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Biogeography--study of the distributions of
organisms on the earth
Biota—the flora and fauna of a region
Objectives of Biogeography
• Classifying geographic regions based on
their biotas
• Reconstructing the historical development
of biotas, including their origin, spread,
and diversification
• Explaining differences in numbers and
types of species among geographic
Objectives of Biogeography
• Explaining geographic variation in
characteristics of individuals and
populations of closely related species
Zoogeography—the distributions of animal
• However, phytogeography and
zoogeography are closely linked
Zoogeography synthesizes data from
Evolutionary Biology
Two of many different specialized
areas in biogeography include:
• Historical biogeography
• Ecological biogeography
Two important issues
• Change—earth is dynamic
• Scale
The scientific process
• Identification of patterns
• Development of explanations or
hypotheses for these patterns
• Development of predictions from the
• Testing of predictions with data
Assumption of uniformitarianism or actualism
Darwin’s observations
• Fossils
• Vicariant species
• Galapagos species
The Origin of Species
published in 1859
Biological evolution is simply
changes in gene frequencies within
populations over time.
A population is a group of
organisms of the same species
found together at one place at one
point in time.
Biologists assume changes in gene
frequencies are linked to changes
in the frequencies of
morphological, physiological, and
behavioral characteristics of
Natural selection is one
mechanism of evolution
Necessary and sufficient conditions
for natural selection:
Variability of traits among individuals
Heritability of these traits
Differential reproductive success
associated with these traits
Keep in mind:
Traits which increase reproductive
success, rather than survivorship, are
more likely to increase in frequency in
future generations
Individuals and their traits are acted upon
by natural selection, not species
Other agent of evolution:
• Genetic drift
• Phyletic speciation (anagenesis)
• True speciation (cladogenesis)
Allopatric speciation
• Geographic isolation
• Population divergence
• Why do populations diverge?
• Natural selection
• Genetic drift
Biological species—a group of
actually or potentially
interbreeding natural populations
which are reproductively isolated
from other such groups
Isolating mechanisms (evolved through natural
selection or genetic drift)
Habitat differences
Temporal differences
Ethological differences
Mechanical differences
Post zygotic:
Poor quality offspring
Problems with bsc
• Semi-species
• Ring species
• Allochronic species
• Asexual species
• Allopatric species
• Hybridization
Phylogenetic species concept (PSC)--a
species is the smallest aggregation of
populations diagnosable by a unique
combination of characters and that
share a common ancestor.
Reproductive compatibility is not a
criterion for deciding whether
individuals belong to the same species
or not.
Problems with the PSC
Leads to too many species
Ignores important biological information
such as reproductive compatibility
Species can be diagnosed on the basis
of trivial characters
Too much emphasis on morphology
Evolution is an ongoing process
• Any two individual organisms are
somewhere between very distantly related
and very closely related
• The evolution of new species takes place
over time so any group of organisms may
be somewhere along the line from being
either full conspecifics, or members of fully
separate species