The use of measurable coefficients in process formulations—zooplankton grazing

This paper redefines a construct previously used to model phytoplankton—zooplankton interactions in such a way as to permit the use of measurable quantities as contruct coefficients. The new construct can use unaltered values of the half-saturation constant for zooplankton grazing on total available food (k_s) and the minimum food concentration necessary to stimulate effective feeding (BMIN) reported in the literature. Typical values for these coefficients are 0.1–15 and 0.016–0.19, respectively.     

Foraging in the seed-harvester ant genus Pogonomyrmex: are energy costs important?

Energy intake and expenditure on natural foraging trips were estimated for the seed-harvester ants, Pogonomyrmex maricopa and P. rugosus. During seed collection, P. maricopa foraged individually, whereas P. rugosus employed a trunk-trail foraging system. Energy gain per trip and per minute were not significantly different between species. There was also no interspecific difference in energy cost per trip, but energy cost per minute was lower for P. maricopa foragers because they spent on average 7 min longer searching for a load on each trip. Including both unsuccessful and successful foraging trips, average energy gain per trip was more than 100 times the energy cost per trip for both species. Based on this result, we suggest that time cost incurred during individual foraging trips is much more important than energy cost in terms of maximizing net resource intake over time. In addition, because energy costs are so small relative to gains, we propose that energy costs associated with foraging may be safely ignored in future tests of foraging theory with seed-harvesting ant species.     

Habitat edge, land management, and rates of brood parasitism in tallgrass prairie.

Bird populations in North America's grasslands have declined sharply in recent decades. These declines are traceable, in large part, to habitat loss, but management of tallgrass prairie also has an impact. An indirect source of decline potentially associated with management is brood parasitism by the Brown-headed Cowbird (Molothrus ater), which has had substantial negative impacts on many passerine hosts. Using a novel application of regression trees, we analyzed an extensive five-year set of nest data to test how management of tallgrass prairie affected rates of brood parasitism. We examined seven landscape features that may have been associated with parasitism: presence of edge, burning, or grazing, and distance of the nest from woody vegetation, water, roads, or fences. All five grassland passerines that we included in the analyses exhibited evidence of an edge effect: the Grasshopper Sparrow (Ammodramus savannarum), Henslow's Sparrow (A. henslowii), Dickcissel (Spiza americana), Red-winged Blackbird (Agelaius phoeniceus), and Eastern Meadowlark (Sturnella magna). The edge was represented by narrow strips of woody vegetation occurring along roadsides cut through tallgrass prairie. The sparrows avoided nesting along these woody edges, whereas the other three species experienced significantly higher (1.9-5.3x) rates of parasitism along edges than in prairie. The edge effect could be related directly to increase in parasitism rate with decreased distance from woody vegetation. After accounting for edge effect in these three species, we found evidence for significantly higher (2.5-10.5x) rates of parasitism in grazed plots, particularly those burned in spring to increase forage, than in undisturbed prairie. Regression tree analysis proved to be an important tool for hierarchically parsing various landscape features that affect parasitism rates. We conclude that, on the Great Plains, rates of brood parasitism are strongly associated with relatively recent road cuts, in that edge effects manifest themselves through the presence of trees, a novel habitat component in much of the tallgrass prairie. Grazing is also a key associate of increased parasitism. Areas managed with prescribed fire, used frequently to increase forage for grazing cattle, may experience higher rates of brood parasitism. Regardless, removing trees and shrubs along roadsides and refraining from planting them along new roads may benefit grassland birds.     

Comparison of light- and SST-based geolocation with satellite telemetry in free-ranging albatrosses

Light-based archival tags are increasingly being used on free-ranging marine vertebrates to study their movements using geolocation estimates. These methods use algorithms that incorporate threshold light techniques to determine longitude and latitude. More recently, researchers have begun using sea surface temperature (SST) to determine latitude in temperate regions. The accuracy and application of these algorithms have not been validated on free-ranging birds. Errors in both geolocation methods were quantified by double-tagging Laysan (Phoebastria immutabilis Rothschild) and black-footed (P. nigripes Audubon) albatrosses with both leg-mounted archival tags that measured SST and ambient light, and satellite transmitters. Laysan albatrosses were captured and released from breeding colonies on Tern Island, northwestern Hawaiian Islands (23°52N, 166°17W) and Guadalupe Island, Mexico (28°31N, 118°10W) and black-footed albatrosses from Tern Island. Studies were carried out between December 2002 and March 2003. For all birds combined, the mean ± SD great circle (GC) distance between light-based locations and satellite-derived locations was 400±298 km (n=131). Errors in geolocation positions were reduced to 202±171 km (n=154) when light-based longitude and SST-based latitude (i.e. SST/light) were used to establish locations. The SST/light method produced comparable results for two Laysan albatross populations that traveled within distinctly different oceanic regions (open ocean vs more coastal) whereas light-based methods produced greater errors in the coastal population. Archival tags deployed on black-footed albatrosses returned a significantly higher proportion of lower-quality locations, which was attributed to interference of the light sensor on the tag. Overall, the results demonstrate that combining measures of light-based longitude and SST-based latitude significantly reduces the error in location estimates for albatrosses and can provide valid latitude estimates during the equinoxes, when light-based latitude measurements are indeterminate.Communicated by J.P. Grassle, New Brunswick     

Hydroquinones from defensive secretion of a giant Pacific millipede, <Emphasis Type="Italic">Acladocricus setigerus</Emphasis> (Diplopoda: Spirobolida)

Summary. The presence of considerable quantities of hydroquinones including hydroquinone, 2-methylhydroquinone, 2,3- dimethoxyhydroquinone, 2-methoxy-3-methylhydroquinone, and 2,3-dimethoxy-5-methylhydroquinone renders the defensive secretion of Acladocricus setigerus (Silvestri, 1897) significantly different from that of other quinone-producing millipedes. In addition, two hitherto undescribed compounds, namely, 2,3-dimethoxy-5-methylhydroquinone and 2-methyl-3,4-methylenedioxyphenol, were characterized from the defensive secretion. However, it is uncertain if the latter compound is formed after the release of the secretion. The two major compounds, 2-methyl-1,4-benzoquinone and 2-methoxy-3-methyl-1,4-benzoquinone, constitute about 75% of the defensive fluid. Furthermore, hydrocarbons, which are typically present in the secretions of most other arthropods that use benzoquinones as repellents, are notably absent in the secretion of A. setigerus.     

Insecticidal and growth-reducing activity of foliar extracts from Meliaceae

Summary Thirty-one species in twenty genera of the plant family Meliaceae were assayed for the production of growth-inhibiting phytochemicals, using the generalist herbivorePeridroma saucia. Most species were inhibitory when methanolic extracts were incorporated into artificial diets at concentrations at or below those occurring naturally. In general members of the subfamily Melioideae were more inhibitory than members of the Swietenioideae. Extracts of deciduous species with short leaf lifetimes were significantly more inhibitory than those of evergreen species with longer leaf lifetimes. In a smaller sample of species, evergreen species showed a trend towards having tougher leaves than deciduous species. These results support the resource availability hypothesis of Coleyet al. (1985), and suggest that life history attributes may be of some value in selecting plants for phytochemical prospecting.     

Male capacity as related to sperm production,pregnancy initiation,and sperm competition in deer mice (Peromyscus maniculatus)

Summary Limitations on male capacity may be important to the evolution of mating strategies and behavior. Sperm counts in successive ejaculates of deer mice (Peromyscus maniculatus) decreased progressively through six ejaculations and remained depressed the following day. Males were as effective in inseminating females in cycling estrus with their second two ejaculates as with their first two and as effective in inseminating postpartum females with their fifth as with their first. In sperm competition situations males competed with rested males as effectively with their fourth, fifth, and sixth ejaculates as with their first. Thus, although sperm counts decrease in successive ejaculates, males suffer no apparent functional deficiency as long as they continue ejaculating. It is not clear whether or not deer mice are honest salesmen but they appear to be honest ejaculators and usually are honest intromitters.     

Echolocation by cave swiftlets

Summary The ability of cave dwelling swiftlets (Collocalia spodiopygius) to detect small cylindrical obstacles by echolocation was tested in a 3x9 m flight chamber. Although there was great individual variability, 6.3 mm obstacles were avoided much more often in total darkness than 1.5 wires (P<0.001). Flash photographs showed that the latter were avoided only by chance (about 50% misses). Obstacles 3.0 mm in diameter were avoided only slightly more often than 1.5 mm wires.Even in the light these swiftlets avoided the obstacles in only about 75% of the trials, probably because gentle touches with the primary feathers caused little discomfort.The 3.0 and 6.3 mm obstacles tended to be avoided more often on first encounters after they had been shifted horizontally by 10–30 cm, probably because the birds became more attentive.     

Optimum forage allocation through chance-constrained programming

Most resource allocation models developed to aid resource planning have been deterministic; that is, the ecosystem and economic variables are assumed to be known with certainty. It is these elements that present problems concerning risk and uncertainty involved in decision making. The objective of this study is to present a mathematical approach for optimizing resource allocation in management situations in which random events occur. This particular technique of decision analysis is chance-constrained programming. The model makes possible the investigation of risk and uncertainty associated with resource management decision making. Range decision-makers must often stock their range before they are sure of the available forage; thus, the amount of available forage is a random element with which managers must contend. The chance-constrained approach to decision making may be used when such random events occur and when it is not possible to plan exactly for future events. Two parameters are used to adjust the mean value of constraints; these are the standard deviation of the constraint value (S_bi) and the probability term which is specified by the manager (K_αi). The mean values are adjusted by the product K_αiS_bi. In the study reported here, a K_αi value of 0.57 gave results which appeared to have usefulness. The results indicate that the penalties a rancher must assume for over-estimating his carrying capacity are greater than the penalties for underestimating the carrying capacity. With the value of the standard deviation used in the example, numbers of livestock and the corresponding net revenues should be about 22% less than those indicated by average forage production. With greater variation in forage production, the reduction would be greater. By using these values, the chance-constrained approach can meaningfully incorporate random variables into a decision model.     

The environment as a factor of production

This paper uses firm-level data about electric utilities to develop an empirical model of how electric utilities use and bank SO₂ pollution permits under the Acid Rain Program. The empirical model considers emissions, fuels, and labor as variable inputs with quasi-fixed stocks of permits and capital. Consequently, substitution possibilities between the environment and other production factors can be measured and tested. The results reveal substantial substitution between emissions, permit stocks, capital, fuel, and labor. The empirical findings also indicate that firms bank permits primarily as a hedge against uncertainty and for other firm-specific reasons. Overall, the results suggest that cap-and-trade approaches can reduce the cost of meeting environmental goals by providing a mechanism for addressing regulatory and market risks and by signaling an appropriate price for factor use, especially irreversible capital investments.