Limiting similarity and environmental filtering under drought stress, a case study on diatoms

Abstract

Environmental filters are operated rather on the traits of species, than on species themselves, thus trait composition could explain more the ecosystem functioning than species richness. Based on diatom trait composition the applicability of the concept of “limiting similarity and environmental filtering” was studied in ephemeral streams. We studied whether the divergence and convergence of traits functioning these type of stream. The main question is that which mechanism has the strongest influence on the community structure under drought stress. We studied the effect size which is the value of the distance of trait composition of observed samples confronted to the null distribution. This effect size value can be used to compare the drought-affected and perennial streams. Samples were collected on small and medium-sized lowland rivers and streams in the Hungarian Lowland Region between 2007 and 2015 from the beginning of April to the end of October (vegetation period). Diatom data from two types of watercourses were used as “drought-affected” and “perennial” watercourses. Summers and autumns were extremely dry in the years of 2011, 2012, 2013 and 2014. Many rivers and streams dried out to the sampling period in autumn. These watercourses were called as “drought-affected” streams. Diatom data of those rivers from the year of 2010 which was extremely wet in Hungary were used as data from “perennial” watercourses as well as streams which were not dried in the 2007 and 2015 period. We found that some the divergence and convergence of traits functioning is different in “drought-affected” and “perennial” streams.