Midterm 3

• How can predators and their prey coexist?

  Limited resources for prey and spatial variation in environment
• How can two competing species coexist?

  evolutionary tradeoffs and environmental variation
• What is biocontrol?


  Using natural enemies to control pests
• What are important characteristics of biocontrol organisms that are introduced to control pest population?

  • Adapted to similar habitats where pests are present
  • Host specific (attacks pest, does not attack other species, does not harm humans)
  • Abundant
  • High per capita growth rate
  • Does not drive its prey to extinction
• How are exponential growth equations modified to represent effects of predators and prey on each other in mathematical models?

  Lotka-Volterra equations; include capture efficiency of prey and rate at which predator converts prey to offspring
• How can the outcomes of predator-prey interactions be analyzed graphically?

  Using equilibrium as a guide to predict whether populations are increasing or decreasing
• Exploitative competition: Indirect; caused by the use of a shared resource
• Interference competition: direct; caused by active interactions between individuals
• Interspecific competition: competition between different species
• Intraspecific competition: competition between members of the same species
• How can the logistic equation be modified to represent effects of competitors on each other in mathematical models?

  Lotka-Volterra competition equations; rearrange equation and add competition coefficient to both equations
• How can the outcomes of competition be analyzed graphically?

  Using equilibriums to graph whether populations are increasing or decreasing and if one population will be more successful
• What is coevolution?


  Evolution in two or more species as a response to characteristics of the species it interacts with
• Examples of coevolution:

  • Flowers and pollinators
  • Toxic compounds in plants and resistance by herbivores
• What are the three classes of mutualism?

  Dispersive, defensive, and trophic
• Examples of dispersive mutualism:

  • Plants and pollinators
  • Yucca and Yucca moth
  • Plants and herbivores
• Examples of defensive mutualism:

  • Acacia and ants
  • Ant and bacteria
• Examples of trophic mutualism:

  • Ant and fungus
• How do new species arise?

  Speciation
• Independent communities: communities are random assemblages of species
• Interdependent communities: species occur only in their community
• What are top-down effects on communities?

  Lower levels of food webs regulated by factors higher up (predation)
• What are bottom-up effects on communities?

  Higher levels of food webs regulated by factors lower down (production, prey)