COS 66-2 - Why are some plant-pollinator networks more nested than others?

Tuesday, August 8, 2017: 1:50 PM
D131, Oregon Convention Center
Chuliang Song, Civil and Environmental Engineering, Massachusetts Institute of Technology, CAMBRIDGE, MA, Rudolf P. Rohr, Biology, University of Fribourg, Fribourg, Switzerland and Serguei Saavedra, Civil and Environmental Engineering, MIT, Cambridge, MA

Empirical studies have found that typically the structure of plant-pollinator networks is more nested than expected by chance, while theoretical studies have shown a positive association between nested structures and community persistence. Moreover, it has been shown that some plant-pollinator networks are more nested than others, raising the interesting question of which factors are responsible for such enhanced nested structure. While several studies have linked these factors with various bioclimatic variables, unfortunately, there has been no unified answer. We demonstrate that the reasons for such lack of agreement arises from an extended practice of the current methodology (z-scores) employed to answer these questions, and we provide a rigorous methodology to correct these measures and compare across networks.


We invent a comparison metric of nestedness by investigating the maximum and minimum values of nestedness that a network can reach, and validate its consistence across dimension, connectance and distribution of values. Equipped with this new corrected metrics, we find that higher levels of nestedness are associated with seasonal environments. This empirical result supports theory establishing that nestedness increases the range of demographic conditions under which species can coexist, which should be more advantageous in highly changing environments. While this work may seem methodological in nature, it covers a fundamental area of research in ecology that statistical measures should be carefully tested to avoid inconsistency.