Substrate-depletion pattern mechanism ($J\sim \left(\begin{array}{cc}+& +\\ -& -\end{array}\right)$)

An autocatalytic species promotes its own growth while consuming a substrate that promotes that growth. Its reaction Jacobian has the displayed signs after choosing the activator first. This differs from the activator-inhibitor sign pattern $\left(\begin{array}{cc}+& -\\ +& -\end{array}\right)$, where the activator stimulates its inhibitor. Appropriate magnitudes, diffusivities and admissible spatial modes are needed for a Turing instability; signs alone are insufficient.