A LINEAR-PROGRAMMING MODEL OF DIET CHOICE OF FREE-LIVING BEAVERS

Linear programming has been remarkably successful in predicting the di et choice of generalist herbivores. We used this technique to test the diet choice of free-living beavers (Castor fiber) in the Biesbosch (T he Netherlands) under different Foraging goals, i.e. maximization of i ntake of energy, nitrogen, phosphorus or sodium, or minimization of fe eding time. Three food types were distinguished, Le, woody food, herbs and roots of monocots. We assessed forage quality by measuring the dr y matter, energy and mineral contents of the food plants as well as fo od intake rates, digestibility and metabolisability in captive beavers . Actual diet was in accordance with the predicted food choice in the summer when the beavers were minimizing feeding time by mainly eating woody food. However, in the winter and spring, the beavers were predic ted to feed upon non-woody food, whereas they (again) nearly exclusive ly are woody food. The major reasons for this discrepancy might be: (1 ) the foraging constraints were inappropriate, (2) the foraging goals were inadequately defined, or (3) the beavers were not foraging optima lly. We suggest that future work should take some additional constrain ts and foraging goals into account.