Species & Speciation

Morphological Species Concept Species are based on comparison and differences existing in the physical characteristic between organism

Morphological Problems Two organisms that appear to be different species may be the same species Likewise, organism with similar characteristics may be place in the same taxonomic groups when they shouldn’t be (fish and whales)

Evolution & Phylogeny After the publication of On the Origin of Species in 1859 by Charles Darwin classification took on new meaning. Phylogeny is a form of classification with the goal of representing the evolutionary relationships and history of living organisms

Biological Species Concept Species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups. (Mayr, 1942) A species is a group of individuals fully fertile, but barred from interbreeding with other similar groups by its physiological properties. (Dobzhansky, 1935)

Speciation Process by which: a) subpopulations of one species diverge becoming adapted to different environments and reproductively isolated b) descendants of a species become adapted to an environment different than the one in which it was originally adapted such that they are qualitatively distinct from their ancestor

Allopatric Speciation Mode of speciation in which the subpopulations diverge because they are ‘separated by a geographic barrier’ Common barriers include water (oceans to rivers), landforms (canyons and mountains), climate (glacial periods), and habitats (deserts, tropics, etc…).

Geographic Separation Once populations of a species are geographically separated the genes that determine their characteristics can no longer be shared (gene flow stops). If the environment in the different geographic regions is not the same, then each population may diverge in their characters through natural selection. If these populations are segregated long enough the populations may become new species.

Reproductive Isolation Pre-Zygotic Mechanisms 1) Temporal 2) Behavioral 3) Mechanical 4) Ecological 5) Gametic Mortality Post-Zygotic Mechanisms 1) Hybrid Inviability 2) Hybrid Sterility 3) Low Fitness Hybrids

Continental Drift & Speciation Alfred Wegener In the 1930’s suggested that continents were (and are currently) moving relative to each other and that at some time in the past they were joined together forming a super continent Pangea

Evidence for Continent Drift Continental Geography Paleontology and Climate Past Glacial Events

Continental Geography The eastern coast of South America and the western coast of Africa appear to fit nicely together like pieces of a puzzle

Paleontology & Climate The ranges of fossil plant and animal specimens of similar age appear to correlate well across current continental boundaries Tropical fossils exist in Antarctic sediment suggesting that this continent has not always existed in its current location

Past Glacial Events Mapping of the extent of glacial rock remains on the different continent suggests particular connections between the continents in the past

Plate Tectonics Continental Drift was not taken seriously by the geological community until a mechanism that could explain the movement of the continents could be developed Technical developments associated with WWII allowed a better understanding of the Ocean Floor and subsequent development of the mechanism of Plate Tectonics in the 1970’s

Evidence for Plate Tectonics Ruggedness and Age of the Ocean Floor Oceanic Ridges and the process of Sea Floor Spreading Oceanic Trenches and the process of Mountain Formation, Volcanoes, and Earthquakes

Ruggedness of the Ocean Floor Through development of sonar and more extensive use of submarines a picture of a rugged sea floor emerged (previously it was thought that the ocean floor was flat) In fact, the Earth’s largest feature is the Mid-Atlantic Ridge running down the middle of the Atlantic Ocean

Oceanic Ridges At ocean ridges new crust arises from magma within the Earth forcing the existing plate out while a new border for the plate is being made

Magnetic Striping As new magma cools magnetic crystals within it line up with the magnetic poles of the Earth The north end facing north and the south end facing south

As magma in the Earth’s core circulates “magnetic or polar reversals” occur Our current north and south flip such that the magnetic crystal line up opposite of what they would be normally.

Oceanic Trenches Where two plates come together one is subducted under the other forming a trench Tension builds up in the plate laying on top while heat may generate magma below (Mts & Volcanoes)

Mapping of the distribution of Earthquakes across the globe correlates well with places were plates are coming together

Information on Continental Drift and Plate Tectonics