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Biodiversity

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Measuring diversity and the reasons for maintaining it

Measuring diversity

Species diversity is described as the number of species in a community. The more species, the higher the diversity. What if there are two separate communities like this:

Community #1 has 150 individuals per each of 20 different species (3000 individuals in total)
Community #2 has 10 individuals per each of 19 species, and 2990 individuals of the last species (3000 individuals in total)

It doesn't take a complex formula to figure out that community #1 is far more diverse compared to community #2, despite them having the same number of species and individuals. The distribution of individuals to species is important in determining a community's diversity.

The above example is easy enough, but for most purposes a formula is needed. This formula measures the index of diversity, which is simply a measure of diversity in a community. By calculating it and obtaining a numerical value, different communities can be easily compared.

Right, here it comes...


No, don't run away yet! Wait and see how easy it is to work out.

D = Diversity index

N = total number of all organisms

n = total number of organisms of each species

Σ = sum of

Now it's simply a matter of replacing numbers. Look, I made it all purple so you would enjoy looking at it. Let's work out the index of diversity for community #1 (from above).

Firstly, we need a value for N. What's the total number of organisms? 3000. Sorted.

Next, we need a value for N - 1. No calculators! ...2999, sorted.

Finally, we need a value for n and n - 1. n = 150, while n - 1 = 149.

Drawing up a table helps:

 species nn - 1  n(n - 1)
 a150149 22350
 b150  149   22350
 c150  149 22350
 d150  149 22350
 e150  149  22350
 f150  149  22350
 g150  149  22350
 h150  149  22350
 i150  149  22350
 j150  149  22350
 k150  149 22350 
 l150  149 22350
 m150  149 22350 
 n150  149 22350 
 o150  149 22350 
 p150  149 22350 
 q150  149 22350 
 r150  149 22350 
 s150  149 22350 
 t150 149  22350
 Total 3000 2980 447000


                3000*2999      8,997,000
So, D = ----------------- =  --------------- = 20
                  447000            447000

20 in this case is maximum diversity (there are 20 different species). If the index was 1, then diversity would have been non-existent. An index of 10 would indicate moderate diversity.

Now work out the index of diversity for community #2 using the table above and the walk through as a guide. You should get a pretty low value. I know it's a bit confusing that the above numbers are identical in all the columns, but if you work out community #2 then the values for 1 species should be different to the other 19.

Most of the time all species will have different values. The working of it is the same though.

Within the same species, diversity can be measured by looking at the variety of alleles in the gene pool of a population.


Reasons for maintaining biodiversity

Biodiversity is critical to an array of areas broadly split into ethical and economic. Different aspects of biodiversity can both contribute and take away from human activity. For example, many activities that lead to the reduction of biodiversity, such as farming land and using animals as materials or food can be economically positive but ethically negative.

The ethical arguments stem from different views on biodiversity. Anthropocentricism is the view that all issues should revolve around human issues, and so whatever answer benefits humans is the right answer on all matters of preserving biodiversity, the treatment of animals, the use of land, etc.

Biocentrism, on the other hand, regards all members of the biosphere equally in terms of a right to belong and benefit from the Earth. Other viewpoints exist, including ecocentrism which views not only the living components as worthy of consideration, but also the non living aspects of what makes the Earth and life on Earth possible; and cosmocentrism which takes into account the greater cosmos as the environment we operate in. Such great concepts such as those in the broader universe can, arguably, seem too overwhelming to apply to Earth matters or human matters.

Economically, experiments have been carried out to see what the role of species diversity is in the productivity and success of a land area, alongside traditionally considered factors such as climate and soil type. Such experiments have shown that biodiversity contributes to the good functioning of the community, and performs better compared to lower biodiversity controls (identical land areas with fewer different species).

Indeed, such findings contribute to established and emerging practices in farming such as rotating species and permacultures.

Moreover, many top products (some quite evidently) in human economy rely on successful ecosystems. These include food, medicines, toiletries, construction and clothing.


Ex-situ and in-situ conservation

Conservation of species can take place in their original environment (in-situ) or outside of it (ex-situ).

Examples of ex-situ conservation are zoos and seed banks. Zoos host animals outside of their original environment, under highly controlled conditions. Animals are no longer subject to predation, don't have to provide for themselves, and have access to advanced healthcare.

Seed banks preserve the starting unit of many plants. Because seeds have evolved to disperse far and wide, either by wind or carried by insects, even excreted by mammals (hello fruit), they are some of the most resistant biological things in the world. They can stay dormant for very long periods of time, and be used to start a plant culture at a later point. Hence, they are a useful ex-situ plant conservation practice.


The main issue with ex-situ conservation is that it neglects the environment. Animals may be sheltered away from the natural environment they evolved in, but unfortunately this means they will no longer be able to survive and live in what would be their original environment.

Similarly, the environment is ever-changing, so unless the animals are there to experience it and adapt accordingly, their abilities would soon fail to match the pressures of a natural environment they might have otherwise been able to thrive in.

Ex-situ can never truly match the right environment, so the biotic-abiotic balance often remains broken once the animal has been detached from its original habitat.

In-situ conservation includes national parks, sanctuaries and reserves which together form protected areas. Other examples include sacred forests and lakes. The aim of in-situ conservation is to protect the original habitat of species with minimal interference and disturbance, so they may continue to thrive in their corresponding space.

Sometimes this includes preventing human expansion and activity such as shooting, or shielding species from predators at critical times to allow their numbers to recover.



Challenges of in-situ conservation include unreliability of various environmental aspects such as natural disasters and changes in environment which can adversely affect the species being protected. The issues are often the reverse of ex-situ conservation.

Ex-situ conservation provides complete control, but this removes the natural parameters that species require, while in-situ conservation provides complete natural parameters that species require, but this removes control.

Ok byeeeeeee

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