Predation Mortality Research Articles

Do interspecific differences in morphology influence foraging efficiency of juvenile crappie?

Sympatric black crappie ( Pomoxis nigromaculatus Lesueur in Cuvier and Valenciennes, 1829) and white crappie ( Pomoxis annularis Rafinesque, 1818) often differ in ecological performance, such that white crappie outnumber black crappie in turbid waterbodies and black crappie predominate in clear waters with abundant cover. Recent work suggests that this performance difference is driven by juvenile white crappie having a limnetic body form and juvenile black crappie having a littoral body form, resulting in differential predation mortality between the species within open-water and vegetated environments. We tested whether these morphologies also lead to interspecific differences in foraging efficiency between the congeners in structure and open water. Juvenile black crappie spent more time pursuing fish prey than white crappie across all trials, suggesting that energetic gains of piscivory may differ between species. However, both species had similar capture efficiencies when attacking fathead minnows ( Pimephales promelas Rafinesque, 1820) within vegetated and open-water habitats. We conclude that variation in morphology between juvenile black crappie and white crappie does not have a large influence on foraging efficiency, at least on fish prey, in dense cover or open water, and suggest their performance in sympatry is likely not driven by predatory capabilities at the onset of piscivory within these different environmental contexts. Instead, the relationship between morphology and predator evasion may drive the distribution and relative abundance of crappie species within sympatric populations.

Local and global dynamics of a prey–predator system with fear, Allee effect, and variable attack rate

Fear prompts prey to adopt risk-averse behaviors, such as reduced foraging activity, increased vigilance, and avoidance of areas with high predator presence, which affects its reproduction. In a real scenario, a population requires a minimum density to avoid extinction, known as an Allee threshold. In light of these biological factors, we propose a predator–prey model with (i) a fear effect in a prey population, (ii) an Allee effect in a predator population, and (iii) a non-constant attack rate that modifies the functional response. We ensured the non-negativity and boundedness of the solutions and examined the local and global stability status for each existing steady state solutions. We investigated some deep dynamical properties of the system by varying different parameters, such as cost of fear in prey and strength of the Allee effect in predators and their mortality rate. In codimension one bifurcations, we observed saddle node, Hopf, homoclinic, and coalescence of two limit cycles. Additionally, codimension two bifurcations were observed, including Bautin and Bogdanov Takens bifurcations. To provide a clearer understanding of these bifurcations, we conducted biparametric analysis involving the fear and Allee parameters, as well as the fear parameter and predator mortality rate. Our investigation shows that cost of fear and strength of Allee strongly influences the survival status of the predator. Furthermore, bistability and tristability reveal that the survival and extinction of predator are dependent on the initial population level. Numerical simulations and graphical illustrations are provided to support and validate our theoretical findings.

Grey wolves (Canis lupus) shift selection of anthropogenic landscape features following predator control in the Nearctic boreal forest

Conserving endangered species sometimes involves killing their predators. In the case of Nearctic wolves (Canis lupus), rarely are lethal control measures examined for ancillary effects on predator behaviour or community responses in a before-after design. We examined wolf relative abundance and spatial distribution in a northwestern boreal forest landscape for three years before and after the onset of wolf culling intended to conserve threatened woodland caribou (Rangifer tarandus caribou). We hypothesized that wolf occurrence would increase with density of anthropogenic features created by landscape development before the cull, but that wolves would avoid anthropogenic features after the cull due to associated mortality risk. We used generalized linear models in an information-theoretic framework to weigh evidence for our hypotheses. Post-control, independent wolf detections decreased to 24 % of pre-cull numbers, but wolves maintained 75 % of their distribution. Pre-control, wolves were positively associated with linear features, presumably for hunting efficiency, but post-cull wolves were negatively associated with these features. Thus, wolf control caused not only a numerical reduction of wolf numbers, but also a functional change in wolf behaviour that could further reduce predation pressure on caribou. However, post cull wolf occurrence was more strongly associated with anthropogenic block features which provide forage for alternate prey, potentially subsidizing their fast recovery. Conservation actions involving predator mortality alter landscape-scale distributions and behaviors of surviving predators, with potential indirect effects for the mammal community.

Temperature and body size affect movement of juvenile Atlantic cod (Gadus morhua) and saithe (Pollachius virens) at nearshore nurseries.

Seasonal migrations of marine fish between shallow summer feeding habitats and deep overwintering grounds are driven by fluctuations in the biotic and abiotic environment as well as by changes in the internal state. Ontogenetic shifts in physiology and metabolism affect the response to environmental drivers and may lead to changes in migration timing and propensity. In this study, we investigated the effect of temperature and body size on migration timing and depth distribution in acoustically tagged Atlantic cod, Gadus morhua, and saithe, Pollachius virens, during the period of seasonal migration from shallow summer habitats. The results from our study revealed a wide range of horizontal and vertical distribution of age 1 and 2 G. morhua within the fjord. Larger G. morhua inhabited deeper, cooler waters than smaller juveniles, likely reflecting size-dependent thermal preferences and predation pressure. Conversely, juvenile P. virens occupied primarily shallow waters close to land. The variation in depth distribution of G. morhua was mainly explained by body size and not, against our predictions, by water temperature. Conversely, the dispersal from the in-fjord habitats occurred when water temperatures were high, suggesting that seasonal temperature fluctuations can trigger the migration timing of P. virens and larger G. morhua from summer habitats. Partial migration of small juvenile G. morhua from in-fjord foraging grounds, likely influenced by individual body condition, suggested seasonal migration as a flexible strategy that individuals may use to reduce predation and energetic expenditure. Predation mortality rates of tagged juveniles were higher than previously suggested and are the first robust predation mortality rates for juvenile G. morhua and P. virens estimated based on acoustic transmitters with acidity sensors. The results have relevance for climate-informed marine spatial planning as under the scenario of increasing ocean temperatures, increasing summer temperatures may reduce the juveniles' resource utilization in the shallow summer nurseries, resulting in lower growth rates, increased predation pressure, and lower chances of juvenile winter survival.

Killing the predator: impacts of highest-predator mortality on the global-ocean ecosystem structure

Abstract. Recent meta-analyses suggest that microzooplankton biomass density scales linearly with phytoplankton biomass density, suggesting a simple, general rule may underpin trophic structure in the global ocean. Here, we use a set of highly simplified food web models, solved within a global general circulation model, to examine the core drivers of linear predator–prey scaling. We examine a parallel food chain model which assumes microzooplankton grazers feed on distinct size classes of phytoplankton and contrast this with a diamond food web model allowing shared microzooplankton predation on a range of phytoplankton size classes. Within these two contrasting model structures, we also evaluate the impact of fixed vs. density-dependent microzooplankton mortality. We find that the observed relationship between microzooplankton predators and prey can be reproduced with density-dependent mortality on the highest predator, regardless of choices made about plankton food web structure. Our findings point to the importance of parameterizing mortality of the highest predator for simple food web models to recapitulate trophic structure in the global ocean.

Even low levels of cannibalism can bias population estimates for Pacific hake

Abstract By incorporating trophic interactions and temperature-dependent bioenergetics, multi-species models such as CEATTLE (climate-enhanced age-based model with temperature-specific trophic linkages and energetics) are a step towards ecosystem-based stock assessment and management of high-value commercial species such as Pacific hake (Merluccius productus). Hake are generalist predators and previous studies in the California Current Ecosystem have determined that their diet consists of ∼30% cannibalism. We used CEATTLE to include cannibalism in a model of hake population dynamics and re-examined hake diet data to determine the proportion by age that can attributed to cannibalism. The proportion was highly variable, ranging between 0 and 80% of stomach contents by weight. When included in the CEATTLE model, the estimated spawning biomass, total biomass, and recruitment increased by 15, 23, and 58%, on average, relative to the single-species model, due to the estimation of time- and age-varying predation mortality, primarily for age-1 hake. The effects of cannibalism varied over time, with further increases in total biomass and recruitment resulting from the age structure of the population following large cohorts in 1980 and 1984. Results from the cannibalism model could be used to inform the estimation of time- and age-varying mortality in the single-species assessment and as a pathway for including ecosystem information in management through environmental and trophic drivers of variability in mortality.

On the Dynamics of Mortality and the Ephemeral Nature of Mammalian Megafauna.

AbstractEnergy flow through consumer-resource interactions is largely determined by body size. Allometric relationships govern the dynamics of populations by impacting rates of reproduction as well as alternative sources of mortality, which have differential impacts on smaller to larger organisms. Here we derive and investigate the timescales associated with four alternative sources of mortality for terrestrial mammals: mortality from starvation, mortality associated with aging, mortality from consumption by predators, and mortality introduced by anthropogenic subsidized harvest. The incorporation of these allometric relationships into a minimal consumer-resource model illuminates central constraints that may contribute to the structure of mammalian communities. Our framework reveals that while starvation largely impacts smaller-bodied species, the allometry of senescence is expected to be more difficult to observe. In contrast, external predation and subsidized harvest have greater impacts on the populations of larger-bodied species. Moreover, the inclusion of predation mortality reveals mass thresholds for mammalian herbivores, where dynamic instabilities may limit the feasibility of megafaunal populations. We show how these thresholds vary with alternative predator-prey mass relationships, which are not well understood within terrestrial systems. Finally, we use our framework to predict the harvest pressure required to induce mass-specific extinctions, which closely align with previous estimates of anthropogenic megafaunal exploitation in both paleontological and historical contexts. Together our results underscore the tenuous nature of megafaunal populations and how different sources of mortality may contribute to their ephemeral nature over evolutionary time.

Growth and mortality rates of picophytoplankton in the Baltic Sea Proper

Picophytoplankton (<2 µm diameter), a diverse group of picocyanobacteria and photosynthetic picoeukaryotes, are significant contributors to primary production. Predatory mortality controls picophytoplankton biomass and thereby energy transfer in the marine food web. The 2 major pathways of picophytoplankton mortality are grazing and viral lysis. Grazing passes carbon directly to higher trophic levels, while lysis products are passed into the viral loop. Picophytoplankton are abundant in the Baltic Sea but little is known about their predatory mortality. Using a modification of the dilution approach, we calculated growth and mortality rates of picophytoplankton and studied the effect of predation on community structure during late August and September. The experiments were conducted coinciding with the peak in picophytoplankton abundance (∼105 cells ml-1) at the Linnaeus Microbial Observatory in the Baltic Sea Proper. The results showed that grazing is an important controller of picocyanobacteria and photosynthetic picoeukaryote populations, while no significant viral lysis effect was detected. Grazing on picocyanobacteria was proportional to growth rates, while grazing on photosynthetic picoeukaryotes exceeded growth. Selective grazing of phylogenetically distinct picocyanobacterial clades had a significant effect on community structure, suggesting that grazing has an impact on the seasonal dynamics of co-occurring clades. Picocyanobacteria had a higher carbon transfer contribution to higher trophic levels than photosynthetic picoeukaryotes at the time of the experiments. The study shows that picophytoplankton are important contributors to carbon cycling in the Baltic Sea microbial food web and should be considered for future ecological models.

Relative predation intensity of an intertidal gastropod on artificial coastal defense structures.

Despite seawalls becoming ubiquitous coastal features, and having some physical similarities to natural rocky shores, it remains unclear how these urban habitats influence predator-prey interactions. Predators can affect intertidal mobile prey densities through two pathways: (1) successful predation directly influences prey mortality rates, and (2) direct and indirect effects of predation can scare and induce motile prey to seek safer areas. In this study, we investigated whether intertidal predators affect the density of the marine gastropod, Nerita undata, at four seawall sites in Singapore. Using a tethering method that we developed, we monitored the mortality and other evidence of predation (shell state) of tethered N. undata. Field experiments revealed high (22.5%-82.5%) predation potential of N. undata across the four sites, with significantly higher predation risk at lower shore heights and for snails with mixed shell coloration. Observations and analysis of the shell state after 3 days showed that predation on seawalls was primarily by crushing predators such as fish. Other predators of N. undata include predatory snails, with various feeding methods that left behind different predator signatures. Our results add substantially to the limited knowledge on predator-prey interactions on seawalls, particularly for Nerita undata, and suggest that seawall systems are more dynamic than previously thought. This further highlights the role of these artificial structures as important habitats and feeding grounds in urban coastal ecosystems.

Shift in piscivory by salmonids following invasion of a minnow in an oligotrophic reservoir

AbstractPredation can play an important role in structuring ecological communities, and predator–prey dynamics can be altered following the introduction of new species. An unauthorized introduction of redside shiner (Richardsonius balteatus) into reservoirs in the Upper Skagit River, Washington, USA created concern that a consequent shift in predator–prey dynamics in the reservoirs could reduce recruitment and production of native salmonids in the basin. We estimated predation mortality in Ross Lake on nonnative redside shiner and juvenile native salmonids to evaluate the potential role of predation in regulating these populations and limiting survival of native species of concern. We used bioenergetics modelling and stable isotope analysis combined with directed field measurements of growth, seasonal diet and thermal experience of piscivorous salmonids to quantify their consumption demand on prey fishes to evaluate the relative magnitude of predation mortality on invasive redside shiners and native salmonids. While redside shiner are the dominant prey fish species in Ross Lake, the modest biomass of native salmonids consumed could translate into substantial mortality, the magnitude of which depended on the timing and size at which prey fishes were eaten. This information provides important context for how nonnative species may indirectly impact native species through shared predation (apparent competition) and can inform conservation decisions surrounding nonnative species control, sustainability of native salmonids and introductions of anadromous fishes.

The combined effects of predation, fishing, and ocean productivity on salmon species targeted by marine mammals in the northeast Pacific.

Along the northeast Pacific coast, the salmon-eating southern resident killer whale population (SRKW, Orcinus orca) have been at very low levels since the 1970s. Previous research have suggested that reduction in food availability, especially of Chinook salmon (Oncorhynchus tshawytscha), could be the main limiting factor for the SRKW population. Using the ecosystem modelling platform Ecopath with Ecosim (EwE), this study evaluated if the decline of the Pacific salmon populations between 1979 and 2020 may have been impacted by a combination of factors, including marine mammal predation, fishing activities, and climatic patterns. We found that the total mortality of most Chinook salmon populations has been relatively stable for all mature returning fish despite strong reduction in fishing mortality since the 1990s. This mortality pattern was mainly driven by pinnipeds, with increases in predation between 1979 and 2020 mortality ranging by factors of 1.8 to 8.5 across the different Chinook salmon population groups. The predation mortality on fall-run Chinook salmon smolts originating from the Salish Sea increased 4.6 times from 1979 to 2020, whereas the predation mortality on coho salmon (Oncorhynchus kisutch) smolts increased by a factor of 7.3. The model also revealed that the north Pacific gyre oscillation (NPGO) was the most important large-scale climatic index affecting the stock productivity of Chinook salmon populations from California to northern British Columbia. Overall, the model provided evidence that multiple factors may have affected Chinook salmon populations between 1979 and 2020, and suggested that predation mortality by marine mammals could be an important driver of salmon population declines during that time.

Social network shrinking is explained by active and passive effects but not increasing selectivity with age in wild macaques.

Evidence of social disengagement, network narrowing and social selectivity with advancing age in several non-human animals challenges our understanding of the causes of social ageing. Natural animal populations are needed to test whether social ageing and selectivity occur under natural predation and extrinsic mortality pressures, and longitudinal studies are particularly valuable to disentangle the contribution of within-individual ageing from the demographic processes that shape social ageing at the population level. Data on wild Assamese macaques (Macaca assamensis) were collected between 2013 and 2020 at the Phu Khieo Wildlife Sanctuary, Thailand. We investigated the social behaviour of 61 adult females observed for 13 270 h to test several mechanistic hypotheses of social ageing and evaluated the consistency between patterns from mixed-longitudinal and within-individual analyses. With advancing age, females reduced the size of their social network, which could not be explained by an overall increase in the time spent alone, but by an age-related decline in mostly active, but also passive, behaviour, best demonstrated by within-individual analyses. A selective tendency to approach preferred partners was maintained into old age but did not increase. Our results contribute to our understanding of the driver of social ageing in natural animal populations and suggest that social disengagement and selectivity follow independent trajectories during ageing.

Dynamic of coral recruits in the Karimunjawa National Park, Central Java, Indonesia

Abstract. Tarigan SAR, Munasik, Wijayanti DP, Muhidin, Rohman EA, Pardede S. 2024. Dynamic of coral recruits in the Karimunjawa National Park, Central Java, Indonesia. Biodiversitas 25: 869-880. After a disturbance event, coral reefs can recover naturally by recruiting new corals. These can be affected by environmental factors like the substrate's physical and biological structure, predation, and accidental mortality of recruits by grazers, as well as the number and size of parent corals supplying larvae. This study examined the connection between newly recruited corals and biological factors such as sea urchin density, herbivorous fish abundance, and hard coral coverage. The study was monitored changes in coral cover, juvenile coral density, herbivore abundance, and hard coral coverage at 43 locations and two depths (shallow; 2-3 m) and deep (8-10 m) from 2013 to 2022. The locations were distributed across six different zone systems: the core zone, protection zone, tourism zone, traditional fisheries zone, aquaculture zone, and rehabilitation zone. Multiple Linae Regression, ANOVA test, and Principal Component Analysis were employed to assess the relationship between coral recruitment and other variables. Results indicated that the coral recruitment density was not significantly different when comparing different zoning systems (two-way ANOVA test, P-value>0.05). Based on the PCA analysis, we found that in 2013 and 2019, excavator, sea urchin, browser, and hard coral have a positive relationship with coral recruitment, which implies that coral recruitment would increase as sea urchin, browser, and hard coral increase. Meanwhile, in 2019 and 2022, coral recruitment has a negative relationship with scraper, and also with hard coral growth (although only in 2022), implying that coral recruitment would decrease if scraper and hard coral increase. The study recommends restoring the role of herbivorous species in Karimunjawa National Park (KNP) by prioritizing them in conservation efforts and managing their populations.

An analysis of the stability and bifurcation of a discrete-time predator-prey model with the slow-fast effect on the predator.

In many environments, predators have significantly longer lives and meet several generations of prey, or the prey population reproduces rapidly. The slow-fast effect can best describe such predator-prey interactions. The slow-fast effect ε can be considered as the ratio between the predator's linear death rate and the prey's linear growth rate. This paper examines a slow-fast, discrete predator-prey interaction with prey refuge and herd behavior to reveal its complex dynamics. Our methodology employs the eigenvalues of the Jacobian matrix to examine the existence and local stability of fixed points in the model. Through the utilization of bifurcation theory and center manifold theory, it is demonstrated that the system undergoes period-doubling bifurcation and Neimark-Sacker bifurcation at the positive fixed point. The hybrid control method is utilized as a means of controlling the chaotic behavior that arises from these bifurcations. Moreover, numerical simulations are performed to demonstrate that they are consistent with analytical conclusions and to display the complexity of the model. At the interior fixed point, it is shown that the model undergoes a Neimark-Sacker bifurcation for larger values of the slow-fast effect parameter by using the slow-fast effect parameter ε as the bifurcation parameter. This is reasonable since a large ε implies an approximate equality in the predator's death rate and the prey's growth rate, automatically leading to the instability of the positive fixed point due to the slow-fast impact on the predator and the presence of prey refuge.

Lethal competition on joint predators during suppressing brown planthopper population

Joint predator is one technique to control brown planthopper (Nilaparvata lugens) in the rice field by combining two or more predator species having a positive interaction. This study aims to determine the effect of joint predator density (Pardosa pseudoannulata and Phidippus sp) on competition and its predatory rate in suppressing the N.lugens population. The study used a completely randomized design (CRD) by combining P. pseudoannulata or Pp (1,2,3 individuals) and Phidippus sp or Ps (1,2,3 individuals) to become Pp1Ps1, Pp1Ps2, Pp1Ps3, Pp2Ps1, Pp2Ps2, Pp2Ps3, Pp3Ps1, Pp3Ps2, Pp3Ps3. The parameters observed were predation rate, bodyweight, mortality of both predators, and competition model. The results showed that the composition difference between P. pseudoannulata and Phidippus sp affected on competition model and the predation. The predation rate of joint predators at different densities ranged from 40.4 – 47.0 individuals of N.lugens (80.8-94.0%) in one-day observation, and they consumed all prey until the third day’s observation. The highest predation rate occurred for Pp3Ps3, but it was assumed it was not safe because of cannibalism and lethal competition. The Pp1Ps2 composition of joint predators was classified as safe, with 0 and 0.2 individuals’ mortalities and followed by draw competition between two predators.

Depredation rates and spatial overlap between Great Hammerheads and Tarpon in a recreational fishing hot spot

AbstractObjectiveShark depredation, the full or partial consumption of a hooked fish by a shark before it is landed, is an increasing source of human–wildlife conflict in recreational fisheries. Reports of shark depredation in the catch‐and‐release Tarpon (also known as Atlantic Tarpon) Megalops atlanticus fishery in the Florida Keys are increasing, specifically in Bahia Honda, a recreational fishing hot spot and a putative Tarpon prespawning aggregation site.MethodsUsing visual surveys of fishing in Bahia Honda, we quantified depredation rates and drivers of depredation. With acoustic telemetry, we simultaneously tracked 51 Tarpon and 14 Great Hammerheads (also known as Great Hammerhead Sharks) Sphyrna mokarran, the most common shark to depredate Tarpon, to quantify residency and spatial overlap in Bahia Honda.ResultDuring the visual survey, 394 Tarpon were hooked. The combined observed shark depredation and immediate postrelease predation rate was 15.3% for Tarpon that were fought longer than 5 min. Survival analysis and decision trees showed that depredation risk was highest in the first 5–12 min of the fight and on the outgoing current. During the spawning season, Great Hammerheads shifted their space use in Bahia Honda to overlap with Tarpon core use areas. Great Hammerheads restricted their space use on the outgoing current when compared to the incoming current, which could drive increased shark–angler interactions.ConclusionBahia Honda has clear ecological importance for both Tarpon and Great Hammerheads as a prespawning aggregation and feeding ground. The observed depredation mortality and postrelease predation mortality raise conservation concerns for the fishery. Efforts to educate anglers to improve best practices, including reducing fight times and ending a fight prematurely when sharks are present, will be essential to increase Tarpon survival and reduce shark–angler conflict.

Combined impact of fear and Allee effect in predator-prey interaction models on their growth

<p>We considered predator-prey models which incorporated both an Allee effect and a new fear factor effect together, and where the predator predated the prey with a Holling type I functional response. We started off with a two-dimensional model where we found possible equilibria and examined their stabilities. By using the predator mortality rate as the bifurcation parameter, the model exhibited Hopf-bifurcation for the coexistence equilibrium. Furthermore, our numerical illustrations demonstrated the effect of fear and the Allee effect on the population densities, and we found that the level of fear had little impact on the long-term prey population level. The population of predators, however, declined as the fear intensity rose, indicating that the fear effect might result in a decline in the predator population. The dynamics of the delayed system were examined and Hopf-bifurcation was discussed. Finally, we looked at an eco-epidemiological model that took into account the same cost of fear and the Allee effect. In this model, the prey was afflicted with a disease. The prey was either susceptible or infected. Numerical simulations were carried out to show that as the Allee threshold rose, the uninfected prey and predator decreased, while the population of infected prey increased. When the Allee threshold hit a certain value, all populations became extinct. As fear intensity increased, the population of uninfected prey decreased, and beyond a certain level of fear, habituation prevented the uninfected prey from changing. After a certain level of fear, the predator population went extinct and, as a result, the only interaction left was between uninfected and infected prey which increased disease transmission, and so the infected prey increased. Hopf-bifurcation was studied by taking the time delay as the bifurcation parameter. We estimated the delay length to preserve stability.</p>

Chaotic behavior and controlling chaos in a fast-slow plankton-fish model

<abstract><p>The interaction of different time scales in predator-prey models has become a common research topic. In the present article, we concentrated on the dynamics of interactions at two time scales in a plankton-fish system. To investigate the effects of the two time scales on plankton-fish dynamics, we constructed a new parameter with a corrected type that differs from the traditional slow parameter. In addition, zooplankton's refuge from the predator and phytoplankton mortality due to competition are incorporated into the model. Positivity and boundedness of solutions were proved. We then discussed feasibility and stability conditions of the equilibrium. We used a variety of means to support the existence of chaos in the system. Hopf bifurcation conditions were also obtained. Chaos control in the plankton-fish model is one of the main motivations for this study. In the slow-variable parameter case, we explored the control mechanism of gestation delay on chaotic systems, which are calmed by different periodic solutions. Moreover, under seasonal mechanisms, external driving forces can stabilize the system from chaos to periodic oscillations. Meanwhile, the sliding mode control (SMC) approach quickly calms chaotic oscillations and stabilizes it to an internal equilibrium state. The necessary numerical simulation experiments support the theoretical results.</p></abstract>

Analysis of a prey-predator system incorporating the additive Allee effect and intraspecific cooperation

<abstract><p>To understand the influence of the Allee effect and intraspecific cooperation on the dynamics of a predator-prey system, we constructed a model using ordinary differential equations. Our research shows that the system exhibits more complex dynamics, including possible bistability between alternative semi-trivial states and an Allee effect for prey. The Allee effect can destabilize the system. The equilibrium points of the system could change from stable to unstable. Otherwise, even if the system were stable, it would take much longer time to reach a stable state. We also find that the presence of the Allee effect of prey increases the positive equilibrium density of the predator but has no effect on the positive equilibrium density of the prey. It should be noted that the influence of nonlinear predator mortality also causes the system to take a longer time to reach a steady state.</p></abstract>

Does competition between Pardosa pseudoannulata and Menochilus sexmaculatus reduce the predation rate on brown planthopper?

Pardosa pseudoannulata and Menochilus sexmaculatus are classified as natural enemies of the brown planthopper or BPH (Nilaparvata lugens). This study aimed to determine the effect of differences in density on mortality and their predation rate in suppressing the BPH population. This study used a completely randomized design of 15 treatments and 3 replications. The treatments consisted of different densities of two predators (1, 2, and 3 individuals). The variables observed were predator mortality, predation rate, competition between predators, and competition behavior. The results showed that competition between predators at different densities was not directly related to predator mortality and the predation rate of joint predators. Predator density tended to increase the predation rate, especially on M. sexmaculatus (R=0.894), while the density of P. pseudoannulata and joint predators was moderate (Rpardosa=0.587, Rjoint=0.522). M. sexmaculatus won the competition when its population increased. Equal competition occurred in the composition of 1 P. pseudoannulata and 3 M. sexmaculatus (P1M3); in this composition, no deaths were found due to competition, with the predation rate reaching 86.7%. Cannibalism dominates intraspecific competition between individuals of P. pseudoannulata, while interspecific competition occurs between the two species, causing sub-lethal effects.