Types of population interactions:

1
Population interactions

• Types of population interactions

• competition

• predation

• commenalism

• mutualism

• parasitism

Where have all the sea otters gone?
2
Interspecific competition

• Interspecific competition negative interactions
  between species for limited resources

• Classic laboratory experiments demonstrating
  interspecific competition

• Gause (1934) interspecific competition among
  Paramecium

Where have all the sea otters gone?
3
Interspecific competition

• Principle of competitive exclusion if two
  species compete for a limited resource, the
  species that uses the resource more efficiently
  will drive the other species to local extinction

Where have all the sea otters gone?
4
Interspecific competition

• Gause (1935) found some species could coexist

• Species coexist if they do not use resources in
  exact same way

Where have all the sea otters gone?
5
Interspecific competition

• Types of interspecific competition

• interference competition physical confrontations
  for resources (e.g. lions and hyenas at a carcass)

• exploitative competition consumption of shared
  resources (e.g. Paramecium feeding on bacteria)

• Intensity of interspecific competition depends on
  abundance of resource and niche overlap

• Niche all the ways in which an organism uses
  resources in its environment

Where have all the sea otters gone?
6
Interspecific competition

• Two ways to measure the niche of a species

• Fundamental niche entire niche that a species is
  capable of using

• Realized niche actual niche occupied because of
  interspecific interactions such as competition

• Measure fundamental and realized niches with
  removal experiments

• Connell (1961) interspecific competition between
  barnacles on the rocky intertidal zone

Where have all the sea otters gone?
7
Interspecific competition

• Connells (1961) classic experiment

• Two species of barnacles in Scotland

• Chthamalus small size, upper portion of
  intertidal zone

• Semibalanus large, lower-mid portions of
  intertidal zone

• Connell (1961) removed each species to
  investigate the reason for vertical zonation
  between barnacles

Where have all the sea otters gone?
8
Interspecific competition

• Connells (1961) classic experiment

• Chthamalus has larger fundamental niche than
  Semibalanus only Chthamalus can tolerate upper
  site

• Semibalanus outcompetes Chthamalus in mid and
  lower zones

Where have all the sea otters gone?
9
Interspecific competition

• Observational evidence of interspecific
  competition

• If two species evolve in competition, selection
  may favor changes in one or both species that
  leads to resource partitioning (subdivision of a
  niche)

Where have all the sea otters gone?
10
Interspecific competition

• Observational evidence of interspecific
  competition

• Character displacement differences in
  morphology between two species when sympatric but
  not allopatric

Where have all the sea otters gone?
11
Symbiotic relationships

• Coevolution long-term, mutual evolutionary
  changes between closely interacting species

• Coevolution can lead to symbiosis ( two or more
  species living in a close association)

• Types of symbiotic relationships

• Commensalism one species benefits and the other
  species neither benefits or is harmed by the
  association

• Mutualism both species benefit by the association

• Parasitism one species benefits and the other
  species is harmed by the association

• Classifying symbiotic relationships difficult
  requires experiments

Where have all the sea otters gone?
12
Symbiotic relationships

• Commensalism

• Clownfish and sea anemones oxpeckers and grazers

Where have all the sea otters gone?
13
Symbiotic relationships

• Mutualism

• Pollination Ants and Acacia trees

Where have all the sea otters gone?
14
Symbiotic relationships

• Parasitism

• Ectoparasites, endoparasites, brood parasites

Where have all the sea otters gone?