Recent Range Shifts

Despite several species experiencing migrational lag over the past four decades, species across various taxa have extended their ranges to higher latitudes and altitudes in many parts of the world, in line with the direction expected from climate warming, i.e. a polewards migration (Thomas et al., 2004). This illustrates how species are shifting their distributions to track their climatic niche (Bradshaw and Holzapfel, 2006), rather than adapting in situ.

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A European survey showed that out of 35 non-migratory butterfly species, 22 species have shifted northward by 35-240km over the 20^th century, with only 2 species having shifted south. Temporal scales across the 20th century used in this study varied within and among countries, e.g. for Britain this was since the 1950s, for Estonia this was since the 1980s, but for northern Africa (southern margins of some European butterflies) this was since the early 20^th century; for exact dates of change see Parmesan et al. (1999) . Two thirds of the species showing extensions at their northern boundary had southern boundaries that remained stable, thus effectively expanding their range (Parmesan et al., 1999).

Poleward range expansions have also been reported for birds in both Europe and the USA. The northern margins of 59 bird species with distributions in the south of Britain, have moved further north by an average of nearly 19km over a 20 year period; 1988-1991 compared with 1968-1972 (Hughes, 2000). Butterflies and birds are more mobile than the likes of plants, and such observations relating to climate change are easier to spot, but distribution changes have also been observed in certain plant ranges.

4.5.1 Changes in Composition – Alpine Communities

Changes in community composition have been observed, with cool adapted species on mountain ecosystems reacting to climate warming. A study by Pauli et al. (2007) discovered a change in vascular plant species richness on high peaks of the European Alps between 1994 and 2004, with an increase from 11.4 to 12.7 species per plot, a similar finding to that of Grabherr et al. (1994). The altitudinal preferences of plants were reflected in the species change figures; there were significant declines in subnival to nival plants, whereas alpine pioneer species increased at their leading edge. If this trend continues then alpine biodiversity is severely at threat with cold adapted species being driven out of their distribution range, and the consequent possibility of extinction. The climate warming at the Alps has recently been twice as high as the global average and thought to be the main reason for such changes (Pauli et al., 2007).

A study by Holzinger et al. (2008) also had similar findings to Pauli et al. (2007), with there being a common trend of ascending migration rates in the Alps of several metres per decade over the last 120 years of historical records. Another study spanning the entire elevation range (0 - 2600 metres above sea level) of 171 forest plant species in West Europe between 1905 and 1985, and 1986 and 2005, also confirmed a ‘significant upward shift in plant species optimum elevation averaging 29 meters per decade’ (Lenoir et al., 2008). Upward movement of subalpine species has also been

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extensively reported, with young trees found at elevations or altitudes further than the current treeline. This is particularly apparent in most of western North America, where there is an upward expansion of the forest margin after 1890, with establishment peaks between 1920 and 1950 (Peterson, 1994). An observation in Holzinger et al.’s study (2008) was that the increase in alpine migration occurred more on calcareous bedrock, with a presumption of there being more micro-habitats on such bedrock. Many studies looking at shifts in altitudinal gradients in plants have been carried out in Europe, but a study by Britton et al. (2009) on species richness in the Scottish mountains revealed that southern generalist species are also increasing and northern specialist species are decreasing, as would be expected as a consequence of climate change.

The first ever pan-European study into the response of mountain vegetation to climate change found that between 2001 and 2008, the abundance of thermophilic species increased significantly (Gottfried et al., 2012), a process the researchers have termed ‘thermophilization’. A total of 867 vegetation samples above the treeline, from 60 different summits in all major European mountain systems, including the Cairngorms in Scotland to as far south as the mountain ranges in Crete, were analysed for species occurrence and cover. As found in regional studies, cold-adapted species are declining, with no further mountain space to inhabit, whilst warm-loving plants are increasing; the continental scale of this study, however, just reinforces the impact climate change is having, transforming alpine plant composition even over such a short time period. This frames the future of alpine biodiversity as uncertain, with extinction more than likely for species at the end of their range.

4.5.2 Arctic Communities

The effects of climate warming have also been observed in the Antarctica, where the distributions of the only two native vascular plants, Colobanthus quitensis (Antarctic Pearlwort) and Deschampsia antarctica (Antarctic hair grass) have shown dramatic increases in numbers from 1964-1990, with greater rates of seed germination and seedling survival (Smith, 1994). Normally such activities are limited by the number of degree days above 0°C and by the water supply during the cold growing season, so this exemplifies a slight warming. At Galindez Island, D. Antarctica increased from 500 individuals in 1964 to 12,030 individuals in 1990, with similar increases observed at many other locations. This time period included warm summers in the mid 1950, early 1960s, early 1970s and mid-to-late 1980s, with winter temperatures also increasing greatly (Hughes, 2000).

4.5.3 Meta-analysis for Multiple Taxa

The distributions of all terrestrial species studied have shifted their latitudinal and altitudinal range by a median rate of 16.9km and 11.0m per decade respectively (Chen et al., 2011), with the more

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predominant range shifts being where warming has been the highest. These rates are significantly greater than a previous meta-analysis (Parmesan and Yohe, 2003), which reported a shift of range boundaries at ca 6.1km per decade towards higher latitudes, and 6.1m per decade to higher elevation. Although the scale of this study was considerably smaller than Chen et al.’s (2011) and the data includes species of varying mobility, together they demonstrate that species are responding to climate change.

4.5.4 Future Colonisations and Translocations

Some species will be spatially restricted in their ability to shift distribution. Species in the UK with a northern distribution may face extinction if at their northern margin they end up with nowhere to go, i.e. no suitable habitat, or if they occupy mountain tops. Species from continental Europe may colonise the UK if a suitable climatic niche becomes available, assuming they can reach the UK with no dispersal barriers. New colonisations in the UK already include species of bats, damselflies, and several species of birds (Pateman, 2012), with the respondents of the questionnaire (chapter 6) also identifying new species in their local region. These colonisations, however, may not be solely attributable to climate change (other drivers of change are discussed in section 4.9.2). Species extinctions as a result of climate warming have not been observed at the national scale in the UK.

Successful butterfly translocation studies (Pateman, 2012) have shown that they are able to survive beyond their current cool range boundaries. This demonstrates that they are experiencing a migrational lag, and that a suitable climatic niche exists for the future survival of such species.

4.5.5 Overview of Range Extension Studies

The studies reported indicate that the effects of climate change, including the changes to species traits, will be more prominent at higher latitudes and altitudes where the temperature change will be the largest. Yet, climate change is just one of the factors which has an influence over the distributions and health of populations and trait changes.