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 nature of zinc and copper complexes in the oyster Ostrea edulis

The zinc and copper associated with the soft tissues of the oyster Ostrea edulis Linnaeus have been separated into a soluble component and a tissue-residue, cell-debris bound component. In the case of zinc, the tissue-bound component was found to contain at least two species of complex; a firmly-bound species, exchangeable with ⁶⁵Zn²⁺ and a less-firmly, reversibly-bound species, exchangeable with ⁶⁵Zn²⁺. The soluble component, which constitutes some 40% of the total zinc and copper, was fractionated on Sephadex G-25 and the zinc and copper shown to be weakly-complexed to the small molecular weight compounds, taurine, lysine, ATP and possibly homarine (N-methyl--picolinic acid) and to be fully exchangeable with ⁶⁵Zn²⁺. These soluble complexes can act as a freely available mobile reserve of metal to ensure a constant saturation of metal-dependent enzyme systems operating under adverse environments. Sephadex G-25 acts as a weak ion-exchange resin, which can cause a translocation of zinc and copper from its soluble weak complexes and result in the spurious association of the metals with other compounds.     

Effect of salinity adaptation on nitrogen metabolism in the freshwater fish Tilapia mossambica. I. Tissue protein and amino acid levels

Water, proteins and total free amino acids were estimated in different tissues of the euryhaline fish Tilapia mossambica after adaptation to various strenghts of sea water. The water content did not vary significantly in any tissue on salinity adaptation. The soluble and insoluble proteins displayed a general and considerable decrease in muscle, liver and heart; the decrease in the soluble fraction in the heart and the proteins of the muscle in 75% sea water (100% sea water=32.5 S) were significant. The gill proteins did not alter with salinity; the kidney proteins tended to increase slightly in 100% sea water (SW). The total free amino-acid content decreased insignificantly in all tissues on adaptation to 25% SW; in higher salinities, however, the content increased significantly. This increase was sudden and steep in 50% SW, and gradual and less steep in 75 and 100% SW. It is suggested that constancy in water content may contribute to the great adaptability of T. mossambica to heterosmotic media, and that the total free amino acids may be involved in isosmotic intracellular regulation. The possibility of amino acid increase as a result of protein breakdown is also indicated.     

Aspects écologiques de la zonation intertidale sur les côtes rocheuses des îles Galapagos

Features of the intertidal zonation on the rocky shores of the Galapagos Islands are described and discussed in relation to environmental factors, in particular temperature — which varies with regional hydrology and climatology. Owing to the thermal properties of the coastal waters and to the nature of the substrate (mainly basalt), intertidal organisms are exposed to a wide range of temperatures, which fluctuate with tide, day, and season. As a result, life is mostly restricted to the lowest levels of the shore; the middle- and upper-level populations are sparse. Local variations (biofacies) resulting from water agitation are described. Biota consist of tropical, subtropical, and warm-temperate components. Tropical species dominate in sheltered areas and in middle and upper shores.

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Contribution No. 164, the Charles Darwin Foundation.     

Life histories of large and small murexes (Prosobranchia: Muricidae)

One can predict the major features of a muricid's life history from its adult size. Most adults do not grow, and juveniles of all species grow 1 to 2 mm/month, so that larger adults have had fonger juvenile periods. Larger females deposit larger egg capsules and, since each of these contains more eggs, their clutches are larger. Small females deposit several clutches each year, and thus have relatively large annual fecundities. However, large females live longer, so each spawns many more eggs in her life-time than would a smaller female. From 90 to 99% of the juveniles die within their first year. However hatchings of small species are much more likely to complete their first year; a newly hatched Urosalpinx cinerea is 25 times more likely to survive long enough to breed once than a newly hatched Ceratostoma foliatum (Gmelin, 1791).     

Food resource partitioning by the pufferfishes Sphoeroides spengleri and S. testudineus from Biscayne Bay,Florida

Partitioning of the food resources by two coexisting pufferfishes (Sphoeroides spengleri and S. testudineus) from Biscayne Bay, Florida, USA, was investigated. Gut contents from 453 bandtail and 339 checkered puffers were analyzed. The diets of both species consisted of a variety of benthic prey, but only crustaceans and molluscs were important prey groups. While differences were found in the proportions of general prey categories eaten by these fishes, both species consumed substantial quantities of brachyuran crabs, bivalves, and gastropods. Specific identification of the prey items within these three food categories revealed additional differences in prey between the two puffer species. This partitioning of the food resources by bandtail and checkered puffers was found between both species overall, between overlapping size ranges, and between both species' most abundant size group. Differences in food habits between these two fishes illustrate that congeners with virtually identical mouth structure and complete spatial overlap can significantly partition the food resources.Contribution No. 78-58M from the U.S. Department of Commerce, NOAA, National Marine Fisheries Service, Southeast Fisheries Center, Miami Laboratory, Miami, Florida, USA.     

The biology of colonial hydroids. II. The morphology and ultrastructure of the medusa of Eirene viridula (Thecata-Leptomedusa: Campanulinidae)

The free-swimming medusae of Eirene viridula are typical marine hydroids, with distinct subdivisions into body regions, which were studied by comparison of light and electron microscopy. Particular attention is given to the epithelio-muscular and digestive muscle cells. The epidermis — apart from a few nerve cells and cnidocytes-consists of epitheliomuscular cells. At their bases these cells form a musculature and at the apex many secretory vesicles. In the velum, large expansions of the intercellular space are found. The gastrodermis — apart from the mucous and zymogen cells in the manubrium — consists of digestive muscle cells, the structure of which corresponds in principle to that of the epitheliomuscular cells. In its apex, this type of cells contains both normal coated vesicles and discoidal coated vesicles. In the solid tentacles, the digestive muscle cells form a turgescent vesicular tissue. The central nervous system consists of the exumbrellar, subumbrellar, and gastrodermal nerve rings. They are composed of ganglion cells, their processes, and intraepithelial flagella. The static organs are purely ectodermal statocysts which have only one lithocyte and only one sensory cell.     

A test of alternate hypotheses for helping behavior in white-fronted bee-eaters of Kenya

Summary Considerable controversy exists over the question of the importance of kin selection in the maintenance of helping behaviors among birds. We examined nine different hypotheses of how helpers might benefit from engaging in alloparental care activities. We break these into four categories: Through its activities the helper may A) improve its probability of surviving to the following breeding season, B) enhance its probability of becoming a breeder in the future, C) increase its reproductive success when it does become a breeder, and D) increase the production of non-descendent kin. The first three categories provide direct fitness gains to the helper; in the fourth, the benefit is indirect. The hypotheses are not mutually exclusive; rather their fitness effects are additive. Each hypothesis, however, makes specific and often separable predictions about both 1) the type of fitness benefits expected, and 2) the characteristics of the birds that serve as helpers. We tested these predictions using five year's data from a color marked and geneologically known population of white-fronted bee-eaters (Merops bullockoides) in Kenya. A) Survival was not related to status (breeder, helper, non-participant); nor did individuals living in large clans have better survival than those living in small ones. B) Newly formed pairs were equally likely to become future breeders irrespective of whether or not one or both individuals had helped previously. C) The mean number of young fledged by a first time breeder was unaffected by its prior helping experience. Neither were first time breeding pairs more likely to gain the services of others as their helpers than were pairs without prior helping experience. Taken together these results demonstrate that beeeaters gain very little direct benefit from alloparenting. D) Helpers did not enhance the survival of the breeders that they helped. But they did have a major effect in increasing nestling survival. Because bee-eater helpers are closely related to the nestlings they help to rear (average r=0.33), they obtain a large indirect benefit by increasing the production of non-descendent kin. We quantified the relative importance of indirect and direct benefits of helping (to the helper) using Vehrencamp's kin index, I _k (1979). I _k compares the fitness consequences of helping against an alternative strategy and calculates the proportion of the inclusive fitness gain or loss that is due to kin (indirect) benefits. Comparing the strategy sets of helping versus not helping for bee-eaters, I _k=0.89 (indicating that 89% of the benefit derived from helping is indirect). When helping was compared against the alternative of breeding, I _k=2.17. Values of I _k greater than 1.0 indicate that direct fitness gains from the alternate strategy (breeding) are greater than those from helping. The value of 2.17 indicates that the helping strategy would not be maintained except for the indirect fitness gained through the increased production of close kin. Alloparenting in white-fronted bee-eaters can thus be considered as altruistic.     

Development of a new antifouling method for a marine cooling water system

Variations in meristic characters occur within and between samples of milkfish Chanos chanos (Forsskal) collected on June 1977 from five localities in Philippine waters. The unbranched anal and ventral fin rays are the most plastic, and vertebral number is the most stable of nine meristic characters examined. The number of ventral fin rays is the only meristic feature which differed consistently enough to suggest distinct population groups: South China Sea, comprising samples from Ilocos and Panay Island; Pacific Ocean from Bicol; and Celebes Sea, from Zamboanga and Davao. A discriminant analysis which incorporated generalized distance (Mahanalobis D²) and percent overlap of a reduced set of characters indicated several morphometric subgroups of milkfish in Philippine waters, although geographic subgroups were not clearly demonstrated.SEAFDEC Contribution No. 218