Impact Of Predation Research Articles

Relative impact of human harvest and wolf predation on two ungulate species in Central Italy

AbstractData collected from 2000 to 2010 on a predator–prey system in eastern Tuscany (central Italy) were used to investigate the relative impact of human harvest and natural predation by wolves (Canis lupus) on the local populations of their main prey: wild boar (Sus scrofa) and roe deer (Capreolus capreolus). We estimated the percent composition of wolf diet from scat analysis (n = 2,150) and converted it into ingested biomass and number of killed individuals by quantifying the energy requirement of the resident wolf pack based on the field metabolic rate formula. Moreover, we collected data on hunting bags, and investigating the age/weight class preferences of both wolves and hunters compared their impacts on the two ungulate populations. In both prey species, losses due to hunting resulted to be eight to nine times higher than those due to wolf predation. In terms of number of individuals removed per year, the wild boar was the main prey species for wolves (mean ± SD: 83 ± 23) and the most harvested by hunters (mean ± SD: 609 ± 241). Wolves targeted the intermediate weight class (10–35 kg) in wild boar and showed no preference for a specific class of roe deer, while hunters targeted the largest classes in both species. The combined removal by hunters and wolf predation did not exceed the recruitment of both ungulate populations. We can therefore argue that a top‐down force is unlikely to contrast the population growth of the two ungulate species in Central Italy.

DNA Metabarcoding as a Tool for Disentangling Food Webs in Agroecosystems.

Better knowledge of food webs and related ecological processes is fundamental to understanding the functional role of biodiversity in ecosystems. This is particularly true for pest regulation by natural enemies in agroecosystems. However, it is generally difficult to decipher the impact of predators, as they often leave no direct evidence of their activity. Metabarcoding via high-throughput sequencing (HTS) offers new opportunities for unraveling trophic linkages between generalist predators and their prey, and ultimately identifying key ecological drivers of natural pest regulation. Here, this approach proved effective in deciphering the diet composition of key predatory arthropods (nine species.; 27 prey taxa), insectivorous birds (one species, 13 prey taxa) and bats (one species; 103 prey taxa) sampled in a millet-based agroecosystem in Senegal. Such information makes it possible to identify the diet breadth and preferences of predators (e.g., mainly moths for bats), to design a qualitative trophic network, and to identify patterns of intraguild predation across arthropod predators, insectivorous vertebrates and parasitoids. Appropriateness and limitations of the proposed molecular-based approach for assessing the diet of crop pest predators and trophic linkages are discussed.

Understanding diverse approaches to predator management among gamekeepers in England

Abstract Disagreements and disputes over the management of predatory animals are a frequent feature of conservation conflicts. In the UK, there are long‐standing conflicts surrounding legal and illegal killing of predators as part of management fostering game species as quarry for sport shooting. Despite the central role of gamekeepers as stakeholders and actors in this predominant form of predator management, little direct attention has been paid to their perspectives and motivations. We conducted semi‐structured interviews on the subject of predator management with 20 gamekeepers across the south of England and applied a social‐psychological approach to explore the underlying beliefs, norms and information sources associated with their actions. Data were analysed for patterns in terminology, rationalization or subject and synthesized into broad ‘motivations’, which were structured using a framework from the Theory of Planned Behaviour (TPB). Six primary motivations for predator management emerged: professional identity, personal norms, potential penalties, perceived impact, personal enjoyment and perceived ease. Perceived impact of predators on released game, and wildlife more broadly, was a central driver of predator killing. We identified three indirect influences on how this impact is judged: ‘maintaining balance’, ‘appeal to nature’ and ‘problem individuals’. We find that predator killing by gamekeepers is not solely a function of perceived economic loss but a product of multiple factors, including perceived professional norms, a sense of personal responsibility for game and non‐game wildlife, and assessments of predator populations and behaviours based on personal encounters. Motivations were well characterized within the TPB framework, with links to subjective norms, attitudes and perceived behavioural control. Our use of this social‐psychological approach to understanding the actions and preferences of these key stakeholders highlights how behaviours that are central to conservation conflicts have multiple social and ecological drivers. Characterizing the multiple motivations behind predator killing might help address aspects of the social conflicts with which sport shooting is currently associated, if actions, deliberation and, where appropriate, mediation, can be targeted at the key concerns of these central stakeholders and actors. A free Plain Language Summary can be found within the Supporting Information of this article.

Patterns of Vespa velutina invasion in Portugal using crowdsourced data

Abstract The invasive yellow‐legged hornet (Vespa velutina) was first detected in mainland Portugal in September 2011. The lack of information regarding the processes of species spread has hampered the development of adequate measures to mitigate the potential impact of this invasive predator. Crowdsourced data, i.e., information opportunistically reported by citizens, can facilitate the collection of numerous species occurrence records over large spatial scales, which can be valuable to understand the expansion of invasive species. Here, using validated crowdsourced data on the precise location of 49 013 nests, we: (i) update information regarding V. velutina distribution in Portugal; (ii) estimate the species expansion rate; and (iii) analyse the patterns of nests distribution at national and local scales. The species is currently distributed over an area of approximately 57 000 km2, which corresponds to 62% of mainland Portugal. We estimated an average rate of 37.4 ± 13.2 km/year for V. velutina expansion. Vespa velutina nests presented an aggregated distribution and nest density at the urban local‐scale was estimated in 5.4 ± 3.3 nests/km2. The observed decrease in the nearest‐neighbour nest distance over the years suggests that the density of nests has not reached its limit. We advocate that the development of a cheap and rapid method for nest detection and the study of fine‐scale mechanisms leading to V. velutina dispersal are important steps to identify colonisation pathways and plan management approaches aiming to halt species spread and impact in apiaries.

Density dependence mediates the ecological impact of an invasive fish

AbstractAimThe way in which habitat heterogeneity and predator density affect predator–prey dynamics, space use and prey risk are understudied aspects of foraging ecology, particularly for invasive species. Likewise, how an invasive species’ impact scales with its abundance is poorly understood. We used a model invasive species—lionfish (Pterois volitans)—to understand emergent multiple predator effects and influences of habitat heterogeneity on consumption rate and prey mortality risk.LocationFlorida, USA.MethodsWe considered effects of both predator and prey abundance on density‐dependent impact. We used functional response methodology to quantify the per‐capita effect of P. volitans, assessing concomitant influences of prey refuge (3 levels) and predator density (3 levels) on predator–prey space use and predation efficiency across increasing prey densities (7 levels). We then assessed intraspecific interaction outcomes by comparing observed per‐capita effects with predicted estimates based on consumption rates of individual predators. This allowed us to detect the presence of emergent multiple predator effects (MPEs) and tease apart density‐dependent impacts.ResultsLionfish predatory impact was mediated by predator and prey density but unaffected by refugia. Despite incongruent patch preferences between predators and their prey, predator impacts were context‐independent. We also detected nonlinear scaling of impact with increasing predator abundance. Pairs of lionfish had the greatest per‐capita effect, whose cumulative impact on prey matched that expected of independently foraging predators. At the highest predator density (four fish), antagonistic multiple predator effects precipitated prey risk reduction, in which we observed the lowest per‐capita effect. Across predator abundances, prey mortality rates were inversely density‐dependent.Main conclusionsQuantifying non‐independent consumptive effects of multiple conspecific predators across levels of prey abundance can inform better prediction and understanding of invasive species' density‐dependent effects. Additionally, consideration of heterogeneity‐mediated FRs and predator–prey spatial distributions may facilitate more precise and realistic predictions of invader impact across their invaded range.

Role of grasslands in pest suppressive landscapes: how green are my pastures?

AbstractGrasslands are valuable non‐crop habitats in the world's agricultural regions, providing more than simply forage for grazing domestic and wild animals. They provide refuge and resources that support high levels of arthropod biodiversity, most importantly for natural enemies that provide vital biological control services to the surrounding cropped landscape. Ideally, farmers could manage and manipulate grasslands to boost their biocontrol services, although to achieve this, knowledge of the ecological function of these habitats is essential. Unfortunately, grasslands are often bundled together with other habitat types, such as scrubland and forest, under the label ‘non‐crop habitats’, and little is known about the contribution that these specific habitats make towards landscape pest suppression. While recent research has been investigating the importance of other non‐crop habitat such as native vegetation remnants, the contribution that grassland habitats may make towards landscape pest suppression remains a significant knowledge gap in biocontrol research. Here, the current understanding of grassland habitats as biological control service providers in the world's mixed farming systems is reviewed. Limited research into whether grassland habitats support natural enemies, and thus contribute biological control services to the adjacent surrounding cropped landscape, has returned inconclusive, even conflicting, results. Potential explanations for this inconsistency are explored, including the lack of studies, inadequate estimates of predator impact and the variety of different grassland habitat types studied, including their diversity in composition and management practices. Conclusions drawn from these studies are discussed, and suggestions for management are recommended, including increasing grassland floristic diversity, limiting intensive management practices and implementing weed control. Future research directions are proposed, along with the need to develop a universal grassland classification system for research, management and conservation purposes, using grassland type, floristic diversity and management practices as key axes for classification.

Population dynamics and predatory impact of the alien jellyfish Aurelia solida (Cnidaria, Scyphozoa) in the Bizerte Lagoon (southwestern Mediterranean Sea)

Understanding the life cycle strategies and predatory impact of alien jellyfish species is critical to mitigate the impact these organisms may have on local populations, biodiversity, and ultimately on the functioning of food webs. In the Mediterranean Sea, little is known about the dynamics of alien jellyfish, although this area is a biodiversity hotspot and one of the most threatened by an increasing number of alien jellyfish. Here, we investigated the population dynamics and predatory impact of a non-indigenous scyphomedusa, Aurelia solida Browne 1905, in the Bizerte Lagoon, Tunisia. The study was based on a bimonthly survey performed over two consecutive years, from November 2012 to August 2014. Field observations showed that the planktonic phase of A. solida occurs from winter to early summer. Prey composition was investigated by means of gut content and field zooplankton analyses. Calanoid copepods, mollusc larvae and larvaceans represented the main food items of A. solida. To determine the jellyfish feeding rate and their predatory impact on zooplankton populations, the digestion time for zooplankton prey was assessed at three different temperatures: 13, 18 and 23 °C in laboratory conditions, corresponding to the average range of temperatures encountered by A. solida in the Bizerte Lagoon. We found that A. solida consumed 0.5–22.5% and 0.02–37.3% of the daily zooplankton standing stock in 2013 and 2014, respectively. These results indicate a non-negligible but restricted seasonal grazing impact on some mesozooplankton groups, explained by the relatively short lifespan of the medusa stage (5–6 months).

Fresh, frozen or fake: A comparison of predation rates measured by various types of sentinel prey

AbstractArthropod predators and parasitoids support the health and functioning of the world's ecosystems, most notably by supplying biological control services to agricultural landscapes. Quantifying the impact that these organisms have on their prey can be challenging, as direct observation and measurement of arthropod predation is difficult. The use of sentinel prey is one method to measure predator impact; however, despite widespread use, few studies have compared predation on different prey types within a single experiment. This study evaluated the predation rates on four sentinel prey items in grass and wheat fields in south‐east Queensland, Australia. Attack rates on live and dead Helicoverpa armigera eggs, and dead H. armigera larvae and artificial plasticine larvae, were compared and the predators that were attracted to each prey type were documented with the use of field cameras. There was no significant difference in predation rates between sentinel eggs, while dead larvae were significantly more attacked than artificial larvae. Prey were attacked by a diverse range of predators, including ants, beetles, various nymph and juvenile insects and small mammals. Different predators were active in grass and crop fields, with predator activity peaking around dawn and dusk. The same trends were observed within and between the two habitats studied, providing a measure of confidence in the sentinel prey method. A range of different sentinel prey types could be suitable for use in most comparative studies; however, each prey type has its own benefits and limitations, and these should be carefully evaluated to determine which is most suitable to address the research questions.

Impact of pathogenic fungi, herbivores and predators on secondary succession of tropical rainforest vegetation

Abstract There is growing evidence that top–down biotic factors play an important role in plant community dynamics and are able to maintain the high plant diversity of primary tropical forests. However, the top–down impact by herbivores on the accumulation of plant biomass, richness and the community assembly process remains poorly known for the initial stages of secondary ecological succession. Here we test the top–down effects of natural enemies on the biomass, richness, diversity, community composition, trait dynamics and randomness during the assembly process on an early successional community in a lowland tropical forest in Papua New Guinea. We initiated secondary succession on 36 vegetation plots (5 × 5 m) organized in six blocks. After 1 year we evaluated successional community characteristics in each block containing a control plot and five treatment plots: experimentally excluding (a) insects by insecticides, (b) fungal pathogens by fungicides, (c) vertebrate predators and ants with exclosures and traps and experimentally adding (d) low and (e) high levels of a generalist herbivore species. Insects were responsible for increased plant diversity, shifts in plant community composition and a decrease in community weighted mean of leaf dry matter content. The lack of herbivores resulted in a diversifying effect but did not affect plant biomass and stem density. No other treatment had a significant effect on plant diversity during succession. The highest level of artificially increased herbivore density reduced plant biomass, while the fungicide treatment decreased stem density of woody plants. Using a null model approach, we showed that the removal of insects and their vertebrate predators increased randomness during the community assembly processes for woody plants, whilst the same effect was not found for the removal of fungi or elevated herbivore abundances. Synthesis. Early rainforest succession was not entirely plant driven. During the early succession of lowland tropical forest, insect herbivores enhanced plant diversity and caused shifts in community structure by promoting species with acquisitive leaf traits. As expected, the early successional communities were highly variable, but insects and vertebrate predators reduced randomness during the assembly process. Insect and vertebrate communities can thus impact the regeneration dynamics of tropical forests. In contrast, fungal pathogens were less important in maintaining high diversity of successional communities in our system.

Can ocean acidification interfere with the ability of mud snails (Tritia obsoleta) to sense predators?

Nonlethal predator-prey interaction between Dyspanopeus sayi (northern mud crab) and Tritia obsoleta (mud snail) under ocean acidification conditions (OA) were investigated. Nonlethal interactions can influence predator-prey relationships and magnify the ecological impact of predators in marine habitats. Future increases in OA necessitate an understanding of how prey perceive the threat of predation and how this may be impacted by ocean acidification. In baseline experiments at pH 8.1, mud snails responded differently to crab cues compared to crushed conspecifics, burying in the presence of crushed conspecifics and fleeing in the presence of a mud crab. While many predator cue experiments combine these two types of cues, these results suggest that mud snails not only discern between threat cues but also have a nuanced response that is tailored to specific threats. Mud snail responses to predator-prey relationships were delayed under lower pH conditions, as snails in acidified treatments did not exhibit any of the escape responses that they commonly displayed under control conditions. Thus, acidification could shift predator-prey relationships and significantly alter food webs under acidified conditions.

Effects of predation pressure and prey density on short‐term indirect interactions between two prey species that share a common predator

1. Generalist predators are important contributors to reliable conservation biological control. Indirect interactions between prey species that share a common generalist predator can influence both community dynamics and the efficacy of biological control.2. Laboratory cage experiments investigated the impact of the combined consumptive and non‐consumptive effects of predation by adult Hippodamia convergens as a shared predator on the population growth and relative abundance of Acyrthosiphon pisum and Aphis gossypii as prey species. Predation pressure and prey density were varied.3. At low predation pressure the indirect interaction between aphid species was asymmetrical with a proportionally greater negative impact of predation on A. gossypii than on A. pisum. At intermediate predation pressure, the indirect interaction became symmetrical. At high predation pressure and higher levels of prey density, it was asymmetrical with greater negative impact on A. pisum, often driven to local extinction while A. gossypii populations persisted.4. A linear mixed‐effects model including early population growth of both aphid species and predation pressure explained 96% and 92% of the variation in the population growth of A. pisum and A. gossypii, respectively, over an 8‐day period. The overall effect of shared predation on the indirect interaction between the two aphid species is best described as apparent commensalism, where A. pisum benefited from early population growth of A. gossypii, while A. gossypii was unaffected by early population growth of A. pisum. Considering these indirect interactions is important for conservation biological control efforts to be successful.

Threats from the air: Damselfly predation on diverse prey taxa.

To understand the diversity and strength of predation in natural communities, researchers must quantify the total amount of prey species in the diet of predators. Metabarcoding approaches have allowed widespread characterization of predator diets with high taxonomic resolution. To determine the wider impacts of predators, researchers should combine DNA techniques with estimates of population size of predators using mark-release-recapture (MRR) methods, and with accurate metrics of food consumption by individuals. Herein, we estimate the scale of predation exerted by four damselfly species on diverse prey taxa within a well-defined 12-ha study area, resolving the prey species of individual damselflies, to what extent the diets of predatory species overlap, and which fraction of the main prey populations are consumed. We identify the taxonomic composition of diets using DNA metabarcoding and quantify damselfly population sizes by MRR. We also use predator-specific estimates of consumption rates, and independent data on prey emergence rates to estimate the collective predation pressure summed over all prey taxa and specific to their main prey (non-biting midges or chironomids) of the four damselfly species. The four damselfly species collectively consumed a prey mass equivalent to roughly 870 (95% CL 410-1,800) g, over 2months. Each individual consumed 29%-66% (95% CL 9.4-123) of its body weight during its relatively short life span (2.1-4.7days; 95% CL 0.74-7.9) in the focal population. This predation pressure was widely distributed across the local invertebrate prey community, including 4 classes, 19 orders and c. 140 genera. Different predator species showed extensive overlap in diets, with an average of 30% of prey shared by at least two predator species. Of the available prey individuals in the widely consumed family Chironomidae, only a relatively small proportion (0.76%; 95% CL 0.35%-1.61%) were consumed. Our synthesis of population sizes, per-capita consumption rates and taxonomic distribution of diets identifies damselflies as a comparatively minor predator group of aerial insects. As the next step, we should add estimates of predation by larger odonate species, and experimental removal of odonates, thereby establishing the full impact of odonate predation on prey communities.

Feeding behaviour of red fox and domestic cat populations in suburban areas in the south of Paris

Among medium-sized carnivores, red foxes (Vulpes vulpes) and domestic cats (Felis silvestris catus) are the most abundant species in human-dominated landscapes worldwide. Both are known to be generalist predators that exploit a wide range of prey groups (e.g., mammals, birds, and invertebrates). Identifying red fox and domestic cat predation pressure on shared prey could shed light on their ecological role in shaping wildlife communities in human-dominated landscapes. Here, we assess the seasonal diet of red foxes and domestic cats in terms of composition, breadth, and overlap. Over two years, we collected their scats across three human-dominated study sites: park (n = 220 for foxes and n = 0 for cats), agricultural land (n = 159 for foxes and n = 146 for cats), and managed forest (n = 169 for foxes and n = 47 for cats). We detected similar diet breadth (B) for red foxes and domestic cats (B = 0.32 and B = 0.36, respectively) as well as strong dietary overlap (O = 0.83) between them. Moreover, the diet composition of both predators varied according to the study sites and seasons. Our results confirm the highly flexible trophic behaviour of these carnivores at the study sites, probably as a consequence of prey availability, and also the simultaneity of their predation over the same prey groups. Future studies should simultaneously monitor predator diet as well as predator and prey abundance in human-dominated landscapes to better understand the predatory impact of red foxes and domestic cats.

Diet of an endangered Neotropical catfish (Kalyptodoras bahiensis) from the Paraguaçu River, Bahia, Brazil

ABSTRACT The present study investigates the diet composition and the feeding strategy of Kalyptodoras bahiensis by verifying variations during the hydrological cycle and between males and females. Samples were collected during the periods of rain and drought using various fishing gears adapted to each microhabitat. In laboratory, the fishes were weighed and measured. An abdominal incision was made to observe the gonads for sex determination and the stomach was removed for identification and quantification of food items. The importance of each item in the diet was calculated using the Feeding Index. Amundsen graphic analysis was used to define the feeding strategy. Kalyptodoras bahiensis was classified as an omnivorous species with an invertivorous tendency. The species presented a generalist feeding strategy and many individuals fed on Melanoides tuberculatus, an exotic mollusk that has spread to Brazilian rivers, causing damages to the native community. The high amount and frequency of M. tuberculatus in the diet of K. bahiensis suggest that the species may have a predatory impact on the local population of this mollusk. However, further studies are needed to better understand the interaction between K. bahiensis and M. tuberculatus.

The Elephant in the room: What can we learn from California regarding the use of sport hunting of pumas (Puma concolor) as a management tool?

Puma (Puma concolor) management in the western United States is highly contentious, particularly with regard to the use of sport hunting as a management tool. Since the 1970s, puma in ten western states have been managed by state fish and game agencies through the use of a sport hunt. The rationale presented by wildlife managers is that sport hunting, in addition to providing recreational hunting opportunities, also reduces threats to human safety and livestock safety, and increases populations of the puma’s ungulate prey, namely deer (Odocoileus sp.) and elk (Cervus elepus). We evaluated these claims using the state of California as a control, which has prohibited sport hunting since 1972, and employing data obtained from state and federal agencies with authority and control over puma management. Specifically, we tested four hypotheses: 1) sport hunting will suppress puma populations, 2) sport hunting will reduce the number of problematic puma-human encounters; 3) sport hunting will reduce puma predation on domestic livestock, and 4) sport hunting will reduce the impact of puma predation on wild ungulate numbers, resulting in increased hunting opportunities for the sport hunt of ungulates. Our results indicated, respectively, that relative to the 10 states where puma are hunted, California had 1) similar puma densities, 2) the 3rd lowest per capita problematic puma-human encounters, 3) similar per capita loss of cattle (P = 0.13) and a significantly lower (t = 5.7, P < 0.001) per capita loss of sheep, and 4) similar average deer densities while changes in annual deer populations correlated with changes in other states (F = 95.4, P < 0.001, R2 = 0.68). In sum, our analysis of the records obtained from state and federal wildlife agencies found no evidence that sport hunting of pumas has produced the management outcomes sought by wildlife managers aside from providing a sport hunting opportunity. Consequently, and particularly because other research suggests that sport hunting actually exacerbate conflicts between pumas and humans, we recommend that state agencies re-assess the use of sport hunting as a management tool for pumas.

Native Gammarus fossarum affects species composition of macroinvertebrate communities: evidence from laboratory, field enclosures, and natural habitat

Despite the fact that native species of amphipods have been recognized as active predators similarly to invasive species, little is known about their predatory impact on aquatic communities. In this study, we used a laboratory experiment, a field enclosure experiment, and an analysis of natural community data to demonstrate how Gammarus fossarum affects the species composition of benthic communities by imposing survival selection on its prey. Our laboratory single-prey experiment brought a clear evidence that tube-less chironomids are vulnerable prey and that the predation rate on the tube-dwelling chironomids decreases with increasing tube toughness (from the soft tubes made of detritus to the hard tubes made of sand or calcium carbonate grains). We found that the introduction of G. fossarum to field enclosures significantly changed the species composition of a macroinvertebrate community at an experimental spring fen site. The soft-bodied, slow moving, and tube-less taxa were depleted the most. It appears that the observed patterns were a result of predator’s preference rather than encounter rate. Survival selection was detected also in natural communities across a large spatial scale. In accordance with the experiments, high densities of G. fossarum limited the proportion or abundance of vulnerable prey. Our study (1) provides the first convincing evidence that biotic interactions have a structuring effect on the spring fen communities, (2) documents how the predatory effect in a community depends on an interplay between the prey handling behaviour of the predator and species-specific susceptibility of prey, and (3) shows that an omnivorous native amphipod may have a strong impact on aquatic communities despite it is regarded less aggressive than its invasive relatives.

Precipitation and predation risk alter the diversity and behavior of pollinators and reduce plant fitness.

Biotic and abiotic factors may individually or interactively disrupt plant-pollinator interactions, influencing plant fitness. Although variations in temperature and precipitation are expected to modify the overall impact of predators on plant-pollinator interactions, few empirical studies have assessed if these weather conditions influence anti-predator behaviors and how this context-dependent response may cascade down to plant fitness. To answer this question, we manipulated predation risk (using artificial spiders) in different years to investigate how natural variation in temperature and precipitation may affect diversity (richness and composition) and behavioral (visitation) responses of flower-visiting insects to predation risk, and how these effects influence plant fitness. Our findings indicate that predation risk and an increase in precipitation independently reduced plant fitness (i.e., seed set) by decreasing flower visitation. Predation risk reduced pollinator visitation and richness, and altered species composition of pollinators. Additionally, an increase in precipitation was associated with lower flower visitation and pollinator richness but did not alter pollinator species composition. However, maximum daily temperature did not affect any component of the pollinator assemblage or plant fitness. Our results indicate that biotic and abiotic drivers have different impacts on pollinator behavior and diversity with consequences for plant fitness components. Even small variation in precipitation conditions promotes complex and substantial cascading effects on plants by affecting both pollinator communities and the outcome of plant-pollinator interactions. Tropical communities are expected to be highly susceptible to climatic changes, and these changes may have drastic consequences for biotic interactions in the tropics.

Phenotypic plasticity of senescence in Daphnia under predation impact: no ageing acceleration when the perceived risk decreases with age.

Recognising the nature of the predation risk, and responding to it accurately, is crucial to fitness. Yet, even the most accurate adaptive responses to predation risk usually entail costs, both immediate and lifelong. Rooting in life-history theory, we hypothesize that an animal can perceive the nuances of prey size and age selectivity by the predator and modulate its life history accordingly. We test the prediction that—contrary to the faster or earlier senescence under predation risk that increases with prey size and age—under predation risk that decreases with prey size and age either no senescence acceleration or even its deceleration is to be observed. We use two species of indeterminate growers, small crustaceans of the genus Daphnia, Daphnia Pulex and Daphnia magna, as the model prey, and their respective gape-limited invertebrate predators, a dipteran, midge larva Chaoborus flavicans, and a notostracan, tadpole shrimp Triops cancriformis. We analyse age-specific survival, mortality and fertility rates, and find no senescence acceleration, as predicted. With this study, we complete the picture of the expected non-consumptive phenotypic effects of perceived predation pressure of different age-dependence patterns.

Disturbance-mediated consumer assemblages determine fish community structure and moderate top-down influences through bottom-up constraints.

Disturbance is a strong structuring force that can influence the strength of species interactions at all trophic levels, but controls on the contributions to community structure of top-down and bottom-up processes across such gradients remain poorly understood. Changes in the composition of predator and consumer assemblages, and their associated traits, across gradients of environmental harshness (e.g. flooding), are likely to be a particularly important influence on the strength of top-down control and may drive bottom-up constraints. We examined how consumers with particular traits, and the predators that consumed them, varied across a gradient of stream flooding disturbance and used experiments to assess the predation impact on those contrasting consumer communities (ultimately quantifying how flood disturbance altered the strength of top-down control). Consumer community composition and mobility were strongly related to flood disturbance; the biomass and drift of protected primary consumers (i.e. those with morphological defences) decreased with increasing flood disturbance. Predatory fish species had different disturbance niches, and path analysis identified that both direct flood disturbance effects and indirect bottom-up constraints of flood disturbance on consumers influenced predatory fish composition and biomass. Fish generally fed most effectively on consumer types associated with their particular niche, but all fish were strongly size-selective when feeding on protected consumers. Although protected consumers did not grow large enough to escape predation, an in situ experiment showed protected consumers were at a reduced risk of predation as disturbance increased compared to unprotected consumers. Overall, top-down control declined with flood disturbance, but the effect depended on consumer traits. Predatory fish were only capable of exerting top-down control on protected consumers in benign habitats but impacted unprotected consumers across a larger range of the disturbance gradient. Collectively our findings suggest that a shift towards a more disturbed state will probably result in reduced predator impacts and a weakening of top-down control. Moreover, predicted increases in the frequency and intensity of climatic events causing disturbance, such as flooding, are likely to result in a community shift that disproportionately impacts protected consumers and the predators that utilize them as prey through the subsequent bottom-up constraints.

Quantifying the relative predation pressure on bumblebee nests by the European badger (Meles meles) using artificial nests.

Bumblebee populations are declining. Factors that impact the size and success of colonies act by either limiting resource availability (bottom‐up regulation) or causing mortality, for example, pesticides, disease, and possibly predation (top‐down regulation). The impact of predation has not been quantified, and so, the current study used novel artificial nests as a proxy for wild bumblebee nests to quantify the relative predation pressure from badgers in two habitats: woodland and grassland, and at two nesting depths: surface and underground. Badgers occur across most parts of the UK and are known to predate on bumblebee nests. We found that significantly more artificial nests (pots containing bumblebee nest material) were dug up compared with control pots (pots without bumblebee nest material). This shows that artificial nests have the potential to be used as a method to study the predation of bumblebee nests by badgers. In a location of high badger density, predation pressure was greater in woodland than grassland, whereas no difference was observed in relation to nest depth. Woodland and grassland are shared habitats between bumblebees and badgers, and we suggest that higher predation may relate to activity and foraging behavior of badgers in woodland compared with grassland. We discuss how badger predation in different habitats could impact different bumblebee species according to their nesting behaviors. Understanding the relative impact of badger predation on bumblebee colonies provides key information on how such top‐down regulation affects bumblebee populations.