Population genetic analysis of a recent range expansion: mechanisms regulating the poleward range limit in the volcano barnacle Tetraclita rubescens

As range shifts coincident with climate change have become increasingly well documented, efforts to describe the causes of range boundaries have increased. Three mechanisms—genetic impoverishment, migration load, or a physical barrier to dispersal—are well described theoretically, but the data needed to distinguish among them have rarely been collected. We describe the distribution, abundance, genetic variation, and environment of Tetraclita rubescens, an intertidal barnacle that expanded its northern range limit by several hundreds of kilometres from San Francisco, CA, USA, since the 1970s. We compare geographic variation in abundance with abiotic and biotic patterns, including sea surface temperatures and the distributions of 387 co‐occurring species, and describe genetic variation in cytochrome c oxidase subunit I, mitochondrial noncoding region, and nine microsatellite loci from 27 locations between Bahia Magdalena (California Baja Sur, Mexico) and Cape Mendocino (CA, USA). We find very high gene flow, high genetic diversity, and a gradient in physical environmental variation coincident with the range limit. We infer that the primary cause of the northern range boundary in T. rubescens is migration load arising from flow of maladapted alleles into peripheral locations and that environmental change, which could have reduced selection against genotypes immigrating into the newly colonized portion of the range, is the most likely cause of the observed range expansion. Because environmental change could similarly affect all taxa in a region whose distributional limits are established by migration load, these mechanisms may be common causes of range boundaries and largely synchronous multi‐species range expansions.     

Use of TLC‐FID and GC‐MS/FID to examine the effects of migratory state,diet and captivity on preen wax composition in White‐throated Sparrows Zonotrichia albicollis

Preen wax is important for plumage maintenance and other functions. Its chemical composition is complex, and separating and quantifying its components, commonly by gas chromatography (GC), can be challenging. We present a simple analytical system consisting of thin‐layer chromatography/flame ionization detection (TLC‐FID) using a solvent system of 100% toluene to analyse the complex compound classes present in preen wax. We used GC and TLC‐FID to investigate the effects of migratory status, diet and captivity on the preen wax composition of White‐throated Sparrows Zonotrichia albicollis, and to measure the quantity of preen wax on the head, primary and tail feathers. White‐throated Sparrows produced preen wax containing only monoesters regardless of migratory state. The monoesters contained several isomers consisting of homologous series of fatty alcohols (C10–C20) and fatty acids (C13–C19) esterified together in different combinations to form monoesters with total carbon numbers ranging from C23 to C38. Weighted average monoester carbon number was greater in captive birds than in wild birds and was greater in captives fed a formulated diet enriched with sesame oil than in birds fed the same diet enriched with fish oil. Captivity and migratory state also affected the complexity of the mixture of monoesters. There was significantly more preen wax on head feathers compared with primary and tail feathers. We suggest that among its many functions, preen wax may play a role in drag reduction by affecting the physical properties of feathers, and/or the fluid flow at their surfaces.     

Use and misuse of the IUCN Red List Criteria in projecting climate change impacts on biodiversity

Recent attempts at projecting climate change impacts on biodiversity have used the IUCN Red List Criteria to obtain estimates of extinction rates based on projected range shifts. In these studies, the Criteria are often misapplied, potentially introducing substantial bias and uncertainty. These misapplications include arbitrary changes to temporal and spatial scales; confusion of the spatial variables; and assume a linear relationship between abundance and range area. Using the IUCN Red List Criteria to identify which species are threatened by climate change presents special problems and uncertainties, especially for shorter‐lived species. Responses of most species to future climate change are not understood well enough to estimate extinction risks based solely on climate change scenarios and projections of shifts and/or reductions in range areas. One way to further such understanding would be to analyze the interactions among habitat shifts, landscape structure and demography for a number of species, using a combination of models. Evaluating the patterns in the results might allow the development of guidelines for assigning species to threat categories, based on a combination of life history parameters, characteristics of the landscapes in which they live, and projected range changes.     

Climate envelope, life history traits and the resilience of birds facing global change

Few studies have examined how life history traits and the climate envelope influence the ability of species to respond to climate change and habitat degradation. In this study, we test whether 18 species-specific variables, related to the climate envelope, ecological envelope and life history, could predict recent population trends (over 17 years) of 71 common breeding bird species in France. Habitat specialists were declining at a much higher rate than generalists, a sign that habitat quality is decreasing globally. The lower the thermal maximum (temperature at the hot edge of the climate envelope), the more negative are the population trends and the less tolerant these species are climate warming, regardless of the thermal range over which these species occur. The life history trait 'the number of broods per year' was positively related to recent trends, suggesting that single-brooded species might be more sensitive to advances in food peak due to climate change, as it increases the risk of mistiming their single-breeding event. Annual fecundity explained long-term declines, as it is a good proxy for most other demographic rates, with shorter-lived species being more sensitive to global change: individuals of species with higher fecundity might have too short a life to learn to adapt to directional changes in their environment. Finally, there was evidence that natal dispersal was a predictor of recent trends, with species with high natal dispersal experiencing smaller population declines than species with low natal dispersal. This is expected if the higher the natal dispersal, the larger the ability to shift spatially when facing changes in local habitat or climate, in order to track optimal conditions and adapt to global change. Identifying decline-promoting factors allow us to infer mechanisms responsible for observed declines in wild bird populations facing global change, and by doing so allow for a more pre-emptive approach to conservation planning.     

Functional Anatomy of the Association Between Motor Units and Muscle Receptors

Muscle spindles and tendon organs occur in most somatic musclesof the mammal and are particularly concentrated in muscles subservingfine movements, including postural muscles and small musclesof the distal extremities. In those mixed muscles in which thedifferent fiber and motor unit types are "compartmentalized,"the spindles, and perhaps tendon organs also, are virtuallylimited to those compartments predominated by "oxidative" musclefibers. These morphological observations based on a broad arrayof muscles in many species, complement electrophysiologicalstudies which have emphasized that (1) the "oxidative" motorunits have low reflex thresholds and (2) segmental proprioceptivereflexes may be primarily concerned with the control of finelygraded contractions. Consideration of the functional anatomyof the association between motor units and muscle receptorssuggests the need for detailed structural-functional analysesof those muscles with specializations in architecture, fiber-typecomposition and distribution, and in the number and distributionof their muscle spindles and tendon organs. An electrophysiologicalanalysis of the relationship between the spinal cord and suchmuscles might also reveal certain strategies and mechanismsunderlying segmental motor control which are either absent orobscured in the analysis of that select number of "homogenously-mixed"muscles conventionally used in the study of the mammalian segmentalmotor control system.     

Characterizing a tropical deforestation wave: a dynamic spatial analysis of a deforestation hotspot in the Colombian Amazon

Tropical deforestation is the major contemporary threat to global biodiversity, because a diminishing extent of tropical forests supports the majority of the Earth's biodiversity. Forest clearing is often spatially concentrated in regions where human land use pressures, either planned or unplanned, increase the likelihood of deforestation. However, it is not a random process, but often moves in waves originating from settled areas. We investigate the spatial dynamics of land cover change in a tropical deforestation hotspot in the Colombian Amazon. We apply a forest cover zoning approach which permitted: calculation of colonization speed; comparative spatial analysis of patterns of deforestation and regeneration; analysis of spatial patterns of mature and recently regenerated forests; and the identification of local‐level hotspots experiencing the fastest deforestation or regeneration. The colonization frontline moved at an average of 0.84 km yr^?1 from 1989 to 2002, resulting in the clearing of 3400 ha yr^?1 of forests beyond the 90% forest cover line. The dynamics of forest clearing varied across the colonization front according to the amount of forest in the landscape, but was spatially concentrated in well‐defined ‘local hotspots’ of deforestation and forest regeneration. Behind the deforestation front, the transformed landscape mosaic is composed of cropping and grazing lands interspersed with mature forest fragments and patches of recently regenerated forests. We discuss the implications of the patterns of forest loss and fragmentation for biodiversity conservation within a framework of dynamic conservation planning.