I would say immigration only.
emigration would theoretically reduce the genetic variation as unique individuals leave, but immigration would bring unique traits into circulation in an ecosystem.
I'm not super great at biogy tho so this might not be right... :)
<span>The question says, vertebrates have notochord during early embryonic development. The statement is true. A notochord is a cartilaginous skeletal rod which support the body in all embryonic and some chordate animals. It has essential role in vertebrate development. It is a primitive beginning of the spinal cord.</span><span />
Bird vocalization is often a mating behavior; however, bird vocalization can be used to warn other birds if danger is nearby, or for other means of communication.
Ductile and devolves readily in Dilutes in acid
