Martin Warren

Rapid responses of British butterflies to opposing forces of climate and habitat change

Habitat degradation and climate change are thought to be altering the distributions and abundances of animals and plants throughout the world, but their combined impacts have not been assessed for any species assemblage. Here we evaluated changes in the distribution sizes and abundances of 46 species of butterflies that approach their northern climatic range margins in Britain—where changes in climate and habitat are opposing forces. These insects might be expected to have responded positively to climate warming over the past 30 years, yet three-quarters of them declined: negative responses to habitat loss have outweighed positive responses to climate warming. Half of the species that were mobile and habitat generalists increased their distribution sites over this period (consistent with a climate explanation), whereas the other generalists and 89% of the habitat specialists declined in distribution size (consistent with habitat limitation). Changes in population abundances closely matched changes in distributions. The dual forces of habitat modification and climate change are likely to cause specialists to decline, leaving biological communities with reduced numbers of species and dominated by mobile and widespread habitat generalists.

Distributions of occupied and vacant butterfly habitats in fragmented landscapes

SummaryWe found several rare UK butterflies to be restricted to relatively large and non-isolated habitat patches, while small patches and those that are isolated from population sources remain vacant. These patterns of occurrence are generated by the dynamic processes of local extinction and colonization. Habitat patches act as terrestrial archipelagos in which long-term population persistence, and hence effective long-term conservation, rely on networks of suitable habitats, sufficiently close to allow natural dispersal.

Flight areas of British butterflies: assessing species status and decline

Geographical range size is a key ecological variable, but the consequences of measuring range size in different ways are poorly understood. We use high–resolution population data from British butterflies to demonstrate that conventional distribution maps, widely used by conservation biologists, grossly overestimate the areas occupied by species and grossly underestimate decline. The approximate flight areas occupied by 20 out of 45 colonial British species were estimated to cover a median of only 1.44% of the land surface within occupied regions. Common species were found to be declining faster than conventional distribution maps suggest: common and rare species had no significant difference in their population-level rates of extinction. This, combined with the log–normal form of the range–size frequency distribution, implies that species–level extinction rates may accelerate in the medium to long term. Population–level conservation is a matter of great urgency for all species, not just for the rarest.

The development of butterfly indicators in the United Kingdom and assessments in 2010

The United Kingdom (UK) Government has national and international commitments to tackle the rate of biodiversity loss by 2010. Biodiversity indicators are used to measure and communicate progress in meeting these commitments. From 2005 onwards, butterflies have been adopted as Governmental biodiversity indicators in England, Scotland and for the UK as a whole. The indicators are compiled using butterfly abundance data collected through the UK Butterfly Monitoring Scheme, at a network of site established from 1976 onwards. The indicators show that butterfly numbers have fluctuated considerably from year-to-year, though analysis of the underlying smoothed multi-species trends for (habitat) ‘specialist’ species show significant long-term declines in each country since the 1970s. Trends in wider countryside ‘generalist’ species vary at the country-level from little or no overall change in Scotland and across the UK, to declines over selected years in England. Comparisons of changes in butterfly abundance before and after the 2010 target was set in 2002 suggest that the rate of decline at the UK-level is increasing for specialist species. In spite of large amounts of investment since 2000 to improve the habitat condition of protected areas, the trend for butterfly populations is no different in protected areas compared to elsewhere. Analysis by policy sector in England, shows that butterflies are declining rapidly in both forestry land and farmland, although in the latter habitat type, improvements are being seen on land entered into agri-environment schemes. We conclude by assessing the extent to which butterflies may represent broader biodiversity and help inform and evaluate conservation policy.

Assessing national conservation priorities : An improved Red List of British butterflies

Abstract An objective method of determining national conservation priorities is vital to use scarce resources effectively, but no method is yet widely accepted. The ‘Conservation Cube’ method of Avery et al. (1995: Ibis 137, 232–239), which includes three biological axes (National Status; International Importance; and European/global status), is tested for a highly threatened group of animals, British butterflies. The results are compared with Red Lists constructed using old and new IUCN criteria. A new feature of both procedures is the evaluation of threat due to rate of decline, and new thresholds are suggested to assess the decline of butterflies from published 10-km grid square distribution maps. The analysis shows that almost half (49%) of the 59 resident British butterflies are extinct or threatened: 8% are extinct; 12% are a high priority largely owing to their rapid rate of decline; whereas 29% are a medium priority owing to their moderate rates of decline. Most high priority species qualify as Vulnerable under the new IUCN criteria using UK guidelines, but many medium priority species fail to qualify. We suggest that all globally threatened species are classified at least as Vulnerable at national level and that two new Lower Risk categories are created: Internationally Significant and Moderate Decline. The two procedures would then form a comparable, rational procedure for identifying conservation priorities that is applicable to all animal groups for which distributional data are available.

Prime Butterfly Areas of Europe: An Initial Selection of Priority Sitesfor Conservation

The Red Data Book of European Butterflies, published in 1999, showed that butterflies have declined seriously across Europe and that 71 of the 576 species are threatened (12% of the total) either because of their extreme rarity or rapid decline. Many more species were shown to be declining in substantial parts of their range. A follow up project was conducted in 2002–3 to identify Prime Butterfly Areas (PBAs) in Europe where conservation should be targeted as a priority. Due to constraints of time and resources, this concentrated on identifying the most important (prime) areas for 34 target species, using a network of national compilers. The book gives details of 431 areas covering 1.8% of the land surface of Europe, and shows that target butterflies are declining in one quarter of PBAs, indicating that breeding habitats are continuing to deteriorate even though many are protected by national designation. Chief threats are from agricultural intensification, afforestation, abandonment of traditional practices, and isolation. We make nine recommendations: (1) Produce detailed descriptions of the PBAs within each country and protect all PBAs under national law; (2) Protect PBAs under relevant international EU law (e.g. EU Habitats and Species Directive); (3) Provide adequate protection of PBAs in non EU countries; (4) Ensure sound habitat management within PBAs and sympathetic management in surrounding areas; (5) Take measures to conserve the wider environment and whole landscapes within and surrounding PBAs in order to sustain viable metapopulations; (6) Monitor populations of target species and conduct research to identify appropriate habitat management techniques. (7) Revise pan-European legislation to take account of the new information provided in the Red Data Book of European butterflies (e.g. Bern Convention and the EU Habitats and Species Directive); (8) Conduct a more comprehensive review of Important Butterfly Areas in Europe as soon as possible; (9) Keep the list of Prime Butterfly Areas up-to-date (e.g. via the internet).

A new red list of British butterflies

1. Over the last century butterflies have undergone substantial changes in abundance and range in Great Britain and monitoring has improved markedly. These changes, together with a major revision of International Union for Conservation of Nature (IUCN) criteria, render previous Red List assessments outdated.

The status of the health fritillary butterfly Mellicta athalia Rott. in Britain

Abstract An extensive survey was made of known and potential sites of the heath fritillary butterfly Melllicta athalia Rott. in Great Britain in 1980. The size of every colony found was measured and information obtained on its habitat preferences and larval foodplants. Details of all the sites that still support this butterfly are summarised and its habitat requirements are assessed. The survey confirmed that the heath fritillary is probably the most endangered resident butterfly in Britain. It has declined severely in recent years and is now restricted to five sites in SW England and to three woodland blocks in E Kent. Thirty-one colonies were discovered (6 in the SW, 25 in Kent), but 24 of these contained fewer than 200 adults on the peak day. Moreover, several occurred close to larger populations and may only be offshoots that would not be viable on their own. The heath fritillary has different habitat requirements in SW England and Kent, although in both regions it needs sunny sheltered woodland that is at an early stage of succession or regeneration. Such habitat is ephemeral and must be generated continuously within fairly small areas if it is to be utilised, for the butterfly rarely flies long distances. Nearly all documented extinctions have been caused by a loss of suitable habitat from the locality, for this is only occasionally created by most modern forms of silviculture. In Kent, the heath fritillary survives mainly in the ever-decreasing areas where traditional coppicing has continued, but the future of this practice is now in doubt. Few colonies survive in SW England, although some are now being managed specifically to safeguard the butterfly.

Ten challenges for 2010 and beyond to conserve Lepidoptera in Europe

Butterflies and moths have undergone a serious decline in most European countries following rapid changes in land use in recent decades. The main drivers of loss have been agricultural and forestry intensification, abandonment of marginal land (especially in mountainous regions), loss of traditional management of grasslands and woodlands, and urban spread. Over the same period the science and practice of Lepidoptera conservation has developed considerably and concerted action to save biodiversity has been taken in many countries, with vast areas designated as nature reserves or national parks. Despite this effort, Lepidoptera are still declining at an alarming rate and it is clear that the 2010 target of halting biodiversity loss will not be met. We suggest ten challenges that conservationists in Europe need to address if we are to be successful in halting these losses over coming decades. In this continent, Lepidoptera and their habitats often rely on traditional farming and forestry systems. How can these be brought together in harmony to create a healthier environment in which both humans and wildlife can thrive? The ten challenges include reform of agricultural support, identifying and supporting beneficial forestry systems, managing the matrix between habitats, managing habitats on a landscape scale, mitigating for climate change, creating a robust planning system that protects key sites, developing a comprehensive monitoring programme for Europe, securing long term funding for nature conservation, and ensuring both political and public support.

The European Grassland Butterfly Indicator: 1990–2011

This report presents the European Grassland Butterfly Indicator, based on national Butterfly Monitoring Schemes (BMS) in 19 countries across Europe, most of them in the European Union. The indicator shows that since 1990 till 2011 butterfly populations have declined by almost 50 %, indicating a dramatic loss of grassland biodiversity. This also means the situation has not improved since the first version of the indicator published in 2005. Of the 17 species, 8 have declined in Europe, 2 have remained stable and 1 increased. For six species the trend is uncertain. The main driver behind the decline of grassland butterflies is the change in rural land use: agricultural intensification where the land is relatively flat and easy to cultivate, and abandonment in mountains and wet areas, mainly in eastern and southern Europe. Agricultural intensification leads to uniform, almost sterile grasslands for biodiversity. Grassland butterflies thus mainly survive in traditionally farmed low‑input systems (High Nature Value (HNV) Farmland) as well as nature reserves, and on marginal land such as road verges and amenity areas. (Less)