Advanced Ornithology
by
Maryam Riasat
ADAPTIVE RADIATIONS IN BIRDS

Evolution
 Evolution is the process by which species
adapt over time in response to their changing
environment
 The change in the characteristics of a species
over several generations relies on the process
of natural selection
 Simple to complex
 Sometimes backward, complex to simple

Types of Evolution
 Retrogressive evolution
 Micro evolution
 Macro evolution
 Divergent evolution
 Convergent evolution
 Parallel evolution

Retrogressive evolution
 Backward evolution
 Complex to simple
 The formation of simple organs from complex
 Complex organisms evolve into simpler forms
 Flightless birds have evolved from flying birds
as they lost the ability to fly e.g. Penguins

Micro evolution
 Variations within species
 A change that occurs in a population due to
changes in allelic frequencies is known as
microevolution
 These are subtle changes that can occur in very
short periods of time, and may not be visible to a
casual observer
 These changes may be due to mutations, which
can introduce new alleles into a population

Macro evolution
 Speciation
 Large-scale and visible changes that occur above
the level of species are known as macroevolution
 Macro evolution cannot occur directly, micro
evolution leads to macro evolution
 It is the result of micro evolution taking place
over many generations
 Macro evolution may involve evolutionary
changes in two interacting species or it may
involve the emergence of one or more new
species

Divergent evolution
 Share common ancestor
 Divergent evolution occurs when two organisms with a
common ancestor end up as different species
 It occurs when related species develop unique traits
due to different environments or selective pressures
 A classic example of divergent evolution is the
Galapagos finches, which Darwin discovered in
different environments
 The finches beaks adapted differently in different
patches

Convergent evolution
 Do not share common ancestor
 The phenomenon by which two or more species
independently evolve a similar trait
 The evolution of flight/wings in birds, insects and
bats which do not share a common ancestor
 They have separate evolutionary origins, but are
superficially similar because they have both
experienced natural selection that shaped them
to play a key role in flight
 Analogies are the result of convergent evolution

Parallel evolution
 They may share common ancestors or may not
 Parallel evolution occurs when independent
species acquire similar characteristics while
evolving together at the same time in the
same space
 Formation of similar structures in two
unrelated species