Many factors affect the extent to which a species fully occupy—or realize—their ecological niches. With highly dynamic and comparable distributions, invasive species can offer unique opportunities to study the dynamics of species distributions and realized niches.
Combining systematic historical and recent surveys of the presences of crayfish species in the Iberian Peninsula, this study assessed how two recent invaders from North America affected the niche and distribution of the Italian crayfish (Austropotamobius fulcisianus), introduced to Spain in the late 16th century.
The authors thoroughly collated occurrence data for the three species, relying on geographical diaries and books for historical records of A. fulcisianus and biodiversity databases including GBIF for the newcomers, the red swamp crayfish (Procambarus clarkii) and the signal crayfish (Pacifastacus leniusculus).
The historical mapping showed that the Italian crayfish’s distribution expanded until the late 1960s, then shrank drastically after the introduction of the two other species. The two North American species eventually occupied the entirety of the Italian crayfish’s niche with little to no co-occurrence, shifting the distribution of A. fulcisianus to limited areas in rough, high-elevation territories.
Using ecological niche modelling, the authors demonstrated how the changes in distribution were reflected in the realized niche, expanding from the 1850s until its collapse, unfilled significant portions of its fundamental niche after 1960. These results demonstrate the dynamics of a species’ realized niche and how it may shift in response to global change processes, such as biological invasions.