• 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:
  • 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.
  We call this cycle of population growth, starvation and migration a "boom and crash cycle".
• 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.

• 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.

• 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
  • Pesticides
  • Fertilizers
  • Machinery
  • 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 the development of agricultural technologies must be in a constant race with the evolution of pathogens and accumulation of environmental problems, if disaster is to be forestalled. 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:

• The Irish Potato Famine (1845-1851):
  • Prior to potato, roughly 1/3 of Ireland was too boggy or rocky to be arable by conventional means.
  • Ireland's economy was dominated by absentee landlords who rented parcels to tenant farmers. Laws favoring landlords discouraged actual residents from making improvements to property.
  • Changed with introduction of potato in 1590 - a low-maintainance crop that grew in otherwise waste regions. Indeed, the potato was more nutritious than alternative crops, and by 1800 Ireland was a potato monoculture for purely rational reasons.
  • Between 1845 and 1851 the potato crop was largely destroyed by a fungal blight recently imported from the New World (Phytophthora infestans). During that interval Ireland's population dropped by roughly 20% (12% starved, 8% emmigrated) as food production failed and the economic system collapsed. (By British policy, food relief was to be funded by taxes on landlords who became bankrupt as they could no longer collect rent from starving tenants.)
  • As bad as it was, the famine was mitigated by:
    • Eventual aid from the British Crown.
    • Proximity to places of refuge (England and North America)
    • The fact that the blight was local.

  Just IMAGINE a similar blight today effecting rice in mainland Asia.

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:

• 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.

• 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 vertebrate diversity from the World Wildlife Fund's Living Planet Report.

• habitat loss and degradation
• climate change
• chemical contamination
• infectious disease, notably the fungal infection Chytridiomycosis
• interactions with invasive species
• over-harvesting

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:

• 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 190th centuries - Large-scale hunting and extinctions. E.G. the passenger pigeon, heath hen, labrador duck.
• Well-intentioned folly: Deliberate introductions of exotic species, including
  • Eurasian starlings to Central Park, NY
  • Mongooses to Hawaii
  • Cane toads to Queensland, Australia. (BONUS! Check out the Cane Toad Song from the film Cane Toads.)

• 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.)

• Great apes face impending extinction.
  • Orangutans - suffering from logging/habitat destruction Expected for fall below critical thresholds within 50 years.
  • Chimpanzees/Gorillas Logging indirectly threatens by facilitating ebola transmission, in addition to habitat destruction.

  What are we getting in return for letting these creatures become extinct (even the "useless" ones), more golf courses?

We've talked about the taxonomic origin and evolution of disease pathogens. What about their geographic origins?

• 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 the late 20th century.)

• Reasons for fear: We haven't seen the worst case scenario.