Behavioural modification of range-extending coral reef fishes in temperate ecosystems

1. Coral-reef fishes are shifting their distributions poleward in response
to human-mediated ocean warming, yet the consequences for recipient
temperate fish communities remain poorly understood. Behavioural
modification is often the first response of species to environmental
change, but we know little about how this might shape the ongoing
colonisation by tropical fishes of temperate-latitude ecosystems under
climate change. 2. In a global hotspot of ocean
warming (southeast Australia), we quantified 14 behavioural
traits of invading tropical and local co-occurring temperate fishes at 10
sites across a 730 km latitudinal gradient as a proxy of species
behavioural niche space in different climate ranges (subtropical,
warm-temperate, cold-temperate). 3. We found that tropical fishes (4
species) modified their behavioural niches as well as increased their
overall behavioural niche breadth in their novel temperate ranges
where temperate species predominate, but maintained a moderate to high
niche segregation with native temperate species
across latitudinal range position. Temperate species (3
co-occurring species) also modified their niches, but in contrast to
tropical species, experienced an increased niche breadth towards
subtropical ranges. Alterations to feeding and
shoaling behaviours contributed most to niche modifications in
tropical and temperate species, while behaviours related to alertness and
escape from potential threats contributed least. 4. We here show that at
warmer and colder range edges where community structures are being
reshuffled due to climate change, behavioural generalism and niche
modification are potential mechanisms adopted by tropical range
extenders and native-temperate fishes to adjust to novel species
interactions under climate change.