In a book about community ecology, I learned about Lotka-Volterra models and dynamic food web models (I am not an ecologist in the first place). 

In one of the chapters, a Jacobian matrix of partial derivatives of the Lotka-Volterra model at equilibrium densities is given:
\begin{bmatrix}-&-&0&0\\+&0&-&0\\0&+&0&-\\0&0&+&0\end{bmatrix}
where + and – represent positive or negative values. 

This matrix is later interpreted in terms of direction of trophic links in a food web, but the reasoning allowing to jump form one to the other is not detailed.  

So what is the biological meaning of these values?