Impact Of Predation Research Articles

Comparative functional responses predict the predatory impact of the highly invasive fish Cichla kelberi

Peacock basses (genus Cichla) are a group of Amazonian predatory fishes that invaded many systems worldwide. Severe ecological impacts have been reported, but no study investigated the functional response of these fishes to variations in prey abundance, a crucial information to determine predator consumption and impact. In this study, we evaluated the functional response of the highly invasive Cichla kelberi toward prey species of different taxonomic groups, and compared it to the response of the wolf fish Hoplias malabaricus, a voracious predator used as baseline. We hypothesized that higher feeding rates drive the predatory impact of the invasive predator. Using a non-replacement experimental setup, we manipulated prey densities (fish and shrimp) in 1000-L mesocosm tanks to quantify the consumption response of each predator during 24 h. Both predators consumed more fish than shrimp, but C. kelberi consumed significantly more than H. malabaricus. We found that C. kelberi consistently displayed higher Type-II functional response than H. malabaricus toward both prey species. There was a non-significant effect of predator species on attack rates, but C. kelberi presented significantly lower handling time values and higher maximum feeding rates. Our findings provide empirical evidence that high individual consumption rates explain the predatory impact of the highly invasive C. kelberi, and predict strong effects on invaded communities.

Wild dog/dingo conservation, control and management: The impact beyond the paddock

The impact of predation by dingoes/wild dogs on livestock creates extreme amounts of stress, angst and anger within rural communities. How do we return to a well-managed landscape and once again have positive communication between stakeholders? Wild dogs attack livestock. Dingoes attack livestock. This is the reality. Livestock predation has impacts that extend far beyond the animals that are attacked. It affects people. The basic tools for controlling dingoes are simple, traps, guns, fences and poison. Dingo control fails when these tools are not applied correctly, or one tool is relied on and overused. Proactive management is the only way to avoid generational problems. All stakeholders must invest in the issue. To me, this dilemma is not about the dingoes. It’s not just about the sheep and cattle, it’s about the people and our communities.

Mortality of light brown apple moth egg masses in coastal California: Impact of resident Trichogramma parasitism and predation

Egg mortality of light brown apple moth (LBAM), Epiphyas postvittana (Walker), was studied during the early years of its discovery and establishment in California from 2008 to 11. Sentinel egg cards were used to quantify mortality by parasitoids and predators at an intensively monitored location in Santa Cruz to reveal seasonality, and at other sites in Santa Cruz and San Francisco to measure spatial variation and parasitoid species composition. In addition to egg mortality, egg mass use efficiency by Trichogramma parasitoids was also examined under field conditions. The egg parasitoids primarily consisted of three Trichogramma species, T. deion, T. fasciatum and T. platneri. Previously unknown to California, T. fasciatum was shown to displace the indigenous T. platneri over a two-year period as the predominant egg parasitoid attacking LBAM egg masses. Based on the number of parasitized eggs per sentinel egg card, it is argued that individual females of at least some Trichogramma species have the capacity to oviposit more than 50 eggs in the egg mass of a host, warranting further studies to document the egg mass use efficiency and oviposition traits of other trichogrammatids under field conditions. Although egg parasitism was limited to causing elevated mortality during the summer and fall only, egg predation occurred more consistently throughout the year and is likely to be of considerable significance in suppressing LBAM populations in California. Combined with the use of a Type II survivorship curve, the importance of using a temperature-dependent physiological time scale to quantify egg mortality is illustrated when sentinel hosts are exposed to natural enemies in the field for less than the entire duration of the ‘window of susceptibility’ to parasitism and predation.

Testing the hypothesized antipredator defence function of stridulation in the spiny orb-weaving spider, Micrathena gracilis

The observable diversity of antipredator defences across organisms demonstrates predation's impact on trait evolution. The functions of many traits that are presumed to have an antipredator function have never been directly tested. The spiny orb-weaving spider, Micrathena gracilis, for example, stridulates when grasped. While stridulation was first hypothesized to be an antipredator defence nearly 50 years ago, no data exist to support this hypothesis. To explore the form and function of M. gracilis stridulation, we first quantified the behavioural and acoustical properties of sound production. Next, using laboratory assays, we directly tested the effect of stridulation on survival with an avian predator – blue jays, Cyanocitta cristata . Finally, we conducted a large mark–recapture field study in which we compared the natural survival of experimentally manipulated adult female M. gracilis that could not stridulate (silenced) versus could stridulate (control). Stridulatory pulses produced broadband frequency spectra, consistent with acoustic antipredator defences in other taxa. We also observed stridulation by male M. gracilis for the first time. In staged laboratory interactions with captive blue jays, we found no differences in survival between silenced and control M. gracilis . Similarly, in our mark–recapture field study, we found no differences in survival estimates between silenced and control groups, nor an effect of stridulation rate. While M. gracilis stridulation closely resembles antipredator stridulation in other arthropods, our behavioural data do not yet provide solid support for an antipredator function in M. gracilis . • We tested whether M. gracilis uses stridulation in antipredator defence. • We quantified behavioural and acoustical properties of stridulation. • We tested survival of silenced and control adult females in the laboratory/field. • Survival of silenced and control females did not differ. • Stridulation may not serve an antipredator function in M. gracilis.

Impact of adult predator incited fear in a stage-structured prey–predator model

A two-species predator–prey model where the predators are separated into juvenile and mature predators has been considered in this article. Here, functional response in linear form is considered to know the impact of adult predator-induced fear in the stage-structured prey–predator model. Positivity and boundedness of the model system have been checked. Persistence conditions and existence condition(s) of each equilibria have been derived. The local and global stability analysis have been implemented both analytically and numerically along with Hopf bifurcation analysis with direction. From the analysis of the model system, it is observed that the mature predator-induced fear and rate of transition from juvenile (minor) predator to mature predator plays a crucial role in controlling the system dynamics.

Feldman M.G. Estimation of the number of sockeye salmon adults and their distribution by spawning stations in the basin of Lake Nachikinskoye (Kamchatka) in 2019

Data on quantitative distribution of early and late spawners of sockeye salmon in the Lake Nachikinskoye basin were collected in 2019 using quadcopter. Features of sockeye spawning in certain sectors of the lake coast and at the spawning stations are analyzed. The spawning starts earlier on the eastern coast, and then on the western coast. The late sockeye spawning is considered in details at the spawning stations on littoral shelves, on steep coastal slopes, in key limnocrenes, in algae fields at the depths up to 5 m, and in the river tributaries. Environmental conditions of the stations are compared quantitatively by several parameters, as water flows and their gradients, water temperature, dissolved oxygen content, soils composition, impact of predators and waves. Each station has its advantages and disadvantages. The lake shallows dominate among the spawning grounds, but their diversity provides stability and even growth of local sockeye salmon stocks. Spatial distribution of the sockeye spawning grounds is described. The number of spawned fish is assessed using the trapezoid approximation (TAUC) as 55 . 103 ind. for early sockeye and 132 . 103 ind. for late sockeye that shows a considerable growth of the stocks of sockeye salmon in Lake Nachikinskoye since the middle of last century.

Bird Census Data Do Not Indicate a Lack of Impact on Songbirds From the Growth of Avian Predator Populations in Britain in the Late 20th Century

The possible role of avian predators in limiting songbird populations has been largely discounted since the publication of findings showing a lack of statistical association in UK bird census data between changes in prey species populations and those of a range of predatory species, including raptors and corvids. I re-applied the methodology behind these findings, covering a wider range of prey species and using site-level modelling to estimate predator abundance instead of a mixture of spatial modelling and raw count data. A significant aggregate predator effect was found in 33 out of 40 prey species, compared to only 10 out of 27 in the original study, as well as a higher rate of significant individual predator effects, with 41 significantly negative and 84 significantly positive effects out of a total of 320. The greater explanatory power of predator variables estimated using site-level modelling suggests that this has significant advantages over the use of predator variables derived from spatial modelling, which may not capture variation in predator abundance at a local scale, or from raw count data, which may lead to attenuation of effect estimates. The prevalence of positive associations between predators and prey is consistent with a common response to local habitat variation, which may absorb negative covariance resulting from the impact of predators on prey populations. Both positive and negative predator-prey associations may also occur as a result of independent demographic processes that manifest as sequential habitat occupation or withdrawal. Analyses of census data cannot discriminate among these possible scenarios and may therefore have limited value in determining whether predators have been limiting prey populations. Inference to a lack of impact of avian predators on prey populations from such analyses may therefore be unsafe, and a role for increased predator numbers remains a viable hypothesis with respect to bird population declines. The recent neglect of this possibility should therefore be urgently reversed, with a particular need for field experiments that can support strong inference regarding population limitation of songbirds by avian predators.

Within‐population variation in dietary traits: implications for vulnerability and impact of imperiled keystone predators

AbstractWithin a population of apex predators, differences among individuals can influence both their ecological impact and their vulnerability to threatening processes. Our field studies on a large monitor lizard (Varanus panoptes) in the Australian wet–dry tropics show that diets shift seasonally and depend upon a lizard’s sex and body size. Individuals that had previously been recorded to consume frogs were most at risk following biological invasion by toxic cane toads (Rhinella marina), as were individuals with broad diets during the wet season. As a result, mortality of those individual predators likely reduced predation pressure on other taxa (invertebrates and reptiles) that were frequently consumed by the same lizards that ate frogs, but with less benefit for taxa (e.g., rodents) that were consumed by non‐anuran‐eating individuals within the predator population. In particular, individuals killed by cane toads often had consumed agamid lizards, a group whose abundance has been reported to increase due to toad‐induced mortality of V. panoptes. To understand the vulnerability of apex predators, or the ecological consequences of their extirpation, we need to incorporate the role of variation among individuals in critical ecological traits.

A Survey of New South Wales Sheep Producer Practices and Perceptions on Lamb Mortality and Ewe Supplementation.

Simple SummaryHigh lamb mortality rates following birth reduce on-farm profitability and contribute to perceived lower animal welfare standards of the sheep industry. The aim of this study was to understand producer knowledge of lamb mortality rates, causes of lamb mortality, and to investigate practices and perceptions of producers that may contribute to lamb deaths. Approximately 50% of producers estimated less than 10% lamb mortality between birth and marking, compared to published data in Australia reporting around 20–25% mortality rate. Clostridial vaccination of lambs was undertaken by 96% of producers; however, 17% of Merino and 23% of crossbred lamb producers indicated only one vaccination was administered, instead of the recommended initial vaccination plus booster. This lower estimated mortality rate and misuse of vaccination may lead to producers underestimating the perceived benefits of management strategies, as the number of lambs lost is of less concern. It is important producers are aware of the actual on-farm lamb losses to allow accurate determination of the benefits of management strategies, such as pre-lambing supplementation and vaccination.High lamb mortality rates reduce profitability and reduce the perceived animal welfare standards of the industry. This study aimed to understand producer knowledge of lamb mortality rates and causes of lamb mortality, and to investigate various practices and perceptions of producers that may contribute to lamb deaths. Postal and online surveys gathered data on Australian sheep producer’s knowledge and practices around lambing and management practices. Based on results, approximately 50% of producers estimated less than 10% mortality of lambs between birth and marking, compared to published data estimates of 20–25% mortality. Pre-lambing vaccination of ewes was not undertaken by 10–20% of producers. Ninety-six percent of producers vaccinated lambs; however, 17% of Merino and 23% of crossbred lamb producers only gave a single vaccination instead of the recommended initial vaccine and booster. The lower estimated mortality impacts producer’s perceived benefits of management strategies being undertaken. Research undertaken needs to be more effectively distributed to producers via extension services to ensure producers understand the causes of mortality. Important messages to convey to producers include the limited impact of predation in most cases and the total costs of lamb mortality on-farm.

Nutrient Pollution and Predation Differentially Affect Innate Immune Pathways in the Coral Porites porites

Reef-building corals face a multitude of threats not only from global climate change but also local stressors such as nutrient pollution. Nutrient enrichment can amplify the negative effects of predation on corals by facilitating dysbiosis in the coral microbiome that leads to coral mortality. These patterns suggest that nutrient pollution might suppress the capacity of the coral immune system to respond to microbial infections that follow mechanical injury from predation. Here, we measured the impact of nutrient enrichment and predation on tyrosinase-type and laccase-type phenoloxidase (PO) activities, which are key components of immune defense pathway involved in melanin synthesis and wound healing in corals. Corals were exposed in situ to either ambient or enriched nutrient levels in combination with either no damage, mechanical damage, or predation damage from parrotfishes. The activity of PO enzymes in response to both tyrosinase-type substrates significantly decreased under nutrient enrichment, suggesting that corals became immune-compromised. Predation damage also increased laccase activity, implicating it in tissue repair and potentially defense from pathogens. Our findings highlight the need to mitigate nutrient pollution on coral reefs, as higher nutrient levels suppress important coral immune pathways and likely contribute to patterns of increased coral disease and subsequent mortality on reefs plagued by nutrient enrichment.

Impact of smallmouth bass predation on subyearling fall Chinook salmon over a broad river continuum.

Smallmouth bass (Micropterus dolomieu) predation on subyearling fall Chinook salmon (Oncorhynchus tshawytscha) was examined in the Snake River (USA) to identify seasonal and habitat-related changes in bass diets, and associated subyearling consumption and loss in various riverine and impounded reaches. Smallmouth bass diets reflected opportunistic foraging that at times showed predation on subyearlings is influenced by the consumption of other prey such as crayfish, sand roller (Percopsis transmontana), and smaller invertebrates. Estimated loss of subyearlings was influenced by bass abundance and consumption rates. The highest bass abundances (> 1,000 bass/river kilometer) were observed in the upper reach of Hells Canyon early in April and May, and in Lower Granite Reservoir. Peak consumption rates of subyearlings (≥ 0.12 subyearlings/bass/day) occurred in the upper reach of Hells Canyon during May and in most reservoir reaches in June. Predation losses accumulated evenly along the river continuum from riverine to reservoir habitats. We estimated that 869,371 subyearlings could be lost to smallmouth bass predation between riverine production areas and Lower Granite Dam in a given year. To provide a context for this estimated loss, we provide an illustration of its potential effect on the adult population. Assuming no juvenile mortality occurred downstream of the dam and depending on smolt-to-adult return rates, this represented up to 3.9–16.0% of the potential adult run that could have returned to Lower Granite Dam had no subyearling predation by smallmouth bass occurred upstream of the dam. Although this study was limited by a number of assumptions and constraints, it does provide an illustration of how predation affects juvenile and adult salmon loss over a broad, changing river landscape.

Blue mussel (Mytilus edulis L.) association with conspecifics affects mussel size selection by the common seastar (Asterias rubens L.)

Prey selection by predators is of interest to community ecologists. By choosing some prey over others, predators affect prey population dynamics and the strength of food webs. According to Optimal Diet Theory (ODT), as prey density increases predators will select more profitable prey. Thereby, prey population dynamics can also affect predator behaviour. Prey profitability involves the prey energetic value, energetic costs associated to predation (time spent searching, capturing and handling prey) and certain characteristics such as body size, abundance and behaviour. We examined the effect of the blue mussel (Mytilus edulis) association with conspecifics at different densities on prey selection and behaviour by the seastar Asterias rubens. Contrary to ODT prediction, when mussels were tightly clumped in high densities, the size range of the mussels consumed by A. rubens did not differ of the size range of the mussel population. Mussel association at high density caused seastars to feed locally, reducing their exposition to risks. Moreover, preying without selecting for a specific mussel size did not result in a decrease of net profit, rather it was increased. We concluded that under certain circumstances, not selecting prey results in an increase of net profit at prey size.We discuss our results in the context of the mussel industry where the effect of prey selection on the prey population dynamics is of importance. Mussel size selection by seastars, as described in previous works, will impact the size distribution of mussels within cultured populations affecting growth of the population and reproductive output among others, thus increasing the impact of seastar predation beyond that of just removing mussels from the population. However, this study shows that seastars prey upon availability at high densities, typically encountered in cultivated populations, and therefore their effect on mussel population is restricted to removal of mussels without affecting the size distribution of the population.

Exploring individual and population eco-evolutionary feedbacks under the coupled effects of fishing and predation

Intensive fishing that selects for large and old individuals can have pervasive effects on traits directly associated with the fecundity and survival of the target species. The observed reduction in fish body size can result in earlier sexual maturity at a smaller body size, leading to a lower individual reproductive output and population productivity in the long term. In addition, increased predation can induce similar responses in age and size at maturity due to the release of intraspecific competition and the lower population density. Thus, the combined impact of fisheries and predation is more difficult to predict due to their competition for fish, ultimately limiting and directing the prey size selectivity of each competitor. This can lead to various responses of fish on individual and population levels, depending on how the impacts of fisheries and predation affect each other. To explore this topic, we used an individual-based model to investigate the responses of the European hake (Merluccius merluccius) to the coupled pressures of the prevailing fishing regime and predation by bottlenose dolphins (Tursiops truncatus) as a study system. By simulating the growth trajectories of hake with consideration to its pronounced sexual size dimorphism (SSD), we applied Holling’s Type II and III functional responses (FRII and FRIII, respectively) and the Rosenzweig-MacArthur predator model to describe prey–predator dynamics. Our results demonstrate how the intensity, duration, and prey sizes selected by predation and fisheries determine the potential for evolutionary changes in hake life-history traits. Additionally, pronounced SSD in hake as well as the predation type play a pivotal role in hake resilience and recovery following a period of overexploitation. Different types of predation reveal the discrepancy in the intensity of competition between predators and fisheries for fish, as well as predator survival, which is relevant for sustainable fisheries management and effective predator conservation strategies.

The lethal 23%: predator demography influences predation risk for threatened prey

AbstractGlobally, wildlife managers often control predator populations to protect biodiversity, livestock or other valued resources. Most assume that the predation impact of each individual predator is the same and that removing any individual predator produces a benefit to the target species. However, research suggests predation efficacy can vary within a predator species according to phenotypic characteristics. Understanding these individual differences may be critical for managing predation impacts on particular categories of prey including small populations where predation effects are amplified. We used dietary data from 1748 feral cats euthanized over 30 years during a control programme in arid Australia to determine whether any predator attributes could predict their effect on different prey weight classes. Feral cats in our study ate a wide range of prey including reptiles, mammals, birds and invertebrates. Demography (body mass) was a highly significant predictor of diet. Cats weighing 3 kg fed predominantly on prey <50 g increasing to >500 g when cats attained a body mass of 6 kg. Of more significance was that diet varied between demographic groups but also within a single demographic group (adult males) based on body mass, with results having significant implications for threatened prey. Modelling indicated that for a fixed predator population size, the predation rate on prey in a >500 g weight class increased by 28% when the ratio of large (>4.2 kg) to small adult males varied according to its natural range (12%–80% over the 30‐year study). Results suggest that variations in predator demography can significantly impact predation rates on prey species and should be included in predator–prey models for small prey populations. On average, large male cats comprised 23% of the population and our findings suggest that targeting this ‘lethal demographic’ and manipulating predator demography should be prioritized along with lowering predator density to reduce predation impacts on prey weighing more than 500g.

Impacts of parrotfish predation on a major reef-building coral: quantifying healing rates and thresholds of coral recovery

Parrotfishes are important Caribbean herbivores that are believed to indirectly benefit corals by grazing algae; yet, some species also feed on live coral, which may have direct negative impacts on coral growth and survivorship. Caribbean parrotfishes prey upon multiple coral species but have particularly high rates of predation on Orbicella annularis, a major framework building coral and an endangered species. While some researchers have suggested that parrotfishes may have significant long-term impacts on heavily targeted species such as O. annularis, the patterns of coral recovery from parrotfish predation scars remain poorly understood. To address this knowledge gap, we tracked the fate of parrotfish bite scars on O. annularis colonies across two Caribbean islands for up to 2 months. We evaluated differences in coral healing between islands in response to a number of variables including the initial scar surface area, scar abundance per coral colony, colony surface area, and water depth. We used these data to develop a predictive model of O. annularis tissue loss from recent parrotfish bite scars. We then applied this model to surveys of the distribution of bite scars at a point in time to estimate long-term tissue loss of O. annularis colonies from a standing stock of bite scars. Our findings suggest that the initial scar surface area is one of the most important predictors of coral tissue loss. The data also indicate that there are thresholds in patterns of coral tissue regeneration: we observed that small scars (≤ 1.25 cm2) often fully heal, while larger scars (≥ 8.2 cm2) had minimal tissue regeneration. The vast majority of observed scars (~ 87%) were 1.25 cm2 or less, and our model predicted that O. annularis colonies would regenerate nearly all the corresponding scar area. In contrast, while scars greater than or equal to 8.2 cm2 were infrequent (~ 6% of all observed scars), our model predicted that these larger scars would account for over 96% of the total tissue loss for grazed colonies. Overall, our results suggest that the immediate negative impacts of parrotfish predation on coral tissue loss appear to be driven primarily by a few exceptionally large bite scars. While further work is needed to understand the long-term impacts of corallivory and quantify the net impacts of parrotfish herbivory and corallivory on Caribbean coral reefs, this study is an important step in addressing factors that impact the recovery of a heavily targeted and ecologically important Caribbean coral from parrotfish predation.

Mesomechanics of a three-dimensional spider web

Spiders, silks and webs are abundant and can be found in most ecosystems: in the corner of houses, on top of bushes, or even spanning rivers. They are the proof of an evolutionary success as they were able to survive and prosper for millions of years despite being subjected to environmental and human threats, such as the displacement of spider web silk attachments or impact of prey, predators, and debris. Their success is in part due to the excellent mechanical properties of silk and webs that originate from their hierarchical structure of silk, ranging from silk protein, to fibers, to spider webs. Here, we investigate the mechanical behavior of highly complex Cyrtophora Citricola 3D spider web, the architecture of which has been digitally modeled with micron-scale details from images of full-scale laboratory experiments, under stretching and projectile impact, using coarse-grain bead-spring simulations. We show that the interplay between the nonlinear behavior of spider silk and the redundancy of complex 3D spider web structures is crucial for the robustness and resilience of spider webs. The tangle region of the spider web allows prey to fly through and be caught in the dense tent web region, providing food to the spider. It also filters out predators at low impact velocity, and consequently protects the spider located in the tent region. Understanding the role of the interplay between silk mechanics and 3D web structure in webs’ evolutionary fitness could lead to high-performance and lightweight fiber network composite for structural, material and biomedical engineering.

European bird declines: Do we need to rethink approaches to the management of abundant generalist predators?

Abstract Bird species are declining across Europe. Current European policy, that is, the Birds and Habitats Directives, focus on habitat management as a way of halting the declines. This paper explores the role of predation in causing bird population declines and asks if we need to reconsider our approach to the management of generalist predators. We analysed bird population trends and distribution changes across Europe, Britain and Ireland, reflecting an increasing gradient of generalist predator abundance (principally red fox Vulpes vulpes and species of the family Corvidae). We tested if ground‐nesting bird species, considered more vulnerable to predation, were in greater decline compared to other nesting strategies. We also compared Annex I designated species to non‐designated species as a proxy for habitat management. We found that across Europe, 74% of ground‐nesting bird species were in decline, compared to 41% of other species. This was especially evident in Britain, where the pattern was 66% compared to 31%, and in Ireland, 71% compared to 20%. Ground‐nesting species were significantly more likely to be declining than other species. These patterns are consistent with the idea that population declines are at least partially related to the increased abundance of generalist predators. In Britain, ground‐nesting species were less likely to be in decline if covered by Annex I designation. However, in Europe and Ireland, Annex I status did not mitigate the effect of nesting strategy. Policy implications. Current legislation is clearly insufficient to prevent widespread declines in ground‐nesting birds, and this is the case across Europe, in Britain and Ireland. Ignoring the role of generalist predators in modern landscapes may lead to further declines and losses. We urgently need large‐scale experiments to establish causality in the impact of generalist predators on ground‐nesting birds in different landscapes. If we value our ground‐nesting bird species, consideration needs to be given to the control of widespread generalist predators, at least until landscapes are restored.

Comparative studies of egg parasitoids of the pine processionary moth (Thaumetopoea pityocampa,Den. & Schiff.) in historic and expansion areas in France and Bulgaria

AbstractTo investigate enemy pressure across the range of the pine processionary moth (Thaumetopoea pityocampa, Den. & Schiff.) as it spreads northwards in Europe because of climate change, a survey of 206 egg batches from historical and newly colonized areas at both the westernmost and the easternmost ends of the front was carried out in 2016–2018. Out of them, 97 egg batches were collected from nine locations in three regions in France and 109 from four localities in two regions in Bulgaria, both within historical and newly colonized ranges of the pest. The average number of eggs per batch collected in Bulgaria (226.6 ± 43.2) was higher than that in France (194.3 ± 50.1). However, the hatching percentage was higher in French samples, varying from 69.8 to 95.7, vs 49.8 to 85.2 per cent in Bulgarian samples. Four primary parasitoids (Ooencyrtus pityocampae, Baryscapus servadeii, Anastatus bifasciatus, Trichogramma sp.) and a hyperparasitoid (Baryscapus transversalis, found only in two regions of the historical range in Bulgaria) were identified. The oligophagous species B. servadeii was present at all sites within the historical range of the pest. In newly colonized areas, the impact of primary parasitoids on the host was distinctly low, suggesting that they lag behind the range expansion of pine processionary moth. In France, the most abundant species in the T. pityocampa parasitoid complex were B. servadeii in Ré Island and Orléans (97.3 and 87.4 per cent, respectively), and Trichogramma sp. (99.7 per cent) in a newly colonized locality in Fréhel. Ooencyrtus pityocampae prevailed in three of four Bulgarian localities (72.1 per cent in Sandanski, 89.7 per cent in Maglizh and 65.7 per cent in Sladak kladenets), whereas B. servadeii was the most abundant in Gega (75.4 per cent). Mortality of B. servadeii and O. pityocampae caused by the hyperparasitoid B. transversalis amounted to 4.8–6.2 per cent. The impact of predators on the pine processionary moth in the egg stage was negligible at most sites, reaching 12.5 per cent in only one site (Maglizh).

Impact of brood parasitism and predation on nest survival of the fan‐tailed gerygone in New Caledonia

Predation and brood parasitism are common reasons for nesting failure in passerine species and the additive impact by invasive species is a major conservation concern, particularly on tropical islands. Recognising the relative contribution of the different components of nesting failure rates is important to understand co‐evolutionary interactions within brood parasite–host systems. In the remote archipelago of New Caledonia, the fan‐tailed gerygoneGerygone flavolateralisis the exclusive host of the brood‐parasitic shining bronze‐cuckooChalcites lucidus. Additionally, invasive rodents also possibly have an impact on breeding success. To estimate the impact of potential nest predators, we 1) video monitored nests to identify predators, 2) estimated the probability of predation based on nest visibility and predator abundance and 3) tested the possibility that the location of experimental nests and lack of odour cues decrease the predation by rodents. In addition, we estimated nest survival rates using data collected in different habitats over the course of eight breeding seasons. Nesting success of fan‐tailed gerygones was relatively low and predation was the main cause of nesting failure. We recorded mainly predation by native birds, including the shining bronze‐cuckoo, whereas predation by rats was rare. In open habitats predation by cuckoos was much lower than predation by other avian predators. Neither predator activity around nests nor nest visibility influenced the probability of predation. Experimental nests in more accessible locations and containing an odorous bait were more exposed to rodent predation. Apparently, the fan‐tailed gerygone has either never been specifically vulnerable to predation by rats or has developed anti‐predator adaptations.

Experimental clearance rates of Aurelia coerulea ephyrae and medusae, and the predation impact on zooplankton in Jiaozhou Bay

The population explosion of jellyfish Aurelia coerulea occurred in Jiaozhou Bay, China in 2009. The potential predation impact of A. coerulea on zooplankton was investigated. Population clearance potential and residence time (t1/2) for copepods were calculated from laboratory clearance rates and measurements of jellyfish size and abundance from May to August 2009 in Jiaozhou Bay. Clearance rates varied widely with prey organisms, but they were not significantly different among various prey concentrations. Medusae captured rotifers, fish larvae and hydromedusae more efficiently than fish eggs, copepods and chaetognaths. Ephyrae captured rotifers and hydromedusae more efficiently than fish larvae and copepods. Clearance rate linearly increased with the cross sectional area of A. coerulea (size from 0.3 to 7.1 cm). Water temperature also had a marked effect on clearance rate and this was related to the increased beat frequency as water temperature increased. In early May 2009, A. coerulea potentially cleared the volume of water in the Bay less than 0.001 times a day, but this value was estimated to be more than 0.3 times a day in July. The t1/2 for copepods was less than 6 d in June and July. Abundances of copepods, hydromedusae and chaetognaths were extremely low in 2009 compared to 2008 and 2010 (jellyfish non-bloom years). Large predation pressure by the A. coerulea population occurred to control zooplankton communities in Jiaozhou Bay. A. coerulea, when present at a high population level, can be a keystone species in Jiaozhou Bay and control the trophic structure here.