Does Bertrand's rule apply to macronutrients?

It has been known for over a century that the dose-response curve for many micronutrients is non-monotonic, having an initial stage of increasing benefits with increased intake, followed by increasing costs as excesses become toxic. This phenomenon, termed Bertrand's rule, is widely assumed not to apply to caloric macronutrients. To date this assumption has been safe, owing to the considerable methodological challenges involved in coaxing animals to over-ingest macronutrients in a way that enables the effects of specific food components to be isolated. Here we report an experiment which overcomes these difficulties, to test whether the second phase (incurring costs with excessive intake) applies to carbohydrate intake by the generalist-feeding caterpillar Spodoptera littoralis. The results showed that excess carbohydrate intake caused increased mortality, thus extending Bertrand's rule to macronutrients.     

How does the 50/500 rule apply to MVPs?

The 50/500 rule has been used as a guiding principle in conservation for assessing minimum viable effective population size (N(e)). There is much confusion in the recent literature about how the 500 value should be applied to assess extinction risk and set priorities in conservation biology. Here, we argue that the confusion arises when the genetic basis for a short-term N(e) of 50 to avoid inbreeding depression is used to justify a long-term N(e) of 500 to maintain evolutionary potential. This confusion can result in misleading conclusions about how genetic arguments alone are sufficient to set minimum viable population (MVP) thresholds for assessing the extinction risk of threatened species, especially those that emphasize that MVPs should be in the thousands to maintain evolutionary potential.     

Does the hygiene hypothesis apply to COVID-19 susceptibility?

In this commentary we argue that the hygiene hypothesis may apply to COVID-19 susceptibility and also that residence in low hygienic conditions acts to train innate immune defenses to minimize the severity of infection. We advocate that approaches, which elevate innate immune functions, should be used to minimize the consequences of COVID-19 infection at least until effective vaccines and antiviral therapies are developed.     

Does the Animal Welfare Act apply to free-ranging animals?

Despite the long-standing role that institutional animal care and use committees (IACUCs) have played in reviewing and approving studies at academic institutions, compliance with the Animal Welfare Act (AWA) is not always complete for government natural resource agencies that use free-ranging animals in research and management studies. Even at universities, IACUCs face uncertainties about what activities are covered and about how to judge proposed research on free-ranging animals. One reason for much of the confusion is the AWA vaguely worded exemption for "field studies." In particular, fish are problematic because of the AWA exclusion of poikilothermic animals. However, most university IACUCs review studies on all animals, and the Interagency Research Animal Committee (IRAC) has published the "IRAC Principles," which extend coverage to all vertebrates used by federal researchers. Despite this extended coverage, many scientists working on wild animals continue to view compliance with the AWA with little enthusiasm. IACUCs, IACUC veterinarians, wildlife veterinarians, and fish and wildlife biologists must learn to work together to comply with the law and to protect the privilege of using free-ranging animals in research.     

Are arctic soft-sediment macrobenthic communities impoverished?

 Samples of the macrobenthic fauna of soft sediments were collected from around Svalbard during the 1991 Arctic EPOS cruise of RVPolarstern. Although faunal variability could be related to sediment granulometry and depth, all stations to the south and east of the Archipelago lay within the broadly defined central Barents Sea community. In this community, α-diversity was variable and sampled between 77 and 337 m showed no clear relationship to depth. Diversity in the area close to the polar front was notably high, rarefaction predicting that 43±5.5 species might occur in a sample of 201 individuals. k-Dominance plots suggested that muddy sand communities around Svalbard were no less diverse than similar assemblages in the North Sea. Received: 27 March 1995/Accepted: 30 July 1995     

Does universal temperature dependence apply to communities? An experimental test using natural marine plankton assemblages

The metabolic theory of ecology (MTE) is an intriguing but controversial theory that tries to explain ecological patterns at all scales on the basis of first principles. Temperature plays a pivotal role in this theory. According to MTE, the Arrhenius relationship that describes the effect of temperature on biochemical reactions extends to a 'universal temperature dependence' that encompasses all kinds of processes and scales up to the cellular, the organismal, and the community level. In this study we test the prediction that community growth rate is temperature dependent in an Arrhenius-like way. First, we performed a literature review of the scanty data on the temperature dependence of the rates of metabolism, photosynthesis and growth of communities. In contrast to the predictions of MTE, the community activation energies did not cluster around 0.32 eV, the activation energy of photosynthesis and primary production or around 0.65 eV, the activation energy of metabolism. However, in none of the published studies the conditions were sufficiently controlled to allow firm conclusions. We therefore also performed replicated and controlled experiments using natural assemblages of marine plankton. As predicted by MTE, the maximal growth rates of community biomass increased linearly in an Arrhenius plot, with a slope close to 0.32 eV. However, a diversity of other models for the temperature dependence of community growth rates fit our data equally well. Hence, our results are at best a weak confirmation of MTE.     

Does Liebig's law of the minimum scale up from species to communities?

Liebig's law of the minimum, which states that only one element limits the growth of organisms at any given time, is widely used in ecology. This principle is routinely applied to organisms, populations and communities, but can it really be applied indistinguishably across these different scales? Here we show, by prediction of a resource ratio conceptual model and with an experimental test carried out in microcosms with bacteria that, unlike single species, communities are likely to adjust their stoichiometry to that of their resources. This adjustment results from competitive exclusion and coexistence mechanisms, and is sensitive to the overall diversity of species in the community. It guaranties co‐limitation, i.e. simultaneous limitation by multiple resources, at the community scale and optimal use of resources and maximization of community biomass for wide ranges of resource ratios. These results question the applicability of the Liebig's law of the minimum at the community level, and the relevance of ecosystem models relying on this principle.     

Disease mutations in disordered regions--exception to the rule?

Intrinsically disordered proteins (IDPs) have been implicated in a number of human diseases, including cancer, diabetes, neurodegenerative and cardiovascular disorders. Although for some of these conditions molecular mechanisms are now better understood, the big picture connecting distinct structural properties and functional repertoire of IDPs to pathogenesis and disease progression is still incomplete. Recent studies suggest that signaling and regulatory roles carried out by IDPs require them to be tightly regulated, and that altered IDP abundance may lead to disease. Here, we propose another link between IDPs and disease that takes into account disease-associated missense mutations located in the intrinsically disordered regions. We argue that such mutations are more prevalent and have larger functional impact than previously thought. In addition, we demonstrate that deleterious amino acid substitutions that cause disorder-to-order transitions are particularly enriched among disease mutations compared to neutral polymorphisms. Finally, we discuss potential differences in functional outcomes between disease mutations in ordered and disordered regions, and challenge the conventional structure-centric view of missense mutations.     

Does Pseudomonas aeruginosa use intercellular signalling to build biofilm communities?

Pseudomonas aeruginosa is a Gram-negative bacterial species that causes several opportunistic human infections. This organism is also found in the environment, where it is renowned (like other Pseudomonads) for its ability to use a wide variety of compounds as carbon and energy sources. It is a model species for studying group-related behaviour in bacteria. Two types of group behaviour it engages in are intercellular signalling, or quorum sensing, and the formation of surface-associated communities called biofilms. Both quorum sensing and biofilm formation are important in the pathogenesis of P. aeruginosa infections. Quorum sensing regulates the expression of several secreted virulence factors and quorum sensing mutant strains are attenuated for virulence in animal models. Biofilms have been implicated in chronic infections. Two examples are the chronic lung infections afflicting people suffering from cystic fibrosis and colonization of indwelling medical devices. This review will discuss quorum sensing and biofilm formation and studies that link these two processes.     

Evolution of body size in food webs: does the energetic equivalence rule hold?

The energetic equivalence rule (EER), which is derived from empirical observations linking population density and body size and from the allometric law linking metabolism and body size, predicts that the amount of energy used by the various species should be independent of body size. Here, we examine this hypothesis using a model that allows entire food webs to emerge from coevolution of interacting species. Body size influences both individual metabolism and interactions among species in the model. Overall, population density does decrease with body size roughly following a power law whose exponent is variable. We discuss this variability in the light of empirical data sets. The emerging relationship between the flux of resources exploited by the various species and their body size follows a decreasing power law, thus contradicting the EER. Our model emphasizes the importance of considering the influence of body size on species interactions in attempting to explain large-scale patterns related to body size.     

Does the universality of the species–area relationship apply to smaller scales and across taxonomic groups?

The universality of the shape of the species–area relationship (SAR) is subject to regular debate. Recently, Storch et al. (2012) argued that species–area relationships collapse into a single curve at continental scales after the axes are rescaled adjusting the area‐axis being to the mean range size of species and the species‐axis to the species richness of an area equal to mean range size. It has been claimed that this rescaling generates a universal model, invariant of taxon and continent, and that it is driven by differences in range sizes. Here, we test the universality of the rescaled SAR across scales smaller than the continental level, using presence data for plants, birds and butterflies. We also test an alternative rescaling approach, by using the total extent of the study area and total species richness. At the scales analysed here, we found that the proposed rescaling by Storch et al. adjusts for differences in the extent of the study area and for variation in gamma diversity. Consequently, while the rescaled curves were closely aligned, they did not converge into a single curve. The observed remaining variation is independent of scale and biogeographical region, and is correlated with beta diversity; thus, it reflects the differentiation of species composition in space.     

Does an extreme drought event alter the response of grassland communities to a changing climate?

Global temperatures and atmospheric CO₂ concentrations are expected to both increase, but their combined effect on plant communities has been far less investigated than the single factors of global change. Moreover, drought events are expected to become more frequent and intense in the near future what might alter plant responses to the changing climate.In this study synthesised grassland communities in a current or future climate were subjected to several drought levels (0, 15, 22 and 35 days of drought). The grassland communities were grown in six sunlit, climate-controlled chambers. Three of the chambers were exposed to ambient temperature and CO₂ (current climate), while the other three were continuously warmed 3 °C above ambient temperature at 620 ppm of CO₂ (future climate).The aim of this study was to investigate the effect of drought on the response of grassland communities to a future climate. Therefore, the response to future climate was observed (1) in the absence of drought and (2) in the occurrence of an extreme drought event, both early and late in the growing season.

• (1)In the absence of drought, plant productivity was positively affected by future climate early in the growing season. Later in the growing season this effect tended to turn negative, resulting in a disappearance of the overall effect of climate at the end of the growing season.
• (2)During drought there was a stronger decrease in net CO₂ assimilation rate (A_sat) in future than in current climate due to stronger stomatal closure. Consistently, the beneficial biomass response to future climate stagnated during drought. At the end of the season, after a period of recovery, there was no effect of climate on plant productivity. As in the absence of drought, plant productivity was not affected by climate at the end of the growing season. Hence, the occurrence of an extreme drought event during the growing season did not alter the overall response of plant productivity to a future climate.

     

Does long-term fertilization treatment affect the response of soil ammonia-oxidizing bacterial communities to Zn contamination?

Experiments were conducted to examine the effects of long-term fertilization and acute Zn toxicity on the size, nitrification activity and community structure of autotrophic ammonia-oxidizing populations of the β-subgroup of the class Proteobacteria in arable soils. Plots under different long-term fertilization regimes were sampled, and then different concentrations of ZnCl₂ were spiked into soil samples for 8 weeks. It was found that long-term fertilization significantly increased nitrification rates and population size, and there was a positive correlation between them. A shift in the composition of AOB was also detected in samples fertilized with mineral N fertilizer (NPK) and organic matter (OM) as compared to unfertilized sample. EC50 values suggested that there was no significant difference in Zn toxicity to nitrification rates among the three fertilization treatments. Long-term fertilization did not improve the resilience of AOB activity to Zn toxicity.     

Spatial and temporal patterns of intertidal macrobenthic populations in the Oosterschelde: are they influenced by the construction of the storm-surge barrier?

The construction of a storm-surge barrier in the mouth of the Oosterschelde caused important hydrodynamical and morphological changes that could influence the macrobenthic populations. This paper is one in a series of five all dealing with the effects of the storm-surge barrier on macrozoobenthos and analyses the spatial and temporal distribution of macrozoobenthos in the Oosterschelde and its relationship with some environmental parameters, based on two large scale sampling campaigns, one before and one after the completion of the barrier.The sediment of the sampling stations was fine, well sorted sand, with an average mud content of about 2.5 %. Only in the Krabbenkreek the sediment was coarser in 1989. The tidal elevation of the sampling sites decreased significantly in 1989.The density of macrozoobenthos was significantly lower, the biomass higher in 1989. The density was dominated by deposit feeders, the biomass by filter feeders. The difference in biomass between both years was mainly due to a substantial increase of the biomass of filter feeders in 1989. The number of species per station was significantly smaller in 1989 than in 1985. Between 1985 and 1989, frequency of occurrence decreased in 34 versus 13 which increased, density increased in 13 species and decreased in 34 species, biomass increased in 18 species and decreased in 29 species.Based on TWINSPAN several clusters of stations, each with a different faunal composition, were identified. These clusters did not form distinct zones on the tidal flats but were dispersed widely.The relationship between density and biomass of different trophic groups and the mud content of the sediment and the depth was analysed. This relationship sometimes differed clearly between years. The correlation coefficient of a multiple regression between density and biomass of individual species and environmental factors, although significant in most cases, was very low, indicating that only a small proportion of the species variability was explained. The relationship between benthos and environmental factors was further analysed by canonical correlation analysis and multivariate discriminant analysis that gave different results for the 1985 and 1989 data. This is probably due to the broad tolerance of the species to the range of the environmental variables found in our study area. From a TWINSPAN of the density data of 1985 and 1989 together we could conclude that, although the environmental parameters in a group of stations, showing a large faunal similarity in one year, did not change, the faunal composition did. This indicates that faunal changes are not necessarily linked to changes in the measured environmental parameters.In the discussion the different factors affecting macrobenthic populations are situated and it is suggested that the macrobenthic populations are probably more towards the nonequilibrium end of the continuum between nonequilibrium and equilibrium communities as defined by Wiens (1984).Although the impact of the construction of the barrier on the macrobenthic community seems at present to be rather small this does not mean that on the long-term there will be no effect.     

Why apply ecological laws to epidemiology?

Using ecological laws, or rules, is a useful strategy for epidemiological observations. The application of Taylor's power law to epidemiology and evolutionary ecology of parasites is exemplified here. Taylor's power law takes the form of s2=amb, where s2 is the variance in population abundance, m is the mean abundance of the population, a represents a constant parameter and b represents an index of spatial heterogeneity. Although Taylor's power law reflects the aggregation of parasite (or pathogen) individuals among host population, the values of b could reflect regulation processes in host-parasite systems. Illustrations are given showing how b value is linked to various epidemiological situations: pathogen emergence, the impact of vaccination or the level of host immune defence.     

Does proximity to mature trees influence ectomycorrhizal fungus communities of Douglas-fir seedlings?

The influence of mature trees on colonization of Douglas-fir (Pseudotsuga menziesii) seedlings by ectomycorrhizal fungi (EMF) is not well understood. Here, the EMF communities of seedlings planted near and far from trees are compared with each other, with EMF of seedlings potted in field soils and with EMF of mature trees. Seedlings were planted within 6 m, or beyond 16 m, from residual Douglas-fir trees in recently harvested green-tree retention units in Washington State, USA, or potted in soils gathered from near each residual tree. Mature tree roots were sampled by partly excavating the root system. The EMF communities were assessed by polymerase chain reaction-restriction fragment length polymorphism and sequence analysis of ribosomal RNA genes. Seedlings near trees had higher species richness and diversity of EMF communities compared with seedlings far from trees. The EMF communities of seedlings near trees were more similar to those of mature trees, while seedlings far from trees were more similar to glasshouse seedlings. By enhancing the EMF diversity of seedlings, residual trees may maintain or accelerate the re-establishment of mycorrhizal communities associated with mature forests.