Distribution Of Predators Research Articles

The landscape of fear as an emergent property of heterogeneity: Contrasting patterns of predation risk in grassland ecosystems.

The likelihood of encountering a predator influences prey behavior and spatial distribution such that non‐consumptive effects can outweigh the influence of direct predation. Prey species are thought to filter information on perceived predator encounter rates in physical landscapes into a landscape of fear defined by spatially explicit heterogeneity in predation risk. The presence of multiple predators using different hunting strategies further complicates navigation through a landscape of fear and potentially exposes prey to greater risk of predation. The juxtaposition of land cover types likely influences overlap in occurrence of different predators, suggesting that attributes of a landscape of fear result from complexity in the physical landscape. Woody encroachment in grasslands furnishes an example of increasing complexity with the potential to influence predator distributions. We examined the role of vegetation structure on the distribution of two avian predators, Red‐tailed Hawk (Buteo jamaicensis) and Northern Harrier (Circus cyaneus), and the vulnerability of a frequent prey species of those predators, Northern Bobwhite (Colinus virginianus). We mapped occurrences of the raptors and kill locations of Northern Bobwhite to examine spatial vulnerability patterns in relation to landscape complexity. We use an offset model to examine spatially explicit habitat use patterns of these predators in the Southern Great Plains of the United States, and monitored vulnerability patterns of their prey species based on kill locations collected during radio telemetry monitoring. Both predator density and predation‐specific mortality of Northern Bobwhite increased with vegetation complexity generated by fine‐scale interspersion of grassland and woodland. Predation pressure was lower in more homogeneous landscapes where overlap of the two predators was less frequent. Predator overlap created areas of high risk for Northern Bobwhite amounting to 32% of the land area where landscape complexity was high and 7% where complexity was lower. Our study emphasizes the need to evaluate the role of landscape structure on predation dynamics and reveals another threat from woody encroachment in grasslands.

Top predators constrain mesopredator distributions

Top predators can suppress mesopredators by killing them, competing for resources and instilling fear, but it is unclear how suppression of mesopredators varies with the distribution and abundance of top predators at large spatial scales and among different ecological contexts. We suggest that suppression of mesopredators will be strongest where top predators occur at high densities over large areas. These conditions are more likely to occur in the core than on the margins of top predator ranges. We propose the Enemy Constraint Hypothesis, which predicts weakened top-down effects on mesopredators towards the edge of top predators’ ranges. Using bounty data from North America, Europe and Australia we show that the effects of top predators on mesopredators increase from the margin towards the core of their ranges, as predicted. Continuing global contraction of top predator ranges could promote further release of mesopredator populations, altering ecosystem structure and contributing to biodiversity loss.

Predator‐mediated negative effects of overabundant snow geese on arctic‐nesting shorebirds

AbstractOverabundant species can strongly impact ecosystem functioning through trophic cascades. The strong increase in several arctic geese populations, primarily due to changes in agricultural practices in temperate regions, can have severe direct impacts on tundra ecosystems through vegetation degradation. However, predator‐mediated negative effects of goose overabundance on other tundra species can also be significant but are poorly understood. We tested the hypothesis that goose abundance negatively affects arctic‐nesting shorebirds by increasing nest predation pressure. We used six years of data collected within and near a greater snow goose colony (Chen caerulescens atlantica) to evaluate the effect of geese on the spatial variation in (1) the occurrence of shorebird nest predators, (2) the nest predation risk (with artificial shorebird nests), and (3) the occurrence of nesting shorebirds. We found that the goose colony had a strong influence on the spatial distribution of nest predators and nesting shorebirds. Occurrence of predators decreased, while occurrence of nesting shorebirds increased with distance from the centroid of the colony. The strength of these effects was modulated by lemming density, the preferred prey for predators. Shorebird nest predation risk also decreased with distance from the colony. Overall, these results indicate that goose abundance negatively affects arctic‐nesting shorebirds through shared predators. Therefore, we show that the current decline of some arctic shorebird populations may be in part mediated by a negative effect of an overabundant species.

Distribution and habitat models of the Eurasian otter, Lutra lutra, in South Korea

Eastern populations of the Eurasian otter (Lutra lutra) have declined throughout Asia. Although the South Korean government designated the Eurasian otter as an Endangered Species and Natural Monument, limited information exists on the distribution and habitat of this top predator in riparian ecosystems at this terminus of its distribution. We documented the distribution and modeled the habitat of this species using sign survey data collected in 2009 and 2010. We analyzed otter presence with 21 raster data sets using environmental niche modeling. We evaluated 31 variables as explanatory variables for logistic regression models that considered detection and non-detection data. We detected otter sign at 83% (3,288 of 3,957) of survey sites within 63% (680 of 1,074) of survey cells. In our MaxEnt presence-only model, land cover type was the main contributing factor to predicting habitat suitability, with secondary influences from isothermality, precipitation in the wettest month, elevation, and temperature seasonality. Water quality and human disturbance were the main variables significantly associated with otter occurrence based on the regression model that included detection and non-detection data. Direct measures of human activity, such as traffic volume and land price, were better predictors than stationary factors such as density of buildings. Our results suggest that otters and humans can coexist in highly populated areas. Our information on the distribution and habitat characteristics of Eurasian otters in South Korea will assist habitat management and recovery projects in natural and anthropogenic environments.

Biogeography of top predators – seabirds and cetaceans – along four latitudinal transects in the Atlantic Ocean

The distribution, abundance, and species assemblage of top predators - seabirds and cetaceans - can be correlated to water masses as defined by hydrological parameters. In comparison to other oceans, information about the structuring effects of water masses on top predators in the Atlantic Ocean is limited. The present study aims 1) to provide baseline distributional data of top predators for future comparisons, for instance in the course of climate change, and 2) to test how water masses and seasons affect distributional patterns of seabirds and cetaceans in the temperate and tropical Atlantic. During four trans-equatorial expeditions of the RV Polarstern between 2011 and 2014, at-sea observation data of seabirds, cetaceans and other megafauna were collected. Counts of top predators were generally low in the surveyed regions. Statistical analyses for the eight most abundant seabird species and the pooled number of cetaceans revealed water masses and seasons to account for differences in counts and thus also distribution. In most cases, borders between water masses were not very distinct due to gradual changes in surface water properties. Thus, top predator counts were correlated to water masses but, in contrast to polar waters, not strongly linked to borders between water masses. Additional factors, e.g. distance to locally productive areas (upwelling), competition effects, and seabird associations to prey-accumulating subsurface predators may be similarly important in shaping distributional patterns of top predators in the tropical and temperate Atlantic, but could not be specifically tested for here.

Survival of white‐tailed deer neonates in Louisiana

ABSTRACTChanging predator communities have potential to complicate management focused on ensuring sustainable white‐tailed deer (Odocoileus virginianus) populations. Recent research reported that predation on neonates by coyotes (Canis latrans) and bobcats (Lynx rufus) can limit recruitment. However, no research has been conducted in areas of the southeastern United States with 3 sympatric neonate predators such as coyote, American black bear (Ursus americanus), and bobcat. Our objectives were to estimate neonate survival rates, identify causes of neonate mortality, and determine which biological and landscape characteristics were related to neonate survival. During 2013–2015, we captured 70 neonates with the aid of vaginal implant transmitters on Tensas River National Wildlife Refuge in northeastern Louisiana, USA. We monitored neonates every 8 hours until 6 weeks of age and daily until 12 weeks of age, and assigned cause of death from field and DNA evidence. Survival of neonates to 12 weeks was 0.271 (95% CI = 0.185–0.398). Of 51 mortalities, 45 (88%) were attributed to predation, 4 (8%) to starvation, 1 (2%) to other causes, and 1 (2%) to unknown causes. We used an information‐theoretic approach to compare Cox proportional hazards models containing various combinations of biological and habitat covariates. Our best‐supported model contained sex, mass at birth, distance to cropland, young reforestation (planted 2000–2009), and old reforestation (planted 1980–1989). Based on hazard ratios, survival was 81% higher for males than females, and survival increased 81% with every 1‐kg increase in birth mass. Survival increased 8% for every 100‐m increase in distance from cropland or young reforestation, and decreased 11% with every 100‐m increase in distance from old reforestation, which may be a result of spatial variation in predator distribution. Our results emphasize the importance of site‐specific monitoring of neonate recruitment rates in areas with burgeoning predator communities. We conclude, however, that although predation pressure was high, survival rates were similar to those observed in 2‐predator systems in the region, suggesting the possibility that an upper limit to predation rates may exist for white‐tailed deer neonates. © 2017 The Wildlife Society.

When does fishing forage species affect their predators?

This paper explores the impact of fishing low trophic level “forage” species on higher trophic level marine predators including other fish, birds and marine mammals. We show that existing analyses using trophic models have generally ignored a number of important factors including (1) the high level of natural variability of forage fish, (2) the weak relationship between forage fish spawning stock size and recruitment and the role of environmental productivity regimes, (3) the size distribution of forage fish, their predators and subsequent size selective predation (4) the changes in spatial distribution of the forage fish as it influences the reproductive success of predators. We show that taking account of these factors generally tends to make the impact of fishing forage fish on their predators less than estimated from trophic models. We also explore the empirical relationship between forage fish abundance and predator abundance for a range of U.S. fisheries and show that there is little evidence for a strong connection between forage fish abundance and the rate of change in the abundance of their predators. We suggest that any evaluation of harvest policies for forage fish needs to include these issues, and that models tailored for individual species and ecosystems are needed to guide fisheries management policy.

Informing recovery in a human-transformed landscape: Drought-mediated coexistence alters population trends of an imperiled salamander and invasive predators

Understanding the additive or interactive threats of habitat transformation and invasive species is critical for conservation, especially where climate change is expected to increase the severity or frequency of drought. In the arid southwestern USA, this combination of stressors has caused widespread declines of native aquatic and semi-aquatic species. Achieving resilience to drought and other effects of climate change may depend upon continued management, so understanding the combined effects of stressors is important. We used Bayesian hierarchical models fitted with 10-years of pond-based monitoring surveys for the federally-endangered Sonoran Tiger Salamander (Ambystoma mavortium stebbinsi) and invasive predators (fishes and American Bullfrogs, Lithobates catesbeianus) that threaten native species. We estimated trends in occupancy of salamanders and invasive predators while accounting for hydrological dynamics of ponds, then used a two-species interaction model to directly estimate how invasive predators affected salamander occupancy. We also tested a conceptual model that predicted that drought, by limiting the distribution of invasive predators, could ultimately benefit native species. Even though occupancy of invasive predators was stationary and their presence in a pond reduced the probability of salamander presence by 23%, occupancy of Sonoran Tiger Salamanders increased, annually, by 2.2%. Occupancy of salamanders and invasive predators both declined dramatically following the 5th consecutive year of drought. Salamander occupancy recovered quickly after return to non-drought conditions, while occupancy of invasive predators remained suppressed. Models that incorporated three time-lagged periods (1 to 4years) of local moisture conditions confirmed that salamanders and invasive predators responded differently to drought, reflecting how life-history strategies shape responses to disturbances. The positive 10-year trend in salamander occupancy and their rapid recovery after drought provided partial support for the hypothesis of drought-mediated coexistence with invasive predators. These results also suggest management opportunities for conservation of the Sonoran Tiger Salamander and other imperiled organisms in human-transformed landscapes.

Three-dimensional temperature fields of the North Patagonian Sea recorded by Magellanic penguins as biological sampling platforms

Temperature is a primary determinant of biogeographic patterns and ecosystem processes. Standard techniques to study the ocean temperature in situ are, however, particularly limited by their time and spatial coverage, problems which might be partially mitigated by using marine top predators as biological platforms for oceanographic sampling. We used small archival tags deployed on 33 Magellanic penguins (Spheniscus magellanicus), and obtained 21,070 geo-localized profiles of water temperature, during late spring of 2008, 2011, 2012 and 2013; in a region of the North Patagonian Sea with limited oceanographic records in situ. We compared our in situ data of sea surface temperature (SST) with those available from satellite remote sensing; to describe the three-dimensional temperature fields around the area of influence of two important tidal frontal systems; and to study the inter-annual variation in the three-dimensional temperature fields. There was a strong positive relationship between satellite- and animal-derived SST data although there was an overestimation by remote-sensing by a maximum difference of +2 °C. Little inter-annual variability in the 3-dimensional temperature fields was found, with the exception of 2012 (and to a lesser extent in 2013) where the SST was significantly higher. In 2013, we found weak stratification in a region which was unexpected. In addition, during the same year, a warm small-scale vortex is indicated by the animal-derived temperature data. This allowed us to describe and better understand the dynamics of the water masses, which, so far, have been mainly studied by remote sensors and numerical models. Our results highlight again the potential of using marine top predators as biological platforms to collect oceanographic data, which will enhance and accelerate studies on the Southwest Atlantic Ocean. In a changing world, threatened by climate change, it is urgent to fill information gaps on the coupled ocean-atmosphere system allowing to link the hydrothermal process to the at-sea distribution of top predators.

Predation on transmission stages reduces parasitism: sea anemones consume transmission stages of a barnacle parasite

While parasites serve as prey, it is unclear how the spatial distribution of parasite predators provides transmission control and influences patterns of parasitism. Because many of its organisms are sessile, the rocky intertidal zone is a valuable but little used system to understand spatial patterns of parasitism and elucidate the underlying mechanisms driving these patterns. Sea anemones and barnacles are important space competitors in the rocky intertidal zone along the Pacific coast of North America. Anemones are voracious, indiscriminate predators; thus, they may intercept infectious stages of parasites before they reach a host. We investigate whether a sea anemone protects an associated barnacle from parasitism by Hemioniscus balani, an isopod parasitic castrator. At Coal Oil Point, Santa Barbara, California USA, 29% of barnacles were within 1 cm from an anemone at the surveyed tidal height. Barnacles associated with anemones had reduced parasite prevalence and higher reproductive productivity than those remote from sea anemones. In the laboratory, anemones readily consumed the transmission stage of the parasite. Hence, anemone consumption of parasite transmission stages may provide a mechanism by which community context regulates parasite prevalence at a local scale. Our results suggest predation may be an important process providing parasite transmission control.

Competitors and predators alter settlement patterns and reproductive success of an intraguild prey

AbstractThe spatial distribution of predators is affected by intra‐ and interspecific interactions within the predator guild. Studying these interactions under fluctuating food availability, while taking habitat characteristics into account, offers a quasi‐experimental setup to determine the relative impact of con‐ and heterospecifics on reproductive success of predators. We analyzed the settlement decisions and reproductive success of Eurasian Pygmy Owls (Glaucidium passerinum) in the presence of both breeding conspecifics and their competitor and intraguild predator, Tengmalm's Owls (Aegolius funereus), under fluctuating abundance of their primary prey (voles). We used detailed data, collected across 11 years in a large study area (1300 km²), on the spatial and temporal variation of habitat characteristics in all available nesting sites, local densities of both species, and vole abundance. We found that Pygmy Owls strongly avoided breeding close to conspecifics but did not avoid Tengmalm's Owl nests. Nest box occupation of Pygmy Owls was positively correlated to the proportion of old spruce, mature and old pine forests, and farmlands, and occupation probability was higher at high vole abundance and in areas occupied in previous years. Pygmy Owl avoidance of conspecifics decreased when voles were abundant. At high conspecific density, Pygmy Owls showed lower hatching success and delayed hatching date, in agreement with the observed spatial avoidance. Finally, even though breeding Pygmy Owls did not spatially avoid Tengmalm's Owls, the density of heterospecifics correlated with low hatching and fledging success in Pygmy Owls. This suggests short term fitness costs when living close to competitors, even when lethal effects of intraguild interactions are subtle. Our results suggest that joint costs of exploitative and interference competition by Tengmalm's Owls, as well as intraguild predation, were lower than those induced by intraspecific competition only. This result might be due to the similar body size between the species considered, Tengmalm's Owls being only twice as large as Pygmy Owls. Interactions among con‐ and heterospecifics can therefore modify the spatial settlement and reproductive success of individuals on a landscape scale, also within the predator guild.

Modeling Exposure of Mammalian Predators to Anticoagulant Rodenticides

Anticoagulant rodenticides (AR) are a widespread and effective method of rodent control but there is concern about the impact these may have on non-target organisms, in particular secondary poisoning of rodent predators. Incidence and concentration of AR in free-living predators in Denmark is very high. We postulate that this is caused by widespread exposure due to widespread use of AR in Denmark in and around buildings. To investigate this theory a spatio-temporal model of AR use and mammalian predator distribution was created. This model was supported by data from an experimental study of mice as vectors of AR, and was used to evaluate likely impacts of restrictions imposed on AR use in Denmark banning the use of rodenticides for plant protection in woodlands and tree-crops. The model uses input based on frequencies and timings of baiting for rodent control for urban, rural and woodland locations and creates an exposure map based on spatio-temporal modelling of movement of mice-vectored AR (based on Apodemus flavicollis). Simulated predator territories are super-imposed over this exposure map to create an exposure index. Predictions from the model concur with field studies of AR prevalence both before and after the change in AR use. In most cases incidence of exposure to AR is predicted to be greater than 90%, although cessation of use in woodlots and Christmas tree plantations should reduce mean exposure concentrations. Model results suggest that the driver of high AR incidence in non-target small mammal predators is likely to be the pattern of use and not the distance AR is vectored. Reducing baiting frequency by 75% had different effects depending on the landscape simulated, but having a maximum of 12% reduction in exposure incidence, and in one landscape a maximum reduction of <2%. We discuss sources of uncertainty in the model and directions for future development of predictive models for environmental impact assessment of rodenticides. The majority of model assumptions and uncertainties err on the side of reducing the exposure index, hence we believe the predictions to be robust and to indicate that the scale of the problem may be large.

Graph-Theoretical Method to the Existence of Stationary Distribution of Stochastic Coupled Systems

In this paper, by linking Fokker–Planck equations with stochastic coupled systems, a new method is provided to investigate the existence of a stationary distribution of stochastic coupled systems. Based on the graph theory and the Lyapunov method, an appropriate Lyapunov function associated with stationary Fokker–Planck equations is constructed. Moreover, a Lyapunov-type theorem and a coefficients-type criterion are obtained to guarantee the existence of a stationary distribution. Furthermore, theoretical results are applied to explore the existence of a stationary distribution of stochastic predator–prey models with dispersal and a sufficient criterion is presented correspondingly. Finally, a numerical example is given to illustrate the effectiveness of our results.

Environmental drivers of diurnal visits by transient predatory fishes to Caribbean patch reefs.

Video cameras recorded the diurnal visitation rates of transient (large home range) piscivorous fishes to coral patch reefs in The Bahamas and identified 11 species. Visits by bar jack Caranx ruber, mutton snapper Lutjanus analis, yellowtail snapper Ocyurus chrysurus, barracuda Sphyraena barracuda and cero Scomberomorus regalis were sufficiently frequent to correlate with a range of biophysical factors. Patch-reef visitation rates and fish abundances varied with distance from shore and all species except S. regalis were seen more frequently inshore. This pattern is likely to be caused by factors including close proximity to additional foraging areas in mangroves and on fore-reefs and higher abundances close to inshore nursery habitats. Visitation rates and abundances of C. ruber, L. analis, O. chrysurus and S. regalis also varied seasonally (spring v. winter), possibly as fishes responded to temperature changes or undertook spawning migrations. The abundance of each transient predator species on the patch reefs generally exhibited limited diurnal variability, but L. analis was seen more frequently towards dusk. This study demonstrates that the distribution of transient predators is correlated spatially and temporally with a range of factors, even within a single lagoon, and these drivers are species specific. Transient predators are considered an important source of mortality shaping reef-fish assemblages and their abundance, in combination with the biomass of resident predators, was negatively correlated with the density of prey fishes. Furthermore, transient predators are often targeted by fishers and understanding how they utilize seascapes is critical for protecting them within reserves.

Evaluation of a Long‐Term Predator Removal Program: Abundance and Population Dynamics of Invasive Northern Pike in the Yampa River, Colorado

AbstractThe Northern Pike Esox lucius is invasive in the upper Green and Yampa River basins of Colorado and Utah and impedes endangered fish recovery in the upper Colorado River basin. Mechanical removal was implemented in 2004, but Northern Pike population dynamics and removal efficacy were not well understood. We analyzed mark–recapture records from 8,929 individual Northern Pike captured during 2004–2010 from three reaches of the Yampa River: Hayden to Craig (upstream reach), South Beach–Little Yampa Canyon–Juniper (middle reach), and Maybell–Sunbeam (downstream reach), encompassing 175 river kilometers. Annual survival rates for Northern Pike of the mean TL (465 mm) were highest downstream (mean = 0.54; range = 0.36–0.71) and lowest upstream (mean = 0.25; range = 0.12–0.38). Annual abundance exhibited the opposite pattern, as it was highest upstream (annual range = 1,144–4,078 fish) and lowest downstream (range = 232–746 fish). After removal occurred each year, Northern Pike abundance increased annually by nearly 1,000% in the upstream reach, over 875% in the middle reach, and over 375% in the downstream reach due to recruitment and immigration. Resulting densities were 4–58 times higher than those for a native apex predator, the endangered Colorado Pikeminnow Ptychocheilus lucius. Northern Pike movement was mostly (90%) downstream and sometimes extensive, which may have promoted establishment of additional populations. Removal rates were inadequate to reduce Northern Pike abundance in the Yampa River because recruitment and immigration exceeded removal and mortality. Investigation of reproduction and recruitment, along with source management, spawning disruption, and increased removal, are needed to further reduce Northern Pike abundance and to aid recovery of native and endangered fishes. These findings underscore the need for sustained, comprehensive, and often costly removal efforts—including evaluation of their effects—in the face of the expanding distribution and abundance of invasive predator species.Received April 16, 2015; accepted March 29, 2016Published online September 19, 2016

Determinants of Distribution Patterns and Management Needs in a Critically Endangered Lion Panthera leo Population

The lion Panthera leo is Critically Endangered in West Africa and is known to occupy only four protected areas within the region. The largest population persists in the trans-boundary W-Arly-Pendjari (WAP) ecosystem, in the border region of Benin, Burkina Faso, and Niger. WAP harbors an estimated 350 individuals, or 90% of West Africa’s lions. We modeled lion occupancy across WAP using systematic, vehicle-based spoor counts to assess how landscape variables related to biotic factors, management and human impact influence lion distribution across WAP. We surveyed 1110 km of roads across WAP in 2012, obtaining 79 lion detections in 32 of our 167 15 x 15 km sampling units (naive occupancy = 0.41). Overall occupancy (Ψ) was 0.71 (95% SE = 0.56-0.83) when accounting for imperfect detection (p = 0.22, 95% SE = 0.18-0.27). The best predictors of lion occupancy were numbers of permanent protected area staff and mean monthly dry season precipitation. Model-averaged estimates suggest greatest lion occupancy in the Arly and Pendjari management blocks, with lowest occupancy in the tri-national W National Park. Our results suggest that lions in WAP are equally limited by management and biotic factors, and demonstrate how unevenly distributed protection effort limits the distribution of an apex predator across a protected landscape. We strongly recommend increased funding and better protection to increase lion occupancy in WAP, most urgently in the W National Park.

A fully coupled ecosystem model to predict the foraging ecology of apex predators in the California Current

MARINE ECOLOGY PROGRESS SERIES Mar Ecol Prog Ser Vol. 556: 273–285, 2016 doi: 10.3354/meps11849 Published September 8 A fully coupled ecosystem model to predict the foraging ecology of apex predators in the California Current J. Fiechter 1, *, L. A. Huckstadt 2 , K. A. Rose 3 , D. P. Costa 2 Institute of Marine Sciences, University of California Santa Cruz, 1156 High St, Santa Cruz, CA 95064, USA Department of Ecology and Evolutionary Biology, University of California Santa Cruz, 1156 High St, Santa Cruz, CA 95064, USA Department of Oceanography and Coastal Sciences, Louisiana State University, 1002-Y Energy, Coast & Environment Building, Baton Rouge, LA 70803, USA ABSTRACT: Results from a fully coupled end-to-end ecosystem model for the California Current Large Marine Ecosystem are used to describe the impact of environmental variability and prey availability on the foraging ecology of its most abundant apex predator, the California sea lion Zalophus californianus. The ecosystem model consists of a biogeochemical submodel embedded in a regional ocean circulation submodel, both coupled with a multi-species individual-based sub- model for forage fish (sardine and anchovy) and California sea lions. Sardine and anchovy are explicitly represented in the model as they are commonly found in the diet of sea lions and exhibit significant interannual and decadal variability in population abundances that reflect variations in their environment and lower trophic level prey. Output from a 20 yr run (1989−2008) of the model demonstrates how different physical and biological processes control habitat utilization and forag- ing success of California sea lions on interannual time scales, with the dominant modes of variabil- ity linked to sardine abundance and coastal upwelling intensity. The results also illustrate how variability in environmental conditions, forage fish distribution, and prey assemblage affect sea lion feeding success. While specifically focusing on the foraging ecology of sea lions, the modeling framework has the ability to provide a more complete understanding of the physical and biologi- cal mechanisms impacting trophic interactions in the California Current, or other regions where similar fully coupled ecosystem models may be implemented. KEY WORDS: Ecosystem model · Foraging ecology · California Current · Upwelling · Sea lions · Marine predators · Zalophus californianus Resale or republication not permitted without written consent of the publisher Determining the relationships between environ- mental variability, prey field dynamics, and the foraging ecology of marine mammals and other apex predators has been an on-going research topic for several decades (Fiedler et al. 1998). However, re - cent pro gress in animal tagging has shed new light on the mechanisms through which changing environmental conditions may impact the habitat selection of pelagic predators (Block et al. 2011, Irvine et al. 2014). Such information is critical to identify the underlying physical and biological processes that control the foraging and migratory behavior of higher trophic level species (Weise et al. 2006, Bailey et al. 2009). Understanding the linkages among environmental variability, prey availability, and predator distribution should ulti- mately lead to a better characterization of biologi- cal ‘hot spots’ in the ocean and how these hot spots may respond to changing climate conditions (Pala- cios et al. 2006). *Corresponding author: fiechter@ucsc.edu © Inter-Research 2016 · www.int-res.com INTRODUCTION

Drastic decrease in high Arctic gulls—ivory Pagophila eburnea and Ross’s Rhodostethia rosea—density in the northern Greenland Sea and Fram Strait between 1988 and 2014

Our long-term study on top predator (seabirds and marine mammals) distribution in polar marine ecosystems aims at detecting possible temporal and spatial population changes, especially in the context of global changes in temperature and ice cover. Quantitative data on the seabird distribution were collected in the northern Greenland Sea and Fram Strait onboard the icebreaker RV Polarstern between 1988 and 2014, applying 30-min transect counts from the bridge, without width limitation (n = 7320). A drastic decrease in numbers by a factor of seven was detected for the ivory gull Pagophila eburnea from 2007 on. These data confirm the decrease of ivory gull previously detected in North Canada and North Greenland, leading to the conclusion that the species is “endangered” or “near threatened”. These changes are discussed in relation to the decreasing Arctic pack ice coverage leading to the opening of the Northwest and Northeast Passages in 2007, at the time the year with the lowest ice coverage ever recorded. On the other hand, the decrease was even stronger for Ross’s gull Rhodostethia rosea after 1993, apparently reflecting changes in migratory habits. The third high Arctic gull, Sabine’s gull Xema sabini, was only tallied in very low numbers, without any clear temporal evolution in numbers.

Nonconstant Positive Steady States and Pattern Formation of 1D Prey-Taxis Systems

Prey-taxis is the process that predators move preferentially toward patches with highest density of prey. It is well known to have an important role in biological control and the maintenance of biodiversity. To model the coexistence and spatial distributions of predator and prey species, this paper concerns nonconstant positive steady states of a wide class of prey-taxis systems with general functional responses over 1D domain. Linearized stability of the positive equilibrium is analyzed to show that prey-taxis destabilizes prey–predator homogeneity when prey repulsion (e.g., due to volume-filling effect in predator species or group defense in prey species) is present, and prey-taxis stabilizes the homogeneity otherwise. Then, we investigate the existence and stability of nonconstant positive steady states to the system through rigorous bifurcation analysis. Moreover, we provide detailed and thorough calculations to determine properties such as pitchfork and turning direction of the local branches. Our stability results also provide a stable wave mode selection mechanism for thee reaction–advection–diffusion systems including prey-taxis models considered in this paper. Finally, we provide numerical studies of prey-taxis systems with Holling–Tanner kinetics to illustrate and support our theoretical findings. Our numerical simulations demonstrate that the $$2\times 2$$ prey-taxis system is able to model the formation and evolution of various striking patterns, such as spikes, periodic oscillations, and coarsening even when the domain is one-dimensional. These dynamics can model the coexistence and spatial distributions of interacting prey and predator species. We also give some insights on how system parameters influence pattern formation in these models.

Spatial and temporal distribution of gerrid (Heteroptera) and predation on microcrustaceans from a tropical shallow lake.

Predator-prey interactions involving an aquatic insect and zooplanktonic prey of different sizes were investigated to quantify prey mortality exposed to predators. Laboratory experiments were undertaken with the young and adult gerrid Rheumatobates crassifemur to test predation and size selectivity on the cladocerans Daphnia gessneri, Ceriodaphnia richardi, and Bosmina tubicen. Population fluctuations and spatial distribution of the gerrid were also evaluated in a small and shallow Brazilian lake throughout 12 months in fortnightly samples. The insects were more abundant in the littoral (mean density 7.0 ± 1.2 ind.m-2) compared to the limnetic zone. The period with the highest densities was late January to June, in both zones. Predation by young instars on Daphnia and Ceriodaphnia was significant (mean ingestion rate of 1.3 ± 0.1 D. gessneri and 0.7 ± 0.1 C. richardi per predator per hour). Adult insect fed only the large-sized prey (mean ingestion rate of 1.0 ± 0.1 D. gessneri per predator per hour). Young gerrids have greater potential to prey on cladocerans than adults, and size selectivity occurred for both predators. Preference of adults by the larger prey is probably related to difficulties in manipulating smaller planktonic prey, such as Ceriodaphnia. Due to higher densities of insects in the littoral, higher predation on zooplankton in this zone is expected. This study does contribute to a better understanding of trophic interactions in tropical shallow lakes and is the first to investigate predation of a gerrid on cladocerans in laboratory experiments.