Tim G. Shreeve

Habitats and Resources: The Need for a Resource-based Definition to Conserve Butterflies

Current definitions of habitat are closely allied to the concept of patch and matrix. This concept is, for instance, central to the prevailing metapopulation models of population dynamics. But, butterfly population dynamics, mobility and spatial structure can only properly be understood in the context of a resource-based definition of habitats. In criticising current definitions of habitat, we illustrate how habitat is best understood in terms of resource distributions. These transcend vegetation-based definitions of habitat and lie at the root of life history strategies, the vulnerability of butterflies to environmental changes and extinction, and govern conservation status. We emphasise the need for a resource-use database and demonstrate the shortcomings of current data for conserving butterflies; patch based definitions of habitats are inappropriate for some species and for others do not provide a universal panacea, inadequately explaining spatial occurrence when scaled over space and time. A resource-based habitat definition challenges the bipolar, patch vs. matrix view of landscape; the alternative is to view landscape as a continuum of overlapping resource distributions. We urge greater attention to the details of butterfly behaviour and resource use as the keys to understanding how landscape is exploited and therefore to successful conservation at the landscape scale.

Host plants and butterfly biology. Do host‐plant strategies drive butterfly status?

Abstract.  1. To determine whether rarity and decline is linked to organism ecology, associations have been examined between butterfly larval host‐plant competitive, stress‐tolerant, ruderal (C‐S‐R) strategies and butterfly biology.

Corridors and barriers in biodiversity conservation: a novel resource-based habitat perspective for butterflies

Habitat loss and fragmentation, exacerbated by projected climate change, present the greatest threats to preservation of global biodiversity. As increasing habitat fragmentation and isolation of residual fragments exceeds the dispersal capacity of species, there is the growing need to address connectivity to maintain diversity. Traditionally, habitat corridors have been proposed as a solution. But, the concept of corridors (barriers) is poorly understood; typically they are defined as linear habitats linking up habitat patchwork, and are advocated without a detailed understanding of the elements making up species’ habitats and the cost-effectiveness of alternative solutions. Yet, landscapes comprise an enormous range of ‘linear’ structures that can function in different ways to promote species’ persistence and diversity. In this review, a functional definition of corridor (barrier) is developed to give prominence to connectivity as opposed to ad hoc structures purported to advance connectivity. In developing the concept, urgency to accommodate environmental changes compels a growing emphasis on organism diversity rather than a preoccupation with single species conservation. The review, in focusing on butterflies to address the issue of corridors for patchwork connectivity, draws attention to fundamental divisions among organisms in any taxon: generalists and specialists. Both groups benefit from large patches as these necessarily house species with specialist resources as well as generalists with very different resource types. But, generalists and specialists require very different solutions for connectivity, from short-range habitat corridors and gateways for specialists to habitat and resource stepping stones (nodes, surfaces) for generalists. Connectivity over extensive areas is most critical for moderate generalists and their conservation requires emphasis being placed on space–time resource heterogeneity; landscape features, of whatever dimensionality and structure, provide a vital framework for developing the variety of suitable conditions and resources for enhancing their diversity.

Landscape scale conservation: resources, behaviour, the matrix and opportunities

Landscape scale conservation efforts are becoming more commonplace in conservation, with a move from single species to multi-species initiatives. These initiatives are reliant on modelling processes, largely underpinned by metapopulation models. We argue that generic models developed for individual species in particular landscapes over selected time periods may only be applicable to alternative landscapes and time periods in restricted circumstances. Variability in species responses to landscapes and environmental conditions is dependent on a range of species-specific intrinsic characteristics, dependent on their responses to resources, (including weather) and also individual states. We propose that the behavioural component of how species respond to resources needs to be taken into account in modelling species responses to landscape, and therefore how limited resources for conservation are deployed. Species behaviours are inherently complex. We argue that because of this complexity the conservation of the majority of species, especially of the least rare, may be best served if conservation effort is additionally focused on increasing landscape heterogeneity and disturbance. This may also facilitate persistence in the face of climate change. We suggest that heterogeneity should be promoted through agri-environment schemes.

Sequence recombination and conservation of Varroa destructor virus-1 and deformed wing virus in field collected honey bees (Apis mellifera).

We sequenced small (s) RNAs from field collected honeybees (Apis mellifera) and bumblebees ( Bombus pascuorum ) using the Illumina technology. The sRNA reads were assembled and resulting contigs were used to search for virus homologues in GenBank. Matches with Varroa destructor virus-1 (VDV1) and Deformed wing virus (DWV) genomic sequences were obtained for A. mellifera but not B . pascuorum . Further analyses suggested that the prevalent virus population was composed of VDV-1 and a chimera of 5’-DWV-VDV1-DWV-3’. The recombination junctions in the chimera genomes were confirmed by using RT-PCR, cDNA cloning and Sanger sequencing. We then focused on conserved short fragments (CSF, size > 25 nt) in the virus genomes by using GenBank sequences and the deep sequencing data obtained in this study. The majority of CSF sites confirmed conservation at both between-species (GenBank sequences) and within-population (dataset of this study) levels. However, conserved nucleotide positions in the GenBank sequences might be variable at the within-population level. High mutation rates (Pi>10%) were observed at a number of sites using the deep sequencing data, suggesting that sequence conservation might not always be maintained at the population level. Virus-host interactions and strategies for developing RNAi treatments against VDV1/DWV infections are discussed.

Gains and losses of French butterflies: tests of predictions, under-recording and regional extinction from data in a new atlas

New data appearing in the second of two French atlases within one and a half years confirm that there was substantial under-recording of butterfly species in France for the production of the first atlas, particularly in the south and west of the country. Under-recording is still a prominent feature of the southwest region and eastern border. The new data also reveal contractions in the ranges of 60 species suggesting real losses as a result of regional extinction especially in the north of the country. This finding links adjacent areas of ongoing high regional extinction in continental European Lepidoptera extending from the Netherlands through Belgium into northern France. The new data also demonstrate that predictions of species numbers and species incidences based on records in the first atlas, using regression techniques on geographical and neighbourhood variables, have been largely successful (76% correct prediction of new records for departements). This supports the application of such techniques to targeting surveys for mapping spatial units and species to improve atlas databases; the recent rapid changes in distributions underlines the importance of having a suitable framework for continuing recording after atlas publication.

Marginality: scale determined processes and the conservation of the British butterfly fauna

Marginality describes the impact that environmental and landscape factors have in decreasing the probability of population survival and persistence. It may be imposed by extreme conditions or resource scarcity. Typically, it affects populations at the range edge but can also affect populations within the core of ranges, and produces a number of symptoms: characteristically demographic, but also morphological, physiological, biochemical and genetic. In this paper, the causes and effects of marginality on British butterflies are compared in edge and centre of range populations. Issues of temporal and spatial scales are examined, as is the relevance of marginality to the conservation of single and multiple species populations. The recognition of marginality questions the appropriateness of many so-called spatially realistic models of populations and highlights areas of research which have hitherto been ignored. Projected changes in land use and climate have implications for marginality in core and peripheral populations; in view of this, current scales of mapping are found to be unsuitable for monitoring fragmentation and the increasing marginalization of butterfly species in the British landscape.

How accurate are single site transect data for monitoring butterfly trends? Spatial and temporal issues identified in monitoring Lasiommata megera

Multiple transect counts following Butterfly Monitoring Scheme (UKBMS) guidelines and Jolly–Seber estimates of population size were used to monitor the abundance of second generation Lasiommata megera on a single site in southern England. The two methods resulted in different patterns of emergence being detected. The proportion of the population (estimated by Jolly–Seber) recorded with transect counts depended on the time of day and weather with afternoon transect counts best recording the trend in abundance over the flight period, but even then counts recorded a variable fraction of the population (6.2–51.3%). Increasing the frequency with which transect counts are carried out per week reduced variation and increased the fit of transect counts to Jolly–Seber generated population estimates. However, indices of abundance generated from randomly selected transect counts for L. megera within sampling weeks varied 4-fold and indices for other butterfly species were also highly variable. For L. megera, transect count variability is attributed to non-representative placement of the transect route and changes in the behaviour and spatial distribution in relation to population size and season. We suggest that transect counts need to be fully validated before the data are used to monitor changes of butterfly populations at individual sites.

Butterflies of European islands: the implications of the geography and ecology of rarity and endemicity for conservation

Depending on their faunal content islands can function as important ‘vehicles’ for conservation. In this study, we examine data on 440 butterfly species over 564 European islands in 10 island groups. To determine the status of the butterfly fauna, we have adopted two approaches, island-focused and species-focused, examined using principal components analysis and regression modelling. In the former, we relate species richness, rarity and endemicity to island geography (area, elevation, isolation and location in latitude and longitude); in the latter, species occurrence on islands is examined in relation to distribution, range, range boundaries, and altitudinal limits on the continent as well as species’ ecology (number of host plants) and morphology (wing expanse). Species on islands are also assessed for their status on the continental mainland, their distributional dynamics (extinctions, distribution changes) and conservation status (Red Data Book, European Habitat Directive, Species of European Conservation Concern and Bern Convention listing. Unexpectedly, we find that a large fraction of the European butterfly species is found on the islands (63.4%; 59% on small islands) comprising some 6.2% of the land area of Europe. Although species occurring on the islands tend, on the whole, to have lower conservation status and are not declining over Europe, 45 species are endemics restricted to the islands. Species richness shows only a weak locational pattern and is related as expected to isolation from the continental source and island area; but, both rarity and endemicity have distinctive geographical bias to southern Europe, on islands now under increasing pressure from climate change and increasingly intensive human exploitation. The vulnerability of species on islands is emphasised in the relationship of island occurrence (% occurrence and presence/absence of species on any island) with continental distributions. A large proportion of the variation (84%) is accounted by continental distribution, the southern range limit and lower altitudinal limit. Most species (69%) occur on very few islands (<5%). In view of ongoing species dynamics on islands, migrations and extinctions of species, island repositories of species depend in large part on conservation of butterflies at continental sources. The unique faunas and rare species on islands also depend on appropriate concern being given to the island faunas. Conservation of European islands is thus a two-way process, sustaining sources and conserving island refuges. Residuals from the regressions (islands with more or fewer species, rare and endemic species; species occurring more or less frequently than expected on islands) provide warning signals of regions and islands deserving immediate attention.

A comparison of geographical and neighbourhood models for improving atlas databases. The case of the French butterfly atlas

Abstract We use data from the French national butterfly atlas to compare the potential of direct geographical and neighbourhood models to account for numbers of species and incidence of species in French departements. Direct geographical models use data on latitude, longitude and altitude, whereas neighbourhood models use information from adjacent areas. Both geographical models and neighbourhood models account for a large proportion of the variance in species richness (68–78%). However, neighbourhood models are more successful than models based solely on simple geographical variables. A large number of individual species distributions are accounted for by logistic and autologistic regression models (222 of 246 species, 90.2%). The autologistic models incorporate information on neighbouring areas. The exceptions are rare species, five of six of which occur in a single administrative unit only (2.4%), or virtually ubiquitous species found in >90% of units (7.3%). Autologistic models dominate logistic models in accounting for species incidences using stepwise logit regressions, neighbourhood variables appearing in 64.5% of successful species models (absent in 22.8%) and then always entering first. A simple neighbourhood (distance-unweighted) measure (C2) dominates more models (89 of 246 species, 36.2%) than a distance-weighted neighbourhood measure (C1; 77 of 246 species, 31.3%). The models are here demonstrated to be potentially valuable for identifying under-recording and losses from regional extinction and for filling gaps in recording. The findings reveal substantial, apparent, losses of species in western and northern France as well as substantial discrepancies (differences) in numbers of species, for some administrative units (departements) and for both post-1970 and total records, compared with numbers predicted to occur. We use two distinct approaches on total species and individual species to provide comparative estimates of the numbers of species expected within spatial units and we present the number of additional units in which species are expected to occur. The probabilities for these species in French departements are available on Web site: http://www.brookes.ac.uk/schools/bms/research/data/ecology/butterfly.html .