Understanding
the factors that explain species distribution is one of the main focus of ecology.
Although many previous studies have already analysed the importance of
different variables for the distribution of freshwater fish species, we statistically
compare, for the first time, the importance of environmental and anthropogenic variables
in mediating the distribution of primary (i.e. strict freshwater), secondary (i.e.
salt-tolerant) and peripheral (i.e. diadromous and estuarine) native and alien fish
species, and study the relationship between these factors and fish traits. We provide
the first comprehensive distribution
modelling
exercise of the
most common freshwater fish (68 species: 51 native and 17 alien) across the Iberian Peninsula. We computed the variable importance for the
ensemble model to estimate the most influential factors and compare them among the
fish groups studied. Our results
show that geographical and environmental variables (e.g. basin, distance to the
sea or mean annual temperature) are more important than anthropogenic factors (e.g.
land use or hydrological alteration) in explaining freshwater fish
distribution. We found significant differences in predictive
accuracy and the importance of variables explaining the distribution of native
and alien species but especially among primary, secondary and peripheral fish. River
basin was the most important predictor for primary native and many alien species,
whereas distance to the sea was the most relevant predictor for secondary and
peripheral species. Mean temperature and upstream reservoir capacity had
positive effects on the distribution of alien species but were less important
for native fishes. The reduction of flow variability by damming and associated environmental
degradation in the Iberian Peninsula has mainly favored phytophilic, water-column,
warm-water alien fishes introduced from more hydrologically stable habitats such
as central European and southeastern North American regions. Overall, our
results show marked differences in the factors regulating the distribution of
native and alien species but that Darlington’s classification (i.e. primary,
secondary, and peripheral divisions) is even more important.
Funding
This research was financially supported by the Spanish Ministry of Science, Innovation and Universities (project CGL2016‐80820-R). Further funding support was provided by the 2015-2016 BiodivERsA COFUND call and the Spanish Ministry of Science (projects: ODYSSEUS, BiodivERsA3-2015-26, PCIN-2016-168; and RED2018‐102571‐T) and the Government of Catalonia (ref. 2017 SGR 548). CC benefitted from a pre-doctoral fellowship of the Spanish Ministry of Science (ref. BES-2017-081999).