3.12 Biodiversity

Diversity is a fundamental characteristic of life itself

Biological diversity or biodiversity is an expression used to describe the richness or variety of living organisms found in an area or type of environment, including both the number and frequency of genes, species and ecosystems.
Biodiversity is usually divided into three fundamental categories:

  • genetic diversity; the genetic variation within each species
  • diversity of species: the different species in a given area or habitat
  • diversity of ecosystems. The natural environment comprises many different types of habitats.

The Earth’s biological resources – the incredibly complex pool of genes giving the biosphere its abundance of species and almost endless variations of life – is under severe threat. There are more species being extinguished per year now than 6o million years ago when the dinosaurs disappeared. How do we halt the destruction of species? How do we secure the diversity of the genetic pool of the biosphere?

The problems

Elimination or change of habitats

There are limits to how much any biological resource can be exploited, and in too many cases mankind is exceeding those limits. The elimination or change of habitats is the leading cause of loss of biodiversity.  Global warming and climate change are seriously threatening the survival of many species


Many species now migrate towards the poles or towards mountain tops to avoid the warmer climates. At times further migration is not possible. Photo. Å. Bjørke

Alien species

The introduction of non-native or alien species to the habitat also causes severe problems, like diseases and harder competition. (Examples: Rabbits in Australia, Nile perch and water hyacinth in Lake Victoria). Invasive or opportunistic species also mean harder competition.
Invasive species often have no natural enemies or competitors in the new habitat.
(Example: Water hyacinth in many shallow lakes in the tropics)


Free floating water hyacint – an invasive species – in Lake Victoria, Kenya. Photo: Å. Bjørke


Overhunting and overharvesting in addition to the factors already mentioned may also cause extinction of some species.
Others become rare or disappear from the habitats locally.


Human encroachments, like urban settlements, roads, clearcutting of forests, dams and mass tourism tend to fragment the habitats, making it difficult for species needing large, continuous areas of habitat to survive. 

Coral bleeching


Coral reefs are the most diverse and beautiful of all marine habitats. Large wave resistant structures have accumulated from the slow growth of corals. The development of these structures is aided by algae that are symbiotic with reef-building corals. Coralline algae, sponges, and other organisms, combined with a number of cementation processes also contribute to reef growth. Photo: Glenn Edney

Coral reefs are important breeding grounds for fish and very rich in biological diversity.

Coral reefs are often termed “rainforests of the oceans”.
When ocean temperatures  rise above 27 centigrades, the algae living in symbiosis with the coral tend to leave. As a consequence, the coral bleeches and die.
Global warming is thus a serious threat to marine biodiversity

GRID-Arendal: Coral reefs  |   What are coral reefs?

The El Niño that formed in 2015 has the pronounced effect of warmer ocean temperatures, and if sea surface temperatures remain that way for too long, the algae living in coral eventually give up the ghost. This algae is what makes coral reefs so stunning to look at, especially those with brilliant, vibrant colors.
NOAA 2016
Dramatic new video and still shots of coral bleaching on the Great Barrier Reef’s Lizard Island show the sort of damage that has prompted the Great Barrier Reef Marine Park Authority to lift its response to Level 3—the highest response level.
Ecowatch 2016

Why conserve biological diversity?

Species extinction is a natural part of the evolutionary process. Due to human activities, however, species and ecosystems are more threatened today than ever before in recorded history. The losses are taking place in tropical forests — where 50 – 90 per cent of identified species live — as well as in rivers and lakes, deserts and temperate forests, and on mountains and islands. The most recent estimates predict that, at current rates of deforestation, some two to eight per cent of the Earth’s species will disappear over the next 25 years.

While these extinctions are an environmental tragedy, they also have profound implications for economic and social development. At least 40 per cent of the world’s economy and 80 per cent of the needs of the poor are derived from biological resources. In addition, the richer the diversity of life, the greater the opportunity for medical discoveries, economic development, and adaptive responses to such new challenges as climate change.
It is well known that the more species there are living in an
ecosystem, the more stable the ecosystem is. Increasing the number of species, increases the productivity and the ability to withstand e.g.drought.

To date, an estimated 1.7 million species have been identified. The exact number of the Earth’s existing species, however, is still unknown. Estimates vary from a low of 5 million to a high of 100 million. Zoos and botanical gardens are unable to cater for more than a small fraction of the species already known. As the majority of species are still unknown, it is obvious that preserving a few species in a human made habitat is rather futile. – The only way to preserve the present biodiversity is by preserving the species in their original habitats. It is crucial to establish a sufficient number of large enough areas to sustain at least the more important habitats.

The variety of life is our insurance policy. Our own lives and livelihood depend on it.


Clearcutting of forests leads to siltation. In combination with pollution, eutrophication, global warming and climate change, many lakes dry out. Entire habitats may disappear. Here Lake Chilwa, Malawi. Photo: Å. Bjørke

While some effects of climate change are already manifest, there are still steps which can be taken to lessen the damage of a rapidly changing climate. On a global scale, we can cut the amount of carbon dioxide ploughed into the atmosphere by finding clean alternatives to fossil fuels – such as solar or wind power. On a more personal scale, even small changes to everyday habits can make a difference. IUCN (2015) The 101 on climate change – and how protected areas can help address it

Climate change is set to be one of the major drivers of species extinctions in the 21st century: approximately 20 to 30 per cent of plant and animal species are likely to be at increasingly high risk as global mean temperatures rise. IUCN: Species and climate change

EEA: What is ‘biodiversity’, and why do we need it? Video lecture

Climate change and biodiversity

Many plant and animal species are adapted to a certain environment – their habitat.
When climate changes quickly, many species are unable to adapt at the same speed.
They either have to move and find a new habitat where they can survive, or die.


Sea turtle – a threatened species (Photo: Å. Bjørke)

When it gets warmer, they either can move towards the poles, to colder regions, or they can seek higher altitudes in the mountains.

However, with human settlements, roads and various activities, overexploiation, overfishing and pollution, there are several impediments to migration.
Sooner or later, there are no places to go for some species.

The extermination of species is now over one thousand times quicker than natural. The current rate of extermination is so severe that it can be compared to the extermination rates 55-65 million years ago, under the Paleo-Eocene termic maximum (PETM) and when dinosaurs died out.

Global warming, human encroachments, human transport of alien species from anywhere to everywhere, deforestation, land degradation and pollution  must be managed much better to avoid an increasing number of ecological disasters.


Invasive species response to climate change – Hydrilla spp, current and 2080 habitat suitability As climate change alters Arctic ecosystems and enables greater human activity, biological invasions are likely to increase in the Arctic. To some extent, Arctic terrestrial ecosystems may be predisposed to invasion because many invasive plants are adapted to open disturbed areas. Range map scenarios developed for 16 highly invasive plants either occurring in or at risk of invading Alaska also paint a sobering outlook for the future. This map depicts the potential expansion of one invasive aquatic plant, Hydrilla veticillata, well up into Arctic Alaska ecosystems and even into far eastern Russian aquatic systems. Another recent study examining global distribution trends associated with climate change predicted that marine communities in the Arctic and Antarctic will be the most at risk from climate induced invasions. Author: Hugo Ahlenius, GRID-Arendal & CAFF

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Home Chapter 3 3. Impacts
3.1 More water vapor
3.2 Sea level rise
3.3 Polar sea ice
3.4 Air pollution
3.5 Acidification
3.6 Health
3.7 Extreme weather
3.8 Economy
3.9 Refugees and conflicts
3.10 Glaciers
3.11 Tipping points
3.12 Biodiversity
3.13 Water
Chapter 4 4. Ecosystems