Krešimir Žganec

Differences in aggressive behaviour along the expanding range of an invasive crayfish: an important component of invasion dynamics

AbstractAggressive interactions are essential for resource distribution and population dynamics of many animal species. Aggression can also help invasive species to wrestle the resources from other species and invade new habitat. To examine the effects of intra-species aggression on range expansion, we compared aggression levels of signal crayfish (Pacifastacus leniusculus) at the core and front of the invasion range in recently invaded regions of Croatia. More pronounced aggression was observed in core populations with high population densities, indicating potentially greater importance of highly aggressive behaviour in populations with higher competitive pressure. Despite better overall physical condition, individuals at the invasion front generally displayed lower levels of aggression and regularly lost interactions to individuals from the invasion core. Rather than providing a competitive advantage during range expansion, aggression may be more expressed in established populations, priming the individuals for future expansions while also driving the dispersal outward. The observed difference in aggression along the invasion pathway demonstrates that traits that help individuals to overcome challenges of their environment, such as competition against conspecifics, can drive the invasion dynamics of a successful invader in a new environment in terms of both niche competition and intrinsic expansion dynamics.

Aquatic Macroinvertebrates of the Sava River

The objective of this chapter is to present the data on aquatic macroinvertebrate communities along the Sava River, based on investigation performed during 2011 and 2012 at 12 sampling sites within the sector between Vrhovo (Slovenia) and Belgrade (confluence to the Danube). During our study 227 macroinvertebrate taxa were recorded in the Sava River. Having in mind that upper stretch of the Sava River was not covered by this work (alpine and subalpine stretch), as well as based on the review of previous works on the macroinvertebrate fauna of the Sava River, more than 300 species will be confirmed for the Sava River. The data on the distribution of aquatic macroinvertebrates revealed five different stretches—alpine, subalpine, Upper Sava plain, Middle Sava and Lower Sava. Physical habitat degradation, pollution and pressure caused by biological invasions were found to be the main factors of endangerment of aquatic macroinvertebrate fauna diversity. There is an obvious need for further investigation of the Sava River in order to complete the data on aquatic macroinvertebrates and to provide the basis for accurate assessment of environmental status of the river.

Marshland vegetation of Plitvice Lakes National Park (Croatia)

Abstract Stančic, Z., K. Žganec & S. Gottstein (2010). Marshland vegetation of Plitvice Lakes National Park (Croatia). Candollea 65: 147–167. In English, with English and French abstracts. The Plitvice Lakes National Park is located in a mountainous region of Croatia, and is of world renown for its karstic lakes separated by tufa barriers, and its waterfalls. In many places around the lakes, and along the streams, marshland vegetation of the class Phragmito-Magnocaricetea Klika 1941 has developed. This vegetation has been studied in accordance with the Braun-Blanquet methodology. As a result, 13 communities were distinguished, three being found for the first time in Croatia: Caricetum rostratae Rübel 1912, Eleocharitetum uniglumis E. G. Almq. 1929 and Equisetetum fluviatilis Steffen 1931. Through numerical classification it was found that traditionally accepted communities match very well with the clusters obtained. Some ecological characteristics of the communities were estimated by calculating Ellenberg indicator values. Through analysis of plant life forms, specific features of marshland communities were also derived, especially at the level of vegetation alliances. The most common association of the study area is Phragmitetum australis Schmale 1939, which spreads in habitats of Ligularia sibirica (L.) Cass., a rare and threatened species throughout Europe. From the aspect of nature conservation, marshland vegetation in the Plitvice Lakes shows both positive and negative features. There is a positive effect in the enrichment of biodiversity, while most communities have developed as a consequence of the eutrophication of oligotrophic karstic lakes, which must be considered negative.

New records of the invasive amphipod Echinogammarus ischnus (Stebbing, 1899) in Croatia

The Ponto-Caspian alien and invasive amphipod, Echinogammarus ischnus (Stebbing, 1899), was found in Croatia at three sites in the lower course of the Drava River and at three sites in the Danube River (Batina, Borovo and Ilok). The most upstream site in the Drava where the species was found is a locality near Donji Miholjac, approximately 82 km upstream from the confluence with the Danube River. At this site as well as at two downstream sites (Osijek and Belisce) in Drava it was found together with the dominant invasive amphipods Dikerogammarus villosus and Chelicorophium curvispinum, while at the Donji Miholjac site it also co-occurs with two native species, Gammarus fossarum and G. roeseli.