S3: W11 (Prof. Kelsey) Flashcards
(52 cards)
Dispersal-Vicariance attributes? (5)
• Before plate tectonics was accepted, dispersal was the only mechanism that could be used to explain many distributions.
• Darwin’s Ho was LJD.
• Vicariance biogeographers: “Dispersal can be invoked to explain any distributio. It cannot be tested & is not science”.
• Vicariance biogeographers were WRONG! because dispersal does happen and it can be tested.
• Vicariance is often the most parsimonious explanation. If so, it is the best & simplest explanation.
Hypotheses we consider in Dispersal-Vicariance? (2)
• Dispersal hypothesis.
• Vicariance hypothesis.
Dispersal hypothesis?
= depends on the biology of organisms (do you know/are you provided with the biology of the organism?).
Vicariance hypothesis?
= often the simplest explanation as it simply says that a mountain popped up & separated populations, resulting in their divergence (for example).
Eg of Dispersal-Vicariance?
Panama isthmus.
Explain Panama isthmus? (3)
● Species pairs across the isthmus (key to species vicariance).
● Pattern repeated in shrimp, fish, snails.
● Vicariance in that isthmus rose up out of ocean, divided those populations & those populations started to diverge.
Dispersal-Vicariance vs Secular migration?
● Secular migration
= species divergence due to adaptation.
● Dispersal-Vicariance
= species divergence due to separation/barrier.
Thing to note about Panama isthmus eg?
Species pairs give you an idea of what causes divergence.
Eg of Dispersal hypothesis/Dispersal?
Juncus.
Eg of Vicariance hypothesis/Vicariance?
Northofagus.
Explain eg of Juncus? (5)
● Wind-blown in roaring 40s.
● Little genetic structure.
● No common community links (no coupling of organisms).
● Volcanic islands & continents.
● Good eg of LJD.
Explain eg of Nothofagus? (5)
● Seeds don’t survive in sea water.
● Strong genetic structure (high Fst).
● Community structure exists.
● Continental landmasses only.
● Phylogenetic relationships.
Goelogical Time Scales (GTS) attributes? (6)
• Hierarchical (eons, eras, periods & epochs).
• Transitions among the geological strata & the associated fossils.
• Names are based on sediments exposed during that time.
• Length of time.is different.
• Time scale is non-linear so you have to think about whether it is logarithmic or shortened.
• Defining a time point is based on biodiversity & change in geology.
What is defining a time point based on? (2)
• Biodiversity during that time.
• Change in geology (chemical composition– Ur to Pb).
Geology attributes? (2)
• ½ life of difference elements help you figure out the dates of time.
• Correlate to biodiversity by indicating a shift in biodiversity.
Plate tectonics attributes? (6)
• Original name was Continental drift.
• Most profound & important impact on the study of biogeography.
• How they are situated on the Earth informs decisions on species diversity & distribution.
• Highly speculative idea in the early 1900s to a well-established fact in the 1960s.
• Continents have rafted across the surface of the Earth on the upper mantle of the Earth’s crust.
• Today, it is conclusive.
Why is Plate tectonics conclusive today? (2)
It’s because of:
• Evidence (direct & indirect).
• We know more about the mechanisms.
Wegener’s continental drift attributes? (6)
• German meteorologist.
• Remarkable insights & formulated intuitive ideas around plate tectonics.
• Noted the alignment of the continents across the Atlantic & realized many things.
• Wegener’s ideas were met with huge resistance.
• Most evidence only came to light decades after he died.
• Made many insightful hypotheses.
What are the “things” that Wegener realized? (5)
● Coal beds in N. America & Europe indicate a more tropical climate in the past.
● The tillites in subtropical Afriac indicated a much cooler climate at one time.
● Tillites in Africa & S. America are continuous with each other.
● Many biogeographic patterns are more easily explained if continents had been joined.
● In these times, the continental shelf had not been mapped.
Tillite?
= lithified till that is evidence of much older glaciation.
What were Wegener’s insightful hypotheses? (10)
● Continental rocks (sial) are less dense, thicker & less magnetized than those of the ocean floor (which is composed largely of basaltic rock & is collectively called sima).
● Lighter sialic blocks, which form the continents, float on a layer of viscous fluid mantle.
● Proposed that the major landmasses of the Earth were once united as a single super-continent called Pangaea.
● Pangaea broke into smaller continental plates, which moved apart as they floated on the mantle.
● Break up of Pangaea began as a rift valley.
● Mid-oceanic ridges mark where continents were once joined.
● Trenches formed where plates come together (site of major earthquakes & active volcanism).
● Suggested speeds from 0.3–36m/year, and the fastest at the moment is Greenland, which separated from Europe 100 000 years ago.
● The forces that cause the movement are radioactive. Whatever they were, they are not catastrophic.
● Ongoing forces are are moving these plates & there’s a continuous movement.
Plate tectonics attributes regarding evidences & discoveries? (4)
• Hard evidence came about 50 years after Wegener’s proposal.
• Best-fit data, Carey (1955) & Bullard (1965).
• Coastal is not the edge of the continental shelf.
• Discoveries about ocean floor/evidences for plate tectonics.
Discoveries about the ocean floor/Evidences for plate tectonics? (4)
● Ocean floor basalt under a layer of sediment.
● Mid-oceanic ridges & trenches.
● Age of sea floor was never older than 200 million years (young over the entire ocean of Earth).
● Magnetized Fe & Titanium oxides.
Magnetism of the sea floor attributes? (3)
• Happened many times through history.
• Patterns were found to be mirror images.
• Position of N is not constant & every so often reverses (the polarity of the N & S poles switches).