Edinburgh Napier University

  There is increasing interest in understanding the implications of biological invasions within the context of ecosystem functioning. Non‐native crustaceans are of particular interest within fresh waters because of their important contributions to leaf‐litter processing. The alien amphipod Dikerogammarus villosus is spreading rapidly through Europe where it has displaced native gammarids including Gammarus pulex. The resultant change in shredder communities has considerable implications for the dynamics of resource availability within invaded systems.

The invasive success of D. villosus has been attributed to many characteristics, including its ability to tolerate a wide range of environmental conditions and to exploit a wide feeding niche. These characteristics are thought to give D. villosus an advantage over native species, especially in habitats subject to changing environmental conditions.

The leaf (Salix alba) shredding efficiency, defined as the leaf mass consumed over the 4‐day experiment per amphipod‐day, was measured for D. villosus and G. pulex under extreme temperature and conductivity conditions, in single species and mixed species aquaria.

At high temperatures (25°C), D. villosus shredded significantly more leaves than size‐matched G. pulex. Conductivity extremes had no species effect; overall leaf‐shredding efficiency was significantly greater at low conductivity (250 μS cm‐1) than high conductivity (1870 μS cm‐1).

An inspection of daily leaf disc consumption found that the two species showed significantly different leaf consumption patterns, with D. villosus consuming more leaves earlier in the experiment.

These results suggest that D. villosus invasion could lead to ecosystem‐level changes in leaf processing, such as greater leaf processing earlier in autumn and at higher temperatures, which could alter nutrient dynamics and community assemblages within invaded systems. Such effects may not be reflected in biotic indices used to assess ecological status, as these indices do not currently distinguish between native and invasive species in the same family.