24.1 The Biological Species Concept
emphasizes Reproductive Isolation
The Biological Species Concept
• A species is a
population or group of
populations that can
interbreed and produce
FERTILE offspring, but
cannot produce viable
offspring with other
groups.
• Eastern meadowlark
• western meadowlark
Reproductive Isolation
• Biological species are
defined in terms of
reproductive
compatibility.
• When members of a
species are isolated
reproductively, the
members of the now two
separate populations
cannot interbreed and
produce fertile offspring.
• Usually having some sort
of barrier can on occasion
lead to hybrids, many
barriers can isolate an
organism altogether.
• Not all barriers are
obvious.
Reproductive Barriers
Prezygotic/postzygotic Barriers
Prezygotic Barriers
Postzygotic barriers
• Block fertilization from
occurring. Typically through
geographic, temporal, or
behavioral isolation.
• Various mishaps can
prevent hybrids from being
successful.
Limitations to the Biological Species
Concept
• The Biological Species Concept is defined by the
absence of gene flow (meaning hybrids typically
are not a viable option).
• Even though gene flow can occur between to
organisms (i.e. the grolar bear which is a
combination of a grizzly and polar bear).
• The Biological Species concept also doesn’t
include asexually reproducing prokaryotes.
Other Species Concepts
• Morphological Species Concept: categorizes a species
based on its morphological characteristics.
• Ecological Species Concept: Categorizes organisms
based on their niche (role in the environment).
• Phylogenetic Species Concept: categorizes a species as
the smallest group of individuals that share a common
ancestor. Compare morphology and molecular
genetics.