Non‐native species introductions affect freshwater communities by changing community compositions, functional roles, trait occurrences and ecological niche spaces. Reconstructing such changes over long periods is difficult due to limited data availability. We collected information spanning 215 years on fish and selected macroinvertebrate groups (Mollusca and Crustacea) in the inner‐Florentine stretch of the Arno River (Italy) and associated water grid, to investigate temporal changes. We identified an almost complete turnover from native to non‐native fish (1800: 92% native; 2015: 94% non‐native species) and macroinvertebrate species (1800: 100% native; 2015: 70% non‐native species). Non‐native fish species were observed ~50 years earlier compared to macroinvertebrate species, indicating phased invasion processes. In contrast, α‐diversity of both communities increased significantly following a linear pattern. Separate analyses of changes in α‐diversities for native and non‐native species of both fish and macroinvertebrates were nonlinear. Functional richness and divergence of fish and macroinvertebrate communities decreased non‐significantly, as the loss of native species was compensated by non‐native species. Introductions of non‐native fish and macroinvertebrate species occurred outside the niche space of native species. Native and non‐native fish species exhibited greater overlap in niche space over time (62%–68%) and non‐native species eventually replaced native species. Native and non‐native macroinvertebrate niches overlapped to a lesser extent (15%–30%), with non‐natives occupying mostly unoccupied niche space. These temporal changes in niche spaces of both biotic groups are a direct response to the observed changes in α‐diversity and species turnover. These changes are potentially driven by deteriorations in hydromorphology as indicated by alterations in trait modalities. Additionally, we identified that angling played a considerable role for fish introductions. Our results support previous findings that the community turnover from native to non‐native species can be facilitated by, for example, deteriorating environmental conditions and that variations in communities are multifaceted requiring more indicators than single metrics.

SUMMARYThe paper studies nonlinear dynamics and bifurcations of a class of memristor oscillatory circuits obtained by replacing the nonlinear resistor of a Chua's oscillator with a flux-controlled memristor. A recently developed technique, named flux-charge analysis method, has shown that the state space of such circuits can be decomposed in invariant manifolds, where each manifold is characterized by a different dynamics and different attractors. Goal of the paper is to investigate the use of the harmonic balance method in combination with flux-charge analysis method in order to study the different kinds of bifurcations generated by changing the circuit parameters on a fixed manifold, changing manifold for a fixed parameter set (bifurcations without parameters), or changing simultaneously circuit parameters and manifolds. The main result is that the harmonic balance method is quite simple to apply in this rich bifurcation context and is effective to detect Hopf and to accurately predict period-doubling bifurcations of all these different kinds.

Parasitic castrators, specifically rhizocephalan barnacles, considered as important regulators of host population density, were proposed as control agents for invasive decapod crustaceans. The temporal variability of the invasive parasitic barnacle Heterosaccus dollfusi prevalence was examined a decade after its introduction into the Mediterranean, with the purpose of elucidating whether it is indeed an efficient control agent of its invasive host, the swimming crab, Charybdis longicollis. Despite the high prevalence of the parasite and its injurious impact on the host reproduction, the Erythrean invasive host-parasite pair reached a modus vivendi with no noticeable reduction in the host population, and high rates of infestation and multiple infestation.

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The effects of the invasive rhizocephalan parasite Heterosaccus dollfusi on the agonistic behavior of the invasive swimming crab Charybdis longicollis were quantitatively analyzed under standardized conditions. The behavior of uninfected male crabs contained more aggressive elements than that of uninfected females. In encounters between infected males, markedly fewer and less aggressive elements were displayed than in encounters between uninfected males, whereas in encounters between infected females, more aggressive elements were displayed than in encounters between uninfected females. It is suggested that the presence of the parasite reduces belligerence in male crabs, possibly to avoid injury and to enhance the life expectancy of host and parasite.

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A stochastic reaction-diffusion model is studied on a networked support. In each patch of the network two species are assumed to interact following a non-normal reaction scheme. When the interaction unit is replicated on a directed linear lattice, noise gets amplified via a self-consistent process which we trace back to the degenerate spectrum of the embedding support. The same phenomenon holds when the system is bound to explore a quasi degenerate network. In this case, the eigenvalues of the Laplacian operator, which governs species diffusion, accumulate over a limited portion of the complex plane. The larger the network, the more pronounced the amplification. Beyond a critical network size, a system deemed deterministically stable, hence resilient, may turn unstable, yielding seemingly regular patterns in the concentration amount. Non-normality and quasi-degenerate networks may therefore amplify the inherent stochasticity, and so contribute to altering the perception of resilience, as quantified via conventional deterministic methods.Models of interacting populations are of paramount importance in a broad range of applications of interdisciplinary breath. Beyond the simplified arena of deterministic approaches, stochastic effects play a role of paramount importance and might yield a large of plethora of non trivial behaviors. Furthermore, to account for the inherent complexity of the existing interactions, the inspected model are embedded on a network architecture. In this paper, we show how a non-normal reaction model coupled to a directed, quasi-degenerate, network can drive a resonant amplification of the noisy component of the dynamics. This observation, that we here substantiate analytically, calls for a revised concept of resilience, the ability of a system to oppose external disturbances.

from various intertidal environments along the southern Somalian coast and, to a lesser extent, from Kenya and the Mascarene Islands. The material belongs to 39 species of which 13 are new for the Somalian coast, 5 for the East African coast and 2 for the western Indian Ocean: Charybdis hawaiensis Edmondson 1954 previously known only for Hawaii and Carupella banlaensis Tien 1969 only known for the Tonkin Gulf.