Interaction among Species

• Resources


  used as nutrition or habitat
• Competitors

  engage with same resources (I.e., food, territory)
• Enemies

  predators or parasites
• Mutualists

  each species obtain a benefit from one another
• Symbiosis

  intimate association between species
• Coevolution

  Reciprocal genetic change in interacting species, owing to natural selection imposed by each on the other
• Coevolution

  Selection that species exert on each other differ among populations
• Coevolution

  The nature and strength of an interaction between two species may vary depending on the genotype, environmental conditions, and other species which those species interact
• Specific coevolution

  Two species evolve in response to each other
• Diffuse coevolution

  Several species are involved and their effects are not independent
• • Escape-and-radiate coevolution

  Species evolves a defense against enemies, hence are enabled to radiate into diverse descendant species to which different enemies may later adapt.
• Red Queen Hypothesis

  Leigh Van Valen (1973)

  Conceptual basis: species (or populations) must continually evolve new adaptations in response to evolutionary changes in other organisms to avoid extinction.
• (R.A. Fisher)

  “probably more important than the changes in climate will be the evolutionary changes in progress in associated organisms"
• • Escalation (evolutionary arms race)

  • Occur if the capture rate of the prey by the predator increases with the difference between the defensive trait of a prey
  • Characteristics of both species will evolve in one direction
• Oscillation

  • Occur if the capture rate of the prey by the predator depends on a close match between the predator and prey traits
  • Results in continuing cycles of change in the characteristics of both species, contributing to cycles in population density.
• Aposematism (Aposematic mechanism)

  • Biological means by which an organism advertises its dangerous nature to a potential predator
  • Subject to positive frequency-dependent selection, and thus tend to be disadvantageous
  • Might be caused by genetic drift or when selection by predators are relaxed.
• Mimicry

  • Form of convergent evolution
  • Resemblance between different species has evolved because it is advantageous for members of one species to resemble another
• Defensive mimicry

  • most common kind; often based on aposematic coloration of other species
• Batesian mimicry

  • palatable species mimics an unpalatable species
• Batesian mimicry

  • Selection on a mimetic phenotype depend on its density and degree of unpalatability of the model species
• Müllerian mimicry

  • two or more unpalatable species are co-mimics (or co-models) that jointly reinforce aversion learning by predators
• Müllerian mimicry

  Causes positive frequency-dependent selection, since common phenotypes will be better recognized and avoided
• Secondary compounds

  • plant products that play little or no role in primary metabolism
  • Many are toxic and repellent to animals
  • insects and other herbivores impose selection for chemical and other defenses
  • Eventually, herbivores from other hosts shift to these plants, adapt to the defense, and give rise to adapted clade of herbivores.
• Overcoming the host's defenses

  Movement from one host to another


  2 greatest challenges for a parasite:
• Vertical transmission

  Horizontal transmission


  movement of one host to another by:
• Vertical transmission


  from host parent to its offspring
• Horizontal transmission


  via the environment
• Virulent Parasites


  parasites that reduce survival and reproduction of hosts
• In a host with multiple, unrelated genotypes of parasites, selection will favor the one with highest reproductive rate (may be highly virulent)
• Virulent genotypes in horizontally transmitted parasites > vertically transmitted
• If host can only support parasite reproduction for a short time, selection favors rapid parasite reproduction (greater virulence)
• Mutualisms

  • Interactions between species that benefit individuals of both species

  • Important basis for adaptation and evolution of biochemical complexity

  • Some provide one or both partners with new capabilities

  • Some have arisen from parasitic or other exploitative relationships
• However, many species “cheat” — but several factors can reduce fitness of the cheater genotypes to maintain a mutualistic relationship

  • Punishment, to prevent overexploitation
  • Reward the most cooperative/beneficial individuals or exclude cheaters
  • Selection to favor “honest” genotypes
• Intraspecific competition

  • Competition for resources between members of the same species
  • Leads to evolution of better adaptation within species
  • Basic factor in natural selection
• Interspecific competition

  • Competition for resources between members of different species
• Extinction

  Specialization


  Two major effects of interspecific competition
• Specialization

  occur when competing species evolve to different adaptations
• Extinction

  occur when >2 competing species for the same resources cannot coexist indefinitely
• Ecological Character Displacement

  Divergence in response to competition between species
• Ecological Release

  Species (or population) exhibits greater variation in resource use, and in associated phenotypic characters, if it occurs alone

  Basis: competition for resources can sustain diversity of both species and of genotypes within species