Conquerors or exiles? Impact of interference competition among invasive Ponto-Caspian gammarideans on their dispersal rates

Abstract

Ponto-Caspian gammarids have invaded European waters, affecting local communities by predation and competition. Their ranges and dispersal rates vary across Europe, which may result from their interspecific interactions, accelerating or reducing migrations. We checked this hypothesis by testing interference competition among co-occurring invaders: Dikerogammarus villosus, D. haemobaphes and Pontogammarus robustoides. We used 140-cm long tanks (gravel substratum), divided into seven compartments. We introduced 25 ''residents'' into the outermost compartment, separated with a barrier. After 1 h, we introduced 25 ''intruders''. After the next 1 h, we removed the barrier and the gammarids dispersed in the tank. After 4 or 20 h, we counted the gammarids in the compartments. We tested all pairwise species combinations and single-species controls. Dikerogammarus villosus displaced other species (P. robustoides only after 4 h) and reduced its own motility after 20 h in their presence. Pontogammarus robustoides stimulated the short-time migrations of D. villosus intruders and of D. haemobaphes. As P. robustoides migrated spontaneously much more than Dikerogammarus spp., its impact decreased after longer time. Dikerogammarus haemobaphes stimulated the short-time movement of P. robustoides intruders but reduced the longtime relocation of this species. In general, gammarid dispersal increased in the presence of stronger competitors (D. villosus and P. robustoides, especially residents) and decreased in response to weaker competitors (D. haemobaphes). Thus, competitive interactions may affect dispersal of invasive gammarids and contribute to the fastest spread of the weakest competitor, D. haemobaphes observed in the field, whereas the strongest species, D. villosus was the latest newcomer in many novel areas.

Substrate preferences of coexisting invasive amphipods, Dikerogammarus villosus and Dikerogammarus haemobaphes, under field and laboratory conditions

“…A slightly larger proportion of D. villosus individuals were recorded on the coarsest substrate (cobbles) which may indicate some limited form of intraguild competition. Evidence from experimental studies suggests that D. villosus is the strongest competitor of all Ponto-Caspian amphipod invaders and, as a result, intraguild predation (IGP), is likely to be responsible for the displacement or eradication of ecologically homogenous amphipods (Kobak et al , 2016. In the River Odra in Poland, D. villosus was observed to displace and dominate D. haemobaphes (Gruszka and Woźniczka 2008).…”

“…A second invasive amphipod, Dikerogammarus villosus (killer shrimp), was first recorded in the UK 2010 (MacNeil et al 2010) and to date is geographically confined to five known locations (GBNNSS 2017). It is likely that the geographical distribution of this species will expand in the future across the globe (Kobak et al 2016) and it is anticipated that it is only a matter of time before D. villosus invades North America (Bollache et al 2008).…”

An enemy of your enemy is your friend: Impact of predators on aggregation behavior of gammarids

“…Thus, when suitable shelters are available, it does not need to change its behavior in the presence of danger. On the other hand, P. robustoides is much more mobile and spends more time outside shelters (Kobak et al., ). This was also observed in our study, as they more often grouped outside the shelters than D. villosus .…”

Abiotic factors affecting habitat selection by two invasive gammarids Dikerogammarus villosus and Pontogammarus robustoides

“…Alien gammarids are ''sit and wait'' animals, which usually stay in the shelters, but sometimes they do migrate, e.g. to find better food areas or mating partners as well as to avoid predators or competitors (Kobak et al, 2016). In such situations, they have to expose themselves to the local flow conditions.…”