Measuring Diversity

There can't be many of you who haven't watched a David Attenborough documentary, or even a series of documentaries, in which he waxes lyrical about the Natural World. Whether he is talking about marine life, plant life, animals or insects, a constant theme running through his narrative is diversity. In my last post I attempted to define diversity, but when I was introduced to evolution, I thought how do we measure diversity? Darwin's theory of evolution based on Natural Selection, came out of the many observations he made on the differences between the beetles he collected at home or the finches he collected in the Galapagos Islands. There seem to be 250,000 described species of plants, 12,000 species of roundworm, only 4,000 described species of mammals, but there are over 350,000 beetle species, at the last count! Why are there over 350 000 species of beetles? Why is there a gradual change in the shape of the beak of the Galapagos finches? Both observations share a common thread: diversity.

The chart on the left from the University of Berkeley's evolution resources, reveals the range of species numbers (as percentages of the total estimated number of species on the planet). Even if it isn't a perfect set of proportions, and in fact it  excludes  bacteria and their viruses, (which will be discussed separately below), it makes quite a statement! Humans (grouped under vertebrates) represent much less than 1%  of the species on the planet. However, an interesting point for group discussion might be. While humans are in the minority species on planet Earth, they seem to have the biggest influence on the future of our planet?  Is this true? What does it say about the "balance of power" in any society or ecosystem? Do all humans have the same level of power? If not why not? 

Back to measuring diversity. There are a few ways of measuring diversity of species. The concept of species richness is perhaps the simplest (but also the least reliable). Typically you might take a small section of ground (repeated several times to improve confidence in the measurements) and simply count the number of different species/organisms. Some will be easy; insects and plants, others will require more sophisticated methods; e.g. bacteria, fungi and viruses. The experiment is an easy one to conduct and popular early on in ecology classes, whilst it does have some limitations (can you think what they might be?), it does allow comparisons to be made between different ecological niches. [The word niche comes from the Latin nidus for nest, and then from the French version, niche. In Biology it is used to describe a space occupied by a group of organisms: in business it means a segment of the market. You may have heard the expression, "niche market" which means a specialist market, such as that for vinyl records in the world of digital music?] You might carry out a survey of elephants by monitoring a section of land in Africa over a few weeks, as another example. There are of course more robust methods, which I wont discuss here. But can you find the most reliable resources (and sources) for measuring the diversity of anything from baked bean manufacturers to spoken languages? How do the numbers (or metrics) vary from one source to the next? Can you use the population of the school to measure the diversity of something. Maybe three groups could measure the diversity of the same thing and then reflect on any variation in measurements? Anything will do!

In June, 2000, President Bill Clinton and Prime minister Tony Blair stood alongside scientists from around the world to celebrate the completion of the human genome project. An international consortium of scientists had collaborated for over 10 years, to determine the number and precise sequence of the nucleotides (the building blocks of DNA) that define the human genome. But whose genome was it? In fact we don't know! Since we are all more than 99.9% identical in terms of our genes: despite the ethnic diversity that we are all aware of, the human internet genome is a "composite" of 5 unknown individuals, selected at random from a group of approved (consent was provided) donors. I think we can all agree, that everyone is unique, with exception of identical twins. So how diverse is the human genome? What's more, what makes humans different from our nearest relatives on Earth? This is an important challenge for the Biologists among you. Just like the species richness method, you might want to think about how you assess the differences in numbers and types of genes. You might want to ask what characteristics make us visibly (or audibly!) different from our closest genomic relative? I'll give you a hint. How many primates have developed language skills? But there are other, even more obvious differences. What are they and what is their significance?

The human genome contains approximately 21,000 genes, spread over 23 pairs of chromosomes. For comparison simple bacteria, like E.coli have around 3,000 genes and even the fruit fly, Drosophila melanogaster, has around 10,000. There are some fundamental genes that we share with fruit flies, and even it seems with bacteria. How might you go about investigating this? Well the answer comes from computer science and I will be writing a post on this topic separately. I hope this might be of interest to those of you who are more computer minded. This is the field of Bioinformatics. And more on this soon. It is worth contemplating this. Humans represent less than 1% of the species on the planet and we only have twice as many genes as a fly. Bacteria (see below) are the second most abundant species on the planet, and they have on average one fifth the number of genes as a human.

Before I finish this post, I want to introduce you to the species that outnumber all of those I have discussed so far: microbes and their viruses (which we call bacteriophage).  In the news, we often read about bacterial pathogens, but most of the Earth's bacteria are found in the sea and the soil. It is estimated that there are approximately 4 × 10³¹ cells in total (4 with 31 0s after it!). Bacteria are often associated with humans and animals which provide many niche environments within them. By the time we reach adulthood, we are probably carrying around with us just under 1kg of bacteria every day! That's more individual bacterial cells than human cells in our own bodies. And that mixture is also diverse (see the above image)! And just as we are susceptible to the occasional viral infection, so to are bacteria. It is estimated that there are around 10 bacteriophage for every single species of bacteria. Making the bacteriophage the most abundant species of all, on planet Earth!

Next the diversity of languages. Have a good weekend!