A cautionary tale: Pulsed allochthonous subsidy of cicadas into aquatic systems may have dramatic short-term effects, but no long term effects on populations.
Stevens, M. Henry*,1, Shukla, Amit2, Nowlin, Weston3, Vanni, Michael3, Gonzalez, Maria3, Fields, Matthew4, 1 Department of Botany, Oxford, OH, USA2 Department of Manufacturing and Mechanical Engineering, Oxford, OH, USA3 Department of Zoology, Oxford, OH, USA4 Department of Microbiology, Oxford, OH, USA
ABSTRACT- Pulsed spatial subsidies of resources may stabilize or destabilize recipient populations and ecosystems. The emergence and subsequent death of adult periodic cicadas, with 13 and 17 y life cycles, may represent of a substantial but infrequent subsidy to aquatic food webs, such as low order streams and small woodland ponds. Here we combine recent energetics-based food web models of detrital dynamics and omnivory to explore the potential transient and long term impacts of this cicada flux on a representative aquatic food web. We constructed a model with external recalcitrant and labile allochthonous inputs, and trophospecies representative of fungi, bacteria, periphyton, phytoplankton, zooplankton, vertebrate herbivores, invertebrate herbivores, and an omnivorous predator. Following convention of energetics/allometric based models, we selected species parameters based on average body size and energetic functional type. The magnitude and timing of external inputs were selected to represent annual autumn leaf fall (recalcitrant detritus), and periodic (17 y) cicadas (labile detritus). This parameter set caused all trophospecies to have strong responses to annual detrital inputs, and caused small-bodied trophospecies to exhibit strong within-year oscillations, while large-bodied trophospecies primarily tracked annual allochthonous inputs. Cicada input caused strong short-term responses, but these responses damped out quickly, within a year. Comparisons of the long-term population dynamics with and without cicadas showed virtually no difference in population medians, minima, and coefficients of variation. These results suggest that in spite of the dramatic and substantial flux of carbon from terrestrial to aquatic systems, cicada inputs neither threaten nor benefit aquatic populations. This lack of effect appears due to the low frequency of cicada inputs, relative the metabolic rates of the recipient populations, and to the strong influence of annual detrital inputs.
Key words: cicada, allochthonous subsidy, stability, detritus
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