THREATS TO GLOBAL BIODIVERSITY

The worst thing that can happen during the 1980s is not energy depletion, economic collapse, limited nuclear war, or conquest by a totalitarian government. As terrible as these catastrophes would be for us, they can be repaired within a few generations. The one process ongoing in the 1980s that will take millions of years to correct is the loss of genetic and species diversity by the destruction of natural habitats. This is the folly that our descendents are least likely to forgive us.

E.O. Wilson, 1985

THREATS TO GLOBAL BIODIVERSITY

We wish to know:What is biodiversity?What are the threats to

biodiversity?How can we estimate rates of

species loss?

What is Biodiversity?

the variety and variability among living organisms and the ecological complexes in which they occur

number and variety of species, ecological systems, and the genetic variability they contain.

In its narrowest sense biodiversity refers to the number of species on the planet

How Many Species Exist?

1.4 million species are "known to science" -- meaning that they have been classified by a specialist

Most experts estimate the world's species diversity at 10 to 30 million, but that is very approximate

Except for land vertebrates and flowering plants, the number of undescribed species (greatly) exceeds the number described

Number of Known, Living, Species

Among species known to science, the insects are overwhelming in number. For this reason, most animal species live on land, but more phyla, the highest level of classification, live in the sea.

Number of Animal Species Currently Known

Number of Living Species of Higher Plants

Plant diversity of the world consists primarily of the flowering plants (angiosperms), which is divided into the grasses and other monocots, and a great variety of dicots. Most flowering plants live on land; algae prevail in the sea.

The Geography of Biodiversity

The number of species is greatest near the equator, and declines as one moves towards the poles. Tropical rain forests are especially rich

Certain areas harbor an unusually rich local diversity, perhaps because conditions favor evolutionary diversification.

Certain areas (islands in particular) contain species unique (“endemic”) to that locale

Global Biodiversity

GLOBAL BIODIVERSITY map of the distribution of some of the most highly valued terrestrial biodiversity world-wide (mammals, reptiles, amphibians and seed plants), using family-level (red for high biodiversity and blue for low biodiversity). http://www.nhm.ac.uk/science/projects/worldmap/

Threats to Biodiversity

Human actions now threaten species and ecosystems to an extent rarely seen in earth history.

Over-harvestinghabitat destruction (degradation, fragmentation)exotic speciesdomino effectspollutionclimate change

Over-Exploitation

Hunting, especially commercial hunting and poaching, has driven many species to extinction.

Passenger pigeon for meat, snowy egret for fashion, rhinos for their horns.

Bushmeat harvest is a crisis of tropical forests today

Invading Species

Non-indigenous species (invaders) often are more effective predators or competitors, thereby eliminating native species. Island (and lake) species may be especially vulnerable.

Nutria (Coypu)

The nutria is a 7-kg rodent native to South America, introduced into many areas of the USA and UK for fur.

They devour crops and native plants, burrow into dikes and levees.

A six-year campaign in Britain exterminated the nutria in 1989

Maryland DNR hopes to accomplish their eradication from the Blackwater National Wildlife Refuge on Maryland’s eastern shore.Nutria begging for duck food at a

park in Louisiana http://www.keigh.com/nutria.html

A Michigan Invader

The gypsy moth arrived in the U.S. in the early 1900s, and in Michigan in the 1950s. With few natural enemies, it devours the leaves of forest trees. Although some defoliation is tolerable, if in two successive years and coupled with a drought, trees can be killed.

Global Deforestation

Original tropical forest extent was ~ 15 m km2; today it is about 8 m km2. At present rates of loss, ~ 10% of the original tropical forests will remain by end of century.

As climate warms in northern Minnesota, conifer and broadleaf forests will be replaced by savannah and woodland.

Under a 2 x CO2 scenario, the bobolink’s habitat would shift northwards

Forests at Risk from Global Warming -- WWF

Studies of plant and animal biogeography have established a log-linear relationship between number of species in an area, and areal extent. An example for the reptiles and amphibians for the Caribbean is shown with the area axis reversed, to illustrate that reduction in area leads to a reduction in species.

Using this relationship and estimated rates of tropical forest loss

Estimating Rates of Species Loss

The relationship between number of species and area of habitat is S = c A z

the rate of loss of tropical forest from satellite imagery is 1-2% annually

the resulting loss rate of species results in an overall loss of 25 - 50% of the world’s species by 2020

Assuming tropical forests harbor 10 million species, this loss is 27,000/yr (and 3/hr)

Summary

Biodiversity refers to the number and variety of species, of ecosystems, and of their genetic variation

Some 1.4-1.8 million species are known to science. Because many species are undescribed, some 10-30 million species likely exist at present

Biodiversity is threatened by the “sinister sextet”Habitat loss represents the single biggest threatProtected lands comprise about 5% of the earth’s land

area. Management of the remaining 95% must also be part of a biodiversity protection strategy