Correspondence between bird and plant hotspots of the St Lawrence river and influence of scale on their location

Abstract

Various approaches can be adopted for selecting reserves to protect the species of a given territory. The strategies outlined in this study for protecting breeding birds and rare plants associated with the St Lawrence River are based on the concept of hotspots for species richness and rarity. These hotspots (100 km 2 squares) were defined separately for vascular plants and birds. Limited data on vascular plants allowed us to designate only rarity hotspots at the coarse-mesh level of the St Lawrence as a whole, while the more extensive data available on birds allowed for a definition of richness and rarity hotspots at three geographical levels of analysis. Bird hotspots, whether defined on the basis of species richness or the presence of rare species, were generally home to over 80% of bird species. Bird rarity hotspots are home to a significantly greater number of rare species than bird richness hotspots, although the latter support more rare species than ordinary squares. Moreover, rarity hotspots for birds did not correlate with rarity hotspots for plants, and the number of rare species of one group found in the hotspots for rare species of the other group is comparable to the number found in other squares. Our results show that to maintain the populations of a large proportion of bird species inhabiting the various ecosystems of the St Lawrence, protected areas should be selected on the basis of analyses carried out at the section or regional level, with the greatest conservation priority on sites with a large number of rare species at these levels of analysis. Indeed, the number of squares required to represent all riverine birds is proportional to the number of rare species. Bird rarity hotspots can serve as a guideline to pinpoint priority areas where more detailed investigation may permit the establishment of meaningful protected areas for riverine birds, particularly in the Gulf of St Lawrence.