Individual-Based Ant-Plant Networks: Diurnal-Nocturnal Structure and Species-Area Relationship

Abstract

Despite the importance and increasing knowledge of ecological networks, sampling effort and intrapopulation variation has been widely overlooked. Using continuous daily sampling of ants visiting three plant species in the Brazilian Neotropical savanna, we evaluated for the first time the topological structure over 24 h and species-area relationships (based on the number of extrafloral nectaries available) in individual-based ant-plant networks. We observed that diurnal and nocturnal ant-plant networks exhibited the same pattern of interactions: a nested and non-modular pattern and an average level of network specialization. Despite the high similarity in the ants’ composition between the two collection periods, ant species found in the central core of highly interacting species totally changed between diurnal and nocturnal sampling for all plant species. In other words, this “night-turnover” suggests that the ecological dynamics of these ant-plant interactions can be temporally partitioned (day and night) at a small spatial scale. Thus, it is possible that in some cases processes shaping mutualistic networks formed by protective ants and plants may be underestimated by diurnal sampling alone. Moreover, we did not observe any effect of the number of extrafloral nectaries on ant richness and their foraging on such plants in any of the studied ant-plant networks. We hypothesize that competitively superior ants could monopolize individual plants and allow the coexistence of only a few other ant species, however, other alternative hypotheses are also discussed. Thus, sampling period and species-area relationship produces basic information that increases our confidence in how individual-based ant-plant networks are structured, and the need to consider nocturnal records in ant-plant network sampling design so as to decrease inappropriate inferences.

Positive Relation Between Abundance of Pericarpial Nectaries and Ant Richness in Tocoyena formosa (Rubiaceae)

“…Unlikely our findings, Dáttilo et al (2014) did not find a clear correlation between ant richness and EFNs, even when analyzing three plant-bearing EFN species. They indicated two alternative not mutually exclusive hypotheses, though: 1) that EFNs has been monopolized by few dominant ant species that have competitively excluded other ant species or, 2) that the tree height in Cerrado are relatively low, which eases the resource domination by few ant species.…”

“…The absence of modulation in the network is commonly found in facultative mutualistic networks, which suggests a homogeneous and cohesive network (Díaz-Castelazo et al, 2013;Dáttilo et al, 2014). In our system, the non-modularity may be explained by the short period that PNs are active during a year, preventing the emergence of restrictive relations with some species of ants.…”

“…In our system, the non-modularity may be explained by the short period that PNs are active during a year, preventing the emergence of restrictive relations with some species of ants. It also occurs because ants do not usually show foraging fidelity in the same group of plant individuals (Dáttilo et al, 2014), which is indicated by the low specialization that we found in T. formosa individuals with high numbers of PNs. These two results (modularity and specialization) are complementary and reinforce the idea of seasonality acting on the organization of these interactions.…”

“…Network analysis shows associations (links) between species (nodes) in a community, and is a commonly used approach in order to study how interactions are organized (Dáttilo et al, 2014;Blüthgen et al, 2015;Del-Claro et al, 2016). Several studies have been using this method for either community networks (Lange et al, 2013;Maruyama et al, 2014Maruyama et al, , 2015 or individual-based ones (Baker-Méio & Marquis, 2012;Gomez & Perfectti, 2012;Dáttilo et al, 2014). This analysis provides a great number of metrics and, for our aim, we selected six: complementary specialization (H2'), species specialization (d'), degree (k), specialization and 1 depicts a perfect specialization (Blüthgen et al, 2006;Dormann et al, 2009).…”

“…Several studies have focused in finding attributes of the ant-plant interaction that can predict the organization of such mutualistic associations (Chamberlain & Holland, 2009;Dáttilo, 2012;Gomez & Perfectti, 2012;Dáttilo et al, 2014, Dátillo et al, 2017. Commonly used metrics are species degree (k), specialization (d), centrality betweenness (CB) and centrality closeness (CC).…”