Prey Density Research Articles

Low apex carnivore density does not release a subordinate competitor when driven by prey depletion

Conservation of competitively subordinate carnivores presents a difficult challenge because they are limited by dominant competitors. Prey depletion is one of the leading causes of large carnivore decline worldwide, but little is known about the net effect of prey depletion on subordinate carnivores when their dominant competitors are also reduced. African wild dogs are often limited by high densities of dominant competitors, particularly lions. We measured African wild dog density and survival, using mark-recapture models fit to 8 years of data from 425 known individuals in the Greater Kafue Ecosystem, Zambia. The GKE is affected by prey depletion, particularly of large herbivores, and thus the density of lions is significantly lower than ecologically comparable ecosystems. Counter to expectations from mesopredator release theory, wild dog density in GKE was far lower than comparable ecosystems with higher lion and prey density, though annual survival rates were comparable to large and stable populations. Average pack size was small and home range size was among the largest recorded. Our results show that low lion density did not competitively release the GKE wild dog population and we infer that the low density of wild dogs was a product of low prey density. Our results suggest that there is an optimal ratio of prey and competitors at which wild dogs achieve their highest densities. This finding has immediate implications for the conservation of the endangered African wild dog, and broad implications for the conservation of subordinate species affected by resource depletion and intraguild competition.

Terpenes from herbivore‐induced tomato plant volatiles attract Nesidiocoris tenuis (Hemiptera: Miridae), a predator of major tomato pests

Biological control plays a key role in reducing crop damage by Tuta absoluta (Meyrick) and Trialeurodes vaporariorum (Westwood), which cause huge yield losses in tomato (Solanum lycopersicum L.). The mirid predator Nesidiocoris tenuis (Reuter) preys heavily on these pests, with satisfying control levels in tomato greenhouses. Although N. tenuis is known to be attracted to volatiles of tomato plants infested by T. absoluta and whitefly, little is known about the specific attractive compounds and the effect of prey density on the predator response. Y-tube olfactometer bioassays revealed that the attraction of N. tenuis to tomato volatiles was positively correlated with the density of T. absoluta infestation, unlike T. vaporariorum infestation. The predator was also attracted to volatiles of T. absoluta larval frass, but not to T. vaporariorum honeydew or T. absoluta sex pheromone. Among the herbivore-induced plant volatiles (HIPVs) that characterised the attractive plants infested with 20 T. absoluta larvae, olfactometer bioassays revealed that N. tenuis is attracted to the monoterpenes α-pinene, α-phellandrene, 3-carene, β-phellandrene and β-ocimene, whereas (E)-β-caryophyllene was found to repel the predator. In dose-response bioassays, the five-component blend of the attractants elicited a relatively low attraction in the predator, and removal of β-phellandrene from the blend enhanced the attraction of the predator to the resulting four-component blend, suggesting synergism among four monoterpenes. These findings suggest that a four-component blend of α-pinene, α-phellandrene, 3-carene and β-ocimene could be used as a kairomone-based lure to recruit the predator for the biological control of T. absoluta and T. vaporariorum.

Functional response and egg production of a native Typhlodromus recki Wainstein, 1958 (Acari: Phytoseiidae) population to Tetranychus urticae Koch, 1836 (Acari: Tetranychidae)

In this study, which was conducted to determine predation potential of Typhlodromus recki Wainstein, 1958 (Acari: Phytoseiidae) at Ege University, Faculty of Agriculture, Department of Plant Protection in 2018-2019. Functional response and egg production of the predatory mite, T. recki fed on different biological stages (egg, larva, protonymph, deutonymph and adult male) of the two-spotted spider mite (green form), Tetranychus urticae Koch, 1836 (Acari: Tetranychidae) were studied under laboratory conditions (25±1°C, 60±10% RH and 16:8 h L:D photoperiod). In the experiments, seven prey densities (2, 4, 8, 16, 32, 64 and 128) for each biological stage of the prey were offered daily to the predatory mite. The results of logistic regression analysis indicated that T. recki had a Type II functional response on each developmental stage of its prey according to Holling’s models. The attack rate (α) and the handling time (Th) varied based on the biological stages of the prey. The highest α and the lowest Th values were determined as 1.035 and 0.001 when the predator fed on larvae and eggs of its prey, respectively. The highest average daily mean number of the eggs consumed by T. recki was 111 at 128 prey densities. The highest average daily mean number of eggs deposited by the predator were found to be 1.05 when it fed on the eight-prey density of T. urticae protonymphs. In addition, the lowest average daily mean number of eggs deposited by the predator was 0.15 when fed on the two-prey density with T. urticae adult males. The study indicates that T. recki could be effective and promising biological control agent for T. urticae .

Interannual variations in diet of Japanese jack mackerel (Trachurus japonicus) juveniles in the southwestern Sea of Japan in relation to recent growth rate

AbstractWe examined interannual variations in the diet of Trachurus japonicus juveniles in relation to prey density and recent 5‐day instantaneous growth rate (IGR) in the southwestern part of the Sea of Japan (SJ) in late spring during 2011–2013. Habitat temperature of juveniles in 2011 was lower than the other 2 years. In all 3 years, more than 97% of juveniles had food in the stomach. Small juveniles <35‐mm standard length (SL) fed mainly on adult female Paracalanus parvus s.l., the most dominant calanoid copepod in the water column, without a significant interannual difference. In 2011 and 2012, large juveniles ≥35‐mm SL predated heavily upon adult female Calanus sinicus which form a high‐energy food for the juveniles. In contrast, in 2013, the large juveniles preyed on a large number of a variety of small‐sized prey items, such as P. parvus s.l., euchaetid copepods, and ostracods. In 2011 when the feeding condition was considered to be favorable, but the habitat temperature was lowest, the IGR of large juveniles was markedly lower than in the other 2 years. Meanwhile, there was no significant difference in the IGR between 2012 and 2013 when the diet composition was markedly different, but habitat temperature was comparable. The present observations indicate that the between‐year difference in juvenile IGR was not explained well by variations in the diet composition. Instead, habitat temperature was concluded to be the more dominant factor causing the observed between‐year differences in the IGR in the southwestern SJ.

Functional and numerical responses of Iphiseius degenerans (Berlese) (Acari: Phytoseiidae) to different biological stages of Eutetranychus orientalis (Klein) (Acari: Tetranychidae)*

Functional and numerical responses of the predatory mite, Iphiseius degenerans (Berlese) (Acari: Phytoseiidae) to four different biological stages (egg, larva, protonymph and adult male) of the citrus brown mite, Eutetranychus orientalis (Klein) (Acari: Tetranychidae) were determined under laboratory conditions. In the experiments, six different prey densities (5, 10, 20, 40, 60 and 80) for each biological stage of the prey were provided to the predatory mite for 24 hours. Results showed that the proportion of prey consumption of I. degenerans decelerated with increasing prey densities of all biological stages of the prey. Logistic regression analysis indicated that I. degenerans showed a Type II functional response regardless of prey stage. The attack rate (α) and the handling time (Th) varied based on the biological stages. The highest α (1.596) and the lowest Th (0.014) values were determined when the predator fed on adult males and larvae of E. orientalis, respectively. The numerical response curves were similar to those of Type II functional response. The efficiency of conversion of ingested food (ECI) of female I. degenerans decreased on all biological stages when prey density increased. The highest and the lowest average daily mean number of eggs laid by I. degenerans were found as 0.45 and 1.90 when it fed on eggs and larvae of its prey, respectively. According to the results, I. degenerans has a potential to be used as a predator in biological control of E. orientalis.

Response of Understory Avifauna to Annual Flooding of Amazonian Floodplain Forests

The annual flooding in the Amazon basin transforms the understory of floodplain forests into an aquatic environment. However, a great number of non-aquatic bird species occupy the understory and midstory of these forests. In general, these birds are thought to be sedentary and territorial, but the way they adapt to this dramatic seasonal transformation has never been described in detail. In this study, we describe avifaunal strategies to cope with seasonal flooding in the lower Purus region, central Amazonia, Brazil. We conducted focal observations of five insectivorous species occupying the lowest forest strata in two types of floodplain forest (black- and whitewater) during the low- and high-water seasons. For each observation, the height of the bird above the substrate (ground or water), its vertical position in the forest, and vegetation density around the bird were noted. All species remained present in the floodplain forests during the two seasons and were not recorded in adjacent unflooded (terra firme) forest. In general, birds migrated vertically to higher forest strata and most species (three of the five) occupied similar vegetation densities independent of water level. Despite the tendency of all species to rise in relative vertical position at high water, there was a reduction in height above substrate for four of the five species, suggesting that their position relative to water was not an important microhabitat element for them. Responses were similar in the two floodplain forest types. It is likely that the decrease in available space during the flood, combined with similar vertical displacement in arthropods, leads to increased prey density for understory insectivorous birds and permits year-round territoriality without major habitat shifts.

Effect of Prey Species and Prey Densities on the Performance of Adult Coenosia attenuata.

Simple SummaryThe predaceous fly Coenosia attenuata Stein has received attention because of its ability to effectively suppress a wide range of agricultural pests, such as fungus gnats, whiteflies and leaf miners. An effective level of control requires large numbers of C. attenuata to be available at low cost for release. Adult fungus gnats and drosophilids are now the main prey used to rear C. attenuata adults. However, previous studies showed C. attenuata fertility is lower when fed drosophilids compared to fungus gnats. The current study investigated the performance of C. attenuata adults when reared on different densities of adult Drosophila melanogaster Meigen or Bradysia impatiens (Johannsem). Results showed that the optimal prey density in the mass rearing of adult C. attenuata was 12–24 adult B. impatiens daily per predator. Additionally, C. attenuata adults suffered more wing damage, at some of the prey densities, when reared on D. melanogaster compared to B. impatiens. This information will be used to optimize rearing methods and decrease the cost of mass rearing in C. attenuata.Mass production of Coenosia attenuata Stein at low cost is very important for their use as a biological control agent. The present study reports the performance of C. attenuata adults when reared on Drosophila melanogaster Meigen or Bradysia impatiens (Johannsem). Different densities (6, 9, 15, 24 and 36 adults per predator) of D. melanogaster or (6, 12, 24, 36 and 48 adults per predator) of B. impatiens were used at 26 ± 1 °C, 14:10 (L:D) and 70 ± 5% RH. The results concluded that C. attenuata adults had higher fecundity, longer longevity and less wing damage when reared on B. impatiens adults compared to D. melanogaster adults. Additionally, C. attenuata adults demonstrated greater difficulty catching and carrying heavier D. melanogaster adults than lighter B. impatiens adults. In this case, 12 to 24 adults of B. impatiens daily per predator were considered optimal prey density in the mass rearing of adult C. attenuata.

Do Gray Whales Count Calories? Comparing Energetic Values of Gray Whale Prey Across Two Different Feeding Grounds in the Eastern North Pacific

Predators must consume enough prey to support costly events, such as reproduction. Meeting high energetic requirements is particularly challenging for migrating baleen whales as their feeding seasons are typically restricted to a limited temporal window and marine prey are notoriously patchy. We assessed the energetic value of the six most common nearshore zooplankton species collected within the Oregon, United States range of the Pacific Coast Feeding Group (PCFG) gray whale (Eschrichtius robustus) feeding grounds, and compared these results to the energetic value of the predominant amphipod species fed on by Eastern North Pacific (ENP) gray whales in the Arctic. Energetic values of Oregon zooplankton differed significantly between species (Kruskal–Wallis χ2= 123.38, df = 5,p< 0.0001), with Dungeness crab (Cancer magister) megalopae displaying the highest mean caloric content of all tested species (4.21 ± 1.27 kJ g– 1). This value, as well as the mean energetic value of the mysidNeomysis rayii(2.42 ± 1.06 kJ g– 1), are higher than the mean caloric content ofAmpelisca macrocephala, the predominant Arctic amphipod. Extrapolations of these results to daily energetic requirements of gray whales indicate that lactating and pregnant gray whales feeding in the PCFG range would require between 0.7–1.03 and 0.22–0.33 metric tons of prey less per day if they fed on Dungeness crab megalopae orN. rayii, respectively, than a whale feeding onA. macrocephalain the Arctic. Yet, these results do not account for differences in availability of these prey species to foraging gray whales. We therefore suggest that other factors, such as prey density, energetic costs of feeding, or natal philopatry and foraging site fidelity play a role in the differences in population sizes between the PCFG and ENP gray whales. Climate change is implicated in causing reduced body condition and increased mortality of both PCFG and ENP gray whales due to decreased prey availability and abundance. Therefore, improved understanding of prey dynamics in response to environmental variability in both regions is critical.

Habitat selection by wolves and mountain lions during summer in western Montana.

In the Northern Rockies of the United States, predators like wolves (Canis lupus) and mountain lions (Puma concolor) have been implicated in fluctuations or declines in populations of game species like elk (Cervus canadensis) and mule deer (Odocoileus hemionus). In particular, local distributions of these predators may affect ungulate behavior, use of space, and dynamics. Our goal was to develop generalizable predictions of habitat selection by wolves and mountain lions across western Montana. We hypothesized both predator species would select habitat that maximized their chances of encountering and killing ungulates and that minimized their chances of encountering humans. We assessed habitat selection by these predators during summer using within-home range (3rd order) resource selection functions (RSFs) in multiple study areas throughout western Montana, and tested how generalizable RSF predictions were by applying them to out-of-sample telemetry data from separate study areas. Selection for vegetation cover-types varied substantially among wolves in different study areas. Nonetheless, our predictions of 3rd order selection by wolves were highly generalizable across different study areas. Wolves consistently selected simple topography where ungulate prey may be more susceptible to their cursorial hunting mode. Topographic features may serve as better proxies of predation risk by wolves than vegetation cover-types. Predictions of mountain lion distribution were less generalizable. Use of rugged terrain by mountain lions varied across ecosystem-types, likely because mountain lions targeted the habitats of different prey species in each study area. Our findings suggest that features that facilitate the hunting mode of a predator (i.e. simple topography for cursorial predators and hiding cover for stalking predators) may be more generalizable predictors of their habitat selection than features associated with local prey densities.

Integrated assessments call for establishing a sustainable meta-population of Amur tigers in northeast Asia

With most large carnivore populations and habitats suffering massive declines across the world, efforts to restore their populations in the wild are of high conservation priority. China attaches great importance to protecting Amur tigers and has made considerable progress towards this goal, but most efforts have been focused on the single Laoyeling landscape. Here we assess all four major forested landscapes (including Laoyeling, Zhangguangcailing, Wandashan and Lesser Khinghan Mountains) that may be suitable for tigers in northeast China. Between 2013 and 2018, in total 55 wild Amur tigers were recorded through camera trap surveys and 30 individuals were identified through genetic analyses. The finite rate of increase of the population in the Laoyeling landscape, the only landscape with a breeding population, fluctuated greatly, but averaged 1.51. Total habitat used by Amur tigers during this period amounted to 47,813 km2. We estimated that based on density and home range sizes in nearby Russia, these landscapes could support 310 tigers, including 119 resident breeding females. However, prey density, especially of preferred prey, was extremely low, and likely a primary constraint to population recovery in landscapes other than Laoyeling, especially the Wandashan and Lesser Khingan Mountains landscapes. To achieve the goal of a large meta-population of Amur tigers across northeast Asia, in addition to prey restoration, we recommend extensive landuse planning, reducing anthropogenic impacts, improving ecology connectivity, and extensive international cooperation, as well as a feasibility assessment for introducing orphaned cubs as a means of speeding recovery in landscapes without breeding females.

A bioenergetics model for seasonal growth of Indian oil sardine (Sardinella longiceps) in the Indian west coast

The Indian oil sardine (Sardinella longiceps) fishery was observed with wide stock fluctuation. Ecological parameters, mainly temperature and prey density, had a profound influence on the growth of S. longiceps and hence the production. In this study, a fish bioenergetics model, coupled with a lower trophic level model, was developed to reproduce the seasonality in the growth of S. longiceps. For this, we have used an Indian Ocean adaptation of an intermediate complex ecosystem model called North Pacific Ecological Modeling for Understanding Regional Oceanography (NEMURO) for marine productivity simulations. The model has 11-component ecosystem variables such as two types of phytoplankton (small and large including flagellates and diatoms), three types of zoo-planktons (small, large, and predatory, which includes ciliates, copepods, and euphausiids), particulate and dissolved organic matter, opal, cycling of nitrate, ammonia, and silicate. The prey densities derived from the NEMURO were input to the sardine bioenergetics model. The coupled model reproduced the appropriate growth rate and wet-weight of S. longiceps in its seasonal cycle in four major fishery regions such as Kochi, Goa, Ratnagiri, and Mumbai as verifiable from the available observation. In Kochi, the mean wet weight was 72.0 ± 12.8 g (June to September), 65.4 ± 5.3 g (October to November), 82.4 ± 2.7 g (December to February), and 66.7 ± 3.8 g (March to May). Goa and Ratnagiri have moderate weights with mean wet weight as 73.6 ± 10.6 g (June to September), 87.4 ± 3.2 g (October to November), 95.5 ± 4.3 g (December to February), and 76.2 ± 6.8 g (March to May). In the Mumbai region, maximum weight is simulated with mean wet weight as 97.4 ± 13.3 g (June to September), 102.1 ± 1.6 g (October to November), 104.8 ± 1.3 g (December to February), and 101.6 ± 1.2 g (March to May). Sensitivity analysis revealed the importance of temperature and consumption in the growth of sardine. Detailed model validation with available observations is presented.

Positive species interactions strengthen in a high-CO2 ocean.

Negative interactions among species are a major force shaping natural communities and are predicted to strengthen as climate change intensifies. Similarly, positive interactions are anticipated to intensify and could buffer the consequences of climate-driven disturbances. We used in situ experiments at volcanic CO2 vents within a temperate rocky reef to show that ocean acidification can drive community reorganization through indirect and direct positive pathways. A keystone species, the algal-farming damselfish Parma alboscapularis, enhanced primary productivity through its weeding of algae whose productivity was also boosted by elevated CO2. The accelerated primary productivity was associated with increased densities of primary consumers (herbivorous invertebrates), which indirectly supported increased secondary consumers densities (predatory fish) (i.e. strengthening of bottom-up fuelling). However, this keystone species also reduced predatory fish densities through behavioural interference, releasing invertebrate prey from predation pressure and enabling a further boost in prey densities (i.e. weakening of top-down control). We uncover a novel mechanism where a keystone herbivore mediates bottom-up and top-down processes simultaneously to boost populations of a coexisting herbivore, resulting in altered food web interactions and predator populations under future ocean acidification.

Direct evidence of a prey depletion “halo” surrounding a pelagic predator colony

Colonially breeding birds and mammals form some of the largest gatherings of apex predators in the natural world and have provided model systems for studying mechanisms of population regulation in animals. According to one influential hypothesis, intense competition for food among large numbers of spatially constrained foragers should result in a zone of prey depletion surrounding such colonies, ultimately limiting their size. However, while indirect and theoretical support for this phenomenon, known as "Ashmole's halo," has steadily accumulated, direct evidence remains exceptionally scarce. Using a combination of vessel-based surveys and Global Positioning System tracking, we show that pelagic seabirds breeding at the tropical island that first inspired Ashmole's hypothesis do indeed deplete their primary prey species (flying fish; Exocoetidae spp.) over a considerable area, with reduced prey density detectable >150 km from the colony. The observed prey gradient was mirrored by an opposing trend in seabird foraging effort, could not be explained by confounding environmental variability, and can be approximated using a mechanistic consumption-dispersion model, incorporating realistic rates of seabird predation and random prey dispersal. Our results provide a rare view of the resource footprint of a pelagic seabird colony and reveal how aggregations of these central-place foraging, marine top predators profoundly influence the oceans that surround them.

Predation of mosquitos by odonates in a tropical urban environment: insights from functional response and field mesocosm experiments

Mosquito borne diseases (e.g., dengue fever, Zika fever, chikungunya fever) are a recurring problem worldwide. Using the natural predators of mosquitoes, such as odonates (dragonflies and damselflies), provides an alternative, more sustainable approach towards vector control. We assessed the biological control potential of the larvae of three common urban odonates (Crocothemis servilia, Ischnura senegalensis, Orthetrum sabina) using laboratory-based functional response and field-based mesocosm experiments. Functional response experiments using fourth instar Aedes albopictus mosquito larvae as prey revealed Type II functional responses in all three odonate species, highlighting their predatory efficiencies at low prey densities and demonstrating that urban odonates can consume substantial numbers of mosquito larvae (up to 44 per day) under experimental conditions. Complementary field-based experiments, however, showed little impact of odonate larvae predation on the overall composition of naturally colonizing aquatic macroinvertebrate communities, but revealed substantial size-selective predation by odonate larvae on mosquito larvae. Our results provide the first assessment of the predation efficiencies of urban odonate larvae, and highlight their potential as biological control agents of mosquitoes and other aquatic insect pests in highly modified urban landscapes.

Delay-induced patterns in a reaction–diffusion system on complex networks

Pattern formations in reaction–diffusion (RD) systems with time delay constitute a vital class of dynamical mechanisms extensively investigated for biological and chemical processes, where Hopf bifurcation usually occurs. Recent studies show that pattern formations differ significantly between RD systems with large-time and small-time delay. Therefore, in this paper, we aim to explore the exact role of the time delay in RD systems based on complex networks, which would affect the form of patterns. Depicting networked dynamics of the predator–prey system by a set of RD equations, it is found that boundaries of Hopf bifurcation are decided by diffusion coefficients, as well as the Eigen-spectra of networks. We also obtain mathematical expressions of the boundaries in both large-time and small-time delay cases. Through extensive simulations, it is unveiled that the connectivity structures of networks hardly have impact on the trend of evolutionary processes. Compared to large-time delay cases, the oscillation cycle of average prey density becomes shorter red with small-time delay, and the oscillation amplitude also decreases. We finally reveal the evolution process of the prey density and discover the thick-tailed phenomenon in large-time delay cases.

When carnivores collide: a review of studies exploring the competitive interactions between bobcatsLynx rufusand coyotesCanis latrans

AbstractBobcatsLynx rufusand coyotesCanis latransare two widespread mesopredators with a complex history of sympatry. The competitive interactions between these species are of interest to biologists due to the furbearer status of bobcats, the recent range expansion of coyotes, and the recolonisation of several parts of North America by bobcats following their extirpation. Although studies exploring the dynamics and competition between bobcats and coyotes span decades, there is a lack of understanding regarding what factors influence exploitative or interference competition, and what methodologies are conducive to identifying these types of competition.We gathered a comprehensive list of research papers (n = 41) exploring bobcat–coyote competitive interactions in North America. From them, we collected the following: study site characteristics, number and types of research methods, number and types of metrics explored, history of sympatry of the two species at the study location, presence of apex predators, and documentation of interference and/or exploitative competition.Using generalised linear models, we determined that interference competition between bobcats and coyotes was observed primarily in open habitat. However, habitat heterogeneity, the number of research methods and metrics used, presence of an apex predator, and history of sympatry could not be used to predict the occurrence of interference competition. Studies that included diet overlap were less likely to observe interference competition than studies that used other metrics to infer competition.Competitive interactions between coyotes and bobcats are largely a function of prey availability. Our findings suggest that habitat type may be a surrogate for prey availability, which many researchers mention, but do not explicitly measure. Future studies investigating bobcat–coyote interactions should include the quantification of prey densities to gain a more comprehensive understanding of the system at large, and should avoid using solely diet or habitat overlap as metrics to assess competition.

Metabolic Reliance on Photosynthesis Depends on Both Irradiance and Prey Availability in the Mixotrophic Ciliate, Strombidium cf. basimorphum.

Many species of the ciliate genus Strombidium can acquire functional chloroplasts from a wide range of algal prey and are thus classified as generalist non-constitutive mixotrophs. Little, however, is known about the influence of irradiance and prey availability on their ability to exploit the photosynthetic potential of the chloroplasts, and how this may explain their spatial and temporal distribution in nature. In this study, inorganic carbon uptake, growth, and ingestion rates were measured for S. cf. basimorphum under three different irradiances (10, 40, and 120 μmol photons m–2 s–1) when acclimated to three different prey densities (5 × 103, 1 × 104, and 4 × 104 cells mL–1), as well as when allowed to deplete the prey. After prey depletion, cultures survived without prey longest (∼6 days) at the medium irradiance treatment (40 μmol photons m–2 s–1), while ciliate density, inorganic carbon uptake rates, and cellular chl-a content declined fastest at the highest irradiance treatment. This indicates that the ciliates may be unable to maintain the chloroplasts functionally without replacement at high irradiances. Ingestion rates were not shown to be significantly influenced by irradiance. The maximum gross growth efficiency (GGE) in this study (1.1) was measured in cultures exposed to the medium test irradiance and lowest prey density treatment (5 × 103 cells mL–1). The relative contribution of inorganic carbon uptake to the ciliate carbon budget was also highest in this treatment (42%). A secondary GGE peak (0.99) occurred when cultures were exposed to the highest test irradiance and the medium prey density. These and other results suggest that S. cf. basimorphum, and other generalist non-constitutive mixotrophs, can flexibly exploit many different environmental conditions across the globe.

Do fine-scale experiments underestimate predator consumption rates?

Understanding ecological processes across spatial scales helps link observations and predictions from experiments to ecological patterns occurring at coarser scales relevant to management and conservation. Using fish, we experimentally manipulated the size of arenas to test the spatial scaling of predator-prey interactions. We measured variation in predator consumption and prey behaviour (prey aggregation, spatial overlap with predators and movement) across arena sizes. Variation in prey behaviour across arena sizes was hypothesized to drive consumption patterns by altering prey vigilance and encounter rates with predators. Per capita consumption and movement were highest in the largest arena relative to the smallest and we observed a mismatch between where bass were present and the highest densities of prey across all arena sizes. We hypothesize more movement in largest arenas increased encounter rates and drove the observed increase in consumption with increasing arena size. Consumption estimates obtained in experimental studies may underestimate consumption, but understanding the mechanisms driving bias across scales helps predict the outcomes of predator-prey interactions in natural systems.

Poaching Threatens the Establishment of a Lynx Population, Highlighting the Need for a Centralized Judiciary Approach

Illegal hunting represents a major threat to the conservation of predators, but its impact remains difficult to assess as there are strong incentives to conceal this criminal activity. Attributing declines of carnivores to poaching is therefore an important conservation challenge. We present a case study of the Eurasian lynx (Lynx lynx) in the Swiss Alps (Valais) where the current distribution range is smaller than in the recent past and population density is by ≥80% lower than in the adjacent Swiss Prealps. We tested four hypotheses to explain this lower density: (1) a too low density of camera-traps deployed for lynx surveys in Valais compared to the Prealps (methodological artifact); (2) less favorable environmental conditions around the camera-trap sites; (3) lower densities of the main prey; and (4) poaching. We estimated lynx and ungulate densities and environmental conditions at trail camera sites and could clearly reject the first three hypotheses because: (1) the survey protocol was similarly effective; (2) environmental conditions around the trapping sites in Valais were even more favorable for lynx detection than in the Prealps; and (3) prey supply was even larger in Valais. Concerning hypothesis 4, we discovered a network of illegal lynx traps (neck snares) in the main immigration corridor into Valais from the thriving adjacent lynx population in the Prealps, suggesting intense local poaching. Our findings substantiate the suspicions of long-lasting lynx poaching as a threat to the establishment and survival of the Valais population. The fact that instances of poaching were publicly known since 1995 but remained unabated for at least two decades, until the first conviction occurred, questions the commitment of local authorities to address this case of wildlife crime. Our study demonstrates the need for inquiries about poaching of top predators to be carried out at the highest levels of jurisdiction to avoid any risk of collusion between law enforcement agents and poachers.

Effects of incubation and gestation periods in a prey–predator model with infection in prey

In this paper, we study a wide spectrum of dynamical features of a prey–predator model with infection in prey population only. In the model formulation, we consider nonlinear incidence for infection transmission and Holling type II as response function of predator. We analyze the model for local stability and Hopf bifurcation, and the theoretical results are validated and extrapolated by numerical simulations. Also, we perform sensitivity analysis to explore the significance of the crucial parameters influencing the densities of prey and predator populations. Our numerical results show that disease persists in the system even if the basic reproduction number is below unity. The rates of predation on susceptible and infected prey populations are shown to dramatically change the behavior of eco-epidemiological system. We extend our model by considering the fact that the newly infected prey becomes productively infectious after the effective contact between susceptible and infectious preys, and some time lag is involved in this biological process; also the conversion process conceals some time. We analyze our eco-epidemiological model with two time delays (incubation delay and predator’s gestation delay) for stability and bifurcation. From numerical simulations, we observe that both the delay parameters substantially affect the stable configuration of the system.