ehaviour|
|Geographic:||Geographic Scope: Australia Geographic Code: 8AUST Australia|
Spiders have often been used as model organisms when examining
facets of predator-prey interactions and optimal foraging theory, both
as predators (e.g., Olive 1982; Janetos 1982a) and as prey (e.g.,
Rypstra 1984; Wise & Chen 1999). Web building spiders have
especially attracted the attention of researchers, in part because many
are relatively easy to find and work with in the field and in the
laboratory. Some rebuild all or part of their webs almost daily and so
have the potential to react quickly to applied stimuli. A variety of
models and ingenious measurement techniques have allowed researchers to
estimate aspects of the cost of web construction with respect to the
expenditure of silk and energy (e.g., Tanaka 1989; Nakata & Ushimaru
When a spider moves to a new web site there are potential costs from loss of hunting time, risks in entering an area of unknown quality with possible predators, as well as the costs in silk production and energy expenditure. For spiders that build materially expensive webs and do not recycle silk proteins, the high cost of silk and associated energy investment appears correlated to long web site residence times (Janetos 1982a; Tanaka 1989). In many orb web building species in the families Araneidae, Tetragnathidae, and Nephilidae ingestion of most of the web occurs before the spider moves away from a web site. The silk proteins, therefore, are largely recycled (Peakall 1971 in Janetos 1982a). This minimization of material costs has allowed researchers to focus on the other factors that affect orb web spiders' decisions to move, such as the effects of disturbance (e.g., Enders 1976) or prey abundance (McNett & Rypstra 1997). Two sources of information have most frequently been utilized: the temporal pattern of the movements and the frequency of relocation.
Temporal pattern of movements.--Janetos (1982a) showed that orb web building spiders with relatively low material costs of relocation may show non-random patterns of residence times at web sites, either tending to move on more quickly than expected, or staying much longer than expected. The implication of this finding is that these species are not constrained by costs and can move whenever it is most appropriate in terms of prey abundance or other factors. In contrast, some sheet-weaving spiders (Linyphiidae), which do not recycle their silk proteins, have a much greater energy cost when moving to a new site (Janetos 1982a). Accordingly, the relocation patterns of these sheet-weavers did not differ significantly from that expected due to random events (i.e., the cost of abandoned silk and energy is a strong deterrent to relocation unless necessitated by other factors). Based on this premise, a spider that recycles silk but has a random pattern of movement nonetheless may have a high cost of moving due to some other factor. An increased risk of predation during and after relocation was identified as this factor in the case of the orb web spider Nephila clavipes (Linnaeus 1767) (Vollrath & Houston 1986).
Frequency of relocation.--In work on orb web spiders, the frequency of relocation, or its inverse, the average length of residence at a site, has been used to demonstrate a response to factors such as changes in prey levels (Olive 1982; Vollrath 1985) , web damage (Enders 1976), and intraspecific interactions (Smallwood 1993). These are among the many factors that together influence the suitability of a site for any particular spider at any given time (Riechert & Gillespie 1986) . What may be most difficult to quantify are the negative influences, (i.e., those such as an increased risk of predation that could cause a spider to move less frequently than might otherwise be expected). These factors may be easiest to examine indirectly by comparing the habits of different species and their respective life histories, and considering the differences among them. As an example, Miyashita (2005) found that the likelihood of risk-taking in two Nephila Leach 1815 sp