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.     

Mitochondrial DNA Variability of the Gray Wolf: Genetic Consequences of Population Decline and Habitat Fragmentation

The gray wolf is a large, highly mobile predator whose original geographic range included most of the Northern Hemisphere. High rates of genetic exchange probably characterized even distantly-separated populations in the past, but recent population declines and habitat fragmentation have isolated previously contiguous populations, especially in the Old World. We examine mitochondrial DNA (mtDNA) variability among twenty-six populations of wolves from throughout their geographic range. We find eighteen mtDNA genotypes in gray wolves, seven of these are derived from hybridization with coyotes, four are confined to the New World, six are confined to the Old World and one is shared by both areas. Genetic differentiation among wolf populations is significant but small in magnitude. In the Old World, most localities have a single unique genotype, whereas in the New World several genotypes occur at most localities and three of the five genotypes are nearly ubiquitous. The pattern of genetic differentiation in the gray wolf contrasts with that of another large, highly vagile canid, the coyote, in which genetic differentiation among populations is not significant even among widely separated localities. We suggest that the difference between these two species reflects the rapid, recent increase in coyote numbers and expansion of their geographic range, and the coincident decline in gray wolf populations. Apparent genetic differences among extant wolf populations may be a recent phenomenon reflecting population declines and habitat fragmentation rather than a long history of genetic isolation.     

Can Eco-Labels Tune a Market? Evidence from Dolphin-Safe Labeling

In this paper we test whether the dolphin-safe labels altered consumer purchases of tuna. We also provide a partial measure of the total welfare effects of the dolphin-safe labeling policy. The results confirm our hypothesis that the dolphin–tuna controversy and the subsequent implementation of dolphin-safe labeling affected consumer behavior. Further, the paper provides market-based evidence that consumers can respond to eco-labels; the dolphin-safe label increased the market share of canned tuna. The welfare analysis provides a partial measure of society's willingness to pay to avoid personally contributing to dolphin mortality as a result of tuna fishing.     

Brood dispersal and multiple central place foraging by Lapland longspur parents

Summary Lapland longspur chicks continued to be fed by their parents for 2 weeks after nest departure. Shortly after they left the nest, broods were divided evenly into two units each tended by a single parent. Female-tended brood units dispersed away from the nest at a faster average distance per day than those tended by males. The distance between offspring within a brood unit also increased as chicks got older. For the first 8–10 d after nest departure, parents were multiple central place foragers, making 1–8 foraging trips away from each dispersed chick (i.e. the central place) before moving on to feed another chick in a similar fashion. During the final 5–7 d before independence, chicks were quite mobile and followed parents on their foraging bouts. A simulation model shows that brood dispersal reduced total parental travel time per chick, primarily because each chick moved closer to a foraging site. By comparing models for a variety of brood division and foraging itinerary scenarios, we also show that multiple central place foraging by parents visiting different, separated brood units is less energetically expensive than other reasonable alternatives.Although brood dispersal is usually considered to be an adaptation for avoiding predation, it can also help parents reduce the energetic costs of parental care.     

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)     

Acid mine drainage from inactive eastern coal operations

The most widely used technique for abatement of acid drainage from inactive surface mines and refuse disposal areas is revegetation of a soil cover applied to the waste material. Nonetheless, acid production often persists and in some cases, limits establishment of vegetation. This paper reports on several field studies intended to determine the location of pyrite oxidation zones and migration pathways of oxidation products at inactive spoil and refuse sites. Oxygen required for pyrite oxidation is believed to he provided in the gaseous state from the atmosphere. Therefore, the oxygen concentration in unsaturated mine waste should provide an estimate of the weathering tendency in the local environment. We are currently monitoring gas composition in refuse and spoil at six sites. Barren refuse appeared to be oxygenated (>2% 0₂) in a shallow zone extending less than 1 metre below the surface during most of the year. Preliminary data from coal spoil showed that oxygen can be available throughout the unsaturated thickness, even at a revegetated site. Gas composition varied vertically and laterally at a single site and also appeared to show seasonal dependence. Hydrologic factors are also important in acid production and transport. Discharge monitoring alone does not adequately describe the mass transport of acid products through the spoil. For example, at one reclaimed mine the mean sulfate content in six monitoring wells ranged from 24% to 240% of the mean concentration at the discharge point. Sources of recharge and relative flow rates determine the contribution of a particular zone to overall discharge quality. These basic studies of acid production and transport indicate some shortcomings of standard reclamation practices at certain sites. This information will he used to develop alternative abatement technology designed to mitigate acid production at the source.     

Food threshold territoriality in a water strider (Gerris remigis)

Summary Summer generation 3rd, 4th and 5th instar nymphs plus adults of Gerris remigis were satiated for 2 days in a laboratory tray then deprived of food. Within 1/2–2 days, 19 of 27 nymphs and 10 of 30 adults began to exhibit territoriality, continued being so for 3–9 days, then ceased shortly before becoming quiescent. In the field, muscid flies fed to different territorial striders at a rate of 0, 1, 2, or 3 flies/day, resulted in 8 of 10 striders (at 2 flies/day) and 10 of 10 striders (at 3 flies/day) ceasing territoriality, whereas 5 of 8 controls (at 0 flies/day) remained territorial. Thus, lower and upper food thresholds were demonstrated, the upper threshold approached both from above (laboratory study) and below (field study).     

Intergenerational equity: The capital-environment trade-off

This paper examines the trade-off between capital accumulation and environmental quality that determines an intergenerationally equitable program according to the Rawls maximin criterion. This trade-off is explored by an analysis of regular maximin programs in the framework developed by Brock. This results in a constant utility path supported by competitive prices with government imposed effluent charges and environmental rentals. Sufficient conditions for a regular maximin path to satisfy a Hartwick rule in deciding on the combination of capital and environmental quality left to future generations are given.