I. Plate tectonics, palaeoclimates, and speciation Flashcards
What is phylogenetic diversity?
The number of different families that species belong to.
High species richness doesn’t guarantee high PD because could all be in one family.
The principle thing is that tropical rainforests will have highest PD because of optimal, warm and wet conditions, “perfect” growing conditions.
Outline the academic history of ideas surrounding explanations for the uneven distribution of species across the planet.
1707-1788: Linnaeus - accepted Noah’s Ark Theory; and Buffon - countered NAT and Biblical explanations, noticed different species compositions within same biome
1830-50s: Lyell - climate and surface have changed, species haven’t; and Darwin - evolutionary dispersal theory
1920s: Wegener - proposed tectonic plate theory
1950s: dispersal theory widely accepted but then overshadowed by acceptance of tectonics in wake of the theory of continental drift
Outline the timeline of tectonic events in the neotropics (7 stages).
200 Ma: Pangaea
150 Ma: Laurasia splits off (nothern), Gondwana in south
125 Ma: Africa and S America start to split
100 Ma: S America splits from Africa, but still joined to Antarctica which is joined to Australia
80 Ma: Australia splits off
60 Ma: almost all split with the exception of land bridges
30 Ma: S America splits completely from Antarctica
What affect did this tectonic movement have?
Major influence on oceanic circulation and climate, as well as the ability for mobile organisms to move further than before, opportunities for speciation (mostly vicariance type) and adaptations, new niches filled (i.e. interchange) etc.
What are the contestations that have arisen around tectonics and biogeography?
The extent to which varied species evolution was enabled by dispersal or the joining together/splitting of continents.
E.g. Isthmus of Panama = Great American Biotic Interchange -> proposed as the cause of ALL variation in Latin American legumes BUT in looking at molecular phylogenies, it seems the species is too young i.e. dispersal can overwrite the effects of tectonics (Lavin et al., 2004, 2005)
Species younger than timings of tectonic convergence/divergence point towards dispersal theory - enabled through dated phylogenetic trees.
What is the Great American Biotic Interchange?
When the Isthmus of Panama formed (when NA and SA joined for first time), mammalian species evidenced to have crossed and mixed e.g. N. American species found in Amazonian locations at younger dates, and vice versa.
Cody et al. 2010.
Is the GABI applicable to plants? Why/why not?
So far there is a major lack of fossil records for plants.
Use of dated phylogenetic trees -> S. American taxa ‘switching’ to Central American taxa, BUT evolutions required inbetween not yet found.
Some families date to before the closure of the IoP - why did the interchange happen for animals and not plants?
Answers: 1) closed later than thought, maybe 15 rather than 30 Ma; or 2) plants disperse more effectively than animals i.e. don’t need land and can self-fertilise i.e. don’t need a mate!
How did tectonic change influence neotropical climates and habitats?
Current forced to go around the continent instead of between when IoP closed -> Gulf Stream. Humboldt current (S-N on W of S. America), a cold current that prevents moist Pacific air reaching S. America.
Andean uplift -> orographic rainfall causing different climates on either side: W side, only get moisture from mist, up W flank very arid, E flank very moist at points but prevents winds from Atlantic and Amazon
NB. Uplift thought to result in wider scale climate alterations i.e. increased erosion and weathering, more storage of C, cooling trend Earth History -> how did these climates influence the movement of plants?
How did plate tectonics influence biogeographic methods and thinking?
Became dominant, would be nice to have a single universal explanation, but world more complex than that. A dominant paradigm but not necessarily applicable in all contexts.
For plants in particular dispersal appears to be a pervasive explanation i.e. via altering climates and creation of new habitats, plants have to be highly adapted and thrive -> in situ adaptations -> role of speciation!
How else could plant species have reached South America post-isolation from Gondwana?
Dick and Pennington (2019): evidence of a large amount (50%) of Ecuadorean forest tree species descend from ‘immigrant lineages that colonized S America during Cenozoic (since 66 Ma) through long-distance/intercontinental dispersal through a review of the history of Neotropical tree diversity over past 100 million years.
Sudden appearance of tree -> raft-dispersal? Marine dispersal.
Species in clades from outside S. America when isolated in Cenozoic -> “immigrant lineages”
Why is speciation important to consider?
Because all species have descended VIA SPECIATION from a common ancestor.
What are species and how are they differentiated?
Often identified through their morphology (shapes) but this occurs through reproductive isolation i.e. when a community that occupies a specific niche in nature can reproduce. (Mayr, 1982).
What is key to speciation, and its 2 aspects?
GENETIC DIFFERENTIATION
1) Natural selection: mutation in genome generates variety, the alleles that are adaptive/suited increase at expense of less adaptive
2) Genetic drift: random changes in allele frequencies due to chance survival and reproduction
What counters genetic variation?
GENE FLOW - the movement of seeds/pollen. This means that geographic isolation must play a crucial role in the evolutionary process since dispersal can be limited/enabled by environmental changes.
Outline the general process of speciation in 4 steps.
- Isolation (geographic) allows two populations to diverge genetically
- Change in gene frequency (through adaptation or drift)
- Evolution of new stable genotypes in separate populations
- Incompatability of two genotypes, leading to further isolation
