Effects Of Resource Depletion Research Articles

COLONIZATION HISTORY DETERMINES ALTERNATE COMMUNITY STATES IN A FOOD WEB OF INTRAGUILD PREDATORS

Several recent studies suggest that community composition can take on alternate, apparently stable, states. For the most part, these studies are observational in nature and have not shown that alternate states arise from the order of species arrival during community assembly. Previous studies also provide little insight into the mechanisms that create alternate states, especially when direct species interactions, rather than environmental feedback, control their formation. We conducted experiments in identical physical environments to show that differences in the sequence of community assembly can create alternate species compositions that persist for many generations. Assembly sequence determined whether experimental food webs contained a single intraguild predator, or two intraguild predators. When the intraguild predator, Blepharisma americanum, became established in communities before the introduction of Tetrahymena vorax, combined effects of resource depletion and intraguild predation prevented the establishment of Tetrahymena. In contrast, when Tetrahymena preceded Blepharisma, both species frequently coexisted. Supporting experiments describe the exploitative competitive abilities of both intraguild predators, document the population dynamics of each species in less complex community modules, and determine the ability of Tetrahymena to invade Blepharisma cultures in the absence of competing prey. These results show that both competition and predation contribute to the formation of two alternate community states and confirm that one stable state resists transformation to the other.

Changes in vigilance with group size under scramble competition.

Animals often interrupt foraging to scan the surrounding environment. In several taxa, such vigilance decreases with group size (Elgar 1989). The decline in vigilance is usually interpreted as a decrease in the predation risk to an individual in large groups. Mechanisms such as increased detection ability and numerical dilution of risk may provide more protection to foragers in large groups, thus leading to lower vigilance (Pulliam 1973; Roberts 1996; Bednekoff and Lima 1998). Nevertheless, recent work indicates that the decrease in vigilance with group size may be mitigated against if individuals in large groups scan more to avoid displacements by aggressive companions (Slotow and Coumi 2000; Treves 2000) or to locate the food discoveries of other group members (Beauchamp 2001). We explore the role of resource availability on vigilance patterns. In earlier vigilance models, a decrease in vigilance would allow foragers either to decrease the total amount of time needed to accumulate a fixed amount of resources (Pulliam et al. 1982) or to increase feeding rate over a given time horizon (McNamara and Houston 1992). In either case, no competition for resources is assumed to take place. However, when resources are limited, a reduction in vigilance may allow individuals to allocate more time to foraging and so obtain a greater share of the re-

Sources of change in petroleum drilling productivity in onshore Louisiana in the US, 1977–1994

Productivity of petroleum exploration and development drilling in the contiguous US has increased over the last 15 years, thereby suggesting that the effects of some other factors may be offsetting the expected negative effect of resource depletion. In this paper, we disentangle empirically, using a region-specific petroleum drilling and discovery model, the effects of resource depletion and other intervening factors on petroleum reserve additions in a typical mature petroleum basin in the US — Louisiana onshore basin. Our empirical results confirm the expectation of diminishing marginal returns to exploration and development drilling with increasing drilling effort. The results also indicate that while technical progress significantly reduced the negative effects of depletion on petroleum reserve additions by as much as 7.5% in north Louisiana and 6.7% in south Louisiana, its overall impact on reserve additions has not dominated the effects of depletion in Louisiana state jurisdiction.

A simulation model to illustrate feedbacks among resource consumption, production, and factors of production in ecological-economic systems

A system dynamics production model illustrates feedbacks between economic growth and resource depletion. Man-made capital, renewable natural capital, nonrenewable natural capital, and human capital are factors of production in a Cobb–Douglas production function. Technology in production sets the overall level of efficiency in production. Feedbacks between production and factors of production, and biological and physical limits on the availability of natural resources, place limits on the scale of consumption of those resources. Output rises smoothly or dives toward zero depending on resource consumption strategies and the specification of the technology term in the race against a growing, resource-consuming population. Adjusting parameters within the model and changing the specification of some variables illustrates the isolated effect of resource depletion, technological development, or other factors, on per-capita production. These experiments with the model illustrate competing world views expressed in models of production and resource use, notably in Meadows et al.'s (1972 The Limits to Growth, Universe Books,NY, pp. 204; 1992 Beyond the Limits, Chelsea Green, Vermont, pp. 300) world model and the models of its critics.

When the mind is otherwise engaged: resource depletion and social stereotyping

This study investigated the effects of resource depletion on stereotyping. Participants were instructed to form an impression of a target, and whilst performing this task, they overheard a tape-recorded conversation. The conversation was manipulated so that it was more or less relevant to the participants. Results in general supported the prediction that when participants eavesdrop on a relevant conversation, attentional capacity will be diminished, and target evaluations will be stereotypic in implication. Findings are discussed in terms of contemporary treatments of stereotyping. © 1998 John Wiley & Sons, Ltd.

Resource Depletion and Technical Change: Effects on U.S. Crude Oil Finding Costs from 1977 to 1994

A dramatic decline in U.S. crude oil finding costs has provoked intense interest in the extent to which technical progress has mitigated the effects of resource depletion. Analysis of depletion and technical change using data for 27 large U.S. oil producers from 1977-1994 is conducted using a translog cost function. The translog provides a flexible representation of the underlying production function, and controls for changing factor prices. The model also controls for the effect of prospect highgrading. Results show that an accelerating rate of technical change reduced average finding cost 15 percent (onshore) and 18 percent (offshore) per year by 1994. Resource depletion increased cost at an average annual rate of 7 percent onshore and 12 percent offshore. Technical change was relatively labor-using both onshore and offshore.

Physical and economic aspects of resource quality: The cost of oil supply in the lower 48 United States, 1936–1988

For the past half century, the average cost of finding new oil in the lower 48 U.S. has increased in a non-linear fashion. The average cost of producing oil decreased then increased over the same period, with costs rising since the mid-1960s. These results indicate that the cost increasing effects of resource depletion have outweighed the cost decreasing effects of technological improvements in the two primary stages of the oil supply process. Finding and production costs are also highly correlated with the rate of effort expended in each stage, and short-run changes in the rate of effort drive average costs above or below the long-run trend. Previous models which ignored the interplay between short- and long-run effects on cost produced misleading results concerning the scarcity of crude oil in the U.S. The drilling boom of the early 1980s arrested the rate of decline in new additions to reserves, but the average costs associated with those additions were the highest on record. Attempts to sustain production in the lower 48 U.S. through massive drilling programs targeting the large number of undiscovered small fields and infill drilling in existing fields are likely to drive average costs even higher.

The Effect of Resource Depletion on the Feeding Behaviour of a Browser: Winter Foraging by Moose on Scots Pine

(1) The foraging dynamics of a browser, the moose Alces alces L. exploiting depleting resources was studied experimentally. It was hypothesized that: (a) differences in the intake of twig biomass between tree stands in early foraging sessions would tend to even out as resource depletion progressed; (b) food item selectivity within stands would decrease, and (c) bite diameters would increase with time. (2) Artificial stands, composed of one browse species or a mixture of species, were set up in a forest area. The species included were Scots pine Pinus sylvestris L., aspen Populus tremula L. and grey alder Alnus incana (L.) Moench. Special attention was paid to the analysis of the pattern of Scots pine exploitation because this tree is of commercial interest. Moose browsing was assessed by counting bites and by measuring bite diameters. (3) Initially the total consumption of twig biomass in the pine + aspen stand was twice as high as that in the other two stands. This difference remained until almost half of the available biomass in the pine + aspen stand had been consumed. Within stands the preference for aspen over pine increased over time, whereas the preference for pine over alder decreased. Bite diameter on Scots pine showed a significant decline over time. (4) Browsing on Scots pine was only slightly affected by the species composition of the tree mixtures. Browsing intensities on individual pines was positively correlated with the amounts consumed on adjacent stems.

An Optimal Control Theory of Diet Selection: The Effects of Resource Depletion and Exploitative Competition

A model of optimal diet selection on depletable resources is presented which considers the effects of exploitative competitors on the optimal behavior.In the absence of any competitors, one of three behaviors may be optimal : (1) generalist, (2) specialist, (3) accept some proportion of the encountered poor quality food items

Substitution Possibilities for Unpriced Natural Resources: Restricted Cost Functions for the Canadian Metal Mining Industry

A bstract -The effects of resource depletion on economic growth depend critically on the elasticities of substitution between non-renewable natural resources and reproducible inputs. Estimation of the elasticities of substitution for natural resources has been hindered by the absence of data on their prices, which results from the prevalence of vertical integration in natural resource industries. In this paper we use the theory of restricted cost functions to develop a general procedure for estimating substitution possibilities for unpriced inputs. Estimation of the model with data for the Canadian metal mining industry indicates that the elasticities of substitution for the natural resource, metallic ore, are equal to unity.

Exponential growth and atmospheric carbon dioxide

The adequacy of assumptions required to project atmospheric CO2 concentrations in time frames of practical importance is reviewed. Relevant issues concern the form assumed for future fossil fuel release, carbon cycle approximations, and the implications of revisions in fossil fuel patterns required to maintain atmospheric CO2 levels below a chosen threshold. In general, we find that with a judiciously selected exponential fossil fuel release rate, and with a constant airborne fraction, we can estimate atmospheric CO2 growth over the next 50 years based on essentially surprise free scenarios. Resource depletion effects must be included for projections beyond about 50 years, and on this time frame the constant airborne fraction approximation has to be questioned as well (especially in later years when the fossil fuel use begins to taper off). For projections for over 100 years, both energy demand scenarios and currently available carbon cycle models have sufficient uncertainties that atmospheric CO2 levels derived from them are not much better than guesses.