The influence of food supply on foraging behaviour in a desert spider
TL;DR: It is suggested that digestive constraints prevented supplemented spiders from fully utilizing the available prey, and by reducing foraging activities on the surface, spiders in a prey-rich habitat can reduce the risk of predation.
Abstract: We tested the alternative hypotheses that foraging effort will increase (energy maximizer model) or decrease (due to increased costs or risks) when food supply increased, using a Namib desert burrowing spider, Seothyra henscheli (Eresidae), which feeds mainly on ants. The web of S. henscheli has a simple geometrical configuration, comprising a horizontal mat on the sand surface, with a variable number of lobes lined with sticky silk. The sticky silk is renewed daily after being covered by wind-blown sand. In a field experiment, we supplemented the spiders' natural prey with one ant on each day that spiders had active webs and determined the response to an increase in prey. We compared the foraging activity and web geometry of prey-supplemented spiders to non-supplemented controls. We compared the same parameters in fooddeprived and supplemented spiders in captivity. The results support the "costs of foraging" hypothesis. Supplemented spiders reduced their foraging activity and web dimensions. They moulted at least once and grew rapidly, more than doubling their mass in 6 weeks. By contrast, food-deprived spiders increased foraging effort by enlarging the diameter of the capture web. We suggest that digestive constraints prevented supplemented spiders from fully utilizing the available prey. By reducing foraging activities on the surface, spiders in a prey-rich habitat can reduce the risk of predation. However, early maturation resulting from a higher growth rate provides no advantage to S. henscheli owing to the fact that the timing of mating and dispersal are fixed by climatic factors (wind and temperature). Instead, large female body size will increase fitness by increasing the investiment in young during the period of extended maternal care.
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TL;DR: 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.
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?
321 citations
TL;DR: The presented estimates of the global annual prey kill and the relative contribution of spider predation in different biomes improve the general understanding of spider ecology and provide a first assessment of theglobal impact of this very important predator group.
Abstract: Spiders have been suspected to be one of the most important groups of natural enemies of insects worldwide. To document the impact of the global spider community as insect predators, we present estimates of the biomass of annually killed insect prey. Our estimates assessed with two different methods suggest that the annual prey kill of the global spider community is in the range of 400–800 million metric tons (fresh weight), with insects and collembolans composing >90% of the captured prey. This equals approximately 1‰ of the global terrestrial net primary production. Spiders associated with forests and grasslands account for >95% of the annual prey kill of the global spider community, whereas spiders in other habitats are rather insignificant contributors over a full year. The spider communities associated with annual crops contribute less than 2% to the global annual prey kill. This, however, can be partly explained by the fact that annual crop fields are “disturbed habitats” with a low buildup of spider biomass and that agrobiont spiders often only kill prey over short time periods in a year. Our estimates are supported by the published results of exclusion experiments, showing that the number of herbivorous/detritivorous insects and collembolans increased significantly after spider removal from experimental plots. The presented estimates of the global annual prey kill and the relative contribution of spider predation in different biomes improve the general understanding of spider ecology and provide a first assessment of the global impact of this very important predator group.
214 citations
Cites background or methods from "The influence of food supply on for..."
...Due to adverse environmental conditions, prey availability in deserts is very low and these biomes are often populated by spiders in very low densities (Shook 1978; Polis 1991; Lubin and Henschel 1996; Henschel 1997)....
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...In the case of desert spiders, a daily food ingestion rate of 0.01–0.04 mg per milligram spider body mass was used (see Lubin and Henschel 1996; Henschel 1997)....
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TL;DR: Evidence is provided that the behaviour of trap‐building predators is not stereotypic or fixed as was once commonly accepted, rather it can vary greatly, depending on the individual's internal state and its interactions with external environmental factors.
Abstract: Foraging theory was first developed to predict the behaviour of widely-foraging animals that actively search for prey. Although the behaviour of sit-and-wait predators often follows predictions derived from foraging theory, the similarity between these two distinct groups of predators is not always obvious. In this review, we compare foraging activities of trap-building predators (mainly pit-building antlions and web-building spiders), a specific group of sit-and-wait predators that construct traps as a foraging device, with those of widely-foraging predators. We refer to modifications of the trap characteristics as analogous to changes in foraging intensity. Our review illustrates that the responses of trap-building and widely-foraging predators to different internal and external factors, such as hunger level, conspecific density and predation threat are quite similar, calling for additional studies of foraging theory using trap-building predators. In each chapter of this review, we summarize the response of trap-building predators to a different factor, while contrasting it with the equivalent response characterizing widely-foraging predators. We provide here evidence that the behaviour of trap-building predators is not stereotypic or fixed as was once commonly accepted, rather it can vary greatly, depending on the individual's internal state and its interactions with external environmental factors.
143 citations
Cites background from "The influence of food supply on for..."
...Indeed, hungry spiders and antlions were often documented to increase the investment in trap size (Riechert, 1981; Sherman, 1994; Lubin & Henschel, 1996; Herberstein et al., 2000b; Arnett & Gotelli, 2001; Lomascolo & Farji-Brener, 2001)....
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TL;DR: Experienced web-building spiders constructed more asymmetric webs than conspecifics deprived of any prior building experience over a period of several months, revealing that experience can contribute to intraspecific as well as to individual variations in web design.
Abstract: A typical feature of vertical orb-webs is the ‘top/bottom’ asymmetry, where the lower web region is larger than the upper web region. This asymmetry may improve prey capture success, because, sitting in the hub of the web, a spider can reach prey entangled below the hub faster than prey entangled in the area above the hub. While web asymmetry is known to vary intraspecifically, we tested if this variation also exists at the individual level and whether it is the result of experience, using two orb-web spider species, Argiope keyserlingi and Larinioides sclopetarius. The results reveal that experienced web-building spiders constructed more asymmetric webs than conspecifics deprived of any prior building experience over a period of several months. Experienced individuals invested more silk material into the web region below the hub, which covered a larger area. Moreover, web asymmetry was also influenced by previous prey capture experiences, as spiders increased the lower region of the web if it intercepted the most prey over a period of 6 days. Consequently, spiders may be able to use long-term web-building experience as well as short-term prey capture experience to build better traps. In contrast to previous views of spiders, experience can contribute to intraspecific as well as to individual variations in web design.
99 citations
References
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TL;DR: In this article, age and size at maturity at maturity number and size of offspring Reproductive lifespan and ageing are discussed. But the authors focus on the effects of age and stage structure on fertility.
Abstract: Prologue Part I: Evolutionary explanation Demography: age and stage structure Quantitative genetics and reaction norms Trade-offs Lineage-specific effects Part II: Age and size at maturity Number and size of offspring Reproductive lifespan and ageing Appendices Glossary References Author index Subject index.
10,338 citations
TL;DR: The book aims to instill in students an ability to think through biological research problems in such a way as to grasp the essentials of the experimental or analytical setup to know which types of statistical tests to apply in a given case and to carry out the computations required.
Abstract: This text develops the science of biometry from an elementary introduction up to the advanced methods necessary for biological research and for an understanding of the published literature. This text is aimed primarily at the academic biologist including general zoologists botanists microbiologists geneticists and physiologists in universities research institutes and museums. This book while furnishing ample directions for the analysis of experimental works also stresses the descriptive and analytical statistical study of biological phenomena. It is intended both as a text to accompany a lecture course and as a complete course for self-study. The book aims to instill in students an ability to think through biological research problems in such a way as to grasp the essentials of the experimental or analytical setup to know which types of statistical tests to apply in a given case and to carry out the computations required. Chapters cover biological data data handling descriptive statistics probability estimation and hupothesis testing analysis of variance linear regression correlation multiple and curvilinear regression analysis of frequencies and miscellaneous methods.
4,145 citations
Book•
04 Feb 1993
TL;DR: The spider in the ecological play is a central character in the story of how spiders avoid competition and the impact of spiders on insect populations and competitionist views of spider communities are examined.
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.
914 citations
TL;DR: This paper presents a meta- Ecology of Insect Folivores of Woody Plants: Nitrogen, Water, Fiber and Mineral Considerations, andritional Ecology of Grass Foliage-Chewing Insects and Phytophagous Mites.
Abstract: Nutritional Ecology of Forb Foliage-Chewing Insects Nutritional Ecology of Insect Folivores of Woody Plants: Nitrogen, Water, Fiber and Mineral Considerations Nutritional Ecology of Grass Foliage-Chewing Insects Nutritional Ecology of Phytophagous Mites Nutritional Ecology of Lichen/Moss Arthropods Nutritional Ecology of Arthropod Gall-Makers Nutritional Ecology of Bruchid Beetles Nutritional Ecology of Seed-Sucking Insects Nutritional Ecology of Stored-Product Insects Nutritional Ecology of Stored-Product and House Dust Mites Ecology of Nectar and Pollen Feeding in Lepidoptera.
793 citations
"The influence of food supply on for..." refers background in this paper
...The short pauses in activity may occur because time is required to digest the prey or to renew the digestive enzymes before resuming foraging (Riechert and Harp 1987)....
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01 Jan 1991
TL;DR: Barth et al. as discussed by the authors observed that the physiognomy or physical structure of environments has an important influence on the habitat preferences of spider species, and ultimately on the composition of spider communities.
Abstract: Spiders are extremely common inhabitants of most terrestrial communities, yet, compared to other animal taxa, they have only recently become the subject of ecological research (Turnbull, 1973; Witt and Rovner, 1982; Wise, 1984; Shear, 1986; Nentwig, 1987, for reviews). From the earliest studies, it has been clear that the physiognomy or physical structure of environments has an important influence on the habitat preferences of spider species, and ultimately on the composition of spider communities. This is certainly no coincidental observation for two important reasons:
1.
Many spiders build webs for prey capture, and the attachment of these webs to surrounding structures often requires the presence of specific architectural features or arrangements (Riechert and Gillespie, 1986).
2.
The nature of both web-building and non-web-building spiders’ primary sensory modalities (they perceive vibration through mechanoreceptors) dictates that they perceive their environment using tactile and vibratory cues (Barth, 1985).
403 citations