Aim: Identifying niche shifts is key for forecasting future species distributions. Non-indigenous species (NIS) are one of the greatest threats to biodiversity, and understanding how niche shifts affect the spread of NIS is fundamental. Here, we modelled the native and introduced niches, as well as the potential geographical extent of a widely distributed NIS, the Pacific oyster Magallana gigas. We then tested for niche shifts in environmental space and predicted spread under contemporary climate change (CCC) conditions.
Methods: We used: (1) the two-dimensional Centroid shift, Overlap, Unfilling and Expansion (COUE) framework and (2) the n-dimensional hypervolume framework (NDH) to quantify the niches in both analogue and total environmental spaces. Niches were tested for equivalency by comparing the observed and randomized overlaps. Ensemble ecological niche models (ENMs) were then used to predict habitat suitability for the present-day and two future CCC scenarios.
Results: The NDH framework indicated that the introduced niche of M. gigas has shifted into new environmental conditions compared to the native niche. In contrast, COUE framework implied no niche shift, but the first two dimensions only accounted for a small proportion of the overall environmental variability. Ensemble ENMs revealed suitable areas where M. gigas has yet to be recorded and predicted both a poleward expansion and a tropical contraction of suitable habitat for M. gigas by 2100.
Main conclusions: We found that M. gigas has rapidly shifted its niche in both analogue and non-analogue environmental spaces since it was first recorded as introduced species over 50 years ago. Our results suggested that niche shifts facilitate both present-day and future spread of NIS. Additionally, our study demonstrated the importance of modelling niche dynamics in multidimensional space for predicting range shifts of NIS under CCC.