\begin{table}
\caption{The numbers of first-ranked, satellite and isolated galaxies in
different environments}
\label{Tab2}
\begin{tabular}{ccccc}
\hline\hline
\noalign{\smallskip}
Population  & D1    & D2 & D3 & D4 \\
            & Void  & Filament & Supercluster & SC Core \\
            & $D\!\leq1.5$ & $1.5<\!D\!\leq4.6$ & $4.6<\!D\!\leq7$ & $D\!>7$ \\
\hline
\noalign{\smallskip}
First-ranked &  5499 & 11979 & 3511 & 2261 \\
Satellites   &  8196 & 24078 & 9561 & 8582 \\
Isolated gal. & 36813 & 40553 & 8263 & 4359 \\
\hline
\end{tabular}
\begin{list}{}{}
\item The density parameter $D$ is the global environmental density in
  units of the mean density (see Sect.~\ref{sec:2.3} for more
  information).
\end{list}
\end{table}