Specialist Predators Research Articles

Trophic ecology and length-weight relationship of Hypoatherina temminckii (Bleeker, 1854) in the seagrass ecosystem of Semak Daun Island, Kepulauan Seribu

Semak Daun Island is commonly used as a tourist destination site in the Kepulauan Seribu Marine National Park. Seagrass beds are found along the coast of this small island and have an essential role as shelter and feeding areas for various aquatic biotas, such as small-sized fishes of Samoan Silverside, Hypoatherina temminckii. Samoan silverside is usually used as bait in the tuna fishery. The present study aimed to determine growth pattern, diet composition, trophic level, guild, and feeding strategy of Samoan silverside in the seagrass ecosystem of the Semak Daun Island. Fish samples were captured using seine net monthly from February 2018 to March 2019. A total of 1,481 H. temminckii were collected, and all were juvenile. Results indicate that juveniles of Samoan silverside feed mainly on zooplankton and shows specialist predator as its feeding strategy. Moreover, this species occupies trophic levels ranging from 3.00-3.99 and exhibits a positive allometric growth pattern. Thus, the current study confirms that the seagrass ecosystem of the Semak Daun Island is the nursery and feeding grounds for the juvenile of Samoan silverside.

Restoring vertebrate predator populations can provide landscape-scale biological control of established invasive vertebrates: Insights from pine marten recovery in Europe.

Invasive species pose one of the greatest global threats to biodiversity. There has been a long history of importing coevolved natural enemies to act as biological control agents to try to suppress densities of invasive species, with historically limited success and frequent adverse impacts on native biodiversity. Our understanding of the processes and drivers of successful biological control has been focussed on invertebrates and is evidently limited and potentially ill‐suited with respect to biological control of vertebrate populations. The restoration of native vertebrate predator populations provides a promising nature‐based solution for slowing, halting, or even reversing the spread of some invasive vertebrates over spatial scales relevant to the management of wildlife populations. Here, we first review the growing literature and data from the pine marten‐red and grey squirrel system in Europe. We synthesise a multi‐decadal dataset to show that the recovery of a native predator has resulted in rapid, landscape‐scale declines of an established invasive species. We then use the model system, predator–prey interaction theory, and examples from the literature to develop ecological theory relating to natural biological control in vertebrates and evolutionary processes in native‐invasive predator–prey interactions. We find support for the hypotheses that evolutionary naivety of invasive species to native predators and lack of local refuges results in higher predation of naive compared to coevolved prey. We apply lessons learnt from the marten‐squirrel model system to examine the plausibility of specific native predator solutions to some of the Earth's most devastating invasive vertebrates. Given the evidence, we conclude that depletion of vertebrate predator populations has increased ecosystem vulnerability to invasions and thus facilitated the spread of invasive species. Therefore, restoration of vertebrate predator populations is an underappreciated, fundamental, nature‐based solution to the crisis of invasive species and should be a priority for vertebrate invasive species management globally.

Taking the bait: Developing a bait delivery system to target free-ranging crocodiles and varanid lizards with a novel conservation strategy.

In tropical Australia, conditioned taste aversion (CTA) can buffer vulnerable native predators from the invasion of a toxic prey species (cane toads, Rhinella marina). Thus, we need to develop methods to deploy aversion‐inducing baits in the field, in ways that maximize uptake by vulnerable species (but not other taxa). We constructed and field‐tested baiting devices, in situ with wild animals. Apparatus were set next to waterbodies and baited concurrently at multiple locations (over water, water's edge, and on the bank). Baits were checked and replaced twice daily during the trial; remote cameras recorded visitation by native predators. Bait longevity was compared at sun‐exposed and shaded locations over 12 h. The strength required to remove baits from apparatus was measured in varanids and crocodiles. The device promoted high rates of bait uptake by freshwater crocodiles (47% baits consumed), varanid lizards (19% baits consumed), and non‐target taxa (34% baits consumed). Targeting specific predators can be achieved by manipulating bait location and time of deployment, as well as the force required to dislodge the bait. Crocodiles were best targeted with over‐water baits, whereas varanid lizards preferred baits located at the edges of waterbodies. When testing bait longevity in ambient conditions, during the daytime baits desiccated fully within 12 h, and faster in the sun than in the shade. Based on studies using captive animals, the “pulling force” strength of reptilian predators scaled with body size and was greater in crocodiles than in varanid lizards. We present the first conservation baiting protocol designed specifically for reptiles. Our results demonstrate the feasibility of widespread and taxon‐specific deployment of aversion‐inducing baits to buffer the impacts of invasive cane toads, and our methods are applicable (with modification) to other research and management programs globally.

Analysis of the male annual antler cycle, reproductive behavior and spotted fawn presence in the tropical white-tailed deer

The rutting season of the white-tailed deer (Odocoileus virginianus) is seasonal in North America, but in tropical latitudes it occurs year-round with peaks locally variable. Reproductive cycle of this species in Costa Rica is variable, clearly seasonal in San Lucas Island but continuous with two birth peaks in Palo Verde and Santa Rosa national parks in northwestern Costa Rica. In Hacienda y Refugio de Vida Silvestre Curú in the Nicoya Peninsula, a site south of these parks but in a different life zone, we observed males with hard antlers in 2015 but only from July to November. We therefore hypothesized that white-tailed deer have a continuous reproductive cycle during the year in Curú because the rainfall pattern is the same as in Palo Verde and Santa Rosa. We visited Curú every month and recorded the status of white-tailed deer antler growth: nubs, velvet, and hard, from January 2016 to December 2019. We also recorded other rut behaviors and the presence of spotted fawns. We recorded 1,134 observations of the status of antler growth, 13 observations on reproductive behavior and 133 observations of spotted fawns. The antler cycle was seasonal in the four years of study. Male antler casting took place from mid-November to mid-February and the growth of new antlers began in mid-December and lasted until mid-March. Velvet shedding occurred in April, May and June, and by July males had hard antlers. The rutting season lasted three months from mid-June to mid-August. Small spotted fawns were observed from the middle of the dry season to the beginning of the rainy season. All this highly contrasts with the reproduction pattern observed in Santa Rosa. Lack of seasonal variation in the photoperiod is likely an important factor that allows deer to reproduce throughout the year in these protected areas, but this variation does not exist in Curú either, where the species is seasonal. The reproductive patterns of white-tailed deer in Central and South America may have evolved in response to seasonal fluctuations in specific food availability, competition, or predation, all of which may be directly related to rainfall patterns. Greater knowledge of the link between rainfall patterns and food availability for deer would be of great help to further our understanding of factors driving the reproduction cycle of the White-tailed deer.

The effect of advection on a predator–prey model in open advective environments

This paper deals with a reaction–diffusion–advection system that characterizes the interactions between predators and prey in open advective environments, subject to an unidirectional flow, such as streams or rivers. To explore the influence of advection rates on the dynamics of this system, we study its dynamical classification by taking advection rates of two species as the variable parameters. It turns out that there exist some critical curves in the parameter plane of advection rates, which classify the dynamics of this system into several scenarios: (i) coexistence, (ii) persistence of prey only, (iii) persistence of predators only, (iv) extinction of both species. Furthermore, some qualitative properties of these critical curves are given by rigorous mathematical analysis and numerical computations. Our analytical and numerical results show that predators can invade successfully when they take relatively small advection rates. Especially, specialist predators always coexist with the prey when they invade successfully because they must keep pace with the prey for food. Nevertheless, generalist predators can take over the habitats when the prey’s advection rate is suitably large, which implies that the prey’s advection can facilitate the invasion of generalist predators. In addition, we numerically observe that the boundary loss rate has a significant influence on the dynamical classification. All of these results provide us with some deep insights into the dynamics of this system.

DIVERSIDAD Y GRUPOS FUNCIONALES DE HORMIGAS EN CULTIVOS DE Citrus sinensis CON DIFERENTE RÉGIMEN DE RIEGO

Ants have an important ecological role and they can help in prevention and pests management. That is why is important to know the species and understand the function they perform in different systems. The main propose of this work was to study the ants diversity on the ground in Citrus sinensis crop, with irrigation (IC) and without (NC). Pitfall traps, foliage patterns, manual capture and sifting litter were used to characterize ant assemblages and compare the ant diversity between treatments. In total, 26 species and 13 genera were collected, grouped in 5 families. The irrigated crop presented the higher richness, abundance and diversity index values, although the differences between crops were not significant. Nine ant guilds were recognized, distributed in three groups (epigeas, arboreal and hypogea). The epigeous ant group was the one that presented the most abundance in both crops. In the two treatments the three general groups were found, even though in NC crop, the Specialist predators (Sp) and Agile pseudomyrmicinae (Ap) guilds were not registered, which were exclusives of treatment CR. Sf index showed big functional similarity between both treatments. This study provides four new species records for Corrientes province: Cephalotes bruchi, Cephalotes minutus, Cyphomyrmex transversus y Pheidole jelskii.

Blood-red colour as a prey choice cue for mosquito specialist predators

Specialist predators are innately and distinctively proficient at targeting specific prey types. This is enabled by behavioural, perceptual and cognitive mechanisms that can only be understood using carefully designed experiments. Evarcha culicivora is an East African jumping spider that feeds on vertebrate blood acquired indirectly by actively targeting blood-carrying female mosquitoes as preferred prey. Here we asked whether these spiders use the colour red to identify this prey. In Objective 1, we used spectrophotometry to document the changing redness of mosquitoes in the first 17 h following blood meals. In Objective 2, we used vision-based choice tests to document how E. culicivora's preference for blood-carrying mosquitoes changes over time (using an interval comparable to that in Objective 1). We found the strongest preference for blood-carrying mosquitoes during the first 6 h after those mosquitoes had fed on blood and that this time interval corresponded to when mosquitoes exhibit the reddest coloration. Based on this, we then took mosquitoes that had never fed on blood and manipulated their colour using a blend of red food dye to make them appear blood-fed (i.e. by matching their spectral properties to mosquitoes that had fed on blood within the previous 6 h). We also created grey-dyed mosquitoes that matched the spectral properties of those that had never fed on blood. In Objective 3, there was no evidence of E. culicivora visually discriminating between our red-dyed mosquitoes and blood-carrying mosquitoes; this indicates that, to E. culicivora, our red-dyed mosquitoes appropriately resembled blood-carrying mosquitoes. Finally, in Objective 4, we show that E. culicivora consistently preferred red-dyed mosquitoes over grey-dyed mosquitoes, supporting the hypothesis that E. culicivora uses some aspect of red coloration to identify their preferred prey. We discuss how these findings relate to cognitive processes, colour-based communication and sensory exploitation.

Landscape configuration affects probability of apex predator presence and community structure in experimental metacommunities

Biodiversity is declining at an unprecedented rate, highlighting the urgent requirement for well-designed protected areas. Design tactics previously proposed to promote biodiversity include enhancing the number, connectivity, and heterogeneity of reserve patches. However, how the importance of these features changes depending on what the conservation objective is remains poorly understood. Here we use experimental landscapes containing ciliate protozoa to investigate how the number and heterogeneity in size of habitat patches, rates of dispersal between neighbouring patches, and mortality risk of dispersal across the non-habitat ‘matrix’ interact to affect a number of diversity measures. We show that increasing the number of patches significantly increases γ diversity and reduces the overall number of extinctions, whilst landscapes with heterogeneous patch sizes have significantly higher γ diversity than those with homogeneous patch sizes. Furthermore, the responses of predators depended on their feeding specialism, with generalist predator presence being highest in a single large patch, whilst specialist predator presence was highest in several-small patches with matrix dispersal. Our evidence emphasises the importance of considering multiple diversity measures to disentangle community responses to patch configuration.

Hunting cooperation among slowly diffusing specialist predators can induce stationary Turing patterns

In this work we consider the spatio-temporal extension of a class of prey–predator models with hunting cooperation in the specialist predator population. Three different types of parametrization of functional response are used and the corresponding pattern formation scenario has been studied analytically with supportive numerical simulations. The main outcome of this work is that lower diffusivity of predator than the prey can lead to generation of stationary Turing patterns like spots, stripes and mixture of the two. Other non-Turing patterns like spirals and spatio-temporal chaos are also generated for parameter values outside the Turing domain and vividly discussed. Dispersal of the specialist predator lower than the diffusivity of the prey supports the formation of stationary patches as the hunting cooperation among the predators can support the success in predation.

Evidence that reduction of the apertural closing apparatus has no decisive effect on water loss in the land snail family Clausiliidae (Gastropoda: Stylommatophora)

Abstract Apertural barriers of land snails are thought to increase their shell’s effectiveness against dehydration and predation. The most complex apertural barrier among stylommatophoran snails is the clausiliar apparatus (CA) of Clausiliidae. Alopia is a unique genus in having a remarkably high proportion of taxa with a naturally reduced CA, representing at least five independent reduction events. We tested the prevailing hypothesis that the primary role of the CA within the door snail family is to help retain body moisture. In a laboratory experiment, we compared the water loss of two Alopia taxa with naturally reduced and two Alopia taxa with complete CAs. There was a detectable difference in the rate of water loss, but no relationship with the presence/absence of the CA could be shown. In another laboratory experiment, this time in Alinda biplicata, we did not detect significantly higher water loss in specimens from which the clausiliar plate was artificially removed compared to those left intact. These results suggest that the CA has no significant role in water retention but its actual function remains speculative. A possible explanation, which requires further work, could be that the CA provides protection against specific predators intruding through the aperture.

The Isotopic Ecology of the Mammoth Steppe

The Mammoth Steppe was the dominant terrestrial biome of the Northern Hemisphere during the late Pleistocene. It encompassed a nonanalog community of animals living in a cold and treeless steppe-tundra landscape. The high diversity of species, including megafauna, could be supported by a productive environment. The carbon-13 and nitrogen-15 abundances in bone collagen confirmed that the coexistence of the large herbivores was facilitated by a pronounced dietary niche partitioning, with some species relatively flexible in the exploitation of browse and graze, while others were more specialized. The isotopic abundances of carbon and nitrogen in carnivores confirm a dietary partitioning, probably based on the size of prey, with an increasingly generalist behavior emerging after the Last Glacial Maximum with notable exceptions. Isotopic investigation reveals dynamic processes of ecological displacement and replacement, shedding new light on the potential niche spectrum of extant species that are now present as relic populations. ▪ The Mammoth Steppe is an extinct nonanalog ecosystem with high productivity and biodiversity despite the cold and dry conditions of the Last Glacial Period. ▪ Stable isotopes reveal that niche partitioning among herbivores and carnivores is a dominant trait of the Mammoth Steppe. ▪ Switches in preferred prey and ecological replacement are observed among carnivores over time, with the few highly specialized predators going extinct. ▪ Warmer and more humid conditions preceding the Holocene impacted large herbivores in most regions of the Mammoth Steppe, driving some of the largest ones to extinction.

Modeling ecological issues in fish dynamics: Competing predators, invasiveness, and over-harvesting

A mathematical model of a three-species dynamical system is employed to analyze some ecological issues in fish dynamics, namely, competition between predators, effect of an invasive species, and over-harvesting of either the prey or one of the predators. To address the issue of competition between predators, we assume that one of the predators is a specialist predator using a Holling Type II response while the other one is a generalist predator using a Holling Type III response. The latter assumption is also used to analyze the effect of having an invasive species as a second predator. We use an analytical approach to compute the equilibria and investigate the linear stability of each point. We also compute the bionomic equilibria and find conditions for their existence. We use a numerical approach to analyze the effects of harvesting efforts on the prey and on one of the predators. The proposed dynamical system may be used to analyze special fish dynamics in the Chesapeake Bay with the Atlantic menhaden as prey as well as striped bass and catfish as competing predators. In particular, we address a recent policy on eating-the-invaders as a way to control the growth of the catfish as an invasive species in the Chesapeake Bay.

Individual specialization and generalization in predator-prey dynamics: The determinant role of predation efficiency and prey reproductive rates

Individual specialization and generalization refer to the breadth of prey types consumed by predators among all available prey. The ecological factors mechanistically determining individual differences and the coexistence of foraging strategies remain to be clarified. Formal quantitative models can elucidate the complex nonlinear mechanisms underlying predator–prey interactions. In this study, we built a dynamical model with multiple prey, with different nutritional values and reproductive rates, which are consumed by specialist and generalist predators. We then analyzed the viability of individual foraging strategies in all possible scenarios. Relative prey fertility and relative efficiency of predation, rather than prey nutritional value, determined the success of specialists and generalists. Less reproducing prey and the specialists relying on them face the highest danger of extinction, while generalists cannot thrive where specialists are sufficiently efficient in relation to the number of available prey. Our study provides new perspectives for empirical studies on individual specialization.

Gudermannian neural networks using the optimization procedures of genetic algorithm and active set approach for the three-species food chain nonlinear model.

The present study is to investigate the Gudermannian neural networks (GNNs) using the optimization procedures of genetic algorithm and active-set approach (GA-ASA) to solve the three-species food chain nonlinear model. The three-species food chain nonlinear model is dependent upon the prey populations, top-predator, and specialist predator. The design of an error-based fitness function is presented using the sense of the three-species food chain nonlinear model and its initial conditions. The numerical results of the model have been obtained by exploiting the GNN-GA-ASA. The obtained results through the GNN-GA-ASA have been compared with the Runge–Kutta method to substantiate the correctness of the designed approach. The reliability, efficacy and authenticity of the proposed GNN-GA-ASA are examined through different statistical measures based on single and multiple neurons for solving the three-species food chain nonlinear model.

The omnivorous predator Macrolophus pygmaeus induces production of plant volatiles that attract a specialist predator

It has become clear that omnivorous predators can induce plant defences that affect the performance and host plant choice of herbivores. They are also known to induce the production of plant volatiles that can affect the behaviour of herbivores searching for plants. These volatiles may also affect the searching behaviour of other predators, which was investigated here. The predatory mite Phytoseiulus persimilis preferred plants previously exposed to the omnivorous mirid Macrolophus pygmaeus over clean plants. The mites were equally attracted to plants previously exposed to the omnivore and subsequently infested by spider mites (Tetranychus urticae, prey of the predatory mite and the omnivore) and plants infested with spider mites alone. Moreover, the mites were more attracted to plants infested with prey and subsequently exposed to the omnivore than plants infested with prey but not exposed to the omnivore. The predatory mites were also significantly more attracted to plants on which the omnivores were still present. Experience of the predatory mites with volatiles from plants previously exposed to the omnivore and without prey resulted in a loss of the preference for volatiles emitted by plants exposed to the omnivore. Analysis of the volatiles showed that plant exposure to omnivores induced qualitative and quantitative changes in the volatile blend. Together, these results suggest that omnivorous predators induce the production of plant volatiles that can interfere with the searching behaviour of other predators. The consequences of such interference for biological pest control remain to be investigated.

Assessment of Feeding Behavior of the Zoo-Housed Lesser Anteater (Tamandua tetradactyla) and Nutritional Values of Natural Prey

Very little information is available to zoo managers on the nutritional preferences of the lesser anteater, a highly specialized predator. By studying lesser anteater feeding behavior, we expect to contribute to improved management decisions and individual welfare experiences. We studied the response of zoo-housed lesser anteaters (n = 7) to feeders with live ants (Acromyrmex lundi) and termites (Cortaritermes fulviceps), and we also evaluated the nutritional values of these prey. We individually evaluated each lesser anteater (3 sessions), recording activities by camera. We ground insect samples into a coarse meal and evaluated in vitro biochemical parameters (humidity, lipids proteins, ash, and carbohydrates). Lesser anteaters spent more time with termites than with ants and consumed more termites. Ant meal presented a higher protein and lipid content than termite meal (35.28 ± 0.18% vs. 18.19 ± 0.34% and 16.95 ± 0.13% vs. 6.54 ± 0.31%, respectively), and carbohydrate digestibility was higher in termites. These findings indicate an association between the level of insect consumption and nutritional and digestibility values. This is the first exploration of lesser anteater responses to the presence of social insects in feeders and may serve to guide the study of food preferences in captivity.

Analytical detection of stationary turing pattern in a predator-prey system with generalist predator

A prey-predator model with Holling type-II functional response and a generalist predator exhibits complex dynamics in response to parameter variation. Generalist predators implicitly exploiting multiple food resources reduce predation pressure on their focal prey species that causes it to become more stable compared to a prey-predator system with specialist predator. In the temporal system, bistability and tristability are observed along with various global and local bifurcations. Existence of homogeneous and heterogeneous positive steady state solutions are shown to exist for suitable ranges of parameter values in the corresponding spatio-temporal diffusive system. Weakly nonlinear analysis, using multi-scale perturbation technique, is employed to derive amplitude equation for the stationary patterns near the Turing bifurcation threshold. The analytical results of the amplitude equations are validated using exhaustive numerical simulations. We also identify bifurcation of multiple stable stationary patch solutions as well as dynamic pattern solution for parameter values in the Turing and Turing-Hopf regions.

Predators as a possible strategy for controlling a Xylella epidemic?

In Southern Italy, since 2013, there has been an ongoing Olive Quick Decline Syndrome (OQDS) outbreak, due to the bacterium Xylella fastidiosa, which has caused a dramatic impact from both socio-economic and environmental points of view. Current agronomic practices are mainly based on uprooting the sick olive trees and their surrounding ones, with later installment of olive cultivars more resistant to the bacterium infection. Unfortunately, both of these practices are having an undesirable impact on the environment and on the economy. Here, a spatially structured mathematical model has been proposed to include a predator Zelus renardii as a possible biocontrol agent of the Xylella epidemic. The fact that Z. renardii has been reported to be a generalist predator implies that its introduction is not an efficient control strategy to eradicate a Xylella epidemic. Instead, a specialist predator, whenever identified, would lead to the eventual eradication of a Xylella epidemic. In either cases it has been confirmed that a significant reduction of the weed biomass can lead to the eradication of the vector population, hence of a Xylella epidemic, independently of the presence of predators.

Dynamical complexity in a tritrophic food chain model with prey harvesting

The present investigation deals with a tritrophic food web model with Holling-Tanner type II functional response to clarify the dynamical complexity of the eco-systems in the natural environment. The objective of this study is to explore the harvesting mechanism scenario in a three-dimensional interacting species system such as one prey and two specialist predators. Attention has been given to demonstrate the system characteristics near the biologically feasible equilibria. Specifically, stability, Hopf-Andronov bifurcation for the respective system parameters and dissipativeness has been performed in order to scrutinize the system behaviour. Lyapunov exponents are worked out numerically and an unstable scenario for significant parameters of the model system has been executed to characterize the complex dynamics. In addition to, we put forward a detailed numerical simulation to justify the chaotic dynamics of the present system. We conclude that chaotic dynamics can be executed by the prey harvesting parameters.

Stochastic numerical investigations for nonlinear three-species food chain system

In this work, three-dimensional nonlinear food chain system is numerically treated using the computational heuristic framework of artificial neural networks (ANNs) together with the proficiencies of global and local search approaches based on genetic algorithm (GA) and interior-point algorithm scheme (IPAS), i.e. ANN–GA–IPAS. The three-dimensional food chain system consists of prey populations, specialist predator and top-predator. The formulation of an objective function using the differential system of three-species food chain and its initial conditions is presented and the optimization is performed by using the hybrid computing efficiency of GA–IPAS. The achieved numerical solutions through ANN–GA–IPAS to solve the nonlinear three-species food chain system are compared with the Adams method to validate the exactness of the designed ANN–GA–IPAS. The comparison of the results is presented to authenticate the correctness of the designed ANN–GA–IPAS for solving the nonlinear three-species food chain system. Moreover, statistical representations for 40 independent trials and 30 variables validate the efficacy, constancy and reliability of ANN–GA–IPAS.