Changes in the composition of British butterfly assemblages over two decades

Changes in the abundance and distribution of individual species have been widely documented in Britain and other countries in recent decades, but little has been done to determine changes in community composition over broad geographic areas. Here, we studied species turnover in 51 butterfly assemblages in Britain since 1976, examining extinction and colonisation events together with variation in the abundances of the species. We showed that the species turnover that occurred over 20 years in Britain was associated with colonisation and extinction events and also with variability in the abundance of the species. These changes in community composition differed according to the habitat requirements of the species and their previous distributions, being more evident for habitat specialists and for southerly distributed species. Colonising species often became abundant components of the communities they joined, although this was more evident for generalist than for specialist species. The abundance of species following their arrival, increased with time since colonisation. Species turnover associated with southerly species expanding northwards is consistent with being a response to climate change. The results suggest that climate- and habitat-driven changes in the identity and abundance of species within communities are widespread, and probably ubiquitous. Similar changes are likely to be occurring in other groups of organisms that are similarly undertaking major range shifts associated with climate change.     

Sex and rank in competitive brood hierarchies influence stress levels in nestlings of a sexually dimorphic bird

Studies of sibling competition within brood hierarchies have rarely assessed simultaneously the effects of sex and rank in the brood hierarchy on traits other than offspring mortality and differential growth. We studied the expression of heat-shock proteins (Hsps) to assess the physiological stress response to different combinations of sex and position within competitive brood hierarchies in the black kite Milvus migrans (Bodd.), a sexually dimorphic raptor showing facultative siblicide. Senior males showed higher stress levels than did senior females and younger siblings of each sex as revealed by Hsp60 values. The analysis of Hsp70 levels indicated that nestlings from broods in which the senior chick was a male showed higher stress levels than did nestlings from broods in which the senior chick was a female. In addition, levels of Hsp60 were related negatively to nutritional condition expressed as levels of plasmatic albumin. This suggests that the sex of senior chicks may be key in determining their stress level and that of their siblings, which is probably associated with sibling competition by fighting within brood hierarchies. The comparatively higher stress levels of senior males (and their siblings) may be a consequence of their ability to exploit their potential advantage from being the head start while avoiding a possible competitive disadvantage from being the smaller sex, independent of environmental conditions determining the probability of brood reduction. Differential stress levels depending on sex and rank in the brood hierarchy may be a consequence of parental control of offspring behaviour through differential resource allocation (e.g. yolk androgens) or it may reflect adaptations of particular chicks (senior males) to enhance their competitive ability within brood hierarchies.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 383–390.     

Long-term effects of ungulates on phytophagous insects

Abstract.  1. Most plants interact with a diverse suite of herbivores, allowing the opportunity for the existence of positive and negative interactions between highly dissimilar organisms. However, most studies on herbivorous interactions have been performed under the assumption that they occur mainly between similar species. Consequently, ecologists are still far from a full understanding of the ecological factors that determine insect population dynamics.
2. In this study, a 7-year field experiment was conducted that manipulated the presence of ungulates to evaluate their effects on the abundance, attack rate, and survival of four guilds of co-occurring herbivorous insects living on the same host plant: seed predators, stem borers, gall makers and sap suckers. These four guilds differed in habits and behaviour, the first three being sessile and endophytic and the last being free-living.
3. This study shows that the abundance of all four guilds was negatively affected by ungulates. However, the effect on attack rate differed among guilds, as mammals do not affect the seed predator attack rate. Ungulates also differentially affected insect survival, ingesting only seed predators and gall makers.
4. In summary, this study suggests that diverse mechanisms may affect different insect guilds in different ways. Therefore, competition between disparate herbivores appears to be complex and can be provoked by multiple mechanisms.     

Antisense RNA decreases AP33 gene expression and cytoadherence by <Emphasis Type="Italic">T. vaginalis</Emphasis>

Background  

Host parasitism by Trichomonas vaginalis is complex. Adherence to vaginal epithelial cells (VECs) is mediated by surface proteins. We showed before that antisense down-regulation of expression of adhesin AP65 decreased amounts of protein, which lowered levels of T. vaginalis adherence to VECs. We now perform antisense down-regulation of expression of the ap33 gene to evaluate and confirm a role for AP33 in adherence by T. vaginalis. We also used an established transfection system for heterologous expression of AP33 in T. foetus as an additional confirmatory approach.     

Morphometric analysis and taxonomic revision of the Vriesea paraibica complex (Bromeliaceae)

The species related to Vriesea paraibica (Bromeliaceae, Tillandsioideae) have controversial taxonomic limits. For several decades, this group has been identified in herbarium collections as V. × morreniana, an artificial hybrid that does not grow in natural habitats. The aim of this study was to assess the morphological variation in the V. paraibica complex through morphometric analyses of natural populations. Two sets of analyses were performed: the first involved six natural populations (G1) and the second was carried out on taxa that emerged from the first analysis, but using material from herbarium collections (G2). Univariate ANOVA was used, as well as discriminant analysis of 16 morphometric variables in G1 and 18 in G2. The results of the analyses of the two groups were similar and led to the selection of diagnostic traits of four species. Lengths of the lower and median floral bracts were significant for the separation of red and yellow floral bracts. Vriesea paraibica and V. interrogatoria have red bracts; these two species are differentiated by the widths of the lower and median portions of the inflorescence and by scape length. These structures are larger in the former and smaller in the latter. Of the species with yellow floral bracts, V. eltoniana is distinguished by longer leaf blades and scapes and V. flava is characterized by its shorter sepal lengths. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 163–181.     

Hydrologic regulation of gross methyl chloride and methyl bromide uptake from Alaskan Arctic tundra

The Arctic tundra has been shown to be a potentially significant regional sink for methyl chloride (CH₃Cl) and methyl bromide (CH₃Br), although prior field studies were spatially and temporally limited, and did not include gross flux measurements. Here we compare net and gross CH₃Cl and CH₃Br fluxes in the northern coastal plain and continental interior. As expected, both regions were net sinks for CH₃Cl and CH₃Br. Gross uptake rates (−793 nmol CH₃Cl m⁻² day⁻¹ and −20.3 nmol CH₃Br m⁻² day⁻¹) were 20–240% greater than net fluxes, suggesting that the Arctic is an even greater sink than previously believed. Hydrology was the principal regulator of methyl halide flux, with an overall trend towards increasing methyl halide uptake with decreasing soil moisture. Water table depth was one of the best predictors of net and gross uptake, with uptake increasing proportionately with water table depth. In drier areas, gross uptake was very high, averaging −1201 nmol CH₃Cl m⁻² day⁻¹ and −34.9 nmol CH₃Br m⁻² day⁻¹; in flooded areas, gross uptake was significantly lower, averaging −61 nmol CH₃Cl m⁻² day⁻¹ and −2.3 nmol CH₃Br m⁻² day⁻¹. Net and gross uptake was greater in the continental interior than in the northern coastal plain, presumably due to drier inland conditions. Within certain microtopographic features (low‐ and high‐centered polygons), uptake rates were positively correlated with soil temperature, indicating that temperature played a secondary role in methyl halide uptake. Incubations suggested that the inverse relationship between water content and methyl halide uptake was the result of mass transfer limitation in saturated soils, rather than because of reduced microbial activity under anaerobic conditions. These findings have potential regional significance, as the Arctic is expected to become warmer and drier due to anthropogenic climate forcing, potentially enhancing the Arctic sink for CH₃Cl and CH₃Br.