Oscil.lacions en models d'epidèmies de còlera

En aquest treball ens hem centrat en models matemàtics per Còlera, una malaltia present en molts països en vies de desenvolupament. Hem considerat primer un model descrit per equacions diferencials ordinàries a paràmetres constants. La introducció de distribucions de probabilitat més realistes per als períodes d'immunitat que un individu adquireix davant la malaltia dóna lloc a solucions periòdiques, les quals no són possibles en la consideració clàssica de distribucions exponencials. El Teorema de la bifurcació de Hopf ens anuncia l'existència d'aquestes òrbites periòdiques. Pel model més senzill en el que existeixen òrbites periòdiques estables hem realitzat un anàlisi detallat d'existència i estabilitat de les solucions. La introducció de paràmetres dependents del temps en el sistema d'equacions dóna lloc a dinàmiques molt diverses, que també hem estudiat i simulat.. Es tracta d'estudiar fenòmens oscil·latoris en models de sistemes d'equacions diferencials ordinàries que modelen epidèmies com les de còlera en les que la població pot estructurar-se en grups (Susceptibles, Infectats, Recuperats) amb una retoalimentació (SIRS). Es tractaria de veure els efectes de les condicions estacionals i també els esdeveniments climàtics puntuals

Oscil.lacions en models d'epidèmies de còlera

En aquest treball ens hem centrat en models matemàtics per Còlera, una malaltia present en molts països en vies de desenvolupament. Hem considerat primer un model descrit per equacions diferencials ordinàries a paràmetres constants. La introducció de distribucions de probabilitat més realistes per als períodes d'immunitat que un individu adquireix davant la malaltia dóna lloc a solucions periòdiques, les quals no són possibles en la consideració clàssica de distribucions exponencials. El Teorema de la bifurcació de Hopf ens anuncia l'existència d'aquestes òrbites periòdiques. Pel model més senzill en el que existeixen òrbites periòdiques estables hem realitzat un anàlisi detallat d'existència i estabilitat de les solucions. La introducció de paràmetres dependents del temps en el sistema d'equacions dóna lloc a dinàmiques molt diverses, que també hem estudiat i simulat.. Es tracta d'estudiar fenòmens oscil·latoris en models de sistemes d'equacions diferencials ordinàries que modelen epidèmies com les de còlera en les que la població pot estructurar-se en grups (Susceptibles, Infectats, Recuperats) amb una retoalimentació (SIRS). Es tractaria de veure els efectes de les condicions estacionals i també els esdeveniments climàtics puntuals

Trophic strategies of a non-native and a native amphibian species in shared ponds.

One of the critical factors for understanding the establishment, success and potential impact on native species of an introduced species is a thorough knowledge of how these species manage trophic resources. Two main trophic strategies for resource acquisition have been described: competition and opportunism. In the present study our objective was to identify the main trophic strategies of the non-native amphibian Discoglossus pictus and its potential trophic impact on the native amphibian Bufo calamita.We determine whether D. pictus exploits similar trophic resources to those exploited by the native B. calamita (competition hypothesis) or alternative resources (opportunistic hypothesis). To this end, we analyzed the stable isotope values of nitrogen and carbon in larvae of both species, in natural ponds and in controlled laboratory conditions. The similarity of the δ15N and δ13C values in the two species coupled with isotopic signal variation according to pond conditions and niche partitioning when they co-occurred indicated dietary competition. Additionally, the non-native species was located at higher levels of trophic niches than the native species and B. calamita suffered an increase in its standard ellipse area when it shared ponds with D. pictus. These results suggest niche displacement of B. calamita to non-preferred resources and greater competitive capacity of D. pictus in field conditions. Moreover, D. pictus showed a broader niche than the native species in all conditions, indicating increased capacity to exploit the diversity of resources; this may indirectly favor its invasiveness. Despite the limitations of this study (derived from potential variability in pond isotopic signals), the results support previous experimental studies. All the studies indicate that D. pictus competes with B. calamita for trophic resources with potential negative effects on the fitness of the latter

Evaluando los factores que afectan a la tasa de mortalidad en la carretera: el caso de Sapo Común Bufo bufo, cerca de un área de reproducción

The Common Toad Bufo bufo is the amphibian with the highest rates of road mortality in many European countries. This elevated incidence of road kills has frequently been associated with migration to breeding sites. In this study, we analysed the mortality of the Common Toad in the road network in Catalonia (NE Spain), and investigated the related causative factors on four roads near a breeding site in the Pyrenees. Results suggest that the high mortality rate is due to a combination of factors: toad abundance, traffic density and quality of water bodies for breeding. On the road with the highest incidence of road kills we investigated whether deaths occurred at specific spots or in a random manner. The road was divided into 500 m sections and each section was classified according to biotic (type of vegetation) and abiotic (presence of streams, roadside topography) variables. Multiple correspondence analysis showed that sections with streams crossing under the road had the highest mortality rate, suggesting that such water bodies flowing into the breeding pond are the toads’ main migratory pathways for hibernation and breeding. As toads use the same migratory routes each year, it is critical to identify areas with a high potential mortality so that efficient measures can be designed to increase wildlife permeability, and thereby reduce habitat fragmentation. This methodology could be applied in other areas with high amphibian mortality. Key words: Amphibian, Common Toad, Bufo bufo, Landscape fragmentation, Migration, Mortality, Road permeability, Pyrenees.El Sapo Común Bufo bufo, es el anfibio con mayor tasa de mortalidad en la carretera en numerosos países de Europa. Esta elevada mortalidad se debe principalmente a las migraciones que realiza hacia las zonas de reproducción. En este estudio se analiza la mortalidad del Sapo Común en la red de carreteras de Cataluña (NE España) y más específicamente qué factores influyen sobre dicha mortalidad en cuatro carreteras cercanas a un punto de reproducción en los Pirineos. Los resultados sugieren que la alta tasa de mortalidad se debe a la combinación de tres factores: abundancia de sapos, densidad de tráfico y calidad de los puntos de agua para la reproducción. En la carretera con mayor índice de atropellos, se analizó si existía agregación en los animales atropellados o estos se distribuían al azar. Para ello, la carretera se dividió en tramos de 500 m, cada uno de los cuales se caracterizó por el tipo de vegetación circundante, así como otros factores que pudieran influir sobre la migración de los sapos (p.e. inclinación del margen de la carretera, presencia de riachuelos, etc.). El análisis de correspondencias múltiple demostró que los tramos con torrentes cruzando bajo la carretera presentaban mayor mortalidad. Esto sugiere que dichos torrentes son las vías principales usadas por los sapos para acudir a los puntos de reproducción. Dado que los sapos utilizan cada año las mismas vías migratorias, es fundamental identificar dichos puntos para predecir cuáles presentan mayor mortalidad potencial y así diseñar más eficazmente los mecanismos de permeabilidad para la fauna en las vías de comunicación. Esta metodología puede ser aplicada a otras zonas con elevada mortalidad de anfibios en la red de carreteras. Palabras clave: Anfibio, Sapo Común, Bufo bufo, Fragmentación del paisaje, Migración, Mortalidad, Permeabilidad de la carretera, Pirineos

Variation in developmental rates is not linked to environmental unpredictability in annual killifishes

Comparative evidence suggests that adaptive plasticity may evolve as a response to predictable environmental variation. However, less attention has been placed on unpredictable environmental variation, which is considered to affect evolutionary trajectories by increasing phenotypic variation (or bet hedging). Here, we examine the occurrence of bet hedging in egg developmental rates in seven species of annual killifish that originate from a gradient of variation in precipitation rates, under three treatment incubation temperatures (21, 23, and 25 degrees C). In the wild, these species survive regular and seasonal habitat desiccation, as dormant eggs buried in the soil. At the onset of the rainy season, embryos must be sufficiently developed in order to hatch and complete their life cycle. We found substantial differences among species in both the mean and variation of egg development rates, as well as species-specific plastic responses to incubation temperature. Yet, there was no clear relationship between variation in egg development time and variation in precipitation rate (environmental predictability). The exact cause of these differences therefore remains enigmatic, possibly depending on differences in other natural environmental conditions in addition to precipitation predictability. Hence, if species-specific variances are adaptive, the relationship between development and variation in precipitation is complex and does not diverge in accordance with simple linear relationships

Genetic response to human-induced habitat changes in the marine environment: A century of evolution of European sprat in Landvikvannet, Norway

Habitat changes represent one of the five most pervasive threats to biodiversity. However, anthropogenic activities also have the capacity to create novel niche spaces to which species respond differently. In 1880, one such habitat alterations occurred in Landvikvannet, a freshwater lake on the Norwegian coast of Skagerrak, which became brackish after being artificially connected to the sea. This lake is now home to the European sprat, a pelagic marine fish that managed to develop a self-recruiting population in barely few decades. Landvikvannet sprat proved to be genetically isolated from the three main populations described for this species; that is, Norwegian fjords, Baltic Sea, and the combination of North Sea, Kattegat, and Skagerrak. This distinctness was depicted by an accuracy self-assignment of 89% and a highly significant FST between the lake sprat and each of the remaining samples (average of ≈0.105). The correlation between genetic and environmental variation indicated that salinity could be an important environmental driver of selection (3.3% of the 91 SNPs showed strong associations). Likewise, Isolation by Environment was detected for salinity, although not for temperature, in samples not adhering to an Isolation by Distance pattern. Neighbor-joining tree analysis suggested that the source of the lake sprat is in the Norwegian fjords, rather than in the Baltic Sea despite a similar salinity profile. Strongly drifted allele frequencies and lower genetic diversity in Landvikvannet compared with the Norwegian fjords concur with a founder effect potentially associated with local adaptation to low salinity. Genetic differentiation (FST) between marine and brackish sprat is larger in the comparison Norway-Landvikvannet than in Norway-Baltic, which suggests that the observed divergence was achieved in Landvikvannet in some 65 generations, that is, 132 years, rather than gradually over thousands of years (the age of the Baltic Sea), thus highlighting the pace at which human-driven evolution can happen.publishedVersio

Differential trophic traits between invasive and native anuran tadpoles

How trophic resources are managed is a key factor in our understanding of the success of invasive species. In amphibians that usually occupy ephemeral ponds, the capacity to acquire resources and food selection are especially important because as a pond dries, the larval density increases and food resources are limited. Abundant and high-quality food can increase the final size and reduce the duration of development of amphibians. The aim of this work was to assess the trophic traits of tadpoles of the invasive (originally North African) anuran Discoglossus pictus compared to those of native European Epidalea calamita tadpoles under laboratory conditions. Food of two different levels of quality was supplied, and the feeding activity and food preference of the two species were analysed alone and in co-occurrence. D. pictus was capable of modifying its behaviour and food preferences; while E. calamita displayed much milder differences between treatments. Both alone and in co-occurrence with the native species, the invasive tadpoles obtained higher feeding activity values and showed a stronger preference for high-quality food. Additionally, when high densities of the two species shared food resources, the feeding activity results indicated potential displacement of the native tadpoles to lowquality resources. D. pictus thus presents trophic traits that are favourable for invasion and could limit the fitness of E. calamita when resources are limited or there is a risk of pond desiccation

How repeatable is the Environmental Impact Classification of Alien Taxa (EICAT)? Comparing independent global impact assessments of amphibians

The magnitude of impacts some alien species cause to native environments makes them targets for regulation and management. However, which species to target is not always clear, and comparisons of a wide variety of impacts are necessary. Impact scoring systems can aid management prioritization of alien species. For such tools to be objective, they need to be robust to assessor bias. Here, we assess the newly proposed Environmental Impact Classification for Alien Taxa (EICAT) used for amphibians and test how outcomes differ between assessors. Two independent assessments were made by Kraus (Annual Review of Ecology Evolution and Systematics, 46, 2015, 75‐97) and Kumschick et al. (Neobiota, 33, 2017, 53‐66), including independent literature searches for impact records. Most of the differences between these two classifications can be attributed to different literature search strategies used with only one‐third of the combined number of references shared between both studies. For the commonly assessed species, the classification of maximum impacts for most species is similar between assessors, but there are differences in the more detailed assessments. We clarify one specific issue resulting from different interpretations of EICAT, namely the practical interpretation and assigning of disease impacts in the absence of direct evidence of transmission from alien to native species. The differences between assessments outlined here cannot be attributed to features of the scheme. Reporting bias should be avoided by assessing all alien species rather than only the seemingly high‐impacting ones, which also improves the utility of the data for management and prioritization for future research. Furthermore, assessments of the same taxon by various assessors and a structured review process for assessments, as proposed by Hawkins et al. (Diversity and Distributions, 21, 2015, 1360), can ensure that biases can be avoided and all important literature is included.We show that the newly proposed Environmental Impact Classification for Alien Taxa is fairly robust if used by different assessors for amphibians. Bias can be avoided through clear statement of the goals of the respective study using the scheme. We further suggest a thorough review process to be developed and implemented.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136716/1/ece32877.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136716/2/ece32877_am.pd

Evaluating factors affecting amphibian mortality on roads: the case of the Common Toad Bufo bufo near a breeding place.

The Common Toad Bufo bufo is the amphibian with the highest rates of road mortality in many European countries. This elevated incidence of road kills has frequently been associated with migration to breeding sites. In this study, we analysed the mortality of the Common Toad in the road network in Catalonia (NE Spain), and investigated the related causative factors on four roads near a breeding site in the Pyrenees. Results suggest that the high mortality rate is due to a combination of factors: toad abundance, traffic density and quality of water bodies for breeding. On the road with the highest incidence of road kills we investigated whether deaths occurred at specific spots or in a random manner. The road was divided into 500 m sections and each section was classified according to biotic (type of vegetation) and abiotic (presence of streams, roadside topography) variables. Multiple correspondence analysis showed that sections with streams crossing under the road had the highest mortality rate, suggesting that such water bodies flowing into the breeding pond are the toads' main migratory pathways for hibernation and breeding. As toads use the same migratory routes each year, it is critical to identify areas with a high potential mortality so that efficient measures can be designed to increase wildlife permeability, and thereby reduce habitat fragmentation. This methodology could be applied in other areas with high amphibian mortality