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Critical Comments / 4 O3.1.1 Intrinsic Visibility of an Orb Online Material Contents O3.1 The importance of visibility: critical comments / 4 O3.1.1 Intrinsic visibility of an orb / 4 O3.1.2 Effects of visual background / 5 O3.1.3 UV reflectance of stabilimenta / 5 O3.1.4 Evolutionary origins vs. maintenance /7 O3.2 Difficulties in modeling orb web performance / 7 O3.2.1 Variation I: “The” mesh size / 7 O3.2.2 Variation II: “The” properties of silk lines / 8 O3.2.3 Variation III: The “available” prey / 8 O3.2.4 Variation IV: “The” habitat / 10 O3.2.5 Temporal variation / 10 O3.2.6 Ontogenetic changes (and lack of them) / 11 O3.2.7 Other variables that vary widely / 11 O3.2.8 Tradeoffs between functions / 12 O3.2.9 Different currencies / 12 O3.2.10 Biological realism – further calibrations of models / 12 O3.3 Possible relations between silk composition, prey impact traits, and orb designs / 12 O3.4 The function(s) of silk stabilimenta: critical evaluations of the evidence / 13 Box O3.1 Uloborid stabilimenta: multiple lines of indirect evidence point (mostly) to one conclusion / 13 Box O5.1 The domed sheet plus tangle web of the pholcid Modisimus guatuso / 15 O6.1 Further details of the behavior of M. duodecimspinosa and A. diadematus / 16 O6.1.1 Stages of construction / 16 O6.1.1.1 Exploration and establishing early lined / 16 O6.1.1.2.1 Use previous lines or start from scratch? / 16 O6.1.1.1.2 Gathering sensory information / 16 O6.1.1.1.3 The end of exploration and the hub transition / 17 O6.1.1.2 The other primary frames / 17 O6.1.1.3 Secondary radii / 17 O6.1.1.3.1 Radii at final angles / 18 O6.1.1.3.2 Upper exit radius / 18 O6.1.1.3.3 Successive radii to opposite sides / 19 O6.1.1.3.4 Hub loops / 19 O6.1.1.4 Secondary frames / 19 O6.1.1.5 Temporary spiral and tertiary radii / 19 O6.1.1.6 Sticky spiral: translating cues into behavior / 20 O6.1.2 Orb web repair / 20 O6.1.3 Web removal and recycling / 20 O6.2 Details of the movements by Micrathena duodecimspinosa / 21 O6.2.1 Exploration and establishing new lines / 21 O6.2.1.1 Break and reel behavior / 21 O6.2.1.2 “Fishing” by floating lines on the breeze / 22 O6.2.1.3 Snubbing attachments to the substrate / 23 O6.2.1.4 Probable tension adjustments / 23 O6.2.1.5 Following behavior / 23 O6.2.1.6 Sliding tarsus IV along the dragline / 23 O6.2.1.7 Exploratory descents / 23 O6.2.2 Secondary radii and frame lines / 23 O6.2.3 Hub construction / 24 O6.2.4 Temporary spiral construction / 24 O6.2.5 Sticky spiral construction / 24 O6.2.6 Hub modification / 25 1 O6.3 Comparisons with other taxa of orb weavers / 26 O6.3.1 Exploration and establishing early lines / 26 O6.3.2 Radii / 26 O6.3.2.1 Other araneids and tetragnathids / 26 O6.3.2.2 Nephila / 26 O6.3.2.3 Uloborids / 27 O6.3.2.4 Theridiosomatids / 28 O6.3.2.5 Symphytognathoid orb weavers / 28 O6.3.3 Frame lines / 28 O6.3.3.1 Other araneids and tetragnathids / 28 O6.3.3.2 Nephila / 28 O6.3.3.3 Uloborids / 29 O6.3.3.4 Theridiosomatids and symphytognathoids / 29 O6.3.4 Hub loops / 29 O6.3.4.1 Other araneids and tetragnathids / 29 O6.3.4.2 Nephila / 29 O6.3.4.3 Uloborids / 30 O6.3.4.4 Theridiosomatids / 30 O6.3.5 Temporary spiral and tertiary radii / 30 O6.3.5.1 Other araneids and tetragnathids / 30 O6.3.5.2 Nephila / 31 O6.3.5.3 Uloborids / 31 O6.3.5.4 Theridiosomatids and symphytognathoids / 32 O6.3.6 Sticky spiral / 32 O6.3.6.1 Other araneids / 32 O6.3.6.2 Tetragnathids / 34 O6.3.6.3 Nephilids / 34 O6.3.6.4 Uloborids / 34 O6.3.6.4.1 Inner loop localization / 34 O6.3.6.4.2 To attach or not to attach: skipping radii / 35 O6.3.6.4.3 Sticky lines on and beyond frame lines / 35 O6.3.6.4.4 Other details / 36 O6.3.6.5 Theridiosomatids and symphytognathoids / 36 O6.3.7 Hub modification / 37 O6.3.7.1 Other araneids / 37 O6.3.7.2. Other families / 37 O6.3.8 Other modifications following sticky spiral completion / 37 O6.3.8.1 Supplementary radii / 37 O6.3.8.1.1 Uloborids: two enigmatic web types / 37 O6.3.8.1.2 Symphytognathoids / 38 O6.3.8.2 Silk stabilimenta construction / 39 O6.3.8.3 Orb destruction and repair / 39 O9 Case studies of functions of diverse, convergent web designs / 41 O9.1 Tangles near orbs / 41 O9.2 Webs made by mature males / 42 O9.3 Angle of web plane with horizontal / 43 O9.4 Special spinneret morphology that facilitates moulting on a web / 44 O10 Final thoughts and future research / 44 Tables O2.1. Lines grasped by the spider’s tarsi in orb-weavers waiting at the hubs of orbs when the spider was apparently “alert” for prey / 45 O2.2. A tentative list of possible deep uniformities in two details of leg movements, following, and prolateral vs retrolateral short-distance shearching movements, that are performed during orb construction / 48 O3.1. A sample of orb-weaving species in which the angles between the web plane and horizontal were measured in the field for at least five different adults / 50 O3.2. A sampler of orb-weaving species that incorporate detritus or egg sacs into their orbs, and in which other natural history details are known / 53 O3.3. Types of data that have been used to test the major hypotheses regarding the function of silk stabilimenta / 54 O3.4. A critical (and unavoidably somewhat subjective) summary of the implications of the evidence in Table O3.3 for the 2 four major hypotheses for stabilimentum (stab) function / 59 O3.5. A summary of several types of possible weaknesses in lab and field studies of the effects of stabilimenta on the attraction of prey to orbs / 66 O4.1. The mix of correlations and lack of correlations between the design features of the webs and attack speeds in a small, somewhat arbitrary sample of species with particularly rapid and particularly slow attacks / 69 O6.1. This undoubtedly incomplete list of the “vocabulary” of different motor patterns used during the early stages of orb construction by a few arbitrarily chosen species / 71 O6.2. Comparisons of the sequences in which different operations in web construction were performed by different taxa of orb weaving spiders / 72 O6.3. Uniformity from diversity: the movements and probable mechanical functions of the legs of the araneid Micrathena duodecimspinosa (AR) during construction of the outer loops (2-6) of the sticky spiral / 73 O8.1. Mean height of the hub above the ground (± one standard deviation) for a sample of 14 species in four families (mostly from Valderrama 2000, in a high elevation tropical forest) / 75 O10.1 Important but easily-filled gaps in current understanding / 76 Figure captions / 91 3 Online Files for “Spider webs: behavior, function and evolution” These online files complement the text in Chapters 2, 3, 6 and 9-10 in various ways. The numbers of the different sections here correspond to the chapter numbers in the book with an “O” added; table numbers are also coordinated with chapters (e.g., Table O2.1 complements topics discussed in chapter 2). Some sections focus largely on the limits of some previous studies: O3.1concerns the possible importance of orb visibility; O3.2 largely concerns difficulties in attempts to model orb web function. Tables O3.2– O3.5 constitute the most complete summary and critical evaluation of evidence concerning the controversial topic of the function(s) of silk stabilimenta yet compiled; they form the empirical basis for the discussion in section 3.3.4. Sections O6.1 – O6.3 greatly extend the descriptions of construction behavior in Chapter 6. O6.1 provides additional details of the behavior of the two “focus” species, Micrathena duodecimspinosa and Araneus diadematus. O6.2, provides new, previously unpublished details of M. duodecimspinosa orb construction behavior. They are based on video recordings, and provide a finer level of detail than that available to date for any other species. And O6.3 adds observations of orb construction behavior of many other taxa. These sections open the door for detailed comparative studies of other species. Sections O9.1- O9.3 present concrete examples of a major theme of Chapter 6, the tendency to converge on particular web designs in widely diverse taxa. O3.1. The importance of orb visibility: critical comments O3.1.1 Intrinsic visibility of an orb There is little doubt that prey sometimes avoid orb webs that they have apparently perceived visually, at least in certain situations when there is no wind and webs are well illuminated and have simple visual backgrounds (section 3.3.3.2). Demonstrating that the degree to which an orb is visible affects prey capture under more natural conditions in the field is more complicated: the visibility of an orb is undoubtedly influenced by complex interactions among reflectance properties of silk lines, web architecture, ambient light, visual backgrounds, and insect visual capabilities, and avoidance by flight patterns and speeds in the field. This Appendix examines critically the evidence for some published conclusions regarding the importance of web visibility for selection on orb web designs.
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