Ecology Exam 3

• ecological relationships


  competing species are more likely to coexist when they use resources in a different way
• Competition coefficients alpha and beta represent:

  • If 2 species are competing, and individual of one species negatively affects the growth rate of the other
  • Term that adds in the inhibitory effect of each species on the growth rate of the other: a competition coefficient
  • If 2 species are not competing for resources alpha and beta = 0
  • Competition coefficients (alpha and beta) can be thought of as factors to convert the number of competing species
• alpha (competition coeffcient)


  extent to which the use of resources by an individual of 2 species decreases the per capita growth rate of species 1
• When alpha = 1 individuals of the 2 species are identical in their effects on each other

  • Alpha = beta then species have the same effect on each other as they have on the same species (symmetric competition)
• Alpha < 1 individual of species 2 decreases the growth rate of species 1 by a smaller amount than does an individual of species 1

  • Intraspecific > interspecific competition
  • Species 1 has a larger effect on itself
• Competitive interactions can be modeled using the logistic equation
• Environmental conditions can result in a competitive reversal

  • The species that was inferior competitor in one habitat becomes the superior competitor in another
• Disturbances such as fires or storms can kill or damage individuals while creating opportunities for others
• Outcome of competitive interactions can be altered by predation, the physical environment, and disturbance events
• Role of consumers in an ecosystem is to obtain energy by feeding on other organism and sometimes transfer energy to other consumers
• Consumption 


  Relationship where one species consumes another individual
• Predator-prey interactions have consequences for local community structure

  • Agents of natural selection = co-evolution of predator and prey
  • Predator lowers the prey’s fitness
• Predator

  Consume another organism (prey)
• Carnivore


  Feed on different species of animal
• Cannibal


  Predator and prey are the same species
• Parasite


  Lives in or on another organism (host) and feeds on or parts of it
• Herbivore


  Eats the tissue or internal fluids of living plants
• Interactions between predators and prey are often described using food chains
• All organisms are subject to mortality e.g starvation, disease, predation
• Parasitoids


  Insects that an egg on or in another insect host

  • Most insect parasitoids only attack a particular life stage of one or several related species
  • After hatching, larva remain in host, which they eat and usually kill
  • Adults are free-living and may be predaceous
• Predators and herbivores share some similarities

  • Most eat a broad range of prey species, without showing preferences (generalist)
• Many predators will select for prey that is most abundant in the environment

  • Some move throughout their habitat in search of food
• Specialist


  Consumers that do show preference
• Mobile predators


  Concentrate their efforts in areas that yield abundant prey
• Sit-and-wait predators


  Remain in 1 place and attack prey that move within striking distance

  • Relocate from areas where prey are scarce to abundant
  • Blend in with environment very well
• Grazer herbivore


  Consumer plant parts (mostly green) near substrate

  Ex: snails graze algae, antelope graze grass
• Browsers(herbivore)


  Consume plant parts (mostly green) well above substrate

  Ex: Deer browse leaves of shrubs and saplings
• Frugivore (herbivore)


  Consume fruits (sometimes) without damaging seeds within

  • Relationship is mutualistic
• Loss of foliage decreases plant biomass, reduce plant vigor, place the individual at a competitive disadvantage and lowers the amount of energy available for reproduction

  • Moderate grazing can increase plant biomass, but usually at some cost to the plant
  • Degree of stimulation depends on species, nutrient supply, and moisture
• Most carnivores have broad diets and most herbivores have relatively narrow dietary breadth
• Zero population growth isoclines used to see what happens to predator and prey populations over long periods of time

  • Prey abundance increases when their growth rate is greater than the predator’s ability to capture them
  • Predator populations increase when their death rates are low relative to their feeding efficiency and ability to capture prey
• Parasitoids and parasites and their hosts are symbionts

  • 2 types of organisms living in close association
  • Stressful environment
  • Decreases energy available for host – decreases survivability and lower population sizes
• Parasitoids consume entire body of a prey organism (host)

  • +/- interaction
• Parasites and parasitoids typically feed on only 1 or few host species, but HOST species have MULTIPLE parasites
• Some parasitoids have parasitoids = hyperparasitoids
• Characteristics of parasitoids

  • Insects whose larvae consume the body of a host
  • Specialized choice of host
  • Only females search for hosts
  • Different parasitoid species attack different life stages of host
• Biological control


  Method of controlling nuisance species (insects, mites, plants, disease) using other organisms

  • Usually management of native predators/parasitoids but sometimes introductions (biological homogenization)
• Parasites are huge contributor to biodiversity – often hidden in their hosts and exhibit patchy special distributions

  • Difficult to detect and sample
  • Poor knowledge of parasite diversity, distributions, and extinction rates
• (Parasites and diversity) Adaptive advantage to decrease complexity

  • Multiple patterns are repeated across multiple lineages
  • Adapted to survive/flourish in definitive hosts
• Microparasites


  Viruses, bacteria, protozoans - typically pathogens

  • Multiply in their definitive host (full cycle completed in host)