Author Question: Which of the following categories includes manatees and dugongs? A) Cetacean B) Cnidaria C) ... (Read 21 times)

fox · **on:** Aug 22, 2018

Which of the following categories includes manatees and dugongs?
A) Cetacean
B) Cnidaria
C) Sirenia
D) Teleost

Question 2

What is DDT? What affect did it have on the population of brown pelicans in the 1960s?

adf223 · **Reply #1 on:** Aug 22, 2018

Answer to Question 1

C

Answer to Question 2

DDT is a chlorinated hydrocarbon. It was used as a pesticide until it was discovered it was causing damage to the ecosystem.
The damage caused by DDT was high due to biological amplification. This occurs when levels of synthetic chemicals increase and concentrate into the flesh of organisms in higher trophic levels. The DDT began in plankton, but became stronger in concentration as the food web reached the brown pelican.
The brown pelicans began to decline in number because the DDT softened the shells of the eggs. The eggs would crack before a chick would hatch. Then the adults would abandon the nest. The population declined rapidly.
Rachel Carson wrote the book Silent Spring which discussed this very case in a way that was easy for everyone to understand. She began environmental activism and conservation in a way. She definitely changed the perspective about the impacts of humans on ecosystems