Flow directionality, mountain barriers and functional traits determine diatom metacommunity structuring of high mountain streams.

Xiaoyu Dong,Bin Li,Haomiao Zhang,Qinghua Cai,Yuan Gu,Wen Xiao,Fengzhi He,Shuoran Liu,Meiqin Sun,Lu Tan

doi:10.1038/srep24711

Abstract

Stream metacommunities are structured by a combination of local (environmental filtering) and regional (dispersal) processes. The unique characters of high mountain streams could potentially determine metacommunity structuring, which is currently poorly understood. Aiming at understanding how these characters influenced metacommunity structuring, we explored the relative importance of local environmental conditions and various dispersal processes, including through geographical (overland), topographical (across mountain barriers) and network (along flow direction) pathways in shaping benthic diatom communities. From a trait perspective, diatoms were categorized into high-profile, low-profile and motile guild to examine the roles of functional traits. Our results indicated that both environmental filtering and dispersal processes influenced metacommunity structuring, with dispersal contributing more than environmental processes. Among the three pathways, stream corridors were primary pathway. Deconstructive analysis suggested different responses to environmental and spatial factors for each of three ecological guilds. However, regardless of traits, dispersal among streams was limited by mountain barriers, while dispersal along stream was promoted by rushing flow in high mountain stream. Our results highlighted that directional processes had prevailing effects on metacommunity structuring in high mountain streams. Flow directionality, mountain barriers and ecological guilds contributed to a better understanding of the roles that mountains played in structuring metacommunity.

Highlights

Metacommunity theory has provided an insightful view and a mechanism approach to study the dynamics of community patterns, species diversity and distribution at both local and regional scales[18], which addresses ‘a set of local communities that are linked by dispersal of multiple potentially interacting species’[19]
Another situation may arise if limiting dispersal (LD) occurs among patches, in that situation, the low-rate dispersal prevents species from being sorted to their optimal patches, and metacommunity presents a patch-dynamic paradigm[23,24,25]
There were three dominant species in our study: Achnanthidium rivulare Potapova & Ponader, Achnanthidium minutissimum (Kützing) Czarnecki, and Achnanthidium minutissimum f. inconspicuum (Østrup) Compère & Riaux-Gobin, with relative abundance of 29.7%, 21.4%, and 13.2%, all belonging to the low-profile guild

Summary

Introduction

Attempts to fully understand the mechanisms behind metacommunity structuring in high mountain streams must account for the intense environmental gradients and all kinds of dispersal limitation. To cover the unique characters of high mountain streams, geographical distance, topographic distance and network distance along flow direction were applied to model all pathways of dispersal (Fig. 2). Relative contributions of these three dispersal processes were assessed to understand how high mountains restricted dispersal processes. We proposed three hypotheses based on the unique characters of high mountain streams and species traits of benthic diatoms: H1: Owing to steep slopes and high discharge, dispersal among streams will be limited, downstream along streams will be promoted

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Methods

Results

Discussion

Conclusion