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Predation on Social and Solitary Individuals of the Spider Stegodyphus Dumicola (araneae, Eresidae)
| Content Provider | Semantic Scholar |
|---|---|
| Author | Henschel, Johannes R. |
| Copyright Year | 1998 |
| Abstract | Encounters and effects of predators were examined for group-living and solitary dispersers of the spider Stegodyphus dumicola Pocock 1898 (family Eresidae) in Namibia. Birds and araneophagous spiders were major predators of solitary spiders ; group members living in large, tough, complex nests were less vulnerable . Arboreal pugnacious ants Anoplolepis steingroeveri (Forel 1894) frequently attacked S. dumicola colonies of all sizes . As a means of defense against ants, the spiders produced copious amounts of sticky cribellar silk. Solitary spiders were incapable of sustaining this resistance for as long as groups could and usually died when ants attacked . Solitary individuals were, however, less likely to contract a contagious fungal disease that spread in large, old nests after rain . I ..onclude that the action of predators may explain why S. dumicola tend to be avidly social as well as prudently solitary . Group living has behavioral, ecological and genetic consequences for spiders (Buskirk 1981 ; Rypstra 1993; Aviles 1993, 1996) . The fundamental ecological reasons why some spiders spend their entire lives in groups may differ in different species . Safety from predators is often invoked as an explanation for grouping in animals (Inman & Krebs 1987) . The encounter effect predicts that individuals encounter predators at a lower rate, due to foraging constraints by the predators . Once an encounter occurs, the dilution effect predicts that a member's probability of being captured decreases with group size . Groups of non-territorial permanently-social spiders (hereafter referred to as social spiders) may have the possibility to lower their predation risk by using large, complex, communal retreats that provide physical protection. Cooperative defense is another possibility. The potential for cooperation is one of the distinguishing characteristics of social spiders (Aviles 1996), but its manifestations are not well-known. The suggested increased safety via communal fortification (Seibt & Wickler 1988a) and defense has not been confirmed . Here I examine how Stegodyphus dumicola Pocock 1898 (Eresidae), living in groups or solitarily (Le Roy 1979 ; Seibt & Wickler 1988a; Henschel 1993), are affected by various kinds of predators (Meikle 1986 ; Seibt & Wickler 1988a ; Griswold & Meikle 1990) . In 61 particular, I examined the roles of the silk and of defense in providing protection . Stegodyphus dumicola occupy nests that are attached to tree branches at heights of 0 .5-1 .5 in. Cribellar sheet webs extend from the nests in different directions . Nest entrances point downwards and the tops are sealed. Colonies of S. dumicola are polydomous, i.e ., different nests are interconnected with one web, or monodomous, i .e ., having isolated nests, including founder colonies of solitary dispersing females. Generations are annual and the secondary sex-ratio is female-biased (12% males on average; Henschel, Lubin & Schneider 1995a) . In Namibia, females mature from January onwards (mid-summer), produce eggs during February and March, care for offspring during March and April, and die during April to June when they are consumed by gerontophagous juveniles (Seibt & Wickler 1987) . Most solitary dispersal by females occurs during January to March . Males mature in midsummer, but are short-lived and apparently :mate within the parent colony (Henschel et al . 1995a) . Males that emigrate do not establish :new nests, but perhaps join solitary females . 'The current study concentrates on females . I examined (a) the predator encounter rates, vulnerability, and survival of S. dumicola individuals and colonies, and (b) the responses and anti-predator measures of S. dumicola towards each predator. These factors are dis- |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://americanarachnology.org/joa_free/joa_v26_n1/joa_v26_p61.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
