Diet composition of the lizard Podarcis lilfordi (Lacertidae) on 2 small islands: an individual-resource network approach

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 2 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.

Contrasting size-dependent life history strategies of an insular lizard

“…Individuals from NG, which are ∼10–14% smaller than those in the other 2 islets (MO and ES), exhibited size-independent fertility and have a higher mortality in large size classes compared to the other islands, but both lizard diet ( Santamaría et al. 2019 ) and population density ( Ruiz de Infante et al.…”

“…In contrast, the largest islet, MO, has a complex plant community and constant food availability; mice Mus musculus and geckos Tarentula mauritanica are present as possible competitors but their population density is not comparable with that attained by lizards ( Tenan et al 2013 ). NG presents the same plant community as MO with comparable plant species that provide constant food as well ( Santamaría et al. 2019 ).…”

Individual environmental niches in mobile organisms

“…Environmental niches in our study exhibited a nested pattern. Examples of nested patterns in dietary niches exist, although these are usually based on binary, bi-partite diet networks and not on hypervolume analysis 47,51,52,[57][58][59] . Nested diets are often attributed to a "shared preferences" model, based on optimal foraging theory, in which competition forces individuals to seek less-preferred food items and individuals differ in their willingness to accept these items 28,57 .…”

Individual‐resource network between Xylocopa bees and plant resources: generalist species, specialist individuals?

“…The resource partitioning hypothesis (Schoener, 1974) states that sympatric, morphologically, and functionally similar species present temporal separation or low food overlap to avoid interspecific competition (Aguiar et al, 2013;Carvalho et al, 2013;Rabelo et al, 2014;Lima et al, 2017). However, individuals within populations may also present the differential use of food resources, as demonstrated for several groups of animals (Bolnick et al, 2003;Araújo & Gonzaga, 2007;Tinker et al, 2012;Santamaría et al, 2019). Variations in the use of Correspondence: Solange Cristina Augusto, Instituto de Biologia, Universidade Federal de Uberlândia, Umuarama, Bloco 2D, 38400-902, Uberlândia, MG, Brazil.…”