Figure: Time series for two populations, each fluctuating in size. At time zero, I start a long-term study, and can choose either of the two populations (open circles). At some other time, I recensus (closed circles). Red arrows show net population change.
On any given day it’s hard not to notice another headline about a population in decline. Amphibians are in decline, songbirds are in decline, bumblebees are in decline, fish stocks are in decline. Nature is under relentless human pressure, both direct and indirect, and before I proceed to make my point today, I need to be very clear that this pressure is real and severe and I don’t doubt for a moment that it’s driving down population sizes of many, many species.
But there’s a very simple but pervasive statistical problem with the data behind population declines. Continue reading