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Title: The comparative biology of the orb-web spiders Zygiella x-notata and Zygiella atrica
Author: Smout, Norman
ISNI:       0000 0001 3469 3472
Awarding Body: University of London
Current Institution: Royal Holloway, University of London
Date of Award: 1976
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The aim of this investigation is to compare the ecology and behaviour of the orb-web spiders Zygiella x-notata and Zygiella atrioa. Differences between them in their choice of habitat, as cited in the literature, are generally confirmed by a preliminary field survey. Mixed populations do occur but hybridisation has not been detected, although the close morphological similarity, especially in the immature stages, is emphasized. Field studies show that the species also build basically similar webs with respect to spider size, retreat position and habitat structure. However, the larger number of radii in Z. atrioa middle instar webs is of interest. Life histories are compared in a two-year study of two natural populations and differences in mating behaviour are described. In conjunction with the field studies, which include microclimatic measurement, laboratory experiments on the effects of temperature, humidity and feeding rates on development; humidity and temperature preferences; and changing reactions to light are detailed. Tolerances to temperature extremes, desiccation and starvation are investigated. These experiments indicate several differences between the species. Z. x-notata eggs hatch more quickly than Z. atrioa at equivalent temperatures. Z. x-notata prefers higher temperatures and can also withstand greater extremes. At 25°C, for example, Z. atrioa males show high mortality during the final moult. The preference shown for low humidities is more pronounced in Z. x-notata and it is more resistant to desiccation and also food deprivation. Limited feeding results in reduced size and increased instar length, but there is some compensation by reduction in instar numbers, especially for Z. x-notata. In conclusion the differences detected in morphology, life histories, webs, preference and tolerances in both field and laboratory indicate that Z. x-notata is more adaptable, and this may well help to explain its wider and more varied pattern of distribution.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Zoology