Distribution Of Predators Research Articles

Habitat modelling of tracking data from multiple marine predators identifies important areas in the Southern Indian Ocean

AbstractAimThe distribution of marine predators is driven by the distribution and abundance of their prey; areas preferred by multiple marine predator species should therefore indicate areas of ecological significance. The Southern Ocean supports large populations of seabirds and marine mammals and is undergoing rapid environmental change. The management and conservation of these predators and their environment relies on understanding their distribution and its link with the biophysical environment, as the latter determines the distribution and abundance of prey. We addressed this issue using tracking data from 14 species of marine predators to identify important habitat.LocationIndian Ocean sector of the Southern Ocean.MethodsWe used tracking data from 538 tag deployments made over a decade at the Subantarctic Prince Edward Islands. For each real track, we simulated a set of pseudo‐tracks that allowed a presence‐availability habitat modelling approach that estimates an animal's habitat preference. Using model ensembles of boosted regression trees and random forests, we modelled these tracks as a response to a set of 17 environmental variables. We combined the resulting species‐specific models to evaluate areas of mean importance.ResultsReal tracking locations covered 39.75 million km2, up to 7,813 km from the Prince Edward Islands. Areas of high mean importance were located broadly from the Subtropical Zone to the Polar Frontal Zone in summer and from the Subantarctic to Antarctic Zones in winter. Areas of high mean importance were best predicted by factors including wind speed, sea surface temperature, depth and current speed.Main conclusionsThe models and predictions developed here identify important habitat of marine predators around the Prince Edward Islands and can support the large‐scale conservation and management of Subantarctic ecosystems and the marine predators they sustain. The results also form the basis of future efforts to predict the consequences of environmental change.

Spatial separation without territoriality in shark communities

Spatial separation within predator communities can arise via territoriality but also from competitive interactions among and within species. However, linking competitive interactions to predator distribution patterns is difficult and theoretical models predict different habitat selection patterns dependent on habitat quality and how competition manifests itself. While models generally consider competitors to be either equal in ability, or for one phenotype to have a fixed advantage over the other, few studies consider that an animal may only have a competitive advantage in specific habitats. We used  10 years of telemetry data, habitat surveys and behavioral experiments, to show spatial partitioning between and within two species of reef shark (grey reef Carcharhinus amblyrhinchos and blacktip reef sharks C. melanopterus) at an unfished Pacific atoll. Within a species, sharks remained within small ‘sub‐habitats’ with very few movements of individuals between sub‐habitats, which previous models have suggested could be caused by intra‐specific competition. Blacktip reef sharks were more broadly distributed across habitat types but a greater proportion used lagoon and backreef habitats, while grey reef sharks preferred forereef habitats. Grey reef sharks at a nearby atoll where blacktip reef sharks are absent, were distributed more broadly between habitat types than when both species were present. A series of individual‐based models predict that habitat separation would only arise if there are competitive interactions between species that are habitat‐specific, with grey reefs having a competitive advantage on the forereefs and blacktips in the lagoons and backreef. We provide compelling evidence that competition helps drive distribution patterns and spatial separation of a marine predator community, and highlight that competitive advantages may not be constant but rather dependent on habitats.

Predators and parasitoids of rice insect pests under rice ecosystems of Manipur valley

Field surveys on predators and parasitoids of rice ecosystem during kharif season (2012–2014) in the four valley districts (Imphal East, Imphal West, Thoubal and Bishnupur) of Manipur were conducted. Altogether 33 species of predators belonging to 26 genera under 15 families of 5 orders and 15 species of parasitoids belonging to 5 families of Hymenoptera were listed. Among the predators, spider (Pardosa pseudoannulata Boes et. str. Tetragnatha maxillosa Thorell and Oxyopes javanus Thorell), damselflies (Agriocnemis femina Brauer, Agriocnemis pygmeae Rambur and Ishnura aurora Hagen), and dragonflies (Orthetrum sabina Drury and Sympetrum sp.) were found as dominant species. In case of parasitoids Cotesia rufricus Haliday and Apanteles sp. were found to be dominant in all the rice fields. One way ANOVA was done to evaluate the variation in the distribution of predators and parasitoids among the four study sites: among the predators, spider was found to be dominating (73.0) over other groups in Site 4 (Bishnupur District) whereas among the parasitoids, Cotesia rufricus (11.0) was dominating in Site 1 (Imphal East). The data revealed the significant variation in the distribution of predators and parasitoids (p<0.01). It was also observed that spiders existed with maximum density in all the four sites (57.4–73.0) while among the parasitoids, Cotesia rufricus was observed with maximum density (5.4–11.0).

Home range and foraging habitat preference of Scopoli's shearwater Calonectris diomedea during the early chick‐rearing phase in the eastern Mediterranean

Pelagic seabirds that breed colonially are central‐place foragers; their spatial distribution is restricted to marine areas around their colonies during the chick‐rearing period, when attendance and food provision to their chicks has to be intense. In this study we analyzed the foraging trips of 11 Scopoli's shearwater Calonectris diomedea breeders that were tagged with GPS data loggers during 2014 in oligotrophic waters (Ionian Sea, western Greece), and assessed the range and oceanographic parameters of their foraging habitat. Contrary to previous findings suggesting a varying foraging strategy depending on the breeding stage, the tracked shearwaters made short trips, less than 4 days long, in the vicinity of the colony. By applying the Adaptive Kernel method, their 50% and 95% foraging range was estimated at 6871 km2 and 23 014 km2 respectively. In addition, generalized additive models showed that sea surface temperature (&lt;25.5°C), minimum distance from the colony (&lt;100 km), fishing pressure index from small scale fisheries (medium values) along with a two‐dimensional soap film smoother for space (easting, northing) were the most significant factors affecting at‐sea distribution of this marine top predator during the early chick‐rearing period (i.e. 99.9% of the final model deviance). Our study will contribute to the revision of the boundaries of the local Special Protection Area (SPA) of Strofades. It will also address the implementation of specific conservation measures for the species at regional and national scale, and the development of a management plan for the protection of the study area.

Changes in future potential distributions of apex predator and mesopredator mammals in North America

Climate change has determined shifts in distributions of species and changing climates are likely to continue to affect species in the future. In this study, we used Maxent, an ecological niche modeling algorithm, to estimate the potential future distributions of apex predator and mesopredator mammals in boreal forest and tundra biomes of North America. We projected the climatic niche models of apex predators and mesopredators on future climate datasets based on three global circulation models (Beijing Climate Center Climate System Model, Hadley Global Environment Model, and Model for Interdisciplinary Research on Climate Earth System Model) and four greenhouse gas emission scenarios (RCP2.6, RCP4.5, RCP6, and RCP8.5). Under future climate projections, the potential distributions of most of the predators studied increased by 2050 and 2070. The potential distributions of two apex predators (brown bear, Ursus arctos, and polar bear, U. maritimus) and two mesopredator species (Canadian lynx, Lynx canadensis, and Arctic fox, Vulpes lagopus) were predicted to decline under all emission scenarios, by 2050 and 2070. The only apex predator that was predicted to increase its distribution under all greenhouse gas emission scenarios was U. americanus (American black bear). Similarly, distributions of mesopredators like Mephitis mephitis (striped skunk), and Procyon lotor (raccoon) were predicted to increase greatly under future climate conditions of all four emission scenarios. Predicted expansions of distribution ranges of most mesopredators and contractions of distribution ranges of apex predators included in this study may result in changes of species interactions in North American boreal forests and tundras in the future.

Stationary distribution and extinction of a stochastic predator–prey model with distributed delay

In this paper, we focus on a stochastic predator–prey model with distributed delay. We first obtain the existence of a stationary distribution to the positive solutions by stochastic Lyapunov function method. Then we establish sufficient conditions for extinction of the predator population, that is, the prey population is survival and the predator population is extinct.

Stationary distribution and extinction of a stochastic predator–prey model with additional food and nonlinear perturbation

In this paper, we formulate and analyze a stochastic predator–prey model with additional food and nonlinear perturbation. Firstly, by constructing a suitable stochastic Lyapunov function, we establish sufficient conditions for the existence of an ergodic stationary distribution of the positive solution to the model. Then we obtain sufficient conditions for extinction of the predator species in two cases, one is the prey species surviving and the predator species extinction; the other is both the prey and predator species are extinct. Finally, some examples together with numerical simulations are provided to illustrate the analytical results.

Noise shapes the distribution pattern of an acoustic predator

Noise, an obvious effect of urbanization, has a negative impact on animal vocalizations and the hunting efficiency of acoustic predators. However, the influence of noise pollution on the spatial distribution of populations remains understudied. The aim was to assess the factors shaping the distribution pattern of an acoustic predator (long-eared owl Asio otus) in an urban–farmland matrix. We hypothesized that the probability of an acoustic predator occurring decreases with growing nocturnal noise emission. This owl survey was conducted in Kraków (S Poland) on 79 randomly selected sample plots (1 km × 1 km). Six habitat variables (area of parks, woodlands, grassland, arable land, habitat diversity index, and noise pollution) were identified and correlated with the probability of the species’ occurrence. Proximity to pedestrian routes and roads, habitat fragmentation, and noise intensity was also defined at nest sites and random sites. Long-eared owls occurred on 37% of the sample plots. Occupied plots had a greater area of grassland and arable land as well as a lower level of noise pollution than the unoccupied ones. A multivariate model revealed that area of grassland and nocturnal noise emission was significantly correlated with the probability of long-eared owls occurring and that the high probability of occurrence recorded on plots with large areas of grassland was reduced by noise pollution. The noise intensity recorded at nest sites was also significantly lower than at random sites. This study suggests that apart from habitat factors, the distribution of acoustic predators in an urban matrix is driven by noise pollution. This highlights the importance of proper landscape management, that is, maintaining large grassland areas and preventing noise from increasing within them.

Biogeography of seabirds within a high-latitude ecosystem: Use of a data-assimilative ocean model to assess impacts of mesoscale oceanography

Abstract We assessed the biogeography of seabirds within the Bering Sea Large Marine Ecosystem (LME), a highly productive and extensive continental shelf system that supports important fishing grounds. Our objective was to investigate how physical ocean conditions impact distribution of seabirds along latitudinal gradients. We tested the hypothesis that seabird biogeographic patterns reflect differences in ocean conditions relating to the boundary between northern and southern shelf ecosystems. We used a grid-based approach to develop spatial means (1975–2014) of summertime seabird species' abundance, species' richness, and a multivariate seabird assemblage index to examine species composition. Seabird indices were linked to ocean conditions derived from a data-assimilative oceanographic model to quantify relationships between physics (e.g., temperature, salinity, and current velocity), bathymetry and seabirds along latitudinal gradients. Species assemblages reflected two main sources of variation, a mode for elevated richness and abundance, and a mode related to partitioning of inner/middle shelf species from outer shelf-slope species. Overall, species richness and abundance increased markedly at higher latitudes. We found that latitudinal changes in species assemblages, richness and abundance indicates a major shift around 59–60°N within inner and middle shelf regions, but not in the outer shelf. Within the middle shelf, latitudinal shifts in seabird assemblages strongly related to hydrographic structure, as opposed to the inner and outer shelf waters. As expected, elevated species richness and abundance was associated with major breeding colonies and within important coastal foraging areas. Our study also indicates that seabird observations supported the conclusion that the oceanographic model captured mesoscale variability of ocean conditions important for understanding seabird distributions and represents an important step for evaluating modeling and empirical studies. Biogeographic assessments of LMEs that integrate top predator distributions resolve critical habitat requirements and will benefit assessment of climate change impacts (e.g., sea-ice loss) predicted to affect high-latitude marine ecosystems.

Generation and maintenance of predation hotspots of a functionally important herbivore in a patchy habitat mosaic

Abstract By modifying how critical ecosystem functions are distributed across the landscape, the spatial configuration and characteristics of patches can play a strong role in structuring communities. In strongly predator‐controlled ecosystems, this patchy distribution of function can have complex downstream consequences, subjecting some areas to disproportionately high rates of predation, leaving other areas susceptible to herbivore outbreaks. In this study, we assess how spatial attributes at patch and landscape scales potentially influence the spatial and temporal distribution of predation on a functionally important herbivore in a patchy Mediterranean marine macrophyte community characterized by strong top‐down control. We experimentally tracked how predation risk of tethered sea urchins varied across space over a 10‐day period in a patchy seagrass meadow. We related these patterns with patch and landscape‐level attributes across the habitat mosaic. At the level of the patch, predation risk was the highest in seagrass patches with low canopies, without access to sheltering rocks. Scaling up to the landscape mosaic however, predation risk increased in dense aggregations of patches with high perimeter‐to‐area ratios close to rocky habitats. Predation aggregated in spatially explicit hotspots and coldspots that were maintained through time. Interestingly, this pattern of predation risk correlated well with the natural abundance of sea urchins. Our results show that spatial patch configuration can be a strong mediator of top trophic functions in marine ecosystems, causing significant clumping in the way predation—and therefore herbivory—are distributed across space. Given the importance of top‐down control for these shallow marine ecosystems, it is crucial to incorporate landscape attributes in understanding the impact of functionally important herbivores on highly fragmented habitats. A plain language summary is available for this article.

Correction: Drivers of abundance and spatial distribution of reef-associated sharks in an isolated atoll reef system.

[This corrects the article DOI: 10.1371/journal.pone.0177374.].

Periodic Solution and Stationary Distribution of Stochastic Predator–Prey Models with Higher-Order Perturbation

In this paper, two stochastic predator–prey models with general functional response and higher-order perturbation are proposed and investigated. For the nonautonomous periodic case of the system, by using Khasminskii’s theory of periodic solution, we show that the system admits a nontrivial positive T-periodic solution. For the system disturbed by both white and telegraph noises, sufficient conditions for positive recurrence and the existence of an ergodic stationary distribution to the solutions are established. The existence of stationary distribution implies stochastic weak stability to some extent.

Ecosystem variability in the offshore northeastern Chukchi Sea

Understanding influences of cumulative effects from multiple stressors in marine ecosystems requires an understanding of the sources for and scales of variability. A multidisciplinary ecosystem study in the offshore northeastern Chukchi Sea during 2008–2013 investigated the variability of the study area’s two adjacent sub-ecosystems: a pelagic system influenced by interannual and/or seasonal temporal variation at large, oceanographic (regional) scales, and a benthic-associated system more influenced by small-scale spatial variations. Variability in zooplankton communities reflected interannual oceanographic differences in waters advected northward from the Bering Sea, whereas variation in benthic communities was associated with seafloor and bottom-water characteristics. Variations in the planktivorous seabird community were correlated with prey distributions, whereas interaction effects in ANOVA for walruses were related to declines of sea-ice. Long-term shifts in seabird distributions were also related to changes in sea-ice distributions that led to more open water. Although characteristics of the lower trophic-level animals within sub-ecosystems result from oceanographic variations and interactions with seafloor topography, distributions of apex predators were related to sea-ice as a feeding platform (walruses) or to its absence (i.e., open water) for feeding (seabirds). The stability of prey resources appears to be a key factor in mediating predator interactions with other ocean characteristics. Seabirds reliant on highly-variable zooplankton prey show long-term changes as open water increases, whereas walruses taking benthic prey in biomass hotspots respond to sea-ice changes in the short-term. A better understanding of how variability scales up from prey to predators and how prey resource stability (including how critical prey respond to environmental changes over space and time) might be altered by climate and anthropogenic stressors is essential to predicting the future state of both the Chukchi and other arctic systems.

Predator–prey interactions influenced by a dynamic river plume

Marine predator–prey interactions are often influenced by oceanographic processes that aggregate prey. We examined density distributions of seabirds and prey fish associated with the Columbia River plume to determine whether variation in plume size (i.e., volume or surface area) or location influences predator–prey interactions. Common murre (Uria aalge), sooty shearwater (Ardenna grisea), and forage fish, including northern anchovy (Engraulis mordax) and juvenile salmon (Oncorhynchus spp.), occurred disproportionately in plume waters relative to adjacent marine waters. Water clarity, an indicator of plume-influenced waters, was a significant predictor of seabird and prey densities throughout the survey area. Murres occurred within 20 km of the plume center of gravity, whereas shearwaters occurred ∼100 km north of the plume center of gravity, concurrent with the highest densities of prey fish. Global indices of collocation were relatively low between murres and prey compared with the high values between shearwaters and prey. Seabird densities were negatively correlated with plume size, suggesting that seabirds concentrate in the plume to maximize foraging effort. We conclude that variation in Columbia River plume size and location influences predator distributions, which increases predation pressure on prey, including threatened salmonid species.

Stable isotope analyses of feather amino acids identify penguin migration strategies at ocean basin scales.

Identifying the at-sea distribution of wide-ranging marine predators is critical to understanding their ecology. Advances in electronic tracking devices and intrinsic biogeochemical markers have greatly improved our ability to track animal movements on ocean-wide scales. Here, we show that, in combination with direct tracking, stable carbon isotope analysis of essential amino acids in tail feathers provides the ability to track the movement patterns of two, wide-ranging penguin species over ocean basin scales. In addition, we use this isotopic approach across multiple breeding colonies in the Scotia Arc to evaluate migration trends at a regional scale that would be logistically challenging using direct tracking alone.

Behavioral mechanisms leading to improved fitness in a subsidized predator.

General mechanisms underlying the distribution and fitness of synanthropic predators in human-influenced landscapes remain unclear. Under the consumer resource-matching hypothesis, synanthropes are expected to distribute themselves among habitats according to resource availability, such that densities are greater in human-subsidized habitats, but mean individual fitness is equal among habitats because of negative density dependence. However, "under-matching" to human food resources can occur, because dominant individuals exclude subordinates from subsidized habitats and realize relatively high fitness. We integrated physiological, behavioral, and demographic information to test resource-matching hypotheses in Steller's jays (Cyanocitta stelleri), a synanthropic nest predator, to understand how behavior and social systems can influence how synanthropes respond to food subsidies. Jays consumed more human foods at subsidized (park campground) sites than jays at unsubsidized (interior forest) sites based on stable isotope analyses. Jays that occurred at higher densities were in better body condition (based on feather growth bars and lipid analyses), and had greater reproductive output at subsidized than unsubsidized sites. Jays with breeding territories in subsidized sites maintained relatively small home ranges that overlapped with multiple conspecifics, and exhibited a social system where dominant individuals typically won contests over food. Thus, jays appeared to be under-matched to prevalent resource subsidies despite high densities and behaviors expected to lead to resource matching. Our results also indicate that local resource subsidies within protected areas can result in source habitats for synanthropes, potentially impacting sensitive species over broader spatial scales.

Modeling changes in predator functional response to prey across spatial scales

Extrapolation of predator functional responses from laboratory observations to the field is often necessary to predict predation rates and predator-prey dynamics at spatial and temporal scales that are difficult to observe directly. We use a spatially explicit individual-based model to explore mechanisms behind changes in functional responses when the scale of observation is increased. Model parameters were estimated from a predator-prey system consisting of the predator Delphastus catalinae (Coleoptera: Coccinellidae) and Bemisia tabaci biotype B (Hemiptera: Aleyrodidae) on tomato plants. The model explicitly incorporates prey and predator distributions within single plants, the search behavior of predators within plants, and the functional response to prey at the smallest scale of interaction (within leaflets) observed in the laboratory. Validation revealed that the model is useful in scaling up from laboratory observations to predation in whole tomato plants of varying sizes. Comparing predicted predation at the leaflet scale, as observed in laboratory experiments, with predicted predation on whole plants revealed that the predator functional response switches from type II within leaflets to type III within whole plants. We found that the magnitude of predation rates and the type of functional response at the whole plant scale are modulated by (1) the degree of alignment between predator and prey distributions and (2) predator foraging behavior, particularly the effect of area-concentrated search within plants when prey population density is relatively low. The experimental and modeling techniques we present could be applied to other systems in which active predators prey upon sessile or slow-moving species.

Opportunistic top predators partition food resources in a tropical freshwater ecosystem

Abstract The structure of food webs may be strongly influenced by the distribution of top predators in space and time. The Amazon biome is the only region in the world where four alligatorid species are known to occur in sympatry, and they attain high densities in some regions. As top predators with a diverse range of prey species occupying different trophic levels, their impact upon food webs should be substantial, but the degree to which crocodilians differ in their food sources, and potentially avoid competitive exclusion where they occur syntopically is not well understood. Although most crocodilians are considered generalist opportunistic predators that feed on any source of protein available in the environment, Amazonian crocodilians show broad differences in the proportions of prey items they consume. It is believed that these differences may in part reflect habitat use, but it is unknown to what extent they represent interspecific differences in prey preferences or are a direct function of habitat selection. Stable carbon isotope data (δ13C) of crocodilians and their potential prey were used to assess differences in reliance on terrestrial versus aquatic resources. These data were then placed in a spatial context using classified maps that reflect habitat types (headwater streams, mid‐order flooded‐forest streams and várzea floodplains) to elucidate whether dietary differences are explained by habitat selection or are more likely a reflection of prey preferences. We found evidence for differences in types of basal resources supporting these crocodilians. Mean δ13C values were highest in Paleosuchus trigonatus (Schneider's dwarf caiman, −25.7 ± 1.2‰), intermediate in Caiman crocodilus (spectacled caiman, −27.4 ± 1.2‰) and Paleosuchus palpebrosus (Cuvier's dwarf caiman, −27.7 ± 1.1‰) and lowest in Melanosuchus niger (black caiman, −29.9 ± 1.3‰). A progressive decrease in δ13C values of crocodilian tissues occurred from headwaters to floodplains, which most likely reflects a progressive increase in autochthonous over allochthonous inputs in lower reaches of streams. The shift from terrestrial to aquatic resources sustaining these sympatric predators mirrors their spatial distribution along this ecotone. However, after taking into account the habitat in which pairs of syntopic individuals of distinct species occurred, significant differences in δ13C values suggest that P. trigonatus and P. palpebrosus have different prey bases. Thus, despite being opportunistic predators, our results show that differences in crocodilian diets likely result from prey preferences and not only from habitat selection. These findings suggest that some species of crocodilians may be less generalist than traditionally thought and their influence on terrestrial or aquatic food webs might be species specific.

Quantifying predation on Baltic cod early life stages

Predation on cod (Gadus morhua) eggs by sprat (Sprattus sprattus) and herring (Clupea harengus) is known to be one of the processes influencing reproductive success of the eastern Baltic cod and has been reported to have contributed to lack of recovery of the stock in the 1990s. This study quantifies the predation on cod eggs in the Bornholm Basin, the major spawning area of cod in the central Baltic Sea, in the 1990s in comparison with the second half of the 2000s. The analyses involve estimating daily consumption rates of predator populations, which are then compared with corresponding daily egg production rates. As a methodological advancement compared with earlier studies, spatially resolved information on predator distribution and abundance is utilized in quantifying predator stock size. This resulted in more realistic consumption estimates in relation to overall egg production compared with earlier studies that consistently overestimated predation pressure by clupeids. Our results suggest a generally lower predation pressure on cod eggs in the mid- to late 2000s, due to a combination of reduced predator abundance and lower daily rations by individual predators.

Drivers of abundance and spatial distribution of reef-associated sharks in an isolated atoll reef system.

We investigated drivers of reef shark demography across a large and isolated marine protected area, the British Indian Ocean Territory Marine Reserve, using stereo baited remote underwater video systems. We modelled shark abundance against biotic and abiotic variables at 35 sites across the reserve and found that the biomass of low trophic order fish (specifically planktivores) had the greatest effect on shark abundance, although models also included habitat variables (depth, coral cover and site type). There was significant variation in the composition of the shark assemblage at different atolls within the reserve. In particular, the deepest habitat sampled (a seamount at 70-80m visited for the first time in this study) recorded large numbers of scalloped hammerhead sharks (Sphyrna lewini) not observed elsewhere. Size structure of the most abundant and common species, grey reef sharks (Carcharhinus amblyrhynchos), varied with location. Individuals at an isolated bank were 30% smaller than those at the main atolls, with size structure significantly biased towards the size range for young of year (YOY). The 18 individuals judged to be YOY represented the offspring of between four and six females, so, whilst inconclusive, these data suggest the possible use of a common pupping site by grey reef sharks. The importance of low trophic order fish biomass (i.e. potential prey) in predicting spatial variation in shark abundance is consistent with other studies both in marine and terrestrial systems which suggest that prey availability may be a more important predictor of predator distribution than habitat suitability. This result supports the need for ecosystem level rather than species-specific conservation measures to support shark recovery. The observed spatial partitioning amongst sites for species and life-stages also implies the need to include a diversity of habitats and reef types within a protected area for adequate protection of reef-associated shark assemblages.