Interactions between different predator–prey states: a method for the derivation of the functional and numerical response

Journal of Mathematical Biology - In this paper we introduce a formal method for the derivation of a predator’s functional response from a system of fast state transitions of the prey or...     

When sinks become sources: Adaptive colonization in asexuals*

The establishment of a population into a new empty habitat outside of its initial niche is a phenomenon akin to evolutionary rescue in the presence of immigration. It underlies a wide range of processes, such as biological invasions by alien organisms, host shifts in pathogens, or the emergence of resistance to pesticides or antibiotics from untreated areas. We derive an analytically tractable framework to describe the evolutionary and demographic dynamics of asexual populations in a source-sink system. We analyze the influence of several factors on the establishment success in the sink, and on the time until establishment. To this aim, we use a classic phenotype-fitness landscape (Fisher's geometrical model in n dimensions) where the source and sink habitats have different phenotypic optima. In case of successful establishment, the mean fitness in the sink follows a typical four-phases trajectory. The waiting time to establishment is independent of the immigration rate and has a “U-shaped” dependence on the mutation rate, until some threshold where lethal mutagenesis impedes establishment and the sink population remains so. We use these results to get some insight into possible effects of several management strategies.     

Synthesis and FTIR Conformational Studies of Peptides From the Basic Region of c-Jun: a Critical Analysis on the Basis of CD and NMR Data

Abstract

The peptide (35 residues) corresponding to the basic subdomain (bSD) of c-Jun (residues 252–281) and its fragments NP (N-terminal peptide, 1–19) and CP (C-terminal peptide, 1635) were synthesized in stepwise solid-phase using the tert-butyloxycarbonyl/benzyl strategy. In a previous paper, we have shown that during its binding to the DNA site CRE (cAMP- responsive element) the bSD structure was converted into α-helix from an initial random coil conformation [Krebs, D., Dahmani, B., El Antri, S., Monnot, M., Convert, O., Mauffret, O., Troalen, F. & Fermandjian, S. Eur. J. Biochem. 231, 370–380 (1995)]. Our results suggested both a high flexibility and a helical potential in bSD, these two properties seeming crucial for the accommodation of the basic subdomain of c-Jun to its specific DNA targets. In this work, we assessed the conformational variability of bSD through the study of the secondary structures of its NP and CP fragments in trifluoroethanol (TFE)/²H₂O mixtures, using Fourier transform infrared (FTIR) spectroscopy. The IR results were critically analyzed in light of our previously reported circular dichroism (CD) and NMR data [Krebs, D., Dahmani, B., Monnot, M., Mauffret, O., Troalen, F. & Fermandjian, S. Eur. J. Biochem. 235, 699–712 (1996)]. Upon addition of TFE, the relative areas of the seven components of the amide I band (1700–1620 cm^?1) reflected the conversion of a large amount of random coil conformation into α-helix for the two fragments and bSD. This effect was accompanied by more subtle variations of the less populated structures, in agreement with the results of CD and NMR experiments. The IR results stipulated the conservation of the parent bSD secondary structures in both fragments; however, NP and CP peptides did not display similar random-to-α-helix stabilization pattern upon additions of TFE to aqueous solutions. The profile from CD signal at 222 nm was found sigmoidal for NP and almost linear for CP, while that corresponding to the parent peptide bSD was just in between those of its fragments. Thus, the present study confirms the high flexibility and helix propensity of the c-Jun basic subdomain and suggests that the N- and C-terminal parts of the peptide do not follow the same random-to-helix conversion profile during their complexation with DNA.     

Texture perception through direct and indirect touch: An analysis of perceptual space for tactile textures in two modes of exploration

Considerable information about the texture of objects can be perceived remotely through a probe. It is not clear, however, how texture perception with a probe compares with texture perception with the bare finger. Here we investigate the perception of a variety of textured surfaces encountered daily (e.g., corduroy, paper, and rubber) using the two scanning modes—direct touch through the finger and indirect touch through a probe held in the hand—in two tasks. In the first task, subjects rated the overall pair-wise dissimilarity of the textures. In the second task, subjects rated each texture along three continua, namely, perceived roughness, hardness, and stickiness of the surfaces, shown previously as the primary dimensions of texture perception in direct touch. From the dissimilarity judgment experiment, we found that the texture percept is similar though not identical in the two scanning modes. From the adjective rating experiments, we found that while roughness ratings are similar, hardness and stickiness ratings tend to differ between scanning conditions. These differences between the two modes of scanning are apparent in perceptual space for tactile textures based on multidimensional scaling (MDS) analysis. Finally, we demonstrate that three physical quantities, vibratory power, compliance, and friction carry roughness, hardness, and stickiness information, predicting perceived dissimilarity of texture pairs with indirect touch. Given that different types of texture information are processed by separate groups of neurons across direct and indirect touch, we propose that the neural mechanisms underlying texture perception differ between scanning modes.     

Do stream fish track climate change? Assessing distribution shifts in recent decades

Understanding the ability of species to shift their distribution ranges in response to climate change is crucial for conservation biologists and resources managers. Although freshwater ecosystems include some of the most imperilled fauna worldwide, such range shifts have been poorly documented in streams and rivers and have never been compared to the current velocity of climate change. Based on national monitoring data, we examined the distributional changes of 32 stream fish species in France and quantified potential time lags in species responses, providing a unique opportunity to analyze range shifts over recent decades of warming in freshwater environments. A multi‐facetted approach, based on several range measures along spatial gradients, allowed us to quantify range shifts of numerous species across the whole hydrographic network between an initial period (1980–1992) and a contemporary one (2003–2009), and to contrast them to the rates of isotherm shift in elevation and stream distance. Our results highlight systematic species shifts towards higher elevation and upstream, with mean shifts in range centre of 13.7 m decade^?1 and 0.6 km decade^?1, respectively. Fish species displayed dispersal‐driven expansions along the altitudinal gradient at their upper range limit (61.5 m decade^?1), while substantial range contractions at the lower limit (6.3 km decade^?1) were documented for most species along the upstream–downstream gradient. Despite being consistent with the geographic variation in climate change velocities, these patterns reveal that the majority of stream fish have not shifted at a pace sufficient to track changing climate, in particular at their range centre where range shifts lag far behind expectation. Our study provides evidence that stream fish are currently responding to recent climate warming at a greater rate than many terrestrial organisms, although not as much as needed to cope with future climate modifications.     

Another call for the end of invasion biology

The restriction of invasion biology to non‐native species has been laid down as one founding principle of the discipline by many researchers. However, this split between native and non‐native species is highly controversial. Using a phenomenological approach and a more pragmatic examination of biological invasions, the present paper discusses how this dichotomy has restricted the relevance of the field, both from theoretical and practical viewpoints. We advocate the emergence of a broader disciplinary field.     

Habitat selection in translocated gregarious ungulate species: An interplay between sociality and ecological requirements

The adaptation of translocated organisms to a new environment in the first years after their release is crucial in translocation programs because it may affect survival and reproductive success. Therefore, identifying the factors determining resource selection by the relocated animals is essential to improve the planning and the outcome of such programs. Using data collected in 2006–2009 in the framework of a restocking program, we studied the temporal variation of habitat selection in 14 translocated Alpine ibex (Capra ibex) during the year of their release and the following 3 years. We hypothesized a progressive adaptation of the translocated individuals, highlighted by a gradual decrease in the dissimilarities between translocated and resident individuals in ecological characteristics and social behavior. We tested the differences in habitat selection and home range size between the translocated and resident individuals and compared the spatial overlap between the groups. As expected, the dissimilarities decreased annually. The translocated and resident ibex almost immediately selected the same habitat resources, but the translocated individuals required 3 years to become fully socially assimilated. Our results indicated that habitat selection by gregarious species in a new environment is primarily driven by specific ecological requirements and that sociality plays a significant role. The translocated individuals tended to colonize areas already occupied by residents, either to fulfill social requirements and/or because the location of resident individuals may indicate high-quality habitat. This pattern of behavior must be considered in the planning of translocation programs because habitat selection can affect the outcomes of the programs. © 2013 The Wildlife Society.     

Water stress impact on young seedling growth of Acacia arabica

Drought is the major constraint in arid regions throughout the world and identification of drought-resistant plants is therefore of crucial importance. Since young seedling stage is especially sensitive to water stress, the present work analyzed the physiological behavior of seedling from Acacia arabica issued from a dry area, grown under controlled environmental conditions and subjected to progressive soil drying. Although soil gravimetric water content (g H₂O g^?1 soil dry weight) dropped from 80 % to less than 35 %, most plants remained alive until the end of the water stress. Seedlings were able to efficiently close their stomata to reduce water losses and accumulated high amounts of proline. Despite osmotic adjustment, turgor pressure decreased in stressed plants and could explain the stress-induced inhibition of plant growth. Decrease in net photosynthesis was related to stress-induced decrease in stomatal conductance and not to any impact on chlorophyll concentration or fluorescence-related parameter: both PSII efficiency and photochemical quenching remained unaffected by water stress while drought-induced increase in non-photochemical quenching should be regarded as a strategy to avoid over-energisation of the photosynthetic apparatus. Instantaneous water use efficiency increased in stressed plants comparative to controls. Oxidative stress estimated by malondialdehyde concentration was recorded only at the end of the treatment, suggesting that stressed plants remained able to cope with reactive oxygen species. Water stress induced an increase in anthocyanins, while aglycone flavonols decreased. Those compounds were not involved in the management of oxidative stress. It is concluded that A. arabica is a promising drought-resistant plant species for rehabilitation of dry areas.