Pulsed acorn production and consumer communities: Linearities, nonlinearities, and feedbacks.
Ostfeld, Richard*,1, Schmidt, Kenneth1, 2, Schauber, Eric1, 3, Canham, Charles1, Keesing, Felicia1, 4, Jones, Clive1, 1 Institute of Ecosystem Studies, Millbrook, NY, USA2 Texas Tech University, Lubbock, TX, USA3 Southern Illinois University, Carbondale, IL, USA4 Bard College, Annandale-on-Hudson, NY, USA
ABSTRACT- Pulsed resources in the form of acorn masting have revealed the nature and extent of key species interactions in oak forests. More than 10 yrs of observational and experimental studies of acorn production, populations of acorn consumers (mainly white-footed mice), and their prey, parasites, pathogens, and predators, reveal a diverse array of direct and indirect interactions. Effects of acorn and mouse abundance on numbers of blacklegged ticks infected with the Lyme disease pathogen have been positive, linear, and highly predictable. In contrast, acorn and mouse effects on abundance of ground-nesting songbirds has been strongly nonlinear. Despite a strong, linear correlation between summer mouse abundance and attack rates on nests, effects of mice on subsequent songbird abundance were complex. We observed a unimodal relationship between prior acorn/mouse abundance and songbird abundance, which appears to result from the numerical response by raptors to rodent prey followed by raptor switching to songbirds when rodents crash. Similarly, we observed strongly linear relationships between summer mouse abundance and total attack rates on gypsy moth pupae. However, experimental deployment of pupae revealed that mice employ a Type 3 functional response, such that attack rates decelerate at both very low and high moth densities. Moreover, gypsy moth populations are capable of escaping regulation by predators and reaching outbreak levels that can result in massive tree defoliation. Defoliation-caused morbidity and mortality strongly alter acorn production by oaks in both the short and long terms, leading to a strong potential for feedback in this system. Direct interactions between species pairs in our system often are linear; inclusion of third-party effects or time lags sometimes shift those relationships from linear to nonlinear. Because a gypsy moth defoliation event has not occurred during the monitoring period, we cannot yet incorporate the effects of this feedback on system dynamics. Explication of these complex interactions is facilitated by focusing on pulsed resources as a guiding principle.
Key words: indirect interactions, Lyme disease, Peromyscus leucopus, disease ecology
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