Comparing resource pulses in aquatic and terrestrial ecosystems

Resource pulses affect productivity and dynamics in a diversity of ecosystems, including islands, forests, streams, and lakes. Terrestrial and aquatic systems differ in food web structure and biogeochemistry; thus they may also differ in their responses to resource pulses. However, there has been a limited attempt to compare responses across ecosystem types. Here, we identify similarities and differences in the causes and consequences of resource pulses in terrestrial and aquatic systems. We propose that different patterns of food web and ecosystem structure in terrestrial and aquatic systems lead to different responses to resource pulses. Two predictions emerge from a comparison of resource pulses in the literature: (1) the bottom-up effects of resource pulses should transmit through aquatic food webs faster because of differences in the growth rates, life history, and stoichiometry of organisms in aquatic vs. terrestrial systems, and (2) the impacts of resource pulses should also persist longer in terrestrial systems because of longer generation times, the long-lived nature of many terrestrial resource pulses, and reduced top-down effects of consumers in terrestrial systems compared to aquatic systems. To examine these predictions, we use a case study of a resource pulse that affects both terrestrial and aquatic systems: the synchronous emergence of periodical cicadas (Magicicada spp.) in eastern North American forests. In general, studies that have examined the effects of periodical cicadas on terrestrial and aquatic systems support the prediction that resource pulses transmit more rapidly in aquatic systems; however, support for the prediction that resource pulse effects persist longer in terrestrial systems is equivocal. We conclude that there is a need to elucidate the indirect effects and long-term implications of resource pulses in both terrestrial and aquatic ecosystems.     

Quantity and quality: unifying food web and ecosystem perspectives on the role of resource subsidies in freshwaters

Although the study of resource subsidies has emerged as a key topic in both ecosystem and food web ecology, the dialogue over their role has been limited by separate approaches that emphasize either subsidy quantity or quality. Considering quantity and quality together may provide a simple, but previously unexplored, framework for identifying the mechanisms that govern the importance of subsidies for recipient food webs and ecosystems. Using a literature review of > 90 studies of open-water metabolism in lakes and streams, we show that high-flux, low-quality subsidies can drive freshwater ecosystem dynamics. Because most of these ecosystems are net heterotrophic, allochthonous inputs must subsidize respiration. Second, using a literature review of subsidy quality and use, we demonstrate that animals select for high-quality food resources in proportions greater than would be predicted based on food quantity, and regardless of allochthonous or autochthonous origin. This finding suggests that low-flux, high-quality subsidies may be selected for by animals, and in turn may disproportionately affect food web and ecosystem processes (e.g., animal production, trophic energy or organic matter flow, trophic cascades). We then synthesize and review approaches that evaluate the role of subsidies and explicitly merge ecosystem and food web perspectives by placing food web measurements in the context of ecosystem budgets, by comparing trophic and ecosystem production and fluxes, and by constructing flow food webs. These tools can and should be used to address future questions about subsidies, such as the relative importance of subsidies to different trophic levels and how subsidies may maintain or disrupt ecosystem stability and food web interactions.     

Canadian perspectives on aluminum

Summary The multi-media approach to aluminum exposure will allow a more informed decision on the inclusion or exclusion of various exposure media in future epidemiological studies.Knowledge of the types of Al (speciation) and their respective bioavailability will enable interpretation of the importance of specific media.     

Effects of stricter environmental regulations on resource development

This analysis seeks to understand whether changes in oil regulation brought about by the shale revolution have restricted the pace of drilling and production. This hypothesis is tested using data on North Dakota and Montana both before and after North Dakota increased regulations that raise fixed costs. Results generally find that the new regulations had no statistical impact on the pace of drilling and production, however it is found that smaller operators reduced their production and exited. These results are instructive for policymakers who weigh the loss of economic welfare against improved environmental quality when deciding on new regulations.     

Temporary natural resource cartels

We analyze the behavior of a nonrenewable resource cartel that anticipates being forced, at some date in the future, to break up into an oligopolistic market in which its members will then have to compete as rivals. Under reasonable assumptions about the value function of the individual firms in the oligopolistic equilibrium that follows the breakup, we show that the cartel will then produce more over the same interval of time than it would if there were no threat of dissolution, and that its rate of extraction is a decreasing function of the cartel's life; that there are circumstances under which the cartel will attach a negative marginal value to the resource stocks, in which case the rate of depletion will be increasing over time during the cartel phase; that, for a given date of dissolution, the equilibrium stocks allocated to the post-cartel phase will increase as a function of the total initial stocks, whereas those allocated to the cartel phase will increase at first, but begin decreasing beyond some level of the total initial stocks.     

Coastal directories and beyond: Providing multidisciplinary coastal zone resource information for resource management

Baseline resource information in an easily accessible form is a vital starting point for developing coastal zone management. On behalf of a wide-ranging group of organizations involved in the management of the U.K. maritime zone, the Joint Nature Conservation Committee (JNCC) is compiling a series of 16 regional volumes. The volumes contain multidisciplinary coastal zone resource information arranged in ten chapters under the general title ‘Coasts and Seas of the UK’. These volumes form part of a series of paper and electronic publications of coastal information being produced by JNCC's Coastal Directories Project and are designed to meet the needs of planners and all others involved in decision-making and management of the coast.     

Renewable resource management and extinction

Several authors have noted that extinction of a biological resource could be consistent with a policy of maximizing the discounted present value of economic rent. However, the arguments put forward in support of this assertion have hitherto been based on autonomous models. In this note we discuss the nonautonomous case, which turns out to be considerably more difficult to analyze.     

Constraints on global fire activity vary across a resource gradient

We provide an empirical, global test of the varying constraints hypothesis, which predicts systematic heterogeneity in the relative importance of biomass resources to burn and atmospheric conditions suitable to burning (weather/climate) across a spatial gradient of long-term resource availability. Analyses were based on relationships between monthly global wildfire activity, soil moisture, and mid-tropospheric circulation data from 2001 to 2007, synthesized across a gradient of long-term averages in resources (net primary productivity), annual temperature, and terrestrial biome. We demonstrate support for the varying constraints hypothesis, showing that, while key biophysical factors must coincide for wildfires to occur, the relative influence of resources to burn and moisture/weather conditions on fire activity shows predictable spatial patterns. In areas where resources are always available for burning during the fire season, such as subtropical/tropical biomes with mid-high annual long-term net primary productivity, fuel moisture conditions exert their strongest constraint on fire activity. In areas where resources are more limiting or variable, such as deserts, xeric shrublands, or grasslands/savannas, fuel moisture has a diminished constraint on wildfire, and metrics indicating availability of burnable fuels produced during the antecedent wet growing seasons reflect a more pronounced constraint on wildfire. This macro-scaled evidence for spatially varying constraints provides a synthesis with studies performed at local and regional scales, enhances our understanding of fire as a global process, and indicates how sensitivity to future changes in temperature and precipitation may differ across the world.     

Coastal directories and beyond: providing multidisciplinary coastal zone resource information for resource management

Baseline resource information in an easily accessible form is a vital starting point for developing coastal zone management. On behalf of a wide-ranging group of organizations involved in the management of the U.K. maritime zone, the Joint Nature Conservation Committee (JNCC) is compiling a series of 16 regional volumes. The volumes contain multi-disciplinary coastal zone resource information arranged in ten chapters under the general title ‘Coasts and Seas of the UK’. These volumes form part of a series of paper and electronic publications of coastal information being produced by JNCC’s Coastal Directories Project and are designed to meet the needs of planners and all others involved in decision-making and management of the coast.     

A note on the effect of tax brackets on non-renewable resource extraction

Tax brackets are a common feature of non-renewable resource taxes. Although the introduction of brackets would seem to be an innocuous way of approximating a non-linear tax system, the dynamic effects are surprising. This paper shows that the presence of tax brackets in both a severance tax system and a profits tax system can induce the extractive firm to depart from the well-known monotonically declining extraction profile and to choose instead a profile which has constant extraction rates over some interval of time.     

基于GIS的广东省土壤资源信息系统构建研究

研究应用地理信息系统构建广东省土壤资源信息系统的总体模式,建立了土壤资源信息系统的基本功能构成;探索了土壤资源空间信息与文献资料的Internet网络化这一土壤研究新领域,并实现了土壤资源空间信息Internet网络化.     

Competition among eucalyptus trees depends on genetic variation and resource supply

Genetic variation and environmental heterogeneity fundamentally shape the interactions between plants of the same species. According to the resource partitioning hypothesis, competition between neighbors intensifies as their similarity increases. Such competition may change in response to increasing supplies of limiting resources. We tested the resource partitioning hypothesis in stands of genetically identical (clone-origin) and genetically diverse (seed-origin) Eucalyptus trees with different water and nutrient supplies, using individual-based tree growth models. We found that genetic variation greatly reduced competitive interactions between neighboring trees, supporting the resource partitioning hypothesis. The importance of genetic variation for Eucalyptus growth patterns depended strongly on local stand structure and focal tree size. This suggests that spatial and temporal variation in the strength of species interactions leads to reversals in the growth rank of seed-origin and clone-origin trees. This study is one of the first to experimentally test the resource partitioning hypothesis for intergenotypic vs. intragenotypic interactions in trees. We provide evidence that variation at the level of genes, and not just species, is functionally important for driving individual and community-level processes in forested ecosystems.     

Impact of contaminant exposure on resource contests in an invasive fish

There is increasing concern for the disruptive effects seen in aquatic species exposed to environmental contaminants. However, few studies have investigated the impact of such contaminants on the behavior of individuals living in exposed waters. Contaminant exposure can affect animal populations by disrupting behaviors including feeding, locomotion, and mating. In this study, we examined how living in an ecosystem polluted by combinations of polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and heavy metals (arsenic, cadmium, iron, lead, zinc) impacts contest behavior in the round goby (Neogobius melanostomus). Fish collected from heavily contaminated and cleaner sites in Lake Ontario were subjected to a resource contest to determine the effect of these contaminants on aggression and the establishment of dominance hierarchies, which in turn influence access to food, shelter, and mating opportunities. Dominance establishment (a clear resource winner) was less obvious among fish from the contaminated site compared to the more stable hierarchies that formed between pairs of fish from the clean site. Pairs of fish from the contaminated site performed more assessment displays compared to fish from clean sites. These results suggest that the costs of living in an environment under exposure can shape behavioral repertoires. The altered conflict resolution strategies of contaminated fish may reflect impaired cognitive function, sensory perception, and/or higher metabolic load associated with aggression. This study provides support for the utilization of quantifiable behavioral differences as ecologically relevant measures of contaminant exposure.     

A note on discreteness and Jevonsian deterioration in non-renewable resource exploration

Arrow and Chang's model of mineral exploration can be extended naturally to allow for deterioration in land quality, including the possibility that some land will remain unexplored even if the resource is indispensable. Discreteness is central to the necessary and sufficient conditions.     

Understanding conservationists’ perspectives on the new‐conservation debate

A vibrant debate about the future direction of biodiversity conservation centers on the merits of the so‐called new conservation. Proponents of the new conservation advocate a series of positions on key conservation ideas, such as the importance of human‐dominated landscapes and conservation's engagement with capitalism. These have been fiercely contested in a debate dominated by a few high‐profile individuals, and so far there has been no empirical exploration of existing perspectives on these issues among a wider community of conservationists. We used Q methodology to examine empirically perspectives on the new conservation held by attendees at the 2015 International Congress for Conservation Biology (ICCB). Although we identified a consensus on several key issues, 3 distinct positions emerged: in favor of conservation to benefit people but opposed to links with capitalism and corporations, in favor of biocentric approaches but with less emphasis on wilderness protection than prominent opponents of new conservation, and in favor of the published new conservation perspective but with less emphasis on increasing human well‐being as a goal of conservation. Our results revealed differences between the debate on the new conservation in the literature and views held within a wider, but still limited, conservation community and demonstrated the existence of at least one viewpoint (in favor of conservation to benefit people but opposed to links with capitalism and corporations) that is almost absent from the published debate. We hope the fuller understanding we present of the variety of views that exist but have not yet been heard, will improve the quality and tone of debates on the subject.     

Economic aspects of natural resource exploitation

Low entropy accumulations of matter and energy are more economic for humans to exploit as natural resources. This accumulation of a resource takes place over time and the most concentrated resources, such as fossil fuels, are created over geological ages. As the most concentrated resources become depleted it may be possible for technology to enable the exploitation of less concentrated resources, such as low-grade metal ores or thinly populated fishing grounds. Analysis of the timescales necessary to create different types of natural resource reveals three distinct groups. Further consideration of economic characteristics of resources, including ownership and access, and rate of consumption relative to rate of supply confirms the grouping of resources into the three distinct groups. Rate of change of entropy as a resource is exploited is an indicator of its impact on the environment. Consideration of this again suggests three distinct groups of resources, and this paper identifies them as: continuous natural resources (CNR), such as solar power and wind power; potentially renewable resources (PRR), such as fish and forests; and non-renewable resources (NRR), such as fossil fuels and metals.     

Microbial productivity in variable resource environments

The rate, timing, and quality of resource supply exert strong controls on a wide range of ecological processes. In particular, resource-mediated changes in microbial activity have the potential to alter ecosystem processes, including the production and respiration of organic matter. In this study, we used field experiments and simulation modeling to explore how aquatic heterotrophic bacteria respond to variation in resource quality (low vs. high) and resource schedule (pulse vs. press). Field experiments revealed that one-time pulse additions of resources in the form of dissolved organic carbon (DOC) caused short-lived (< or =48 h) peaks in bacterial productivity (BP), which translated into large differences across treatments: cumulative BP was twice as high in the pulse vs. press treatment under low resource quality, and five times as high under high resource quality. To gain a more mechanistic understanding of microbial productivity in variable resource environments, we constructed a mathematical model to explore the attributes of bacterial physiology and DOC supply that might explain the patterns observed in our field experiments. Model results suggest that the mobilization rate of refractory to labile carbon, an index of resource quality, was critical in determining cumulative differences in BP between pulse and press resource environments (BPPu:Pr ratios). Moreover, BPPu:Pr ratios were substantially larger when our model allowed for realistic changes in bacterial growth efficiency as a function of bacterial carbon consumption. Together, our field and modeling results imply that resource schedule is important in determining the flow of material and energy from microbes to higher trophic levels in aquatic food webs, and that the effects of resource quality are conditional upon resource schedule. An improved understanding of the effects of resource variability on microorganisms is therefore critical for predicting potential changes in ecosystem functioning in response to environmental change, such as altered DOC fluxes from terrestrial to aquatic ecosystems.