Chapter 41:  Community Ecology

 

I.  Concepts of Community Structure

  1. Individualistic hypothesis
  2. Interactive hypothesis

C.     Species diversity = species richness + relative abundance

  1. Intraspecific competition
  2. Interspecific competition

 

II.  Interspecific Interactions

A.     Coevolution

1.   secondary compounds

  1. Predation

1.      herbivory and plant defenses

a.       secondary compounds:  some secondary metabolites, like morphine, caffeine, nicotine, strychnine etc., are toxic to many plant predators

2.   animal defenses against predators

a.       cryptic coloration:  camouflage

b.      aposematic coloration

c.       deceptive coloration

d.      Batesian mimicry

e.       Mullerian mimicry

3.   parasitism

4.   parasitoidism

C.     Interspecific competition

1.      interference competition:  actual fighting over resources.

2.      exploitative competition.

3.      competitive exclusion principle

4.      ecological niches:  a niche is the description about how an organism utilizes its habitat

a.       Fundamental niche: everywhere an organism should be found.

b.      Realized niche:  part habitat in which the organism is actually found

c.       resource partitioning:  similar species actually have slightly different niches.

d.      character displacement:  in sympatric species competition causes selection and divergence of one or more characters.  Can result in resource partitioning.

F.      Mutualism and commensalism

 

III.  Interspecific Interactions and Community Structure

A.     Predator influences

1.      keystone species.

2.      switching behavior

B.  Mutualism and parasitism

C.  Interspecific competition and exotic species

1.   exotic species are introduced into an area or new habitat to which they are not endemic.  Sometimes the introduced or exotic species can out compete and exclude native or endemic community members.

D.  Environmental patchiness

1.  spatial - microhabitats

2.  temporal - seasons

 

IV.  Community Development

A.     Disturbance and stability:  disturbance and stability need to be recognized as relative terms with regard to different communities and ecosystems.

1.      monoclimax theory:  over time and after enough seres eventually an inevitable true homogenous climax community, with little diversity, would emerge.

2.      polyclimax theory:  local conditions in a broader ecosystem can support a diversity of climax vegetation types.

3.      pattern-climax theory:  recognizes a continuum of vegetation gradients forming regional variations in climax communities.

  1. Ecological succession

1.      primary succession:  the development of a community in an area previously devoid of one.

a.       Sere:  a particular successional stage

b.      Pioneer species:  first to colonize a new or primary successional area

2.   secondary succession:  redevelopment of a community where a disturbance has altered the previous one.

a.   Opportunist species:  take advantage of disturbance

3.   facilitation:  community development produces the conditions necessary for latter successional species to colonize.  Each sere paves the way for the next sere.

4.      inhibition:  suppression of colonization by a species by organisms already present in the community.

5.      tolerance