Dampening prey cycle overrides the impact of climate change on predator population dynamics : a long-term demographic study on tawny owls

Funded by ERA-Net BiodivERsA NERC. Grant Numbers: NE/E010660/1, NE/F021402/1, NE/G002045/1Peer reviewedPublisher PD

Characteristics of Collapsing Ecosystems and Main Factors of Collapses

The synergistic effects of direct human perturbations and climate change have been causing the mass extinction of species. Here, I present the deterministic factors of collapses in present ecosystems. I captured and synthesized the key deterministic traits and processes before a collapse in the peer-reviewed literature. The results of the literature review show that deterministic factors can be used as early warning signals of collapses. The literature also suggests that we have entered the middle stage of global mass extinction, which may be irreversible

Indirect effects of primary prey population dynamics on alternative prey

We develop a theory of generalist predation showing how alternative prey species are affected by changes in both mean abundance and variability (coefficient of variation) of their predator's primary prey. The theory is motivated by the indirect effects of cyclic rodent populations on ground-breeding birds, and developed through progressive analytic simplifications of an empirically-based model. It applies nonetheless to many other systems where primary prey have fast life-histories and can become locally superabundant, which facilitates impact on alternative prey species. In contrast to classic apparent competition theory based on symmetric interactions, our results suggest that predator effects on alternative prey should generally decrease with mean primary prey abundance, and increase with primary prey variability (low to high CV) - unless predators have strong aggregative responses, in which case these results can be reversed. Approximations of models including predator dynamics (general numerical response with possible delays) confirm these results but further suggest that negative temporal correlation between predator and primary prey is harmful to alternative prey. We find in general that predator numerical responses are crucial to predict the response of ecosystems to changes in key prey species exhibiting outbreaks, and extend the apparent competition/mutualism theory to asymmetric interactions

Possible impact of winter conditions and summer temperature on bank vole (Myodes glareolus) population fluctuations in Central Norway

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To eat or to be eaten : Modelling part of the vertebrate food web of the boreal forest ecosystem in Fennoscandia

Trophic relationships, amongst others, define the structure of an ecosystem. They are mostly simplified and described as plant-herbivore and predator-prey interactions. Modelling trophic interactions are one way to improve our understanding of the functioning, impact and management of ecosystems. In this study, I explore how the cyclic vole and lemming populations affect the dynamics of the boreal forest in Fennoscandia. Specifically, I ask what mechanism controls the food web in years with peak and low densities of small rodents, the impact of small rodents on primary producers and how predator densities influence small rodents. To strengthen the conclusions, I test how robust the models are to ± 20% changes in parameter values. To answer these questions, I applied Ecopath, a mass-balance modelling approach, to explain trophic relationships in a system. The main output of the model is Ecotrophic Efficiency (EE), a measure to capture the consumed production of each trophic level. I modelled the vertebrate food web primarily connected to the cyclic voles and lemmings in the boreal forests, and built models according to their cycle phases. This is the first time this boreal forest community is modelled using Ecopath. The models showed a top down control on the bottom layer (mosses, lichens and fungi) in peak rodent years. The densities of small rodents would need to increase 16 fold from observed densities to negatively affect the field layer (shrubs, herbs, grasses and grass-like species). Predator density would need to increase 4 times to be able to control their prey. In addition the model were robust to parameter changes up to 20%. The system shows a strong herbivore-plant interaction in peak rodent years, but in low rodent years no control mechanism was apparent, indicating surplus resources for all components of the food web. Small rodents, specifically lemmings, deplete the bottom layer (mosses) in peak density years. Predators seem to only have a minor influence on the cycle dynamic. With this model approach a first systematic picture of the boreal forest community is captured, which to some extent coincides with hypothesis on small rodents population dynamics

Climate variability and density-dependent population dynamics: Lessons from a simple High Arctic ecosystem

Ecologists are still puzzled by the diverse population dynamics of herbivorous small mammals that range from high-amplitude, multiannual cycles to stable dynamics. Theory predicts that this diversity results from combinations of climatic seasonality, weather stochasticity, and density-dependent food web interactions. The almost ubiquitous 3- to 5-y cycles in boreal and arctic climates may theoretically result from bottom-up (plant–herbivore) and top-down (predator–prey) interactions. Assessing, empirically, the roles of such interactions and how they are influenced by environmental stochasticity has been hampered by food web complexity. Here, we take advantage of a uniquely simple High Arctic food web, which allowed us to analyze the dynamics of a graminivorous vole population not subjected to top-down regulation. This population exhibited high-amplitude, noncyclic fluctuations—partly driven by weather stochasticity. However, the predominant driver of the dynamics was overcompensatory density dependence in winter that caused the population to frequently crash. Model simulations showed that the seasonal pattern of density dependence would yield regular 2-y cycles in the absence of stochasticity. While such short cycles have not yet been observed in mammals, they are theoretically plausible if graminivorous vole populations are deterministically bottom-up regulated. When incorporating weather stochasticity in the model simulations, cyclicity became disrupted and the amplitude was increased—akin to the observed dynamics. Our findings contrast with the 3- to 5-y population cycles that are typical of graminivorous small mammals in more complex food webs, suggesting that top-down regulation is normally an important component of such dynamics

Seasonality shapes the amplitude of vole population dynamics rather than generalist predators

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Analysis of The Dynamics of The Number of Mammalian Populations in The Conditions of The Southern Aral Sea

The article presents the results of research analysis of the dynamics of the number of mammalian populations in the conditions of the Southern Aral Sea Small mammals serve as bio indicators in the study of environmental conditions. Bio topic distribution, nutrition, age and sex structures were studied on the example of Microtus Ileus populations. The long-term joint dynamics of the populations of the most typical predator-prey system for this region in the conditions of the Southern Aral Sea region is investigated. It is shown that the specifics of the dynamics of natural processes in the conditions of the crisis of the Aral Sea region require the development of special simulation models taking into account the control parameters and order parameters of the destabilized ecosystem

Moving forward in circles: challenges and opportunities in modelling population cycles

Population cycling is a widespread phenomenon, observed across a multitude of taxa in both laboratory and natural conditions. Historically, the theory associated with population cycles was tightly linked to pairwise consumer–resource interactions and studied via deterministic models, but current empirical and theoretical research reveals a much richer basis for ecological cycles. Stochasticity and seasonality can modulate or create cyclic behaviour in non-intuitive ways, the high-dimensionality in ecological systems can profoundly influence cycling, and so can demographic structure and eco-evolutionary dynamics. An inclusive theory for population cycles, ranging from ecosystem-level to demographic modelling, grounded in observational or experimental data, is therefore necessary to better understand observed cyclical patterns. In turn, by gaining better insight into the drivers of population cycles, we can begin to understand the causes of cycle gain and loss, how biodiversity interacts with population cycling, and how to effectively manage wildly fluctuating populations, all of which are growing domains of ecological research

Declining reproductive output in capercaillie and black grouse – 16 countries and 80 years

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