Beginning with Emlen (1966) and MacArthur and Pianka (1966) and extending through the last ten years, several authors have sought to predict the foraging behavior of animals by means of mathematical models. These models are very similar,in that they all assume that the fitness of a foraging animal is a function of the efficiency of foraging measured in terms of some "currency" (Schoener, 1971) -usually energy- and that natural selection has resulted in animals that forage so as to maximize this fitness. As a result of these similarities, the models have become known as "optimal foraging models"; and the theory that embodies them, "optimal foraging theory." The situations to which optimal foraging theory has been applied, with the exception of a few recent studies, can be divided into the following four categories: (1) choice by an animal of which food types to eat (i.e., optimal diet); (2) choice of which patch type to feed in (i.e., optimal patch choice); (3) optimal allocation of time to different patches; and (4) optimal patterns and speed of movements. In this review we discuss each of these categories separately, dealing with both the theoretical developments and the data that permit tests of the predictions. The review is selective in the sense that we emphasize studies that either develop testable predictions or that attempt to test predictions in a precise quantitative manner. We also discuss what we see to be some of the future developments in the area of optimal foraging theory and how this theory can be related to other areas of biology. Our general conclusion is that the simple models so far formulated are supported are supported reasonably well by available data and that we are optimistic about the value both now and in the future of optimal foraging theory. We argue, however, that these simple models will requre much modification, espicially to deal with situations that either cannot easily be put into one or another of the above four categories or entail currencies more complicated that just energy.

Citation classic - optimal foraging - a selective review of theory and tests

Spiders (Araneae) useful for pest limitation and bioindication

A general discussion of the designs and functions of the silk structures spiders use to capture prey has not been attempted since the book of Witt et al (319). Knowledge has increased so greatly in the intervening years that complete coverage is now impossible in a review article. I have cited primarily more recent and general publications. Related aspects of web biology not emphasized here are reviewed in papers on particular taxonomic groups (260), general feeding ecology (233), choice of websites (131, 232, 234), interand intra-specific competition (and the lack of it) (273, 275, 314), ecophysiology (192), web removal (20), sexual behavior (139, 238), vibration transmission in webs (175), neurobiology (3), attack behavior (237, 279), communication (320), energetics of web-building (227), timing of web construction (229), cues used for orientation during web construction (80, 308), structure and composition of web lines (224, 290), physical properties of silk (109, 322), and silk glands (138). Due to the numbers of papers on orb webs, orbs are emphasized over non-orbs. The imbalance in research is strong (the ratio in the reference section is about 2: 1 orb: non-orb, despite the fact that the ratio in numbers of species must be closer to 1: 2 (H. W. Levi, personal communication). At least partially repairing this imbalance is a pressing need.

Function and Phylogeny of Spider Webs

A conceptual framework is presented for the study of the factors affecting the distribution, dispersal and abundance of spiders in agricultural systems. It is useful to consider how factors operate at three levels of a spatial hierarchy, namely micro-habitat, habitat and landscape. The size and distribution of spider populations are determined by factors influencing survival, reproduction and dispersal. Modes of dispersal vary in terms of the efficiency of sampling new habitats and the level of risk. A literature survey of proximal factors (micro-climate, habitat structure, disturbance, prey availability, predation, and territoriality) affecting micro-habitat usage by spiders showed that the relative importance of these factors varied according to spider species. Spider abundance and diversity were found, in general, to be positively correlated with environmental diversity at different spatial scales. Within-field habitat diversifications were found to be more effective in increasing spider populations when interspersed throughout the crop (e.g., polycultures and reduced tillage) than when spatially segregated (e.g., strip management). Two approaches (modeling and experimental) to studying the effects of landscape level phenomena on spider distribution and abundance are discussed. Manipulation of habitats at the edge of fields has not, in the main, resulted in increased spider density within fields. Opportunities were identified for increasing regional populations of spiders, and optimizing pest control, by management of the annual shift in the crop mosaic to maximize spider transfer rates from senescing crops to young crops.

Scale-dependent dispersal and distribution patterns of spiders in agricultural systems: A review

There is a large body of evidence indicating that predator behavior may strongly influence patterns and processes at the population and community level. Site selection is a major component of fitness in sit-and-wait predators, especially when relocation is rare. Although several review articles dealt with these issues in web-building spiders, this is the first attempt to summarize the effects of biotic and abiotic factors on site selection and relocation in another group of sit-and-wait predators, the pit-building antlions (Neuroptera: Myrmeleontidae). Our synthesis shows that prey abundance may have relatively little effect on pit relocation and that physical properties of the habitat or competition often override its effect. We suggest that owing to a variety of constraints such as physiological constraints or difficulties in assessing site quality, site selection and relocation are not necessarily optimal and thus food intake rate is not maximized. We call for a multi-factorial study on a single species in order to pinpoint the dominant factors and to assess to what extent they influence site selection and relocation. We conclude by proposing new research directions, such as studying whether pit relocation is an adaptive response, when controlling for possible phylogenetic effects.

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Factors Influencing Site Abandonment and Site Selection in a Sit-and-Wait Predator: A Review of Pit-Building Antlion Larvae

Web-building behaviour in the orb-weaving spider Zygiella x-notata: influence of experience.

Presence of potential prey affects web-building in an orb-weaving spider Zygiella x-notata

The distribution of the spider Zygiella x-notata was examined using field populations of adult females occupying the outside frames of windows. The structure of the populations was aggregative, and the distribution of individuals on the window frames and the size of the webs were density dependent. Also, the sizes of the webs of neighbouring spiders on the same window alternated. This spatial organization involves interactions between neighbours. If one spider out of two is removed, and if all the webs are destroyed, remaining spiders that previously had small webs significantly increase the size of their construction. In contrast, individuals that previously had large webs do not modify the size of their construction. This shows that individuals of Z. x-notata respond to the presence of neighbours. The influence of intraspecific interactions in such a population is discussed.

Influences of aggregative behaviour on space occupation in the spider Zygiella x-notata (Clerck)

Stegodyphus lineatus (Eresidae) is a desert spider that builds an aerial capture web on bushes in the Negev desert in southern Israel. Web building for spiders is costly in energy, time, and risk of predation. Spiders should trade-off these costs with the benefits in terms of prey capture. We tested the hypothesis that the previous foraging success of the spider influences the effort invested in foraging. Specifically, we asked whether an increase in food intake causes spiders to reduce web renewal activity and web size. Alternatively, time constraints on foraging and development, resulting from a short growing season, could induce spiders to continue foraging even when supplemented with prey. The cost of web building was measured as time and mass loss. To build an average size web (about 150 cm 2 ), we calculated that a spider requires 6 h and that spiders lose 3%‐7% of their weight. In field experiments, spiders responded differently to food supplementation in 2 different years. In 1994, they improved their condition compared to individuals whose webs were removed to reduce foraging opportunities and compared to control spiders. In 1995, spiders tested earlier in the season than the previous year did not improve their condition in response to prey supplementation. Nonetheless, in both years, food-supplemented spiders built significantly smaller webs than food-deprived and control spiders. This result was confirmed in a laboratory experiment where prey intake was controlled. We conclude that for S. lineatus immediate foraging risks outweigh the potential time constraints on foraging. Key words: Eresidae, food supplementation, optimal foraging, spiders, Stegodyphus lineatus, web building. [Behav Ecol 10:115‐121 (1999)] F oraging effort can be viewed as a compromise between the energetic needs of the individual for maintenance, growth, and reproduction and the costs or risks associated with foraging activity (Lima and Dill, 1990). The benefits of foraging are frequently traded off against costs, which may vary in accordance with the condition or ‘‘state’’ of the forager (Krebs and Kacelnik, 1991). These foraging trade-offs provide a fertile field for investigating decision-making processes in animals and, in particular, the ways that conflicts are resolved between competing requirements over different time scales—for example, over the time scale of a foraging bout versus the time scale of the forager’s life span. For web-building spiders, foraging costs associated with the capture web include the energy required to construct and maintain the web (silk production and costs of activity) and the risks associated with being exposed while active on the web (Lubin, 1973; Uetz, 1992). The benefit from building a web is derived from prey caught in the web. The presence of an effective capture web determines the spider’s energy budget in the short term. Thus, the decision to build a web is a foraging decision, which, in the context of optimal foraging theory, should be sensitive to the expected ratio of benefits to costs summed over the duration of the web (Higgins, 1990; Higgins and Buskirk, 1992; Riechert and Luczak, 1982). The web-building process is repeated at intervals during the spider’s lifetime, and the number of webs built during the lifetime varies among species. In some species new webs are constructed daily, while in others both the frequency and the extent of web renewal are more variable (Eberhard, 1986; Lu

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Previous foraging success influences web building in the spider Stegodyphus lineatus (Eresidae)

In numerous spider species, reproductive success of adult females has been shown to be positively correlated with their body mass. We suggest, however, that spiders may incur greater foraging costs as their body mass increases due to the numerous and complex locomotor bouts needed to build an orb-web. Such a body-mass-dependent cost should, in turn, affect the web-building decisions of spiders. In the laboratory, we tested the influence of body mass on energetic expenditure (measured as mass loss) during web-building behavior in Zygiella x-notata. Our results showed (1) that energetic costs associated with web-building were closely related to body mass and to web-building activity, and (2) that as their body mass increased, spiders reduced the amount of silk used per web, while their foraging effort simultaneously increased. This work gives new insights into web-building behavior and energy allocation strategies of weaving spiders.

Raymond Leborgne

Papers

Web-building behaviour in the orb-weaving spider Zygiella x-notata: influence of experience.

Presence of potential prey affects web-building in an orb-weaving spider Zygiella x-notata

Influences of aggregative behaviour on space occupation in the spider Zygiella x-notata (Clerck)

Previous foraging success influences web building in the spider Stegodyphus lineatus (Eresidae)

Body-mass-dependent cost of web-building behavior in an orb weaving spider, Zygiella x-notata