Herpetology Chapter 13
Ecological and Historical Biogeography
Both approaches predict similar numbers of species at various latitudes
Nevertheless, many species can live in locations outside their natural distribution
Cane Toads (Australia) Pythons (Everglades) Species of Mediterranean geckos (Hemidactylus) that have colonized the New World Brown tree snake (Boiga irregularis) in Guam Thus, physiological tolerances are not the only factors limiting and determining distributions.
In historical biogeography
the perspective shifts from the recent past of ecological biogeography to the distant past
Biogeography definition
the study of distributions of animal and plant species across the planet and through time
-Climate (micro and macro) -Resource Availability -Interspecific Interactions
-Abiotic Tolerance -Biotic Tolerance -A * B Tolerance
Elevation Gradient Hypothesis vs. Riverine Barrier Hypothesis
Complex pattern of relationships in the frog Physalaemus petersi No differentiation along W-E elevation gradients (Andes to Amazon) One of the rivers (Madre de Dios) appears to have been an important barrier. Secondary contact of expanding lineages rather than divergence explains the pattern.
Molecular Systematics as a Revolutionary Tool (late 20th century)
Could now estimate time periods of major evolutionary shifts in a particular group of organisms based on calibrated molecular clocks Fit molecular patterns of divergence to independently derived estimates of time based on the fossil record and geological data.
What makes C. bicintores most interesting is that introgression appears to have occurred at least three different times in about the same place during the last few million years.
Crotaphytus bicintores has remained morphologically distinct from C. collaris but has picked up mitochondrial gene sequences through hybridization repeatedly with C. collaris
Historical Determinants of Species Distributions
Current theory and analyses are based on either a dispersal or a vicariance viewpoint
Present distribution of many species matches the past continental connections proposed by the plate tectonic (drifting continents) theory --- pleurodiran turtles
Distribution of pleurodiran turtles reflects the historical geologic links between Australia, southern Africa, and South America, a Gondwanan distribution.
Ecological Determinants of Species Distributions
Ecological approach to distributions combines physiological traits of organisms with relevant environmental variables. Each organism has specific physiological tolerances and requirements Because a species consists of multiple local populations, the species' distribution represents the total occurrences of its populations Borders of each species' distribution represent tolerance limits
Anolis nitens complex and a test of the Vanishing Refuge Hypothesis
Hypothesis posits that environmental fluctuations during the Pleistocene (2 million to 10 thousand years before present) resulted in repeated expansions and contractions of rain forest, resulting in repeated isolation of faunas in habitat patches and resultant speciation. Under this hypothesis, isolation had resulted in divergence of A. n. brasiliensis, and similar isolation events had produced other subspecies. In 2001, Rich Glor and colleagues tested this hypothesis using a molecular phylogeny of the A. nitens complex and several outgroups, many of which are also Amazonian. Results show that divergences occurred much earlier than the Pleistocene, thus falsifying the Vanishing Refuge Hypothesis for these species.
Prior to continental drift and plate tectonics what was the only available explanation for global patterns of distribution
Land bridges
Unlike ecology, biogeography...
No concern for abundance the way Ecology as a field was concerned
Present distribution of many species matches the past continental connections proposed by the plate tectonic (drifting continents) theory --- pipid frogs
Pipid frogs occur in both Africa and South America.
The Theory of Island Biogeography
Published by MacArthur and Wilson (1967) Field changed dramatically, and biogeography became a predictive science rather than simply a descriptive one.
Present distribution of many species matches the past continental connections proposed by the plate tectonic (drifting continents) theory --- slamanders
Salamanders occur mainly in the Holarctic (Nearctic + Palearctic) region; These distributions match the Mesozoic split of Pangaea into northern Laurasia and southern Gondwana Cryptobranchid, plethodontid, and salamandrid salamanders occur both in North America and Eurasia, suggesting an ancient distribution throughout Laurasia.
Difference between Ecological and Historical Biogeography in terms of evolutionary relationships
The ecological approach pays little attention to the underlying evolutionary relationships of organisms at any particular place on the planet, whereas the historical biogeography approach interprets patterns of species richness in the context of evolutionary relationships.
Glaciers
The modern continents were essentially at their present positions during the Pleistocene, the plates upon which they sit probably having moved no more than 100 km relative to each other since the beginning of the period. Pleistocene climate was marked by repeated glacial cycles in which continental glaciers pushed to the 40th parallel in some places. It is estimated that, at maximum glacial extent, 30% of the Earth's surface was covered by ice. Each glacial advance tied up huge volumes of water in continental ice sheets 1,500 to 3,000 metres (4,900-9,800 ft) thick, resulting in temporary sea-level drops of 100 metres (300 ft) or more over the entire surface of the Earth. During interglacial times, such as at present, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions. The effects of glaciation were global.
Biogeography is considered
a historical science in that distributions change through time
Most empirical studies reveal a strong correlation between the number of species and island size, if all else is equal
and island size, if all else is equal Distance of islands from mainland habitats (sources of species) also affects number of species (richness).
Biomes
are based on the similarity of the overall structure of the plant community (e.g., height and shape of plants, leaf structure, deciduous or evergreen vegetation) relative to climate. Ignores animals. Examples: tundra, boreal coniferous forest (taiga)
Ecological biogeography
center on extant or relatively recent correlates of present-day distributions
Historical biogeography (plate tectonics and its correlates)
centers on long-term (geologic time) patterns of distribution and diversification and thus correlates origins and patterns of diversification of faunas with the geologic history of the Earth.
Phylogeography
combines gene genealogies with data on present distributions to determine what led to present-day distributions
Because the evolution of life was occurring as continents moved, studies of biogeography changed radically when
continental drift and plate tectonics were accepted by the scientific community
historical biogeography
emphasizes the evolutionary history of the organisms of interest
Vicariance
event that physically separates populations (continents breaking apart, mountain ranges uplifting)
Molecular Systematics as a Revolutionary Tool (late 20th century) caused historical biogeography to
for all practical purposes, reinvented
Historical Determinants of Species Distributions assumes that
taxonomic groups are geographically static geological events produce barriers biota diverges subsequent to isolation
The Theory of Island Biogeography Posits that the number of species in a given area can be predicted based on a few key variables
island size, immigration rate, and extinction rate
The theory of island biogeography can be applied to ecological questions, particularly in
landscape ecology and conservation biology (patch dynamics, metapopulations, gene flow).
Dispersal
moving across land or water to reach new areas. Assumes taxonomic groups have a center of origin, and each group disperses from its center of origin across barriers.
Unlike plate tectonics, land bridges, and changes in ocean levels, island biogeography centers on
patch size and distance from sources and is most applicable to predicting numbers of species and immigration and extinction rates in a relatively short time period (ecological time).
Biogeographic realms
realms (also called ecozones) are based on the evolutionary and historic distribution patterns of animals and plants. Derived from higher-order relationships, typically relatively large clades, and reflect past geological events (continental drift, barriers and connections for species dispersal).
niche evolution
refers to divergence in niche characteristics.
Niche conservatism
refers to individual species maintaining ecological traits similar to those of their sister taxon and ancestors
What was missing?
was the ability to independently date divergence patterns in taxonomic groups of interest. Dated phylogenies have changed that line of thinking dramatically, and historical biogeography has transformed into phylogeography with the ability to explicitly test hypotheses.
When the phylogenetic relationships are examined
we find that ecologically similar species are often each others' closest relatives (but recall Caribbean Anolis ecomorph-example of adaptive radiation).
Niche conservatism explains
why sets of species in one region are often more similar to each other than they are to species in other regions