  Let $G^\rightarrow$ be a simple connected directed graph on $n \geq 2$
vertices and let $V^*$ be a non-empty subset of $V(G^\rightarrow)$ and denote
the undirected subgraph induced by $V^*$ by, $\langle V^* \rangle.$ We show
that the \emph{competition graph} of the Jaco graph $J_n(1), n \in \Bbb N, n
\geq 5,$ denoted by $C(J_n(1))$ is given by:\\ \\ $C(J_n(1)) = \langle V^*
\rangle_{V^* = \{v_i|3 \leq i \leq n-1\}} - \{v_iv_{m_i}| m_i = i +
d^+_{J_n(1)}(v_i), 3 \leq i \leq n-2\} \cup \{v_1, v_2, v_n\}.$\\ \\ Further to
the above, the concept of the \emph{grog number} $g(G^\rightarrow)$ of a simple
connected directed graph $G^\rightarrow$ on $n \geq 2$ vertices as well as the
general \emph{grog number} of the underlying graph $G$, will be introduced. The
\emph{grog number} measures the efficiency of an \emph{optimal predator-prey
strategy} if the simple directed graph models an ecological predator-prey
web.\\ \\ We also pose four open problems for exploratory research.
