Quantifying food limitation in redback spiders (Latrodectus hasselti) in the field

Food availability is a key factor affecting the growth, reproduction and survival of animals.  Many studies support the idea that spiders are food-limited in nature.  However, it has been much more difficult to quantify the degree to which food or nutrients may limit the growth of spiders in nature relative to their needs.  We compared the nutrient ingestion of redback spiders (Latrodectus hasselti) in the field with a quantitative study of how nutrient ingestion affected growth of spiders in the laboratory to quantify the degree of food limitation of spider growth in the field.  Ingestion rates of lipid and protein had large effects on development time, size and nutrient reserves of redback spiders.  As expected, spiders were food-limited in the field and our results allowed us to provide quantitative estimates of the predicted growth rates of spiders at our study sites.  In addition, we were able to examine the relative importance of a range of prey for spider growth.  Interestingly, small urban-adapted lizards were a significant contributor to the diet of redback spiders and their availability may aid in increasing population densities of spiders in urban areas.  Our results provide an example of how detailed studies of nutritional ecology can provide estimates of food availability for predatory arthropods in nature, which can be a key factor influencing population dynamics and success in different habitats.