BIOL1020 - Week 9.1

biological species concept (BSC) and some short comings

• populations who interbreed in nature but do not interbreed with other group

• shortcomings:

• hard to test reproduction

• cannot test geographically separated populations

• does not apply to asexual organisms

hybridization and its importance

• individuals from different species mate and exchange genes

• species are not always completely reproductively isolated

morphospecies concept and its strengths and limitations

• defines species based on physical appearance

• strengths:

  • works for fossils and asexual organisms

• limitations:

  • cryptic species: different species look similar

  • same species can look very different

shortcomings of the morphospecies concept

• high variation within species:

  • individuals look very different

  • one species mistaken for many

• low variation between species:

  • different species look similar

  • multiple species mistaken as one

ecological species concept (ESC)

• defines species by ecological niche

• strengths:

  • works for asexual organisms

  • focuses on environmental roles and resource use

shortcomings of the ESC

• same species can occupy different niches

• different species can have similar niches

• based only on ecology, ignores reproductivity

phylogenetic species concept (PSC)

• all individuals descend from the same ancestor

• form distinct branches on a phylogenetic tree

• species can persist or go extinct as a unit

strengths and limitations of PSC

• strengths:

  • works for asexual organisms

  • uses genetic data and evolutionary relationships

  • good for identifying cryptic species

• limitations:

  • scale: too broad → different organisms grouped together; too narrow → too many species created

reproductive isolation

• barriers that prevent species from interbreeding

pre-zygotic isolating factors

acts before fertilziation

• ecological: live in different areas

• temporal: reproduce at different times

• behavioural: different courtship signals

• mechanical: physical differences prevent mating

• gamete: sperm and egg cannot fuse

post-zygotic isolating factors

acts after fertilization

• reduced hybrid viability: offspring weak or don’t survive

• reduced hybrid fertility: offspring sterile

• hybrid breakdown: later generations weak or sterile