Non-renewable resource prices: Deterministic or stochastic trends?

In this paper, we examine temporal properties of 11 natural resource real price series from 1870 to 1990. Recent studies by Ahrens and Sharma [Trends in natural resource commodity prices: deterministic or stochastic? J. Environ. Econom. Manage. 33(1997)59–74], Berck and Roberts [Natural resource prices: will they ever turn up? J. Environ. Econom. Manage. 31(1996)65–78], and Slade [Grade selection under uncertainty: least cost last and other anomalies, J. Environ. Econom. Manage. 15(1988)189–205], among others, find that many non-renewable resource prices have a stochastic trend. We revisit this issue by employing a Lagrangian multiplier unit root test that allows for two endogenously determined structural breaks with and without a quadratic trend. Contrary to previous research, we find evidence against the unit root hypothesis for all price series. Our findings support characterizing natural resource prices as stationary around deterministic trends with structural breaks. We additionally show that both pre-testing for unit roots with breaks and allowing for breaks in the forecast model can improve forecast accuracy. Overall, the results in this paper are important in both a positive and normative sense; without an appropriate understanding of the dynamics of a time series, empirical verification of theories, forecasting, and proper inference are potentially fruitless.     

Localization of infaunal prey by the sea star<Emphasis Type="Italic"> Leptasterias polaris</Emphasis>

We performed field and laboratory studies to investigate how large adult Leptasterias polaris detect and locate their major prey, large infaunal bivalves, in the sediment bottom community. A field survey using SCUBA diving showed that 95% of the locations where L. polaris dug into the sediment bottom were over bivalves and this success rate was much greater than if digging was done at random (22%). Furthermore, when sea stars were provided with a low density of randomly distributed prey in a laboratory arena, they dug exclusively in locations where a clam had been buried. These observations indicated that L. polaris locates infaunal prey prior to investing energy into digging. Studies in a laboratory flow tank showed that L. polaris readily detected and moved towards its preferred prey Ensis directus whereas its responses to less preferred prey Mya truncata and Spisula polynyma were much weaker. The degree to which it oriented towards these three common prey seemed to reflect potential energy intake relative to foraging costs (which likely increase with the depth of the different prey) and risks from interactions with other carnivores (which are greatest when feeding on large prey). This is the first study to clearly demonstrate that sea stars use prey odours to locate infaunal prey.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00227-004-1497-1Communicated by R.J. Thompson, St. Johns     

Effects of Social Structure and Prey Dynamics on Extinction Risk in Gray Wolves

Extinction models based on diffusion theory generally fail to incorporate two important aspects of population biology—social structure and prey dynamics. We include these aspects in an individual-based extinction model for small, isolated populations of the gray wolf (Canis lupus). Our model predicts mean times to extinction significantly longer than those predicted by more general (diffusion) models. According to our model, an isolated population of 50 wolves has a 95% chance of surviving just 9 years and only a 30% chance of surviving beyond 100 years. Reflecting the influence of social structure, a wolf population initially comprising 50 individuals is expected to persist only a few years longer, on average (71 years), than is a population initially comprising just a single reproductive pair (62 years). In contrast, substantially greater average prey abundance leads to dramatically longer expected persistence times. Autocorrelated prey dynamics result in a more complex distribution of extinction times than predicted by many extinction models. We contend that demographic stochasticity may pose the greatest threat to small, isolated wolf populations, although environmental stochasticity and genetic effects may compound this threat. Our work highlights the importance of considering social structure and resource dynamics in the development of population viability analyses.     

Defensive secretion of a flightless grasshopper: Failure to prevent lizard attack

Summary We tested the role of a grasshopper defensive secretion in deterring lizard predation. Adults, but not young larvae, of the chemically defended lubber grasshopperRomalea guttata (=microptera) froth a volatile secretion when attacked by predators. The lizardAnolis carolinensis failed to strike juvenile lubbers (which lack secretion) in laboratory trials. Survivorship of palatable crickets loaded with secretion offered toA. carolinensis was not significantly different from survivorship of control crickets. In experiments designed to investigate if lizards learn an aversion to the secretion, striking times forSceloporus undulatus fed wax worms coated with secretion were not significantly different over three days of trials. Three primary conclusions are drawn from these data. First, the secretion may not be necessary for lubber protection from lizards. Second, lubber secretion does not appear to deter lizards from attacking or eating prey items. Third, lizards do not appear to develop an aversion to the secretion.     

Systemic retention of ingested cantharidin by frogs

Summary Frogs(Rana pipiens) fed on blister beetles (Meloidae) or cantharidin, retain cantharidin systemically. After cessation of feeding, they void the compound relatively quickly. Systemic cantharidin does not protect frogs against ectoparasitic feeding by leeches(Hirudo medicinalis) or predation by snakes(Nerodia sipedon). As suggested by our data, and from reports in the early literature, ingestion of cantharidin-containing frogs can pose a health threat to humans.Paper no. 95 of the seriesDefense Mechanisms of Arthropods; no. 94 is LaMunyon & Eisner, Psyche (in press)     

Estrus cycle asynchrony in wild female chimpanzees, Pan troglodytes schweinfurthii

Although estrous synchrony has been reported in a number of mammalian species, most often among primates, methodological and analytical problems make it difficult to interpret these results. We developed a novel estrous synchrony index and employed a randomization procedure to analyze long-term observations of female chimpanzee (Pan troglodytes schweinfurthii) estrous cycles at the Mahale Mountains National Park, Tanzania. Our results revealed that female chimpanzees at Mahale avoid synchronizing their estrous periods with each other. We also found that birthrates decreased as the breeding sex ratio increased. We suggest that estrous asynchrony decreases female–female competition for mates. Asynchrony may also reduce the potential for male sexual coercion by nonpreferred mating partners.     

The mating system of two hybridizing species of water striders (Gerridae)

Summary We studied oviposition, feeding and mating behavior of the water striders Limnoporus dissortis and L. notabilis in sympatric and allopatric populations occurring on semi-permanent ponds in Alberta and British Columbia, Canada. Here we describe the mating system of the species and consider the evolution and maintenance of reproductive strategies employed by both sexes. Females of both species oviposited along edges of floating vegetation, either with a guarding, postcopulatory male in attendance, or alone and independent of copulation. Some females ovipositing alone were discovered by males, and when pressed for copulation, either (1) abandoned oviposition or (2) copulated and then resumed oviposition. Females that oviposited with a guarding male laid more eggs than those that completed oviposition alone. Most breeding females accepted prey offered experimentally, while a large proportion of males rejected prey but responded to model gerrids with aggressive displays and mating behavior. Males displayed three mating tactics: (1) territorial-signaling (TS), (2) patrol-signaling (PS), and (3) silent patrolling (SP). All territorial males produced surface waves from oviposition sites before attempting to mate. Some patrolling males signaled, while approaching potential mates as an aid in sex discrimination, but others did not signal and mounted both males and females. When presented with dead gerrid models, males of L. notabilis discriminated between sexes while those of L. dissortis mounted both male and female conspecifics. Collectively, males employing TS tactics fertilized more eggs than patrolling males and TS males of L. notabilis fertilized relatively more eggs than those of L. dissortis. Individual males switched frequently between territorial and patrolling behavior both under natural conditions and in field exclosures. TS males gave more signals per encounter than PS males suggesting that signaling varies with male dominance. Choice of tactic did not depend upon hunger level and was not associated with significant differences in body length in single-species populations. However, in a mixed population, the smaller males of L. dissortis were rarely territorial and signaled infrequently.     

Arsenic management in shale oil upgrading

Although the timing remains uncertain, the production of synthetic crude from oil shale seems to be a likely response to diminishing petroleum reserves. Although not unique to shale oil, the presence of arsenic, ranging in concentration from a few to over 100 parts per million, poses a special concern.Arsenic is typically removed from the shale oil by a hydro-processing technique and is concentrated on a catalyst as thermally stable metal arsenides and metal arsenous sulfides. Because this arsenic is still slightly soluble in water, making the spent catalyst a hazardous material, passivation and extraction techniques were investigated to make the catalyst safe for disposal. Passivation techniques were not successful. While extraction procedures were capable of removing over 75% of the arsenic, treated material may still be acceptable.     

The “dawn chorus” and incubation in the coot (Fulica atra L.)

Summary It has been proposed that both acoustic and non-acoustic factors could explain the dawn peak of territorial advertisement in birds. The coot is a territorial waterbird which does not use vocal advertisement either to attract mates or defend territory boundaries. In spite of the absence of acoustic factors affecting the time budgeting of advertisement, this species shows a dawn peak of display and aggressive behaviours. This trend occurs both in the presence and absence of non-territorial prospecting birds, but the trends are quantitatively different in these two cases (Fig. 1). Males participate in display and fighting more often than females, probably because of their greater size and effectiveness in defence. This asymmetry in defence abilities governs the time budgeting of incubation, the male tending to take time off the nest when territorial defence is most necessary (Fig. 2).