The structure, sampling and dynamics of plant pollinator network from the argentinean deset

CHACOFF, NATACHA

Araras

Simposio; I Simposio brasileiro de Polinizacao; 2014

The structure, sampling and dynamics of plant- pollinator network from the Argentinean desert Natacha Chacoff Instituto de Ecologia Regional, Fac. de Ciencias Naturales e IML, Universidad Nacional de Tucumán, Argentina Over the last decade, the use of networks for describing community wide plant-pollinator systems has captured the attention of ecologists and resulted in an upsurge of studies. This network approach has been stimulated by recent theoretical and methodological advances, which have allowed identifying several apparently general structural properties of networks. For instance, the number of links per species is highly skewed (few species with many links and many species few links), interactions tend to be highly asymmetric and organized in a nested fashion and exhibit some degree of modularity (the existence of groups of species with high internal connectance and few connections to other species in the network). We investigated the determinants of the observed structure, we assessed the accuracy of our sampling and the dynamics of the interactions over a 5 years plant-pollinator network from the Monte desert of Argentina. The structural properties of mutualistic networks is likely to result from the simultaneous influence of neutrality and the constraints imposed by complementarity in species phenotypes, phenologies, spatial distributions, phylogenetic relationships, and sampling artifacts. We developed a conceptual and methodological framework to evaluate the relative contributions of these potential determinants and found that information on relative abundance and phenology suffices to predict several aggregate network properties (connectance, nestedness, interaction evenness, and interaction asymmetry). However, such information falls short of predicting the detailed network structure (the frequency of pairwise interactions), leaving a large amount of variation unexplained. Sampling artifacts such as sampling design can be responsible of the observed network structure and also might affect some network properties. Describing networks involves estimating the richness (qualitative or unweighted networks), relative abundance (quantitative or weighted networks) and composition of interactions for each species in the network. For this reason, network studies are subject to the same sampling issues of any study of diversity, with the additional problem that the estimated diversity of interactions is a function of the diversities of both groups of interacting species. By using rarefaction methods we evaluated the completeness of detection of the community-wide pollinator fauna, of the pollinator fauna associated with each plant species and of the plant?pollinator interactions. We found that in spite of our high sampling effort, and although we sampled 80% of the pollinator fauna, we recorded only 55% of the interactions. Furthermore some species need more sampling to detect their interactions, indicating that a sample based on equal number of census per species might be inappropriate for sampling networks. Our analysis allowed estimating the completeness of our sampling, the additional effort needed to detect most interactions and the plant traits that influence the detection of their interactions. Very little is known about how temporally dynamic these networks are in their interactions and structure. Most studies are qualitative and don?t consider any temporal variation explicitly, and look at one single season. We quantified the interannual variability of plants, pollinators, plant-pollinator interactions, and network properties, and found metrics and traits of species and interactions that relates to the stability of the interactions. Across the five years of sampling 64% of the interactions were observed in a single year, 17% in two years, 10% in three years, 6% in four years, and only 3% in all five years. Furthermore we detected that the frequency of interactions and the distance to the core of the networks were positively related to the stability of the interactions. These studies helped us to understand the functioning of plant-pollinators networks and to have solid information for management and conservation purpose of this system.