The nitrogen and carbon stable isotope values for four populations of rodents on two islands (Lower Keys and Sanibel-Captiva) in southern Florida, USA. The corresponding ellipses represent the posterior distributions of estimated bi-variate ellipses used to compare isotopic overlap. Shown also are the means (black dots) and standard deviations (coloured crosses) of the stable isotope values of the three taxa of potential food items (i.e. sources).