Resisting annihilation: relationships between functional trait dissimilarity, assemblage competitive power and allelopathy

Abstract Allelopathic species can alter biodiversity. Using simulated assemblages that are characterised by neutrality, lumpy coexistence and intransitivity, we explore relationships between within-assemblage competitive dissimilarities and resistance to allelopathic species. An emergent behaviour from our models is that assemblages are more resistant to allelopathy when members strongly compete exploitatively (high competitive power). We found that neutral assemblages were the most vulnerable to allelopathic species, followed by lumpy and then by intransitive assemblages. We find support for our modeling in real-world time-series data from eight lakes of varied morphometry and trophic state. Our analysis of this data shows that a lake's history of allelopathic phytoplankton species biovolume density and dominance is related to the number of species clusters occurring in the plankton assemblages of those lakes, an emergent trend similar to that of our modeling. We suggest that an assemblage's competitive power determines its allelopathy resistance

Dynamics of asymmetric intraguild predation with time lags in reproduction and maturation

A three dimensional (3D) stage-structured predator–prey model is proposed and analyzed to study the effect of intraguild predation with harvesting of the adult species. Time lags in reproduction and maturation of the organism are introduced in the system and conditions for local asymptotic stability of steady states of delay differential forms of the ODE model are derived. The length of the delay preserving the stability is also estimated. Moreover, it is shown that the system undergoes a Hopf bifurcation when the time lags cross certain critical values. The stability and direction of the Hopf bifurcations are determined by applying the normal form method and the center manifold theory. Computer simulations have been carried out to illustrate various analytical results

Dynamics of a Filippov predator-prey system with stage-specific intermittent harvesting

The invasion of Indo-Pacific lionfish (Pterois volitans) together with unsustainable harvesting of herbivorous fish has caused major ecological changes in the western Atlantic and Caribbean coral reefs. Developing an effective harvesting policy of herbivorous reef fish and the invasive lionfish is necessary to minimize the adverse ecological impacts. To evaluate the potential efficacy of controlling the growth of lionfish population, we have proposed a non-smooth two-stage-structured mathematical model with two harvesting policies (non-selective and selective) of lionfish determined by a control function with a discontinuity at a critical herbivorous fish density. We study the sliding mode dynamics of the Filippov system, the boundary equilibrium bifurcation, and the pseudo-saddle-node bifurcation. We use threshold harvesting with hysteresis that helps in preventing the collapse of the herbivorous fish population through a bounded oscillation about pseudo-equilibrium. Our results show that a longer herbivorous fish harvesting period can be achieved in selective harvesting policy without compromising the herbivorous fish stock

Effects of Predator-Driven Prey Dispersal on Sustainable Harvesting Yield

Dispersal of organisms between patches is a common phenomenon in ecology and plays animportant role in predator–prey population dynamics. We propose a nonsmooth Filippovpredator–prey model in a two-patch environment characterized by a generalist predator-drivenintermittent refuge protection of an apprehensive prey along with a balanced dispersal of theprey between refuge and nonrefuge areas. By employing qualitative techniques of nonsmoothdynamical systems, we see that the switching surface is a repeller whenever the interior equilibriaare virtual, causing long-term population fluctuations.We find that the level of prey vigilanceand the rate of prey dispersal play pivotal roles in the total harvesting yield. We observe thata sustainable high harvesting yield is possible when the prey is less vigilant and obtain theharvesting efforts for maximum sustainable total yield (MSTY). We further modify the modelby considering a continuous threshold predator-driven prey dispersal and show that the modelexhibits a Hopf bifurcation when the level of prey vigilance exceeds some critical threshold value.By comparing the dynamics of the two models we see that for a sustainable high harvesting yieldof the system with continuous threshold dispersal, the prey needs to be highly vigilant comparedto that of the system with intermittent dispersal of the prey. Further, we find numerically thatthe estimated MSTY from both models remains the same

Potential effects of invasive Pterois volitans in coral reefs

The invasion of predatory lionfish (Pterois volitans) represents a major threat to the western Atlantic coral reef ecosystems. The proliferation of venomous, fast reproducing and aggressive P. volitans in coral reefs causes severe declines in the abundance and diversity of reef herbivores. There is also widespread cannibalism amongst P. volitans populations. A mathematical model is proposed to study the effects of predation on the biomass of herbivorous reef fishes by considering two life stages and intraguild predation of P. volitans population with harvesting of adult P. volitans. The system undergoes a supercritical Hopf bifurcation when the invasiveness of P. volitans crosses a certain critical value. It is observed that cannibalism of P. volitans induces stability in the system even with high invasiveness of adult P. volitans. The dynamic instability of the system due to higher invasiveness of P. volitans can be controlled by increasing the rate of harvesting of P. volitans. It is also proven that P. volitans goes extinct when the harvest rate is greater than some critical threshold value. These results indicate that the dynamical behaviour of the model is very sensitive to the harvesting of P. volitans, which in turn is useful in the conservation of reef herbivores

Herbivore harvesting and alternative steady states in coral reefs

summary:Coral reefs can undergo relatively rapid changes in the dominant biota, a phenomenon referred to as phase shift. Degradation of coral reefs is often associated with changes in community structure towards a macroalgae-dominated reef ecosystem due to the reduction in herbivory caused by overfishing. We investigate the coral-macroalgal phase shift due to the effects of harvesting of herbivorous reef fish by means of a continuous time model in the food chain. Conditions for local asymptotic stability of steady states are derived. We have shown that under certain conditions the system is uniformly persistent in presence of all the organisms. Moreover, it is shown that the system undergoes a Hopf bifurcation when the carrying capacity of macroalgae crosses certain critical value. Computer simulations have been carried out to illustrate different analytical results

A novel naproxen derivative capable of displaying anti-cancer and anti-migratory properties against human breast cancer cells

BACKGROUND: Increasingly, the role of chronic inflammation and its mediators in tumor generation and progression is gaining importance in the field of cancer research. In this context, candidature of non steroidal anti-inflammatory drugs (NSAIDs) as potential anti-tumor therapeutic agent is being evaluated globally. In the present study we have evaluated the anti-cancer effect of a series of newly synthesized naproxen derivatives on human breast cancer cell lines. METHODS: MCF-7 (poorly invasive) and MDA-MB-231 (highly invasive) cells were treated with different concentrations of naproxen sodium and its derivatives in vitro, and the underlying mechanism of action was monitored by employing studies related to induction of apoptosis, activation of caspases, cell-cycle progression, synthesis of PGE(2) and cellular migration. RESULTS: After a preliminary screening using MCF-7 and MDA-MB-231 cells, it was evident that naproxen derivative 4 has a better killing property compared to its parent compound naproxen sodium (NS). On further investigation, it was apparent that the observed growth inhibitory activity on MDA-MB-231 cells after treatment with 4, was not due to cell cycle arrest but due to an early induction of apoptosis and subsequent induction of caspases 3 and 9. Derivative 4 could also inhibit COX activity in MDA-MB-231 cells as evidenced by reduction in prostaglandin E2 secretion. Moreover, 4 was capable of delaying the overall migration rate of MDA-MB-231 cells in vitro. CONCLUSION: In this study we report that a naproxen-derivative (4) has powerful anti-inflammatory and anti-tumor properties as it induces appreciable amount of apoptosis in breast cancer cell line, and can also delay migration of cancer cells (MDA-MB-231) which would in turn delay cancer cell invasion and formation of secondary tumours in primary breast cancer patients. Thus, we propose that 4 is worthy of further investigation due to its potential as a therapeutic agent in anti-tumor treatment regimen