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2 spring migratory birds

1 species earlier arrival

Chambers et al., 2005

F = flowering; LU =, leaf-unfolding; - advance; + delay. * indicates mean of significant trends only.

F = flowering; LU =, leaf-unfolding; - advance; + delay. * indicates mean of significant trends only.

turning points in the respective spring temperature series (Dose and Menzel, 2006).

Records of the return dates of migrant birds have shown changes in recent decades associated with changes in temperature in wintering or breeding grounds or on the migration route (Tryjanowski, 2002; Butler, 2003; Cotton, 2003; Huppop and Huppop, 2003). For example, a 2 to 3 day earlier arrival with a 1°C increase in March temperature is estimated for the swallow in the UK (Sparks and Loxton, 1999) and Ireland (Donnelly et al., 2004). Different measurement methods, such as first observed individual, beginning of sustained migratory period, or median of the migratory period, provide different information about the natural history of different species (Sokolov et al., 1998; Sparks and Braslavska, 2001; Huppop and Huppop, 2003; Tryjanowski et al., 2005).

Egg-laying dates have advanced in many bird species (Hussell, 2003; Dunn, 2004). The confidence in such studies is enhanced when the data cover periods/sites of both local cooling and warming. Flycatchers in Europe (Both et al., 2004) provide such an example, where the trend in egg-laying dates matches trends in local temperatures. Many small mammals have been found to come out of hibernation and to breed earlier in the spring now than they did a few decades ago (Inouye et al., 2000; Franken and Hik, 2004). Larger mammals, such as reindeer, are also showing phenological changes (Post and Forchhammer, 2002), as are butterflies, crickets, aphids and hoverflies (Forister and Shapiro, 2003; Stefanescu et al., 2003; Hickling et al., 2005; Newman, 2005). Increasing regional temperatures are also associated with earlier calling and mating and shorter time to maturity of amphibians (Gibbs and Breisch, 2001; Reading, 2003; Tryjanowski et al., 2003). Despite the bulk of evidence in support of earlier breeding activity as a response to temperature, counter-examples also exist (Blaustein et al., 2001).

Changes in spring and summer activities vary by species and by time of season. Early-season plant species exhibit the strongest reactions (Abu-Asab et al., 2001; Menzel et al., 2001; Fitter and Fitter, 2002; Sparks and Menzel, 2002; Menzel, 2003). Short-distance migrating birds often exhibit a trend towards earlier arrival, while the response of later-arriving long-distance migrants is more complex, with many species showing no change, or even delayed arrival (Butler, 2003; Strode, 2003). Annual plants respond more strongly than congeneric perennials, insect-pollinated more than wind-pollinated plants, and woody less than herbaceous plants (Fitter and Fitter, 2002). Small-scale spatial variability may be due to microclimate, land cover, genetic differentiation, and other non-climate drivers (Menzel et al., 2001; Menzel, 2002). Large-scale geographical variations in the observed changes are found in China with latitude (Chen et al., 2005a), in Switzerland with altitude (Defila and Clot, 2001) and in Europe with magnitude of temperature change (Menzel and Fabian, 1999; Sparks et al., 1999). Spring advance, being more pronounced in maritime western and central Europe than in the continental east (Ahas et al., 2002), is associated with higher spatial variability (Menzel et al., 2006a).

As the North Atlantic Oscillation (NAO) is correlated with temperature (see Trenberth et al., 2007), the NAO has widespread influence on many ecological processes. For example, the speed and pattern (Menzel et al., 2005b), as well as recent trends of spring events in European plants, has also changed consistently with changes seen in the NAO index (Chmielewski and Rotzer, 2001; Scheifinger et al., 2002; Walther et al., 2002; Menzel, 2003). Similarly, earlier arrival and breeding of migratory birds in Europe are often related to warmer local temperatures and higher NAO indices (Hubalek, 2003; Huppop and Huppop, 2003; Sanz, 2003). However, the directions of changes in birds corresponding to NAO can differ across Europe (Hubalek, 2003; Kanuscak et al., 2004). Likewise, the relevance of the NAO index on the phenology of plants differs across Europe, being more pronounced in the western (France, Ireland, UK) and north-western (south Scandinavia) parts of Europe and less distinct in the continental part of Europe (see Figure 1.4a; Menzel et al., 2005b). In conclusion, spring phenological changes in birds and plants and their triggering by spring temperature are often similar, as described in some cross-system studies; however, the NAO influence is weaker than the temperature trigger and is restricted to certain time periods (Walther et al., 2002) (Figure 1.4b).

135.2 Changes in species distributions and abundances

Many studies of species abundances and distributions corroborate predicted systematic shifts related to changes in climatic regimes, often via species-specific physiological thresholds of temperature and precipitation tolerance. Habitat loss and fragmentation may also influence these shifts. Empirical evidence shows that the natural reaction of species to climate change is hampered by habitat fragmentation and/or loss (Hill et al., 1999b; Warren et al., 2001; Opdam and Wascher,

2004). However, temperature is likely to be the main driver if different species in many different areas, or species throughout broad regions, shift in a co-ordinated and systematic manner. In particular, some butterflies appear to track decadal warming quickly (Parmesan et al., 1999), whereas the sensitivity of tree-line forests to climate warming varies with topography and the tree-line history (e.g., human impacts) (Holtmeier and Broll,

2005). Several different bird species no longer migrate out of Europe in the winter as the temperature continues to warm. Additionally, many species have recently expanded their ranges polewards as these higher-latitude habitats become less marginal (Thomas et al., 2001a). Various studies also found connections between local ecological observations across diverse taxa (birds, mammals, fish) and large-scale climate variations associated with the North Atlantic Oscillation (NAO), El Nino-Southern Oscillation (ENSO), and Pacific Decadal Oscillation (Blenckner and Hillebrand, 2002). For example, the NAO and/or ENSO has been associated with the synchronisation of population dynamics of caribou and musk oxen (Post and Forchhammer, 2002), reindeer calf survival (Weladji and Holand, 2003), fish abundance (Guisande et al., 2004), fish range shifts (Dulcic et al., 2004) and avian demographic dynamics (Sydeman et al., 2001; Jones et al., 2002; Almaraz and Amat, 2004).

Changes in the distribution of species have occurred across a wide range of taxonomic groups and geographical locations

Figure1.4. (a) Differences between the mean onset of spring (days) in Europe for the 10 years with the highest (1990, 1882, 1928, 1903, 1993, 1910, 1880, 1997, 1989, 1992) and the lowest (1969, 1936, 1900, 1996, 1960, 1932, 1886, 1924, 1941, 1895) NAO winter and spring index (November to March) drawn from the period 1879 to 1998. After Menzel et al. (2005b). (b) Anomalies of different phenological phases in Germany (mean spring passage of birds at Helgoland, North Sea; mean egg-laying of pied flycatcher in Northern Germany; national mean onset of leaf unfolding of common horse-chestnut (Aesculus hippocastanum) and silver birch (Betula pendula) (negative = earlier)), anomalies of mean spring air temperature T (HadCRUT3v) and North Atlantic Oscillation index (NAO) (http://www.cru.uea.ac.uk/cru/data/). Updated after Walther etal. (2002).

Figure1.4. (a) Differences between the mean onset of spring (days) in Europe for the 10 years with the highest (1990, 1882, 1928, 1903, 1993, 1910, 1880, 1997, 1989, 1992) and the lowest (1969, 1936, 1900, 1996, 1960, 1932, 1886, 1924, 1941, 1895) NAO winter and spring index (November to March) drawn from the period 1879 to 1998. After Menzel et al. (2005b). (b) Anomalies of different phenological phases in Germany (mean spring passage of birds at Helgoland, North Sea; mean egg-laying of pied flycatcher in Northern Germany; national mean onset of leaf unfolding of common horse-chestnut (Aesculus hippocastanum) and silver birch (Betula pendula) (negative = earlier)), anomalies of mean spring air temperature T (HadCRUT3v) and North Atlantic Oscillation index (NAO) (http://www.cru.uea.ac.uk/cru/data/). Updated after Walther etal. (2002).

during the 20th century (Table 1.9). Over the past decades, a poleward extension of various species has been observed, which is probably attributable to increases in temperature (Parmesan and Yohe, 2003). One cause of these expansions is increased survivorship (Crozier, 2004). Many Arctic and tundra communities are affected and have been replaced by trees and dwarf shrubs (Kullman, 2002; ACIA, 2005). In north-western Europe, e.g., in the Netherlands (Tamis et al., 2001) and central Norway (EEA, 2004), thermophilic (warmth-requiring) plant species have become significantly more frequent compared with 30 years ago. In contrast, there has been a small decline in the presence of traditionally cold-tolerant species. These changes in composition are the result of the migration of thermophilic species into these new areas, but are also due to an increased abundance of these species in their current locations.

Altitudinal shifts of plant species have been well documented (Grabherr et al., 2001; Dobbertin et al., 2005; Walther et al., 2005a) (Table 1.9). In several Northern Hemisphere mountain systems, tree lines have markedly shifted to higher elevations during the 20th century, such as in the Urals (Moiseev and Shiyatov, 2003), in Bulgaria (Meshinev et al., 2000), in the Scandes Mountains of Scandinavia (Kullman, 2002) and in Alaska (Sturm et al., 2001). In some places, the position of the tree line has not extended upwards in elevation in the last halfcentury (Cullen et al., 2001; Masek, 2001; Klasner and Fagre, 2002), which may be due to time-lag effects owing to poor seed production/dispersal, to the presence of 'surrogate habitats' with special microclimates, or to topographical factors (Holtmeier and Broll, 2005). In mountainous regions, climate is a main driver of species composition, but in some areas, grazing,

Table 1.9. Evidence of significant recent range shifts polewards and to higher elevations.

Location

Species/Indicator

Observed range shift due to increased temperature (if nothing else stated)

References

California coast, USA

Spittlebug

Northward range shift

Karban and Strauss, 2004

Sweden Czech Republic

Tick (Ixodes ricinus)

Northward expansion 1982-1996 Expansion to higher altitudes (+300 m)

Lindgren et al., 2000 Daniel et al., 2003

Washington State, USA

Skipper butterfly

Range expansion with increased Tmin

Crozier, 2004

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