As a creature becomes extinct, it will never return as the dinosaurs were so. 
Furthermore
, since each living creature is closely related to the other in nature, the extinction of one creature can collapse the balance of the ecosystem and have a great impact on the whole natural environment. 
Linking Words
First
 of all, there are many factors that threaten the habitats of animals but the most significant one might be human activities. Linking Words
For example
, the area of  ice in the northern part of the world is shrinking; Linking Words
therefore
, the number of polar bears is decreasing and there is a risk of vanishing  on the earth. Linking Words
Furthermore
, gorillas are Linking Words
also
 on the endangered list and the case is the destruction of their habitat. As humans developed the land for the use of their living or constructing factories, the forests and jungles are destroyed. To sum up, it is obvious that  humans are causing Linking Words
this
 problem significantly.
Linking Words
Secondly
, the way to tackle Linking Words
this
 issue might be to raise awareness among individuals. Since many people are not familiar with Linking Words
this
 problem, by letting them know how it is crucial, they can think about how they can protect the animals and make an action. Volunteering activities are a good example. Since pollution is Linking Words
also
 a significant factor of animal disappearance, as volunteers gather a certain amount of people and clean seashore or reduce rubbish in forests, Linking Words
this
 may foster an awareness of the issue and Linking Words
also
 actually leads to an improvement.
In conclusion, I believe that the reason for the endangerment of many animal species is a negative impact on the environment because of human activities. Linking Words
This
 could be tackled by increasing awareness among people in society and let them take an action.Linking Words