Spatial patterns of genetic diversity, community composition and occurrence of native and non-native amphipods in naturally replicated tributary streams.

Florian Altermatt,Elvira Mächler,Roman Alther

doi:10.1186/s12898-016-0079-7

Abstract

BackgroundWorldwide, natural communities are invaded by non-native species, with potentially devastating effects on the native communities. A large part of past research aimed at finding traits and characteristics of the invading species or the invaded community explaining observed invasions. Only recently, the focus shifted on the spatial patterns during invasions per se. Empirical data, however, are limited, as invasions are often unique incidences of a complex spatio-temporal process. In order to identify generalities of invasion patterns, we studied 13 naturally replicated tributary streams draining into Lake Constance, and studied the occurrence of native and non-native amphipods along linear transects from the stream outlets to the upstream headwater reaches.ResultsWe found repeated spatial patterns of community composition and the occurrence of native and non-native amphipod species across two different years. Specifically, occurrence as well as abundance of two non-native amphipod species decreased from the stream outlets at the lake site towards upstream headwater reaches. Populations of the most common native amphipod species were largest at the uppermost headwater reaches. All populations of this native species, however, showed significant signals of recent genetic bottlenecks, irrespective of the stream position and occurrence of non-native species. Contrary to our expectations, this native species also showed no longitudinal genetic differentiation within individual tributaries as postulated for headwater versus outlet populations.ConclusionsOur results indicate that invasions of river-systems may overall follow predictable patterns on the level of spatial distributions and community composition. However, effects of invading organisms on the genetic diversity and genetic structure of native populations observed at larger scales may not necessarily be directly reflected at the scale of smaller tributaries.Electronic supplementary materialThe online version of this article (doi:10.1186/s12898-016-0079-7) contains supplementary material, which is available to authorized users.

Highlights

Worldwide, natural communities are invaded by non-native species, with potentially devastating effects on the native communities
In total, we found amphipods belonging to five different species. 4839 individuals belonged to Gammarus fossarum, 2148 individuals belonged to Gammarus roeseli, 391 individuals belonged to Dikerogammarus villosus, 56 individuals belonged to Gammarus pulex, and 20 individuals belonged to Gammarus lacustris
We found a highly significant interaction between the occurrence of native versus non-native amphipods and upstream distance (Chi2 value = 16.03, p value

Summary

Introduction

Natural communities are invaded by non-native species, with potentially devastating effects on the native communities. For example by Skellam [12], found invasions to be highly predictable by species-specific growth rates and diffusion coefficients, and the validity of this process has recently been experimentally confirmed [13] Invasions of invertebrates, such as amphipods, could be described in similar ways, for example in the well-documented invasion of the river Rhine [7], where the invading species completely shifted abundance and structure of native invertebrate species communities. The lack of naturally replicated invasions at smaller scales is reducing our ability to derive general principles regarding invasion patterns, and especially reduces our ability to better understand the variance of invasion processes This is especially unfortunate in the context of a continuing worldwide proliferation of invasions

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