Weak and strong invaders: which biotic factors shape interactions among Ponto-Caspian invasive gammaridean species
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The aim of this thesis was to investigate interactions and possible biotic factors that could be agents modulating coexistence and dispersal of three most widespread Ponto-Caspian species Dikerogammarus villosus (Sovinsky, 1894), Dikerogammarus haemobaphes (Eichwald, 1841) and Pontogammarus robustoides (G.O. Sars, 1894). Each chapter presented in this thesis is focused on a different biotic factor that defines the boundaries of possible coexistence of the studied species. This thesis fills some gaps in knowledge about possible ecological mechanisms that stand behind the invasion of those animals. Thus, their temperature preferences were investigated to find whether this factor might determine coexistence of species by relocation leading to their spatial segregation among microhabitats. Ponto-Caspian amphipods are often highly infected with microsporidian parasites, which coevolved with them in their native region and undergo the invasion with their hosts to Europe, Thus, incorporation of microsporidia into study upon thermal preferences of Ponto-Caspian amphipods allowed to investigate both infection presence and temperature selection as agents capable of determining the possibility of coexistence of the studied amphipods. Therefore, physical and chemical contact with competitors, thermal preferences and possible modulators of these factors – microsporidian parasites were chosen as imsportant factors potentially affecting the intensity and direction of amphipod migrations. All ecological experiments were conducted with intention to define behaviour of each studied species while facing with those factors.