Hi again, @jessegrabowski! I appreciate your interest, and sorry for the late response.
Yes, it is a mix of (time, delta1, delta2) longitudinal observations, where delta1 and 2 are isotope values. The animals sampled are random individuals from two co-occurring species. Also, yes, the environmental factors are from the corresponding time windows and correspond to the area where the animals were sampled.
If I were to put it in some sort of mathematical notation, it would be something like this:
[delta1, delta2]_(sp, y) ~ X1_y + X2_y + X3_y
Where sp is the species, and y is the year.