  We study inelastic collisions between CaF molecules and $^{87}$Rb atoms in a
dual-species magneto-optical trap. The presence of atoms increases the loss
rate of molecules from the trap. By measuring the loss rates and density
distributions, we determine a collisional loss rate coefficient $k_{2} = (1.43
\pm 0.29) \times 10^{-10}$ cm$^{3}$/s at a temperature of 2.4 mK. We show that
this is not substantially changed by light-induced collisions or by varying the
populations of excited-state atoms and molecules. The observed loss rate is
close to the universal rate expected in the presence of fast loss at short
range, and can be explained by rotation-changing collisions in the ground
electronic state.
