Abstract
The fluvial systems in the north-east of the Iberian Peninsula are highly disturbed habitats, with widespread occurrence of alien species. Previous studies have shown that alien species have a major impact on native freshwater fauna, but it is not known what effect they have on semi-aquatic reptiles. Here the author investigated the factors that influence the occurrence of three species of semi-aquatic reptiles, one turtle (Mauremysleprosa) and two snakes (NatrixastreptophoraandNatrixmaura), at 261 sites in seven rivers/streams in Girona (north-eastern Spain). The studied semi-aquatic reptiles are habitat generalists which can occupy sections of rivers with altered regimes. The relationships of reptile presence to abiotic niche parameters and the presence of alien species were evaluated, as well as the patterns of pairwise co-occurrence between the reptiles. The presence of alien species did impact one out of three reptiles in this community. The association between both species of natricines was weakly negative, suggesting that interspecific competition does not structure their co-occurrences. The removal of alien species is the most appropriate strategy to preserve the complete diversity of native semi-aquatic reptiles.
Highlights
The Mediterranean region has a high diversity of reptiles, including many endemic species (Sindaco and Jeremčenko 2008)
During the surveys, four reptile species (E. orbicularis, M. leprosa, N. astreptophora and N. maura) were found, while the alien turtle species that occurs in the study region was not detected
Natrix astreptophora and N. maura showed a positive association with this axis, while E. orbicularis and M. leprosa showed a negative correlation (Fig. 2)
Summary
The Mediterranean region has a high diversity of reptiles, including many endemic species (Sindaco and Jeremčenko 2008). As a consequence of human activities, the populations of several semi-aquatic reptiles are in severe decline (Filippi and Luiselli 2000; Cox et al 2006) This is attributable to a decline in habitat quality and the increasing presence of alien species that are, in many cases, superior competitors in disturbed environments (Cadi and Joly 2003; Metzger et al 2009). The lower reaches of the major rivers of the region have been subject to substantial habitat degradation, associated with watershed regulation and the widespread occurrence of alien species (Saurí et al 2001; Ordeix et al 2014). The headwaters of the rivers are subject to greater seasonality, have been colonised by fewer alien species and constitute important shelters for native fauna (Boix et al 2010; Maceda-Veiga et al 2010)
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