18 research outputs found
Enhancing Luminescence and X-ray Absorption Capacity of Eu3+:LaF3 Nanoparticles by Bi3+ Codoping
Bi3+ codoping has been proposed in this work with a twofold objective, namely, enhancing the luminescence emission of Eu3+:LaF3 nanoparticles (NPs) and increasing their X-ray attenuation capacity, with the purpose of obtaining a bimodal bioprobe for luminescence bioimaging and X-ray computed tomography. The synthesis method, reported here for the first time for LaF3 particles, allowed obtaining uniform, nonaggregated NPs using a homogeneous precipitation in polyol medium at room temperature in just 2 h. The simplicity of the synthesis method allows the large-scale production of NPs. LaF3 NPs with different Eu3+ contents were first synthesized to find the critical Eu3+ concentration, producing the highest emission intensity. This concentration was subsequently used to fabricate Bi3+-Eu3+-codoped LaF3 NPs using the same method. The emission intensity of the codoped NPs increased in more than one order of magnitude, thanks to the possibility of excitation through the Bi3+ Âż Eu3+ energy-transfer band. The luminescence properties of the codoped NPs were analyzed in detail to find the mechanism responsible for the emission enhancement. Finally, it was demonstrated that the high atomic number of Bi3+, higher than that of lanthanides, was an added value of the material because it increased its X-ray attenuation capacity. In summary, the LaF3 NPs codoped with Eu3+ and Bi3+ presented in this work are promising candidates as a bimodal bioprobe for luminescence bioimaging and X-ray computed tomography
Accounting for data heterogeneity in patterns of biodiversity: An application of linear mixed effect models to the oceanic island biogeography of spore-producing plants
The general dynamic model of oceanic island biogeography describes the evolution of species diversity properties, including species richness (SR), through time. We investigate the hypothesis that SR in organisms with high dispersal capacities is better predicted by island area and elevation (as a surrogate of habitat diversity) than by time elapsed since island emergence and geographic isolation. Linear mixed effect models (LMMs) subjected to information theoretic model selection were employed to describe moss and liverwort SR patterns from 67 oceanic islands across 12 archipelagos. Random effects, which are used to modulate model parameters to take differences among archipelagos into account, included only a random intercept in the best-fit model for liverworts and in one of the two best-fit models for mosses. In this case, the other coefficients are constant across archipelagos, and we interpret the intercept as a measure of the intrinsic carrying capacity of islands within each archipelago, independently of their size, age, elevation and geographic isolation. The contribution of area and elevation to the models was substantially higher than that of time, with the least contribution made by measures of geographic isolation. This reinforces the idea that oceanic barriers are not a major impediment for migration in bryophytes and, together with the almost complete absence of in situ insular diversification, explains the comparatively limited importance of time in the models. We hence suggest that time per se has little independent role in explaining bryophyte SR and principally features as a variable accounting for the changing area and topographic complexity during the life-cycle of oceanic islands. Simple area models reflecting habitat availability and diversity might hence prevail over more complex temporal models reflecting in-situ speciation and dispersal (time, geographic connectivity) in explaining patterns of biodiversity for exceptionally mobile organisms. © 2013 The Authors
Endemic plant species are more palatable to introduced herbivores than non-endemics
Islands harbour a spectacular diversity and unique species composition. This uniqueness is mainly a result of endemic species that have evolved in situ in the absence of mammal herbivores. However, island endemism is under severe threat by introduced herbivores. We test the assumption that endemic species are particularly vulnerable to generalist introduced herbivores (European rabbit) using an unprecedented dataset covering an entire island with enormous topographic, climatic and biological diversity (Tenerife, Canary Islands). With increasing endemism, plant species are more heavily browsed by rabbits than non-endemic species with up to 67% of endemics being negatively impacted by browsing, indicating a dramatic lack of adaptation to mammal herbivory in endemics. Ecosystems with high per cent endemism are most heavily browsed, suggesting ecosystem-specific vulnerability to introduced herbivores, even within islands. Protection of global biodiversity caused by disproportionally high endemism on oceanic islands via ecosystem-specific herbivore control and eradication measures is of utmost importance.Peer reviewe
Cubas, J.; irl, S.D.H.; Villafuerte, R.; Bello Rodriguez, V.; RodrĂguez Luengo, J.L.; Del Arco, M.; MartĂn Esquivel, J.L.; GonzĂĄlez Mancebo, J.M.
Islands harbour a spectacular diversity and unique species composition. This uniqueness is mainly a result of endemic species that have evolved in situ in the absence of mammal herbivores. However, island endemism is under severe threat by introduced herbivores. We test the assumption that endemic species are particularly vulnerable to generalist introduced herbivores (European rabbit) using an unprecedented dataset covering an entire island with enormous topographic, climatic and biological diversity (Tenerife, Canary Islands). With increasing endemism, plant species are more heavily browsed by rabbits than non-endemic species with up to 67% of endemics being negatively impacted by browsing, indicating a dramatic lack of adaptation to mammal herbivory in endemics. Ecosystems with high per cent endemism are most heavily browsed, suggesting ecosystem-specific vulnerability to introduced herbivores, even within islands. Protection of global biodiversity caused by disproportionally high endemism on oceanic islands via ecosystem-specific herbivore control and eradication measures is of utmost importance
Variation in species composition and vegetation structure of succulent scrub on Tenerife in relation to environmental variation
On Tenerife, the occurrence of environmental gradients
over short distances provides a unique opportunity to
investigate the relationship between vegetation and environmental
factors. In the semi-arid coastal region of Tenerife,
floristic composition, species richness and vegetation structure
of perennial plants have been studied in 67 locations
covering the existing precipitation gradient.
On the island as a whole, variation in species composition
could be best explained by mean annual precipitation; at
coastal sites, substrate age and soil characteristics also played
a significant role. On the other hand, substrate chemistry and
the type of eruptive material explained little of the floristic
variation. Stand biomass was strongly correlated with mean
annual precipitation and was, on the youngest lava flows
studied, also affected by substrate age. The native stem succulent
species made up the bulk of total biomass along the whole
precipitation gradient. Disturbed and undisturbed sites differed
significantly in stand biomass and cover. Species richness
was correlated with precipitation and substrate age. Distribution
of plant functional types was also related to the
precipitation gradient. The relative abundance of hemicryptophytes
and shrubs with non-hairy leaves increased with
increasing precipitation whereas the ratio of shrubs with hairy/
non-hairy leaves and succulent plants decreased. Some alien
plants were quite frequent at disturbed sites but, on the whole,
they contributed little to the species spectrum and to the stand
biomass. Undisturbed sites remained almost free of introduced
species not considering annuals
Size does matter: morphology, sexual expression and sex ratios in Pseudoscleropodium purum across Europe
Peer reviewe