Greater Resource Availability Research Articles

Does the Oil Price Adjust Optimally to Oil Field Discoveries?

The Hotelling rule argues that the price for a non-renewable resource adjusts to the shadow value of the resource, reflecting its remaining availability. This study provides an empirical test of this hypothesis. It investigates whether the price of crude oil does adjust to unexpected news about oil field discoveries. The observed price reaction is compared with a prediction of the price decline as derived from the Hotelling model. This study finds evidence for an adjustment of the price to news about greater resource availability: the price of crude oil declines on average by 0.88% on discovery days. The degree of adjustment to the new level of scarcity is not found to differ significantly from the social optimum. Thus, there is evidence for the existence of a shadow cost component - a necessary pre-requisite for the Hotelling rule to hold.

Floristic and Functional comparision of karst pastures and karst meadows from the North Adriatic Karst

In the present study, we compared the species richness and the floristic and functional composition of two types of extensively managed, species rich dry grasslands (class Festuco-Brometea) from the North Adriatic Karst: karst pastures (alliance Satureion subspicatae) and karst meadows (alliance Scorzonerion villose). Karst pastures are characterized by shallow rocky soils, high pH, and dry, warm conditions, whereas karst meadows have developed on deeper soil, with more humus and moisture and neutral to alkaline pH. The data set included a table with 100 phytosociological relevés of the studied grasslands and a matrix with 15 functional traits determined for 180 plant species. we found high species richness in these grasslands but no statistically significant differences in species richness between karst pastures and meadows. Differences in floristic composition were analysed with Detrended Correspondence Analysis, which supported a clear division between the two vegetation types and indicated that species composition could best be explained in terms of soil humidity and nutrient availability. We also detected several differences in plant functional traits between meadows and pastures. Some of the traits indicate greater resource availability on karst meadows (in particular, high SLA, low LDMC). In contrast, karst pastures have more slow-growing species with a combination of traits that can be interpreted as an avoidance strategy in relation to disturbance (e.g., grazing) in low productive habitats (e.g., low SLA, high LDMC, early flowering species and plants with rosette). A lower relative proportion of competitors (C) and ruderals (R), and a higher relative proportion of stress-tolerators (S) in karst pastures also suggested that these grasslands generally experience higher intensities of stress when compared to karst meadows, presumably owing to lower resource availability on stony, shallow soil. we could conclude that karst meadows and pastures differ significantly in both floristic composition and functional trait means, owing to their distinctive land-use (disturbance) and environmental conditions.

Selection for positive illusions

Everybody knows that overconfidence can be foolhardy. But a study reveals that having an overly positive self-image might confer an evolutionary advantage if the rewards outweigh the risks. See Letter p.317 Overconfidence is a major puzzle in evolutionary biology, economics and political science, because despite causing costly errors and policy failures, it remains a widespread bias in human judgement and decision-making. Animals too, in examples seen during conflict behaviour, are liable to overconfidence. Dominic Johnson and James Fowler use game theory to model the situations under which overconfidence is an advantage, and find that they occupy a large part of the parameter space. They also show that overconfidence and conflict tend to increase with greater resource availability. As long as the prize at stake sufficiently exceeds the cost of competing for it, it seems, fortune favours the brave.

Availability of healthcare resources, positive ratings of the care experience and extent of service use: an unexpected relationship.

Two main avenues are advocated to improve the capability of healthcare systems to satisfy the public's needs and expectations: more resources and better organization. This paper sheds some light on this debate. It assesses the extent to which patients' positive rating of their healthcare experience and the extent to which they use services are related to the availability of healthcare resources. Findings indicate that patients' evaluations of their care experience and use of services were higher when the availability of resources was either limited or average. In no case were positive ratings of services and greater use of them associated with greater resource availability. Thus, simply adding resources runs the risk of diminishing, rather than improving, users' healthcare experience.

How do Unanticipated Discoveries of Oil Fields Affect the Oil Price?

The Hotelling rule argues that the price for a nonrenewable resource adjusts to the shadow value of the resource, reflecting the remaining availability of the resource. We empirically test the Hotelling rule on the effect of unanticipated oil field discoveries. We do not find evidence for a significant adjustment of the price of crude oil to news about greater resource availability and therefore conclude that the price for crude oil does not follow the theoretically optimal price path.

The effects of customer and competitor orientations on performance in global markets: a contingency analysis

Should companies adjust their orientations toward customers or toward competitors in global markets? To answer this question, we use contingency theory and examine how the effects of customer and competitor orientations on performance are moderated by different environmental conditions. Our results from the global hotel industry indicate that a customer orientation works better in economically developed markets, as well as in markets with good local business conditions, greater resource availability, and demanding customers. In contrast, a competitor orientation is more effective in markets that are economically developing, have poor local business conditions, and face resource scarcity.

A comparative study of the diets of two sympatric carnivores – the golden jackal (Canis aureus) and the common genet (Genetta genetta) – in Kabylia, Algeria / Etude comparative des régimes alimentaires de deux carnivores sympatriques – le chacal doré (Canis aureus) et la genette commune (Genetta genetta) – en Kabylie, Algérie

Increased human activity and the disappearance of large predators may affect competition among species, thus threatening the survival of those animals that are more vulnerable to environmental change. In Kabylia (Algeria), competition may occur between the golden jackal ( Canis aureus ), which is a habitat-opportunistic species, and the common genet ( Genetta genetta ), which favours woodland environments. We tested the hypothesis of interspecific competition in disturbed habitats by comparing the diets of the jackal and genet in different environmental settings. Index values of interspecific food overlap were constantly high. Opportunistic behaviour prevailed in both species and was reflected by the alternation between two dominant prey items (mammals and insects) and other resources, such as poultry and high-energy plants. It is thought that greater availability of resources in the latter categories particularly benefits the jackal because of its broad niche spectrum. Résumé L'anthropisation accrue des milieux et la disparition progressive des super-prédateurs modifient fortement les modes et les niveaux de compétition entre les espèces prédatrices subsistantes. Ces modifications peuvent menacer la survie des espèces les plus vulnérables à l'évolution des milieux. En Kabylie (Algérie), le risque peut exister entre le chacal doré ( Canis aureus ), espèce ubiquiste, et la genette commune ( Genetta genetta ), plus particulièrement associée aux formations boisées peu fragmentées. Nous nous proposons de tester l'hypothèse d'une compétition interspécifique entre ces deux espèces en calculant le degré de chevauchement de leurs niches alimentaires dans deux types d'éco-systèmes. Les valeurs des indices de chevauchement sont élevées tout au long de l'année. Un comportement opportuniste prévaut constamment chez les deux espèces. Il se traduit par une alternance entre deux types de proies dominantes (mammifères et insectes) et par une forte propension à tirer parti des oiseaux domestiques et des végétaux énergétiques. En raison de capacités d'exploitation des milieux plus grandes chez le chacal, il est présumé qu'une disponibilité accrue de ces types d'aliments favorisera plus particulièrement le chacal.

Influence of host size on the clutch size and developmental success of the gregarious ectoparasitoid Eulophus pennicornis (Nees)(Hymenoptera: Braconidae) attacking larvae of the tomato moth Lacanobia oleracea (L.) (Lepidoptera: Noctuidae)

The relationship between clutch size, host size and progeny survival in the gregarious ectoparasitoid Eulophus pennicornis was investigated in a number of scenarios. When naive parasitoids were exposed singly to Lacanobia oleracea hosts, clutch size was strongly correlated with the size of the host. However, survival of parasitoid offspring was negatively affected by the size of the host such that, in larger hosts, greater wasp larval and pupal mortality was recorded. As a result, no gain in realised fecundity was achieved through parasitizing L. oleracea larvae of mass >0.4 g over hosts of mass between 0.2-0.3 g. When exposed to populations of mixed stadium hosts (larvae in the fourth, fifth and sixth instars) during the entire lifespan of the wasp, host size and clutch size were correlated in early ovipositions (first three ovipositions). However, as the wasps aged, the relationship was much less apparent. When the parasitoid was restricted to foraging upon populations of sixth instar hosts only, no relationship between host size and clutch size was apparent. Exposure of the parasitoid to mixed and fixed stadium host populations showed that final (sixth) stadium hosts were the most frequently parasitized (ca. 96% of parasitized hosts) and that the average numbers of eggs laid per wasp, and the number of hosts parasitized, was significantly lower when the parasitoid was provided with fourth or fifth instar hosts only. The results indicate that the reproductive success of E. pennicornis does not increase with increasing host size or greater resource availability above a certain threshold, and that the physiological status of the host at the time of parasitism is the governing factor determining oviposition decisions and parasitoid survival. We conclude that E. pennicornis has been selected to preferentially utilize those hosts that maximize progeny survival and to adapt clutch size to the size of such hosts. We hypothesize that the major driver leading to the evolution of this strategy is the ability of the parasitoid to physiologically regulate the host.

Effects of labile carbon addition on a headwater stream food web

We added dextrose for two 8-week periods (summer and autumn) to a highly heterotrophic headwater stream in North Carolina, U.S.A., to examine the responses of its benthic food web to increased labile carbon. We hypothesized that addition of labile carbon would elevate microbial abundance and activity, resulting in greater resource availability and higher macroinvertebrate production and that the effect of dextrose addition would be less marked during the autumn due to lower ambient stream temperatures and large seasonal inputs of leaf litter. Bacterial densities were significantly higher in the treatment reach during both additions. Thick microbial mats of sheathed bacteria and the aquatic hyphomycete Lemonniera pseudofloscula developed on bedrock outcrops. Increased microbial growth led to higher respiration rates on leaf disks and a threefold increase in instantaneous growth rates of chironomid larvae. The abundance and biomass of invertebrate collector-gatherers and predators increased significantly on bedrock during the summer addition but not in the autumn; however, shredder biomass increased significantly in the autumn. On mixed substrates, shredder abundance and scraper biomass increased significantly during the autumn addition. During both additions, all functional feeding groups, including predators, assimilated isotopically distinct dextrose, despite high standing stocks of coarse particulate matter during the autumn addition. Consumers of epilithon and fine particles showed the greatest response. Assimilation of dextrose and increases in invertebrate abundance and biomass suggest that the added carbon stimulated biological activity even in a stream with abundant organic carbon.

The roles of extinction and colonization in generating species–energy relationships

Summary Positive correlations between energy and species richness are frequently observed, but the causal mechanisms of such species–energy relationships have rarely been identified conclusively. The more individuals hypothesis (MIH) describes one possible cause of positive species–energy relationships. It suggests that greater resource availability in high‐energy areas increases population sizes, reducing local extinction rates and promoting species richness. It predicts that extinction rates will be lower in high‐energy areas and that, because a given change in population size has a greater influence on extinction risk when initial populations are small, such relationships will be more pronounced in numerically rare species than more abundant ones. Colonization rates may also influence local species richness, and they may respond positively to the greater resource abundance in high‐energy areas. We provide the first empirical test of relationships between extinction/colonization rates and energy availability and of the influence of population size on these relationships. We use data on the changing distributions of British birds, in which positive species–energy relationships have previously been documented. We find that extinction rates are lower in high‐energy areas, but that such patterns are stronger in more abundant species. Spatial variation in colonization rates is influenced less markedly by energy availability, but such patterns are also more marked in numerically abundant species. While these results provide little overall support for the MIH, nor some of its alternatives, they add to increasing evidence that common species drive much of the spatial variation in species richness.

Spatial and Temporal Variation in the Response of Understory Vegetation to Disturbance in a Central Appalachian Oak Forest

SMALL, C.J. AND B.C. MCCARTHY (Department of Environmental and Plant Biology, Ohio University, Athens, Ohio 45701). Spatial and Temporal Variation in the Response of Understory Vegetation to Disturbance in a Central Appalachian Oak Forest. J. Torrey Bot. 129: 136-153. 2002.-Understory vegetation in stand-initiating (7 year clearcuts) and understory-reinitiating (> 125 year mature second-growth) oak-dominated forest stands in southeastern Ohio was examined relative to topographic aspect, micro-environmental conditions, and sampling season to explore patterns of understory dynamics and stand development following management disturbance. Plots were established on upper and lower slopes across a range of aspect positions and sampled in spring and summer to capture topographic and seasonal changes in herb layer dynamics. Micro-site light, temperature, and physical soil properties differed significantly with stand age whereas fertility and moisture varied with aspect. Species richness was greater in clearcut than mature forest stands, associated with greater resource availability and spatial heterogeneity. Herb richness and abundance were greater on NWand SE-facing slopes and lower slope positions, corresponding to greater soil moisture and fertility. Greater frequencies of non-native species were also found in resource rich, clearcut plots. Canonical correspondence analysis showed stand age, aspect, and fertility to strongly influence herb layer composition. Non-metric multidimensional scaling showed compositional divergence of spring vs. summer and clearcut vs. mature forest herb samples. Composition of clearcuts and mature forests differed markedly in June, suggesting that management influences may be more pronounced in summer herb communities. Most studies of understory dynamics in eastern forests fail to account for spatial and temporal variations in site and vegetation characteristics, however, understory disturbance response appears strongly linked to these ecosystem properties. A better understanding of these factors is needed to fully understand the effects of forest management on herb layer communities in our eastern forests.

Testing the ecophysiological basis for the control of monoterpene concentrations in thinned and unthinned balsam fir stands across different drainage classes.

Stand thinning across different soil drainage types was used to test the ecophysiological basis for the control of foliar monoterpenes in current-year foliage of balsam trees [Abies balsamea (L.) P. Mill.] the year following treatment. Photosynthetic capacity (A max) was greater on mesic sites than on sub-hygric and hydric sites (1.81, 1.33 and 0.88 µmol m-2 s-1, respectively) and greater in mid-July than at the end of June (1.86 vs 0.77 µmol m-2 s-1). Foliar N was greater on thinned plots than control plots (2.6 vs 2.2g m-2); starch was greater on mesic control plots than mesic thinned plots (16.3 vs 10.9g m-2); and total soluble sugars (TSS) were higher in mid-July than at the end of June (16.5 vs 12.8g m-2). Total monoterpenes, as well as five individual monoterpenes, showed a complex interaction between site drainage class, thinning treatment and time of sampling (P<0.05). For all sites and dates combined, total monoterpenes were negatively correlated with specific leaf area (r 2=0.46), and positively but weakly correlated with A max (r 2=0.35), foliar N (r 2=0.29) and TSS (r 2=0.24). Total monoterpenes were not correlated with the different measures of carbon to nitrogen ratio as predicted by the carbon-nutrient balance hypothesis. Our results offer partial support to the different hypotheses proposing that foliage having greater resource availability, enzymatic machinery and potential for building storage structures will have greater monoterpene content. However, the strength of the relationships with monoterpenes often varied with sampling date, suggesting that phenological development may play a strong role in determining which factors control monoterpenes at a given time.

Influence of resource level on maternal investment in a leaf-cutter bee (Hymenoptera: Megachilidae)

Fisher's (1930) prediction of equal investment for each sex in a panmictic population is influenced by a number of ecological factors, among which resource availability plays a major role, particularly when the population exists under changing resource availability. Rosenheim et al. proposed a multifaceted parental investment model based on the underlying assumption that individual females determine their sex investment according to resource availability and oocyte availability to maximize reproductive success. The model predicts that greater availability of resources used for provisions will lead to (1) an increase in the proportion of females produced (when the female is the larger sex) and (2) an increase in the amount of provisions per offspring and thus an increase in offspring size. I tested these predictions by a controlled experiment using a leaf-cutter bee, Megachile apicalis. I presented two levels of food resources to the nesting females, which were allowed to forage and nest in cages. The experimental results supported these parental investment model's predictions.

Population Structure, Reproduction, and Lipid Cycling in the Dusky Shiner (Notropis cummingsae) in Contrasting Streams

To document the reproductive and lipid cycle of the dusky shiner, and to determine how environmental differences can influence patterns of reproduction and lipid storage, I sampled dusky shiners from January 1989 to June 1991 from two streams in west central South Carolina: Upper Three Runs and Four Mile Creek. The streams were chosen because of likely differences in primary productivity. Sex, ovary mass, reproductive stage, somatic dry mass, and lipid mass were quantified, as appropriate, for all individuals sampled. There were many differences between the two streams that suggested shiners in Four Mile Creek had greater resource availability during most years, including greater monthly growth, larger ovaries, a longer spawning season, and higher maximulm somatic lipid levels. In both streams, females accumulated lipid prior to ovarian enlargement and depleted lipid through a spawning season that spanned three or four months. Males accumulated and depleted lipid in a pattern similar to that seen in females but not to the same extent. There was no apparent lipid acclmulation or depletion in immature individuals. There was a clear temporal relationship between lipid accumulation and ovarian enlargement. Lipid accumulation appears to be a prerequisite for reproduction. Lipid accumulation in fall appears to be facultative and not a prerequisite for winter survival. Size-specific differences in reproductive performance appear to be the product of size-specific differences in lipid storage. Large adults became rare in late summer when lipid levels were low. The differences between the two populations are consistent with the theoretical expectation that greater resource availability favors earlier maturation and greater allocation to reproduction.

INSECT HERBIVORES: DIFFERENT REASONS FOR BEING A GENERALIST

Two very different factors favor generalist herbivores over specialist herbivores: greater resource availability, which should be universally beneficial, and the possibility of mixing foods to improve nutrient balance or to reduce exposure to high levels of particular allelochemicals. In this work, four species of Lepidoptera and three species of Hemiptera were fed single or mixed foods to test the hypothesis that individual generalists would benefit from mixing their diets. In all cases, insects were provided with one of three different host plants, or a mixture of all three. For most species, several different experiments were performed. Survivorship, gain in mass, and fecundity were used as measures of performance. In no case was there evidence that mixtures were better than single foods. It is argued that, in these taxa, the value of being a generalist lies largely with versatility for use of different hosts, rather than for dietary mixing. The contrast with Orthoptera, in which individuals commonly obtain substantial benefit from dietary mixing, is also discussed.

Sex Ratios and Multifaceted Parental Investment

Although theories of parental investment and sex ratio generally assume that a single resource limits reproduction, many organisms invest two or more qualitatively different types of resources in the production of offspring. We examine the consequences of multifaceted parental investment for offspring provisioning and sex allocation, building our argument around a study of the nest-building Hymenoptera (wasps, bees, and ants). We review empirical studies that demonstrate that lifetime reproductive success may be constrained not only by resources used to provision offspring but also by the supply of mature oocytes or, in some cases, by the availability of space within nest sites or the time required to defend nests. Under multifaceted parental investment, the factor limiting parental fitness determines the currency of the optimiza- tion problem; parents are predicted to adjust reproductive behavior to maximize fitness returns per unit of the limiting resource. We develop simple models that predict that a greater availability of resources used for provisions will lead to an increase in the amount provisioned per offspring and an increase in the numerical or biomass proportion of females produced. These predictions explain widely observed patterns of variation in offspring provisioning and sex allocation in the nest-building Hymenoptera.

Facilitation between Higher Plant Species in a Semiarid Environment

A major role of facilitation between higher plant species, particularly in stressful environments, has recently been reported in several papers that suggest that beneficial interactions could be more important in the dynamics of plant communities than has been recognized to date. In a semiarid region in southeastern Spain we determined the effect of a leguminous shrub, Retama sphaerocarpa, on its environment, testing the hypothesis that facilitation by the shrub of one species of its understory, Marrubium vulgare, is reciprocal and that the shrub benefits from sheltering herbs beneath its canopy. Marrubium plants under Retama had greater specific leaf area, leaf mass, shoot mass, leaf area, more flowers, a higher nitrogen (N) concentration in leaf tissue, and more N per plant than isolated plants, suggesting a facilitative effect of Retama on Marrubium including increased availability of resources. Biomass of 1—yr—old cladodes, total biomass, total nitrogen content of 3—yr—old branches, and shoot water potential at midday were higher for Retama shrubs with Marrubium beneath them than in shrubs without Marrubium. Retama strongly improved its own environment, facilitated the growth of Marrubium and other species underneath its canopy, and at the same time obtained benefits from sheltering herbs underneath. The interaction between these two species was indirect, associated with differences in soil properties and with improved nutrient availability under shrubs compared with plants growing on their own. We propose that the mutual benefit of the association between Retama and Marrubium is best termed a facultative mutualism. Each partner benefits from greater availability of resources in the “island of fertility” that results from their association. If beneficial plant—plant interactions as described here are widespread, positive relationships may have a major role in determining the pattern and structure of plant communities.

GENDER‐RELATED DIFFERENCES IN GAS EXCHANGE ARE NOT RELATED TO HOST QUALITY IN THE XYLEM‐TAPPING MISTLETOE, PHORADENDRON JUNIPERINUM (VISCACEAE)

Male and female individuals of dioecious species often differ in morphology, physiology, growth, and habitat distribution. Where habitat distribution differences have been demonstrated, female plants generally occupy those habitats with greater resource availability (“rich” habitats). Gender‐specific habitat preferences are often presumed to be a consequence of greater resource requirements, per gamete, of female reproduction. Previous work has shown that Phoradendron juniperinum, a xylem‐tapping dioecious mistletoe that parasitizes Juniperus species in western North America, displays the opposite pattern: males are relatively more numerous than females in richer sites (i.e., branches with relatively high light and low evaporative demand within the host tree). We report here differences in host (“site”) quality and gas‐exchange properties between the sexes. To minimize environmental variation, all measurements were made on sunlit foliage between 9:00 a.m. and 2:00 p.m. Males had significantly higher photosynthetic rates (4.0 [SE = 0.2] μmol m‐2 sec‐1) than either females (2.9 [0.3] μmol m‐2 sec‐1) or nonreproductive individuals (3.0 [0.2] μmol m‐2 sec‐1). Female photosynthetic rates were not statistically different from those of nonreproductive individuals. No concomitant differences in stomatal conductance were observed. Gas exchange data were independently confirmed by significant differences in carbon isotope ratio (δ13C). Gender‐related differences were not related to host quality as measured by foliar N, foliar δ13C, or water potential of the host tree. The fate of the additional photosynthate in males is unknown, but we discuss the possibility that carbon costs of reproduction in males have been underestimated in past work.

Reproductive enhancement by helpers and an experimental inquiry into its mechanism in the bicolored wren

As part of continuing studies of sociality in the wren genus Campylorhynchus we have been studying the bicolored wren — a facultatively cooperative breeder — for the past 6 years in the central Venezuelan savanna. Reproductive groups have ranged in size from 2 to 5. In one of our study populations, only about 15% of the groups contained helpers, and nearly all these contained only a single male helper (Fig. 2). In an adjacent population, the majority of groups contained helpers, and more than half of these contained several helpers of either sex. Territory size is, on average, much smaller in the latter population. In these populations the presence of a single helper is associated with a three-fold increase in reproductive success (Table 1). Additional helpers are not associated with further reproductive enhancement. Enhancement is chiefly due to an increased proportion of nest starts that eventually produce independent juveniles. This reproductive enhancement is not merely an epiphenomenon resulting from the presence of helpers on territories which are superior for other reasons, such as greater resource availability or the quality of particular parents. It is also not a function of the mean or variance in nestling feeding rate. Predator exclusion experiments, in which certan nests were artificially protected from terrestrial predators, suggested that the mechanism of reproductive enhancement was heightened effectiveness of nest defense. Helpers are usually nondispersers from the parental territory, and have always been found to be close relative of the nestlings that they assist in rearing.