Guide Population Cycles: The Case for Trophic Interactions

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Interestingly, the bank vole has been shown to occupy an intermediate position between mice and other vole species [34] , supporting its generalist character shown in this study. Stable isotope analysis allowed us to obtain direct quantitative evidence for dietary convergence between the rodent species during mast events.

However, isotopic similarity between oak, hornbeam, lime and Norway spruce did not allow us to distinguish among these masting trees. While the Bayesian mixing models will always fit a solution to the input data, we note that such models become more informative when coupled with other dietary information that can constrain the range of possible solutions.

In our case, it would be particularly interesting to know how subtle isotopic changes in rodent tissues measured through masting cycles translate into actual dietary shifts. Stable isotopes have been used to investigate the long-term use of hoarded pulsed resources [20] , the trophic shift of pulse consumers [35] or the influence of marine [18] , [36] and terrestrial subsidies [15] on animal populations. However, they have been rarely used to provide empirical evidence of resource pulse use in studies dealing with numerical responses of primary and secondary pulse consumers [18].

The present study also reveals the potential of faeces and pellets of predators as a source of samples for isotope analysis, of special interest when covering long periods of time.

Alan A. Berryman

Although masting is widely recognised as the main factor triggering population outbreaks in mast consumers in temperate deciduous forests [1] , [2] , [5] — [8] , [23] , factors associated with the population crash are still debatable [9] , [37]. Our results show that the two species showed a different functional response to the seed pulse, providing insights into how resource fluctuations may influence competitive interactions.

Winter reproduction occurs in both species just following the mast, which indicates low intra- and interspecific competition in that period [5]. In the post-mast year, which coincides with the maximum densities of rodents and the beginning of the population crash [5] , the species clearly segregate. It can be hypothesized that during periods of food shortage the most dominant species, the yellow-necked mouse [24] , likely monopolise mast, the most valuable food, forcing the bank vole to exploit other food resources and diversify its dietary niche.

Mice may experience stronger variations in intraspecific competition, which may also be highest during shortage periods post-mast years. Bank voles may consume mast only in periods of high availability, when foraging costs, including those associated with the presence of competitors, are low.

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Although their numerical response is similar, fluctuations in vole numbers are much higher than in yellow-necked mice [5] , [6] , [23] suggesting also that the numerical response to the pulse of the generalist species was stronger. In summary, our results demonstrate that stable isotope analysis are a reliable approach to track nutrient flow in pulsed resources scenarios and encourage to investigate the role that competitive interactions, mediated by resource pulses, may play in rodent fluctuations in forest dominated by mast-producing trees.

Predicted mean contributions of vegetation groups to diets of yellow-necked mice and bank voles based on SIAR mixing model corresponding to the convex polygon shown in figure 1.

Trophic Interaction Cycles in Tundra Ecosystems and the Impact of Climate Change

For illustrative purposes, to demonstrate the largely non informative nature of the mixing model whereby consumer tissues data fall generally centrally within the mixing bivariate spec, we only present results of overall means using the siarsolomcmcv4 command in SIAR. Vegetation endpoints are: 1. Coniferous forest ground vegetation, 2. Deciduous forest ground vegetation, 3. Vaccinium sp.

How Ecosystems Work - Biology - Ecology

Pinus sylvestris seeds, 5. Corylus avellana seeds, 6. Two anonymous reviewers provided useful comments on an earlier draft of this manuscript. Browse Subject Areas? Click through the PLOS taxonomy to find articles in your field. Abstract How different functional responses of consumers exploiting pulsed resources affect community dynamics is an ongoing question in ecology.

Introduction 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] — [3].

Materials and Methods a Ethics Statement All necessary permits were obtained for the described field studies. Download: PPT. Figure 1. Convex mixing polygon excluding lichens used to model potential rodent dietary inputs. Figure 2. Isotope values of the rodent species along mast cycles.

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Table 1. Table 2. Discussion This study provides exceptional quantitative data on the different dietary response of two consumers to resource pulses. Supporting Information. Table S1. Table S2. Table S3. References 1.

Alan A. Berryman

Ostfeld RS, Keesing F Pulsed resources and community dynamics of consumers in terrestrial ecosystems. Trends Ecol Evol — View Article Google Scholar 2. Ecology — View Article Google Scholar 3. Ecol Monogr — A food chain or a food web defines who is eaten by whom in a given ecosystem. Body size is a key factor in the feeding behaviour of organisms. In aquatic food webs in particular, individual organisms often change in body size over several orders of magnitude during their life cycle.

Therefore, trophic links are mainly dictated by the individual body size rather than species identity [3]. The Norwegian Sea is a good example of an open Large Marine Ecosystem in which various species or groups of organisms respond to the physical environment and define the food webs for example via seasonal patterns of plankton production, the trophic couplings between plankton and fish populations. Ecological efficiency is the efficiency with which production at one trophic level is converted into production at the next level.

This corresponds mainly to assimilation and growth efficiencies. Supporting this, models that integrate ecological and evolutionary timescales show that the speed of adaptation at the two trophic levels, either relative to the ecological dynamics or to each other, strongly affects eco-evolutionary dynamics 18 , 19 , Thus, gaining a mechanistic understanding of how the interaction between ecology and evolution shapes community dynamics requires maintaining the full complexity of eco-evolutionary models.

At the same time, it is imperative that we move beyond descriptive analysis of their dynamics, and towards a more fundamental understanding of the underlying mechanisms generating them. We develop a new approach to gain such fundamental understanding, by extending a well-established mathematical decomposition for deconstructing eco-evolutionary dynamics into their component effects the Geber method 1. Through analyzing the temporal dynamics and interactions between these components, we disentangle how changes in prey biomass, predator biomass, and prey and predator traits impact and drive predator-prey dynamics.

We apply this approach to a specific question: when and how does coevolution result in antiphase cycles? For this we use a model with a single prey and predator type, each with an adaptive trait defense for prey, offense for predators; see Methods for details. The effective prey biomass is a measure of how much prey biomass is available to the predator, and is determined by prey biomass and trait dynamics. We use our component analysis to demonstrate how the dynamics of the effective prey biomass, and through this the predator-prey phase relationship, are determined by the interaction between between prey biomass and trait dynamics, resulting in a surprisingly simple predictive theory for phase relationships under predator-prey coevolution.

In antiphase cycles, rapid high-amplitude changes in defense are followed by slower changes in offense, with especially the decrease in offense lagging behind that of defense Fig. Eco-evolutionary dynamics and dynamics of components resulting from Geber method decomposition. Top row: prey solid green and predator solid blue dynamics.

Second row: defense dashed green and offense dashed blue dynamics. Third row: how the change in the prey growth rate W x is affected by changes in prey biomass E x x , solid green , predator biomass E y x , solid blue , defense E u x , dashed green and offense E v x , dashed blue.

Bottom row: how the change in the predator growth rate W y is affected by the changes in prey biomass E x y , predator biomass E y y , defense E u y and offense E v y. Time is measured in time steps after the first 30, time steps of the simulation.

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This pattern is highly consistent across all other parameters we varied Fig. Surprisingly, the speed of prey adaptation has little impact on the predator-prey phase relationship, although it may affect whether the predator persists the predator may go extinct if prey adapt much more rapidly, especially if the handling time is long; Fig.

Effect of the speed of adaptation in prey and predator. First column: phase lag between prey biomass and predator biomass; second column: phase lag between effective prey biomass and predator biomass; third column: phase lag between prey biomass and effective prey biomass. White: stable equilibrium; grey: extinction of predator. In the cost analysis, the relative costliness of defense and offense, rather than their absolute values, has the strongest impact on the nature of predator-prey dynamics including the phase relationship Fig.

If offense is much more costly than defense, the predator invariably goes extinct, because it cannot achieve a sufficiently high attack rate to sustain itself.