The biosphere, the totality of life is a membrane of organisms wrapped around the earth so thin that it cannot be seen edgewise from the space shuttle. And yet it is so complex that most of the species within it, close to 90 percent , remain undiscovered.
Estimates of the number of species range from 3.6 million to over 100 million species. The Census of Marine Life puts the number at 8.7 million, give or take .
How does biodiversity contribute to the sustainability of an ecosystem?
It is commonly believed that the more diversity of life within an ecosystem the stronger it is and the better able it is to sustain itself in the face of external stresses.
This is because species in an ecosystem depend upon each other for food, keeping birth and death rates in a balance that is sustainable for the ecosystem.
If there are a great number and variety of species, the disappearance of one species for whatever reason will not have as much effect on the ecosystem as a whole than it would if the extinct species had played a critical role, that is offered a function upon which other species relied exclusively .
Ecosystem services provided by biodiversity
Biodiversity is also key for the continued provision of ecosystems services it provides, which serve both humans and the systems themselves, although the term is largely used in relation to the benefits reaped by us.
The list of services ecosystems perform for us is extensive and includes:
- clean air and water
- climate regulation
- decomposing and cycling organic matter
- carbon sequestration
- gas exchange
- formation of soil
- soil detoxification
- maintenance of soil structure
- plant growth control
- medicines production of food, fiber for textiles and shelter, fuel and energy
- the suppression of pests and human diseases .
Other benefits of biodiversity
While the medicinal value of plants is mentioned above as one of the services provided by an ecosystem, this service deserves specific attention. Many of our most potent medicines are derived from plants .
Plant-derived drugs are anticipated to account for 39.2 billion dollars in sales by 2022 and botanical drugs to $425 million by 2022 . Stories abound of the discovery of life-saving plant-derived drugs just before the last of the species was eliminated by deforestation.
Antibiotics, fungicides, anticancer drugs, blood-clotting agents and thinners, anesthetics, cardiac regulators and fever suppressants are among the drugs we have obtained from wild biodiversity .
Seventy percent of the plants identified as having anti-cancer characteristics by the US National Cancer Institute are found only in the tropical rainforest .
The problem is that we don’t know what we are losing, especially when it comes to life in the rainforest, where so many species have adapted amazing defenses to predators, pests, infections and diseases over thousands of years, defenses that we humans might use in our fight against cancer and other serious diseases .
Other benefits of biodiversity include cultural, spiritual and recreational values. Because people evolve with their environments, their history and identity is embedded there. The loss of an entire ecosystem can be socially disassembling. Likewise, it is well-documented that nature contributes to the emotional well-being of humans .
That is the reason for parks in urban areas. An aesthetic appreciation of biodiversity itself has also been documented. This includes the deep feeling of being interconnected with other species on earth. Nature also provides many opportunities for recreation from ziplining to canoeing.
Three levels of biodiversity
Scientists examine the amount of biodiversity of life at three levels: the genetic level; the species level; and, at the level of ecosystems sustaining the life within them.
All forms of life from microbes to plants to humans contain genes.
Genes carry traits and characteristics. When species reproduce, the genes of each mate contribute to the characteristics of the progeny. Accordingly, no two members of the same species are exactly alike.
When there is a large population from which to reproduce, there can be more combinations of genes in the offspring. If a population is minimized and must cross-pollinate or inbreed with the survivors, successive generations will have fewer different genes and it is most often the case that susceptibilities are magnified and reduced infertility occurs, so that smaller populations carry illnesses or crippling enough defects that they soon die out.
Conversely, genetic diversity is significant in helping a species adapt to changes in its environment. With more variations in the genes it is more likely that a member of the species has genes that are well-suited or resistant to the changes being faced, whether it is a poorer air quality or a spreading disease.
A wider range of genetic diversity allows species to build resistances to diseases, as shown in studies on leaf-cutting ant colonies and fruit flies, and strengthens the possibility that at least some individuals will survive, and by making them less susceptible to inherited disorders.
In short, a population has a better chance of survival if there is more genetic diversity.
Genetic erosion of crops is an issue of concern today. Only a few major crops are feeding most of the world. Ninety percent of the world’s food supply is from only 100 crops and three: rice, maize and wheat account for almost 70 percent of the calories people derive from plants . Should a drought, pest or disease threaten one of these crops, the entire world’s food supply will diminish appreciably.
Concerned about the rapidly increasing loss of genetic diversity the UN Food and Agricultural Organization supports a trust of diverse seed collections around the world to maintain food security. The goal is to save the seeds of crops best able to provide high yield of nutritional content and to survive climate change and pests and disease .
If there are more types of plants, there can be more food with a variety of nutritional content, as well as a better selection of effective medicines.
Generally, a species is a group of similar individuals capable of interbreeding and producing offspring.
Species diversity then is the number of different species co-existing within a community, for example bear, humans, birds and dogs.
When species are examined for biodiversity, three elements are looked at:
- Species richness: which is how many members of the species exist within the community.
- The genetic relationship between different groups of the species, or phylogenetic diversity: This looks toward common ancestry of a species or organism.
- Species evenness: that is a comparison of the numbers of each species. For example, are there ten times more fox than deer? Ten times more bear than fish? Looking at these things presents a clearer picture of the sustainability of populations living within the area being studied.
The greater the variety of species, the healthier the ecosystem is. The more links in the food chain there are, like more fish for the bear, the healthier everyone up the chain can be.
A food web is a more complex arrangement where some of the species have a couple different food options. The more links that exist in the web the more stable the ecosystem as the removal of one link will not have a dramatic effect if there are other links that can fill the void.
Diversity is important for species in order to maintain resilience against unexpected events, such as sudden climate changes or natural disasters, like forest fires or floods. If a fire tears through a forest where only one species exists and is wiped out by the fire, the forest ecosystem is less likely to deal with this loss than if only one out of 20 species disappeared.
Although some ecosystems may be insensitive to species loss, due to variations in ecosystem types, or the presence of multiple species that perform a similar role, or due to their relative unimportance, or because of other abiotic factors, it is clear that higher numbers of species are needed to ensure stable provision of ecosystem services.
A nice example of species diversity can be found when looking at a lake. If a lake has many different types of fish and other marine life like turtles and frogs and many different types of plants and insects, then there is a great biodiversity of genes and species all contributing to the sustainability of the ecosystem of the lake.
The lake may be important to humans as a food source, an income source from for example, a kayak rental business and as a source of recreation. It may have cattails that filter and clean the water.
Its aquatic life may contribute to the quality of the soil by aerating it and enriching it with its waste and carcasses. And the soil may then travel to a place where these nutrients are absorbed and used, perhaps by plants which then exhale oxygen and enrich our air.
The largest scale of biodiversity generally examined is ecosystem diversity. Ecosystem diversity looks at the number and variability of ecosystems in an area.
The earth itself has ecosystem diversity: for example, it has forests, oceans, deserts, wetlands and grasslands. California has prairies, deserts, lakes, forests and beach.
A study of ecosystem diversity looks at these different ecosystems within the region and considers their sustainability, their impact on the surrounding environment and possibly even their impact on human existence.
Ecosystems are all of the animals, plants, and micro-organisms as well as physical aspects of the area. For example, an ecosystem being studied may be as small as a patch of lichen on a rock or patch of moss on a tree trunk or it could be an entire coral reef and all of the life that it sustains and that sustain it . An entire rain forest may be examined for the adverse effects on human life of its deforestation.
Ecosystem diversity is also used to refer to the number and variety of interactions in a certain area. For example, a coral reef generally has a very great variety of life within it, a greater ecosystem diversity than say Antarctica, which is covered by a sheet of ice .
Ecological diversity within an ecosystem is more diverse when it contains varied topography, allowing more places for shelter and for escape, a lot of sunlight and rainfall, allowing for more rapid growth of plants as a food source and stable temperatures, making adaptation easier for species.
Why is biodiversity one of the earth’s greatest resources?
Ecosystems affect the biosphere, or life on earth. Sustainability is the ability of the ecosystem to maintain its ecological processes, the composting of debris into soil, the exchange of carbon and air, the production of rainfall, photosynthesis, the life-giving processes required to maintain life as we know it on earth.
To be considered sustainable an ecosystem must be able to maintain these processes over time and in the face of external stresses that may occur like fires or pollution. High biodiversity in an ecosystem, that is a large variety of species and genes in the ecosystem contribute to a stronger ecosystem.
Human life relies on our ecosystems providing the life-sustaining services of providing oxygen, detoxifying our soil and water, providing materials for clothing and shelter and providing our food and the nutrients we require.
If our ecosystems fail, if too many species become extinct or disabled from performing their functions, then humans will not be able to survive on earth.
Where are the highest levels of biodiversity on our planet?
Not surprisingly, given the abundance of sunlight and rainfall and varied topography, the highest levels of biodiversity on our planet are in our rainforests.
The most detailed scientific study of the world’s greatest biodiversity was compiled by The Center for Tropical Forest Science, a consortium of forestry agencies, universities, research institutes and other nongovernmental agencies and published by the Smithsonian Institution in 2002.
Until that time, it had been widely believed that Amazonia was the richest ecosystem on earth. But the findings showed that in fact there was a greater number of diverse species in tropical forests over a greater distance in Panama .
And the warm waters of the Indian and Pacific Oceans are considered to have the most diverse marine environments .
How is the biodiversity of an ecosystem measured?
Biodiversity is measured not only by the richness of an area in the number of diverse species living there, but it also considers the evenness of the species.
This is because the more equal species are in proportion to each other, the more stable it is because there are not dominant species. Dominant species may reflect an imbalance in the food chain which will likely lead to the extinction of the prey. Or a dominant species could be an invasive plant that will overtake the native plants in the competition for soil.
This could lead to the displacement of animals relying on the native plants for food or shelter. In either event, the unevenness will cause a domino effect of instability on all of the species in the ecosystem .
In essence, any reduction of the diversity of life, whether by human hands or by natural causes, weakens the links that exist among species and habitats.
Given the interconnected nature of ecosystems, where a change in one area can have far reaching effects elsewhere, it is therefore vital to maintain as great a variety of species as possible in order to ensure the continued healthy existence of the planet.
 Wilson, Edward O., The Future of Life, A.A. Knopf, NY, NY 2002, p.119-126.