Abstract
How different functional responses of consumers exploiting pulsed resources affect community dynamics is an ongoing question in ecology. Tree masting is a common resource pulse in terrestrial ecosystems that can drive rodent population cycles. Using stable isotope (δ13C, δ15N) analyses, we investigated the dietary response of two fluctuating rodent species, the yellow-necked mouse Apodemus flavicollis and the bank vole Myodes glareolus, to mast events in Białowieża Forest (NE Poland). Rodent hair samples were obtained non-invasively from faeces of their predators for an 11-year period that encompassed two mast events. Spectacular seed crops of deciduous trees, namely oak Quercus robur and hornbeam Carpinus betulus, occur after several intermediate years of moderate seed production, with a post-mast year characterised by a nil crop. While a Bayesian isotopic (SIAR) mixing model showed a variety of potential vegetation inputs to rodent diets, the isotopic niche of the yellow-necked mouse was strongly associated with mast of deciduous trees (>80% of diet), showing no variation among years of different seed crop. However, bank voles showed a strong functional response; in mast years the vole shifted its diet from herbs in deciduous forest (∼66% of diet) to mast (∼74%). Only in mast years did the isotopic niche of both rodent species overlap. Previous research showed that bank voles, subordinate and more generalist than mice, showed higher fluctuations in numbers in response to masting. This study provides unique data on the functional response of key pulse consumers in forest food webs, and contributes to our understanding of rodent population fluctuations and the mechanisms governing pulse–consumer interactions.
Highlights
Resource pulses, defined as brief and infrequent events of high resource availability, are widespread phenomena in nature that have tremendous impacts on consumer communities, including bottom-up effects with consequences for multiple trophic levels [1,2,3]
Assuming only a two-source, two isotope mixing model to derive potential use of deciduous forest herbs vs. mast, we found that while mice depended largely on mast throughout the period of investigation, voles shifted from herbs to mast in mast years (Table 2, Figure 2)
Hair d15N values for bank voles were significantly different among mast, post-mast and intermediate years (F2,66 = 8.18, p,0.001, Figure 2, Table S3)
Summary
Resource pulses, defined as brief and infrequent events of high resource availability, are widespread phenomena in nature that have tremendous impacts on consumer communities, including bottom-up effects with consequences for multiple trophic levels [1,2,3]. We used a stable isotope approach to investigate the dietary response of two sympatric and ecologically similar rodent species to mast cycles (consisting of mast, post-mast and intermediate years) in the Białowiez_a primeval forest (NE Poland). This approach allowed us to avoid some of the shortcomings of tracing nutrient flow through animal communities using conventional dietary analysis techniques [19]. Our main objective was to investigate trophic segregation between two rodents, the bank vole Myodes glareolus and the yellownecked mouse Apodemus flavicollis, by tracing the consequences of superabundant food pulses provided by mast events Both species follow population fluctuations triggered by masting; their numerical response has been well documented [5,6,23]. We expected a functional response of both species to mast cycles, with larger variation in the food niche of bank voles, the smaller and subordinate species [12,24]
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