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Microbiomes confer beneficial physiological traits to their host, but microbial diversity is inherently variable, challenging the relationship between microbes and their functional contribution to host health. Here, we compare diversity and architectural complexity of the epidermal microbiome from 74 individual whale sharks (Rhincodon typus) across five aggregations, globally. We hypothesised co-occurrence patterns would occur independently of diversity patterns. Whale shark aggregation was the most important factor discriminating taxonomic diversity patterns. Microbiome network architecture was similar across all aggregations with degree distributions matching Erdos-Renyi graphs. However, networks had greater modularity than expected, indicating definitive microbiome structure. In addition, whale sharks hosted 35 ‘core’ microbiome members supporting the high modularity observed in microbiomes. Therefore, while variability in microbiome diversity is high, network structure and core taxa are inherent characteristics of the microbiome in whale sharks. We suggest host-microbiome and microbe-microbe interactions which drive self-assembly of the microbiome are, in part, the result of emergent functions that support functionally redundant key core microbial members. Teaser Sentence: The skin microbiome of whale sharks has emergent co-occurrences structure despite distinct diversity patterns.

The benefits of composite products are well known to users of data from optical sensors: cloud-cleared composite reflectance or index products are commonly used as an analysis-ready data (ARD) layer. No analogous composite products are currently in widespread use that is based on spaceborne radar satellite backscatter signals. Here, we present a methodology to produce wide-area ARD composite backscatter images. They build on the existing heritage of geometrically and radiometrically terrain corrected level 1 products. By combining backscatter measurements of a single region seen from multiple satellite tracks (incl. ascending and descending), they are able to provide wide-area coverage with low latency. The analysis-ready composite backscatter maps provide flattened backscatter estimates that are geometrically and radiometrically corrected for slope effects. A mask layer annotating the local quality of the composite resolution is introduced. Multiple tracks are combined by weighting each observation by its local resolution, generating seamless wide-area backscatter maps suitable for applications ranging from wet snow monitoring to land cover classification or short-term change detection.

Information on the timing of melt onset over sea ice is important for understanding the Arctic's changing climate. The daily temporal resolution of passive microwave brightness temperatures provides the most widely utilized observations to detect melt onset but are limited to a spatial resolution of 25 km. Wide-swath synthetic aperture radar (SAR) imagery provides a much higher spatial resolution (20–100 m) but melt onset detection remains challenging because of i) insufficient temporal resolution to facilitate accurate melt onset detection, ii) inconsistent viewing geometries and iii) limited image availability across the Arctic. Here, we construct high temporal resolution composite gamma nought backscatter products (1 day, 1–2 day and 2–4 day) using Sentinel-1 and RADARSAT-2 over a close-to-seamless revisit region located in northern Canadian Arctic and Greenland for estimating melt onset over Arctic sea ice in 2016 and 2017. We employ the necessary radiometric terrain flattening and local resolution weighting techniques to generate normalised backscatter over the entire study region, removing restrictions limiting analysis to a single sensor or track's swath width by integrating both ascending and descending passes into the composite products. Results indicate that higher temporal resolution multi-sensor composite gamma nought products (1 day) that make use of the most imagery provide a robust temporal evolution of the backscatter. This allows for more representative estimates of melt onset as it is easier to separate the melt onset threshold from winter variability that is otherwise a considerable challenge for SAR based melt onset algorithms because of inconsistent temporal resolution. Multi-sensor composite gamma naught melt onset detection is in good agreement with melt onset estimates derived from the Advance Scatterometer (ASCAT) backscatter values and passive microwave brightness temperatures over homogenous sea ice regions but very noticeable improvement was found within narrow channels and regions with more heterogeneous sea ice. In anticipation of the availability of data from even more SAR satellites with the launch of the RADARSAT Constellation Mission, the multi-sensor composite gamma nought approach presented here may offer the most robust approach to estimate the timing of melt onset over sea ice across the Arctic using high spatiotemporal resolution SAR.

Following the general warming trend in Greenland, an increase in calving rates, retreat and ice flow has been observed at ocean-terminating outlet glaciers. These changes contribute substantially to the current mass loss of the Greenland Ice Sheet. In order to constrain models of ice dynamics as well as estimates of mass change, detailed knowledge of geometry and ice-flow are needed, in particular on the rapidly changing tongues of ocean-terminating outlet glaciers. In this study, we validate velocity estimates and spatial patterns close to the calving terminus of such an outlet derived from an iterative offset tracking method based on SAR intensity data with a collection of three independent reference measurements of glacier flow. These reference data sets are comprised of measurements from differential GPS, a Terrestrial Radar Interferometer (TRI) and repeated UAV surveys. Our approach for the SAR-velocity processing aims achieving at high spatial and temporal resolution in order to best resolve the steep velocity gradients in the terminus area and to exploit the 12 day repeat interval of the single-satellite Sentinel-1A sensor. Results from images of the medium-sized ocean terminating outlet glacier Eqip Sermia acquired by Sentinel-1A and RADARSAT-2 exhibit a mean difference of 8.7 % when compared to the corresponding GPS measurements. An areal comparison of our SAR velocity-fields with independently generated velocity maps from TRI and UAV showed a good agreement in magnitude and spatial patterns, with mean differences smaller than 0.7 md−1. In comparison with existing operational velocity products, our SAR-derived velocities showed a strongly improved spatial velocity pattern near the margins and calving front. There 10 % to 20 % higher surface ice velocities are produced, which has substantial implications on ice fluxes and on mass budget estimates of ice sheets. Further, we showed that offset tracking from SAR intensity data at a high spatio-temporal resolution is a valid method to derive glacier flow fields for fast-flowing glacier termini of outlet glaciers and, given the repeat interval of 12 days of the Sentinel-1A sensor (6 days with Sentinel-1B), has the potential to be applied operationally in a quasi-continuous mode.

Federal law requires managers (directors) of issuing companies (bonds, stocks) to report proprietary trading activities within 3 days after the trade. As a part of insider regulations, disclosure of directors‘ dealings aims at preventing unlawful use of insider information not available to other market participants. We present event-study based evidence from 868 directors‘ dealings in the period of 2008 to 2017 from the Austrian stock market (stock purchases and sales) and show that directors‘ dealings and their disclosure impact market prices and trading activity. We further document different market reactions depending on the type of the director (e.g. Supervisory board members) and the dollar-valued size of the transaction. Finally, directors seem to have particular abilities in market timing, i.e. they buy at relative low prices and vice versa liquidate their holdings after notable price inclines.

The reproduction of raptors strongly depends on food resources. It is unclear whether predators experience superabundant food during cyclic peaks of prey populations. In order to test this hypothesis, four pairs of Great Horned Owls Bubo virginianus with two young were subjected to brood size manipulations during high densities of cyclic Snowshoe Hare Lepus americanus populations in southwestern Yukon, Canada. Broods older than 35 days were temporarily enlarged by one, and then by two, young. No effects were observed when one owlet was added, but the addition of two young resulted in significant weight losses in manipulated broods. Females with enlarged broods moved farther from their nest sites at night, presumably reflecting increased hunting effort, and also spent less time near the nest during the day. Food additions to enlarged broods returned the parental behaviour to normal. We conclude that these large predators did not experience superabundant food at this stage of the breeding season during a peak in cyclic prey.

We document a shift in roosting behavior of Great Horned Owls (Bubo virginianus) from winter and late spring to summer. During summer, Great Horned Owls roosted near the ground or exposed on open ground, whereas they chose concealed perches at mid-canopy level for the rest of the year as typical for forest owls. This shift of roosting behavior coincided with the emergence of ornithophilic black flies, which transmit avian malaria (Leucocytozoon spp.). The shift in roosting behavior was consistent with measurements of parasite exposure at different habitat positions. Black fly activity was highest at mid-canopy level, and almost no black flies were active on open ground. Ground-roosting was not caused by poorly developed flying capability of juveniles, because solitarily-roosting adult owls showed the same behavioral shift in a second year of study. Black flies and avian malaria are widely distributed, and the effect of the vertical distribution of these parasites in forests on roosting, nesting, and foraging of sylvatic birds deserves further study.

High mortality and poor recruitment in Acacia tree populations in many parts of the Middle East may result in loss of biodiversity. Human activities in recent decades have caused drastic changes in the water regime and the abundance of wild and domestic ungulates, which may negatively affect these trees. We studied the effects of large mammalian herbivores on the establishment of young Acacia raddiana and A. tortilis in the Arava Valley between the Red Sea and the Dead Sea, Israel. Seed accumulation under trees was high when large herbivores were excluded, and direct observations confirmed that ungulates were the main seed dispersers of these Acacia species. Insect seed predators (bruchid beetles) damaged more than 95% of seeds not consumed by ungulates. Seed germination was facilitated by gut passage through ungulates. Seedling survival was determined largely by water availability and was independent of herbivore density. Under present conditions, several years of high rainfall are necessary for successful establishment of young trees. Under severe browsing pressure by ungulates, growth in juvenile trees was delayed and smaller sizes were overrepresented. There was no evidence, however, of effects on the long-term demography of Acacia trees, perhaps because ungulates increased seedling densities by enhancing the viability and germination of seeds. We conclude that large mammalian herbivores are essential components of arid Acacia savannas and that wild and domestic ungulates must be included in future conservation plans. Resumen: La alta mortalidad y el pobre reclutamiento en poblaciones de arboles de Acacia en muchas partes del Medio Oriente puede resultar en la perdida de biodiversidad. Actividades humanas en decadas recientes han ocasionado cambios drasticos en los regimenes de agua y la abundancia de ungulados silvestres y domesticos, lo cual puede afectar negativamente a estos arboles. Estudiamos los efectos de los mamiferos herviboros grandes en el establecimiento de arboles jovenes de Acacia raddiana y A. Tortilis en el valle de Arava entre el Mar Rojo y el Mar Muerto en Israel. La acumulacion de semillas bajo los arboles fue alta cuando los herviboros grandes fueron excluidos y las observaciones directas confirmaron que los ungulados fueron los principales dispersores de semillas de estas especies de Acacia. Los insectos depredadores de semillas (escarabajos) denaron mas del 95% de las semilas que no fueron consumidas por los ungulados. La germinacion de semillas fue facilitada por su paso a lo largo del tracto digestivo de los ungulados. La supervivencia de plantulas estuvo mayormente determinada por la accesibilidad del agua y fue independiente de la densidad de herviboros. Bajo las condiciones actuales, se necesitan varios anos de alta precipitacion pluvial para el establecimiento exitoso de arboles jovenes. Bajo una presion servera de ramoneo por los ungulados, el crecimiento de arboles jovenes seria retardado y los tamanos pequenos estarian sobre-representados. Sin embargo, no existio evidencia de efectos en la demografia de arboles de Acacia a largo plazo, posiblemente debido a que los ungulados incrementaron las densidades de platulas al incrementar la viabilidad y germinacion de semillas. Concluimos que los mamiferos herviboros grandes son componentes escenciales para Acacia de savanas aridas y que los ungulados silvestres y domesticos deben ser incluidos en planes futuros de conservacion.

Predators that aggregate in "hot spots" of high prey density have been hy- pothesized to synchronize population cycles of small mammals. During a peak and decline in a snowshoe hare (Lepus americanus) cycle, we created artificial hot spots of increased hare abundance by adding food and excluding mammalian predators on three 1-km2 blocks and then recorded the response of radio-marked Great Horned Owls (Bubo virginianus) to these food additions. Territorial owls showed a decrease in home range size and patchiness of spatial use as hare densities peaked and declined, although this was better explained by smaller territory sizes due to a growing owl population rather than a direct behavioral re- sponse to changing food density. Experimental owls on food-enriched territories did not show a difference in conventional measurements of home-range size and patchiness of spa- tial use compared with controls, but the distances of owl locations to treatment blocks re- vealed concentrations of spatial use on experimental hot spots. At a larger scale, neither ter- ritorial owls nor nonterritorial floaters showed a tendency to leave poorer patches and move toward hot spots, and the territorial system of Great Horned Owls was largely resistant to extreme variations in prey density. The effect of social interference between predators has been assumed for several models of predator-prey interactions, but empirical evidence has rarely been demonstrated. Our results suggest that territorial behavior, in addition to lim- iting the growth of a predator population, also prevents large aggregations of predators at an intermediate spatial scale. Received 3 July 1997, accepted 29 December 1997.

Most African Acacia trees occur in semi-arid savannas, but some species grow in deserts at the periphery of their range in northern Africa and the Middle East. We studied Acacia raddiana and A. tortilis in the southern Negev desert of Israel. According to the resource availability hypothesis, plants in poor habitats invest heavily into anti-herbivore defense because losses to browsers are costly when growth rates are low. Few plants invest simultaneously in different categories of defense. This suggests that trade-offs exist, although little is known about how individuals allocate resources to defence in natural populations. In a field experiment, we studied chemical and mechanical defences as a response to differential browsing for more than 10 yr. Both Acacia species increased spinescence but there was no clear response in the production of total polyphenols, condensed tannins, and protein-precipitating tannins (only A. raddiana may increase secondary compounds under very high browsing levels). There was an age effect in spinescence but not in secondary compounds for both species, with younger trees investing more into anti-herbivore defense than older individuals. We were unable to find negative correlations between traits of chemical and mechanical defense. We conclude that inducibility and age effects suggest a cost for mechanical but not necessarily for chemical defense. Contrary to the predictions of the resource availability hypothesis, concentrations of secondary compounds were not higher in this desert environment than in savannas.

Black fly feeding alone and in concert with Leucocytozoon spp. infection caused mortality in fledgling great horned owls (Bubo virginianus) in the Yukon, Canada 1990 to 1991. These mortalities occurred during a year of food shortage corresponding with a decline in the population of snowshoe hare (Lepus americanus), the main prey for great horned owls. We hypothesize an interaction between food availability and the consequences of host-parasite interactions.

The ecology and behaviour of non-territorial owls are little known. During a population peak of snowshoe hares,Lepus americanus, the main prey of great horned owls,Bubo virginianus, in the boreal forest, fledglings were equipped with radiotransmitters, and 30 successful dispersers were monitored in 1988–1991. Of those, nine became resident floaters in the study area. Transient floaters were not recorded, although floaters shifted the centre of their home ranges more than territorial owls. Floater home ranges were about five times larger than defended territories, but the space use did not differ significantly. Floaters intruded regularly into territories and their locations overlapped broadly with those of territory owners and other floaters, but were concentrated on the periphery of defended territories. This is consistent with other evidence that territorial behaviour limits the breeding density of great horned owls even at extreme peaks of prey availability. None of the monitored floaters bred as secondary females, and the intrusion rates and movement patterns of floaters did not change during the fertile period of females, as predicted if male floaters were seeking extra-pair copulations.

Large-scale mortality of native Acacia trees has been reported in the Negev desert, Israel. These trees may act as keystone species in this ecosystem due to their nitrogen-fixing abilities. Total mortality was variable and ranged from 0–61%. Contrary to widely-held opinion, aquifer depletion for agriculture and other human uses was not found to be a likely cause of this mortality. We found that the major probable cause of mortality was the absence of culverts under roads cross-cutting the ephemeral river beds where the Acacias are mostly found. Culverts allow water to pass from the upper to lower parts of the river during winter floods. In river beds without culverts, an average of 25% total mortality of trees was recorded downstream from the roads as compared with 12% upstream from the roads. We found that an average of five species of perennial plants disappeared downstream from the roads. An additional cause for concern is the rarity of recruitment of Acacia trees. This may be due to the absence of large mammalian herbivores (both wild and domestic) which eat seed pods and enhance the germination capacity of seeds through scarification of the hard seed coat during digestion.

We show evidence of differential predation on snowshoe hares (Lepus americanus) by great horned owls (Bubo virginianus) and ask whether predation mortality is related to antipredator behaviour in prey. We predicted higher predation on (1) young and inexperienced hares, (2) hares in open habitats lacking cover to protect from owl predation, and (3) hares in above average condition assuming that rich food patches are under highest risk of predation. Information on killed hares was obtained at nest sites of owls and by monitoring hares using radio-telemetry. The availability of age classes within the hare population was established from live-trapping and field data on reproduction and survival. Great horned owls preferred juvenile over adult hares. Juveniles were more vulnerable to owl predation before rather than after dispersal, suggesting that displacement or increased mobility were not causes for this increased mortality. Owls killed ratio-collared hares more often in open than in closed forest types, and they avoided or had less hunting success in habitats with dense shrub cover. Also, owls took hares in above average condition, although it is unclear whether samples from early spring are representative for other seasons. In conclusion, these results are consistent with the hypothesis that variation in antipredator behaviours of snowshoe hares leads to differential predation by great horned owls.

Most bird species have low survival rates in their first year of life, and the highest losses occur when juveniles become independent and disperse. Young great horned owls (Bubo virginianus), monitored by telemetry in the southwestern Yukon, Canada, survived well during the peak of the population cycle of snowshoe hares (Lepus americanus). Subsequently, juvenile survival collapsed parallel to the decline in hare densities. The proportion of starving owls did not increase, but there was a significant increase in mortalities involving parasitism and predation, probably as an interaction with food shortage. The mortality rates of juvenile great horned owls peaked before, not during, dispersal. We propose that extended parental care makes the postfledging stage safe during optimal conditions, but that the relatively slow development during this stage incurs the cost of increased susceptibility to disease and other mortality factors under environmental stress.

We studied hawk-owls in the southwestern Yukon, Canada, from 1987-1993. Most information on hawk-owls originates from studies in Europe, and very little is known about the subspecies Surnia ulula caparoch in North America. The boreal forest communities in the two continents differ remarkably in the composition of cyclic herbivore populations. Fennoscandia is dominated by 3-4 year microtine cycles, whereas northern Canada and Alaska experience a 10-year cycle in snowshoe hare numbers, with voles fluctuating at lower levels. We studied the diets of nine nesting pairs by pellet analysis, and we observed prey deliveries at five nests. The proportion of voles in the diets was lower than reported from Fennoscandia, and snowshoe hares made up 40-50% during the peak of the hare cycle. Estimates of prey densities by live-trapping revealed that hawk-owls strongly prefer voles over snowshoe hares and squirrels. Among voles, Microtus were preferred and Clethrionomys were avoided. Hawk-owls showed, however, a functional response not only to voles but also to juvenile hares, and they may be critically dependent on larger prey during certain nesting stages when vole abundance is moderate or low. Breeding densities and winter observations changed concurrently over years of different prey abundance. Prey selection translated into population consequences: hawk-owls did not respond numerically to Clethrionomys outbreaks, but to the combined densities of Microtus and snowshoe hares. We conclude that the Northern Hawk-Owl is less of a vole specialist and more affected by the prey composition in specific systems than commonly assumed, and we discuss this pattern from an evolutionary perspective

Recent advancements in Global Positioning Systems (GPS) radiocollar technology permit analysis of fine-scale animal movements. We used concurrent aerial and GPS monitoring to determine winter travel rates of Wolves (Canis lupus) in relation to ungulate kill sites in managed forest landscapes in westcentral Alberta. Wolves preyed predominately on Moose (Alces alces) and travelled 4.2 times less when near ungulate kill sites than when away from them. As Wolves are thought to be an important factor in Woodland Caribou (Rangifer tarandus caribou) declines, information is needed to assess predation risk to Caribou from Wolves under a variety of landscape conditions. If Wolves have restricted movements near Moose kill sites, this may lead to decreased encounter rates with Caribou in systems where Moose are abundant. Deer (Odocoileus spp.) are probably an important component of this Wolf-prey system but little is currently known about this relationship. Projecting long-term implications of ongoing development activities requires a more detailed understanding of the responses of all species to landscape change.

The numerical response of great horned owls (Bubo virginianus Gmelin) to the 10-year population cycle of snowshoe hares (Lepus americanus Erxleben) in the boreal forest was examined during 1988-93 in the south-western Yukon, Canada. Demographic parameters were estimated based on censuses (territorial pairs), nest visits (productivity), and radio-telemetry (survival, emigration, and integration of young birds into the population). Hares rose to peak densities in 1990, and almost all resident owl pairs bred and raised large broods during years of increasing and highest prey abundance. In 1991, the first year of hare decline, all breeding parameters including post-fledging survival were reduced, and recruitment in autumn was very low. In 1992 and 1993, reproduction was completely suppressed. Survival of young owls in their first 2 years of life was high during the peak of the hare cycle, and a large number of non-territorial 'floaters' were present. These birds were silent, and moved more than territorial owls. Their ranges overlapped broadly with defended territories, and floaters were affected by the hare decline before territory holders. Most ecological studies on birds are based on the territorial fraction of a population. The results of this study show how a large proportion of secretive floaters can delay the detection of population declines in traditional censuses of territorial birds, and can lead to serious underestimates of the impacts of predation.

We measured the density changes of 22 species of vertebrates during a snowshoe cycle in northern Canada. Hares were the dominant herbivore in the system and changes in their numbers were correlated with changes in numbers of arctic ground squirrel, spruce grouse, ptarmigan, lynx, coyote, great horned owl, goshawk, raven and hawk owl. Hare numbers were not correlated with numbers of red-backed vole which showed peaks during the low, increase, and early decline phases of the hare cycle. Hawk owls were the only predator whose numbers correlated with changes in red-backed voles while boreal owls and weasels were correlated with densities of Microtus. Red squirrel, American kestrel, red-tailed hawk, northern harrier, wolverine, magpie, and gray jay showed no correlation with hare or vole numbers. We conclude that species in the boreal forests of Canada do not exhibit the strong synchrony found between voles and other members of the vertebrate community in northern Fennoscandia. We discuss some of the possible reasons for these differences.

Predator populations often decline with a time log after the peak of prey cycles. Theoretical models of predator-prey interactions predict that this delay is caused by a higher rate of population growth in prey, which leaves predators with super-abundant food after the peak and buffers their decline. This situation is met when predator populations have a lower innate capacity for increase than their prey or when the increase is inhibited because of territorial behaviour. Here, I refer to this hypothesis as 'single prey hypothesis' (SPH) in contrast to the 'multiple prey hypothesis' (MPH), which predicts that the delayed decline is caused by high availability of other prey species. Results on population growth rates of great horned owls showed that the predictions of SPH were met, although the predicted difference was small when floaters were taken into account or social exclusion from breeding was removed in a population model. In their diet, great horned owls relied to a large degree on the main cyclic prey (snowshoe hares), and thus the results were not in agreement with the MPH. Inverse density-dependent growth rates in the territorial population, density-dependent accumulation of floaters, and replacements of territorial vacancies were consistent with the hypothesis that social behaviour limited the number of owl territories. Reproduction of resident owls was immediately affected by the prey decline, indicating that there was no buffering effect of super-abundant food. Therefore, neither MPH nor SPH were satisfactory explanations, and I propose a mechanism based on individual behaviour to explain delayed numerical responses : territorial predators monopolize a disproportionately large amount of resources for reproduction during the increase and peak of the cycle, and are then buffered against prey declines by adjusting their breeding activities. Non-territorial floaters have lower access to resources and their numbers are affected more immediately by declining prey.