Geoscience Reference
In-Depth Information
Patterns of endemism are similar for the three insect orders. Up to 45% of
species occurring in the Iberic-Macaronesian region are endemic and high
fractions of endemic species are also found in Italy, the Balkan ecoregions and
the high mountain ecoregions, such as the Alps and the Carpathians. Species
restricted to springs (crenal zone) are common among the Trichoptera and
Plecoptera, but rare among Ephemeroptera. Most crenal specialists are found in
the Mediterranean and in the high mountain areas, while only very few of such
species occur in Northern Europe. Cold-stenothermic species of Trichoptera
and Plecoptera mainly occur in high mountain areas, while relatively few such
species are distributed in Scandinavia. This is different from Ephemeroptera,
which have generally a low number of cold stenothermic species, predominantly
occurring in Northern Europe.
In general, a south-north gradient in species richness of aquatic insects can
be observed. Similar patterns are found for endemic species and (to a lesser
degree) for crenal specialists and cold-stenothermic species. These patterns
are mainly a result of fluctuations in continental ice cover during the
Pleistocene, which, in turn, caused several range extensions and regressions
of species (Malicky 2000; Pauls et al . 2006). While glaciers covered most of
Northern Europe, species retreated to Southern Europe or to ice-free parts of
high mountain areas. This isolation of populations resulted in many new
species and increased diversity in these areas. Most aquatic insect species
occurring in Northern Europe live in Central or Southern Europe too. Mainly,
generalists and species with a high dispersal capacity recolonized Northern
Europe after the last ice age, while specialist species and those with limited
dispersal capacities extended their range only slightly. In consequence, most
of the species occurring in Northern Europe are likely to be capable of resisting
climate change impacts, since they are generalists or able to rapidly colonize
other areas.
Fish
Temperature and hydrological factors are major environmental determinants for
fish communities, thus alterations induced by climate change are expected to
modify fish assemblage structure (Poff & Allan 1995; Heino 2002). Changing
river discharge causes a reduction in community richness and life cycle changes
(Schindler 2001; Xenopoulos et al . 2005). Water temperature increase may be a
threat to cold stenothermic fish species because habitats for cold stenotherms
decline, isolating them in increasingly confined headwaters (Eaton & Scheller
1996; Hauer et al . 1997; Schindler 2001). As a result, fish assemblages are
expected to shift to fewer cold-water taxa and more warm-water taxa, as well as
fewer northern taxa and more southern taxa (Daufresne et al . 2004). As for
invertebrates, fish responses to water-temperature increase are highly
species-specific and depend on individual thresholds. For example, the size of
Atlantic salmon ( Salmo salar ) is negatively correlated with spring air and water
temperatures and with discharge and precipitation (Swansburg et al . 2002).
Increases in winter temperature and ice break-up may affect winter survival
significantly, particularly in northern populations. Because energetic deficiencies
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