Latitudinal variation in litter size of polar bears: ecology or methodology?

I used data reported in the scientific literature to examine latitudinal va riation in litter size of polar bears in 18 different populations. No relat ionship was found between litter size and latitude using non-weighted regre ssion. Regression weighted by sample size indicated a negative relationship with latitude. However, sampling biases caused by latitudinal differences in the timing of sampling and cub mortality after den emergence could produ ce a latitudinal dine. Stratifying analyses by sampling area, at dens or aw ay from dens, revealed no latitudinal trend in litter size. Observed differ ences in litter size among populations may result from variation in demogra phy and ecosystem productivity that is not simply related to latitude. I co nclude that available data do not provide support for a biologically signif icant latitudinal dine in polar bear litter size.