Why senior authorship is bad for ecology (and probably science in general)

I've been giving a fair bit of thought recently to the concept of "senior authorship". Senior authorship is the practice whereby the last position on an author line is occupied by the leader of the lab in which the project was conducted (i.e., the P.I., the advisor, whatever terminology you prefer). Being the senior author on a paper is considered a sign of leadership on the project and is arguably at least as prestigious as being the first