Effects of a pulsed allochthonous subsidy from a 17-year periodical cicada emergence on woodland pond communities.
Nowlin, Weston*,1, Stevens, M. Henry1, Vanni, Michael1, Gonzalez, Maria1, Valente, Jonathon1, Fields, Matthew1, 1 Miami University, Oxford, Ohio, USA
ABSTRACT- Periodical cicadas emerge in eastern North American forests at high densities (60 to 300 individuals per m2) at regular, relatively long time intervals (every 13 or 17 years). The emergence and ensuing death of periodical cicadas represents a pulsed subsidy to forest ecosystems that has been shown to affect short-term nutrient dynamics and productivity. However, small semi-permanent ponds and low order streams in woodland areas may also receive large numbers of this labile detrital resource, and the deposition of cicadas into aquatic systems could represent an important pulsed allochthonous subsidy. In order to assess the impacts of this pulsed subsidy, we conducted an experiment in which the addition of cicadas was manipulated at four levels (0, 75, 150 and 300 cicadas/m2) in mesocosm tanks (2 m2 surface area, 900 L) containing communities representative of woodland semi-permanent ponds. The densities of cicadas added to mesocosms represented a range of densities found in local forests. Addition of cicadas functioned much like a nutrient pulse perturbation, causing significant temporary increases in soluble reactive phosphorus and ammonium. The addition of cicadas cascaded up the food web causing significant temporary increases in periphyton, phytoplankton, crustacean zooplankton and rotifer biomasses. Rates of phytoplankton primary production and bacterial production were also enhanced by cicada addition. In general, the magnitude of the increase of response variables increased with the density of added cicadas. In addition, we determined the effect of this allochthonous subsidy on the stability of phytoplankton and zooplankton populations by comparing the temporal variability (measured as the temporal coefficient of variation) of these aggregate groups in the four experimental treatments. Phytoplankton and crustacean biomass stabilities were lowest at intermediate levels of cicada addition. Our results indicate that cicadas can have significant, wide-spread effects on aquatic food webs, but the persistence of these effects (effects lasting longer than one growing season) requires further study.
Key words: peridical cicadas, allochthonous subsidy, temporary ponds
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