Bifurcation Analysis of a Delay-Induced Predator–Prey Model with Allee Effect and Prey Group Defense

In this paper, we establish a predator–prey model with focus on the Allee effect and prey group defense. The positivity and boundedness of the model, existence of equilibrium point, and stability change caused by Allee effect are studied. Bifurcation (transcritical bifurcation, Hopf bifurcation) analysis is discussed, and the direction of Hopf bifurcation is determined by calculating the first Lyapunov number. Then we introduce delay into the original model and consider the influence of delay on the stability of the model. By selecting delay as the bifurcation parameter, we obtain the existence conditions of Hopf bifurcation and the direction of Hopf bifurcation. Finally, we verify the theoretical analysis by numerical simulation. Considering both the Allee effect and the prey group defense, the dynamic behavior near the origin becomes more complex than only considering Allee effect or prey group defense in the model. Allee effect can bring the risk of extinction and the change of stability, and the delay effect can make the stable coexistence equilibrium unstable and lead to periodic oscillation.

Diet and feeding strategy of the forkbeard Phycis phycis (Pisces: Phycidae) from the Portuguese continental coast

The diet and feeding behaviour of the forkbeard Phycis phycis was studied based on 246 stomachs collected between May 2011 and April 2012 from a commercial fleet operating off the central west coast of Portugal. A total of 44 prey items were identified in the stomachs which were merged into major groups to avoid problems with low expected frequencies. The following taxonomic categories were considered: non-decapod Crustacea, Caridea, Anomura, Munida spp., Processa spp., Brachyura, Pisces, Trisopterus luscus. In order to investigate possible diet differences between fish size classes, a cluster analysis was performed using the mean abundance of each prey group by forkbeard 5 cm length class, and three length groups (LG) were obtained: <22.5, 27.5–37.5 and >42.5 cm. Seasonally, Caridea was the main prey group during winter and autumn while Pisces was predominant during the rest of the year. Caridea was the most important prey group for LG1 and LG2 while in LG3 Pisces was the principal one. The forkbeard feeding behaviour may be characterized as presenting a shift pattern from a more generalist diet (small Crustacea, mainly Caridea) in the young adults to a more specialist strategy (teleosts) in the adults.

Experimental analysis of predator and prey detection abilities in rainforest: who has the advantage?

Recent theoretical analyses have shown that anti-predator benefits in social groups depend on the attack distance of the predator relative to prey spacing within groups. Both attack distance and prey spacing depend on the ability of predator and prey to detect each other. Previous work on forest predators suggest that many depend on surprise to ambush their prey, thus we test the hypothesis that detection distances by eagles of monkeys are greater than vice versa, despite the supposed advantages of sociality in facilitating detection of predators by prey. We used field experiments in the wild to assess detection distances of both raptor predators and their natural monkey prey. Live hawk-eagles (Spizaetus), under rehabilitation from injury, were placed tethered to perches in the home ranges of two habituated wild study groups of tufted capuchin monkeys (Cebus (apella) nigritus) in Iguazú National Park, Argentina. Analysis of video footage of the eagles during the approach of capuchin monkey groups allowed us to define the first moment of behaviours indicating detection by the eagle; detection behaviours of the monkeys near the eagle were recorded observationally by field assistants. The hawk-eagles always detected the monkeys (average distance 31.9 m) before the monkeys detected the predators (average distance 9.4 m). Predators always initially detected one or two spatially-peripheral individuals of the prey group. Distance of detection by the predators (and thus maximum possible attack distances) was significantly less than the prey group spread of 42–57 m. The short detection (and consequent short attack) distances by eagles of monkey prey in this habitat suggests that early warning of attacking eagles may not be a primary benefit of grouping in this case.