Species and their vulnerability to extinction
Before species become extinct they become rare. Rarity is assessed by three
criteria:
Endemic species often fit these criteria and many are in danger of extinction
around the world.
8.1 The Iberian lynx, endemic to Iberian peninsula in Spain, is down to 100 cats due to habitat loss
Endemic species -species naturally found only in a single geographic area
-expansions caused by humans are not considered part of the species
natural distribution Exs. 1)giant panda is endemic to China even
though they are in zoos around the world 2)English plantain is
endemic to Europe and Asia but is now found throughout the world
because its fruits are easily dispersed. Black locust is a native to
eastern and southern US but is widely planted elsewhere in North
America
-evolved in that region and nowhere else
-isolated areas like remote islands, old lakes, and solitary mountain peaks
often have high endemism. Also high in geologically old, continental
areas with Mediterranean climates like South Africa and California. In
Texas, the Edwards Plateau and Trans Pecos are areas of high
endemism.
Texas is ranked 4th in the USA in numbers of endemic plant species. It
has 379 and only CA, HI, and FL have more
Table 8.1, Figure 8.2
-Madagascar is an example of a hot spot for endemism outside the USA
-80% of land altered or destroyed by humans putting about 1/2 of endemic bird
and mammal species in danger of extinction
-93% of mammal species (28 species of lemurs)
-99% of 144 species of frogs
-90+% of 1500 plant species
8.2 The number of plant species endemic to the different states varies greatly
Species are most vulnerable to extinction for five reasons
Species of desert pupfish of the southwestern U.S. are highly endangered
8.3 Dried ginseng roots are used for traditional Chinese medicine as an aphrodisiac and tonic
10 categories of species closely linked with extinction
1. Species that need a large home range.
Ex. Brown and Grizzly bears
2. Animal species with a large body size.
-have large home ranges, require more food, and are more easily hunted by
humans
Ex. Sri Lanka (Ceylon) -large island off the southern coast of India. Largest
species of carnivores (leopards and eagles) and the largest species of
herbivores (elephants and deer) are currently at the greatest risk for extinction
Fig. 8.4
3. Species that are not effective dispersers.
-environmental changes by humans are rapid enough that adaptation may be
prevented and migration is the only solution Ex. A detailed analysis of
vertebrates of western Australia revealed that modern extinctions were almost
exclusively confined to nonflying mammals with few occurring in birds and
bats
8.4 Body mass of herbivorous mammals that survived arrival of European people (green) and those that went extinct (red).
4. Species that are seasonal migrants.
-depend on two or more distinct habitat types. If either is damaged, the species
may be unable to persist. Ex. neotropical migrants -billions of songbirds of
120 species that migrate between the northern USA and the American
Tropics
5. Species with little genetic variability.
-genetic variability may allow for adaptation to change. When it is low it can
lead to extinction Ex. Primary reason that cheetah is believed to have low
disease resistance
6. Species with specialized niche requirements.
-Ex. wetland plants may need very specific and regular changes in water level
-Ex. salt marsh cord grass is found only in salt marshes
-Ocellated antbird feeds only on insects and other small animals fleeing from
army ants
Fig. 8.5
8.5 Ocellated antbird feeds only on insects and other small animals fleeing from army ants.
Box 8.1 Why are frogs and toads croaking? Below an Australian frog is tested for chytrid fungi:
7. Species that are characteristically found in stable, pristine
environments
8. Species that form permanent or temporary aggregations.
Ex. herds bison, flocks passenger pigeons, bat roosts, sea turtles
Allee effect-inability of social animals to forage, find mates, or defend
territory when populations are small
9. Species that evolved in isolation and had no prior contact with people.
Ex. Rates of recent bird extinction is far lower on Pacific Islands
colonized by Polynesians than on islands not colonized by Polynesians
10. Species that have closely related species that are recently extinct or
are threatened with extinction.
-characteristics that make certain species vulnerable are often shared by
related species
Ex. Sea turtle species are hunted, migrants, and form temporary
aggregations. Because of this they often suffer from the small
population and declining population paradigms
Conservation categories
-developed by the International Union for the Conservation of Nature (IUCN)
-developed categories based on available data
1) observable decline in numbers
2) range of species
3) total number of mature individuals
4) expected decline in number of individuals if the population decline or habitat
destruction continues
5) probability of extinction in a certain amount of time
8.6 The IUCN categories of conservation status
IUCN has evaluated
most bird, amphibian,
and mammal species
but the levels of
evaluation are lower
for reptiles, fish, and
angiosperms resulting
in low apparent
levels of threat Fig. 8.7
U.S. Endangered Species Act of 1973
Basics of the law:
-to "provide a means whereby the ecosystem upon which endangered
and threatened species depend may be conserved [and] to provide a
program for the conservation of such species"
-by law, endangered and threatened mean the following:
1) endangered-those likely to become extinct as a result of human
activity and natural causes in all or a major portion of their range
2) threatened- those likely to become extinct in the near future
-requires all U.S. government agencies to consult with the USFWS and
National Marine Fisheries Service to determine whether their activities
will affect listed species
-also prevents private individuals, businesses and local governments
from harming listed species and their habitats. Fines for individuals
are up to $100,000 and one years imprisonment or up to $200,000
for organizations
-at extremes are overzealous USFWS employees and landowners who
destroy endangered species on their property "shoot, shovel, and shut
up" or those that criticize it for halting development or costing too
much
Ex. Development criticism- 1987-1992 @ 100,000 cases (98,237)
presented involving ESA. About 50 (55) projects were stopped cold.
Much less than 1% (5/100 of 1%)
Ex. Cost criticism- USFWS annually spends around 350 million on
activities related to the act with the largest portion being land
acquisition and legal expenses. From 1977-1995, the average annual
funding was 39 million per year. This is 16 cents per taxpayer per
year or the cost of one mile of interstate highway. The number of
species protected by the ESA has been increasing at a faster rate than
funding. Probably need $650 million per year to create a truly effective
program.
Since 1973, more than 1519 (1500) U.S. species have been added to
the list including many well-known species such as the whooping crane
Fig. 8.9
-most are plants and vertebrates with invertebrates mostly disregarded
(Ex. Only 70 insect species in U.S. are listed)
-on average, animals are listed when about 1000 or less individuals
remain and plants when fewer than 120 individuals remain
-must get data earlier and list before numbers are so low that success is
unlikely
-in the USA, Natural Heritage Data Centers have provided more timely
data
Figure 8.9 Whooping cranes are protected by the U.S. Endangered Species Act and are intensively
managed
USA
-has Natural Heritage Data Centers (NHDC) in 50 states, three provinces in
Canada, and 14 Latin American countries. NHDC is strongly supported by
the Nature Conservancy.
-data is available on NatureServe website
-many of the species that are threatened or vulnerable are associated with
freshwater wetlands
Figure 8.10
In USA, freshwater wetland species have from 40-70% of their animals
(mussels, crayfish, amphibians, and fish) that are extinct or critically
imperiled to vulnerable.
One third of flowering plant species are extinct or critically imperiled to
vulnerable. and about ¼ of conifers and ferns.
Texas also has data on threatened and endangered species at the Texas Parks
and Wildlife website
8.8 Some species groups from the United States ranked as critically imperiled, imperiled, or
vulnerable