What is a species?
There are two concepts about a species: morphological species and biological species. Morpho-species hinges on differences in appearance. Biological species is based on whether or not animals can breed with one another successfully and generate viable fertile offspring. According to morphological species concept, animals belong to same species have similar form, shape and appearance. The advantage of morpho-species concept is its simplicity; the weakness is its ambiguity. Biological species concept generates less ambiguity in classifying species. However, biological species concept is ineffective for organisms that procreate with asexual reproduction; it is also ineffective for extinct organisms, as there is no way to determine if fossilized organisms could mate.
Evolution Relationships and Biodiversity
There are two basic patterns of evolution: anagenesis and cladogenesis. Anagenesis: In terms of the phylogenetic tree, anagenesis is unbranching evolution, which indicates a direct descendant. Cladogenesis is considered to be “Branching Evolution”; one species may be a common ancestor for many other species.
A key biological event in speciation involves isolation of gene pool of a population. Gene pool is the complete set of genes of all members in a population. Isolating a gene pool means producing barriers for interbreeding. There are two types of barriers, external barriers such as geographical isolation and land-shifting and internal barriers such as changes of intrinsic genetic composition. Internal barriers include wrong places (different habitats), wrong behavior, wrong anatomy, sterile offspring, etc.
Sympatric speciation is set of speciation events different from allopatric speciation in the following ways: 1) Internal barriers develop first without initial external barriers; 2) Internal barriers lead to instant reproductive isolation which leads to gene pool isolation. This mechanism of reproductive isolation is usually related to meiotic nondisjunction which results in doubling of gametic chromosomes, and therefore polyploidy is generated and hence inability to mate with usual diploid organisms. Most polyploids go extinct before reproducing. This speciation is more common in plants than animals.