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Global warming brings African butterflies to Catalonia

Many native species could become exctinct as the climate becomes warmer and drier.

A drop in their populalations will have a knock-on effect on other components of the ecosystem.

In Els Aiguamolls de l’Empordà Natural Park some species of butterfly have made their spring appearance up to 5 weeks early.

The sooty copper, Lycaena tityrus, present in many parts of the lowlands of Catalonia until the mid-twentieth century, is now restricted entirely to the Pyrenees.

Butterflies are amongst the organisms that provide most evidence of the effects of climate change on species distribution. Recently, clearly linked to global warming, African species have been sighted in Catalonia, the presence of which had never been previously recorded. Furthermore, in areas such as Els Aiguamolls de l’Empordà Natural Park, butterflies have begun to make their spring appearance up to 5 weeks early.

The Catalan Butterfly Monitoring Scheme, or CBMS, (www.catalanbms.org), financed by the Catalan Department of the Environment and Housing and the Granollers Museum of Natural Science, is a useful tool for the rapid detection of such changes in distribution and habits and also to learn how they become integrated into our native fauna.

Changes in distribution

One of the first reports showing a general change in distribution, in accordance with recent global warming predictions, is based on a series of 57 species of European butterflies. This article, published in Nature in 1999, analysed the changes in range of species present throughout Europe over the last century, both on its northern (nordic countries and United Kingdom) and southern limits (three Mediterranean areas: Catalonia, France and the Maghreb). Based on a comparison of historical data (from collections in natural history museums, such as the Zoological Museum of Barcelona) and recent data (atlas of distribution and monitoring programmes) evidence was provided that more than half the species (35) had shifted their range, and that such changes almost always consisted in a move northwards, coinciding with the shift in isotherms in the same period. An example of this is the case of the sooty copper, Lycaena tityrus, which up until the mid-twentieth century was present in many parts of the lowlands of Catalonia and very common in the Montseny area, but that is currently restricted entirely to the Pyrenees. The Montseny populations have disappeared completely over the last 20 years, with climate change being the most likely cause.

Apart from latitudinal movement, altitudinal movement has also been registered in mountain areas. In this case, the species move to higher altitudes in search of favourable climate conditions as the climate warms.

In Catalonia African species have been sighted, the presence of which had never been recorded before. An example is the famous monarch butterfly, Danaus plexippus, a highly migratory species that maintains stable populations in several parts of North Africa and the Canary Islands, and unstable populations on the coast of Malaga, Granada and Cadiz. In the summer of 2003, coinciding with the historic maximum June and July temperatures in many parts of Catalonia, it appeared in the Ebro Delta for the first time, doubtless as the result of a process of expansion of the populations in Africa or southern Spain. In the summer of 2004 specimens were again seen in the Ebro Delta, again as a result of migration.

Another similar example is the desert orange tip, Colotis evagore, which is native to the desert regions of northern Africa and periodically migrates to the south of the Iberian Peninsula. In the summer of 2004 this species appeared in southern Catalonia for the first time, this time in El Segrià, also as a result of long-distance migration. This meant an extension of the species’ range of over 300 kilometres compared to what was known previously. As in the case of D. plexippus, the following year its presence in the same place was recorded again.

The latest addition to Catalan butterflies is, once again, a species native to northern Africa and the southern Iberian Peninsula, the green-striped white, Euchloe belemia, which appeared in the spring of 2008 on the Torre Negra estate, in Sant Cugat del Vallès, just outside Barcelona. This meant a shift northwards of its range of some 300 kilometres.

So far these African species have been ubable to survive the winter conditions in Catalonia and, therefore, the sightings in successive seasons correspond to new migrations from Africa or southern Spain where there are permanent populations. However, if winters become milder due to climate change, we cannot rule out the possiblity of these colonising species establishing more lasting populations and ending up as part of the Catalan native fauna. This could have serious repercussions on agricultural ecosystems if the species benefitted are moths and other insects of subtropical origin, which could become serious pests to many crops and disperse occasionally to these latitudes, for instance with the entrance of winds from Africa.

Changes in phenology

The development of the immature stages of the butterfly (egg, catapillar and chrysalis) depend greatly on temperature, as with most insects. This means that an increase in temperature translates to an acceleration of the growth of catapillars and advanced emergence of adult butterflies. This prediction has been confirmed by the data gathered under the CBMS. Specifically, it has confirmed that between 1988, when the scheme began and the present day, a large proportion of the species in Els Aiguamolls de l’Empordà Natural Park have started to appear in spring up to 5 weeks earlier.

A phenological indicator is currently being created based on data on some twenty species widely distributed throughout Catalonia. The indicator aims to show quickly and succinctly the change in flight period of butterflies of diverse phenology (species that fly in spring, early and late summer), in different climate regions of Catalonia. The aims are to learn whether the phenological changes consist only of advance and whether this reponse depends on the phenology of the species and of the climate region where the populations studied are found.

Loss of biodiversity

Possibly the most worrying effect of climate change on butterflies is a foreseeable loss of biodiversity in the coming years. Using CBMS data statistical models have been established that relate the number of species in the whole country to environmental variables. All models indicate climate, and most especially aridity, as the most imporotant factor in explaining the number of species that can be found in a given location. Unlike in northern European countries, in Catalonia, and in the Mediterranean in general, the maximum diversity of species is always observed sempre in the relatively cold and humid zones, particularly in the Pyrenees, at altitudes between approximately 800 and 1,400 metres. As we move towards warmer and drier areas, the number of species drops rapidly, above all because the summer droughts strongly limit catapillar development as the quality of the plants they feed on also drops. These models predict a rapid loss of species as the climate in Catalonia becomes hotter and drier, which is exactly the scenario the climate models predict.

This is cause for concern for several reasons. Firstly, because the Mediterranean area in the richest in species in the whole of Europe, and because many of those that live there exclusively are very sedentary and are closely tied to very specific and fragmented habitats. This means that many of them will be unable to cross large areas of land in search of suitable habitats when climate warming forces them towards more northern latitudes. Therefore, the most realistic forecast is the extinction of many of these species as the climate in the areas they currently occupy becomes gradually hotter and drier.

Secondly, because butterflies are a bioindicator of the rest of the ecosystem. This is especially true in the case of terrestrial invertebrates, which constitute the most diverse part of the ecosystem. Several studies show that areas with a high diversity of butterflies also generally have a high diversity of other far less-known insect groups. Therefore, the loss of diversity of butterflies will be accompanied, foreseeably, by a loss of diversity of other species that are more difficult to detect, but no less important in the operation of ecosystems.

Thirdly, butterfly larvae play a crucial role as a food resource for predators (mainly other invertebrates and birds), and adult butterflies also contribute to the pollination of plants when feeding on nectar from flower. A drop in populations would therefore have a domino effect on other components of the ecosystem, which right now is difficult to foresee.

Changes in the composition of communities

Changes in distribution and the loss of biodiversity directly directly a change in the aforementioned processes and are integrated globally to give rise to changes in the composition of animal and plant communities. Despite the difficulty in characterising these large-scale changes, analysis is currently being carried out that will enable us to know the situation in outline compared to what is happening in buutterfly and bird communities on a European scale.

This analysis starts from the huge amount of information provided by bird and buterrfly monitoring programmes in Europa, and from the concepts of Species Temperature Index (STI) and Community Temperature Index (CTI). The STI is the long-term averafe temperatuer a species is exposed to across its range. It is fairly easy to calculate with techniques that use climate envevlope models. The CTI is the average temperature that characterises the whole of a community, and is calculated as the weighted average (by abundance) of all the species present in that community. The monitoring of butterflies (BMS programmes) and birds enable us to establish exactly how communities evolve in a given location over time, because it is based on standardised counts repeated in extensive annual series. The results appear to indicate that the changes are taking place more quickly in the case of butterflies than for birds, a fact that may give rise to a serious lack of synchrony between both groups.

Wednesday, 4 November 2009

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