Euchloe bazae, Fabiano, 1993

Euchloe bazae , an endemic species of the Iberian Peninsula, faces significant threats that justify its

legAl clAssificAtion As “EndAngered” in the SpAnish CAtAlogue of EndAngered Species. Comprehensive conservation efforts are required to protect E. bazae as this species exhibits a disjunct distribution characterised by very limited habitat availability and alarmingly low observed population sizes. Additionally, increasing aridity driven by global climate change may further challenge the persistence of certain populations.

Fragmentation is a consistent characteristic of E. bazae populations, which are distributed across four isolated areas. The linear distance between the two northern and two southern populations is about 435 km ( Fig. 1). Specifically, the populations in Zaragoza and Huesca, Aragón, are separated by approximately 28 km, with various barriers hindering connectivity, especially the absence of the host plant, V. aspera , in the intervening region. The Ebro River, which traverses this region, widens significantly due to the Mequinenza reservoir, further complicating connections between these populations ( Fig. 1). Additionally, extensive reforestation with Pinus halepensis has been identified as another significant obstacle to species dispersal.

Between the populations of Hoya de Baza and Orce there is a gap of approximately 15 km where E. bazae has been consistently absent despite numerous search efforts. The discovery of a fourth population in Orce is extremely positive for conservation efforts. However, fragmentation persists, even within this new population, leading to a lack of connectivity. Isolated subpopulations are likely the result of recent agricultural intensification, which has most likely eliminated large areas of the host plant, and thereby minimised or obstructed connectivity between these subpopulations. While larger communities of V. pseudocytisus have been observed, some numbering in the thousands, the butterfly remains absent from these areas. Geological differences could partially explain this absence, but the extensive use of synthetic chemicals (herbicides, fungicides, pesticides, etc.) in the surrounding cultivated areas likely affect E. bazae and other insect species. Indeed, the low diversity of insect species in these regions sharply contrasts with areas where E. bazae thrives. Furthermore, the species observed in these low-diversity locations tend to be migratory, such as Vanessa cardui (Linnaeus, 1758) ( Lepidoptera : Nymphalidae ), or exhibit high mobility, like Iphiclides feisthamelii (Duponchel, 1832) ( Lepidoptera : Papilionidae ).

Another threat facing the newly discovered population is the habitat reduction of V. pseudocytisus due to the planting of P. halepensis , a concern also highlighted by previous studies ( Benito et al., 2004). This endemic plant, which requires basic soils, competes for space with the pines, which lower the soil pH, leading to the demise of the plant. Numerous dead or dying V. pseudocytisus specimens have been observed at the base of pines ( Fig. 43). In addition to modifying soil conditions, pine plantations reduce the solar radiation received by smaller plants, which also creates competition. This situation is notably impactful in Hoya de Baza and is especially concerning in the municipalities of Benamaurel and Orce, where it seems to correlate with the absence of the butterfly in areas dominated by pines, thereby decreasing habitat quality and extent. Similarly, in Aragón, pine plantations have been observed to act as barriers, hindering the dispersal of the species.

Extensive livestock farming is negatively impacting the new population found in Orce, where excessive browsing by sheep herds has been noted on V. pseudocytisus subsp. orcensis ( Fig. 44). Protective measures for this plant are necessary to preserve the habitat of the butterfly ( Hernández-Bermejo et al., 1999). However, in Aragón, this threat is currently not considered significant, particularly since livestock farming has almost disappeared in a region that once had substantial livestock activity.

The legal protection of V. pseudocytisus is also essential. This species is protected in Madrid, Castilla-La Mancha, and Andalusia. In the latter, which encompasses the newly discovered population of E. bazae , V. pseudocytisus is included in the Andalusian Catalog of Threatened Species under the category "Endangered," identified As “ Vella pseudocytisus L. subsp. pseudocytisus ”. However, this population is currently classified as subsp. orcensis ( Simón-Porcar et al., 2015) , highlighting the need for legislative updates to improve accuracy. This protection is regulated by Law 8/2003, of 28 October, on the Flora and Fauna of the Autonomous Community of Andalusia. Benito et al. (2004) recommended including V. pseudocytisus in the Spanish Catalog of Threatened Species, alongside effective protection measures such as the avoidance of harmful practices, monitoring, and public awareness campaigns. The threats facing both the butterfly and its host plant are interconnected. Previous botanical studies have identified similar threats, and Cabezudo et al. (2005) highlighted forestry, grazing, and agriculture as key risks. Given that these factors are common and well-identified for both taxa, urgent measures are necessary to work synergistically towards the conservation of this plant-butterfly association.

A significant and common risk to both population of E. bazae in the province of Granada is the lack of territorial protection, as the habitat occurs outside Andalusia’ s network of natural spaces and the Natura 2000 network. Much of this habitat is privately owned, which threatens the survival of the species due to potential habitat alterations. In contrast, much of the area occupied by E. bazae in Aragón is included in the Natura 2000 network. Therefore, prioritizing habitat protection in Granada is essential, alongside safeguarding it against threats from wind and solar energy production and transportation infrastructures, activities that are particularly relevant today in Spain. These activities currently represent the most significAnt threAts to the species’ populAtions in the province of Granada. The absence of territorial protection and the fact that the butterfly inhabits privately owned land may facilitate energy companies in establishing such infrastructures in critical habitats. Notably, there is a project for a 400 kilovolt power line that crosses the Baza-Antas area (Fig. 45), whose design and associated mitigation measures are currently under discussion to minimise the impact on the species.

The projected infrastructure has prompted a study assessing the potential impact of the constructions on E. bazae ( Monasterio León & Iglesias Baquero, 2022) , as well as the formulation of numerous objections and the organization of meetings with stakeholders. Support from the ZERYNTHIA Association alongside endorsements from numerous national and international specialists and over 6000 signatures backing the presented arguments, has been instrumental to these efforts. All of this allows us to affirm that, for the first time in Spain, the conservation of a butterfly species may influence decisions regarding the construction of large infrastructures. This achievement is linked to the species’ inclusion in the SpAnish List of ThreAtened Species in 2019 As "EndAngered". As A result, new routing proposals will avoid areas with the highest occupancy of the species, minimizing potential impact. This represents a significant milestone in the conservation of lepidopterans in Spain.

Models developed by Escuer et al. (2022) suggest that the climatically suitable area for E. bazae was less fragmented in the past. These models also suggest a recent decline in habitat quality in the areas currently occupied by the butterfly. While the models also predict a resurgence of climatically appropriate habitats, the limited dispersal capacity of both the butterfly and its host plants of the genus Vella makes it unlikely that their populations can rapidly migrate to mitigate this impact. These factors suggest a future decrease in populations as well as a declining trend.

The distinct geographical, latitudinal and altitudinal locations of each population, along with their ecological differences, contribute to their complementary roles in the conservation of the species. For this reason, they must be considered as separate management units. In the context of current climate chAnge, the populAtions in ArAgón, specificAlly the “iberAe- HuescA” And “iberAe- ZArAgozA” units, which are associated with V. aspera , may play a critical role for the species. Their northern latitude may provide greater resilience compared to the populations in Andalusia, especiAlly for the “iberAe- HuescA” unit which is in the northernmost point. The “bAzAe- HoyA de BAzA ” unit, locAted in HoyA de BAzA And relying on E. vesicaria , would become increasingly important in a future scenario where the two Vella species continue to decline, as it represents the only population relying on a common and abundant host plAnt without conservAtion concerns. MeAnwhile, the “bAzAe- Orce” unit, situAted At the north- easternmost point of its distribution in Andalusia and at the highest altitude within its total distribution range, stands out for its limited range and dependence on V. pseudocytisus . This unit harbours considerable genetic diversity and could be crucial for the survival of the species if the Hoya de Baza population were to experience a significant decline. This population could serve as an important genetic reservoir, helping to mitigate inbreeding issues and increasing the likelihood of the species adapting to environmental changes.

Available observations indicate noteworthy interannual fluctuations in the population abundances of E. bazae , both in Aragón and Granada. These variations appear linked to interannual changes in rainfall and temperature during spring, which is the adult flight period. The steppe-like habitat occupied by E. bazae requires such an adaptation to ensure hatching during favourable springs with sufficient food resources. This interannual abundance variation currently makes the identification of clear trends difficult. However, despite observed peaks in abundance, such as 30 individuals per kilometre in Huesca in 2018 and 7.9 individuals per kilometre in Hoya de Baza in 2022, observations generally reveal low numbers. The accumulated dataset is insufficient to draw firm conclusions about population trends, underscoring the need for continued long-term monitoring, conducted by the ZERYNTHIA Association since 2021.

Consistent counts with low abundance results suggest that this species is extremely sensitive, indicating that its conservation status is not ideal. This highlights the urgent need for measures to conserve its habitat, making every effort to preserve or improve current conditions and avoiding any interventions that could reduce the area or quality of the habitat occupied by the butterfly.

The obtained values for area of occupancy (AOO) at 141 km 2 and extent of occurrence (EOO) at 795 km 2 clearly fall within the thresholds for being considered an endangered species (EN) by the IUCN (2012). Several additional factors warrant consideration: a) the species is severely fragmented and is not known to exist in more than four locations. Given its presumed extinction in Catalonia, the aforementioned impacts on habitats, and the assumption that the Orce population does not represent a recent expansion, it can be reasoned b) that there is a continuous decline, whether observed, inferred, or projected, in (i) extent of occurrence, (ii) area of occupancy, (iii) area, extent, and/or quality of habitat, and (iv) number of locations or subpopulations. Furthermore, c) extreme fluctuations have been noted in (iv) number of mature individuals. Consequently, it is concluded that E. bazae should be classified as "Endangered" [EN B1ab(i,ii,iii,iv)c(iv); B2ab(i,ii,iii,iv)c(iv)]. Therefore, the assessment of its conservation status as "Endangered", obtained by Escuer et al. (2022), is further supported by the evaluation conducted in this study, based on more extensive and recent data. It is imperative for the IUCN Red List to revise its current assessment, which still considers E. bazae as "Least concern" ( van Swaay et al., 2015).