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


RESULTS
We 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.


CONCLUSIONS
Our 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.
Department of Aquatic Ecology, Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, 8600, Dübendorf, Switzerland. florian.altermatt@eawag.ch.|Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstr. 190, 8057, Zurich, Switzerland. florian.altermatt@eawag.ch.
Florian
F
Altermatt
Department of Aquatic Ecology, Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, 8600, Dübendorf, Switzerland.|Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstr. 190, 8057, Zurich, Switzerland.
Roman
R
Alther
Department of Aquatic Ecology, Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, 8600, Dübendorf, Switzerland.|Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstr. 190, 8057, Zurich, Switzerland.
Elvira
E
Mächler
D033304:Amphipoda / Q000235:genetics*; D000818:Animals; D044822:Biodiversity; D017753:Ecosystem; D058865:Introduced Species; D045483:Rivers
Dikerogammarus; Dispersal; Gammarus; Invasion process; Invasive species; Lake Constance; Meta-community; Microsatellites; Stream network