| Summary: | Anthropogenic warming has facilitated the redistribution of species globally. Many tropical species have shifted their ranges poleward either to escape thermally unsuitable conditions or to invade previously inaccessible temperate environments. Climate-driven species redistributions have facilitated range-shifting and local species to interact for available resources. These novel species interactions can modify the pace of species range extensions. In Australia, over 150 tropical fish species have been observed moving poleward into temperate marine ecosystems but often fail to establish due to hostile conditions (winter temperatures and environmental novelty). However, ocean warming could minimise lethal winter effects on range-extending tropical fishes, allowing them to establish at temperate latitudes in the near future. This thesis provides empirical and experimental evidence that current and future climatic conditions (ocean acidification and warming) and novel species interactions can modify the pace of tropicalisation in temperate marine ecosystems and highlights the capacity of local temperate fish communities to respond to tropical fish range extensions. By using a climate-manipulated laboratory experiment, I reveal that ocean acidification might slow tropicalisation through degradation of the shoaling performance of novel tropical-temperate fish shoals (Chapter 2). In addition, I show that future winter conditions negatively affect tropical fish behavioural repertoire and physiological function in temperate ecosystems (Chapters 3 and 4). In contrast, I demonstrate that the temperate fish behaviour remained unchanged but experienced increased growth and physiological performance under future winter conditions compared to current and future summer conditions (Chapters 3 and 4), which could seasonally modify tropical-temperate interactions. I further reveal that tropical fish entering novel temperate environments trade off foraging efficiency for predator vigilance, independent of novel shoaling ...
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