Analysis of trophic structure of two carnivore assemblages by means of guild identification

We evaluated the existence of trophic guild structure, considering seasonal and annual variation, in two terrestrial carnivore assemblages: one from Santa Cruz province (Argentinean Patagonia, composed by six carnivore species), and the other from Doñana National Park (SW Spain, composed by five carnivore species). To identify trophic guilds, we first studied seasonal and annual diets of predators, calculated trophic overlap among species pairs, and then constructed overlap matrices (similarity matrices). We determined guild membership objectively by entering the similarity matrices into the clustering technique unweighted pair-group method with arithmetic averaging. Carnivores from both assemblages were grouped, respectively, into four feeding guilds. Lagomorphs and rodents promoted the formation of two feeding guilds in both study sites, although the taxonomic composition of predator species that composed them was different. The ungulates-edentates feeding guild was only present at Santa Cruz, whereas the birds and reptiles feeding guild was only present at Doñana. Invertebrates and fruits were the base for the formation of a guild composed by species of the same taxonomic origin both in Santa Cruz and Doñana. Guild structure of Santa Cruz and Doñana assemblages did not exhibit seasonal or annual variation, although the specific guild composition changed over the two studied periods for both assemblages. This structure probably responded to discontinuities in resource spectra in Santa Cruz and fluctuations in rabbit abundance in Doñana. Our results support the hypothesis that establishes that guilds are originated by opportunistic convergence of species on abundant and energetically rewarding resources.     

Integration of modelling and policy: Wolf reproductive-site model for Natura 2000 conservation measures in Italian Alps

Ecological knowledge is considered an important factor in environmental policy-making. However, the opportunity for ecologists to influence policy can often occur within discrete time policy windows, and seizing these opportunities has been heavily emphasized as a recent global conservation need. In 2017 the Natura 2000 Conservation Measures have been finalized in Italy, and delineated the management policy and institutional responsibilities of Natura 2000 Sites, after obligations of the EU Habitat Directive. In this timeframe, we developed a multi-scalar hierarchical habitat selection model for wolf reproductive-sites to identify potentially favorable habitat for wolf reproduction in the western Italian Alps, based on 19 years of data. This habitat suitability model was useful for the definition of species conservation requirements within the Natura 2000 Sites, and has been adopted in legislation processes, representing a successful example of ecological modelling fitting into a relevant policy window and informing legal instruments to achieve nature conservation goals.     

Resource-allocation constraint governs structure and function of microbial communities in metabolic modeling

Predictive modeling tools for assessing microbial communities are important for realizing transformative capabilities of microbiomes in agriculture, ecology, and medicine. Constraint-based community-scale metabolic modeling is unique in its potential for making mechanistic predictions regarding both the structure and function of microbial communities. However, accessing this potential requires an understanding of key physicochemical constraints, which are typically considered on a per-species basis. What is needed is a means of incorporating global constraints relevant to microbial ecology into community models. Resource-allocation constraint, which describes how limited resources should be distributed to different cellular processes, sets limits on the efficiency of metabolic and ecological processes. In this study, we investigate the implications of resource-allocation constraints in community-scale metabolic modeling through a simple mechanism-agnostic implementation of resource-allocation constraints directly at the flux level. By systematically performing single-, two-, and multi-species growth simulations, we show that resource-allocation constraints are indispensable for predicting the structure and function of microbial communities. Our findings call for a scalable workflow for implementing a mechanistic version of resource-allocation constraints to ultimately harness the full potential of community-scale metabolic modeling tools.     

A novel in vitro co-culture model to examine contact formation between astrocytic processes and cerebral vessels

Here, we developed a novel in vitro co-culture model, in which process-bearing astrocytes and isolated cerebral microvessels from mice were co-cultured. Astrocytes formed contacts with microvessels from both adult and neonatal mice. However, concentrated localization of the immunofluorescence signal for aquaporin-4 (AQP4) at contact sites between perivascular endfoot processes and blood vessels was only detected with neonatal mouse microvessels. Contact between astrocytic processes and microvessels was retained, whereas concentrated localization of AQP4 signal at contact sites was lost, by knockdown of dystroglycan or α-syntrophin, reflecting polarized localization of AQP4 at perivascular regions in the brain. Further, using our in vitro co-culture model, we found that astrocytes predominantly extend processes to pericytes located at the abluminal surface of microvessels, providing additional evidence that this model is representative of the in vivo situation. Altogether, we have developed a novel in vitro co-culture model that can reproduce aspects of the in vivo situation and is useful for assessing contact formation between astrocytes and blood vessels.     

Recent advances in plasmid-based tools for establishing novel microbial chassis

A key challenge for domesticating alternative cultivable microorganisms with biotechnological potential lies in the development of innovative technologies. Within this framework, a myriad of genetic tools has flourished, allowing the design and manipulation of complex synthetic circuits and genomes to become the general rule in many laboratories rather than the exception. More recently, with the development of novel technologies such as DNA automated synthesis/sequencing and powerful computational tools, molecular biology has entered the synthetic biology era. In the beginning, most of these technologies were established in traditional microbial models (known as chassis in the synthetic biology framework) such as Escherichia coli and Saccharomyces cerevisiae, enabling fast advances in the field and the validation of fundamental proofs of concept. However, it soon became clear that these organisms, although extremely useful for prototyping many genetic tools, were not ideal for a wide range of biotechnological tasks due to intrinsic limitations in their molecular/physiological properties. Over the last decade, researchers have been facing the great challenge of shifting from these model systems to non-conventional chassis with endogenous capacities for dealing with specific tasks. The key to address these issues includes the generation of narrow and broad host plasmid-based molecular tools and the development of novel methods for engineering genomes through homologous recombination systems, CRISPR/Cas9 and other alternative methods. Here, we address the most recent advances in plasmid-based tools for the construction of novel cell factories, including a guide for helping with “build-your-own” microbial host.     

Optimal conservation effort for a population in a stochastic environment

We study the optimal conservation effort for a population in a fluctuating environment. The survivorship of a population is affected by unpredictable environmental fluctuation (noise) and can be improved by conservation effort accompanied by a cost. The optimal effort level is the one that minimizes the total cost, defined as the weighted sum of the population extinction risk and the economic cost of conservation effort. The optimal effort depends on the variance and the probability distribution of the noise, the relative importance of the population's survival vs. the economic cost, the effectiveness of conservation effort, and the time scope over which we optimize. The analysis of dynamic programming illustrates that the choice of extinction risk function greatly affects the optimal effort level. The conservation effort level that is the best solution of a multiple-year optimization may be higher than that for the corresponding single-year optimization, if the population is relatively safe. However, the conservation level for the multiple-year optimization becomes lower than for the single-year optimization if the population is endangered. In a similar manner, the optimal conservation effort level for the problem with a short time scope is either higher or lower than that for the problem with a long time scope, depending on the extinction risk of the population. Next, for each parameter of the model, we define five different sensitivities of extinction probability or of the total cost. We then study the mean increase in the total cost caused by the uncertainty of parameters. To achieve the best conservation result, we need to invest the limited research effort to the parameter with the largest effect to the optimal effort level, rather than to those with large impacts on the extinction probability or on the total cost. The recommended policy should depend critically on the choice of the criterion to optimize, which shows the importance of theoretical study of the relationship in performing proper decision making in conservation practice.     

Periodic coexistence of four species competing for three essential resources

We show the existence of a periodic solution in which four species coexist in competition for three essential resources in the standard model of resource competition. By assuming that species i is limited by resource i for each i near the positive equilibrium, and that the matrix of contents of resources in species is a combination of cyclic matrix and a symmetric matrix, we obtain an asymptotically stable periodic solution of three species on three resources via Hopf bifurcation. A simple bifurcation argument is then employed which allows us to add a fourth species. In principle, the argument can be continued to obtain a periodic solution adding one new species at a time so long as asymptotic stability can be assured at each step. Numerical simulations are provided to illustrate our analytical results. The results of this paper suggest that competition can generate coexistence of species in the form of periodic cycles, and that the number of coexisting species can exceed the number of resources in a constant and homogeneous environment.     

Phenotypic plasticity and interpopulation differences in life history traits of<Emphasis Type="Italic"> Armadillidium vulgare</Emphasis> (Isopoda:Oniscidae)

The hypothesis that the balance of trade-offs between survivorship, growth and reproductive allocation in the terrestrial isopod Armadillidium vulgare will change when resource input is increased has been investigated experimentally. When the quality of food available was increased, by adding a mixture of litter from herbaceous dicotyledonous plants to a background low-quality food of dead grasses, survivorship was found to be the most phenotypically plastic trait, increasing by 168%. Growth rates increased by 99% but reproductive allocation by only 21%. In the field, members of a population from a site with more high-quality food grew more than twice as fast as those from a site where less high-quality food was available. The population from the site with higher food availability, contrary to predictions from the laboratory study, did not survive as well as that from the site with less available high-quality food. This may be because the site that is more favourable for growth has a more stressful physical environment due to much bigger temperature fluctuations, which are known to be an important cause of mortality in this species. When individuals from both populations were reared under controlled laboratory conditions, both the parental and F1 generations from the poor growth environment survived better than those from the good growth habitat. However, even when given an excess of high-quality food those from the poor growth environment continued to grow more slowly and had a lower reproductive allocation than those from the site with higher food availability. We conclude that microevolutionary changes may have occurred in the balance of resource allocation between survivorship, growth and reproductive allocation, to favour higher survivorship during the longer prereproductive period at the site where growth to the threshold size for reproduction takes longer.     

Selective fruit filling in relation to pollen load size in Alstroemeria aurea (Alstroemeriaceae)

 We conducted an experiment in a natural population of Alstroemeria aurea, a clonal perennial, to determine (1) if reproduction was resource limited, and (2) if fruits would be selectively filled based on differences in pollination intensity when pollen loads were adequate for full seed set. Under these conditions, differences in pollination intensity are unlikely to affect seed number, but could affect seed quality, providing an interesting test of the gametophytic competition hypothesis. To test for resource limitation, percent fruit maturation, number of seeds per fruit and average seed weight were compared to paired controls for ramets in which all but one fruit was removed. To test the effect of pollination intensity on selective resource allocation, three types of pollination treatments were performed: (1) all flowers of the single inflorescence received a low pollen load, (2) all flowers received a high pollen load, (3) alternate flowers of the inflorescence received either a high or a low pollen load. We determined the percentage of fruit that reached maturity, counted the number of seeds and ovules and calculated the average seed weight for all capsules in each treatment. Resources appeared to limit reproduction in this population since seed number and weight were significantly higher than in controls when competing capsules were removed. At the whole ramet level, a four fold difference in pollen loads had no significant effect on any of the parameters measured. However, when pollination intensity varied within an inflorescence, the number of seeds per fruit increased by about 10% in flowers that received the higher pollen load. We observed the same trend in each of 2 years, but the increase was significant in only 1 year. The differences, although not great, were only slightly smaller than when all competing fruits were removed, and were consistent with selective resource allocation based on pollination intensity independent of seed set. Received: 28 September 1997 / Accepted: 30 April 1998     

Effects of nutrient and soil moisture on competition between shape Carex stricta,shape Phalaris arundinacea,and shape Typha latifolia

We investigated the importance of nutrients, soil moisture, arbuscular mycorrhizal fungi (AMF), and interspecific competition levels on the biomass allocation patterns of three wetland perennial plant species, Carex stricta Lam., Phalaris arundinacea L., and Typha latifolia L. A factorial experiment was conducted with high-low nutrient levels, high-low soil moisture levels, and with and without AMF inoculation. Under the experimental conditions, plant inoculation by AMF was too low to create a treatment and the AMF treatment was dropped from the total analysis. P. arundinacea and T. latifolia biomass were 73% and 77% higher, respectively, in the high nutrient treatment compared to the low nutrient treatment. Biomass allocation between shoots and roots remained relatively constant between environmental treatments, although shoot:root ratios of P. arundinacea declined in the low nutrient treatment. For C. stricta, the high nutrient and soil moisture treatments resulted in an increase in biomass of 50% and 15%, respectively. Shoot:root ratios were nearly constant among all environmental conditions. Biomass of T. latifolia and C. stricta was greatly decreased when grown with P. arundinacea. The rapid, initial height growth of P. arundinacea produced a spreading, horizontal canopy that overshadowed the vertical leaves of T. latifolia and C. stricta throughout the study. This pattern was repeated in both high and low nutrient and soil moisture treatments. When grown with P. arundinacea, C. stricta and T. latifolia significantly increased their mean shoot height, regardless of the nutrient or soil moisture level. The results of this experiment suggest that C. stricta and T. latifolia were light limited when growing with P. arundinacea and that canopy architecture is more important for biomass allocation than the other environmental conditions tested. The results also suggest that Phalaris arundinacea is an inherently better competitor (sensu Grime 1979) than C. stricta or T. latifolia.