The Biodiversity Crisis, and Why It Matters
The Crass Practicality: We need biodiversity
A Simple Analogy: Lemmings.
What are they?
The common metaphore: Groups of individuals rushing to their destruction.
The deeper biodiversity metaphore, based on Swedish lemming studies of the 1980s.
- Mass drownings are largely a media-perpetuated urban myth based on the 1958 Disney film White Wilderness. That's not to say that lemmings don't suffer regular mass mortality. During intervals of high population density, lemmings will attempt to migrate to less densely populated regions, usually driven by:
We call this cycle of population growth, starvation and migration a "boom and crash cycle".
- Starvation, as their reproduction rate allows them quickly to overwhem their resource base within about 4 years.
- Extermination, as predators that specialize in them like stoats, snowy owls, arctic foxes, and long-tailed skuas also experience populations booms.
- Distinction in behavior between lemmings in forest and tundra regions. Forest lemmings are not known for significant boom and crash cycles. Why not?
- Patchiness vs. uniformity: Lemmings in patchy, variable environments like forests can switch from one habitiat to another when resources in a particular habitat are exhausted. Lemmings living a uniform environment like the tundra are just hosed when its resources are exhaused because there is no readily available alternative.
- Of course, when lemming populations crash, so do those of their predators, who may undertake their own mass migrations looking for food. American bird watchers look forward to the occasional eruption of snowy owls into the continental US durng these events.
Human agriculture and habitat diversity.
The effect of agriculture on world habitats also creates a dichotomy between a varied mosaic of different crops and varieties on a local scale - "patchy agricultural environments" and monoculture agriculture, based on the industrial scale cultivation of a single crop. Consider the US situation in the early 1990s (Union of Concerned Scientists Background Paper 2001):
- Six varieties of corn -> 46 percent of the crop
- Nine varieties of wheat -> half of the wheat crop
- Two types of peas -> 96 percent of the pea crop.
- More than half the world's potato crop is made up of one variety of potato: the Russet Burbank favored by McDonalds.
Monocultures have some awesome advantages, especially in the near term:
- Economies of scale
- Limiting number of crop varieies allows use of few types of generic farm machinery
- Maximizes yield allowing cheap food and surplus to export.
- Stimulates demand for products of allied industries
- Antibiotics and other veterinary pharmaceuticals (keeping many animals at close quarters encourages spread of diseases.)
But it has its down-side:
- Concentration of few and uniform varieties of crops facilitates evolution of pests specifically adapted to them.
- Separation of farming of animals and plants means that waste that was once routinely recycled as fertilizer is now a large scale waste-disposal problem.
- Environmental risks of industrial farming: Pesticide pollution, eutrophication of waterways from fertilizer runoff.
But all of this is minor compared to the long term threat: The day may come when the pests evolve faster than our ability to cope with them. There have been foreshadowings:
- In 1970 the corn-leaf blight destroyed 60% of US corn production in a single summer.
- Human antibiotic use has facilitated the emergence of rather scary new pathogens, including, in recent years, a highly antibiotic-resistant tuberculosis in southern Africa. Of course, humans have been taking antibiotics longer than farm animals, however as antibiotics are administered as a routine, it's only a matter of time.
Thus, the human situation mirrors that of the tundra lemmings, just on a longer time scale. Our agricultural monoculture is productive now, but we must constantly improve the allied technologies to forestall disaster. The worst-case scenario is a full-blown human boom and crash cycle (of which we are now in the boom). We have seen this before on smaller scales:
Is there a more fail-safe approach? In hindsight, Ireland's mistake was to become dependant on a potato monoculture. You can hardly blame them. In near-term costs and benefits, it was the rational course. No one anticipated the sudden appearance of an alien plant pathogen. But by their fruits we shall know them.
The more we limit the diversity of the biological resources (crops) on which we depend, the more we set ourselves up for lemming-like boom and crash cycles. The alternative is deliberately to hedge our bets by cultivating a much wider range of crops than we think we need. In some ways, America is moving in this direction with:
It's a beginning. But where do these foods come from? Natural Biodiversity. There are conceivably many more useful food crops waiting to be domesticated. (Indeed, we already know of some that have been left alone because they are economically infeasible now but might become feasible in the future - oak trees.)
- The current vogue for heirloom varities - a sort of cultivated plant antiquarianism - is keeping alive cultivars that might otherwise perish.
- The immigration of people from all over the world to North America creates a commercial demand for the food they ate back home. Thus items like manioc, jicama, tef, durian, and other crops unheard of in my youth are readily available at Giant or Safeway.
This principle applies even more strongly to medicines. Humans have been mining the biodiversity for food for thousands of years. We are only beginning a new age of discovery of pharmaceuticals.
- Anticarcinogen Taxol from Pacific Yew trees became available in 1996. Used against breast and ovarian cancers, some lung cancers, and leukemia.
- An anticlotting drug based on the venom of the saw-scaled viper, Echis carinatus, that is shortly to become available;
- A compound derived from the venom of a sea snail, Conus purpurascens, that is currently in extended clinical trials as an agent for the relief of chronic pain;
- An alkaloid secreted in the skin of the frog Epidedobates tricolor that is in early clinical trials as another analgesic.
National Council on Biodiversity and Human Health formed by pharmacological industry in 1998.
How are we doing? - The general picture with mammal diversity from Pough et al., 1990.
According to a 2008 report by the International Union for the Conservation of Nature (IUCN), 25% of known mammals are at risk of extincton.
Current special crises in biodiversity reduction:
-Amphibians. We've already seen the potential uses of some of the compounds in their skin.
Canaries in mineshaft becaus eof unique physiology.
and yet they are in serious decline:
According to the 2004 Global Amphibian Assessment, a vast and authoritative study , almost a third of the 5,743 known species are at risk of extinction; up to 122 have disappeared within the last 25 years.
The action plan emerging from this meeting lists six major reasons behind the decline:
- habitat loss and degradation
- climate change
- chemical contamination
- infectious disease, notably the fungal infection Chytridiomycosis
- interactions with invasive species
Working groups drawn from a wide range of scientific institutions and conservation organisations have established budgets for tackling each of these issues; the overall total comes to US$404m .
The problems that comtemporary amphibians are facing are not new. A synopsis of major events in North America:
The practical conclusion is obvious:
- 9,000 BCE - Pleistocene Magafaunal Extinction in which many of the largest land mammals and the predators that depended upon them became extinct at roughly the same time that humans with big game hunting technology colonized the New World.
- 1492 + - The "Columbian Exchange" in which entire suites of exotic creatures were introduced to the New World, seriously disrupting ecosystems.
- 18th and 19th centuries - Large-scale hunting and extinctions. E.G. the passenger pigeon, heath hen, labrador duck.
- Well-intentioned folly: Deliberate introductions of exotic species, including
- Humans must maintain as broad a biological resource base as possible in order to assure a high future living standard.
- Natural biodiversity is the "mine" from which this resource base is derived. When we allow it to be destroyed, we destroy our own safety net.
- This conclusion is based entirely on pragmatic assessments of future needs, not on any sentimental attachment to biodiversity.
- Recent economic analyses that compare pairs of locations with similar environments suggest that the diffuse economic productivity of diverse environments are roughly 100 times that of monocultures. I could believe them being off by a factor of ten. (UMD Geog dept.)
But beyond practicality lie moral issues of environmental stewardship:
But there is another dimension: Natural biodiversity holds out promises but also threats. Whenever humans have radically changed their behavior patterns or invaded habitats and regions in which they did not evolve, they have encountered a flavor of biodiversity for which they are not adapted:
What are disease organisms?
- pathogenic organisms in humans
Origins in domestic animals
- Measels - rinderpest - cattle
- Tuberculosis - cattle
- Smallpox - cattle
- Enfluenza - pigs and poultry
Evolutionary biology of symtoms - pathogen seeks optimum transmission strategy
- Passive transmission through ingestion
- Injection of body fluids (mosqite saliva, semen, etc.)
- Modification of host to facilitate transmission (sores, inducing coughing/sneezing, dirrhea)
- Avoidance of infection provides the adaptive evolutionary basis for our (and many animals') taboo on cannibalism. One is more likely to get sick ingesting germs contained in the body of a member of one's own species than those infecting a distantly related one.
- Microbes optimize their dispersal strategy. Under some circumstances, changing a host organism's biology until it dies maybe optimal.
- tends to be related to population density of host (e.g. Spanish influenza in WWI trenches.)
- In less crowded conditions, less virulence may be appropriate.
- Settled agriculture and the rise of cities encouraged evolution of pathogens that dispersed quickly - crowd diseases. (measels, small-pox, etc.) In large enough populations, these can continue propagating and even entirely "burn out"
- Many modern crowd diseases are sufficiently modified for human infection that they can't back-propagate to animal hosts.
- Others can lie dormant in animal reservoirs (SARS, Ebola)
- Consequence: People regularly exposed develop immune resistance. When these people come in contact with those who aren't there are devastating results.
- Microbial evolution:
- speed of evolution in viruses - considerable
- evolution of antibiotic resistant disease strains.
As humans expand into new habitats, we encounter new disease vectors and take the process of transmission of diseases from animals to a new level. (E.g. Ebola, HIV, SARS)
As mass communications and travel becomes more prevalent, it becomes more difficult to isolate diseases. (E.G. HIV hung out in some small corner of central Africa for centuries before being released in late 20th century.)
Reasons for fear: We haven't seen the worst case scenario.