  We study Renyi and von Neumann entanglement entropies in the ground state of
the one dimensional quarter-filled Hubbard model with periodic boundary
conditions. We show that they exhibit an unexpected dependence on system size:
for L=4 mod 8 the results are in agreement with expectations based on conformal
field theory, while for L=0 mod 8 additional contributions arise. We show that
these can be understood in terms of a "shell-filling" effect, and we develop a
conformal field theory approach to calculate the additional contributions to
the entropies. These analytic results are found to be in excellent agreement
with density matrix renormalisation group computations for weak Hubbard
interactions. We argue that for larger interactions the presence of a marginal
irrelevant operator in the spin sector strongly affects the entropies at the
finite sizes accessible numerically, and we present an effective way to take
them into account.
