This set of 'notes' provides a quick summary of the major points in the powerpoint.
I. What is Biodiversity?
A. What is it?
In short, biodiversity is the sum total of living things in an area. The area can be a small place or the whole planet. Usually, we quantify biodiversity by the number of species in an area, so knowing the identity of species becomes important. At present, we have named about 2 million eukaryote species (and a few thousand bacterial species). As you know, of these, there are 1 million insects, 350,000 plants (mostly angiospersm), 50,000 vertebrates, and 500,000 other invertebrates--mostly other arthropods but also all the other animal phyla. Life is truly an amazing thing. And the fact that it comes in such an astounding array of shapes, sizes, and metabolic diversity will keep anyone interested in that diversity inspired and awe-struck for their entire life. And, since this planet houses ALL of the life in the known universe, I think there is a reasonable argument to be made that it is the most important and interesting product of the entire universe.
B. Why Preserve It?
1. Utility to humans:
We use other species for food, building supplies, clothing, and drugs. We continue to find new species, and new chemicals in known species, that have some structural or pharmacological utility. We are using nature, now, as a teacher--learning how it does things to solve problems, and mimicking these solutions.
2. Functional importance to planetary ecology and the environmental conditions humans need to survive
- At a large scale, the biosphere is a major 'sink' for carbon--it is where it is stored. And, because of seasonal changes in the balance between global photosynthesis and respiration, it cycles atmosphereic gases. The earth 'breathes' because life breathes. The earht is the living planet, and life keeps the Earth's conditions as they are.
- A critical variable is 'productivity'. This is 'biomass'. And plant biomass is called 'Net Primary Productivity'. This is usally measured in grams per square meter per year, and it is a good indication of the toal productivity of an area--because plants are food for everything else (including us). Ecologists have found that DIVERSITY INCREASES PRODUCTIVITY.
This is actually a bit counterintutitve. Suppose you are a farmer, and you want to grow as much food as you can. And, suppose different species of crops produce different amounts of food. It seems logical that, if you want to produce the most food, then you should plant your entire farm in the one most productive crop species. It seems impossible that REPLACING members of the most productive species with LESS productive species could INCREASE total productivity. But that is why science is so COOL... because it is NOT common snese or just lofgic... it is tested with real data. And there are a couple ways that increasing diversity, and decreasing the abundance of the most productive single species, can increase the total productivity of the farm.
a. First, individuals of the same species require about the same stuff... so corn plants all need the same mix of light an nutrients, so you have to space them out so they don't compete--you need them to maximize growth. But differnt species use a differnt mix of nutrients... so they can be planted closer together and both do great. So, if you reduce your corn and space them even farther apart, you can plant squash in between. Squash grows in the shade (not corn), and sues a differnt mix of nutrients and thus doesn't compete with corn. You reduce the amount of corn productivity, but the addition of squash productivy OVERCOMPENSATES for lost corn production. This is called NICHE COMPLEMENTARITY.
b. Second, some interactions among species are positive (not negative like competition). Legumes, like beans, fix nitrogen from the atmosphere into nitrous oxides and ammonium that can be absorbed and use by other plants. So, with beans present, you get more corn, more squash, and beans! These three plants were grwon together by native americas and are called the three sisters. Modern experiments, using random assemblages of species, has also shown that even many randomly constructed multi-species comuunities are more productive than monoculteures of the most productive single species.
c. And when we look at natural commuinties, we see this effect. The most diverse terrestrial and marine commuities, tropical rain forests and coral reefs, are also the most productive.
DIVERSITY INCREASES STABILITY, too!
Diverse communities are more stable than less diverse communities - they are more resistant to pests and pathogens, and this even helps human health. West nile virus is transmitted by blue jays, crows, robins, and sparrows. Unfortunately, these are also the birds that persist in areas developed by humans. So, humans living in low diversity areas have only these birds around, and the virus is transmitted efficiently among the birds and to humans. More humans get sick. But in areas with high bird diversity wher there are lots of resistant species present, the virus is not transmitted efficiently and fewer people get sick! Diversity rules and keeps you healthy!
We depend on a stable, productive supply of food and resources... diversity increases both stability and productivity.
3. Personal Reasons
By personal, I mean in terms of enriching human culture and the human experience, including your personal experience. Cultures evolved in a natural context, and the way we evolved--to learn--was enriched and dependent upon that environment.
- children learn their alphabet faster if natural symbols are used - even those they may not encounter (elephant for 'E').
- language development is dependent on animals as references - they influence HOW we think, and how we construct our cultures, religions, and our personal identities (tribal memberships).
- Psychologically and socially, we are healthier in the present of life than isolated from it; and we learn better, too. In short, we are our best and truest selves--as humans-- when we are engaged with natural and diversity. To lose nature and diversisty will be to diminish humanity.
4. Do we need all these species?
Probably not; there is alot of redundancy in nature (lots of beetles doing similar things).
But for most species, all we have done is give them a name; we don't know the role they play in the environment, and some are far more importnat than others. There are 'keystone' species that maintain the diveristy of the system. Sea otters eat sea ruchins. When sea otters were hunted almost to extinction, the commerical fisheries of the Pacific collapsed. As it happens, removing sea otters allowed sea urchin populations to explode. They grazed down the kelp forests of the pacific coasts, which are important nursery areas for commercially important fish. Without the nursey areas, the small fish were eaten and the populations collapsed, and the economic impact was huge. Removing sea otters caused the system to collapse, just like removing the keystone from an arch. So, until we NKOW which species are critically important, we better keep all of them.
Unfortunately, we aren't doing a very good job of that - we are causing the 6th great extinction event in the planet's history.
C. How we Doin'?
Not too good. At every level: genetic, species, and ecosystem diversity, there are dangerous declines...dangerous for PEOPLE.
1. Genetic diversity: As a species, we used to each 100's of food crops. Now, as a species, we get 60% of or calories from crops from rice, wheat, and corn. If one of these goes belly-up for a year or two, we are in big trouble (AS A SPECIES). In addition, we have reduced their genetic diveristy dramatically. We not only plant monocultures of the most productive crop, we plant monocultures of the most productive CULTIVAR (genotype) of that crop - often ones developed through genetic modification to protect against a pest. However, that popualtion is now genetically uniform with respect to all other characteristics, too, and thus more vulnerable to environmental change.
2. Species diversity. Threatened or endangered: 16% of birds, 25% of mammals, 33% of amphibians, 50% of primates. Rates of extinction are 1000 times higher than the geologic background rate.
3. We are losing species for three reasons: killing them directly for food or bioproducts (like the passenger pigeon, rhinos for their horns, tigers for bones and such used in folklore medicine), eliminating their habitats, and changing their environments through climate change. Know these three things. So, and the level of entire ecosystems, we are cutting them down to use those areas for ourselves. Most recently, the rain forests of Indoneisa and Malaysia are being cut down to plant palm oil - for biodeisel and an array of other products.
And it is not just the absolute reduction in habitat size; a more pernicious force is habitat fragmentation. Consider a large area that supports plants, herbivores, and carnivores. There are n't many carnivores, because energy is not transmitted efficiently up the food pyramid. Carnivores need large ranges to provide the energy needed, in terms of herbivore biomass, to support their population. If this alrge area is subdivided into fragments...even if the total land area is largely the same, each fragment is it's own ecological island. As smaller aras, their is less palnt material on each, and fewer herbivores on each. NONE of thes fragments may be large enought to support carnivores. That and hunting are largely the reason that most largel carnivores are endangered now. And, since carnivores are often keystone specie (like otters), their LOSS results in an explosion of herbivores that overgaze the plants, resulting in soil desctruction and erosion, too. When wolves were returned to Yellowstone, elk stopped brosing down the riparian zone along streams, thr rees grew back along rivers, erosion was reduced, and fish populations rebounded. Keystone predator.
We live in the most amazing place in the universe, and it it amazing because of who we share it with. It is worth protecting.
Study Questions:
1. What fraction of species are insects? Why are their so many species of insects?
2. Why is biodiversity important? Describe utilitarian, functinal, and cultural reasons.
3. Explain how sea otters or wolves are keystone species.
4. How's diveristy doing at genetic, species, and ecosystem levels?
5. How does fragmentation lead to species loss?