CHAP. 11 NOTES - APES
SUSTAINING BIODIVERSITY: A SPECIES
APPROACH
Habitat fragmentation – the breakup of a habitat into
smaller pieces, usually as a result of human activities, i.e.,
logging, building roads, urban development.
Concerns and detriments:
-can create barriers that limit the ability of species to find
food and mates.
- increases edge areas that make some species more
vulnerable to predators.
-may create habitats too small to support the minimum
breeding population of some species.
-may limit the ability of some species to disperse and
colonize new areas.
The larger the area, the better - allows for greater diversity
of species. In cases of islands, it is better if it is a large
island near a mainland – not as isolated.
National Parks can be viewed as habitat islands because
they are often surrounded by logging and industrial
activities, agricultural and energy extraction practices.
Can result in extinction or speciation.
Extinction
1) Local extinction – when a species is no longer found
in an area it once inhabited but is still found elsewhere
in the world.
2) Ecological extinction – when so few members of a
species are left that it can no longer play its biological
roles in the biological communities where it is found.
3) Biological extinction – a species is no longer found
anywhere on the earth. “Gone forever”.
The current rate of extinction annually is 0.01 – 1 %.
All species eventually become extinct, however, the current
extinction crisis differs from previous mass extinctions in
that the current crisis is caused by the human species.
Other major causes of premature extinction included:
- habitat destruction
- population growth
- over-harvesting
- invasive species
The greatest threat to most species is loss of habitat,
especially in the tropical rainforests because it is the most
biologically diverse.
When species are lost to extinction, new species eventually
evolve to take their place.
Characteristics that make species prone to extinction:
- low population density
- specialist species (very narrow niche)
- low reproductive rate
- fixed migratory patterns
Models used to estimate risk of extinction:
- trends in population size
- interactions with other species
- genetic factors
- changes in habitat availability
Threatened species –also known as vulnerable species
- still abundant in its natural range but is declining in
numbers and is likely to become endangered in the
near future.
Endangered species – has so few individual survivors that
the species could soon become extinct.
About half of the species on the U.S. official list of
endangered and threatened species are there in part because
of population declines caused by nonnative species.
Over the last 25 year, the number of species found
exclusively on the U.S. list increased about 10 times.
Other species have become threatened or endangered
because of the exotic pet trade – legal and illegal capture
and sale of wild species of plants and animals for huge
profits.
Identification and listing of endangered species is done by
the Fish and Wildlife Service.
Endangered Species Act of 1973
- Is one of the world’s toughest environmental laws
- Requires all commercial shipments of wildlife enter
or leave the U.S. through one of nine designated
ports
- Authorizes identification of endangered species
solely on a biological basis
- Allows the use of endangered species for approved
scientific purposes or if the use enhances the
survival of the species.
CITES – a treaty controlling the international trade in
endangered species.
Limited by:
- violators receiving only small fines
- spotty enforcement
- member countries exempting themselves from
protecting some species
- much of the illegal trade in wildlife goes in
countries that have not signed the treaty
Sanctuary approach to protecting wildlife:
- National Wildlife Refuges – areas that have been set
aside for the protection of threatened or endangered
species.
- Gene banks
- Botanical gardens
- Wildlife farms
- Zoos and aquariums
All suffer from lack of funding.