A cure for the plague of parameters: constraining models of complex population dynamics with allometries

A major goal of ecology is to discover how dynamics and structure of multi-trophic ecological communities are related. This is difficult, because whole-community data are limited and typically comprise only a snapshot of a community instead of a time series of dynamics, and mathematical models of complex system dynamics have a large number of unmeasured parameters and therefore have been only tenuously related to real systems. These are related problems, because long time-series, if they were commonly available, would enable inference of parameters. The resulting ‘plague of parameters’ means most studies of multi-species population dynamics have been very theoretical. Dynamical models parametrized using physiological allometries may offer a partial cure for the plague of parameters, and these models are increasingly used in theoretical studies. However, physiological allometries cannot determine all parameters, and the models have also rarely been directly tested against data. We confronted a model of community dynamics with data from a lake community. Many important empirical patterns were reproducible as outcomes of dynamics, and were not reproducible when parameters did not follow physiological allometries. Results validate the usefulness, when parameters follow physiological allometries, of classic differential-equation models for understanding whole-community dynamics and the structure–dynamics relationship.     

Food quality for Eudiaptomus gracilis: the importance of particular highly unsaturated fatty acids

1. Development times and survival of nauplii and copepodites of the freshwater calanoid Eudiaptomus gracilis were measured on comparably sized Cryptomonas sp. and two strains of Chlamydomonas reinhardii under food saturated conditions (1 mg C L−1) to investigate the nutritional quality of these algae.
2.  Cryptomonas sp. supported complete ontogenesis of nauplii to adults, whereas both strains of C. reinhardii were inadequate for the development of nauplii and copepodites and resulted in high mortality. The nutritional deficiency of both strains of C. reinhardii was compensated for by Cryptomonas sp. when the latter constituted ≥50% of dietary carbon. Pulses of Cryptomonas sp. had a similar compensatory effect.
3. In comparison to Cryptomonas sp., both strains of C. reinhardii were deficient in the three highly unsaturated fatty acids (HUFAs) stearidonic, eicosapentaenoic and docosahexaenoic acid. We manipulated the fatty acid content of C. reinhardii by externally adding these three HUFAs to the alga so that the fatty acid profile resembled that of Cryptomonas sp. This supplementation did not improve food quality, however, indicating that the nutritional deficiency of both strains of C. reinhardii for the ontogenesis of E. gracilis is not due to a lack of these three HUFAs.     

Utilization of food resources by small and medium‐sized mammals in the Monte Desert biome,Argentina

Theoretical models of species coexistence between desert mammals have generally been based on a combination of food and microhabitat selection by granivorous rodents. Although these models are applicable in various deserts of the world, they cannot explain resource use by mammals in Neotropical deserts. The present study examines diet composition in a mammal assemblage in the Monte desert, Argentina. The results show that two main strategies are used by these mammals: medium‐sized species (hystricognath rodents: Dolichotis patagonum, Lagostomus maximus, Microcavia australis and Galea musteloides; and an exotic lagomorph: Lepus europaeus) are herbivores, whereas small‐sized species (a marsupial: Thylamys pusillus; and sigmodontine rodents: Graomys griseoflavus, Akodon molinae, Calomys musculinus, Eligmodontia typus) are omnivorous. Small mammals also show a tendency towards granivory (C. musculinus), insectivory (A. molinae and T. pusillus) and folivory (G. griseoflavus).     

Rechargeable Dual‐Ion Batteries with Graphite as a Cathode: Key Challenges and Opportunities

Rechargeable graphite dual‐ion batteries (GDIBs) have attracted the attention of electrochemists and material scientists in recent years due to their low cost and high‐performance metrics, such as high power density (≈3–175 kW kg^?1), energy efficiency (≈80–90%), long cycling life, and high energy density (up to 200 Wh kg^?1), suited for grid‐level stationary storage of electricity. The key feature of GDIBs is the exploitation of the reversible oxidation of the graphite network with concomitant and highly efficient intercalation/deintercalation of bulky anionic species between graphene layers. In this review, historical and current research aspects of GDIBs are discussed, along with key challenges in their development and practical deployment. Specific emphasis is given to the operational mechanism of GDIBs and to unbiased and correct reporting of theoretical cell‐level energy densities.     

Encapsulating Trogtalite CoSe2 Nanobuds into BCN Nanotubes as High Storage Capacity Sodium Ion Battery Anodes

Trogtalite CoSe₂ nanobuds encapsulated into boron and nitrogen codoped graphene (BCN) nanotubes (CoSe₂@BCN‐750) are synthesized via a concurrent thermal decomposition and selenization processes. The CoSe₂@BCN‐750 nanotubes deliver an excellent storage capacity of 580 mA h g^?1 at current density of 100 mA g^?1 at 100th cycle, as the anode of a sodium ion battery. The CoSe₂@BCN‐750 nanotubes exhibit a significant rate capability (100–2000 mA g^?1 current density) and high stability (almost 98% storage retention after 4000 cycles at large current density of 8000 mA g^?1). The reasons for these excellent storage properties are illuminated by theoretical calculations of the relevant models, and various possible Na⁺ ion storage sites are identified through first‐principles calculations. These results demonstrate that the insertion of heteroatoms, B–C, N–C as well as CoSe₂, into BCN tubes, enables the observed excellent adsorption energy of Na⁺ ions in high energy storage devices, which supports the experimental results.     

Lipid content of terrestrial arthropods in relation to body size,phylogeny, ontogeny and sex

Energy storage in arthropods has important implications for survival and reproduction. The lipid content of 276 species of adult arthropods with wet mass in the range 0.2–6.13 g is determined to assess how lipid mass scales with body mass. The relative contribution of lipids to total body mass is investigated with respect to phylogeny, ontogeny and sex. The lipid content of adult insects, arachnids, and arthropods in general shows an isometric scaling relationship with respect to body mass (M) (M_{arthropod lipid} = ?1.09 ×M_dry^1.01 and M_{arthropod lipid} = ?1.00 ×M_lean^0.98). However, lipid allocation varies between arthropod taxa, as well as with sex and developmental stage within arthropod taxa. Female insects and arachnids generally have higher lipid contents than males, and larval holometabolous insects and juvenile arachnids have higher lipid contents than adults.     

Rethinking trophic niches: Speed and body mass colimit prey space of mammalian predators

1. Realized trophic niches of predators are often characterized along a one‐dimensional range in predator–prey body mass ratios. This prey range is constrained by an “energy limit” and a “subdue limit” toward small and large prey, respectively. Besides these body mass ratios, maximum speed is an additional key component in most predator–prey interactions.
2. Here, we extend the concept of a one‐dimensional prey range to a two‐dimensional prey space by incorporating a hump‐shaped speed‐body mass relation. This new “speed limit” additionally constrains trophic niches of predators toward fast prey.
3. To test this concept of two‐dimensional prey spaces for different hunting strategies (pursuit, group, and ambush predation), we synthesized data on 63 terrestrial mammalian predator–prey interactions, their body masses, and maximum speeds.
4. We found that pursuit predators hunt smaller and slower prey, whereas group hunters focus on larger but mostly slower prey and ambushers are more flexible. Group hunters and ambushers have evolved different strategies to occupy a similar trophic niche that avoids competition with pursuit predators. Moreover, our concept suggests energetic optima of these hunting strategies along a body mass axis and thereby provides mechanistic explanations for why there are no small group hunters (referred to as “micro‐lions”) or mega‐carnivores (referred to as “mega‐cheetahs”).
5. Our results demonstrate that advancing the concept of prey ranges to prey spaces by adding the new dimension of speed will foster a new and mechanistic understanding of predator trophic niches and improve our predictions of predator–prey interactions, food web structure, and ecosystem functions.

     

Interacting forces of predation and fishing affect species’ maturation size

1. Fishing is a strong selective force and is supposed to select for earlier maturation at smaller body size. However, the extent to which fishing‐induced evolution is shaping ecosystems remains debated. This is in part because it is challenging to disentangle fishing from other selective forces (e.g., size‐structured predation and cannibalism) in complex ecosystems undergoing rapid change.
2. Changes in maturation size from fishing and predation have previously been explored with multi‐species physiologically structured models but assumed separation of ecological and evolutionary timescales. To assess the eco‐evolutionary impact of fishing and predation at the same timescale, we developed a stochastic physiologically size‐structured food‐web model, where new phenotypes are introduced randomly through time enabling dynamic simulation of species'' relative maturation sizes under different types of selection pressures.
3. Using the model, we carried out a fully factorial in silico experiment to assess how maturation size would change in the absence and presence of both fishing and predation (including cannibalism). We carried out ten replicate stochastic simulations exposed to all combinations of fishing and predation in a model community of nine interacting fish species ranging in their maximum sizes from 10 g to 100 kg. We visualized and statistically analyzed the results using linear models.
4. The effects of fishing on maturation size depended on whether or not predation was enabled and differed substantially across species. Fishing consistently reduced the maturation sizes of two largest species whether or not predation was enabled and this decrease was seen even at low fishing intensities (F = 0.2 per year). In contrast, the maturation sizes of the three smallest species evolved to become smaller through time but this happened regardless of the levels of predation or fishing. For the four medium‐size species, the effect of fishing was highly variable with more species showing significant and larger fishing effects in the presence of predation.
5. Ultimately our results suggest that the interactive effects of predation and fishing can have marked effects on species'' maturation sizes, but that, at least for the largest species, predation does not counterbalance the evolutionary effect of fishing. Our model also produced relative maturation sizes that are broadly consistent with empirical estimates for many fish species.

     

Relationship between postabsorptive respiratory exchange ratio and plasma free fatty acid concentrations

The relationship between overnight postabsorptive (fasting) respiratory exchange ratio (RER) and plasma FFA concentrations was addressed using data from three separate protocols, each of which involved careful control of the antecedent diet. Protocol 1 examined the relationship between fasting RER and the previous daytime RER. In Protocol 2 fasting, RER and plasma palmitate concentrations were measured in 29 women and 31 men (body mass index <30 kg·m⁻²). Protocol 3 analyzed data from Nielsen et al. (Nielsen, S., Z. K. Guo, J. B. Albu, S. Klein, P. C. O''Brien, M. D. Jensen. 2003. Energy expenditure, sex and endogenous fuel availability in humans. J. Clin. Invest. 111: 981-988.) to understand how fasting RER and palmitate concentrations relate within individuals during four consecutive measurements. The results were as follows: 1) Fasting RER was correlated (r = 0.74, P < 0.001) with the previous day''s average RER, and less so with RER variability. 2) Fasting RER was correlated (r = −0.39, P = 0.007) with fasting plasma palmitate concentrations. 3) The pattern of the RER/palmitate relationship was similar within individuals and between individuals; a negative slope was observed significantly more often than a positive slope (χ² test; P < 0.001). Our findings suggest that, despite a fixed food quotient, the slight departures from energy equilibrium in a controlled General Clinical Research Center environment can effect plasma FFA concentrations. We suggest that including indirect calorimetry as part of FFA metabolism studies may aid in data interpretation.     

Saturation and Utilization of Nitrate Pools in Pea and Sugar Beet Leaves

The critical periods in the saturation of pea and sugar beet leaves with nitrate absorbed by roots were discriminated. In peas, during the first 14 h, all nitrate penetrating leaf cells was concentrated in the cytosol (metabolic pool). During the second period (14–62 h), nitrate began to flow into the vacuole (storage pool), and the filling of the metabolic pool continued. Metabolic pool was saturated by the end of this period (62 h). During the third period (62–110 h), further nitrate accumulation in the cell occurred because of expanding of the storage pool. Its saturation (similarly as total cell saturation) commenced 86 h after the start of nitrate uptake. In sugar beet leaves, both metabolic and storage nitrate pools were saturated by the end of the first period (14 h), and the sizes of these pools did not change during the second period (14–86 h). When pea plants were transferred to the nitrate-free medium, nitrate efflux began from the storage pool until its complete exhausting after 3 days. In sugar beet leaves, nitrate was still present in the storage pool 4 days after plant transfer to the nitrate-free medium. In both crops, nitrate export from the storage pool was aimed at the maintenance of the optimum nitrate concentration in the metabolic pool and, thus, at the maintenance of nitrate reductase activity. A functional diversity of nitrate compartmentation in the cells of various plant species is discussed.