During the 1992 Convention on Biological Diversity (CBD) held in Rio de Janerio, biodiversity was defined as, 'the variability among living organisms from all sources Including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are a part; this includes diversity within species between species and of ecosystems'.
Unfortunately this seemingly simple description does not account for the magnitude of variation and the infinite task of calculating and quantifying biodiversity. There is a belief that a pattern of biodiversity may exist, providing some congruence from which we can create a world atlas of biological diversity but currently scientific information is not sufficient for such an enormous task.
The Biological Species Concept
To measure the biodiversity by either counting the number of species, or attempting to quantify biodiversity, it is first essential to determine what exactly classifies as a 'species'. The Biological Species Concept is the most widely used and accepted way of differentiating between species: a species is a natural population that is able to interbreed, but is reproductively isolated from other similar groups. In general species are said to occupy specific niches to which they are evolutionarily adapted.
However other measurements exist as alternative methods of defining species using their morphology, ecological habitat, evolutionary lineages, phylogenetics or even the breeding partners that they choose. The dispute within the scientific community means where a different definition for a species exists, there are also potential different classifications, creating inevitable confusion.
Biodiversity Through Time
Despite the incompleteness of the fossil recorded it can still be used as an outline of biodiversity throughout Earth's history. It is suggested our planet is around 4600 million years old and the most recent estimate, yet complex life has only existed for a comparatively short period of time.
Extinction
There have been five mass extinctions recorded from the fossil record, the most famous of which is the K-T extinction that effectively wiped out the dinosaurs along with many other phyla, but surprisingly this was not the first or largest extinction. The earliest recorded was in the late Ordovician epoch and it was the second most damaging to marine life, the most devastating being the Permian extinction where almost all marine organisms and 70% of terrestrial life was wiped out. Other extinctions include; The Late Devonian, and End Palaeozoic.
Speciation
Since the number of species and species richness has remained high and not disappeared entirely over time, the process of extinction must be in equilibrium with the process of speciation. Historically there have been explosions of diversity, some more permanent than others. The most dramatic appearance of phyla sprung from the Cambrian Explosion where organisms with hard shells and bodies emerged, and many of the phyla are still represented in present day ecosystems. The evidence for the Cambrian Explosion was found well preserved in packed sediment within Burgess Shale in the 1960s.
Another more ephemeral explosion of organisms was found partially preserved in Australia, in an area now referred to as The Garden of Ediacara. Around 600 million years ago a rapid diversification of soft body forms, with no mouth or gut arose, thought to be chemosynthetic they were perhaps able to deal with oxygen levels that were a tenth of present levels. However it is thought that after a short period of time the Ediacaran fauna became extinct and may have been only an unsuccessful evolutionary experiment that left no descendants.
The reasons for these sudden bursts of rapid speciation are not entirely known, it could be due to chance, the right genetic variations being available in a gene pool at the right environmental time, or in the case of the Cambrian Explosion the fragmentation of the super continent Pangaea may have been a factor, creating a huge new range of habitats and ecosystems.
Biodiversity Hotspots
Biological diversity is not evenly spread throughout the world; there are areas of high diversity, hot spots and areas of very low diversity. As a general rule the level of diversity increases towards the equator, with only coral reef fish diverging from the pattern. For example species richness is very great in the Amazon rainforest, a tropical region of low latitude; therefore it is a biodiversity hotspot. These hotspots have low levels of extinction with high levels origination.
This article has only skimmed the surface of the biodiversity issues, for example the threats facing the world’s ecosystems and conservation projects. The sheer magnitude of biodiversity on Earth from the microscopic to the macro makes the measurement and conservation of it a huge task to undertake, yet it must be undertaken to preserve the fragile ecosystems of our planet.
References
Gaston, K and J. Spicer. Biodiversity: An Introduction 2nd ed. Blackwell Science, 2004
Information on the Late Ordivician Extinction Park.org Visited 21/05/10
Alex Leeper - Hello, My name is Alex Leeper. I am currently studying an undergraduate degree in Marine Biology and Oceanography and the university of ...
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