Page:Niger Delta Ecosystems- the ERA Handbook, 1998.djvu/74

The Lowland Equatorial Monsoon Ecozone two complementary sets. This overall genetic context is also very important; many traits may only be seen where genes for alternative forms are absent. For example, blue eyes will only be seen if the gene for brown eyes is not present.

The basic patterns of variation and inheritance of individual characteristics were first described by Gregor Mendel; although genetics has advanced enormously over the last century, his first and second laws are still relevant.

Mendel's First Law – Of Segregation: ''Mendel experimented with pairs of traits in pea plants. He found that for each pair of traits, one was dominant and one was recessive. He believed that each form of the trait was caused by a pair of factors, one from each parent. MenedelMendel [sic]'s law of segregation states that during gamete production, these factors separate, and only one member of the pair enters a particular gamete. Fertilisation randomly brings the pairs of factors together and determines the type of trait in the offspring.'' (Mix, Farber and King)

Mendel's Second Law – Of Independent Assortment: factors responsible for two or more traits are inherited independently.

(A gamete is the reproductive cell of a parent—the two gametes coming together are fertilisation leading to production of an offspring.)

Genetic Mutation: for a variety of reasons there is always the chance that a gene will change when it is being copied. An inherited change, or mutation, may be fatal, harmless or advantageous. If a mutation gives advantage to an individual and allows it to reproduce more successfully, this new gene will tend to spread through a population and may become the new 'norm' quite rapidly.

Evolution: this is a product of mutation and 'selection' (the favouring of certain genetic characteristics in given circumstances). To give a simple example; a rat which can run faster than all the other rats will live longer than her sisters who are caught and eaten by the cats. Thus she will have more offspring and the trait allowing faster running will spread through the population. Of course this situation will also encourage the evolution of faster cats, because the slow cats will starve.

Competition for survival tends to limit the number of species in a given area, as the rate of evolution of new species is eventually balanced by extinction of the unsuccessful.

However the high rate of bioactivity and biomass in tropical rainforests means that this balance, or equilibrium, is reached with a wider diversity of forms than in a temperate forest.

For example, a natural oak forest in a temperate zone has lower biomass and bioactivity than the Ogoni forest of the West African LEM, and a correspondingly low biodiversity. In the oak forest are two species of songbirds; the song-thrush and the blackbird (another variety of thrush). The natural Ogoni forest would hold 18 sub-species of the Bulbul alone, and many other species of song-bird. This is against a background of very diverse vegetation; while the range of tree species in a European oak forest is usually two or three (the oaks themselves, plus holly and/or birch), in the Ogoni Forest it would have been about seventy trees alone, in addition to many palms.

5.9 PLANT SPECIES OF THE LEM RAINFOREST

As discussed in Chapter 2, natural rainforests of the Niger Delta LEM would exhibit an even higher diversity of vegetation than neighbouring forests. This is for two reasons. Firstly, rainforests West of the Niger river (such as on the Ogoni plain) survived the ice 72