Metabarcoding prey Araneus diadematus: TREE platform

Trophic interactions may strongly depend on body size and environmental
variation, but this prediction has been seldom tested in nature. Many
spiders are generalist predators that use webs to intercept flying prey.
The size and mesh of orb webs increases with spider size, allowing a more
efficient predation on larger prey. We studied to this extent the
orb-weaving spider Araneus diadematus inhabiting forest fragments
differing in edge distance, tree diversity and tree species. These
environmental variables are known to correlate to insect composition,
richness and abundance. We anticipated these forest characteristics to be
a principle driver of prey consumption. We additionally hypothesised them
to impact spider size at maturity and expect shifts towards larger
prey-size distributions in larger individuals independently from the
environmental context.  We quantified spider diet by means of
metabarcoding of nearly 1000 A. diadematus from a total of 53 forest
plots. This approach allowed a massive screening of consumption dynamics
in nature, though at the cost of identifying the exact prey identity, as
well as their abundance and putative intraspecific variation. Our study
confirmed A. diadematus as a generalist predator, with more than 300 prey
ZOTUs detected in total. At the individual level, we found large spiders
to consume fewer different species, but adding larger species to their
diet. Tree species composition affected both prey species richness and
size in the spider’s diet, although tree diversity per se had no influence
on the consumed prey. Edges had an indirect effect on the spider diet as
spiders closer to the forest edge were larger and therefore consumed
larger prey. We conclude that both intraspecific size variation and tree
species composition shape the consumed prey of this generalist predator.