m13.    What are endangered and threatened species?

Endangered species have so few members that they may become extinct over all or most of their natural range. Included in this list are:

Threatened species are still abundant in the wild but their numbers are declining rapidly. Among those threatened are the Bald Eagle and the Grizzly Bear. Species, which have diminished locally, are better indicators of that ecosystem than those organisms on the endangered or threatened lists.

The greatest threat to wildlife is the loss of habitat. Tropical deforestation is followed by destruction of the coral reefs, wetlands, and grasslands as loss of habitat. About ¾ of the world's 9,007 known bird species are declining in numbers because of habitat loss.

Another threat is commercial hunting and poaching. Subsistence hunting is hunting to provide enough food for subsistence; sport hunting is killing animals for recreation or for extra food. Commercial hunting involves selling meat, hides, etc. for profit. Illegal commercial hunting is poaching.

Some organisms are threatened because of man’s encroachment into habitat with their crops. These folks consider the organisms pests. US fruit farmers hunted the Carolina parakeet to extinction. Since 1929, US ranchers and government agencies have poisoned 99% of the prairie dog population.  This has nearly wiped out the black-footed ferret, which preyed on the prairie dogs.

Other threats to organisms are keeping them as pets or as part of collections. Some 24 million American households have exotic birds as pets.  About 85% of these are imported; 1 in 17 survive the capture and transport. Orchids and cacti are poached for sale to collectors.

Pollution has also taken its toll: DDT and Dieldrin have caused populations of some birds to decline because these substances make the eggs fragile.

Introduced species have devastated native organisms. Kudzu vine from Japan was used to control soil erosion.  Instead it cannot be killed. Wild African (killer) bees came to Brazil to improve honey production.  Instead they reduce honey production and are dangerous. Salt cedar came from the Middle East.  It was to reduce erosion around streambeds, but took most of the water out of the streams.

Population growth also puts organisms in danger.  Both affluence and poverty contribute to extinction.  Both groups want more of the habitat.

e10.    Why do organisms become extinct?  

e11.    What types of old-growth forests are there?

e12.    Where are tropical forests?

g07.    How did plate tectonics affect the diversity of ecosystems?