This form of speciation involves reproductive
isolation in a population such that breeding
between descendants is no longer possible.

This form of speciation involves differences within a
population in the same geographic area, leading to the
emergence of distinct species within this population.

This form of speciation is caused by a geographic change
that isolates one part of a population from the other. Each
evolves into a distinct species from the other over time.

This type of speciation is marked by genetic divergence,
which is the accumulation of genetic differences over time,
creating pre- and postzygotic barriers in a population.

A population of flying insects of the genus Chrysopa lives in a
North American woodland habitat. Some individuals live in conifers (pine trees);
others live in deciduous (oak) trees. Each type of tree produces food for these
insects at different times of year. As a result, distinct breeding cycles emerged
for each group: the pine tree dwellers bred according to food availability in pine
trees, whereas the oak tree dwellers bred according to food availability in oak trees.
Over time, the population diverged into two distinct insect species, with the pine
dwellers unable to mate and produce fertile offspring with the oak dwellers, and vice
versa. Both species continue to share the same woodland habitat.

A mountain lake contains a population of freshwater fish. An avalanche creates
a natural, earthen dam in the middle of the lake. As a result, individuals on one
side of the dam are reproductively isolated from those on the other.

Decades pass.

A scientist studying these populations catches several males and females from each
side of the dam. In her lab, she attempts to breed individuals from one side of the
dam with members of the opposite sex from the other side. She finds that they are
not able to interbreed.