Biogeography
H1: Science & history of biogeography
1.1: What is biogeography?
Biogeography = scientific study of distribution of organisms across space & time, with processes that explain these
distributions (aka where species are found, why they occur there & how historical events have shaped their
presence).
• Traditionally, biogeography focused on documenting distribution of organisms in present & past (includes
recent history & events that occurred millions of years ago, such as continental drift or mass extinctions).
• Modern biogeography now studies patterns of geographic variation in nature at multiple levels, ranging from
genes & species to entire ecosystems. These patterns are analyzed across different geographic gradients (such
as Area, Isolation, Latitude, Elevation & Ocean depth) => Overall, biogeography has 3 main objectives:
o Describing & reconstructing patterns of biodiversity across space & time
o Understanding how these patterns change in past & present
o Identifying processes (ecological & evolutionary) that drive these changes
Questions in biogeography, all relate to 1 central theme = How & why does biological diversity on Earth vary spatially
& temporally?
• Why are different regions of planet, even those with similar soils, climates, & other environmental conditions,
inhabited by distinct biotas?
• How do size, shape, & patterns of overlap of geographic ranges vary among taxa, over evolutionary history of
particular lineages, or across geographic regions & realms (such as across continents & across ocean basins)?
• How have historical events (such as plate tectonics, mass extinctions of once-dominant life forms, glacial
episodes of Pleistocene epoch), & more recent periods of climate change (natural or anthropogenic) shaped
distributions & patterns of geographic variation of extant biotas?
• How are isolated oceanic islands colonized, why are there nearly always fewer species on islands than in same
kind of habitats on continents?
Biogeography as Scientific Discipline, is multidisciplinary field integrating knowledge from Biology,
Ecology, Geography, Geology & Paleontology. Although it has long intellectual history, it is considered
relatively young scientific discipline with its 1st formal books appearing in late 19th century.
1.1.1: Biogeography vs. Ecology
Biogeography => Operates at large spatial & temporal scales. It typically studies patterns across regions to entire
globe, over time spans ranging from thousands to millions of years.
• Its main units of study include: Species, Clades (evolutionary lineages), Geographic ranges
• Key processes of interest are: Speciation, Extinction, & Expansion or contraction of species ranges
• Biogeography often uses descriptive, correlative, & phylogenetic approaches to answer questions like:
o Why are species distributed way they are?
o Which geological events explain current distributions?
o When & where did speciation or extinction occur?
Ecology => Focuses on smaller spatial & temporal scales, typically ranging from local to regional environments & from
individual lifetimes to population cycles.
• Its main units of study include: Individuals, Populations & Communities
• Ecology examines biotic & abiotic interactions that influence species distribution & abundance: Competition,
Predation, Climate & Resource availability
• It relies more on experimental & replicated studies, addressing questions like:
o Why do populations increase or decrease?
o How do species interact with each other?
o Which environmental factors influence biodiversity?
,Overlap Between 2 Fields => There is grey zone between biogeography & ecology, particularly
at regional spatial scales & intermediate timeframes. In this overlap, both ecological
interactions & historical processes are necessary to fully understand species distributions.
1.1.2: 2 schools of biogeography
Ecological biogeography = Studies how current environmental factors influence distribution of organisms.
• It’s about recent processes (such as Climate fluctuations, Environmental gradients, Species interactions), so it
focuses on:
o Short time scales, often from Pleistocene (≈2.58 million years ago) to present
o Smaller spatial scales
o Species or subspecies level
• Questions answered:
o Why is species confined to its present range?
o What enables it to live where it does, & what prevents it from expanding into other areas?
o What roles do soil, climate, latitude, topography & interactions with other organisms play in limiting its
distribution?
o How do we account for replacement of 1 species by another as 1 moves up mountain or seashore, or from
1 environment to another?
o Why are there more species in tropics than in cooler environments?
o Why are there more endemic species in environment X than in environment Y ?
o What controls diversity of organisms that is found in any particular region?
• Examples:
o Map of estimated species richness of most land animals across world.
o Global patterns of vascular plant species richness (related to altitude,
precipitation, T°, ...)
▪ Geographic distribution of richness data of vascular
plants for 1032 geographic regions analyzed in this
study (each dot presents mass centroid of
geographic entity) Regions differ in size & that
species counts have not been standardized.
▪ Species-richness maps show area-standardized
predictions of 3 different global models across equal
area grid based on combined multipredictor model.
Historical biogeography (older than 2,58 ma) = Study species distributions in terms of their evolutionary & geological
history.
• It examines processes (such as Plate tectonics, Continental drift, Evolutionary divergence & Extinction events),
so it focuses on:
o Long time scales (millions of years)
o Large spatial scales (continents, ocean basins)
o Higher taxonomic groups, including extinct taxa
• Questions answered:
o How did taxon come to be confined to its present range in space?
o When did that pattern of distribution come to have its present boundaries, & how have geological or
climatic events shaped that distribution?
o What are species’ closest relatives, & where are they found?
o What is history of group, & where did earlier members of group live?
o Why are animals & plants of large, isolated regions (such as Australia & Madagascar, so distinctive)?
o Why are some closely related species confined to same region, but in other cases they are widely
separated?
, • Examples => Ancient DNA reveals elephant birds & kiwi are sister
taxa clarifies ratite bird evolution. These findings help explain how
plate tectonics & continental drift influenced species distributions
over millions of years
Fields (such as paleoecology & phylogeography) connect ecological & historical
biogeography by linking recent ecological processes with deep evolutionary history.
Anthropologist Thor Heyerdahl demonstrated with Kon-Tiki expedition that natural
dispersal across oceans is possible using simple rafts. => This illustrates principle =
In nature, there are gradients rather than strict boundaries, & same applies to scientific disciplines.
1.1.3: Dispersal & Vicariance biogeography
Dispersal:
Dispersal = movement of organisms (or their offspring) that leads to expansion of species’ geographic range =>
Fundamental process in biogeography that it explains how species spread across space.
Mechanisms of Dispersal = various vectors wind, water & animals. => Example:
• Plant seeds can be transported over long distances by animals or ocean currents.
• Global Spread of Tomato yellow leaf curl virus => Virus originated in
Israel & its host plant (tomato) was domesticated in Andes. Through
human activities (such as Columbian Exchange) tomato spread
worldwide, because virus followed its host, expanding across continents
=> Shows how biological dispersal is often linked to historical events &
human activity.
Vicariance:
Vicariance = Explains how closely related species can occur in different
geographic regions => Refers to splitting of ancestral species’ range into
separate parts due to formation of barrier & this results in disjunct
(discontinuous) distribution. Example:
• Oceans formed by tectonic rifting
• Mountain ranges
• Rivers
• Climatic shifts
• Other geological or environmental changes
When once continuous population is divided by barrier, gene flow between separated populations is interrupted →
Over time, these isolated groups evolve independently → Can lead to formation of new species.
• Example: Distribution of elephants => Although
suitable habitats may exist across multiple regions
(often represented as broad “potential distribution”
areas on maps), elephants are not found everywhere
within those zones. This is because historical barriers &
evolutionary processes have shaped their actual
distribution, resulting in separate species (such as African & Asian elephants).
Biogeographic patterns are rarely explained by 1 single process, but usually result from combination of vicariance,
dispersal, evolution, & extinction.
• Vicariance explains distributions through splitting of ranges
• Dispersal explains distributions through movement of organisms across space
, => To distinguish between these processes, scientists must consider timing of geological events, age of landmasses
(such as islands) & evolutionary relationships between species
When you have 2 closely related species occur on different islands
• If 1 island is younger than divergence time of species => species must have reached island by dispersal.
• If landmass split after species existed => vicariance
In reality with modern data, biogeographers can explain most (but not all) distribution patterns, highlighting
complexity of natural systems.
1) Allopatric Speciation (allos = other, patra = homeland) = form of speciation in which
populations become physically separated by geographic barrier & evolve genetic
differences that eventually prevent interbreeding.
When barrier arises → Gene flow between populations stops → Each population evolves independently → Over
time, reproductive isolation develops => If barrier later disappears, populations may no longer be able to interbreed
& this means they became distinct species.
Allopatric speciation can occur due to various types of barriers:
• Geographical barriers (rivers, mountains)
• Climatic changes (such as warming forcing species uphill) =>
Climate warming can push populations into isolated mountain
habitats, where they evolve separately. If conditions later
change & populations come into contact again, they may no
longer reproduce successfully.
Flickering connectivity hypothesis = repeated cycles of connection & isolation due to environmental changes, which
can accelerate diversification.
Example:
• River Barriers => In Amazon, populations of tamarin monkeys are separated by large rivers. When rivers are
wide & have strong discharge, individuals can’t cross them & this leads to genetic divergence & eventual
speciation.
• Early (Incipient) Speciation => Closely related owl species (such as
Northern spotted owl & Mexican spotted owl) live in different
environments & show
o Slight ecological & behavioral differences
o Emerging genetic divergence
=> They can still interbreed, but their offspring may be less fit.
This is “grey zone” of speciation, where process is ongoing but
not yet complete.
2) Peripatric Speciation = special case of allopatric speciation in which small group from larger population colonizes
new, isolated habitat. => Process involves:
• Founder event (small initial population)
• Strong genetic drift
• Rapid divergence due to isolation & different environmental conditions
Concept was strongly developed by Ernst Mayr.
Differences from Allopatric Speciation => While both involve geographic isolation, peripatric speciation is
characterized by much smaller population size, colonization event & stronger effects of chance (genetic drift).
Typically, colonization occurs from older to younger islands & is followed by speciation.
H1: Science & history of biogeography
1.1: What is biogeography?
Biogeography = scientific study of distribution of organisms across space & time, with processes that explain these
distributions (aka where species are found, why they occur there & how historical events have shaped their
presence).
• Traditionally, biogeography focused on documenting distribution of organisms in present & past (includes
recent history & events that occurred millions of years ago, such as continental drift or mass extinctions).
• Modern biogeography now studies patterns of geographic variation in nature at multiple levels, ranging from
genes & species to entire ecosystems. These patterns are analyzed across different geographic gradients (such
as Area, Isolation, Latitude, Elevation & Ocean depth) => Overall, biogeography has 3 main objectives:
o Describing & reconstructing patterns of biodiversity across space & time
o Understanding how these patterns change in past & present
o Identifying processes (ecological & evolutionary) that drive these changes
Questions in biogeography, all relate to 1 central theme = How & why does biological diversity on Earth vary spatially
& temporally?
• Why are different regions of planet, even those with similar soils, climates, & other environmental conditions,
inhabited by distinct biotas?
• How do size, shape, & patterns of overlap of geographic ranges vary among taxa, over evolutionary history of
particular lineages, or across geographic regions & realms (such as across continents & across ocean basins)?
• How have historical events (such as plate tectonics, mass extinctions of once-dominant life forms, glacial
episodes of Pleistocene epoch), & more recent periods of climate change (natural or anthropogenic) shaped
distributions & patterns of geographic variation of extant biotas?
• How are isolated oceanic islands colonized, why are there nearly always fewer species on islands than in same
kind of habitats on continents?
Biogeography as Scientific Discipline, is multidisciplinary field integrating knowledge from Biology,
Ecology, Geography, Geology & Paleontology. Although it has long intellectual history, it is considered
relatively young scientific discipline with its 1st formal books appearing in late 19th century.
1.1.1: Biogeography vs. Ecology
Biogeography => Operates at large spatial & temporal scales. It typically studies patterns across regions to entire
globe, over time spans ranging from thousands to millions of years.
• Its main units of study include: Species, Clades (evolutionary lineages), Geographic ranges
• Key processes of interest are: Speciation, Extinction, & Expansion or contraction of species ranges
• Biogeography often uses descriptive, correlative, & phylogenetic approaches to answer questions like:
o Why are species distributed way they are?
o Which geological events explain current distributions?
o When & where did speciation or extinction occur?
Ecology => Focuses on smaller spatial & temporal scales, typically ranging from local to regional environments & from
individual lifetimes to population cycles.
• Its main units of study include: Individuals, Populations & Communities
• Ecology examines biotic & abiotic interactions that influence species distribution & abundance: Competition,
Predation, Climate & Resource availability
• It relies more on experimental & replicated studies, addressing questions like:
o Why do populations increase or decrease?
o How do species interact with each other?
o Which environmental factors influence biodiversity?
,Overlap Between 2 Fields => There is grey zone between biogeography & ecology, particularly
at regional spatial scales & intermediate timeframes. In this overlap, both ecological
interactions & historical processes are necessary to fully understand species distributions.
1.1.2: 2 schools of biogeography
Ecological biogeography = Studies how current environmental factors influence distribution of organisms.
• It’s about recent processes (such as Climate fluctuations, Environmental gradients, Species interactions), so it
focuses on:
o Short time scales, often from Pleistocene (≈2.58 million years ago) to present
o Smaller spatial scales
o Species or subspecies level
• Questions answered:
o Why is species confined to its present range?
o What enables it to live where it does, & what prevents it from expanding into other areas?
o What roles do soil, climate, latitude, topography & interactions with other organisms play in limiting its
distribution?
o How do we account for replacement of 1 species by another as 1 moves up mountain or seashore, or from
1 environment to another?
o Why are there more species in tropics than in cooler environments?
o Why are there more endemic species in environment X than in environment Y ?
o What controls diversity of organisms that is found in any particular region?
• Examples:
o Map of estimated species richness of most land animals across world.
o Global patterns of vascular plant species richness (related to altitude,
precipitation, T°, ...)
▪ Geographic distribution of richness data of vascular
plants for 1032 geographic regions analyzed in this
study (each dot presents mass centroid of
geographic entity) Regions differ in size & that
species counts have not been standardized.
▪ Species-richness maps show area-standardized
predictions of 3 different global models across equal
area grid based on combined multipredictor model.
Historical biogeography (older than 2,58 ma) = Study species distributions in terms of their evolutionary & geological
history.
• It examines processes (such as Plate tectonics, Continental drift, Evolutionary divergence & Extinction events),
so it focuses on:
o Long time scales (millions of years)
o Large spatial scales (continents, ocean basins)
o Higher taxonomic groups, including extinct taxa
• Questions answered:
o How did taxon come to be confined to its present range in space?
o When did that pattern of distribution come to have its present boundaries, & how have geological or
climatic events shaped that distribution?
o What are species’ closest relatives, & where are they found?
o What is history of group, & where did earlier members of group live?
o Why are animals & plants of large, isolated regions (such as Australia & Madagascar, so distinctive)?
o Why are some closely related species confined to same region, but in other cases they are widely
separated?
, • Examples => Ancient DNA reveals elephant birds & kiwi are sister
taxa clarifies ratite bird evolution. These findings help explain how
plate tectonics & continental drift influenced species distributions
over millions of years
Fields (such as paleoecology & phylogeography) connect ecological & historical
biogeography by linking recent ecological processes with deep evolutionary history.
Anthropologist Thor Heyerdahl demonstrated with Kon-Tiki expedition that natural
dispersal across oceans is possible using simple rafts. => This illustrates principle =
In nature, there are gradients rather than strict boundaries, & same applies to scientific disciplines.
1.1.3: Dispersal & Vicariance biogeography
Dispersal:
Dispersal = movement of organisms (or their offspring) that leads to expansion of species’ geographic range =>
Fundamental process in biogeography that it explains how species spread across space.
Mechanisms of Dispersal = various vectors wind, water & animals. => Example:
• Plant seeds can be transported over long distances by animals or ocean currents.
• Global Spread of Tomato yellow leaf curl virus => Virus originated in
Israel & its host plant (tomato) was domesticated in Andes. Through
human activities (such as Columbian Exchange) tomato spread
worldwide, because virus followed its host, expanding across continents
=> Shows how biological dispersal is often linked to historical events &
human activity.
Vicariance:
Vicariance = Explains how closely related species can occur in different
geographic regions => Refers to splitting of ancestral species’ range into
separate parts due to formation of barrier & this results in disjunct
(discontinuous) distribution. Example:
• Oceans formed by tectonic rifting
• Mountain ranges
• Rivers
• Climatic shifts
• Other geological or environmental changes
When once continuous population is divided by barrier, gene flow between separated populations is interrupted →
Over time, these isolated groups evolve independently → Can lead to formation of new species.
• Example: Distribution of elephants => Although
suitable habitats may exist across multiple regions
(often represented as broad “potential distribution”
areas on maps), elephants are not found everywhere
within those zones. This is because historical barriers &
evolutionary processes have shaped their actual
distribution, resulting in separate species (such as African & Asian elephants).
Biogeographic patterns are rarely explained by 1 single process, but usually result from combination of vicariance,
dispersal, evolution, & extinction.
• Vicariance explains distributions through splitting of ranges
• Dispersal explains distributions through movement of organisms across space
, => To distinguish between these processes, scientists must consider timing of geological events, age of landmasses
(such as islands) & evolutionary relationships between species
When you have 2 closely related species occur on different islands
• If 1 island is younger than divergence time of species => species must have reached island by dispersal.
• If landmass split after species existed => vicariance
In reality with modern data, biogeographers can explain most (but not all) distribution patterns, highlighting
complexity of natural systems.
1) Allopatric Speciation (allos = other, patra = homeland) = form of speciation in which
populations become physically separated by geographic barrier & evolve genetic
differences that eventually prevent interbreeding.
When barrier arises → Gene flow between populations stops → Each population evolves independently → Over
time, reproductive isolation develops => If barrier later disappears, populations may no longer be able to interbreed
& this means they became distinct species.
Allopatric speciation can occur due to various types of barriers:
• Geographical barriers (rivers, mountains)
• Climatic changes (such as warming forcing species uphill) =>
Climate warming can push populations into isolated mountain
habitats, where they evolve separately. If conditions later
change & populations come into contact again, they may no
longer reproduce successfully.
Flickering connectivity hypothesis = repeated cycles of connection & isolation due to environmental changes, which
can accelerate diversification.
Example:
• River Barriers => In Amazon, populations of tamarin monkeys are separated by large rivers. When rivers are
wide & have strong discharge, individuals can’t cross them & this leads to genetic divergence & eventual
speciation.
• Early (Incipient) Speciation => Closely related owl species (such as
Northern spotted owl & Mexican spotted owl) live in different
environments & show
o Slight ecological & behavioral differences
o Emerging genetic divergence
=> They can still interbreed, but their offspring may be less fit.
This is “grey zone” of speciation, where process is ongoing but
not yet complete.
2) Peripatric Speciation = special case of allopatric speciation in which small group from larger population colonizes
new, isolated habitat. => Process involves:
• Founder event (small initial population)
• Strong genetic drift
• Rapid divergence due to isolation & different environmental conditions
Concept was strongly developed by Ernst Mayr.
Differences from Allopatric Speciation => While both involve geographic isolation, peripatric speciation is
characterized by much smaller population size, colonization event & stronger effects of chance (genetic drift).
Typically, colonization occurs from older to younger islands & is followed by speciation.
