Biodiversity: Types, Patterns, Values/Importance, Loss and Causes

 

Introduction

• Every organism of the living world, whether it is a plant, an animal or a microorganism (viruses, bacteria, unicellular eukaryote) is unique in itself. This uniqueness of individuals is the basis of the diversity that is shown by the living organisms.
• Biodiversity is the variety of the world’s organisms, including their genetic diversity and the assemblage they form.

                          Number of species of bacteria, fungi, plants and animals in the world

Taxon	Number of Species
Higher plants	2,70,000
Algae	40,000
Fungi	72,000
Bacteria (including cyanobacteria)	4,000
Viruses	1,550
Mammals	4,650
Birds	9,700
Reptiles	7,150
Fishes	26,959
Amphibians	4,780
Insects	10,25,000
Crustaceans	43,000
Molluscs	70,000
Nematodes & worms	25,000
Protozoa	40,000
Others	1,10,000

 

Types of Biodiversity

1.       Species Diversity-

• Species is the basic unit of classification and is defined as a group of similar organisms that mate and produce offspring’s with one another, thus, share a common lineage. The number of species of plants and animals that are present in a region constitutes its species diversity.
• A natural forest has a higher species diversity as compared timber plantation, which is usually a monoculture. In the natural system, there are a large number of non-wood products that people depend on such as fruit, fuelwood, fodder, fiber, gum, resin and medicines. Timber plantations do not provide such goods for local consumption.

 

2.       Genetic Diversity-

• Genetic diversity refers to the variations between individuals of a species characteristics passed down from parents to their offspring.
• This is the variability among individuals of a species, e.g., each human being differs widely from all others. This diversity is due to a large number of combinations possible in our genes that give us specific characteristics. This genetic variability is essential for a healthy breeding population of a species. If the number of breeding individuals is reduced, then in-breeding occurs. Eventually , it can lead to the extinction of the species.

3.       Ecosystem or Community Diversity-

• There are a large variety of different ecosystems on earth which have their own complement of distinctive inter linked species based on the differences in the habitat. Ecosystem diversity can be described for a specific geographical region, or a political entity such as a country, a state or a taluka.
• Distinctive ecosystems include landscapes such as forests, grasslands, deserts, mountains, etc. as well as aquatic ecosystems such as rivers, lakes, and the sea.
• There are three perspectives-

(a)    Alpha Diversity- It is the biodiversity within a particular area, community or ecosystem. It is usually expressed by the number of species (i.e., species richness) in that ecosystem. This can be measured by counting the number of taxa (distinct groups of organisms) within the ecosystem (e.g. families, genera and species).

(b)    Beta Diversity- It is a measure of biodiversity which works by comparing the species diversity between ecosystem or along environmental gradients. This involves comparing the number of taxa that are unique to each of the ecosystems. It is the rate of change in species composition across habitats or among communities. It gives a quantitative measure of diversity of communities of that experience changing environments.

(c)     Gamma Diversity- It refers to the total species richness over a large area or region. It is a measure of the overall diversity for the different ecosystems within a region. It is the product of a diversity of component ecosystems.

Patterns of Biodiversity

Latitudinal gradients − 

• The plants and animals are not distributed evenly worldwide. The diversity of living forms decreases as we go from the equator towards the poles. A huge amount of plants and animals are concentrated in the tropical region because of the following reasons.
• Tropical environment is less seasonal and almost constant and predictable as compared to temperate environment.
•  Tropics receive the major part of the solar energy, which contributes to great productivity.
• Speciation is dependent upon time. Tropical areas have remained undisturbed for millions of years unlike temperate regions, which have experienced frequent glaciations in the past.

      Species-Area relationships − Alexander von Humboldt observed that biodiversity increases with increase in explored area. This relationship can be given by,

log S = log C + Z log A

Where,

S = Species richness

A = Area

Z = Slope of the line (regression co-efficient)

C = Y-intercept

Value of Z is found to lie in the range of 0.1 to 0.2 for comparatively smaller areas such as countries while for very large areas such as entire continents, the slope of the line is much steeper with Z value lying from 0.6 to 1.2.

Values/Importance of Biodiversity

The value of the earth’s biological resources can broadly be classified into the following two categories.

(a)Direct values-

• one of the most important values of biological resources is in providing the food.
• Many other values of biological resources is in providing medicines, fuel, building materials, fiber for clothing and industrial products.
• Originally, plants were consumed directly from the wild.
• Ornamental plants are lucrative commodity today. 

(b) Indirect value-

• At the other end of spectrum, biological resources provide values which are not immediately seen but have far- reaching impact on our living conditions. Indirect benefits of biodiversity can be enumerated as follows:
• Protecting areas from soil erosion, floods and other harmful weather condition.
• Reducing the risk of local and global climate change.
• Recycling nutrients.
• Monitoring the health of the environment.
• Pollination, gene flow, etc.
• Absorbing and decomposing pollutants.
• Preserving recreational, aesthetic, socio-cultural, scientific educational, ethical and historical value of natural environments.

Loss of Biodiversity 

• The International Union for Conservation of Nature (IUCN) notes that many species are threatened with extinction. In addition, at threat of extinction are-

       1 out of 8 birds

       1 out of 4 mammals

       1 out of 4 conifers

      1 out of 3 amphibians

     6 out of 7 marine turtles

• 75% of genetic diversity of agricultural crops has been lost.
• 75% of the world’s fisheries are fully or over exploited.
• Up to 70% of the world’s known species risk extinction if the global temperatures rise by more then 3.5°C.
• 1/3^rd of reef- building corals around the world are threatened with extinction.
• Over 350 million people suffer from severe water scarcity.
• The International Union for Conservation of Nature (IUCN) maintains the Red list to assess the conservation status of species, subspecies, varieties and even selected subpopulations on a global scale.
• Extinction risks out pace any conservation successes. Amphibians are the most at risk of extinction in recent years. The reasons vary from overuse of resource by humans, climate change, fragmented habits, habitat destruction, ocean acidification and more.

Causes of Biodiversity Losses

The main cause of the loss of biodiversity can be attributed to influence of human beings on the world’s ecosystem. In fact human beings have deeply altered the environment and have modified the territory, exploiting the species directly for example by fishing and hunting, changing the biogeochemical cycles and transferring species from one area to another of the planet. The threats to biodiversity can be summarized in the following main points.

• Habitat loss and fragmentation − This is the major cause for loss of biodiversity. Habitat destruction is caused by human activities such as deforestation and increasing pollution, leading to the loss of many plants and animals.
• Over-exploitation − Humans due to their greed and increased exploitation of natural resources have contributed to the endangerment of commercially important species of plants and animals. Example − Species such as Steller’s sea cow and passenger pigeon have been extinct due to over exploitation by humans.
• Alien-species invasion − The unintentional or deliberate introduction of alien species causes the declination of the indigenous species. Example − Nile perch introduced in Lake Victoria led to the extinction of more than 200 species of cichlid fish in the lake.
• Co-extinction − When a plant or animal becomes extinct, another plant or animal which is dependent on it in an obligatory way also becomes extinct. Example − In case of plant-pollinator mutualism, the extinction of one partner will eventually lead to the extinction of other also.