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We present a discrete-generation model to study the effect of a seasonally asynchronous alien host on the population dynamics of a native host/parasitoid system. We assume that i) the native host and parasitoid are seasonally synchronous; ii) there is no direct competition for resources between the two host species (one native, one alien); and iii) the introduced alien host population (the alternative host) is in an invasive stage and, consequently, it is not subject to any density-dependent regulation. In our model, variations in the annual number of generations (voltinism) of the alien host greatly alter the dynamics of the native host/parasitoid interaction. When the alien host is synchronous with the native host, the parasitoid is favoured, and the native host population decreases until reaching a new, lower equilibrium or becoming extinct. By contrast, when alien and native hosts are asynchronous with each other, there are population oscillations of the native community members compatible with the pulsating availability of the alien host and, under specific conditions, the parasitoid may rapidly become extinct.

Depensation in a population growth rate, well-known as Allee effect , has dramatic implications for the dynamics and conservation of small or sparse populations, as it can drive low-density populations to extinction when their demographic size is below a critical threshold. Although rarely detected, depensation effects are believed to be common in nature. Here we present experimental evidence for Allee effect in one Mediterranean endemic plant: Anchusa sardoa . Depensation in the population growth rate is demonstrated through a density-based approach by showing the fingerprinting relationship which ties the population density to its per capita growth rate ( pgr ) during specific stages of the plant life-cycle. The pgr –density plots derived from observational data qualitatively compare with a general 2nd order polynomial function which features one of the peculiar trends underlying an Allee mechanism. We found strong evidence for depensation in the seedling and sapling classes, whereas no-depensation effect could be clearly observed in the adult classes. We also point out a characteristic demographic structure of A. sardoa (i.e. number of juveniles > number of adults) which reflects a not common life strategy with respect to Mediterranean endemic plants. By combining dynamical and demographic information, the results of this study suggest a possible scenario by which A. sardoa population could go extinct, and are discussed in the context of the increasing mass tourism in Mediterranean coastal environments.

In ecological and population dynamics, the coupling between random perturbations and the Allee effect could drive small and confined populations of rare species to extinction. In this paper, we propose a general model for describing spatio-temporal dynamics characterized by demographic Allee growth. In this approach, we include the combined contribution of stochasticity and spatial processes, typically dispersal, which is scarcely explored in the literature. The model is formulated in a reaction-diffusion framework, where the dynamics is regulated by a typical Allee–dispersal evolution and the resilience to white noise is probed at different perturbation amplitudes. Preliminary results show that dispersal processes can compensate random fluctuations to favor the stabilization of the species establishment.

Fractal worlds with limited connectivity are the topological result of growing graphs from chaotic series. We show how this model presents original characteristics which cannot be detected by means of the standard network descriptors. In detail, intrinsic inaccessibility to the fully connected configuration is demonstrated to be a universal feature associated with this family of graphs and strictly related to the fractality of a specific “chaotic source”. Here we discuss the potential of our model to be a generator of fractal graphs and also a self-consistent tool for differentiating chaotic dynamics from stochastic processes.

The Belousov–Zhabotinsky (BZ) reaction is the best known example of far from equilibrium self-organizing chemical reaction. Among the many dynamical behaviors that this reaction can exhibit, spatio-temporal chaos attracted particular interest, both for the ferroin and cerium catalyzed systems. In recent years transient chaos was found in the cerium catalyzed BZ reaction, when conducted in batch and unstirred reactors. It was established that the chaotic oscillations, originated by the coupling among chemical kinetics and transport phenomena, appeared and disappeared following a Ruelle–Takens–Newhouse scenario. In this Letter, we show results about the ferroin catalyzed system conducted in batch and unstirred reactors. An aperiodic transient regime was detected and we show that this is a genuine manifestation of spatio-temporal chaos.