The Open Door Web Site
ECOLOGY 

BIODIVERSITY AND CONSERVATION

What is biodiversity?

This is the total number of species living in an ecosystem. Recently attention has been focussed on global biodiversity and the extinction of species due to human activities.

How many species are there?

At present about 1.5 million have been named, but this figure is not certain as there is no common database for all the museum and private collections in the world.

It is impossible to know how many species actually exist for following reasons:

  • We have not explored every part of the biosphere yet.
  • Most species are less than 1mm long so they are easily overlooked.
  • Apart from the popular taxonomic groups like birds and mammals there are not enough experts to identify the more obscure and "esoteric" groups.
  • Species become extinct before they have been discovered.

Estimates of the total number of species, at present, range from 5 to over 30 million.

What are the human activities that are causing a loss of biodiversity?

  • Over exploitation (e.g. over hunting, over fishing, clear felling forests)
  • Islandisation. Dividing and isolating populations of species so that they cannot breed together. The human barriers can be as big as a city or as small as a road.
  • Habitat destruction. The total loss of an organismís habitat will lead to its extinction. Tropical forests are disappearing at a rate of 76 000 km2 per year. This results in the estimated loss of 4000 to 6000 species per year.
  • Introduction of alien species. Species introduced accidentally (e.g. rats) or deliberately (e.g. foxes in Australia) will increase in numbers and out compete or heavily predate native species. The aliens have few or no natural predators to control them. (Kiwis v rats and cats in NZ)
  • Pollution. e.g. plastic bags are killing marine turtles that mistake them for jellyfish their natural food. Global warming due to greenhouse gas emissions is causing a displacement of ecosystems. If species (e.g. trees) cannot disperse themselves fast enough they will be come extinct.

Examples of species which have become extinct in recent times

The passenger pigeon (Ectopistes migratorius) Eastern US

  • Estimated population early 1800s 3 to 5 billion, probably the commonest bird species on Earth.
  • Became extinct in 1914
  • Reason for extermination: Excessive over hunting. The arrival of railways and the telegraph during the period 1860-1890 increased the mobility and co-ordination of the hunters.
  • By 1895 a single flock remained of an estimated 250 000 birds. A hunt in April of that year killed 200 000 and maimed 40 000. About 5 000 escaped.
  • The population was driven below the point where it could recover.
  • By 1912 the last male bird died in captivity. On 1st September 1914 the last female died in Cincinnati Zoo

More details

"When an individual is seen gliding through the woods and close to the observer, it passes like a thought, and on trying to see it again, the eye searches in vain; the bird is gone."

John J. Audubon, on the Passenger Pigeon

Examples of species which have become extinct in recent times

Plant species that become extinct are less well known. They are particularly sensitive to habitat destruction (e.g. draining of marshland). About 47% of plant species are threatened.

The Cry Violet (Viola cryana) France

  • Discovered in 1860 this species had a very local distribution, limited to the limestone outcrops in the region of Cry (Yonne)
  • Limestone quarrying especially for cement led to habitat destruction.
  • Excessive collectors of wild flowers reduced the population to extinction.
  • It became extinct during the 1950s.

Why is biodiversity important?

There are several reasons why we should want to maintain a high biodiversity on Earth and in particular in the tropical rain forests.

Ecological reasons

  • High biodiversity is an indication of the health of an ecosystem (see biotic indices).
  • Ecosystems, which come under stress from over exploitation or pollution, will show low diversity.
  • Once diversity is lost from an ecosystem it cannot recover easily. Species need to migrate back in from neighbouring ecosystems.
  • Once an organism becomes totally extinct it is lost forever.
  • Tropical rainforests cover about 7% of the Earthís land surface (about 9 million km2) but they contain about 50% of the known species.
  • Currently they are being cleared for timber or agriculture at a rate of 76 000 km2 per year. At this rate they will all be cleared in 120 years.

Economic reasons

  • Humans exploit very few species. Just 30 species of plants make up about 95% of human nutrition.
  • The biodiversity of wild species is a very valuable resource for future exploitation.
  • Currently pharmaceutical companies are interested in the products derived from wild species in tropical rain forests. e.g. The rosy periwinkle from Madagascar produces a molecule that is used to fight cancer.
  • Some countries (e.g. Kenya and Tanzania) earn money from their flora and fauna in to form of ecotourism.
  • Wild life programmes on television attract large audiences.
  • Logging earns money for countries (e.g. Indonesia earned $2.2 billion in 1980 from timber exports). This cannot continue of the tropical forests are cleared and not allowed to regenerate.

Aesthetic reasons

  • People like diverse habitats the money people are prepared to spend on it suggests this.
  • Animals and plants give us pleasure.

Ethical reasons

  • Destroying biodiversity is denying a renewable resource to future generations.
  • It is denying a source of pleasure to future generations.
  • When a species becomes extinct a unique combination of genetic information is lost forever.
  • One thinking, reasoning species (Homo sapiens) does not have the moral right to exterminate other species.

Measuring biodiversity

Two factors are taken into consideration

  1. Species richness
  2. The relative abundance of each species

There are several diversity indexes used by ecologists one which is often used is Simpsonís Diversity Index:

Where:

D is diversity

   
 

N is the total number of species

Species richness
 

n is the numbers of each different species

Relative abundance of each species.

Therefore when the total number of species increases so does the diversity index

But if one species becomes very abundant and the other species become rare the diversity index will be lowered, even though the total number of species stays the same.

Indicator species and biotic indices

  • Each species has a set of tolerance limits. These will define its habitat.
  • Some species are so specialised that they only live in a limited area.
  • The presence or absence of these species can indicate what the environment is like (or has been like recently).
  • e.g. The sweet chestnut tree grows on acidic soils not on soil rich in lime. This species is an indicator of soil conditions.
  • Recently particular species have been used as indicators of pollution levels.
  • Several species of different levels of tolerance can be used to judge the level of pollution e.g. lichens which grow on surfaces such as rocks, building materials or trees absorb gases from the atmosphere. They are good indicators of atmospheric pollution especially SO2. The composition of a lichen community can be used to determine the degree of SO2 pollution in an area.
     
  • As the lichens grow slowly over many years it is possible to see the long term effects of pollution which may not be revealed if you measure the concentration of a pollutant in the air at one point in time.
  • As environmental stress due to pollution increases so biodiversity decreases as the sensitive species die out and the tolerant species remain and increase in numbers.
  • Biotic indices use a series of species of different tolerance with a measure of species diversity. Examples include lichens and atmospheric pollution, fresh water invertebrates and organic pollution of water.

 

Privacy Policy

Copyright Information

Sponsored Links

Sponsored Pages

Donating to the ODWS

Advertising on the ODWS

© Paul Billiet 2014