  The pair production rates for spin-zero and spin-$\frac{1}{2}$ particles are
calculated on spaces of the form $M \times {\mathbb R}^{1,1}$ with $M$
corresponding to ${\mathbb R}^2$ (flat), $T^2$ (flat, compactified), $S^2$
(positive curvature) and $H^2$ (negative curvature), with and without a
background magnetic field on $M$. The motivation is to elucidate the effects of
curvature and background magnetic field. Contrasting effects for positive and
negative curvature on the two cases of spin are obtained. For positive
curvature, we find enhancement for spin-zero and suppression for
spin-$\frac{1}{2}$, with the opposite effect for negative curvature.
