Transcript Document

Chapter 18
Human Threats to Biodiversity
Human Threats to Biodiversity: Introduction
• the number of species is unknown:
estimates range from 10 million to 100 million
• ~1.4 million species have been catalogued, many of them are beetles!
• rates of speciation and extinction are also unknown, although
estimates exist
• it is widely believed that significant species loss is occurring, but it is
easier to catalogue habitat loss than species loss
• estimates of habitat loss can lead to estimates of species loss, but that
is complicated because certain species are more important than other
species to their ecosystems: keystone species
Pleistocene and Holocene
Extinctions:
• estimated 70% of large mammal
genera of the late Pleistocene are
extinct. Birds too.
• know significant examples include
Madagascar, New Zealand,
Polynesia, Hawaii
• North American extinctions
include large mammals such as
bison, antelope, mammoth, other
mammals and large birds
• N. American and Australia also
had climate change, hard to isolate
the two effects
• overhunting was the impact prior
to modern days
Modern Extinctions:
• habitat destruction and alteration from land use and land cover change is the
main mechanism for modern extinctions
• for example, Europe has almost no land left of its original forest cover
• Today, greatest rate of species loss is found in the tropical forests: ~6% of land
surface area, but >50% of the earth’s plant and animal species
• Of the ~9000 known bird species, almost half live in Amazon or Indonesia
Tropical Deforestation:
• for every 10x increase in the area of tropical forest, it is believed that the
number of species doubles
• E.O. Wilson concludes that ~27000 species are lost each year from tropical
deforestation. This is believed to be perhaps thousands of times greater than the
average natural rate of extinction
• Tropical forests hold much of the nutrients in the biomass, not in the soil, and so
when trees are removed few nutrients remain
• soils are acidic, and tree seeds are less tolerant to the stressful environmental
conditions, so forests do not grow back easily, or with the same species
• many species live in relatively small geographic areas, and can get wiped out
Tropical
Deforestation: Other
environmental impacts
• temperature, hydrologic
cycle, and nutrient cycling
• DECREASE IN:
ET, precip, soil moisture,
runoff
• INCREASE IN:
temperature
Tropical Deforestation: how?
• logging for agriculture, ranching, hydroelectric projects, mining, human
settlement
• 80,000 km2 per year cleared for agriculture
• slash and burn leaves nutrients in the soil. Buth, they are depleted within a
few years. If given enough regeneration time, this works. Otherwise, problems
with soil fertility, crop yields, and degradation results
• 50,000 km2 per year cleared for wood products (particularly Asia and West
Africa)
• 20,000 km2 per year in latin america cleared for cattle ranching. Usually
results in soil that can not be regenerated due to compaction
Tropical Deforestation: why?
• population growth
• uneven property ownership – many landless, poor people forced to move into
previously uninhabited areas
• government sponsored resettlement programs: Brazil
• cash crops or mineral extraction for export
Hotspots of Habitat Loss: Norman Myers, Oxford
• Land only, no ocean
•areas with many species that live nowhere else, and that are in greatest danger
of extinction as a result of human activities
• “biogeographical units” with distinct and identifiable assemblage of plant and
animal species
• 25 “hotspots” units with at least 0.5% of the worlds 300,000 know vascular
plants, lost at least 70% of its primary vegetation
Hotspots of Habitat Loss: Norman Myers, Oxford
• currently contain only 12% of their original cover
• 1.4% of earth’s land surface, but almost 50% of vascular plant species, and
35% of all vertebrate species (excluding fish)
Why should we care about biodiversity?
Environmental Ethics
• instrumental value how does one species benefit another (usually humans)
• intrinsic value something has value for its own sake, regardless of how it
benefits us
• rights do animals, plants, rocks have rights?
• biodiversity and food supply, ecosystem stability
Coral Reefs
• Coral is an animal found in
shallow tropical seas
• most productive and diverse
ocean ecosystem
• dynamic, fragile, vulnerable,
yet often recovers quickly
• structures made of calcium
carbonate, built from calcium
and carbonate ions in the
ocean water
• symbiotic relationship to
algae necessary to survive
www.chbr.noaa.gov
Coral Reefs
• tolerate temperatures ~21C – 29C (~70F – 85F)
• require sunlight, so grows in the euphotic zone (several meters to 200 m)
• believed to contain at least 25% (33%?) of all marine species, including 700
coral species and >4000 fish species
Coral Reef Bleaching
•corals expel the zooxanthellae, single
celled organisms
• symbiotic relationship – corals can
not live without their nutrients
• corals loose their colors and die
• changes in temperature cause
bleaching
http://earthobservatory.nasa.gov/Study/Coral/coral2.html
Science, May 4 2007, Vol 316, p. 678-681
Threats to Coral Reefs
“besieged by pathogens, predators, and people, the ‘rainforests of the sea’ may
soon face their ultimate foe: rising ocean acidity driven by CO2 emissions
Attempting to regrow reefs that were devastated by the tsunami of Dec 2004
such attemps have been somewhat successful
Science, May 4 2007, Vol 316, p. 678-681
Threats to Coral Reefs are mostly human
• divers destroying the reefs
• shipping and dredging destroying reefs
• pollution and sewage
• over fishing
• rising ocean temperatures
Science, May 4 2007, Vol 316, p. 678-681
• increased acidification
• ~20% of the earth’s coral reefs have been destroyed in the last few decades
• another 50% on the verge of collapse
• vulnerability on “many fronts”: for example, over fishing and/or pollution and
higher temperatures, could in conjunction, make them more vulnerable and less
resilient to predators (certain starfish) and pathogens (certain algae)
• the coral species less resistant to bleaching will die first
Coral Reef / CO2
• CO2 concentrations affect the
availability of carbonate ions in the
ocean water
• increase in CO2 results in increased
acidity, and reduction of carbonate
• it this gets bad enough it will make it
harder for the corals to grow
http://earthobservatory.nasa.gov/Study/Coral/coral2.html
Protecting Coral Reefs
• MPAs – marine protected areas
• range of restrictions, can include
recreation, can bar fishing
• <3% of worlds reefs are within MPAs
• many unprotected reefs are being
“fished out” for human food
Science, May 4 2007, Vol 316, p. 678-681
• many MPAs are not working
due to poor enforcement, and lack of local “buy in”
• reef management after bleaching to prevent over fishing can improve recovery
• no management scheme is considered viable in the long run unless carbon
emissions are curtailed
• IPCC scenarios indicate potential ocean pH lower than in the last 20M yrs
• under all climate scenarios, reefs will be drastically different; under most
scenarios reefs might not survive