Structural change and sustainable development

In this paper, we show that the commonly observed decline in primary (natural resource using) sector output and employment shares, often termed structural change, can be explained as an endogenous response to the presence of nature's constraint. Structural change takes place even if consumer preferences are homothetic, and technological progress does not discriminate against the primary sector. Under certain conditions, structural change allows an open economy to grow with natural resource sustainability. Sustained and environmentally sustainable economic growth is possible even if the natural resource is exploited under open access. Well-defined property rights are neither necessary, nor sufficient for sustainable growth. We show that there is no unique relationship between natural resource endowment and the rate of economic growth over the long run. Resource-rich economies may grow faster or slower than resource-poor ones.     

Renewable resources in an endogenously growing economy: balanced growth and transitional dynamics

We introduce a renewable resource sector into an endogenous growth model of a small economy, deriving the transitional dynamic equilibrium. The model generates a long-run equilibrium in which a resource sector of limited size can coexist with constant ongoing growth elsewhere. The key feature of the model is the allocation of labor between harvesting the resource and its use in the final output sector. This naturally generates the empirically observed negative relationship between resource abundance and growth. We examine both the dynamic and long-run responses of the economy to various shocks pertaining to technological production conditions and resource sector parameters.     

Niche complementarity due to plasticity in resource use: plant partitioning of chemical N forms

Niche complementarity, in which coexisting species use different forms of a resource, has been widely invoked to explain some of the most debated patterns in ecology, including maintenance of diversity and relationships between diversity and ecosystem function. However, classical models assume resource specialization in the form of distinct niches, which does not obviously apply to the broadly overlapping resource use in plant communities. Here we utilize an experimental framework based on competition theory to test whether plants partition resources via classical niche differentiation or via plasticity in resource use. We explore two alternatives: niche preemption, in which individuals respond to a superior competitor by switching to an alternative, less-used resource, and dominant plasticity, in which superior competitors exhibit high resource use plasticity and shift resource use depending on the competitive environment. We determined competitive ability by measuring growth responses with and without neighbors over a growing season and then used 15N tracer techniques to measure uptake of different nitrogen (N) forms in a field setting. We show that four alpine plant species of differing competitive abilities have statistically indistinguishable uptake patterns (nitrate > ammonium > glycine) in their fundamental niche (without competitors) but differ in whether they shift these uptake patterns in their realized niche (with competitors). Competitively superior species increased their uptake of the most available N form, ammonium, when in competition with the rarer, competitively inferior species. In contrast, the competitively inferior species did not alter its N uptake pattern in competition. The existence of plasticity in resource use among the dominant species provides a mechanism that helps to explain the manner by which plant species with broadly overlapping resource use might coexist.     

Complementarity,impatience, and the resilience of natural-resource-dependent economies

We study how society's preferences affect the resilience of economies that depend on more than one type of natural resource. In particular, we analyze whether the degree of complementarity of natural resources in consumer preferences may give rise to multiple steady states and path dependence even when resources are managed optimally. We find that, for a given social discount rate, society tends to be less willing to buffer exogenous shocks if resource good are complements in consumption than if they are substitutes. The stronger the complementarity between the various types of natural resources, the less resilient the economy is, and even more so the higher is the social discount rate.     

Exhaustible Resource Allocation in an Overlapping Generations Economy

This paper analyzes competitive allocations of an exhaustible resource in an overlapping generations economy. Conditions are given for the existence of equilibrium extraction rules such that both extraction and investment in future stocks are increasing and continuous in the current stock. The paper then considers the time paths of equilibrium allocations and shows that there are economies where equilibrium resource extractions and prices exhibit nonclassical behavior. This is illustrated through a finite horizon example in which extractions increase and prices decrease over the entire time horizon and an infinite horizon example where there are persistent cycles in extractions and prices and multiple equilibria. The paper concludes by examining welfare issues.     

Plant competition varies with community composition in an edaphically complex landscape

There is currently no consensus on how physical and biological factors affect competitive intensity. Tests of whether competitive intensity varies along axes of environmental change have commonly been conducted in systems with a single strong environmental gradient, such as productivity, a soil resource, or an environmental stress. Frequently, these same axes are associated with changes in species composition, yet few studies have asked whether shifts in the identity of competitors affect competitive intensity. We ask whether resources (nutrients, water), stressors (heavy metals, Ca:Mg ratio), productivity (aboveground biomass), or species identity (an ordination axis of plant community composition) were the best predictors of the intensity of competition in a heterogeneous grassland landscape that included multiple independent environmental gradients. The reproductive fitness of six annual plant species was measured in the presence and absence of competitors and used to calculate relative interaction intensity (RII). We found that RII was best predicted by community composition. Nutrient availability was also important, and a post hoc test showed that competitive intensity was best explained by the combined effects of community composition and nutrient availability. We argue that community composition may be the most effective metric for predicting competitive intensity in many ecosystems because it includes both the competitive effects of the local community and information about covarying environmental characteristics.     

Environmental policy with upstream pollution abatement technology firms

This paper examines how the existence of an upstream abatement technology sector affects optimal environmental policy. We explore whether the policy should be especially stringent in order to spur a successful export industry based on abatement technology. Furthermore, we investigate if a stringent policy can be used to increase competition in the upstream sector. Our point of departure is a three-stage game between a government in a country with a polluting downstream industry, and a limited number of upstream firms supplying abatement technologies. The government moves first, and may use its environmental policy strategically to influence the behavior of the upstream technology firms. We find that an especially stringent environmental policy towards the polluting downstream sector may be well founded, as it increases competition between the technology suppliers, leading to lower abatement costs. However, to our surprise, an especially stringent environmental policy is not a particularly good industrial policy with respect to developing successful new export sectors based on abatement technology.     

An environmental tax-shift with indirect desirable effects

Imposing environmental taxation on external costs of energy will not only affect the environmental impact of the energy sector itself, but it will tend to decrease environmental damage from other sectors of the economy as well. We have assessed the effects of a shift of taxation from taxing labour to taxation of external costs caused in the energy sector. Several examples give results compatible with the hypothesis that the changing price relation between labour and energy resulting from such a tax shift will make re-use, repairs and recycling increasingly competitive and thus tend to decrease mining as well as waste production. Likewise, less energy-intensive commodities and services in general would become increasingly competitive, and would tend to decrease the environmental load further. These environmentally desirable effects are beyond the taxed external effects of the energy sector itself and occur as an indirect effect of the increased relative price of energy.     

Competitive females are successful females; phenotype,mechanism, and selection in a common songbird

In a variety of taxa, male reproductive success is positively related to the expression of costly traits such as large body size, ornaments, armaments, and aggression. These traits are thought to improve male competitive ability and, thus, access to limited reproductive resources. Females of many species also express competitive traits. However, we know very little about the consequences of individual variation in competitive traits and the mechanisms that regulate their expression in females. Consequently, it is currently unclear whether females express competitive traits owing to direct selection or as an indirect result of selection on males. Here, we examine females of a mildly dimorphic songbird (Junco hyemalis) to determine whether females show positive covariance in traits (morphology and behavior) that may be important in a competition. We also examine whether trait expression relates either to testosterone (T) in terms of mechanism or to reproductive success in terms of function. We found that larger females were more aggressive and that greater ability to produce T in response to a physiological challenge consisting of a standardized injection of gonadotropin-releasing hormone predicted some measures of female body size and aggression. Finally, we found that aggressive females had greater reproductive success. We conclude that T may influence female phenotype and that females may benefit from expressing a competitive phenotype. We also suggest that the mild dimorphism observed in many species may be due in part to direct selection on females rather than simply a correlated response to selection in males.     

How a songbird with a continuous singing style modulates its song when territorially challenged

In songbirds of the temperate zone, often only males sing and their songs serve to attract females and to deter territorial rivals. In many species, males vary certain aspects of their singing behavior when engaged in territorial interactions. Such variation may be an honest signal of the traits of the signaler, such as fighting strength, condition, or aggressive motivation, and may be used by receivers in decisions on whether to retreat or to escalate a fight. This has been studied intensively in species that sing discontinuously, in which songs are alternating with silent pauses. We studied contextual variation in the song of skylarks (Alauda arvensis), a songbird with a large vocal repertoire and a continuous and versatile singing style. We exposed subjects to simulated territorial intrusions by broadcasting conspecific song and recorded their vocal responses. We found that males sing differently if they are singing spontaneously with no other conspecific around than if they are territorially challenged. In this last case, males produced lower-frequency syllables. Furthermore, they increased the sound density of their song: they increased the proportion of sound within song. They seem to do so by singing different elements of their repertoire when singing reactively. Furthermore, they increased the consistency of mean peak frequency: they repeated syllable types with less variability when singing reactively. Such contextual variation suggests that skylarks might use low frequencies, sound density, and song consistency to indicate their competitive potential, and thus, those song features might be important for mutual assessment of competitive abilities.     

Hartwick's rule and maximin paths when the exhaustible resource has an amenity value

This paper studies the maximin paths of the canonical Dasgupta–Heal–Solow model when the stock of natural capital is a direct argument of well-being, besides consumption. Hartwick's rule then appears as an efficient tool to characterize solutions in a variety of settings. We start with the case without technical progress. We obtain an explicit solution of the maximin problem in the case where production and utility are Cobb–Douglas. When the utility function is CES with a low elasticity of substitution between consumption and natural capital, we show that it is optimal to preserve forever a critical level of natural capital, determined endogeneously. We then study how technical progress affects the optimal maximin paths, in the Cobb–Douglas utility case. On the long run path of the economy capital, production and consumption grow at a common constant rate, while the resource stock decreases at a constant rate and is therefore completely depleted in the very long run. A higher amenity value of the resource stock leads to faster economic growth, but to a lower long run rate of depletion. We then develop a complete analysis of the dynamics of the maximin problem when the sole source of well-being is consumption, and provide a numerical resolution of the model with resource amenity. The economy consumes, produces and invests less in the short run if the resource has an amenity value than if it does not, whereas it is the contrary in the medium and long runs. However, and without surprise, the resource stock remains for ever higher with resource amenity than without.     

Ecological opportunity and phenotypic plasticity interact to promote character displacement and species coexistence

We investigated the roles of resource availability and phenotypic plasticity in promoting ecological character displacement (i.e., trait evolution stemming from resource competition between species). Because ecological character displacement generates new populations that differ in resource use, this process should only occur when exploitable resources are available. We tested this hypothesis in two species of spadefoot toads (Spea bombifrons and S. multiplicata) whose tadpoles use phenotypic plasticity to develop into either an omnivore morph, which specializes on detritus, or a physically distinctive carnivore morph, which specializes on shrimp. Both species grow best on shrimp, but when reared together, S. bombifrons outcompetes S. multiplicata for shrimp and S. multiplicata outcompetes S. bombifrons for detritus. We found that when each species occurred alone in the field, they produced similar proportions of omnivores and carnivores. When the two species occurred together, however, they underwent ecological character displacement in larval development, with S. multiplicata producing mostly omnivores, and S. bombifrons producing mostly carnivores. We combined observations of natural populations with experiments to evaluate whether such character displacement was only possible when both shrimp and detritus were relatively abundant. Mixed-species ponds contained abundant detritus and shrimp, in contrast with nearby pure-species ponds, which were deficient in one resource. Experiments revealed that S. multiplicata competed poorly when detritus was rare and that S. bombifrons competed poorly when shrimp was rare. In nature, when one of these two resources was scarce, one species was missing, perhaps through competitive exclusion by the species that was the superior competitor for the remaining resource. Thus, ecological character displacement and, therefore, coexistence of close competitors, was only possible when diverse resources were available. Finally, even if exploitable resources are available, character displacement is not guaranteed to transpire if species cannot utilize such resources expeditiously. Phenotypic plasticity provides a general and important mechanism for facilitating resource partitioning. Thus, by facilitating shifts in resource use, phenotypic plasticity and ecological opportunity may often interact to promote divergence and coexistence of competitors.     

Tradeoffs between forestry resource and conservation values under alternate policy regimes: A spatial analysis of the western Canadian boreal plains

An important element of resource management and conservation is an understanding of the tradeoffs between marketed products, such as timber, and measures of environmental quality, such as biodiversity. In this paper, we develop an integrated economic-ecological spatial optimization model that we then apply to evaluate alternate forest policies on a 560,000 km² study region of managed boreal forest in Alberta and British Columbia, Canada. The integrated model incorporates dynamic forest sector harvesting, current levels of oil and gas sector development, coarse-filter or habitat-based old forest indicators, a set of empirical forest bird abundance models, and statistical models of the natural and current fire regimes. Using our integrated model, economic tradeoff curves, or production possibility frontiers, are developed to illustrate the cost of achieving coarse-filter targets by a set time (50 years) within a 100-year time horizon. We found levels of ecological indicators and economic returns from the timber industry could both be increased if spatial constraints imposed by the current policy environment were relaxed; other factors being equal, this implies current policy should be revised. We explore the production possibility frontier's relationship to the range of natural variation of old forest habitat, and show how this range can be used to guide choices of preferred locations along the frontier. We also show that coarse-filter constraints on the abundance of certain habitat elements are sufficient to satisfy some fine-filter objectives, expressed as the predicted abundances of various species of songbirds.     

Does interspecific competition influence relationships between heterozygosity and fitness-related behaviors in juvenile Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis>)?

Very few studies have investigated the effect of genetic diversity on the behavioral and phenotypic traits linked to the competitive ability of individuals. In this study, we reared juvenile Atlantic salmon (Salmo salar) alone or with the competitive rainbow trout (Oncorhynchus mykiss) in order to: (1) to assess correlations between heterozygosity and traits related to individual competitive ability [i.e., heterozygosity–fitness correlations (HFCs)] in Atlantic salmon, and (2) to evaluate the effect of the competitive rainbow trout on any such HFCs. We also tested whether a few loci had a disproportionately large effect (i.e., the local effect hypothesis) or, on the contrary, if all loci contributed equally (i.e., the global effect hypothesis) in explaining the observed HFCs. We found significant HFCs for phenotypic traits related to the competitive ability of juvenile Atlantic salmon, i.e., the growth rate and the distance to the feeding source. Some HFCs were nonlinear, suggesting that individuals with intermediate levels of heterozygosity were favored. In addition, we found that the competition exerted by rainbow trout only weakly modified these HFCs as the relationships were highly consistent across treatments. We demonstrated that the local-effect hypothesis best explained both linear and nonlinear HFCs. Overall, our results illustrated the importance of genetic diversity in explaining the behavioral variability observed within populations. Moreover, we provide evidence that, even if a competitive species can have strong ecological effects, the relationships between genetic diversity and fitness-related traits in juvenile Atlantic salmon were not influenced by such effects.     

Why male orangutans do not kill infants

Infanticide is widespread among mammals, is particularly common in primates, and has been shown to be an adaptive male strategy under certain conditions. Although no infanticides in wild orangutans have been reported to date, several authors have suggested that infanticide has been an important selection pressure influencing orangutan behavior and the evolution of orangutan social systems. In this paper, we critically assess this suggestion. We begin by investigating whether wild orangutans have been studied for a sufficiently long period that we might reasonably expect to have detected infanticide if it occurs. We consider whether orangutan females exhibit counterstrategies typically employed by other mammalian females. We also assess the hypothesis that orangutan females form special bonds with particular “protector males” to guard against infanticide. Lastly, we discuss socioecological reasons why orangutan males may not benefit from infanticide. We conclude that there is limited evidence for female counterstrategies and little support for the protector male hypothesis. Aspects of orangutan paternity certainty, lactational amenorrhea, and ranging behavior may explain why infanticide is not a strategy regularly employed by orangutan males on Sumatra or Borneo.     

Jointly produced exhaustible resources

Natural resources are often produced jointly from composite ores, which in turn are extracted from fixed reserve endowments. In this paper market behavior is examined for such resources, and it is shown how the price of each resource will depend on its demand, and the demands and storage costs for the other resources present in the ore. The measurement of resource scarcity is discussed and the effects of uncertainty over future resource demands are examined. It is shown that the competitive market will still extract, produce, and store at socially optimal rates if firms are risk neutral and the average cost of storage is constant. Policy implications are noted, particularly with reference to government stockpiling programs.     

Attitudes towards risk and the optimal exploitation of an exhaustible resource

The exploitation of a nonrenewable natural resource, such as petroleum or mineral ores, is analyzed in a stochastic framework with price uncertainty. The market setting may be either monopolistic or competitive. We demonstrate that the rate of extraction varies directly with the resource owner's willingness to accept risk. Rish-preferring owners use the resource more rapidly than risk-neutral owners, who in turn deplete the resource more rapidly than risk-averse owners. It is also seen that the usual practice of increasing the discount rate to account for risk induces a more rapid rate of resource use, when in fact a slower rate of depletion is desired.     

Optimal movement strategies for social foragers in unpredictable environments

Spatial movement models often base movement decision rules on traditional optimal foraging theories, including ideal free distribution (IFD) theory, more recently generalized as density-dependent habitat selection (DDHS) theory, and the marginal value theorem (MVT). Thus optimal patch departure times are predicted on the basis of the density-dependent resource level in the patch. Recently, alternatives to density as a habitat selection criterion, such as individual knowledge of the resource distribution, conspecific attraction, and site fidelity, have been recognized as important influences on movement behavior in environments with an uncertain resource distribution. For foraging processes incorporating these influences, it is not clear whether simple optimal foraging theories provide a reasonable approximation to animal behavior or whether they may be misleading. This study compares patch departure strategies predicted by DDHS theory and the MVT with evolutionarily optimal patch departure strategies for a wide range of foraging scenarios. The level of accuracy with which individuals can navigate toward local food sources is varied, and individual tendency for conspecific attraction or repulsion is optimized over a continuous spectrum. We find that DDHS theory and the MVT accurately predict the evolutionarily optimal patch departure strategy for foragers with high navigational accuracy for a wide range of resource distributions. As navigational accuracy is reduced, the patch departure strategy cannot be accurately predicted by these theories for environments with a heterogeneous resource distribution. In these situations, social forces improve foraging success and have a strong influence on optimal patch departure strategies, causing individuals to stay longer in patches than the optimal foraging theories predict.     

Competitive mimicry: synthesis of a neglected class of mimetic relationships

Protective mimicry has been studied extensively for over a century. Mimicry in a competitive context, however, has remained largely neglected. It has been overlooked in mimicry classification schemes, and few systems have been rigorously studied. We define "competitive mimicry" as mimicry that enables access to a defended resource or aids in defense of a resource. We explain how competitive mimicry fits with existing mimicry classification schemes and outline criteria for identifying competitive mimicry systems. For each form of competitive mimicry, we describe the effects of the mimic on the model and receiver, predict the evolutionary dynamics of the system, and present examples. We then identify key directions for the study of competitive mimicry.     

Consequences of resource competition for sex allocation and discriminative behaviors in a hyperparasitoid wasp

Population-wide mating patterns can select for equal parental investment in both sexes, but limiting resources, such as mates or developmental substrates, can increase competition leading to biased sex ratios in favor of either sex. Such competition for resources typically occurs in spatially structured populations, where dispersal is limited. In this laboratory study, we investigate if and how resource competition affects sex allocation, discriminative behaviors and competitive interactions of the wingless hyperparasitoid Gelis acororum, which exploits patchily distributed hosts. We show that G. acororum sex ratios are male-biased and that this is not a consequence of constrained reproduction by virgin females. Our results suggest that this pattern of reproductive investment, which is only rarely observed in parasitoids, is a consequence of resource limitation, in terms of hosts rather than mates. Further, G. acororum appears not to respond to intrinsic host quality or to prior oviposition in its host. When competing inter-specifically for host resources, G. acororum outcompetes its congener Gelis agilis, but does so mainly when ovipositing on the host first. Overall, our results suggest that host resource limitation could be an important environmental factor shaping sex allocation in G. acororum, with competition taking place both intra- and inter-specifically.