If you pulse it, they will come: Pulse rate of detritus inputs affects richness and abundance of aquatic invertebrates

Resource inputs into aquatic systems often occur in pulses, and these inputs can affect food web properties and community dynamics, although the mechanism for such effects remain elusive.  Natural aquatic microsystems such as tree holes or man-made containers contain complex food webs of invertebrates that depend on periodic inputs of allochthonous detritus from adjacent terrestrial environments.  We investigated the effect of detritus pulse rates on richness, abundance, and population dynamics of invertebrates colonizing water-filled tires in a forest habitat.  Containers received either 2 or 10 equal pulses of detritus (Large or Small pulses, respectively) spread over the same time period.  We used two levels of animal detritus (dead crickets) and three levels of leaf detritus crossed with each pulse rate.  Invertebrates were sampled when the total amount of detritus input was equal between pulse rates (July, September).  We quantified productivity using principal component analysis of detritus amount, type, and conductivity.  Pulse rate had no effect on total richness or abundance, but it did affect the responses of richness and abundance to productivity.  Richness and abundance increased significantly with increasing productivity in June in large-pulse tires, but not in the small-pulse tires; the opposite response occurred in September.  Most species of invertebrates responded to pulse rates or pulse rate and detritus amount, although some species only responded to variation in detritus amount.  The ability of particular key species to track detrital pulses may be vital for understanding the complex responses of communities to pulsed resource inputs.