14 June 2021 Aperto

AperTO - Archivio Istituzionale Open Access dell'Università di Torino Can the extinction of Melitaea britomartis in NW Italy be explained by unfavourable weather? An analysis by Optimal Interpolation This is the author's manuscript Original Citation: Availability: This version is available http://hdl.handle.net/2318/1612768 since 2016-11-16T18:53:24Z Published version: DOI:10.1007/s10841-014-9625-9 Terms of use: Open Access Anyone can freely access the full text of works made available as "Open Access". Works made available under a Creative Commons license can be used according to the terms and conditions of said license. Use of all other works requires consent of the right holder (author or publisher) if not exempted from copyright protection by the applicable law. (Article begins on next page) 25 September 2021 The final publication is available at Springer via http://dx.doi.org/ 1 Running head: weather variability and butterfly extinction Can the extinction of Melitaea britomartis in NW Italy be explained by unfavourable weather? An analysis by Optimal Interpolation. Cristiana Cerrato1, Simona Bonelli1, Nicola Loglisci2 & Emilio Balletto1 1Zoology Unit, Department of Life Sciences and Systems Biology, University of Turin, Via Accademia Albertina 13, 10123 Turin, Italy. e-mail: [email protected]; [email protected]; [email protected] 2 Regional Agency for Environmental Protection, ARPA Piemonte, Turin, Italy e-mail: [email protected] Corresponding author: Simona Bonelli University of Turin Department of Life Sciences and Systems Biology Via Accademia Albertina 13 10123 – Turin ITALY Telephone number 0039 011 6704552 Fax number 0039 011 6704508 e-mail address: [email protected] 2 Abstract (150-250 words) We investigated possible correlations between climate-related factors and butterfly range restrictions by selecting a study case represented by 4 populations of Melitaea britomartis, which become ‘simultaneously’ extinct in NW Italy in 1976-1977 without any observable habitat change. To overcome difficulties related to the analysis of past extinctions and hypothesise causal factors, we applied the Optimal Interpolation method, a statistical method used to create a gridded climatological analysis of temperature and precipitation data, to a historical dataset containing all available information on the Italian butterfly fauna. We tested two different hypotheses: i) the role of climate change, expressed as a general trend in temperature and precipitation data; ii) the role of extreme weather events, expressed as anomalous conditions during the years of extinctions. Our results show that long-term temperature and precipitation data do not present any clear trend at our study site, suggesting that they cannot be involved in the species’ extinction. On the opposite, 1976 and 1977 were climatologically critical for the study area. In particular, 1977 was characterized by the coldest summer in the entire historical dataset (1958-1977), with strong negative temperature anomalies. Moreover, both years experienced unusually many rainy days during spring and summer. The year 1977 in particular, was the wettest within the entire historical dataset. The years of Melitaea britomartis populations’ extinction were characterised by many more cold and rainy days than usual during the species’ flight period. These results allow us to hypothesize a strong component of unfavourable weather in driving populations’ extinction. Key words: butterflies; weather variability; population decline; extinction Introduction Factors leading to populations’ extinctions are many since, even though habitat destruction is probably the most pervasive, a number of others may come into play, either separately or in multiple combinations. Among these factors, climate change is currently attracting the attention of many ecologists. Global warming is held responsible for changes observed in a number of butterfly species, in particular their uphill (Thomas et al. 2006, Wilson et al. 2007), or northwards range shifts (Parmesan et al. 1999, Pöyry et al. 2009), or some observed range contractions (Warren et al. 2001). Climate change has otherwise caused mismatches between the ecological requirements of herbivores and of their larval food-plants (Inouye 2000, Schweiger et al. 3 2008) and most projections based on bioclimatic envelope models have shown that, in the persistence of current scenarios, many butterfly populations are deemed to be at risk of future extinction, particularly in the South of Europe (Settele et al. 2008). Moreover, an increase in climate variability and consequently in the frequency of extreme weather events has been already recorded and a further amplification of such phenomena is strongly hypothesized (Easterling et al. 2000; Parmesan et al. 2000). Consequences on the biotic components, however, have been less explored (Parmesan et al. 2000). Attributing extinctions to a single factor is generally difficult and little evidence of a direct relationship between climate change and local species loss is available (Franco et al. 2006; Cahill et al. 2012). In this paper, we investigated possible correlations between climate-related factors and butterfly range restrictions by selecting a study case, represented by 4 populations of Melitaea britomartis which become ‘simultaneously’ extinct in NW Italy in 1976-1977, causing the species to altogether disappear from this general area without any observable habitat change. To overcome difficulties related to the analysis of past extinctions and to hypothesizing causal factors, we applied a statistical approach used to produce climatological gridded series to a historical dataset in which all the available information on the Italian butterfly fauna has been summarised (Balletto et al. 2007; Bonelli et al. 2011). We tested two different hypotheses: i) the role of climate change, expressed as a general trend in temperature and precipitation data; ii) the role of extreme weather events, expressed as anomalous conditions during the years of extinctions. Methods The Study Case Melitaea britomartis is an oligophagous butterfly (its main larval host plants are Plantago lanceolata and some species belonging to the genus Veronica). It is usually monovoltine, although some cases of partially bivoltine populations have been recorded in NW Italy. The flight period spans from May/June to late July/August. The species is restricted to an altitudinal range of ca. 300-900 m and is characterized by low dispersal ability (Balletto et al. 1985). 4 Melitaea britomartis is among the most seriously threatened butterflies of the Italian fauna (Balletto et al. 2005; Bonelli et al. 2011) and is declining all across Europe (van Swaay and Warren 1999; van Swaay et al. 2010). It is considered highly sensitive to human activities such as, in particular, overgrazing and/or changes in agricultural management (van Swaay and Warren 1999; Schmitt and Rakosy 2007). In Italy Melitaea britomartis is interestingly a hygrophilous species, restricted to the tall wet grasslands occurring in the northern fringes of the plains of the Po river valley, in the North of the country (Balletto et al. 2005), where it reaches its southern European boundary. Only 31 populations are known for having been historically present, scattered through a matrix of unsuitable, agricultural, or highly industrialized areas (Balletto et al. 2007). Of these populations, 24 are now extinct, in most cases without any apparent change in the immediate surrounding and any clear sign of habitat destruction (Bonelli et al. 2011). At present, only 7 populations are extant, all restricted to the North-eastern part of the peninsula (Balletto et al. 2007; Bonelli et al. 2011). Butterfly Data We obtained data on the former geographical distribution and population extinctions of Melitaea britomartis from a database that some of the authors had provided to the Italian Ministry for the Environment (Balletto et al. 2007; see also Bonelli et al. 2011) for the publication of the Atlas of the Italian Fauna (Ruffo and Stoch 2007). In this database, we deemed extinct any population that was published as such in the literature and whose status was never subsequently questioned. We also deemed extinct those butterfly ‘populations’ whose ‘locations’ were actively searched by several (5–10) professional or amateur lepidopterists on at least 3 (consecutive or not consecutive) years during the species’ flight season. Since their discovery, populations of Melitaea britomartis occurring in NW Italy attracted a lot of attention from lepidopterists and the historical record of their extinction is well documented (e.g. Verity 1917, 1950; Leigheb 1978). Although there are rumours that one or two (unconfirmed) individuals may have been observed in the early 1980s, 4 populations went simultaneously extinct in 1976-1977. These populations were located in NW Italy, in the Piemonte region (Montalto Dora-Bienca, Turin) at a mean altitude of 350-400 m. They all occurred within the same climatological grid. 5 Habitats occupied by these populations were not subject to any clear alteration or destruction (no reforestation, or overgrazing, or changes in the water-table) during and before the time of extinction, always retaining dimension adequate to sustain viable populations of Melitaea britomartis (ca. 1 ha or more). We did not take into account any measure of habitat isolation. The Methodological Approach Optimal Interpolation To investigate possible climate-related contributions

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