Question

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?

Answer 1

1. Here discussing the implicit nature of the change that has occurred in the history of evolutionary changes on species and their evolutionary picture by the effect of Pleistocene glaciers retreat is one of the most studies part from Ecology. The environmental changes since the Quaternary on species diversification, changes in their population genetics and demography was thoroughly studied using phylogenetic and phylogeographical approaches.

Well versed with this discussion we will look into an example as Birds, as they are the most well-studied group of all terrestrial vertebrates, regarding they are very much responsive to the climate change over the past history. Species diversification in them in response to the uplift of the habitat they live in, as in a Plateau, in Himalaya region.

Speciation has few intrinsic pattern those are for example, i) No divergence within a single refuge, restricted semi-continuous area, ii) Two divergent lineages with separated refugia, found in some places in the Himalayan region, iii) multiple divergent lineages within some areas of the Himalayas.

Key factors that has induced these changes from the glacial movements had shaped the regions and the patterns. Species distributed mainly in the heavily ice-covered platform have experienced expansion in their population following the retreat of the extensive glaciations, contrasting results have seen on those areas with little or no ice edge, maintained their population size at a stable level. Comparable discussion holds records for demographic stresses on the edge species vs the platform-distributed counterparts have been milder for the former one.

Looking into the area of behavioral and ecological characteristics, we could detail some of them as habitat preference, elevation specificity, dispersal capacity, all of these with evolutionary history might have helped to shape these different phylogeographical patterns.

2. Major mass extinctions: Hierarchical from the past annals till the latest known,

I. Late Ordovician event, ca. 440 million years ago,

II. Late Devonian event, ca. 350 million years ago,

III. End-Permian event, ca 250 million years ago; This was the most drastic af hugely severe event in that era, almost taken our 90% of all marine species from the face of the earth and a large chunk of terrestrials too,

4. Late Triassic event, ca, 200 million years ago,

5. End-Cretaceous event, ca. 65 million years ago. ALso known as the extinction age for the dinosaurs.