Number 16/Life & ecology/Biogeography
The Range-Abundance Lead
The quantity
The interval between detectable range contraction and detectable abundance decline in a declining species.
01Why it matters
It determines which monitoring approach gives earlier warning, and most programmes measure abundance because range is harder.
02Expected value
Years to decades, longest in species with long generation times.
03How it would be measured
Paired range and abundance records for species with documented declines.
04What would refute it
Simultaneous change would make the lead zero.