David H. Wise

Abstract: Preface Acknowledgements 1. The spider in the ecological play 2. Hungry spiders 3. Competitionist views of spider communities 4. Failure of the competitionist paradigm 5. How spiders avoid competition 6. Impact of spiders on insect populations 7. Anchoring the ecological web 8. Untangling a tangled web 9. Spinning a stronger story References Index.

Abstract: Although more consensus is now emerging on the magnitude and frequency of cascading trophic effects in aquatic communities, the debate over their terrestrial counterparts continues. We used meta‐analysis to analyze field experiments on trophic cascades in terrestrial arthropod‐dominated food webs to evaluate the overall magnitude of trophic cascades and conditions affecting their occurrence and strength. We found extensive support for the presence of trophic cascades in terrestrial communities. In the majority of experiments, predator removal led to increased densities of herbivorous insects and higher levels of plant damage. Cascades in which removing predators led to decreased herbivory also were detected but were less frequent and weaker, suggesting a predominantly three‐trophic‐level behavior of arthropod‐dominated terrestrial food webs. Despite the clear evidence that cascades often decreased plant damage, residual effects of predation produced either no or only minimal changes in overall p...

Abstract: Cannibalism among generalist predators has implications for the dynamics of terrestrial food webs. Spiders are common, ubiquitous arthropod generalist predators in most natural and managed terrestrial ecosystems. Thus, the relationship of spider cannibalism to food limitation, competition, and population regulation has direct bearing on basic ecological theory and applications such as biological control. This review first briefly treats the different types of spider cannibalism and then focuses in more depth on evidence relating cannibalism to population dynamics and food web interactions to address the following questions: Is cannibalism in spiders a foraging strategy that helps to overcome the effects of a limited supply of calories and/or nutrients? Does cannibalism in spiders reduce competition for prey? Is cannibalism a significant density-dependent factor in spider population dynamics? Does cannibalism dampen spider-initiated trophic cascades?

Abstract: Knowing how an increase in the resource base of a food web produces effects that propagate through the web is central to developing a clearer understanding of food- web structure and dynamics. In a detritus-based terrestrial food web, we measured the responses of predaceous arthropods to increases in prey arthropods that occurred in response to experimentally enhancing the web's resource base. Open 2 X 5 m plots on the floor of a deciduous forest were randomly assigned to either a Food Enhancement or Control treat- ment. We supplemented the resource base of the arthropod community of the leaf litter layer for 3.5 mo by periodically adding chopped mushrooms, potatoes, and instant fruit fly medium to the Food Enhancement plots. Major taxa of detritivores and fungivores increased in response to added food. Densities of springtails (Collembola) were on average 3 X higher in the Food Enhancement than Control plots. Numbers of adult fungus gnats (Diptera: Sciaridae and Mycetophilidae) did not differ significantly between treatments after 6 wk but were >2X higher in Food Enhancement plots at the end of the experiment. Total Diptera were twice as abundant in Food Enhancement plots on both census dates. Arthropod groups that include a range of feeding strategies also increased. Mites (Ac- arina), which include detritivores, fungivores, and predators, were twice as abundant in the experimental treatment. Staphylinid and carabid beetles (Coleoptera), which are primarily predaceous but include omnivorous species, were several times more numerous in the Food Enhancement plots. Effects of increasing the resource base propagated through the food web, leading to higher densities of the major strictly predaceous arthropod taxa. Centipedes (Chilopoda), pseudoscorpions (Pseudoscorpionida), and spiders (Araneae) were -2X as abundant in the Food Enhancement treatment. Thus, our experiment uncovered substantial bottom-up lim- itation in this detritus-based food web, expressed as responses by predaceous arthropods at least two trophic links removed from the experimentally elevated resource.

Abstract: It is often assumed that prey species consumed by generalist predators are largely, though not entirely, equivalent in terms of their value to the predators. In contrast to this expectation, laboratory feeding experiments uncovered distinctly varied developmental responses of a generalist predator, the wolf spider Schizocosa, to different experimental diets. Naive Schizocosa attacked and fed upon all the prey species offered; however, highly divergent patterns of survival, development, and growth of Schizocosa spiderlings reared on different single-prey diets revealed a wide spectrum of prey qualities. Spiderlings fed the collembolan Tomocerus bidentatus sustained the highest overall rates of survival, growth, and development. Fruit flies (Drosophila melanogaster) were intermediate-quality prey: spiders fed Drosophila initially exhibited rates of survival, growth, and development equal to those of spiders on a diet of T. bidentatus, but after about 3 months, rates declined markedly. Fungus gnats (Sciaridae; Bradysia sp.) and conspecfic spiderlings are low-quality prey for Schizocosa: a sole diet of either of these prey types resulted in positive but markedly submaximal rates of growth, retarded rates of development, and survival rates much lower than that supported by a diet of Drosophila. Worst were the collembolans Folsomia candida and Isotoma trispinata, and the aphid Aphis nerii: spiderlings fed solely one of these species did not grow and died without molting. A. nerii is classified as poor quality because survival was no better than that of starved controls. F. candida and I. trispinata were toxic: survival of Schizocosa hatchlings fed these collembolans was lower than that of starved controls. A mixed diet of T. bidentatus and fruit flies yielded positive synergistic effects with respect to growth, but development and rate of survival were similar to those of spiders on a sole diet of T. bidentatus. Including toxic prey did not produce a better diet, while inclusion of toxic prey with prey of higher quality created diets that were no better than the toxic prey alone. The results of these experiments suggest that prey species that are similar in morphology and behavior, and that are initially killed and consumed, may differ dramatically in their suitability as food for generalist arthropod predators.

Abstract: The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Abstract: Understanding the negative and positive effects of agricultural land use for the conservation of biodiversity, and its relation to ecosystem services, needs a landscape perspective. Agriculture can contribute to the conservation of high-diversity systems, which may provide important ecosystem services such as pollination and biological control via complementarity and sampling effects. Land-use management is often focused on few species and local processes, but in dynamic, agricultural landscapes, only a diversity of insurance species may guarantee resilience (the capacity to reorganize after disturbance). Interacting species experience their surrounding landscape at different spatial scales, which influences trophic interactions. Structurally complex landscapes enhance local diversity in agroecosystems, which may compensate for local high-intensity management. Organisms with high-dispersal abilities appear to drive these biodiversity patterns and ecosystem services, because of their recolonization ability and larger resources experienced. Agri-environment schemes (incentives for farmers to benefit the environment) need to broaden their perspective and to take the different responses to schemes in simple (high impact) and complex (low impact) agricultural landscapes into account. In simple landscapes, local allocation of habitat is more important than in complex landscapes, which are in total at risk. However, little knowledge of the relative importance of local and landscape management for biodiversity and its relation to ecosystem services make reliable recommendations difficult.

Abstract: Understanding the negative and positive effects of agricultural land use for the conservation of biodiversity, and its relation to ecosystem services, needs a landscape perspective. Agriculture can contribute to the conservation of high-diversity systems, which may provide important ecosystem services such as pollination and biological control via complementarity and sampling effects. Land-use management is often focused on few species and local processes, but in dynamic, agricultural landscapes, only a diversity of insurance species may guarantee resilience (the capacity to reorganize after disturbance). Interacting species experience their surrounding landscape at different spatial scales, which influences trophic interactions. Structurally complex landscapes enhance local diversity in agroecosystems, which may compensate for local highintensity management. Organisms with high-dispersal abilities appear to drive these biodiversity patterns and ecosystem services, because of their recolonization ability and larger resources experienced. Agri-environment schemes (incentives for farmers to benefit the environment) need to broaden their perspective and to take the different responses to schemes in simple (high impact) and complex (low impact) agricultural landscapes into account. In simple landscapes, local allocation of habitat is more important than in complex landscapes, which are in total at risk. However, little knowledge of the relative importance of local and landscape management for biodiversity and its relation to ecosystem services make reliable recommendations difficult.

Abstract: The study of interspecific competition has long been one of ecology's most fashionable pursuits. Stimulated in part by a simple theory (Lotka 1932; Volterra 1926; Gause 1934; Hutchinson 1959; MacArthur and Levins 1967), ecologists gathered numerous data on the apparent ways species competitively coexist or exclude one another (reviews in Schoener 1974b, 1983). As is typical in science, most of the early data were observational, and the few experimental studies were mostly performed in the laboratory rather than in the field. Though never lacking its doubters, the belief in the natural importance of interspecific competition is now being severely questioned (review in Schoener 1982). Many of the putatively supportive observations have been challenged as being statistically indistinguishable from random contrivance. Most such attacks have been rebutted, but not without some modification of original conclusions (e.g., papers in Strong et al. 1983). New observations have been gathered for certain systems, suggesting a lack of competitively caused patterns and catalyzing the variable environment view of Wiens (1977) in which competition is seen as a temporally sporadic, often impotent, interaction. Other critics have charged that the lack of experimental field evidence for competition would preclude its acceptance regardless of the quality of observational data. Indeed, results of some of the earlier field experiments are in part responsible for competition's presently beleaguered state. Connell (1975), after reviewing the field experiments known to him through 1973, concluded that predation, rather than competition, appears to be the predominant ecological interaction and should be given "conceptual priority." Shortly afterward, Schroder and Rosenzweig (1975) showed experimentally that two species of desert rodents overlapping substantially in habitat did not appear to affect one another's abundances. This result was interpreted as contradicting a crucial assumption of competition theory, almost its linchpin: the greater the resource overlap between species, the greater the competition coefficient, a measure of the intensity of interspecific competition (relative to intraspecific competition; MacArthur and Levins 1967; review in Roughgarden 1979).

Abstract: MUCKE aims to mine a large volume of images, to structure them conceptually and to use this conceptual structuring in order to improve large-scale image retrieval. The last decade witnessed important progress concerning low-level image representations. However, there are a number problems which need to be solved in order to unleash the full potential of image mining in applications. The central problem with low-level representations is the mismatch between them and the human interpretation of image content. This problem can be instantiated, for instance, by the incapability of existing descriptors to capture spatial relationships between the concepts represented or by their incapability to convey an explanation of why two images are similar in a content-based image retrieval framework. We start by assessing existing local descriptors for image classification and by proposing to use co-occurrence matrices to better capture spatial relationships in images. The main focus in MUCKE is on cleaning large scale Web image corpora and on proposing image representations which are closer to the human interpretation of images. Consequently, we introduce methods which tackle these two problems and compare results to state of the art methods. Note: some aspects of this deliverable are withheld at this time as they are pending review. Please contact the authors for a preview.