The energy–water nexus: are there tradeoffs between residential energy and water consumption in arid cities?

Water scarcity, energy consumption, and air temperature regulation are three critical resource and environmental challenges linked to urban population growth. While appliance efficiency continues to increase, today’s homes are larger and residents are using more energy-consuming devices. Recent research has often described the energy–water nexus as a “tradeoff” between energy and water due to reduced temperatures resulting from irrigated vegetation. Accordingly, some arid cities have implemented landscape-conversion programs that encourage homeowners to convert their yards from grass (mesic) to drought-tolerant (xeric) landscapes to help conserve water resources. We investigated these relationships in Phoenix, Arizona by examining energy and water data for the summer months of June–September 2005 while temperature variability was analyzed from a local heat wave. Results show parallel consumption patterns with energy and water use strongly correlated and newer homes using more of both. The counterintuitive findings show that “drought-resistant” models may not be beneficial for community health, environment, or economics and that this issue is further complicated by socio-economic variables.     

Modelling phosphorus efficiency within diverse dairy farming systems − pollutant and non-renewable resource?

Increased demand for protein rich nutrition and a limited land capacity combine to create a food supply issue which imposes greater dependence on phosphorus, required for yield maximization in crops for humans, and for animal feeds. To determine the technical and environmental efficiency of diverse milk production systems, this work evaluates the use of phosphorus (P), within confined, conventional grazing, and innovative dairy management regimes across two genetic merits of Holstein Friesian cows, by calculating annual farm gate P budgets and applying a series of common and novel data envelopment analysis (DEA) models. Efficiency results provide an insight into P effective dairy management systems as the DEA models consider P as an environmental pollutant as well as a non-renewable resource. We observe that dairy system efficiency differs, and can depend upon, model emphasis, whether it is the potential for losses to the environment, or the finite nature of P. DEA scores generated by pollutant focused models were wider ranging and, on average, higher for genetically improved animals within housed systems, consuming imported by-product feeds and exporting all manure. However, DEA models which considered P as a non-renewable resource presented a tighter range of efficiency scores across all management regimes and did not always favour cows of improved genetics. Divergent results arising from type of model applied generate questions concerning the importance of model emphasis and offer insight into the sustainability of P use within varied dairy systems.     

Fine root tradeoffs between nitrogen concentration and xylem vessel traits preclude unified whole‐plant resource strategies in Helianthus

Recent work suggests variation in plant growth strategies is governed by a tradeoff in resource acquisition and use, ranging from a rapid resource acquisition strategy to a resource‐conservative strategy. While evidence for this tradeoff has been found in leaves, knowledge of root trait strategies, and whether they reflect adaptive differentiation across environments, is limited. In the greenhouse, we investigated variation in fine root morphology (specific root length and tissue density), chemistry (nitrogen concentration and carbon:nitrogen), and anatomy (root cross‐sectional traits) in populations of 26 Helianthus species and sister Phoebanthus tenuifolius. We also compared root trait variation in this study with leaf trait variation previously reported in a parallel study of these populations. Root traits varied widely and exhibited little phylogenetic signal, suggesting high evolutionary lability. Specific root length and root tissue density were weakly negatively correlated, but neither was associated with root nitrogen, providing little support for a single axis of root trait covariation. Correlations between traits measured in the greenhouse and native site characteristics were generally weak, suggesting a variety of equally viable root trait combinations exist within and across environments. However, high root nitrogen was associated with lower xylem vessel number and cross‐sectional area, suggesting a tradeoff between nutrient investment and water transport capacity. This led to correlations between root and leaf traits that were not always consistent with an acquisition–conservation tradeoff at the whole‐plant level. Given that roots must balance acquisition of water and nutrients with functions like anchorage, exudation, and microbial symbioses, the varied evidence for root trait covariation likely reflects the complexity of interacting selection pressures belowground. Similarly, the lack of evidence for a single acquisition–conservation tradeoff at the whole‐plant level likely reflects the vastly different selection pressures shaping roots and leaves, and the resources they are optimized to obtain.     

Does the lack of root hairs alter root system architecture of Zea mays?

Plant and Soil - Root hairs are one root trait among many which enables plants to adapt to environmental conditions. How different traits are coordinated and whether some are mutually exclusive is...     

Is there an optimal root architecture for nitrate capture in leaching environments?

Little is known about root architectural attributes that aid the capture of nitrate from coarse-textured soil profiles of high leaching potential. In this study, a range of root architectures from the herringbone to the dichotomous structure were simulated, and their capacity to take up nitrate leaching through a sandy profile was recorded. All root systems had equal total volume at each point in time, and so were considered cost equivalent. These simulations showed that the root architecture likely to maximize nitrate capture from sandy soils (under the Mediterranean rainfall pattern experienced in Western Australia) is one that quickly produces a high density of roots in the top-soil early in the season, thereby reducing total nitrate leached with opening season rains, but also has vigorous taproot growth, enabling access to deep-stored water and leached nitrate later in the season. This is the first published, spatially explicit attempt to assess the ability of different root architectures equivalent in cost, to capture nitrate from a spatially and temporally heterogeneous soil environment.     

Interactions between extrafloral nectaries, aphids and ants: are there competition effects between plant and homopteran sugar sources?

Broad bean (Vicia faba), an annual plant bearing extrafloral nectaries (EFN) at the base of the upper leaves, is regularly infested by two aphid species, Aphis fabae and Acyrthosiphon pisum. EFN and A. fabae are commonly attended by the ant, Lasius niger, while Ac. pisum usually remains uninfested. Sugar concentration and sugar composition of extrafloral nectar did not change significantly after aphid infestation. The sugar concentration was significantly higher in EFN (c. 271 µg µl^-1) than in the honeydew of A. fabae (37.5 µg µl^-1). The presence of small A. fabae colonies had no significant effect on ant attendance of EFN, which remained at the same level as that on plants without A. fabae. Obviously, there was no significant competitive effect between the two sugar sources. We suggest that the high sugar concentration in the extrafloral nectar may outweigh the higher quality (due to the presence of melezitose) and quantity of aphid honeydew. Ants and the presence of EFN influenced aphid colony growth. While A. fabae colonies generally grew better in the presence of ants, Ac. pisum colonies declined on plants with EFN or A. fabae colonies. We conclude that EFN may provide some degree of protection for V. faba against those sucking herbivores that are not able to attract ants.     

Prey habitat selection under shared predation: tradeoffs between risk and competition?

An individual's choice of habitat should optimize amongst conflicting demands in a way that maximizes its fitness. Habitat selection by one species will often be influenced by presence and abundance of competitors that interact directly and indirectly with each other (such as through shared predators). The optimal habitat choice will thus depend on competition for resources by other species that can also modify predation risk. It may be possible to disentangle these two effects with careful analysis of density‐dependent habitat selection by a focal prey species. We tested this conjecture by calculating habitat isodars (graphs of density assuming ideal habitat selection) of chital deer living in two adjoining dry‐forest habitats in Gir National Park and Sanctuary, western India. The habitats differed only in presence (Sanctuary) and absence (National Park) of domestic prey (cattle and buffalo). Both species are preyed on by Asiatic lions. The habitat isodar revealed at low densities, that chital live in small groups and prefer habitat co‐occupied by livestock that reduce food resources, but also reduce predation risk. At higher densities, chital form larger groups and switch their preference toward risky habitat without livestock. The switch in chital habitat use is consistent with theories predicting that prey species should trade off safety in favor of food as population density increases.     

The architecture of termite mounds: a result of a trade-off between thermoregulation and gas exchange?

We examined the influence of gas exchange on the architectureof termitemounds. In Comoé National Park(Côted'Ivoire), Macrotermesbellicosus builds, as an adaptation toambient temperature conditions,differently shaped mounds inthe shrub savanna and the gallery forest.Previous studies suggestedthat there might be a constraint that limits thedegree of thermalinsulation of the interior (i.e., nest) of the mounds inenvironmentswith relatively low ambient temperatures. This factor causes,inproximate terms, suboptimal low nest temperatures and ultimatelyleads toreduced reproductive success in the gallery forest.In this study, we examinedwhether the necessity for gas exchangemight constrain mound architecture. Wemeasured CO₂ concentrationsin the air channels of mounds indifferent habitats and undermanipulated temperature regimes. During both thedry and therainy season we found higher CO₂ concentrations inmounds ofthe gallery forest than in mounds of the savanna. Additionalmeasurementsin forest mounds, architecturally resembling those of the savannadueto an experimental increase in ambient temperatures, revealedlowerCO₂ concentrations than unmanipulated mounds in this habitat.Generally,concentrations were higher during the rainy season comparedto thedry season and lower during day than during night. Summarizingthese resultswe present a model that illustrates this trade-offbetween thermoregulationand gas exchange under different temperatureregimes. Both factors togetherresult in different mound architecturesunder different environmentaltemperatures and may finally limitthe distribution of this species.     

Patterns of resource partitioning by nesting herons and ibis: How are odonata exploited?

Herons and ibis are colonially nesting waders which, owing to their number, mobility and trophic role as top predators, play a key role in aquatic ecosystems. They are also good biological models to investigate interspecific competition between sympatric species and predation; two processes which structure ecological communities. Odonata are also numerous, diverse, mobile and can play an important role in aquatic ecosystems by serving as prey for herons and ibis. A relationship between prey size and bird predator has been observed in Numidia wetlands (NE Algeria) after analyzing food boluses regurgitated by six species of birds (Purple Heron, Black-crowned Night Heron, Glossy Ibis, Little Egret, Squacco Heron and Cattle Egret) during the breeding period, which also shows a temporal gradient for the six species. Both the Levins index and preliminary multivariate analysis of the Odonata as prey fed to nestling herons and ibis, indicated a high degree of resource overlap. However, a distinction of prey based on taxonomy (suborder and family) and developmental stage (larvae or adults) reveals a clear size dichotomy with large-sized predators (Purple Heron, Black-crowned Night Heron and Glossy Ibis) preying on large preys like Aeshnids and Libellulids and small-sized predators feeding mainly on small prey like Zygoptera. Overall, the resource utilization suggests a pattern of resource segregation by coexisting nesting herons and ibis based on the timing of reproduction, prey types, prey size and foraging microhabitats.     

Comparative Modelling Techniques: Where are we?

The enormous increase in data availability brought about by genomic projects is paralleled by an equally unprecedented increase in the expectations for new medical, pharmacological, environmental and biotechnological discoveries. Whether or not we will be able to meet (at least partially) these expectations will depend on how well we will be able to interpret the data and translate the mono-dimensional information encrypted in genomes into a detailed understanding of its biological meaning at the phenotypic level. The process is far from being trivial, and the obstacles along the road are formidable: even the problem of identifying coding regions in eukaryotic genomes is not completely solved. Far more complex is identification of the function of the encoded proteins, and this will probably represent the most challenging problem for the next generations of scientists.     

Why are there so few evolutionary transitions between aquatic and terrestrial ecosystems?

Insects and flowering plants have rarely invaded the sea. Explanations for this have traditionally centered on the unique shortcomings of these groups in the marine environment. We show, however, that transitions among terrestrial, freshwater, and marine environments are infrequent in all major plant and animal clades except tetrapod vertebrates. In general, well-adapted incumbents are at a competitive advantage over would-be invaders from a physically different habitat. Data on the times and places of transition are consistent with our contention that evolutionary transitions among physically different environments are most likely when incumbents in the recipient environment exist in a regime of low-intensity competition and prcdation, as in terrestrial communities of the middle Paleozoic or the land biotas of oceanic islands. Freshwater environments, in which inferred intensities of predation are lower than in most marine and terrestrial environments, offer less biotic resistance to invaders than do communities in the sea or on land. Most invaders respond to novel physical circumstances by shutting down their metabolic machinery, and therefore add to their subordinate status as competitors with active incumbents. Only active tetrapods, particularly those with high and endothermically driven rates of metabolism, have successfully overcome this limitation.     

Mycelial paper: A potential resource recovery process?

Eleven species of fungi representative of a broad range of cell-wall compositions were evaluated with respect to their papermaking potential as additives to woodpulp furnishes. Some of these species were also examined for their ability to grow on a spent liquor from the pulp-and-paper industry. Handsheets with various levels of incorporated mycelia exhibited a wide range of species-dependent properties. Behavior of the mycelia in the sheets can be modified to a degree by physical and chemical treatments. The overall results suggest that small amounts (5–10% of the sheet constituents) of mycelia, grown inexpensively on waste effluents, might be incorporated into wood fiber paper without serious deleterious effects on paper strength properties. In some cases improved paper is obtained, and larger quantities of mycelia might be used to impart specific properties to the product.     

Moritella cold-active dihydrofolate reductase: are there natural limits to optimization of catalytic efficiency at low temperature?

Adapting metabolic enzymes of microorganisms to low temperature environments may require a difficult compromise between velocity and affinity. We have investigated catalytic efficiency in a key metabolic enzyme (dihydrofolate reductase) of Moritella profunda sp. nov., a strictly psychrophilic bacterium with a maximal growth rate at 2 degrees C or less. The enzyme is monomeric (Mr=18,291), 55% identical to its Escherichia coli counterpart, and displays Tm and denaturation enthalpy changes much lower than E. coli and Thermotoga maritima homologues. Its stability curve indicates a maximum stability above the temperature range of the organism, and predicts cold denaturation below 0 degrees C. At mesophilic temperatures the apparent Km value for dihydrofolate is 50- to 80-fold higher than for E. coli, Lactobacillus casei, and T. maritima dihydrofolate reductases, whereas the apparent Km value for NADPH, though higher, remains in the same order of magnitude. At 5 degrees C these values are not significantly modified. The enzyme is also much less sensitive than its E. coli counterpart to the inhibitors methotrexate and trimethoprim. The catalytic efficiency (kcat/Km) with respect to dihydrofolate is thus much lower than in the other three bacteria. The higher affinity for NADPH could have been maintained by selection since NADPH assists the release of the product tetrahydrofolate. Dihydrofolate reductase adaptation to low temperature thus appears to have entailed a pronounced trade-off between affinity and catalytic velocity. The kinetic features of this psychrophilic protein suggest that enzyme adaptation to low temperature may be constrained by natural limits to optimization of catalytic efficiency.     

How many species are there in apple insect communities?: testing the resource diversity and intermediate disturbance hypotheses

Abstract.

• 1 In European and American apple orchards the insect species richness, calculated from our own, and published data, varied widely (30–940 species). The dominance of insect orders was similar to that found in natural communities.
• 2 To test the predictions of the‘resource diversity hypothesis’(RDH) and the‘intermediate disturbance hypothesis’(IDH) of insect diversity, we analysed the simultaneous impact of vegetational diversity and intensity of orchard management practice on the species richness of characteristic insect categories in six types of apple stands, over 5 years, in Hungary.
• 3 The more diverse was the vegetation adjacent to the orchard and the less intensively was the orchard managed, the greater was the total insect species richness, supporting both hypotheses.
• 4 The number of agricultural pest species found in the apple orchards depended above all on the diversity of adjacent agricultural vegetation, supporting only the RDH.
• 5 The species richness of specialized apple pests was limited only by the intensity of pest control, supporting only the IDH.
• 6 Within the category of generalist natural enemies species richness mainly varied with the diversity of adjacent vegetation, supporting the RDH.
• 7 The aeroentomofauna constituted a surprisingly high percentage (>50%) for both total species and agricultural pests, but was poorly represented within the natural enemies category, and absent from the specific apple pest category.
• 8 A general conclusion is that the number of insect species in perennial orchard-systems within agricultural areas is determined primarily by the regional extra-orchard vegetational diversity and secondly by the degree of local intra-orchard disturbances and plant diversity. Consequently, at the community level the predictions of both hypotheses can be simultaneously valid at different spatial scales and are not mutually exclusive. However, within the community, at the level of the different insect categories studied here, only one of the hypotheses proved to be valid.