  Ecological networks originating as a result of three different ecological
processes are examined and cross-compared to assess if the underlying
ecological processes in these systems produce considerable difference in the
structure of the networks. Absence of any significant difference in the
structure of the networks may indicate towards the possibility of a universal
structural pattern in these ecological networks. The underlying graphs of the
networks derived by the ecological processes, namely host-parasite interaction,
plant pollination and seed dispersion are all bipartite graphs and thus several
algebraic structural measures fail to distinguish between the structure of
these networks. In this work we use weighted spectral distribution (WSD) of
normalized graph Laplacian, which have been effectively used earlier to
discriminate graphs with different topologies, to investigate the possibility
of existence of structural dissimilarity in these networks. Graph spectrum is
often considered a signature of the graph and WSD of the graph Laplacian is
shown to be related to the distribution of some small subgraphs in a graph and
hence represent the global structure of a network.We use random projections of
WSD to $\mathbb{R}^{2}$ and $\mathbb{R}^{3}$ and establish that the structure
of plant pollinator networks is significantly different as compared to
host-parasite and seed dispersal networks. The structures of host parasite
networks and seed dispersal networks are found to be identical. Furthermore, we
use some algebraic structural measures in order to quantify the differences as
well as similarities observed in the structure of the three kinds of networks.
We thus infer that our work suggests an absence of a universal structural
pattern in these three different kinds of networks.
