Geographical range size of tropical plants influences their response to anthropogenic activities

Biodiversity patterns may be influenced by the species geographical range sizes, but this is rarely shown. We used a highly replicated and large-scale study in coastal Ecuador to determine for the first time the importance of latitudinal range size of plant species in their response to land-use activities. We examined herbaceous plant communities of five land-use types with decreasing anthropogenic disturbance (from the most intervened rice and pasture to the less intervened managed agroforest, abandoned agroforest, and forest) in a low and a high impact human-dominated landscape. All species were classified in four latitudinal range size quartiles, from the 25% species with the narrowest to the 25% with the widest range size. We found notable differences between patterns of total species richness and those of individual range size quartiles. Whereas total species richness was higher in more intervened land-use types, percentages of narrow-ranged species were significantly higher in less intervened land-use types. In contrast, percentages of wide-ranging species were higher in more intervened land-use types. Hence, responses of plant species to human activities were influenced by traits that determine their range sizes. An analysis of floristic similarity between land-use types revealed that narrow-ranged species were mainly preserved in forest fragments, but the other land-use types supported many unique narrow-ranged species and therefore made an important contribution to their preservation at the landscape level. Conservation efforts should combine protection of natural habitats with strategies to maintain a diversity of low-intensity land-use types, looking for win-win solutions or trade-offs between biodiversity conservation and human welfare in human-dominated landscapes.     

Surface Trafficking of APP and BACE in Live Cells

Amyloid‐β (Aβ)‐peptide, the major constituent of the plaques that develop during Alzheimer's disease, is generated via the cleavage of Aβ precursor protein (APP) by β‐site APP‐cleaving enzyme (BACE). Using live‐cell imaging of APP and BACE labeled with pH‐sensitive proteins, we could detect the release events of APP and BACE and their distinct kinetics. We provide kinetic evidence for the cleavage of APP by α‐secretase on the cellular surface after exocytosis. Furthermore, simultaneous dual‐color evanescent field illumination revealed that the two proteins are trafficked to the surface in separate compartments. Perturbing the membrane lipid composition resulted in a reduced frequency of exocytosis and affected BACE more strongly than APP. We propose that surface fusion frequency is a key factor regulating the aggregation of APP and BACE in the same membrane compartment and that this process can be modulated via pharmacological intervention.      

Identification and Characterization of Rvs162/Rvs167-3, a Novel N-BAR Heterodimer in the Human Fungal Pathogen Candida albicans

Membrane reshaping resides at the core of many important cellular processes, and among its mediators are the BAR (Bin, Amphiphysin, Rvs) domain-containing proteins. We have explored the diversity and function of the Rvs BAR proteins in Candida albicans and identified a novel family member, Rvs167-3 (orf19.1861). We show that Rvs167-3 specifically interacts with Rvs162 to form a stable BAR heterodimer able to bind liposomes in vitro. A second, distinct heterodimer is formed by the canonical BAR proteins Rvs161 and Rvs167. Purified Rvs161/Rvs167 complex also binds liposomes, indicating that C. albicans expresses two functional BAR heterodimers. We used live-cell imaging to localize green fluorescent protein (GFP)-tagged Rvs167-3 and Rvs167 and show that both proteins concentrate in small cortical spots. However, while Rvs167 strictly colocalizes with the endocytic marker protein Abp1, we do not observe any colocalization of Rvs167-3 with sites of endocytosis marked by Abp1. Furthermore, the rvs167-3Δ/Δ mutant is not defective in endocytosis and strains lacking Rvs167-3 or its partner Rvs162 do not display increased sensitivity to high salt concentrations or decreased cell wall integrity, phenotypes which have been observed for rvs167Δ/Δ and rvs161Δ/Δ strains and which are linked to endocytosis defects. Taken together, our results indicate different roles for the two BAR heterodimers in C. albicans: the canonical Rvs161/Rvs167 heterodimer functions in endocytosis, whereas the novel Rvs162/Rvs167-3 heterodimer seems not to be involved in this process. Nevertheless, despite their different roles, our phenotypic analysis revealed a genetic interaction between the two BAR heterodimers, suggesting that they may have related but distinct membrane-associated functions.     

Prion Protein Does Not Confer Resistance to Hippocampus-Derived Zpl Cells against the Toxic Effects of Cu2+, Mn2+, Zn2+ and Co2+ Not Supporting a General Protective Role for PrP in Transition Metal Induced Toxicity

The interactions of transition metals with the prion protein (PrP) are well-documented and characterized, however, there is no consensus on their role in either the physiology of PrP or PrP-related neurodegenerative disorders. PrP has been reported to protect cells from the toxic stimuli of metals. By employing a cell viability assay, we examined the effects of various concentrations of Cu²⁺, Zn²⁺, Mn²⁺, and Co²⁺ on Zpl (Prnp ^-/-) and ZW (Prnp ^+/+) hippocampus-derived mouse neuronal cells. Prnp ^-/- Zpl cells were more sensitive to all four metals than PrP-expressing Zw cells. However, when we introduced PrP or only the empty vector into Zpl cells, we could not discern any protective effect associated with the presence of PrP. This observation was further corroborated when assessing the toxic effect of metals by propidium-iodide staining and fluorescence activated cell sorting analysis. Thus, our results on this mouse cell culture model do not seem to support a strong protective role for PrP against transition metal toxicity and also emphasize the necessity of extreme care when comparing cells derived from PrP knock-out and wild type mice.     

Distinct intracellular vesicle transport mechanisms are selectively modified by spastin and spastin mutations

Spastin is a microtubule severing ATPase that regulates intracellular and axonal transport of vesicles. Intracellular vesicle trafficking was analyzed in differentiated SH‐SY5Y‐neuroblastoma cells, transfected with spastin wild‐type and three spastin mutations (ΔN, K388R, S44L) to investigate spastin‐mediated effects on the velocity of vesicles, stained with LysoTracker Red®. The vesicle velocity varied considerably between mutations and detailed analysis revealed up to five distinct velocity classes. Microtubule severing by overexpressed wild‐type spastin caused reduced vesicle velocity. S44L and ΔN mutations, which were functionally impaired, showed similar velocities as control cells. K388R‐transfected cells exhibited an intermediate velocity profile. The results support the idea that spastin mutations not only alter axonal transport, but in addition regulate intracellular trafficking in the cell soma as well. J. Cell. Physiol. 226: 362–368, 2011. © 2010 Wiley‐Liss, Inc.     

Endemic predators, invasive prey and native diversity

Interactions between native diversity and invasive species can be more complex than is currently understood. Invasive ant species often substantially reduce diversity in the native ants diversity that act as natural control agents for pest insects. In Indonesia (on the island of Sulawesi), the third largest cacao producer worldwide, we show that a predatory endemic toad (Ingerophrynus celebensis) controls invasive ant (Anoplolepis gracilipes) abundance, and positively affects native ant diversity. We call this the invasive-naivety effect (an opposite of enemy release), whereby alien species may not harbour anti-predatory defences against a novel native predator. A positive effect of the toads on native ants may facilitate their predation on insect vectors of cacao diseases. Hence, toads may increase crop yield, but further research is needed on this aspect. Ironically, amphibians are globally the most threatened vertebrate class and are strongly impacted by the conversion of rainforest to cacao plantations in Sulawesi. It is, therefore, crucial to manage cacao plantations to maintain these endemic toads, as they may provide critical ecosystem services, such as invasion resistance and preservation of native insect diversity.     

Mixed effects of landscape complexity and farming practice on weed seed removal

Agricultural intensification negatively affects farmland biodiversity, and thereby, ecosystem services such as predation of weed seeds. Landscape complexity (large and diverse areas of semi-natural habitats) and organic farming (without pesticides and mineral fertilizers) can counteract this negative trend, but little is known about their relative importance. We experimentally studied seed removal of four economically relevant weed species by excluding (i) vertebrates, (ii) vertebrates plus large invertebrates and (iii) neither vertebrates nor invertebrates (control) at the field edge and in the interior of 22 organically or conventionally managed winter wheat fields, located across a gradient of landscape complexity (41–94% arable land). Arable land (%) was used as a simple predictor of landscape complexity, as it is closely related to landscape parameters such as habitat type diversity. Seed predation and removal were mainly influenced by large invertebrates, seed species identity, with Cirsium arvense being more affected than Poa trivialis, Apera spica-venti and Galium aparine and landscape complexity in interaction with farming practice, as it increased in conventional fields, but decreased in organic fields as landscape complexity decreased. Seed predation and removal did not consistently correspond to seed predator densities, as small mammal abundances decreased in conventional fields, but increased in organic fields as landscape complexity decreased and carabid activity densities were higher in organic compared to conventional fields. Slug activity density showed same response to landscape complexity and farming practice like seed removal and appeared to additionally influence the movement of seeds. In conclusion, our assessment of interacting local and landscape effect adds to the current knowledge of seed predation and removal. Farming practice and landscape complexity affect seed predator species differentially, thereby resulting in complex pattern of seed predation and removal. The service of weed seed predation is provided by small mammals and invertebrates and the disservice of seed dispersal and movement is provided by slugs.     

The effectiveness of flower strips and hedgerows on pest control,pollination services and crop yield: a quantitative synthesis

Floral plantings are promoted to foster ecological intensification of agriculture through provisioning of ecosystem services. However, a comprehensive assessment of the effectiveness of different floral plantings, their characteristics and consequences for crop yield is lacking. Here we quantified the impacts of flower strips and hedgerows on pest control (18 studies) and pollination services (17 studies) in adjacent crops in North America, Europe and New Zealand. Flower strips, but not hedgerows, enhanced pest control services in adjacent fields by 16% on average. However, effects on crop pollination and yield were more variable. Our synthesis identifies several important drivers of variability in effectiveness of plantings: pollination services declined exponentially with distance from plantings, and perennial and older flower strips with higher flowering plant diversity enhanced pollination more effectively. These findings provide promising pathways to optimise floral plantings to more effectively contribute to ecosystem service delivery and ecological intensification of agriculture in the future.     

Spatiotemporal changes of beetle communities across a tree diversity gradient

Aim Plant and arthropod diversity are often related, but data on the role of mature tree diversity on canopy insect communities are fragmentary. We compare species richness of canopy beetles across a tree diversity gradient ranging from mono‐dominant beech to mixed stands within a deciduous forest, and analyse community composition changes across space and time. Location Germany’s largest exclusively deciduous forest, the Hainich National Park (Thuringia). Methods We used flight interception traps to assess the beetle fauna of various tree species, and applied additive partitioning to examine spatiotemporal patterns of diversity. Results Species richness of beetle communities increased across the tree diversity gradient from 99 to 181 species per forest stand. Intra‐ and interspecific spatial turnover among trees contributed more than temporal turnover among months to the total γ‐beetle diversity of the sampled stands. However, due to parallel increases in the number of habitat generalists and the number of species in each feeding guild (herbivores, predators and fungivores), no proportional changes in community composition could be observed. If only beech trees were analysed across the gradient, patterns were similar but temporal (monthly) species turnover was higher compared to spatial turnover among trees and not related to tree diversity. Main conclusions The changes in species richness and community composition across the gradient can be explained by habitat heterogeneity, which increased with the mix of tree species. We conclude that understanding temporal and spatial species turnover is the key to understanding biodiversity patterns. Mono‐dominant beech stands are insufficient to conserve fully the regional species richness of the remaining semi‐natural deciduous forest habitats in Central Europe, and analysing beech alone would have resulted in the misleading conclusion that temporal (monthly) turnover contributes more to beetle diversity than spatial turnover among different tree species or tree individuals.     

Spatial aggregation facilitates coexistence and diversity of wild plant species in field margins

European agri-environment schemes encourage farmers to establish sown field margin strips to protect and enhance wild plant diversity. However, plant diversity in such wild plant sowings based on seed mixtures is often low due to the high competitiveness of few, common species. Here we analysed whether intraspecific aggregation could enhance the performance of less competitive species, and how plant performance is influenced by the number of species in a mixture. We focused on inter- and intraspecific competition between six agricultural wild plant species (Centaurea cyanus, Calendula arvensis, Melilotus officinalis, Poa annua, Bromus mollis, Medicago lupulina), and tested (i) two different seeding patterns (intraspecifically aggregated vs. randomly dispersed) and (ii) three different species mixtures (monocultures, three-species, and six-species mixtures). Plant performance was measured in terms of number of individuals, biomass per individual, and biomass per m². Intraspecific aggregation resulted in higher numbers of individuals of all species, while mixtures generated lower numbers of individuals. The performance of plant species differed depending on their position in the competitive hierarchy. Competitively weak species suffered much less from intraspecific than interspecific competition in terms of biomass, and the competitively weakest species became even excluded in the most species rich and randomly dispersed sowings with high interspecific competition. In conclusion, the performance of wild plant species was influenced by both seeding pattern and number of species in a mixture. Intraspecific aggregation enabled the coexistence of competitively weak species by reducing interspecific competitive exclusion processes. Consequently, agri-environmental schemes designed to preserve and enhance biodiversity should consider small-scale processes influencing the distribution and abundance of plants, and develop new agricultural sowing technologies to cultivate competitively weak and endangered wild plant species.