Refining the metaphor: the web's non-trophic threads

Popular notions of the web of life emphasize feeding relationships between species. A famous example is Charles Darwin's speculation that the abundance of certain flowers might be related directly to the density of cats in the neighborhood. Cats eat mice, which prey upon the nests of humble bees, which alone bear responsibility for transferring pollen between flowers of certain plants. Darwin (1859) asserts ‘… it is quite credible that the presence of a feline animal in large numbers in a district might determine, through the intervention first of mice and then of bees, the frequency of certain flowers in that district!’ The web may be even more intricate than Darwin imagined: cats eat birds, which eat spiders, which eat the bees that visit flowers in search of nourishment. Darwin must have inadvertently overlooked the spider; it certainly belongs in his ‘web of complex relations’ between ‘plants and animals remote in the scale of nature’.

Contemporary community ecology continues to emphasize the contribution of biotic interactions to the structure of ecological communities, an emphasis that led naturally to the metaphor of spiders in ecological webs. In my mind, strands appeared most clearly as connections between spiders and their prey, and between spiders and their natural enemies. Because spiders are generalist carnivores they may simultaneously interact with each other as competitor, predator and prey. This maze of connecting threads resists easy untangling – a topic to be explored in the next chapter.