Effects of resource availability on the web structure of female western black widows: is the web structure constrained by physiological trade-offs?

Finding food often comes at the cost of an increased risk of predation. This could explain why animals often differ in their strategy to obtain food while avoiding predators. We found that spiders did not adjust their web to balance prey capture against predator protection. Instead, changes in web structure caused by variation in the abundance of food that spiders experience are more likely to explain differences among the webs of individual spiders. A major challenge of biological research is to understand what generates and maintains consistent behavioral variation among animals. Time and energy trade-offs, where expressing one behavior is achieved at the expense of another, are often suggested to favor the maintenance of behavioral differences between individuals. However, few studies have investigated how individuals adjust their allocation to different functions over time and depending on resource abundance. Black widow spiders of the genus Latrodectus build persistent webs that include structural threads which protect against predators and sticky trap threads to capture prey. Web structure consistently differs among individuals in the number of trap and structural threads. To quantify the intensity of a trade-off, we assessed the relationship between the number of structural and trap threads and tested whether varying food abundance affected individual differences in web structure. We further quantified how these individual differences change over time and with food abundance. We subjected spiders to three different levels of prey abundance and monitored the structure of their webs every twelve hours. We found no evidence for a trade-off between trap and structural threads. Instead, spiders that produced more structural threads also produced more trap threads, showing that spiders invested equally in both types of threads. Interestingly, the magnitude of individual differences in web structure was greatest when spiders were fed ad libitum and at the beginning of web construction. We suggest that variation in web structure between spiders could be the result of stable developmental differences in morphology or genetic differences.

Automated summary

This study found that spiders do not adjust their webs to balance prey capture and predator protection, but rather tend to change web structure based on variations in food abundance. Individual differences in behavior may be due to stable developmental or genetic differences.