Spider webs, stable isotopes and molecular gut content analysis: Multiple lines of evidence support trophic niche differentiation in a community of Hawaiian spiders

1.Adaptive radiations are typically characterized by niche partitioning among their constituent species. Trophic niche partitioning is particularly important in predatory animals, which rely on limited food resources for survival.2.We test for trophic niche partitioning in an adaptive radiation of Hawaiian Tetragnatha spiders, which have diversified in situ on the Hawaiian Islands. We focus on a community of nine species belonging to two different clades, one web-building and the other actively hunting, which co-occur in wet forest on East Maui. We hypothesize that trophic niches differ significantly both: (a) among species within a clade, indicating food resource partitioning, and (b) between the two clades, corresponding to their differences in foraging strategy.3.To assess niches of the spider species, we measure: (a) web architecture, the structure of the hunting tool, and (b) site choice, the physical placement of the web in the habitat. We then test whether differences in these parameters translate into meaningful differences in trophic niche by measuring (c) stable isotope signatures of carbon and nitrogen in the spiders\u27 tissues, and (d) gut content of spiders based on metabarcoding data.4.We find significant interspecific differences in web architecture and site choice. Importantly, these differences are reflected in stable isotope signatures among the five web-building species, as well as significant isotopic differences between web-builders and active hunters. Gut content data also show interspecific and inter-clade differences. Pairwise overlaps of web architecture between species are positively correlated with overlaps of isotopic signature.5.Our results reveal trophic niche partitioning among species within each clade, as well as between the web-building and actively hunting clades. Based on the correlation between web architecture and stable isotopes, it appears that the isotopic signatures of spiders\u27 tissues are influenced by architectural differences among their webs. Our findings indicate an important link between web structure, microhabitat preference and diet in the Hawaiian Tetragnatha

Sunflower Competition in Wheat

Wheat yield losses from various sunflower densities and durations of competition had not been determined previously. The objectives of the research in this article were to determine the influence of sunflower density, duration of competition and rate of control on wheat yield

Effect of Timing and Intensity of Drought on Perennial Ryegrass Seed Yield

Perennial ryegrass seed worth about $50 million is produced annually in Canterbury, New Zealand (Rowarth 1998). Ryegrass seed production in New Zealand is often affected by drought, reducing both seed number and seed size (Rolston et al., 1994). Irrigation management recommendations are not currently available for farmers growing ryegrass seed crops. To quantify the effect of water stress on perennial ryegrass seed yield, we carried out an experiment in a rainshelter where rainfall was excluded from experimental plots otherwise exposed to normal weather (Martin et al., 1990)

Stochastic modeling of cargo transport by teams of molecular motors

Many different types of cellular cargos are transported bidirectionally along microtubules by teams of molecular motors. The motion of this cargo-motors system has been experimentally characterized in vivo as processive with rather persistent directionality. Different theoretical approaches have been suggested in order to explore the origin of this kind of motion. An effective theoretical approach, introduced by M\"uller et al., describes the cargo dynamics as a tug-of-war between different kinds of motors. An alternative approach has been suggested recently by Kunwar et al., who considered the coupling between motor and cargo in more detail. Based on this framework we introduce a model considering single motor positions which we propagate in continuous time. Furthermore, we analyze the possible influence of the discrete time update schemes used in previous publications on the system's dynamic.Comment: Cenference proceedings - Traffic and Granular Flow 1

Megawatt solar power systems for lunar surface operations

The work presented here shows that a solar power system can provide power on the order of one megawatt to a lunar base with a fairly high specific power. The main drawback to using solar power is still the high mass, and therefore, cost of supplying energy storage through the solar night. The use of cryogenic reactant storage in a fuel cell system, however, greatly reduces the total system mass over conventional energy storage schemes

Murex medic field evaluation.

Trials: 90GE113, 90MO62, 90WH87, 90ME72, 90NO115, 90A24, 90AB17, 90AL35 Locations: Geraldton, New Norcia, Wongan Hills, Merredin, Southern Brook, Avondale, Katanning, Tenderden. The selection SEP29.1 was outstanding for both dry matter production and seed yield over a wide range of sites varying in both rainfall and soil type. On the basis of these trials, six lines have been selected for further evaluation in 1991. They are: SEP29.1 SEP26.2.7 GRC69 GRC87.1 87F01.28 87FB2.36 Trials 90A25 and 90NO116 Redlegged earthmite field experiments. Very low levels of redlegged earthmite and only minor damage to test varieties was recorded in this trial. Damage ratings were recorded at 3, 4 and 5 weeks after sowing and plant yields at 3, 5 and 7 weeks, but the trial was then abandoned due to minimal responses. 90NO116 - This trial was abandoned soon after sowing due to massive germination of contaminant clover present in the paddock and negligible levels of redlegged earthmite