The subspecies concept in butterflies: has its application in taxonomy and conservation biology outlived its usefulness?

Subspecies lie at the interface between systematics and population genetics, and represent a unit of biological organization in zoology that is widely used in the disciplines of taxonomy and conservation biology. In this review, we explore the utility of subspecies in relation to their application in systematics and biodiversity conservation, and briefly summarize species concepts and criteria for their diagnosis, particularly from an invertebrate perspective. The subspecies concept was originally conceived as a formal means of documenting geographical variation within species based on morphological characters; however, the utility of subspecies is hampered by inconsistencies by which they are defined conceptually, a lack of objective criteria or properties that serve to delimit their boundaries, and their frequent failure to reflect distinct evolutionary units according to population genetic structure. Moreover, the concept has been applied to populations largely comprising different components of genetic diversity reflecting contrasting evolutionary processes. We recommend that, under the general lineage (unified) species concept, the definition of subspecies be restricted to extant animal groups that comprise evolving populations representing partially isolated lineages of a species that are allopatric, phenotypically distinct, and have at least one fixed diagnosable character state, and that these character differences are (or are assumed to be) correlated with evolutionary independence according to population genetic structure. Phenotypic character types include colour pattern, morphology, and behaviour or ecology. Under these criteria, allopatric subspecies are a type of evolutionarily significant unit within species in that they show both neutral divergence through the effects of genetic drift and adaptive divergence under natural selection, and provide an historical context for identifying biodiversity units for conservation. Conservation of the adaptedness and adaptability of gene pools, however, may require additional approaches. Recent studies of Australian butterflies exemplify these points. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Variation in abundance across a species' range predicts climate change responses in the range interior will exceed those at the edge: a case study with North American beaver

The absence of information about how abundance varies across species' ranges restricts most modeling and monitoring of climate change responses to the range edge. We examine spatial variation in abundance across the northeastern range of North American beaver ( Castor canadensis ), evaluate the extent to which climate and nonclimate variables explain this variation, and use a species–climate envelope model that includes spatial variation in abundance to predict beaver abundance responses to projected climate change. The density of beaver colonies across Québec follows a roughly logistic pattern, with high but variable density across the southern portion of the province, a sharp decline in density at about 49°N, and a long tail of low density extending as far as 58°N. Several climate and nonclimate variables were strong predictors of variation in beaver density, but 97% of the variation explained by nonclimate variables could be accounted for by climate variables. Because of the peak and tail density pattern, beaver climate sensitivity (change in density per unit change in climate) was greatest in the interior and lowest at the edge of the range. Combining our best density–climate models with projections from general circulation models (GCM) predicts a relatively modest expansion of the species' northern range limit by 2055, but density increases in the range interior that far exceed those at the range edge. Thus, some of the most dramatic responses to climate change may be occurring in the core of species' ranges, far away from the edge-of-the-range focus of most current modeling and monitoring efforts.     

The role of habitat composition in determining breeding site occupancy in a declining Ring Ouzel Turdus torquatus population

Ring Ouzel Turdus torquatus breeding site occupancy in the Moorfoot Hills, southeast Scotland, was determined during the periods 1952–85 and 1998–2000, and sites were classed as either occupied or deserted during the latter period. Site occupancy during 1998–2000 was related to habitat data derived from a supervised classification of a Landsat 7 satellite image. Breeding sites were more likely to have remained occupied if they were at higher altitudes and had more heather cover within radii of both 200 and 450 m, although these effects became non-significant when spatial autocorrelation was accounted for. Using only topographical variables, potential breeding sites were predicted and the habitat surrounding them was compared with actual breeding sites. Actual breeding sites were more likely to have heather or grass–heather mosaic within 100 m than potential breeding sites, but there were no further habitat differences between actual and potential breeding sites within radii of 200 or 450 m. These results indicate that breeding sites at higher altitudes and with a higher cover of heather were less likely to have been deserted, and that lack of heather may prevent otherwise suitable breeding sites from becoming occupied by Ring Ouzels. More detailed field studies are needed to understand the mechanisms underlying these associations.