280 
Psyche 
[Vol. 91 
PATUXENT 
LIBERTY 
STAGE ON 21 JULY 
DEVELOPMENTAL STATUS IN MID-SEPTEMBER: 
PATUXENT 
LIBERTY 
NO. MATURED 
31 
34 
NO. IMMATURE ( alive ) 
10 
31 
TOTAL ( % of no. 
41(100%) 65(79 % 
collected ) 
Figure 6. Development of immature spiders collected from the Patuxent and 
Liberty populations on 21 July 1982 and reared on the porch at Patuxent. The bar 
graph indicates the estimated stages of the spiders when collected. Below the graph is 
summarized the number of spiders that either had matured by mid-September or 
were immature and still alive at that time. 
direct proof of the previously proposed interpretation of the 
observed phenology. 
Causes of Variable Development in the Filmy Dome Spider 
The life history variation existing within Maryland populations of 
the filmy dome spider does not result from a genetic polymorphism 
(Wise, submitted). Instead, most of the variation appears to be 
environmentally induced, resulting from the response of a plastic 
phenotype to variation in proximate limiting factors. 
Laboratory studies of other spiders have demonstrated extensive 
phenotypic plasticity in developmental rate, size at maturity and 
fecundity in response to variation in food supply and physical con- 
