Rareness and specialization in plant-pollinator networks.

Most rare species appear to be specialists in plant-pollinator networks. This observation could result either from real ecological processes or from sampling artifacts. Several methods have been proposed to overcome these artifacts, but they have the limitation of being based on visitation data, causing interactions involving rare visitor species to remain undersampled. We propose the analysis of food composition in bee trap nests to assess the reliability of network specialization estimates. We compared data from a plant-pollinator network in the Monte Desert of Villavicencio Nature Reserve, Argentina, sampled by visit observation, and data from trap nests sampled at the same time and location. Our study shows that trap nest sampling was good for estimating rare species degree. The rare species in the networks appear to be more specialized than they really are, and the bias in the estimation of the species degree increases with the rareness. The low species degree of these rare species in the visitation networks results from insufficient sampling of the rare interactions, which could have important consequences for network structure.

[1]  N. Blüthgen,et al.  Measuring specialization in species interaction networks , 2006, BMC Ecology.

[2]  Luciano Cagnolo,et al.  Evaluating multiple determinants of the structure of plant-animal mutualistic networks. , 2009, Ecology.

[3]  B. Vaissière,et al.  Nesting Biology and Foraging Ecology of the Wood-boring Bee Lithurgus chrysurus (Hymenoptera: Megachilidae) , 2004 .

[4]  J. Bascompte,et al.  Invariant properties in coevolutionary networks of plant-animal interactions , 2002 .

[5]  R. B. Roberts.  Trap-nesting wasps and bees : life histories, nests and associates , 1967 .

[6]  Diego P. Vázquez,et al.  ASYMMETRIC SPECIALIZATION: A PERVASIVE FEATURE OF PLANT-POLLINATOR INTERACTIONS , 2004 .

[7]  H. Wiering.  The bees of the world , 2000 .

[8]  Carsten F. Dormann,et al.  Indices, Graphs and Null Models: Analyzing Bipartite Ecological Networks , 2009 .

[9]  Luciano Cagnolo,et al.  Uniting pattern and process in plant-animal mutualistic networks: a review. , 2009, Annals of botany.

[10]  Jordi Bascompte,et al.  Ecological networks, nestedness and sampling effort , 2007 .

[11]  J. Bosch,et al.  Plant-pollinator networks: adding the pollinator's perspective. , 2009, Ecology letters.

[12]  Jeff Ollerton,et al.  Plant-pollinator interactions: from specialization to generalization. , 2005 .

[13]  Diego P. Vázquez,et al.  NULL MODEL ANALYSES OF SPECIALIZATION IN PLANT–POLLINATOR INTERACTIONS , 2003 .

[14]  Carlos J. Melián,et al.  The nested assembly of plant–animal mutualistic networks , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[15]  Jochen Fründ,et al.  What do interaction network metrics tell us about specialization and biological traits? , 2008, Ecology.

[16]  Joseph Tzanopoulos,et al.  Long-term observation of a pollination network: fluctuation in species and interactions, relative invariance of network structure and implications for estimates of specialization. , 2008, Ecology letters.

[17]  N. Williams,et al.  Consistent mixing of near and distant resources in foraging bouts by the solitary mason bee Osmia lignaria , 2003 .

[18]  Paulo R. Guimarães,et al.  On nestedness analyses: rethinking matrix temperature and anti‐nestedness , 2007 .

[19]  Jordi Bascompte,et al.  Plant-Animal Mutualistic Networks: The Architecture of Biodiversity , 2007 .

[20]  R. Alarcón.  Congruence between visitation and pollen‐transport networks in a California plant–pollinator community , 2010 .

[21]  Werner Ulrich,et al.  A consistent metric for nestedness analysis in ecological systems: reconciling concept and measurement , 2008 .

[22]  J Memmott,et al.  The structure of a plant-pollinator food web. , 1999, Ecology letters.