  We study $\Lambda$ baryons of spin-parity $\frac{1}{2}^{\pm}$ with either a
strange or charm valence quark in full 2+1 flavor lattice QCD. Multiple $SU(3)$
singlet and octet operators are employed to generate the desired single baryon
states on the lattice. Via the variational method, the couplings of these
states to the different operators provide information about the flavor
structure of the $\Lambda$ baryons. We make use of the gauge configurations of
the PACS-CS Collaboration and chirally extrapolate the results for the masses
and $SU(3)$ flavor components to the physical point. We furthermore gradually
change the hopping parameter of the heaviest quark from strange to charm to
study how the properties of the $\Lambda$ baryons evolve as a function of the
heavy quark mass. It is found that the baryon energy levels increase almost
linearly with the quark mass. Meanwhile, the flavor structure of most of the
states remains stable, with the exception of the lowest $\frac{1}{2}^{-}$
state, which changes from a flavor singlet $\Lambda$ to a $\Lambda_c$ state
with singlet and octet components of comparable size. Finally, we discuss
whether our findings can be interpreted with the help of a simple quark model
and find that the negative-parity $\Lambda_c$ states can be naturally explained
as diquark excitations of the light $u$ and $d$ quarks. On the other hand, the
quark-model picture does not appear to be adequate for the negative-parity
$\Lambda$ states, suggesting the importance of other degrees of freedom to
describe them.
