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Selected AbstractsWhen random sampling does not work: standard design falsely indicates maladaptive host preferences in a butterflyECOLOGY LETTERS, Issue 1 2002Michael C. Singer In experiments that investigate species' interactions, individuals are often chosen at random to represent their populations. However, this practice can generate misleading results when individuals of different species do not interact at random. We illustrate this effect by examining oviposition preferences of Euphydryas aurinia butterflies from three populations using three different plant genera. We first offered each insect a randomly chosen member of its own host population and a foreign host (Succisa pratensis) not present in the insect's habitat. The butterflies uniformly preferred the foreign Succisa over their own hosts. Preferences were apparently maladaptive because insects wasted time searching for a nonexistent plant. We repeated the experiment using individual hosts that had naturally received eggs in the field. The overall preference for Succisa and the appearance of maladaptation both disappeared. In the original experiments, our random choice of experimental host individuals had combined with strong within-species discrimination by the butterflies and with overlap of acceptability between host species to obscure the true nature of host preference. [source] The importance of honeydew as food for larvae of Chrysoperla carnea in the presence of aphidsJOURNAL OF APPLIED ENTOMOLOGY, Issue 1 2008P. A. M. Hogervorst Abstract Larvae of the common green lacewing Chrysoperla carnea are predacious and feed on a wide range of small, soft-bodied arthropods. In addition to their feeding on prey arthropods to cover their nutritional requirements for growth and development, the consumption of non-prey foods such as honeydew has been reported. It is commonly believed that these food supplements are primarily exploited by the larvae when prey is scarce or of low nutritional quality. Here, we assess whether C. carnea larvae also use honeydew when high-quality aphid prey are readily available. In a choice experiment, the feeding behaviour of C. carnea larvae was observed in the presence of both aphids and honeydew. The larvae were starved, aphid-fed, or honeydew-fed prior to the experiment. The time spent feeding on honeydew compared with feeding on aphids was highest for starved larvae and lowest for honeydew-fed larvae. Among the three treatments, the aphid-fed larvae spent the most time resting and the least time searching. In an additional experiment food intake was assessed in terms of weight change when larvae were provided with an ad libitum supply of either aphids or honeydew. Larvae yielded a significant lower relative weight increase on honeydew compared with aphids. The reduced weight increase on honeydew was compensated when larvae were subsequently provided with aphids, but not when honeydew was provided again. This study showed that (i) prior honeydew feeding reduces overall aphid consumption, and (ii) larvae do consume honeydew even after they have been given ad libitum access to aphids. The fact that larvae of C. carnea still use honeydew as a food source in the presence of suitable prey underlines the importance of carbohydrates as foods. [source] Animal response to nested self-similar patches: a test with woolly bearsOIKOS, Issue 5 2009Mark F. McClure To gain insight into how animals respond to resource patchiness at different spatial scales, we envision their responses in environments comprised of nested, self-similar patches. In these environments, all resources reside within the smallest patches, and resource density declines as a constant exponent of patch size. Accordingly, we use simple mathematical formulations to describe a self-similar environment and a null model of how animals should respond to this environment if they do not perceive resource distribution. We then argue that animals that can perceive resource distribution should partition space by reducing the relative time searching between patches as patch size increases. On an experimental landscape, we found that woolly bear caterpillars Grammia geneura could partition space in this manner, but the range of patch sizes over which they did so tended to increase with resource aggregation. Nevertheless, scaling efficiency (i.e. the scaling of search time versus the scaling or resource density) was similar in all distributions when averaged over all patch sizes. These disparate patterns with similar outcomes resulted from differences in caterpillars' abilities to discriminate spatially among patches of different sizes via their movement pathways, and differences in their use of speed to detect resource items. Our work is relevant to the characterization of resource availability from an animal's perspective, and to the linking of optimal foraging theory to the modeling of search behavior. [source] Aerial archaeology: a full digital workflow for aerial photographyARCHAEOLOGICAL PROSPECTION, Issue 4 2005Jürg Leckebusch Abstract Aerial archaeology is an established prospection method, but its systems and techniques have changed very little since its first applications. The advent of modern high-resolution digital cameras, with better image resolution and image depth than comparable analogue photography, offers the possibility of a full digital workflow. A new system is being developed to fulfil all the requirements of aerial archaeology. The images are stored on a PC, together with associated geographical data, including the location and orientation of the camera stations. A GIS displays the camera stations together with the flight path. Once the photographic record of a site is finished, the geographical co-ordinates of the target are calculated automatically, and combined with other data from a simple user interface to provide a complete primary data set during the flight. This allows the investigator to spend more time searching for sites during the flight, and simplifies the interpretation and analysis of the images in the office. This paper presents several new approaches to full integration of the systems involved. Copyright © 2005 John Wiley & Sons, Ltd. [source] Helicoverpa armigera (Hübner): can wheat stubble protect cotton plants against attack?AUSTRALIAN JOURNAL OF ENTOMOLOGY, Issue 1 2006Amanda J Cleary Abstract, When investigating strategies for Helicoverpa armigera (Hübner) control, it is important to understand oviposition behaviour. Cotton (Gossypium hirsutum) was sown into standing wheat (Triticum astivum L.) stubble in a closed arena to investigate the effect of stubble on H. armigera moth behaviour and oviposition. Infrared cameras were used to track moths and determine whether stubble acted as a physical barrier or provided camouflage to cotton plants, thereby reducing oviposition. Searching activity was observed to peak shortly before dawn (03:00 and 04:00 h) and remained high until just after dawn (4 h window). Moths spent more time resting on cotton plants than spiralling above them, and the least time flying across the arena. While female moths spent more time searching for cotton plants growing in wheat stubble, the difference in oviposition was not significant. As similar numbers of eggs were laid on cotton plants with stubble (3.5/plant SE ±0.87) and without stubble (2.5/plant SE ±0.91), wheat stubble does not appear to provide camouflage to cotton plants. There was no significant difference in the location of eggs deposited on cotton plants with and without stubble, although more eggs were laid on the tops of cotton leaves in wheat stubble. As the spatial and temporal distribution of eggs laid on the cotton plant is a crucial component of population stability, eggs laid on the upper side of leaves on cotton plants may be more prone to fatalities caused by environmental factors such as wind and rain. Therefore, although stubble did not influence the number of eggs laid, it did affect their distribution on the plant, which may result in increased mortality of eggs on cotton plants sown into standing wheat stubble. [source] Combined Effects of Host Plant Quality and Predation on a Tropical Lepidopteran: A Comparison between Treefall Gaps and the Understory in PanamaBIOTROPICA, Issue 6 2008Lora A. Richards ABSTRACT In tropical forests, light-gaps created from treefalls are a frequent source of habitat heterogeneity. The increase in productivity, through gap formation, can alter food quality, predation and their impact on insect herbivores. We hypothesized that in gaps, herbivores would be less resource-limited and more predator limited, whereas in the understory, we predicted the reverse. In this study, we investigate the combined effects of food quality and predation on the lepidopteran larva Zunacetha annulata feeding on its host plant Hybanthus prunifolius in two habitats; sunny treefall gaps and the shaded understory in Panama. In bioassays, Z. annulata feeding on sun leaves ate 22 percent less leaf area, grew 25 percent faster, and had higher pupal weights than larvae feeding on shade leaves. However, shade leaves had higher nitrogen content and specific leaf area. In gaps, predation was 26.4 percent compared to 13.8 percent in the understory. Larvae on understory plants traveled greater distances and spent more time searching and traveling than larvae on gap plants. These differences in behavior are consistent with lower predation risk and lower quality food in the understory. Using data from bioassays and field experiments we calculated 0.22 percent and 1.02 percent survival to adulthood for larvae in gaps and the understory, respectively. In conclusion, although these habitats were in close proximity, we found that larvae in the understory are more resource-limited and larvae in gaps are more predator limited. [source] | |||||||||||||||||||