Determining if long-term change in a species' population abundance or distribution was caused by specific climate changes is an extremely difficult scientific problem for two reasons: first, both climate and biological factors vary greatly from year to year, and these annual variations often mask long-term trends, making them difficult to detect.
(both climate and biological factors; vary; greatly; T:first) Context(both climate and biological factors vary,List([191, 231))):(Determining if long-term change in a species' population abundance or distribution was caused by specific climate changes; is; an extremely difficult scientific problem) (these annual variations; mask; long-term trends; T:often)
both climate and biological factors vary,List([191, 231))
both climate and biological factors Determining if long-term change in a species' population abundance or distribution was caused by specific climate changes these annual variations
vary is mask
greatly T:first
an extremely difficult scientific problem
long-term trends T:often