Abstract: Despite it is widely accepted that intrapopulation variation is
fundamental to ecological and evolutionary processes, this level of
information has only recently been included into network analysis of
species/population interactions. When done, it has revealed non-random
patterns in the distribution of trophic resources. Nestedness in
resource use among individuals is the most recurrent observed pattern,
often accompanied by an absence of modularity, but no previous studies
examine bipartite modularity. We use network analysis to describe the
diet composition of the Balearic endemic lizard Podarcis lilfordi
in two islets at population and individual levels, based on the
occurrence of food items in fecal samples.Our objectives are to 1) compare niche structure at both levels, 2) characterize niche partition using nestedness and modularity, and 3) assess how size, sex, season, and spatial location influence niche structure. At population-level niche width was wide, but narrow at the level of the individual. Both islet networks were nested, indicating similar ranking of the food preferences among individuals, but also modular, which was partially explained by seasonality. Sex and body size did not notably affect diet composition. Large niche overlap and therefore possibly relaxed competition were observed among females in one of the islets and during spring on both islets. Likewise, higher modularity in autumn suggests that higher competition could lead to specialization in both populations, because resources are usually scarce in this season. The absence of spatial location influence on niche might respond to fine-grained spatio-temporally distribution of food resources. Behavioral traits, not included in this study, could also influence resource partitioning.
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