BIODIVERSITY is the variety of life on earth and their interactions with their environment. This variation exists at three levels:
Genetic diversity: Within each species there is a genetic variability causing each organism from the same group to be different (unique). Differences in features exist in people, whether they are siblings, neighbours or strangers. One example of this unique genetic make-up is the pattern of the grooves on the underside of a person’s fingers. This is different for everyone, except identical twins, and has led to the widespread use of fingerprints as a form of identification. Similarly, there are differences within other species of living things, e.g. dogs are a single species, but there are many different ‘breeds’ of dogs.
•    Species diversity: This variety is the basis for distinguishing organisms into different groups, e.g. humans, insects, cats, dogs, fishes, palms, mangroves etc.
•    Ecosystem diversity: This is the variety of ecosystems in a community of living organisms interacting with each other and their surroundings, e.g. forest, ponds, savannahs, marshes etc.
What is a Species?
There is still some controversy among biologists of a precise definition for species. However, a common and widely-accepted definition is that of a group of organisms capable of interbreeding and producing fertile offspring of both genders and separated from other such groups with which interbreeding does not (normally) happen.
Organisms within a species usually portray some common characteristics and qualities. The word ‘species’ is used in the context of describing organisms in both singular and plural forms.

Species Diversity
Species diversity plays a pivotal role in making life on earth expansive, captivating and unique. Although biologists are not really sure how many species live on Earth, they have agreed that it is an astronomical number, since the estimates range from about 2 million -100 million. To date, most of the organisms that have been classified are vertebrates, however, most of the invertebrates, such as spiders, sponges, insects and crustaceans, etc. remain largely elusive. This can be partially attributed to the fact that most of these organisms are small and live in habitats which are very difficult to access. There are several species of mammals, birds, reptiles, fishes, invertebrates, and plants, etc., many of which remain hidden in the intricate web of life.
Factors affecting Species Diversity
Extinction: According to scientists, since the beginning of the Industrial Revolution, when Man began to use a lot of machinery to make work easier, a large number of species have gone extinct. According to research, human actions have accelerated the rate of extinction to 1000 – 10,000 times faster than natural extinction.
Habitat loss, degradation & fragmentation
The habitat and food of species are specific.  Habitat disruption will therefore affect species productivity due to factors such as food shortage, increase in predators etc. A rapidly increasing human population, and the quest for wealth have been causing significant degradation on the world’s ecosystems.
Invasive Alien Species
This is a very important cause of extinction which is usually overlooked. However, invasive alien species can invade an ecosystem and out-compete the native species, thereby forcing them out.

Pollution
This is another factor which poses serious threats to species, since many species are habitat and food-specific. Contaminants can alter the habitat and food supply of species, thereby affecting their productivity and survival
Climate Change
This is a single indispensable factor which threatens species and ecosystems. The distribution of many species is largely determined by climate. In addition, many species of birds and marine turtles are migratory. The change in climate will shift this distribution and affect the productivity of species, since climate can become relatively unpredictable and difficult to forecast. In addition, changes in climate will cause changes in ecosystems and ultimately habitats, hence many species will be unable to adapt to these changes in conditions, thereby accelerating the rate of extinction.
It is important to note that the existence of biodiversity and the interactions between species and the environment provides us with goods and services to sustain our livelihoods.
Reference:
http://dictionary.reference.com
http://www.fathom.com
http://npgrc.tari.gov
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