Low-productivity Environments Research Articles

Putting plant resistance traits on the map: a test of the idea that plants are better defended at lower latitudes

• It has long been believed that plant species from the tropics have higher levels of traits associated with resistance to herbivores than do species from higher latitudes. A meta-analysis recently showed that the published literature does not support this theory. However, the idea has never been tested using data gathered with consistent methods from a wide range of latitudes. • We quantified the relationship between latitude and a broad range of chemical and physical traits across 301 species from 75 sites world-wide. • Six putative resistance traits, including tannins, the concentration of lipids (an indicator of oils, waxes and resins), and leaf toughness were greater in high-latitude species. Six traits, including cyanide production and the presence of spines, were unrelated to latitude. Only ash content (an indicator of inorganic substances such as calcium oxalates and phytoliths) and the properties of species with delayed greening were higher in the tropics. • Our results do not support the hypothesis that tropical plants have higher levels of resistance traits than do plants from higher latitudes. If anything, plants have higher resistance toward the poles. The greater resistance traits of high-latitude species might be explained by the greater cost of losing a given amount of leaf tissue in low-productivity environments.

Progress in Synthesis and Application of Polyhydroxyl Terephthalic Acid

The applications of polyhydroxyl terephthalic acids in medicines and functional materials have captured much research attentions.This article reviews the synthesis and application of four typical chemicals with utmost importance and value.The preparation process of polyhydroxyl terephthalic acid substances through Koble-Schmitt reaction with phenol-type substances as starting materials has advantages such as simple operation,low production cost and environment benign,and so on.

Antagonistic coevolution across productivity gradients: an experimental test of the effects of dispersal

Coevolution commonly occurs in spatially heterogeneous environments, resulting in variable selection pressures acting on coevolving species. Dispersal across such environments is predicted to have a major impact on local coevolutionary dynamics. Here, we address how co-dispersal of coevolving populations of host and parasite across an environmental productivity gradient affected coevolution in experimental populations of bacteria and their parasitic viruses (phages). The rate of coevolution between bacteria and phages was greater in high-productivity environments. High-productivity immigrants ( approximately 2% of the recipient population) caused coevolutionary dynamics (rates of coevolution and degree of generalist evolution) in low-productivity environments to be largely indistinguishable from high-productivity environments, whereas immigration from low-productivity environments ( approximately 0.5% of the population) had no discernable impact. These results could not be explained by demography alone, but rather high-productivity immigrants had a selective advantage in low-productivity environments, but not vice versa. Coevolutionary interactions in high-productivity environments are therefore likely to have a disproportionate impact on coevolution across the landscape as a whole.

Modelling and integration of customer flexibility in the order commitment process for high mix low volume production

With increasing product variety and dynamic demand fluctuation, manufacturing industry is moving towards a high product mix and low order volume production environment. Consequently, the order commitment process is becoming one of the most important processes for manufacturing firms to meet individual customer's needs with limited resources. However, demands for shortened delivery lead time, diverse customer requirements and more frequent customer orders have made the order commitment task more challenging. This paper attempts to tackle these new challenges by incorporating not only manufacturing flexibility but also flexibility from the demand side. Customer flexibility is characterised by customer indifference to certain product attributes and/or delivery schedules. Intuitively, with the consideration of customer flexibility, both manufacturers’ and customers’ interests can be better served since the solution space of matching demand and supply can be extended beyond the traditional domain purely from a manufacturing perspective. To this end, a systematic approach is developed to characterise and model customer flexibility. A mixed-integer-programming model is formulated to provide optimal order commitment decisions.

Abrupt climate change, sea surface salinity and paleoproductivity in the western Mediterranean Sea (Gulf of Lion) during the last 28 kyr

The planktonic foraminiferal record of core MD99-2346 (Gulf of Lion) shows a decrease of sea surface temperature (SST) at the time of Heinrich event H2 (24–23.5 cal kyr BP), Younger Dryas and during the early to middle Holocene. These events were associated with a decrease of surface water salinity. The salinity lowering events were similar and synchronous to those recorded in the North Atlantic Ocean during H1, H2 and the Younger Dryas. They can be explained by a decrease in the salinity of the Atlantic surface water entering the Mediterranean through the Strait of Gibraltar. This result indicates that the Mediterranean Sea remained a concentration basin and that its freshwater budget was not significantly different from the modern conditions at the time of these low salinity events. Higher abundances of the benthic foraminifer Cibicidoides pachydermus at the time of Heinrich events (H2 and H1) may result from a seasonal, and more pulsed supply of labile organic matter. A high abundance of intermediate and deep infaunal taxa ( Globobulimina spp.) during the warm Bölling/Alleröd period is interpreted as a result of an increased lateral advection of organic matter to the deeper environments of the Gulf of Lion. Surface water productivity, as reflected by the organic flux to the benthic ecosystem, reaches a maximum during the cold Younger Dryas period. It is possible that cold conditions at the time of the Younger Dryas have allowed an enhanced vertical mixing and deep-water cascading in the Gulf of Lion. This may have resulted in an increase of primary and export production. This putative intensification of deep-water cascading would have occurred after the sustained rise of the global sea-level from 16 to 12.5 cal kyr BP. The deglacial sea-level rise may also have played an important role in favouring the downslope movement of dense shelf water enriched in organic matter originating from the early Rhône delta complex. The conditions during the Holocene were characterized by a low surface productivity and oligotrophic environment similar to the modern situation.

Range‐wide reproductive consequences of ocean climate variability for the seabird Cassin's Auklet

We examine how ocean climate variability influences the reproductive phenology and demography of the seabird Cassin's Auklet (Ptychoramphus aleuticus) across approximately 2500 km of its breeding range in the oceanographically dynamic California Current System along the west coast of North America. Specifically, we determine the extent to which ocean climate conditions and Cassin's Auklet timing of breeding and breeding success covary across populations in British Columbia, central California, and northern Mexico over six years (2000-2005) and test whether auklet timing of breeding and breeding success are similarly related to local and large-scale ocean climate indices across populations. Local ocean foraging environments ranged from seasonally variable, high-productivity environments in the north to aseasonal, low-productivity environments to the south, but covaried similarly due to the synchronizing effects of large-scale climate processes. Auklet timing of breeding in the southern population did not covary with populations to the north and was not significantly related to local oceanographic conditions, in contrast to northern populations, where timing of breeding appears to be influenced by oceanographic cues that signal peaks in prey availability. Annual breeding success covaried similarly across populations and was consistently related to local ocean climate conditions across this system. Overall, local ocean climate indices, particularly sea surface height, better explained timing of breeding and breeding success than a large-scale climate index by better representing heterogeneity in physical processes important to auklets and their prey. The significant, consistent relationships we detected between Cassin's Auklet breeding success and ocean climate conditions across widely spaced populations indicate that Cassin's Auklets are susceptible to climate change across the California Current System, especially by the strengthening of climate processes that synchronize oceanographic conditions. Auklet populations in the northern and central regions of this ecosystem may be more sensitive to changes in the timing and variability of ocean climate conditions since they appear to time breeding to take advantage of seasonal productivity peaks.

The grazing impact of microzooplankton off south west Western Australia: as measured by the dilution technique

Grazing rates of microzooplankton feeding on picophytoplankton (Flow-cytometry) and total phytoplankton (Chlorophyll a) were measured in the eastern Indian Ocean off south west Western Australia from February 2003 to December 2004. Three sites representing different oceanographic habitats, the coastal lagoon, the outer shelf and the continental slope (1000 m) were sampled. The dilution method of Landry and Hassett (1982, Estimating the grazing impact of marine micro-zooplankton. Mar. Biol., 67, 283–288) was used and analysed by chlorophyll a analysis and flow-cytometry. During summer, the apparent growth rate of total phytoplankton exceeded loss due to microzooplankton grazing in the lagoon and at the outer shelf. On the slope, the phytoplankton assemblage was always dominated by small cells (<5 μm). Although their apparent growth rates were also higher in summer, these were matched by increasing microzooplankton grazing rates. Saturated feeding responses at the outer shelf and slope stations during summer were detected. In this low prey, low productivity environment, this response is either a new type of threshold feeding or an artefact of the dilution method which would result in an over-estimate of both phytoplankton growth and microzooplankton grazing.

Hydromechanical Deep Drawing of Funerary Vases: A Suitable Alternative to the Traditional Forming Processes

In the present paper a feasibility study of a funerary vase, made of stainless steel, using the Hydromechanical Deep Drawing process, is presented. The component is currently made of bronze and manufactured by die casting technology in a low volume production environment. To investigate the part feasibility, several FE simulations were implemented using the Aquadraw tool of the explicit FE code Pam Stamp 2G 2005®. The FE simulations showed that HDD process can produce the part in one single step without the requirement of finishing operations such as painting or polishing. Furthermore experimental tests were conducted and the first prototypes were successfully produced.

Technology Update: Practical Application of Intelligent Technology in Low-Production Environments

Until recently, implementing intelligent-completion (IC) technology to optimize hydrocarbon production in land-based or shallow water, low-production environments has been economically prohibitive because of the cost of the required equipment compared to its return on investment. Alternatives now exist for reduced capital investment and operating costs, enabling operators to re-evaluate the economic feasibility of IC deployment in mature fields, large fields requiring pressure maintenance, secondary-/tertiary-recovery schemes, and multilayered fields. Approaches for moderate-return environments include an introductory-level option for ICs launched by WellDynamics that incorporates streamlined designs and the use of standard metallurgy. Proprietary SmartWell MC completion technology focuses on the ability to improve management of the recovery methods associated with enhanced oil recovery (EOR), providing real-time monitoring as well as zonal isolation and subsurface flow control in both vertical and horizontal well configurations. The use of this technology in EOR projects offers several benefits that promote enhanced recovery and improved economics, including enhanced recovery of individual layers through commingled production, improved pressure maintenance, controlled drawdown and fluid production from individual zones, and superior management of water cut. Open/close and choking versions of hydraulically actuated interval-control valves (ICVs) in a range of sizes, production and zonal-isolation packers, and modular gauge packages make up the MC line of technologies. The MC2 open/close ICV enables isolation of individual reservoir zones while the MCC ICV enables operators to choke or regulate injection/production by adjusting the valve through multiple incremental positions. Both MC ICVs accommodate a flow rate that exceeds 3,000 BOPD or 5 MMscf/D of gas and are equipped with corrosion-resistant coatings for downhole endurance. The valves can be used with either an automated or a manual control system to meet specific operational requirements. The MC production packer is a single-string, retrievable production packer rated at 5,000 psi for cased hole. The slipless MC isolation packer allows perforated intervals to be segregated in cased hole below a production packer, where tubing loads and pressure differentials are moderate. Eight control lines can be fed through each of the packers. Pressure and temperature-sensing capabilities supplement the MC series. These sensor packages are modular in construction, allowing for adaptation to a multitude of tubing sizes, without altering the primary packaging configuration. Application in Swan Hills EOR Project SmartWell MC products were installed by Devon Energy in a miscible-solvent injection well within the Swan Hills Unit No. 1 oil field, located in north-central Alberta, approximately 120 miles from Edmonton. Devon has been the operator through almost all of the field's life and has taken it through primary, secondary, and tertiary recovery. The chief motivating factors for installing the equipment in this development were the opportunities to reduce well intervention and to accelerate the injection schedule associated with a single well. Considerable workover activity to manage the injection profile had already occurred in the trial well, which was judged to be a particularly risky workover candidate because of issues associated with corrosion, injection debris, and risks to cement integrity caused by frequent acid stimulation.

Genotype‐by‐environment interactions leads to variable selection on life‐history strategy in Common Evening Primrose (Oenothera biennis)

Monocarpic plant species, where reproduction is fatal, frequently exhibit variation in the length of their prereproductive period prior to flowering. If this life-history variation in flowering strategy has a genetic basis, genotype-by-environment interactions (G x E) may maintain phenotypic diversity in flowering strategy. The native monocarpic plant Common Evening Primrose (Oenothera biennis L., Onagraceae) exhibits phenotypic variation for annual vs. biennial flowering strategies. I tested whether there was a genetic basis to variation in flowering strategy in O. biennis, and whether environmental variation causes G x E that imposes variable selection on flowering strategy. In a field experiment, I randomized more than 900 plants from 14 clonal families (genotypes) into five distinct habitats that represented a natural productivity gradient. G x E strongly affected the lifetime fruit production of O. biennis, with the rank-order in relative fitness of genotypes changing substantially between habitats. I detected genetic variation in annual vs. biennial strategies in most habitats, as well as a G x E effect on flowering strategy. This variation in flowering strategy was correlated with genetic variation in relative fitness, and phenotypic and genotypic selection analyses revealed that environmental variation resulted in variable directional selection on annual vs. biennial strategies. Specifically, a biennial strategy was favoured in moderately productive environments, whereas an annual strategy was favoured in low-productivity environments. These results highlight the importance of variable selection for the maintenance of genetic variation in the life-history strategy of a monocarpic plant.

Genetic and phenotypic parameters of body weight in West African Dwarf goat and Djallonké sheep

The International Trypanotolerance Centre's small ruminant breeding programme was initiated in 1995. The aim was to increase the efficiency of meat production and the trypanotolerance of the animals (sheep and goat). To achieve that goal, selection was based on estimated breeding values for daily weight gain from 4 to 12 months of age measured on trypanotolerance challenge. The purpose of this study was to estimate genetic parameters for growth traits and to evaluate genetic trends in West African Dwarf goat and Djallonké sheep resulting from the breeding programme under a low input production environment. Data for West African Dwarf goat and Djallonké sheep included birth weight (BW), weaning weight (W120), yearling weight (W360), pre-weaning (GR0–4) and post-weaning (GR4–12) growth rate. The data were analysed using an animal model that accounted for fixed effects of sex, year of birth, season of birth, parity of the dam, type of birth and the interaction year by season of birth. Estimates of heritability for BW, W120, W360, GR0–4 and GR4–12 were 0.5, 0.43, 0.30, 0.32 and 0.11 for goats and 0.39, 0.54, 0.21, 0.54 and 0.23 for sheep, respectively. The genetic correlation between BW and W120 was high for goats (0.74) and moderate for sheep (0.47). Genetic correlations between W120 and GR4–12 were high (0.92) for goats and moderate (0.49) for sheep. Between GR0–4 and BW the correlation was positive but low for sheep (0.26) and moderate for goats (0.60). Positive trends were found in mean estimated breeding values for animals born in the period 1995–2002 which demonstrated the effectiveness of the implemented breeding programs.

Reproductive Allocation of Biomass and Nitrogen in Annual and Perennial Lesquerella Crops

The use of perennial crops could contribute to increase agricultural sustainability. However, almost all of the major grain crops are herbaceous annuals and opportunities to replace them with more long-lived perennials have been poorly explored. This follows the presumption that the perennial life cycle is associated with a lower potential yield, due to a reduced allocation of biomass to grains. The hypothesis was tested that allocation to perpetuation organs in the perennial L. mendocina would not be directly related to a lower allocation to seeds. * Two field experiments were carried on with the annual Lesquerella fendleri and the iteroparous perennial L. mendocina, two promising oil-seed crops for low-productivity environments, subjected to different water and nitrogen availability. * Seed biomass allocation was similar for both species, and unresponsive to water and nitrogen availability. Greater root and vegetative shoot allocation in the perennial was counterbalanced by a lower allocation to other reproductive structures compared with the annual Lesquerella. Allometric relationships revealed that allocation differences between the annual and the perennial increased linearly with plant size. The general allocation patterns for nitrogen did not differ from those of biomass. However, nitrogen concentrations were higher in the vegetative shoot and root of L. mendocina than of L. fendleri but remained stable in seeds of both species. * It is concluded that vegetative organs are more hierarchically important sinks in L. mendocina than in the annual L. fendleri, but without disadvantages in seed hierarchy.

A nonradioactive assay of bacterial productivity optimized for oligotrophic pelagic environments

The measurement of bacterial production is a cornerstone of research in aquatic biogeochemistry and microbial ecology, yet the standard radioisotope‐based techniques are threatened by increasing logistical obstacles. The two primary goals of this study were (1) the development of a reliable nonradioactive assay of bacterial productivity interpretable in the context of previous 3H‐thymidine (3H‐TdR)—based metrics, and (2) maximizing the sensitivity of the assay to allow routine measurement of bacterial productivity in open‐ocean and low‐productivity environments. We optimize existing methods for immunochemical detection of the incorporation of the thymidine analog 5‐bromo‐2′‐deoxyuridine (BrdU) to present a functional assay of community bacterial productivity comparable to radioisotope‐based assays in economy and field implementation and capable of consistently detecting bacterial production rates within the range of 0.1 to 10 pmol BrdU L−1 h−1. A standardization procedure provides complete separation of radioisotopes from the working methodology and gives statistically consistent results between calibrations with no degradation of the labeled DNA standards. Immunoassayed BrdU incorporation rates were highly correlated with parallel measurements of 3H‐TdR incorporation rates spanning a range of 0.1 to 10 pmol L−1 h−1 (r = 0.96, n = 20, P &lt; 0.001). Model II linear regression (BrdU = 0.65[3H‐TdR] + 0.12) yielded a conversion factor not significantly different from that reported previously comparing incorporation rates measured using radioisotope protocols (3H‐BrdU = 0.69[3H‐TdR] − 0.81). The assay is interpretable in the context of 3H‐TdR—based measures of production, providing continuity as a nonradioactive measure of bacterial production in low‐productivity aquatic ecosystems.

Assessment of durum wheat yield using visible and near-infrared reflectance spectra of canopies

The estimation of grain yield before harvesting could be a very useful tool for breeding programs and productivity forecasting. Canopy reflectance indices have been used for yield estimation, but with limited success. This work was carried out to study the suitability of the visible and near-infrared reflectance spectrum of the canopy for the assessment of grain yield in a set of durum wheat genotypes. Five field experiments, each one including 25 genotypes, were conducted in low, medium and high productivity environments, with average yields of 2.5, 4.5 and 7 t/ha. Spectral reflectance measurements between 400 and 1000 nm were made at anthesis and milk-grain stages. Partial least squares regression (PLSR) was used in the construction of models that were tested by simple regression between genotype means of predicted and observed grain yields. The empirical models for the estimation of grain yield showed generally stronger and more robust assessment of grain yield than previously assayed spectral indices. For the best model, correlation coefficients between genotype means of predicted and measured yield within each of the five environments ranged from 0.53 to 0.76. We concluded that, although the models did not provide an accurate quantification of grain yield, they could still be used to rank genotypes for breeding purposes. The most reliable ranking of genotypes was attained using measurements made at milk-grain stage on medium to high productivity environments.

EGG SIZE EVOLUTION IN TROPICAL AMERICAN ARCID BIVALVES: THE COMPARATIVE METHOD AND THE FOSSIL RECORD

Marine organisms exhibit a wide range of egg sizes, even among closely related taxa, and egg size is widely considered to be one of the most important components of the life histories of marine species. The nature of the trade-off between egg size and number and the consequences of variation in egg size for offspring growth and survivorship have been extensively modeled. Yet, there is little empirical evidence that supports the relative importance of particular environmental parameters in engendering the tremendous variation in egg size seen in marine organisms. This study compares egg sizes between six geminate species pairs of bivalves in the family Arcidae to determine whether egg size differs in predictable directions between geminate species in the two oceans separated by the Central American isthmus, and whether the direction and timing of egg size evolution among geminates in this family is correlated with both modern and paleoceanographic patterns of oceanic productivity. In all modern members of six geminate pairs, egg size was larger in the species in the western Atlantic than in its sister species the eastern Pacific. This pattern supports the hypothesis that optimal egg size differs in the two oceans due to the low productivity and poor larval feeding environment in the western Atlantic relative to the eastern Pacific. The fossil record of one geminate pair shows that egg size has remained consistently large in the western Atlantic from the Miocene to the Recent, while egg size in the eastern Pacific has decreased to the current small size in less than 2 million years; this suggests that modern-day differences between egg sizes in the western Atlantic and eastern Pacific are due to either an increase in productivity in the eastern Pacific and subsequent selection for smaller eggs in that ocean, or differential patterns of extinction that occurred well after the rise of the isthmus. These results agree with ancestral character state reconstruction using linear parsimony, but differ from squared-change parsimony reconstructions.

Implementation of an automated operation planning and optimum operation sequencing and tool selection algorithms

Low volume and high product mix characterize a job shop manufacturing. The CAM software in generating NC programs needs to reduce dependence on human judgment in operation planning in order to be used in low repetitive and high product mix production environments. In this research, a procedure for extracting machining methods for automated operation planning is proposed. Furthermore, an optimum operation sequencing and tool selection algorithm is developed for a CAM system. Practical examples have been provided and comparisons made with a known algorithm. Results indicate that the algorithms proposed in this research establish automated operation planning with reduced dependence on human judgment. They achieved considerable flexibility and adaptability, allowing users to implement particular manufacturing knowledge of both their own and resources available at individual shop sites.

EGG SIZE EVOLUTION IN TROPICAL AMERICAN ARCID BIVALVES: THE COMPARATIVE METHOD AND THE FOSSIL RECORD

Marine organisms exhibit a wide range of egg sizes, even among closely related taxa, and egg size is widely considered to be one of the most important components of the life histories of marine species. The nature of the trade-off between egg size and number and the consequences of variation in egg size for offspring growth and survivorship have been extensively modeled. Yet, there is little empirical evidence that supports the relative importance of particular environmental parameters in engendering the tremendous variation in egg size seen in marine organisms. This study compares egg sizes between six geminate species pairs of bivalves in the family Arcidae to determine whether egg size differs in predictable directions between geminate species in the two oceans separated by the Central American isthmus, and whether the direction and timing of egg size evolution among geminates in this family is correlated with both modern and paleoceanographic patterns of oceanic productivity. In all modern members of six geminate pairs, egg size was larger in the species in the western Atlantic than in its sister species the eastern Pacific. This pattern supports the hypothesis that optimal egg size differs in the two oceans due to the low productivity and poor larval feeding environment in the western Atlantic relative to the eastern Pacific. The fossil record of one geminate pair shows that egg size has remained consistently large in the western Atlantic from the Miocene to the Recent, while egg size in the eastern Pacific has decreased to the current small size in less than 2 million years; this suggests that modern-day differences between egg sizes in the western Atlantic and eastern Pacific are due to either an increase in productivity in the eastern Pacific and subsequent selection for smaller eggs in that ocean, or differential patterns of extinction that occurred well after the rise of the isthmus. These results agree with ancestral character state reconstruction using linear parsimony, but differ from squared-change parsimony reconstructions.

Nitrogen availability and colonization by mycorrhizal fungi correlate with nitrogen isotope patterns in plants.

• Nitrogen isotope (δ 15 N) patterns in plants may provide insight into plant N dynamics. Here, two analytical models of N-isotope cycling in plants and mycorrhizal fungi were tested, as dominant plants in many forest ecosystems obtain most of their N through intereactions with mycorrhizal fungi. • Fungi were treated either as a single well-mixed N pool, or as two N pools (one available, plus one not available, for transfer to the host). Models were compared against complete biomass and 15 N budgets from culture studies of nonmycorrhizal and ectomycorrhizal Pinus sylvestris (colonized with Suillus luteus or Thelephora terrestris ) grown exponentially at low and high N supply. • Fungal biomass and N increased at low N relative to high N supply, whereas needle δ 15 N decreased. Needle δ 15 N correlated strongly and negatively with biomass of extraradical hyphae. Our data and models suggest that low plant δ 15 N values in low productivity and N-limited environments result partly from high retention of 15 N-enriched N by mycorrhizal fungi; this retention was driven by increased C flux to fungi under N-limited conditions. The two-pool model of fungal N accounted for greater variability in plant δ 15 N than the one-pool model. • Plant δ 15 N patterns may indicate relative allocation of fixed C from plants to mycorrhizal fungi under some conditions. Studies are needed on whether patterns observed in culture can be applied to interpret field measurements of δ 15 N.

Using upper boundary constraints to quantify competitive response of desert annuals

Using a target‐neighborhood approach with six annual dicot species in the Negev Desert of Israel, we tested whether neighborhood biomass constrained the upper limit of plant performance and if the slope of the upper boundary was correlated to species trait means, such as relative growth rate (RGR) and seed mass. Target individuals were measured in early spring and then collected at the onset of the dry season along with all naturally occurring neighbors within a 5‐cm radius of the target. Using a minimum of 50 samples for each of the six target species, we found no significant relationships between target performance and either density or aboveground biomass of neighbors, when including all target individuals in the regressions. However, aboveground neighbor biomass did influence the maximum potential size of targets. When regressions were restricted to the largest target plant within classes of neighbor biomass, significant negative relationships were found for all six species, with neighbor biomass explaining 55 to 94% of the variance in maximum target biomass. The slopes of the regressions were used as an index of competitive response. The correlations between competitive response and estimates of species traits were not significant with the possible exception that species with lower RGRmax may be better response competitors (i.e. were less sensitive to competition). These findings indicate the usefulness of the boundary regression technique for describing competitive interactions among neighbors, particularly in low productivity environments.

Patterns of daily activity in the leaf-eared mouse (Phyllotis darwini): effects of food availability

The daily locomotor activity pattern of the nocturnal sigmodontine rodent Phyllotis darwini was analysed when faced with a differential offer of food. Animals with restricted food supply were less active during the day compared to animals who had access to food ad libitum, but no differences in activity were observed during the night. Minimization of energy expenditure may account for this behavioural plasticity, and such flexibility is extremely important in the unpredictable and low productive environments inhabited by P. darwini.