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Psyche 
[Vol. 94 
sunlight which was redirected with a mirror down the plane of the 
web onto the ventral surface of the spider (similar to the sun’s rays 
at noon) caused the spider to assume a posture which minimized the 
body surface exposed to the light/ heat source. In similar experi- 
ments, Biere (1977) redirected the sun’s rays so that the light was 
directly striking individual M. gracilis. He maintained this light/ 
heat source until the spiders retreated from the hub to the upper 
bridge-thread attachment point. Seven of 12 individuals thus treated 
abandoned their former web sites the following day. The relocation 
response observed in this study may be similar to that observed by 
Biere (1977). Exposure to insolation is sporadic in deciduous 
forests, and can usually be dealt with using web orientation and/or 
thermoregulatory postures. It may be that in the pine stand, these 
behaviors were not effective in relieving the effects of prolonged 
exposure to direct sunlight. An additional light-related variable 
which was not measured in this study, yet which could serve as a 
proximate cue, is the difference in light intensity between the two 
habitats. However, Enders (1972) demonstrated that certain forest- 
dwelling orb weavers showed no preference for any particular level 
of light. Similar experiments are needed to clarify whether M. graci- 
lis uses light-levels as a cue in its macrohabitat selection process. 
Events which occur with a constant probability over time inter- 
vals as short as one day follow a negative exponential distribution 
(Bailey 1964; Ross 1970). Such events may be stimuli such as disturb- 
ance due to climatic factors, or cues from vegetation structure 
(Janetos 1982). The distribution of residence times in the pine stand 
followed a negative exponential distribution. This is indirect sup- 
port that vegetation structure and climatic factors influenced the 
frequent relocation in the pine stand. In contrast, the probability of 
moving increased with the number of days at a web site in the 
deciduous forest. In a subsequent study, I have found that this 
nonrandom distribution of residence times in the forest is related to 
hunger, a stimulus that has a cumulative rather than a constant 
probability over time (Hodge 1988). 
Reichert & Gillespie (1986) have identified three components of 
habitat selection by spiders: 1) the incentive to move; 2) movement 
curtailed upon encountering a favorable new environment; and 3) 
active search for a specific microhabitat. In M. gracilis, the incentive 
to move persists in the pine stand, as indicated by the short resi- 
dence times. In the deciduous forest, spiders relocate much less 
