Human Population Growth and the Problem of Biodiversity

• Human population has increased at an almost exponential rate.

• With this growth comes an increase in demand for land, food, water, energy and other resources.

• As human numbers grow species and their habitat diminish.

Biodiversity • Biodiversity is the variety of all forms of life

throughout an ecosystem.• High rates of extinction are quickly reducing

biodiversity especially in areas of the world with high human population density and growth.

• The direct and indirect effects that humans have had on biodiversity is challenging as can be seen from the following flow chart.

Human PopulationSize Resources use

Human Enterprises Agriculture Industry Recreation International Commerce

Land TransformationLand Clearing

ForestryGrazing

Intensification

Biotic Additionsand LossInvasionHuntingFishing

GlobalBiogeochemistry

CarbonNitrogenWater

Climate ChangeEnhanced

GreenhouseAerosols

Land cover

Loss of Biological Diversity

Extinction of speciesAnd populations

Loss of ecosystemsVitousek et. al (1997) Science, 277, p.494-499

Humans Change of the EarthExpressed as % Change

0102030405060708090

100

% Change

Land Transformation

CO2 concentration

Water use

Nitrogen Fixation

Plant Invasion

Bird Extinction

Marine Fisheries

Vitousek et. al (1997) Science, 277, p.494-499

Biodiversity and People • Places on earth with some

of the greatest biodiversity such as: South America, Equatorial Africa, India, Indonesia and Coastal regions also show the greatest density and fastest rate of growth of people.

Biodiversity

World Population

Extinction• Extinction is the natural

order. In fact, of all the species which have ever existed, 99.9 % are now extinct!

• The current extinction rates, however, may be as much as 40 - 100 times the normal “background” or natural rate for extinction.

Extinction• Paul Ralph Ehrlich at Stanford

University predicts that soon, this rate may be as much as 400 times the "normal", average, rate of extinction!

• Much of this increase in extinction rate appears to be due to the impact of humans.– Habitat Depletion– Pollution– Introduction of disease – Introduction of invasive species – Over exploitation

Extinction

• 25% of the earth’s birds species have been driven to extinction by humans (especially on islands).

• Threatened with Extinction– 11% of birds– 18% of mammals– 5% of fish – 8% of plants

Great Auk

Loss of birds

http://www.audubon.org/campaign/population_habitat/

Extinction Rate

The Oceans and the Coast

• Globally, the number of people living within 100 km of the coast increased from roughly 2 billion in 1990 to 2.2 billion in 1995 (39 percent of the world's population).

Coastal Area Population Density

• 3.2 Billion (1/2 of the plant) live and work within 125 miles from a coastline.

• 4 Billion (2/3) live within 250 miles from the coast.

Coastline, Estuaries and Reefs• While 75% of the earth is covered by

oceans, the greatest levels of marine biodiversity are found near the coast.

• This Neritic zone of the ocean has depth of less than 250 meters and so the abundant photosynthetic organisms create a habitat for great biodiversity.

Kelp Forest Near Monterey California

Approximately 50% of mangrove ecosystems globally have been transformed or destroyed by human activity

Great Barrier Reef, Australia

Human causes of Coral Reefs Depletions

• Pollution runoff: nitrates from fertilizers, point-source pollution, oil spills.

• Exploitation: Over 90% of saltwater aquarium fish are taken directly from reefs.

• Increased water temperatures: global warming, increased El Nino.

• Direct Destruction: Boats, fishing nets, removal of coral for sale.

Coastline and Reefs

“With increased human population and improved storage and transport systems, the scale of human impacts on reefs has grown exponentially.”

Dr. Terry Hughes Scientific Director of the Centre for Coral Reef Biodiversity at James Cook University in Queensland, Australia

http://www.audubon.org/campaign/population_habitat/

Over fishing

Culture

0

Global Fish Supply

Year

1980

1950

1960

1970

1990

2000

2025

Mill

ion

Met

ric

Tons

20406080

100120140160

Capture

(Grainger 1998)

1) Aquaculture is a vital aspect of the food-production industry

2) Global human population is expected to rise to over 9 billion by 2050

3) Placing tremendous pressure on food-production systems

Metric tons of fish caught by year

Invasive species• With the increase in ease of travel and shipping,

one of the greatest threats by humans is the introduction of invasive species.

• San Francisco Bay (example)• 1850 – 1970 : new species established every 36 weeks• 1970-1996: new species every 24 weeks• 1996-present: new species every 12 weeks.

Release of Ballast water

Invasive species

Zebra MusselUS and UK

Asian ClamSan Francisco Coqui frog

Hawaii

Brow Tree Snake Guam

RabbitsAustralia

Africanized HoneybeeSouth America

Tropical Rainforests Facts• Contains more than half

of the 5 to 80 million species of plants and animals worldwide.

• Approximately 1/3 of the world’s bird species are found in South American Rainforests.

Tropical Rainforests Facts

• Each year approximately 78 million acres of rainforest are destroyed.

• As many as 137 species are going extinct each day.

• The substrate (soil) is poor with most of the nutrients existing in the trees and plants.

Tropical Rainforest Facts• Poor soil leads to burning the

land to increase top-soil nutrients.

• Burning trees releases carbon into the atmosphere which exacerbates the greenhouse effect and increases temperature.

Tropical Rainforest and Population Growth

• Today, more than 3 billion people live in the tropics alone; more than lived in the entire world in 1950.

• Millions of people are destroying the rainforest simply to survive.

• These people, usually small farmers, have nowhere to grow crops to feed their families, so they wander into the rainforest.

Rainforest and Primates• Out of some 240 known primate species, 19 are

critically endangered, up from 13 in 1996. • Their remaining numbers range from less than a

few hundred to, at most, a few thousand individuals.

• Includes 8 monkeys from Brazil's Atlantic rainforest, where 97 percent of the forest has been lost, 2 apes and a monkey from Indonesia, 3 monkeys from Viet Nam, 1 each from Kenya and Peru, and 3 lemur species from Madagascar.

Rainforest and Primates• In Ghana and parts of the

Ivory Coast, the Miss Waldron’s Red Colobus monkey is now extinct.

• “Chimpanzees lived in what was Africa’s great equatorial forest belt, but it’s not belt anymore just pockets of shrinking forest areas…If things carry on at the present rate in 15 years there will be very, very few chimpanzees left.” Jane Goodall

http://www.audubon.org/campaign/population_habitat/

Conclusion • Humans require a great deal of resources

and space and have not had a record of sharing.

• The earth is losing biodiversity at a rate not seen since the mass extinction that killed the dinosaurs 65 million years ago.

• Our increasing numbers will certainly increase the rate at which animals and plants are lost.

Conclusion

• "For if one link in nature's chain might be lost, another might be lost, until the whole of things will vanish by piecemeal."- Thomas Jefferson