Counterintuitive effects of large-scale predator removal on a midlatitude rodent community

Historically, small mammals have been focal organisms for studying predator-prey dynamics, principally because of interest in explaining the drivers of the cyclical dynamics exhibited by northern vole, lemming, and hare populations. However, many small-mammal species occur at relatively low and fairly stable densities at temperate latitudes, and our understanding of how complex predator assemblages influence the abundance and dynamics of these species is surprisingly limited. In an intact grassland ecosystem in western Montana, USA, we examined the abundance and dynamics of Columbian ground squirrels (Spermophilus columbianus), deer mice (Peromyscus maniculatus), and montane voles (Microtus montanus) on 1-ha plots where we excluded mammalian and avian predators and ungulates, excluded ungulates alone, or allowed predators and ungulates full access. Our goal was to determine whether the relatively low population abundance and moderate population fluctuations of these rodents were due to population suppression by predators. Our predator-exclusion treatment was divided into two phases: a phase where we excluded all predators except weasels (Mustela spp.; 2002-2005), and a phase where all predators including weasels were excluded (2006-2009). Across the entire duration of the experiment, predator and/or ungulate exclusion had no effect on the abundance or overall dynamics of ground squirrels and deer mice. Ground squirrel survival (the only species abundant enough to accurately estimate survival) was also unaffected by our experimental treatments. Prior to weasel exclusion, predators also had no impacts on montane vole abundance or dynamics. However, after weasel exclusion, vole populations reached greater population peaks, and there was greater recruitment of young animals on predator-exclusion plots compared to plots open to predators during peak years. These results suggest that the impacts of predators cannot be generalized across all rodents in an assemblage. Furthermore, they suggest that specialist predators can play an important role in suppressing vole abundance even in lower-latitude vole populations that occur at relatively low densities.     

Diet of young Atlantic bluefin tuna (<Emphasis Type="Italic">Thunnus thynnus</Emphasis>) in eastern and western Atlantic foraging grounds

Atlantic bluefin tuna (Thunnus thynnus) are highly migratory predators whose abundance, distribution, and somatic condition have changed over the past decades. Prey community composition and abundance have also varied in several foraging grounds. To better understand underlying food webs and regional energy sources, we performed stomach content and stable isotope analyses on mainly juvenile (60–150 cm curved fork length) bluefin tuna captured in foraging grounds in the western (Mid-Atlantic Bight) and eastern (Bay of Biscay) Atlantic Ocean. In the Mid-Atlantic Bight, bluefin tuna diet was mainly sand lance (Ammodytes spp., 29% prey weight), consistent with historic findings. In the Bay of Biscay, krill (Meganyctiphanes norvegica) and anchovy (Engraulis encrasicolus) made up 39% prey weight, with relative consumption of each reflecting annual changes in prey abundance. Consumption of anchovies apparently declined after the local collapse of this prey resource. In both regions, stable isotope analysis results showed that juvenile bluefin tuna fed at a lower trophic position than indicated by stomach content analysis. In the Mid-Atlantic Bight, stable isotope analyses suggested that >30% of the diet was prey from lower trophic levels that composed <10% of the prey weights based upon traditional stomach content analyses. Trophic position was similar to juvenile fish sampled in the NW Atlantic but lower than juveniles sampled in the Mediterranean Sea in previous studies. Our findings indicate that juvenile bluefin tuna targeted a relatively small range of prey species and regional foraging patterns remained consistent over time in the Mid-Atlantic Bight but changed in relation to local prey availability in the Bay of Biscay.     

The hypoxia avoidance behaviour of juvenile Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis> L.) depends on the provision and pressure level of an O<Subscript>2</Subscript> refuge

The frequency of low O₂ (hypoxia) has increased in coastal marine areas but how fish avoid deleterious water masses is not yet clear. To assess whether the presence and oxygen pressure (PO₂) level of an O₂ refuge affects the hypoxia avoidance behaviour of fish, individual Atlantic cod (Gadus morhua L.) were exposed to a range of O₂ choices in a 2-way choice chamber at 11.4°C over two different experiments. Cod in the first experiment were allowed access to a fixed O₂ refuge (fully air-saturated seawater) whilst oxygen pressure (PO₂) on the other side was reduced in steps to a critically low level, i.e. 4.3 kPa—a point where cod can no longer regulate O₂ consumption. Under these conditions, cod did not avoid any level of hypoxia and fish swimming speed also remained unchanged. In contrast, strong avoidance reactions were exhibited in a second experiment when fish were again exposed to 4.3 kPa but the safety, i.e. PO₂, of the refuge was reduced. Fish not only spent less time at 4.3 kPa as a result of fewer sampling visits but they also swam at considerably slower speeds. The presence of an avoidance response was thus strongly related to refuge PO₂ and it is unlikely that cod, and possibly other fish species, would enter low O₂ to feed in the wild if a sufficiently safe O₂ refuge was not available. It is therefore hypothesized that the feeding range of fish may be heavily compressed if hypoxia expands and intensifies in future years.     

Trade, technology, and the environment: Does access to technology promote environmental regulation?

Focusing specifically on regulation of coal-fired power plants, we examine how technological innovation by early adopters influences the timing of new environmental regulation in non-innovating countries. We build a general equilibrium model of an open economy to identify the political-economy determinants of regulation. With a newly created dataset of SO₂ and NO_x regulations for coal-fired power plants and a patent-based measure of the technology frontier, we estimate the determinants of environmental regulation diffusion. Our findings support the hypothesis that international economic integration eases access to environmentally friendly technologies and leads to earlier adoption, ceteris paribus, of regulation in non-innovating countries. However, we also find evidence that domestic trade protection promotes earlier adoption allowing shifts of regulatory costs to domestic consumers. Furthermore, international market power permits large countries to shift costs to foreign consumers. Other political economy factors, such as the quality of domestic coal, are also important determinants.     

Changes in microbial community characteristics and soil organic matter with nitrogen additions in two tropical forests

Microbial communities and their associated enzyme activities affect the amount and chemical quality of carbon (C) in soils. Increasing nitrogen (N) deposition, particularly in N-rich tropical forests, is likely to change the composition and behavior of microbial communities and feed back on ecosystem structure and function. This study presents a novel assessment of mechanistic links between microbial responses to N deposition and shifts in soil organic matter (SOM) quality and quantity. We used phospholipid fatty acid (PLFA) analysis and microbial enzyme assays in soils to assess microbial community responses to long-term N additions in two distinct tropical rain forests. We used soil density fractionation and 13C nuclear magnetic resonance (NMR) spectroscopy to measure related changes in SOM pool sizes and chemical quality. Microbial biomass increased in response to N fertilization in both tropical forests and corresponded to declines in pools of low-density SOM. The chemical quality of this soil C pool reflected ecosystem-specific changes in microbial community composition. In the lower-elevation forest, there was an increase in gram-negative bacteria PLFA biomass, and there were significant losses of labile C chemical groups (O-alkyls). In contrast, the upper-elevation tropical forest had an increase in fungal PLFAs with N additions and declines in C groups associated with increased soil C storage (alkyls). The dynamics of microbial enzymatic activities with N addition provided a functional link between changes in microbial community structure and SOM chemistry. Ecosystem-specific changes in microbial community composition are likely to have far-reaching effects on soil carbon storage and cycling. This study indicates that microbial communities in N-rich tropical forests can be sensitive to added N, but we can expect significant variability in how ecosystem structure and function respond to N deposition among tropical forest types.     

Enforcement and price controls in emissions trading

This paper examines how enforcement affects the structure and performance of emissions trading programs with price controls under uncertainty about firms' abatement costs. The analysis highlights how an enforcement strategy can cause abatement-cost risk to be transmitted to enforcement costs via the price of permits. When this occurs, accommodating the effect of abatement-cost risk with an optimal policy results in higher expected emissions and lower expected permit price than their second-best optimal values. However, it is possible to design an enforcement strategy that shields enforcement costs from abatement-cost risk by tying sanctions directly to permit prices. This enforcement strategy stabilizes enforcement effort, the optimal permit supply and price controls are independent of enforcement costs, and the policy produces the second-best optimal outcome.     

Lead uptake by Eichhornia Crassipes

Factors influencing uptake of lead(II) by the water hyacinth (Eichhornia Crassipes), were examined. Two phases of uptake were observed for the concentration range investigated (0.01–1000 ppm). The initial, rapid uptake phase of about 4 hours is followed by a slower, near linear phase extending past 24 hours. Stirring the solution enhanced uptake, suggesting that lead removal is in part diffusion limited. In the range of 4–8, pH has little effect on uptake where as outside this range, uptake is reduced. Increased solution volume or rootmass results in more metal being removed by the plant. The presence of strong complexers blocks the initial rapid uptake phase as does the presence of Zn(II), Cd(II), Hg(II), and Fe(III). Strong complexers can also strip a portion of any lead already removed from solution by the plant.     

Comparative Toxicities of Polar and Non-Polar Organic Fractions From Sediments Affected By the Exxon Valdez Oil Spill in Prince William Sound,Alaska

Abstract

Standardized tests were applied to aromatic and polar fractions of sediment extracts to determine whether polar constituents or oxidative degradation products contributed significantly to the toxicity of sediments oiled by the Exxon Valdez spill. Intertidal sediment and pore-water samples were collected in September 1990 from two heavily oiled sites and an unoiled site in Prince William Sound (PWS). Methylene chloride extracts from these samples were fractionated by liquid chromatography into aliphatic, aromatic and polar fractions, and the aromatic and polar fractions were tested for toxicity using the Microtox^R test, bivalve larval mortality and development (Mytilus); several measures of genotoxicity in Mytilus, including SOS Chromotest^R, anaphase aberrations and sister chromatid exchange; and survival, anaphase aberrations and teratogenicity in coho salmon (Onchorhynchus kisutch). Microtox^R and SOS Chromotest^R protocols were applied in a screening mode to all samples, whereas other tests were applied only to selected fractions from two sites. Samples from Bay of Isles (oiled) were consistently more toxic (usually only 2 to 5-fold) than the Mooselips Bay (unoiled) samples, which gave very low responses in all tests. for both sites, however, responses to polar and aromatic fractions were about the same in most tests, suggesting that while the overall toxicity of the oil was low in these samples, at least part of that toxicity was derived from polar constituents. Compared to the parent hydrocarbons, polar oxidation products partition preferentially into pore-water and are more rapidly diluted and dispersed in the water column. These results suggest that polar oxidation products of petroleum hydrocarbons pose little risk to marine organisms, except possibly for infauna continuously exposed to pore-water in heavily oiled sediments. Independent surveys showed that sediment toxicity in PWS declined during 1989–1991 to near background levels, in accord with previous understanding of oil weathering and toxicity.     

Comparative aspects of mountain land resources management and sustainability: Case studies from India and Canada

India and Canada share a common heritage in natural resources management. Both have a colonial background, settlers and indigenous peoples; there is a history of management agencies with utilitarian attitudes, and a history of treating public lands as commodities for commerce rather than as resources for local livelihoods. This historical context guided the overall goal of this study, which was policy development for the sustainable use of mountain environments. Interviews, workshops and seminars were held with local people and resource management professionals in a comparative case study in two regions; the Kullu area in Himachal Pradesh, India and the Arrow Lakes area in British Columbia, Canada. The paper is organized around two main objectives of the work relating to the successes and failures of mountain environment resource management policies and the development of criteria for assessing and monitoring sustainability in mountain environments, in particular, criteria for examining relevant crosscultural dimensions of sustainable development in these environments. By way of conclusion the paper considers further ways in which traditional resource policy development and implementation is being challenged by changing values and priorities; ecosystems management with people; and co-management and public participation.     

Levels of social behaviors and genetic structure in a population of round-tailed ground squirrels (Xerospermophilus tereticaudus)

Ground-dwelling sciurids exhibit a continuum of sociality and several models predict levels of sociality within this taxon. Models of ground squirrel sociality predict round-tailed ground squirrels (Xerospermophilus tereticaudus) to be solitary; however, previous behavioral studies suggest round-tailed ground squirrels have a matrilineal social structure. To resolve this discrepancy, we combined behavioral observations with genetic analyses of population structure. We assessed levels of agonistic and amicable behaviors combined with fine-scale population genetic structure of round-tailed ground squirrels in a multi-year study in AZ. Only 45 agonistic and 40 amicable interactions were observed between adults in over 137 h of observations. Overall rates of agonistic or amicable interactions between adults were low (≤0.69/h), with no relationship between relatedness of individuals and rates of either amicable or agonistic interactions. Interactions between juvenile littermates were predominantly amicable. Population substructure was not evident with Bayesian analyses, global or pairwise F _ST values; average relatedness among females was not different from males. However, in 2006, the year after a population reduction through targeted animal elimination, a population bottleneck was detected within at least five of seven loci. Contrary to previous behavioral studies, this population of round-tailed ground squirrels, although aggregated spatially, did not exhibit high levels of social behavior nor subpopulation genetic structure. Analyses of the genetic relationships and sociality along a continuum, particularly within aggregates of individuals, may lead to insights into the origin and maintenance of social behaviors by elucidating the mechanisms by which aggregates with intermediate social levels are formed and maintained.