Biodiversity: Concepts and Level

Sanjeet Kumar
sanjeet.biotech@gmail.com

The biosphere constitutes a vital life support system for man and its existence in a healthy and functional state which is essential for the existence of human race. It is the collection of innumerable organisms, the biological diversity, which makes our life pleasant and possible. The term “Biodiversity” was coined by Walter and Rosen in 1985. It was the abbreviated form of Biological Diversity. Life originated on earth almost four billion years ago and nature took more than 1 billion years to develop this wide and complex spectrum of life on earth. Scientists believe that the total number of species on earth is in between 10-80 million. However we are losing this heritage at a very fast rate. The reduction in diversity in life forms is bound to have grave consequence for the entire living world. It has become extremely important to study the various life forms on earth and the causes of their destruction.  The word “Biodiversity” is now very widely used not only in scientific community, but also by the common people, environmental groups’ conservationists, industrialist and economist. So it is very important to have clear idea about the definition of biodiversity which is recognized as a separate science with its own principles. Some important concepts on biodiversity are:  

A.   Biodiversity is the variety of life in all its forms, levels and combinations. It includes species diversity, genetic diversity and ecosystem diversity- concept given by IUCN, UNEP and WWF, 1991.

B.   United Nation Earth Summit in Rio de Janeiro defined- “Biodiversity as the variability among living organisms from all sources including terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part. This includes diversity within species, between species and of ecosystems.

C.   Concept of U.S. Congressional Biodiversity Act – Biological diversity is the variety and variability among living organisms and the ecological complexes in which they occur and encompasses ecosystem diversity, species diversity and genetic diversity.

D.    In simplest, Biodiversity is the variety of life.

Origin of Biodiversity

There are two conditions that cause population diversity. First, new genotypes are constantly cropping up in a population through mutation, recombination and related genetic phenomena. Secondly, diversity is the population eliminated by natural selection and lost through emigration of individuals. Every genetic variation, from gene mutations to entire species, will disappear eventually. This loss can be a very fast process, or the variants can survive for a long period. Species that have survived for extended periods include horseshoe, crabs, which have been around for 200 million years and cockroach, which originates even earlier (350 millions) in the carboniferous period. The speed at which new variants originate in relation to the rate at which they are eliminated determines the actual diversity of the system. Thus diversity is the result of two opposite actions:

1)    The processes that produce new genotypes, new varieties and new species.

2)    Process that eliminate mutations, variants and species from the system.

Natural selection is primarily responsible for the reduction of biodiversity; it acts through differential reproduction and differential mortality.

Values of Biodiversity

Biological diversity is so widely accepted as being valuable that the reasons why it is valued are rarely carefully analyzed. Though not all levels of variation are equally valuable for all reasons, yet the values can be accounted for various reasons as stated below:

a)     Ethical value

b)    Option value

c)     Ameity value

d)    Ecological integrity value

It is a general belief that species diversity is essential for the proper functioning of communities and for the emergence of community level properties.

Types of Biodiversity

Biodiversity is usually at three different levels- Species diversity, Genetic diversity and Ecosystem diversity.

Species diversity: Evolution of species diversity has probably been possible because of habitat diversity. It refers to the variety of species within a region. This diversity could be measured on the basis of number of species in a region. The term biodiversity is commonly uses as a synonym of species diversity. It actually refers to species richness, in terms of number of species in a site or habitat. Global diversity is typically represented in terms of total number of species of different taxonomic groups. As mentioned before, an estimated 1.4 million species have been identified. Species diversity, again, is situated at three levels: alpha diversity (number of species coexisting at a site), beta diversity (different in species complement between patches), and gamma diversity (number of species in a large area, e.g. a country) this series can further be extended to delta diversity for biomes and omega diversity for the entire biosphere. Some authors call it taxon diversity (variety of taxa within a community of an area). It is generally studied at the species level and hence called species diversity.  When the taxonomic levels such as genus and family are considered, the term taxon diversity is more appropriate. This term is similar to taxic diversity. Species richness or the number of species per unit area denotes the measure of species diversity. The number of species richness, greater is the species diversity on the other hand number of individual among the species may also very, resulting into difference in evenness or equitability and consequently indiversity.

Genetic diversity: within a species there are a number of subspecies varieties, forms or strains which slightly differ from each other. These differences are due to slight variations in their genetic organization, so called genetic diversity. A species with a large number of varieties or strains is considered to be rich and diverse in genetic organization. Genetic variations within populations is considered a “Prerequisite for adaptation and evolutionary change”, and as such an important aspect of biodiversity. Genetic variations are often expressed in terms of alleles (Genes occupying the same locus in a chromosome) and are mainly studied at the population level. Genetic variations can be measured by different recent technique such as allozyme analysis, DNA fingerprinting polymerase chain reaction, restricted site mapping and DNA sequencing.

          Now- a- day diversity goes on increasing at the micro level. Differences in the level of varieties are followed by differences among the subspecies. Varieties and species accumulation of these differences at infra-specific level will automatically lead to distinctive characters at the species level.

Ecosystem diversity: In ecosystem, there may exist different land-forms, each of which supports different and specific vegetation ecosystem diversity in contrast to genetic and species diversity is difficult to measure since the boundaries of the communities which constitute the various sub-ecosystems are not distinct. Ecosystem diversity could best the understood if one studies the communities in various ecological niches within the given ecosystem, each community is associated with definite complexes. These complexes are related to composition and structure of biodiversity. Loss of ecosystem diversity may be considered as ultimate cause of loss of species and genetic diversity. Community diversity is synonym of ecosystem diversity and is defined as the diversity of community types within larger areas. It should not be confused with habitat variety which is an expression mainly used for different species of animals which have different habitats.

In general the Indian subcontinent is floristically richer than its fauna. Many cultivated species also originated from this region. Among the various ecosystems, Western Ghats and Eastern and North-Eastern Himalayas appear to be very important habitats for high floristic diversity, i.e. “Hot Spot” region. Diversity at the level of community or Ecosystem has been divided into three groups:

a)     Alpha diversity

b)    Beta diversity

c)     Gamma diversity

Characteristics of Ecosystem diversity: In ecosystem diversity there are number of ecological niches, tropic level and various ecological processes that sustain energy flew, food needs and the recycling of nutrients. The diverse communities are functionally more productive and stable, even under environmental stresses, such as dry and drought conditions.

Evolution of Biodiversity

In 1959, Darwin proposed that species compete and only the fittest survive in nature. It is inferred that under a strong pressure of natural selections the less fit species are eliminated. From this concept has arisen the competitive exclusion principle of Hardin in 1960. It is based on the idea that no two species can be exactly equally fit. It states that if two or more species exists in the same habitat, ultimately all but one of them will be excluded. This is the paradox of biodiversity. According to Newman:

a)     Each species has an exclusive ecological niche and subjected to conditions where it is fitter that its competitors.

b)    A perfect balance is maintained between species loss and gain. The slightly less fit species are eliminated by competitive exclusion, but this process is so slow that there will be time for other species to arise by evolution or to invade from other region.

c)     Competition is reduced or prevented, because the main controls on abundance are physical disturbance, stresses, predation and diseases, hence competitive exclusion does not occur.