Just as humans generally have to live within a monetary budget, it is reasonable to assume that other organisms must live within an energy budget. Particularly when resources are limiting, it must be important to utilize resources as efficiently as possible. Those organisms that do so will presumably be at a competitive and evolutionary advantage compared to others who may be less efficient. These ideas seem sensible, but have been difficult to test. It is often not possible to classify behavioral activities. For example, an animal may be simultaneously involved in several activities including thermoregulating, guarding territory boundaries, and seeking a mate as well as food. In addition, it has been difficult to identify the appropriate resources to measure. It is also not clear how investing energy in searching for food affects growth rate, and size and age at maturity. Variation in development rates and pathways can have tremendous impact on the evolution of a species, but few studies have addressed the nutritional causes that contribute to this variation. Orb-weaving spiders provide an excellent model system for the study of resource partitioning and the developmental consequences of shifts in partitioning. Spiders synthesize their web from physiologically important compounds such as proteins. The activity of spinning the orb web and the nutritional investment into the orb can serve no other purpose than prey capture, the resources allocated to the orb web are unavailable for growth or reproduction during that foraging bout, and all prey capture occurs on the orb web; thus, the web must be maintained through periods of reduced prey capture. We will examine the nutritional ecology of foraging in the large, widely distributed, orb-weaving spider Nephila clavipes. Our experiments will involve NMR and gas chromatographic analysis of orb chemistry using spiders from 3 separate populations. The biology of this orb-weaving spider will allow us to clearly distinguish foraging from other activities and to track how different types or resources partitioned between foraging and other activities. We will also be able to identify resources that, when limiting, necessitate trade-offs between foraging and other activities. In addition, we can quantify how the investment of resources into foraging affects growth and development under a variety of environmental conditions, and we can distinguish patterns that are due to genetic differences from those due to environmental differences. This study will address the long-held assumptions of most classical foraging models (that shifts in foraging investment reflect shifts in resource partitioning and that increased foraging efficiency increases relative fitness) and it will finally allow quantification of resource partitioning between foraging and growth, permitting investigation of the precise relationships between variation in foraging investment and variation in developmental programs.
