What do we Mean by a Species?

Thoughts

1. Gog and Magog, are they different species from humans?
2. Therefore, by definition, humans all belong to the same species.
3. Have Gog and Magog specialized and becomes a different species than humans due to isolation?
4. What about isolated communities like in Siwa, Nubia and other more isolated ones such as in Islands (belonging to India for instance where contact has been attempted yet unsuccessfully).
5. Hybridization in American population, what does it lead to.
6. Inadvertent hybridization of F1 hybrids with other forms of the same species or hybridization among different cultivars of a plant may result in unfavorable results in offspring.
7. What is a cultivar? (A form of ecotype?)
8. Isolated communities of humans, like Siwa and Nubia, have imposed cultural rules of not marrying from outside their communities.
9. Donkeys and horses produce infertile mules when they mate. This fits them perfectly within the definition of being two distinct species (two distinct biospecies).

Hybridization against forces of natural selection

Digest

• Speciation, the forming of distinct species, is a process not a sudden event
• Hybridization and natural selection are two opposing forces
• According to the Mayr-Dobzhansky test, two organisms belong to the same biospecies if they could breed together in nature to produce fertile offspring
• Allopatric speciation vs sympatric speciation
• Ecological speciation is speciation driven by divergent natural selection in distinct subpopulations according to Dolph Schluter (2001)
• Stages of speciation (in the most orthodox view of ecological speciation):
1. Two subpopulations become geographically isolated and natural selection drives genetic adaptation to their local environments
2. Reproductive isolation (pre-zygotic or post-zygotic) builds up between the two subpopulations
3. The two subpopulations re-meet in a phase of secondary contact
4. The hybrids between individuals from the different subpopulations are now of low fitness. Natural selection will then favor any feature in either subpopulation that reinforces reproductive isolation preventing the production of low fitness hybrid offspring. These breeding barriers then cement the distinction between what have now become separate species.
• In northern Europe, the lesser black-backed gull and the herring gull are now two distinct species. They do not hybridize and are therefore true biospecies.  Their 'ancestors' still hybridize freely after spreading east and west from Siberia.

European herring gull (top) and lesser black-backed gull (bottom)

Questions

1. So, what exactly is a species?
2. So, ecotypes are different forms of the same species? Also different forms, like peppered moths (melanic and nonmelanic) belong to the same species?
3. How come species are classified by scientists then reclassified later on in a different way?

Variation within Species with Manmade Selection Pressures

Thoughts

• How does manmade influences affect the species of cats, doges, mice, weasels, doves, hoopoe, craws, home sparrows and bats in urban areas in Cairo? (It probably has a lesser effects on birds, since they travel even more easily than the other animals. On the same token, trees must be affected the most, since they are immobile.)
• Pigeons at Siwa and donkeys at Siwa appeared to be much healthier than those in Cairo. They live amongst nature, feed on a healthy natural diet and live in a healthy environment with no air pollution. (Siwa also is in the North West of Egypt, from wear most of the wind comes, and is located at the lowest place in Egypt, almost, which makes it insusceptible to winds blowing off industrial pollution from anywhere.)
• It is good (for humans) to live away from the direction of wind that brings airborne industrial pollutants. Helwan is one such area where many suffer health issues due to high pollution caused by the presence of cement factories there.

Digest

• Local specialization within species (natural selection in action) has sometimes been driven by manmade ecological forces, especially those of environmental pollution.
• Dark (melanic) forms peppered moth (Biston betularia) increased in industrial polluted areas in the UK
• Many populations of peppered moths in the UK were polymorphic: melanic and nonmelanic forms coexisted
• Transient polymorphism:
• The dark form of moth increase in the UK
• The fall in the population of dark peppered moths after pollution was reduced is again a from of transient polymorphism
• Industrial melanism:
• Definition: Industrial melanims is the phenomenon in which black or blackish forms of species have come to dominate populations in industrial areas
• In the dark individuals, a dominant gene is typically responsible for producing an excess of the black pigment melanin
• Birds preying on peppered moth are those causing natural selection to work, they eat the typical (light colored) moths in industrial places while they prey on the dark ones in pollution free places
• Sulfur dioxide destroyed most of the moss and lichen on tree trunks on which nonmelanic moths rest thus depriving them from their ability to camouflage
• Transition from coal to oil and electricity in addition to legislation passed to impose smoke free zones and to reduce industrial emissions of sulfur dioxide in Western Europe and the US caused the frequency of melanic forms of peppered moth to falll back to near pre-industrial levels

Melanic and non-melanic peppered moth

Questions

1. What manmade factors, other than pollution, can affect selection in species?
2. How does breeding affect the balance of evolution?
3. Can manmade interference in any way have a positive effect on populations and communities compared to leaving them without any manmade influence?

Natural Selection and Adaptation (Cont.)

Digest

• Evolution by natural selection takes place when some individuals survive and reproduce better than others in a particular environment and the heritable characteristics of a population change from one generation to the other due to that.
• Fitness is measured by the number of descendants left by individuals in a population.
• Evolution is not perfect: Evolved individuals might have characteristics that are suited to the environments of their ancestors but not so much to their current environments.
• Fitness is relative: evolved individuals can be the best fit for their current environments but not the perfect fit.
• Precise matches between an organism and its environment may equally be seen as constraints making such organism dependent on such specific environment.

Questions

1. Does fitness depend on the number of offspring only and why?
2. What is the ultimate fitness?

Natural Selection and Adaptation

Digest

• At the heart of ecology lies the relationship between organisms and their environments. Fundamentally, this is an evolutionary relationship.
• Theodosius Dobzhansky, Russian-American biologist, said: "Nothing in biology makes sense, except in the light of evolution." This is also very true of ecology.
• Adaptation: "Organism X is adapted to live in environment Y" means that environment Y has provided forces of natural selection that have affected the life of X’s ancestors and so have molded and specialized the evolution of X. Adaptation means that genetic change has occurred.
• The theory of evolution by natural selection is an ecological theory.
• It was first elaborated by Charles Darwin in 1859.
• Its essence was also appreciated by his contemporary Alfred Russell Wallace.
• The theory of evolution by natural selection rests on a series of propositions:
• Individuals making up a population of a species are not identical
• Some variation among individuals is heritable
• Populations have the potential to populate the whole earth but they do not
• Different ancestors have different numbers of descendants
• Number of descendants an individual leaves depends crucially on the interaction between the characteristics of the individual and its environment

Questions

1. Is evolution a theory in biology or ecology?
2. What is the relationship between organisms and their environment?