please answer both in a clear way, thanks 1. Discuss the implications of the spr

Question

please answer both in a clear way, thanks

1. Discuss the implications of the spread and change of species distributions after the retreat of the Pleistocene glaciers for evolutionary changes in species and for the species composition of ecological communities.

2. Describe the major mass extinctions over geological time. When did each occur? What was the most probable cause for each mass extinction event? What is the evidence to support each cause? How does the background rate of extinction over most of geological time compare to our current rate of extinction in present time?

Explanation / Answer

1. The retreat of Pleistocene glaciers is also called the quaternary glaciation. This period extends from 2.8 million years prior to now. There has been an observation of expanded ice sheets in the region from the exterior of Antarctica and Greenland. This resulted in various natural calamities such as erosions followed by deposition of materials , sea level changes and also pluvial lakes development. This led to major events in speciation that include variations in climatic zones and new pressures of selections. This led to diversification of species in various areas as species would like to move to the areas where they would be more comfortable suiting their climatic preferences. This dispersal of species led to higher selection pressures and development or emergence of new species due to geographical barriers.

2. Major mass extinction events :

- end ordovician : occurred approximately 430 million years ago.

- late Devonian : occurred almost 360 million years ago

- end Permian : occurred almost 250 million years ago

- end Triassic : occurred almost 200 million years ago

- end Cretaceous : occurring almost 65 million years ago when we saw the disappearance of dinosaurs.

One of the main reasons of these mass extinctions was rapid changing carbon dioxide and oxygen levels.

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