Ecology and community dynamics of Kubo people in the tropical lowlands of Papua New Guinea

Kubo producer-units (families and independent bachelors) could have been self-sufficient in the production of bananas but chose not to be. Nor did they seek self-sufficiency in the production of any combination of staple carbohydrate foods (bananas, tubers, sago flour) or, in the long term, strive for balance in the exchange of food with other producer-units. Despite the fact that bananas, which provided 50% of people's energy needs, were a delayed-return crop Kubo communities were very unstable. This instability and the failure to choose the option of self-sufficiency were connected and were mediated through intense intracommunity sharing that, ultimately, served to negotiate a concern with sorcery. The people grew bananas in the way they did, not out of environmental necessity, but to accommodate the crop to the needs of sharing and, thereby, facilitate community living.     

Guild structure in solitary spider-hunting wasps (Hymenoptera: Pompilidae) compared with null model predictions

Abstract.

• 1 Three aspects of prey utilization are documented in a guild of spider-hunting pompilid wasps at a Breckland heath site: female phenology, size, and microhabitat utilization.
• 2 Twenty-four species were present at the site, 59% of the British fauna. Ten species individually represented more than 1% of the guild.
• 3 Pompilid abundance peaked in early July and mid-late August. Anoplius viaticus had a different life-history from other common guild members, making its inclusion in the guild questionable.
• 4 Most species represented by large samples occurred in all microhabitats and time intervals, and all species overlapped in size with all other species except A. viaticus. Arachnospila anceps was numerically dominant in all microhabitats and most time intervals.
• 5 Mean pair-wise overlaps in phenology and microhabitat utilization were significantly lower than predicted by null models, consistent with the idea that interspecific competition has been important in determining guild structure.
• 6 Female size is highly correlated with prey size, but the distribution of mean female sizes did not generally differ from null expectations.
• 7 Interpretation of comparisons with null models is problematic, particularly because it is difficult to quantify evolutionary ‘favourability’ of different resource states. Null models are currently of limited use because the patterns expected to result from key processes such as competition are uncertain in multi-dimensional systems.

     

水资源的忧虑

水是生态系统中生命必需元素得以无限循环的介质。没有水生态系统,生命就不能维持。在当今世界面临的人口、资源、环境三大问题中,水属于人类赖以生存和社会经济发展的重要物质资源,又和其它两个问题有着密切的关系。因此,水资源的开发、利用和管理已成为世界各国普遍重视的一个重要课题。     

Experimental measurement of resource competition between planktonic microalgae and macroalgae (seaweeds) in mesocosms simulating the San Francisco Bay-Estuary,California

Planktonic algae are not abundant in the brackish waters of San Francisco Bay-estuary (mean chlorophyll a 5 µg 1^–1), despite the high level of nutrients usually present due to the input of treated sewage from 3 million people. Macroalgae (seaweeds) are sometimes locally abundant in the Bay. Phytoplankton are abundant (chlorophyll a > 50 µg 1^–1) and seaweeds uncommon in the almost freshwater Delta and upper estuary despite lower nutrient levels. Direct competition between these algal groups could explain the observed distributions.Given the size of the algae, large containers were needed for the determination of possible resource competition. Experiments were carried out in flow-through mesocosms (analog tanks) of 3 m³ volume. The macroalgae Ulva lactuca or Gigartina exasperata and a diatom-dominated phytoplankton, all from San Francisco Bay, were grown separately and together and with and without treated sewage effluent or other artificial nutrient additions. When grown alone phytoplankton and macroalgae were greatly stimulated by wastewater addition to unmodified baywater. The phytoplankton grew much more slowly in the presence of natural densities of Ulva. Allelochemical effects were tested for but not demonstrated.Resource competition for inorganic nitrogen was determined to be the probable cause of the depression of phytoplankton by Ulva. At its rapid growth rates in the flow-through mesocosms (up to 14% day^–1) this macroalga can reduce inorganic nitrogen to low levels. Ulva has a greater affinity (lower KS) for nitrogen than do some of the plankton of the Bay. Ulva may outcompete phytoplankton by reducing nitrogen to levels below those capable of supporting phytoplankton growth. Other macroalgae such as Gigartina and Enteromorpha need to be studied to determine if they also can depress phytoplankton growth by resource competition.     

Resource sharing among ramets in the clonal herb,Fragaria chiloensis

Summary The herbaceous perennial, Fragaria chiloensis, reproduces vegetatively on coastal sand dunes in California by growth of stolons that bear rosettes. Movement of water and photosynthates through stolons integrates water and carbon metabolism of rosettes both before and after they root. New, unrooted rosettes import sufficient water and nitrogen to maintain levels near those of established rosettes; yet support of an unrooted rosette did not decrease growth of a connected, rooted sibling given abundant light, water, and soil nutrients. Under such conditions strings of unrooted rosettes with the associated stolon appeared self-sufficient for carbon; shade and drought induced import of photosynthates. New rosettes produced and maintained a limited root mass upon contact with dry sand, which could increase probability of establishment. Rooting did not induce senescence of stolons. Connection between two established rosettes prevented death by drought and shade, even when neither rosette could have survived singly. Results suggest that physiological integration of connected rosettes may increase total growth of clones of F. chiloensis through sharing of resources among ramets, especially when resource availability is changeable or patchy.     

Defense reactions of mosquitoes to filarial worms: potential mechanism for avoidance of the response by Brugia pahangi microfilariae

The melanization response of Aedes trivittatus and the black-eyed Liverpool (LVP) and Rocke-feller (RKF) strains of Aedes aegypti against intrathoracically inoculated Brugia pahangi microfilariae (mff) that previously had penetrated LVP, RKF, or A. trivittatus midguts in vitro was assessed at 1, 3, and 5 days postinoculation (PI). LVP and RKF midgut-derived mff almost totally avoided the melanization response and developed normally in LVP strain A. aegypti, and although over 90% of these mff died by 5 days PI in RKF mosquitoes, the majority of these were not melanized. A. aegypti midgut-derived mff also were able to avoid the response of A. trivittatus in 33–43% of the cases. Penetration through A. trivittatus midguts, however, did not significantly affect the ability of mff to avoid the melanization response in any of the mosquitoes examined. Allogeneic and xenogeneic tissue inplants were accepted by all three mosquito species examined. Data presented support the hypothesis that mff avoid immune recognition in compatible mosquitoes by coating themselves with midgut material(s) during penetration of the midgut in their migration to the hemocoel.     

A multivariate study of resource partitioning in soft bottom lotic Chironomidae

For two years a community of larval chironomid midges was studied in a sandy-run portion of a fourth order natural stream in SE Ohio, U.S.A. in order to determine if the species partitioned the spatial resources. The habitat structure was simplified from ten habitat variables to three significant principal components. The three eigenvectors were easily interpreted as sediment size, sediment heterogeneity, and organic deposition. Species abundances were loaded on these axes and niche metrics examined. Strong differences in habitat preference were demonstrated for midge species on each component. Also, there were no differences in distributions for the intraspecific instars for each species tested at a given time, but for each of the instars tested, their distributions were found to change from time to time. Apparently, individuals of a species, regardless of instar, simultaneously choose the same habitat, however, the preferred habitat may shift temporally due to change in resource availability, or niche expansion or compression due to competition.     

Heuristic optimization of the general life history problem: A novel approach

Summary The general life history problem concerns the optimal allocation of resources to growth, survival and reproduction. We analysed this problem for a perennial model organism that decides once each year to switch from growth to reproduction. As a fitness measure we used the Malthusian parameterr, which we calculated from the Euler-Lotka equation. Trade-offs were incorporated by assuming that fecundity is size dependent, so that increased fecundity could only be gained by devoting more time to growth and less time to reproduction. To calculate numerically the optimalr for different growth dynamics and mortality regimes, we used a simplified version of the simulated annealing method. The major differences among optimal life histories resulted from different accumulation patterns of intrinsic mortalities resulting from reproductive costs. If these mortalities were accumulated throughout life, i.e. if they were senescent, a bangbang strategy was optimal, in which there was a single switch from growth to reproduction: after the age at maturity all resources were allocated to reproduction. If reproductive costs did not carry over from year to year, i.e. if they were not senescent, the optimal resource allocation resulted in a graded switch strategy and growth became indeterminate. Our numerical approach brings two major advantages for solving optimization problems in life history theory. First, its implementation is very simple, even for complex models that are analytically intractable. Such intractability emerged in our model when we introduced reproductive costs representing an intrinsic mortality. Second, it is not a backward algorithm. This means that lifespan does not have to be fixed at the begining of the computation. Instead, lifespan itself is a trait that can evolve. We suggest that heuristic algorithms are good tools for solving complex optimality problems in life history theory, in particular questions concerning the evolution of lifespan and senescence.     

Root,shoot and soil parameters required for process-oriented models of crop growth limited by water or nutrients

A review is given of the prospects for using process-oriented models of water and nutrient uptake in improving integrated agriculture. Government-imposed restrictions on the use of external inputs will increase the likelihood of (temporary) nutrient or water stress in crop production in NW Europe and thus a better understanding is required of shoot-root-soil interactions than presently available. In modelling nutrient and water uptake, three approaches are possible: 1) models-without-roots, based on empirically derived efficiency ratios for uptake of available resources, 2) models evaluating the uptake potential of root systems as actually found in the field and 3) models which also aim at a prediction of root development as influenced by interactions with environmental factors. For the second type of models the major underlying processes are known and research can concentrate on model refinement on the one hand and practical application on the other. The main parameters required for such models are discussed and examples are given of practical applications. For the third type of models quantification of processes known only qualitatively is urgently needed.