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In this article, we investigate a diffusive two-strain epidemic model with non-monotone incidence rate and virus mutation. The positivity, existence and uniform boundedness of the solutions of the model system are studied. It is found that the system has three equilibrium points, namely the infection-free equilibrium point, the strain-2 endemic equilibrium point and both the strain-1 and strain-2 endemic equilibrium points. The global asymptotic stability analysis of the diffusive model system near all the equilibrium points is carried out by constructing appropriate Lyapunov functional. It is found that the system has no strain-1 endemic equilibrium point possibly due to the virus mutation. So, in this type of diseases, the infection due to strain-1 cannot be persistent in the community.

In the present paper, we propose and study a fractional-order prey-predator type ecological model with the functional response of Holling type II and the effect of harvesting. In addition, we have also considered the influence of a super-predator on the conventional predator. The complex dynamical behaviour of the proposed model system including existence and uniqueness criteria, finiteness and nonnegativity of the solutions have studied rigorously. In addition, we have determined existence criteria of several equilibria and analyzed the asymptotic nature of those equilibria. We have enriched our analysis with the inclusion of fractional Hopf bifurcation and the criteria of global stability of the equilibrium points. Finally, some numerical simulation works have been incorporated to validate the analytical analysis.

In this research work, a delay-induced eco-epidemic model using a reconstructed Leslie–Gower-type growth rate is formulated and analyzed. An extended qualitative nature of the solutions of the model system like boundedness, strong uniform persistence, and permanence is examined to secure the longstanding viability of the system. The stability of the system is investigated at different stationary points, and sufficient conditions are obtained for the local as well as global stability. The dynamics of the delay-induced model system, including the Hopf bifurcation phenomenon, is rigorously studied around the coexisting equilibrium using the normal form method and center manifold theorem. Also, the length of the delay to preserve the stability of the coexisting equilibrium is evaluated. It is observed that the effect of infection on the total harvest is negligible, but the effort to harvest can reduce the infection and preserve the system’s stability. The results may help to determine the point of reference for disease persistence and extinction. Based on our analytical results, several numerical simulations are also performed.

Presently, monkeypox virus infection has spread worldwide in the ongoing outbreak that began in the UK. To study the transmission dynamics of monkeypox, we formulate here a seven-compartmental (five compartments for the human population and two compartments for animals or rodents) fractional-order mathematical model. The existence and uniqueness of the solution of the proposed fractional order model are examined here. The basic reproduction number for humans ( R 0 h ) and animals ( R 0 a ) are obtained through the next-generation matrix approach. Depending on the values of R 0 h and R 0 a , we observed that the fractional order model has three equilibria, namely, monkeypox-free equilibrium, animal-free endemic equilibrium, and endemic equilibrium. Also, the stability of all equilibria is checked in this present article. We found that the model goes through transcritical bifurcation at R 0 a = 1 for any values of R 0 h and at R 0 h = 1 for R 0 a < 1 . Best of our knowledge, this is the first work where the fractional order optimal control for monkeypox is formulated and solved considering vaccination and treatment controls. Several feasible parameter values are used in the simulations to visualize and verify the findings, from which the results show that fractional order is more appropriate. Finally, parameters involved in the expression of R 0 h and R 0 a are scaled using the sensitivity index approach.

Using a generalist predator–prey system, we describe a theoretical aspect of economic and sustainability issues in the context of a complex ecosystem of Sundarbans coastal area, with a larger part located in Bangladesh and a smaller part in India. Predator species are considered only for the purpose of ecotourism and prey species are subject to fishing only. First we have studied the relevance of tourist entrance fee on total income gained from ecotourism and fishing. It is found that the total rent increases with the increase of entrance fee up to a certain threshold and then it decreases. Next the impact of fishing effort is studied on maximizing the total rent, and similar qualitative behavior is found as in the case of tourist entrance fee. Following this, the total rent is optimized in respect to both tourist entrance fee and fishing effort with three different level of tourists sensitivity on predator population. Result show that maximum total rent is always higher if more importance is given to ecotourism than fishing. Finally, MSY policy and its consequences on ecotourism and fishing are also studied. It is observed that MSY approach is a sustainable management policy to protect both the species even if the ecotourism is implemented along with fishing. This model can be used to determine the optimal choice of tourist entrance fee and fishing effort when the real data are available for the Sundarbans.

In this article, we compare the two ecological services known as yield and resilience, for a tri-trophic food chain model consisting of a prey, an intermediate predator and a top predator. For this comparison process, we use both analytical and numerical techniques. It is shown that a variety of patterns are possible based on the intensity of efforts distributed among different trophic levels. Thus we may suggest that fishing down the food chain, as suggested by Pauly et al. (1998) is not bound to happen. Our analysis also shows that balancing the harvest between prey, intermediate predator and top predator could give more yield and stabilizing the ecosystem, than the selective harvesting of any one species. This balanced harvesting may not be a win–win situation for yield and resilience, but it could be a most favourable strategy to balance them. This research would help to correlate resilience with yield and determines the desirable selection of two policies, resilience maximizing yield or maximum sustainable yield to safeguard ecological communities.