • Exploitation competition
  • Apparent competition
  • Indirect mutualism
  • Indirect commensalism
  • Habitat facilitation
  • Trophic cascade
• Pulse experiment: Parameter being measured is only altered or introduced once.

  • Disturbance is transient
  • Direct effects measured
• Press:

  • Disturbance maintained constantly
  • Direct and indirect effects measured constantly
• Bottom upcontrol is when influence is from lower to higher trophic levels (e.g.release of nutrient limitation by phototrophic growth)
• Top down control is when influence is from higher to lower trophic levels (e.g.Myxococcuspredation on E. coli)
• Trophic cascade is when an organism affects another organism two or more trophic levels away from them
• Removing one part or altering numbers of one part will have effects on the food chain
• Myxococcus predate e.coli
• Dominant species are species whose influence on their community is due to their high relative abundance
• Foundation species influence their community by physically changing their environment
• Keystone species are a species whose influence on it’s ecosystem and community is disproportional to it’s abundance.

  • Tend to be high in the food web as their influence is often through trophic interactions (who is feeding on who)
  • Keystone to community structure as they maintain it’s integrity and persistence through time
• Bacteriodes can bind to glycan-rich food particles and mucus and are considered a keystone species in human gut
• r/K selection theory: Selection drives evolution to maximize growth rate (r strategy) or maximum carrying capacity (K strategy)
• r-selected species (opportunistic, generalists)

  • high growth rate, less crowded niche, many offspring, lower survivorship
• K-selected species (equilibrium, specialists)

  • low growth rate, population size near environmental carrying capacity, strong competitors
• long length of life is a K strategy
• Large body size is a K strategy while small body size is a r strategy
• Constant population size is a K strategy
• Good competitors is a K strategy
• high growth rates is a r strategy
• high population density is a K strategy
• Species richness: the number of species within a group of individuals
• Operational Taxonomic Unit: Unit of diversity defined by method rather than species concept
• Operation taxonomical unit often uses function genetic markers

  • Lateral gene transfer functional inference from identity
• Simpson’s Diversity index 1-D:

  D =(n / N) ^ 2

  n = richness (total number of species)

  N = number of all organisms from all species
• 1-D is used so that as diversity increases, the value increase

  • Measure true diversity in that not just the number, but the proportional distribution of species is calculated
• Shannon indexmeasures the entropy, or uncertainty, in the data •That is, when sampling a population, what is the uncertainty in predicting the next individual
• In regards to shannon index:

  R = richness (total number of species)

  Pi= proportional abundance of i
• Species evenness is measured as :

  • J’ (evenness) = H’ / H’max
  • H’ max assume even distribution among species ( i.e.R / number of individuals)
• High diversity systems are thought to be robust to disturbance and permanent change due to genetic redundancy
• Higher diversity makes a system more productive

  • competition will drive selection
  • Selection leads to optimization and innovation
• Communityis a group of interacting organisms constrained in time and space
• Community ecology is the study of changes in the community structure over time and the variation between communities throughout space
• Alpha diversity studies community diversity within a habitat
• Beta diversity studies community diversity between habitats
• •Gamma diversity is the study of large scale landscape diversity (alpha and beta)
• Biogeographyis the study of species geographical distribution
• Diversity is determined by speciation, dispersal and extinction