High Predation Research Articles

Artificial light at night reduces predation and herbivory rates in a nearshore reef.

Artificial light at night (ALAN) is an escalating anthropogenic stressor that can affect ecological communities over a range of spatial scales by altering key ecological processes, such as predation and herbivory. Shallow subtidal reefs are highly diverse and productive habitats that are vulnerable to ALAN. We investigated rates of consumption by fish (predation and herbivory) under different light treatments (ALAN, dark and daylight conditions) using standardised bioassay methods, i.e. squidpops and Ulva pops in situ. We also used GoPros to record predator identity, number of strikes and time to strike in ALAN and daylight treatments. Contrary to previous studies, we found that predation and herbivory rates were significantly lower in ALAN treatments than in daytime and dark treatments. The highest predation and herbivory rates were observed in daytime treatments. The identity of predator species, time to strike and number of strikes also differed between daytime and ALAN treatments. Due to low light conditions, dark treatments were not filmed. Our findings suggest that ALAN can alter predation in unexpected ways, depending on the environmental conditions and species affected. Future coastal management strategies need to account for light pollution as a major stressor to preserve valuable ecological resources.

Ecological and demographic drivers of kin-directed cooperation in a social bird: Insights from a long-term study.

The evolution of sociality is one of the major evolutionary transitions in the history of life and a key step in this transition is the occurrence of kin associations. Yet, the question of what demographic processes and environmental factors generate kin-structured populations and drive kin-directed cooperation remains open. In this review, we synthesise 30 years of studies of the long-tailed tit Aegithalos caudatus, which has a kin-selected cooperative breeding system with redirected help: failed breeders may help to raise offspring of conspecifics, typically relatives, breeding nearby. We describe the use of ecological, demographic, genetic and behavioural approaches to reveal: (a) how kin-structured populations (here 'kin neighbourhoods') arise; (b) why the prevalence of cooperation varies among populations and individuals; and (c) how variation in dispersal and opportunities for cooperation influence individual fitness. The kin neighbourhoods of long-tailed tits arise from three processes. First, natal dispersal is limited and sex-biased so many individuals, especially males, recruit as breeders close to their natal site. Second, neither dispersal nor migration necessarily disrupts kin associations because long-tailed tits often move with close relatives. Third, a small effective population size driven by high nest predation rates enhances within-population relatedness. Together, these processes set the scene for kin-directed helping behaviour by causing spatial clustering of relatives. The prevalence of cooperation within kin neighbourhoods depends on several factors, both at the population-level (annual nest predation rate and length of the breeding season) and individual-level (relatedness, familiarity, sex and condition). However, limited information on prior social association and the reliability of kin discrimination cues hampers our current understanding of individual helping decisions. Finally, variation in dispersal within and between sexes affects the probability of interacting with kin, the likelihood of cooperation, and accrual of the direct and indirect components of inclusive fitness. We use this comprehensive understanding of the factors driving cooperative behaviour in long-tailed tits to highlight gaps in knowledge and suggest future avenues for research in this system, and to make general inferences about the role of dispersal, demography and kinship in social evolution.

Seasonal variation in roost climate and emergence behaviour in a colony of the highly gregarious wrinkle-lipped free-tailed bat (Mops plicatus)

ABSTRACT As obligate nocturnal mammals, most bats spend the day hiding in dark shelters, sometimes as gregarious colonies. Roosting in such large colonies may have the advantage of reducing thermoregulatory costs, as the heat dissipated by thousands of bodies raises the temperature of the cave interior. However, bats in large aggregations may also suffer from increased predation risk. Here we studied the effect of a highly gregarious Palaeotropical bat, the wrinkle-lipped free-tailed bat (Mops plicatus), on cave temperature and the factors that influence its emergence behaviour. We studied cave temperature, prey abundance, emergence behaviour and attack rates by birds of prey during colony emergence. The study was made at Khao Wongkot Cave, counting more than one million individuals. In all seasons, we observed that the presence of M. plicatus caused relatively higher temperatures of around 30°C inside the cave, while temperatures outside were lower and more variable. This suggests that the body heat of aggregated bats raised the temperature inside the cave, presumably close to the thermo-neutral zone at the roosting sites of bats. Arthropod abundance was highest during late pregnancy/early lactation and lowest during late lactation/post lactation. Bats emerged earliest during the late wet season and latest during the hot season. During periods of high predation risk, bats always emerged as a column, whereas during periods of low predation risk (hot and early wet seasons), individual bats left first, before a column of bats formed, 10 to 20 min after the first individuals exited the cave. Our study highlights that large colonies may provide thermoregulatory benefits that could increase individual fitness. However, aggregations also increase predation costs during emergence. Bats form a column when aerial predator attacks are most frequent. Also, bats seem to adjust their emergence timing in response to seasonal changes in predation risk.

Aquatic-terrestrial linkages drive contrasting biodiversity patterns in tropical and temperate forests.

Riparian ecosystems harbour unique biodiversity because of their close interconnections with adjacent aquatic ecosystems. Yet, how aquatic ecosystems influence terrestrial biodiversity over different spatial scales is poorly understood, particularly in the tropics. We conducted field campaigns to collect 235 terrestrial invertebrate assemblages along 150 m transects from 47 streams in both Brazil and the UK, compiling one of the largest known datasets of riparian invertebrate community composition at multiple spatial scales. Invertebrate densities increased towards water in both regions. In Brazil, this was driven by an increase in spiders, with a corresponding decrease in non-predators, resulting in higher predator : prey ratios near water. In the UK, non-predator densities increased towards water, decreasing predator : prey ratios. While pairwise dissimilarity increased with distance from water in both regions, β-diversity was significantly higher in tropical assemblages, with more β-diversity explained by turnover. Spider community composition was significantly structured by distance from water in the Brazilian sites, suggesting tropical assemblages were influenced more by emerging aquatic prey, with a distinct spider community replacing other predators, with possible top-down control of terrestrial prey. High turnover-driven dissimilarity among tropical assemblages suggests that Brazilian riparian ecosystems are better managed at the landscape scale, with an emphasis on in-stream measures preventing disruption of aquatic resource subsidies.

Threat to the predator suppresses defence of its prey.

Many studies have shown that prey can optimize their defence mechanisms based on cues indicating predator presence and pressure. However, little is known about whether prey can assess the actual threat by considering both predator density and the motivational state of cannibalistic predators, which can be influenced by threats from higher order predators. We conducted laboratory experiments to test the hypothesis that high predator density, combined with chemical cues indicating predator stress (e.g. alarm and disturbance cues), may inhibit prey defences. Using Daphnia and Zygoptera/Anisoptera larvae, we observed that Daphnia's strong response to low-density predator kairomones was suppressed when exposed to high-density predator kairomones and disturbance cues. Surprisingly, we found no evidence of a suppressive response to alarm cues. Our study is to our knowledge, the first to show that prey uses predator stress cues to avoid unnecessary defences, suggesting a 'cascade of fear' in which fear at one trophic level reduces fear at a lower level. Furthermore, it is to our knowledge the first to demonstrate that prey can reduce their anti-predator response in the presence of high densities of cannibalistic predators.

Neonicotinoid exposure causes behavioral impairment and delayed mortality of the federally threatened American burying beetle, Nicrophorus americanus.

Among the most immediate drivers of American burying beetle (Nicrophorus americanus Olivier) declines, nontarget toxicity to pesticides is poorly understood. Acute, episodic exposure to neonicotinoid insecticides at environmentally relevant concentrations is linked to negative impacts on beneficial terrestrial insect taxa. Beyond mortality, behavioral indicators of toxicity are often better suited to assess sublethal effects of residual concentrations in the environment. First, Nicrophorus spp. congeners were used to generate and identify a low-dose exposure rate (lethal dose 10%; LD10) from an acute, 24-hour exposure and the concentration-series was confirmed by LC-MS/MS. Next, we evaluated the effects of single and repeated low-dose (LD10 = 58.9 ng/beetle) imidacloprid exposure on N. americanus behavior (10 minutes post-dose) and mortality (10 days post-dose). Behavior parameters were analyzed using EthoVision-XT. Control N. americanus were significantly less mobile, demonstrating death-feigning, an anti-predator behavior. Single LD10 dosed N. americanus were hyperactive, traveling over 4 times farther (total distance; p = 0.03) and faster (mean velocity; p = 0.02) than controls. Single and repeated LD10 dosed N. americanus extended their wings without taking flight and flipped on their backs. All control N. americanus survived 10 days post-dose; single LD10 and repeated LD10 exhibited 30% and 50% mortality, respectively. A single LD10 exposure event was sufficient to significantly elicit greater movement and high predation risk behaviors, whereas repeated LD10 exposure did not worsen behavioral impairment but increased mortality over time. Collectively, generalized linear mixed effects models indicated that distance traveled, velocity, and extended wings were significant predictors of mortality. Recently reclassified, the federally threatened N. americanus may be at greater risk to insecticide exposure than previously thought and vulnerable to episodic, low-dose neonicotinoid exposure.

Living in fear: How experience shapes caribou responses to predation risk

AbstractWild prey can reduce predation risk by avoiding areas used by their predators. As they get older, individuals should be able to fine‐tune this avoidance based on their increased experience with predation risk. Such learning mechanisms are expected to play a key role in how individuals cope with risk during their life, particularly in altered landscapes where human disturbances have created habitat conditions distinct from those of the past. We studied the role of experience on the avoidance of risky areas by boreal caribou (Rangifer tarandus caribou) in a system where they are under high predation pressure from gray wolves (Canis lupus) and black bears (Ursus americanus). Using telemetry data collected on 28 caribou, 31 wolves, and 12 bears, we investigated whether caribou adjusted their level of predator avoidance with passing monitoring years, a proxy of increasing experience. We observed an increase in the avoidance of areas suitable to wolves (during two study periods) and bears (during all study periods) with passing years. Periods during which caribou did not adjust their behavior toward wolves (winter and calving) were characterized by persistent—potentially innate—avoidance. Our results suggest that, in most circumstances, caribou became more efficient at avoiding areas selected by their predators as they gained experience. Future work should attempt to demonstrate whether such tactics are heritable; if so, our results would suggest that, given time, caribou living in disturbed environments would have the potential to adapt to changing levels of risk. This would give hope for the conservation of caribou, a species at risk in Canada, provided levels of risk do not surpass the limits of their behavioral plasticity.

Experimental transplants demonstrate shifts in predation favour evolution of aggressive behaviours in Trinidadian killifish

Abstract Theory asserts larger brains facilitate behaviours that enhance fitness. Research has demonstrated that increased brain size improves cognition and survival. However, the majority of research has focused on cross‐species comparisons. Experiments that manipulate selection to investigate the connection between brain size, behaviour and fitness are needed. Trinidadian killifish (Anablepsoides hartii) live in communities with (high predation: HP) and without (killifish only: KO) predators. Predator absence is associated with high population densities, increased intraspecific competition and evolved larger brain sizes. We tested for evolutionary shifts in behaviour by subjecting second‐generation lab‐reared killifish to a mirror aggression assay. We also quantify selection on brain size and behaviour by transplanting wild HP killifish to KO sites and tracking individual fitness (growth rates) with a mark‐recapture design. Lab‐reared killifish from KO sites—specifically males—exhibited higher levels of aggression than HP killifish. In the transplant experiment, HP killifish exhibited strong increases in aggression following the introduction to KO sites. Increased brain size was correlated with increased growth in transplanted HP killifish, yet there was no association between brain size, aggression and growth. Our results indicate that declines in predation and increased competition favour increases in aggression but further research is needed to determine if and how brain size and behaviour are linked through natural selection. Read the free Plain Language Summary for this article on the Journal blog.

Desert ants avoid ambush predator pits depending on position, visual landmarks and trapped nestmates.

Central-place foragers face high predation risk when repeatedly using routes near their nest, as predators can learn to ambush them there. We investigated the factors influencing the likelihood of desert ant foragers falling into pitfall traps, simulating common predators such as antlions or spiders. We varied the spatial configuration of the pitfall traps, the presence of trapped nestmates and the availability of visual landmarks to study the workers' susceptibility to falling into pits and their foraging success. Our results showed that a zigzag configuration of pits led to the fewest workers reaching the food reward, compared with straight-line and right-angled-triangle configurations. Over successive runs, workers became more efficient, with fewer falls into pits and faster food discovery, suggesting they either learned the locations of the pits or became more cautious. In any case, the ants learned about important landscape features close to their nest and the best way of navigating around it. Additionally, we examined the impact of trapped nestmates and visual landmarks. We found that pits marked with visual landmarks resulted in fewer falls. However, pits containing trapped nestmates attracted more ants, impaired food discovery and increased falling rates into pits, thereby imposing a twofold cost on ant foragers.

Neighbor Density and Post‐Contact Immobility Duration as Antipredator Behavior: Antlion Larvae Do Not Fit the Selfish Prey Hypothesis

ABSTRACTRemaining immobile for an unpredictable period after being touched by a potential predator (post‐contact immobility, PCI) may favor survival. However, the factors that determine variation in PCI duration are poorly understood. We tested whether PCI duration depends on the surrounding conspecific density (the selfish prey hypothesis) in the tropical antlion larvae Myrmeleon crudelis. These insects avoid predation by being immobile or burying themselves. The selfish prey hypothesis predicts a reduction in the PCI duration as conspecific density increases because this high density of conspecifics around can stimulate the redirection of the predator's interest in other nearby potential prey. In the field, we measured PCI and found that its duration was independent of the conspecific density. In the lab, we also measured the PCI of a subset of the same larvae in the absence of neighbors. Using a paired design, we found that PCI duration was lower in the lab in the absence of neighbors than in the field. Our results suggest that the antlion larvae did not follow the selfish prey hypothesis. We propose two alternative explanations. First, the larvae have a limited ability to detect neighbors in the field and keep up with the changing number of surrounding active pits. Second, burying may be more important than PCI as an antipredator strategy. In our lab experiment, larvae had a more accurate idea of the conspecific density around their pit because they explored the area. We propose that knowing the absence of conspecifics triggered a shorter PCI duration. Under a high predation risk (i.e., no other prey to which the predator would redirect its attention), the larvae select the unequivocal antipredator behavior of burying. This work illustrates the relevance of accurate information in deciding how to avoid predation, especially when prey can prioritize between alternative behaviors, with success varying between the contexts.

Costs of induced defenses dissipate by maturity for diploid and triploid oysters

Oyster reef restoration efforts and on-bottom aquaculture are frequently plagued with high predation rates. Oysters are phenotypically plastic, and rearing juvenile oysters, Crassostrea virginica, with predator cues causes them to grow stronger shells that increases survivorship in the field. However, induced defenses (e.g., shell hardening in oysters) are often associated with cost-benefit trade-offs, and the extent the increased shell strength persists into adulthood and alters the growth of somatic and reproductive tissues remains unknown. We raised diploid oysters (used in reef restoration) and triploid oysters (used in aquaculture) with and without predator cues for one month before placing individuals on an oyster farm to grow to market size. Oyster shell characteristics, soft tissue mass, and reproductive investment were measured periodically over one year of culture and compared across treatments. Both diploid and triploid oysters had significantly stronger and smaller shells than controls at the end of their nursery period. However, while diploid shells became 15 % stronger and 17 % smaller than controls, triploid shells became 28 % stronger and 23 % smaller. Additionally, triploid oysters exposed to predator cues returned to the size of controls faster and maintained their shell strength differences longer than diploids. Differences in soft tissue mass between treatments mirrored the patterns exhibited in shell size and weight with greater initial physiological costs and faster recovery for triploid individuals. There was no significant difference in somatic or reproductive tissue mass between induced and control oysters of the same ploidy after seven months in the field. Triploid oysters were 15–110 % larger than diploids depending on the characteristic measured at maturity. Additionally, there was a significant interaction between treatment and ploidy because induced triploids had marginally greater growth than their control counterparts while induced diploids had marginally less growth than controls. These findings demonstrate that physiological costs of oysters reacting to predators in early life stages are minimal by the time individuals reach maturity. Early exposure to predator cues is a promising tool for improving oyster survivorship in restoration and aquaculture operations, especially in regions with high predation pressure.

Background predation risk induces anxiety-like behaviour and predator neophobia in zebrafish

Prey face a major challenge in balancing predator avoidance with other essential activities. In environments with high risk, prey may exhibit neophobia (fear of novelty) due to the increased likelihood of novel stimuli being dangerous. The zebrafish, Danio rerio, is an established model organism for many scientific studies. Although spatial and object neophobia in zebrafish have received previous attention, little is known about the role of background risk in inducing neophobia in zebrafish. Here, we present two experiments using zebrafish to explore whether background predation risk can induce anxiety-like behaviour in a novel environment and neophobic responses when exposed to a novel odour. Over five days, we repeatedly exposed zebrafish to either high background risk in the form of chemical alarm cues (i.e., injured conspecific cues that indicate a predator attack) or a low-risk water control stimulus. In Experiment 1, when tested in a novel tank, zebrafish exposed to high predation risk displayed anxiety-like responses (reduced activity and increased bottom time spent) compared to their low-risk counterparts. Moreover, high-risk individuals showed reduced intra-session habituation to the novel tank compared to low-risk individuals. In Experiment 2, high-risk individuals exhibited fear responses toward a novel odour, unlike low-risk individuals. These results reveal that short-term repeated exposures to high risk can induce anxiety-like behaviour and predator odour neophobia in zebrafish.

The underground cat: burrow use by female black-footed cats (Felis nigripes)

The black-footed cat (Felis nigripes) is the smallest and one of the rarest cats in Africa. Endemic to the semi-arid regions of South Africa, Namibia and Botswana, this nocturnal carnivore spends daytime in burrows, thus avoiding high temperatures and diurnal predators. Despite the importance of burrows, den usage has never been studied in detail for this species. Here we report on the frequency with which female black-footed cats use burrows of different dimensions and compared with burrow availability. The entrances of 50 dens, used by five radio-collared black-footed cats over four weeks, were scanned with LiDAR to measure tunnel width (mean = 15.2 ± 3.9 cm) and height (mean = 13.9 ± 3.6 cm). Of these, 98% (n = 49) most closely matched the dimensions of springhare (Pedetes capensis) burrows. Each cat used a mean of 11.6 den sites and spent a mean of 2.0 consecutive days in a den before selecting a new one. When kittens reached an age of 44–50 days, mothers switched from using a den for a mean of six days-per-den, to changing dens every day. Our results suggest that female black-footed cats are reliant upon springhares to provide suitable daytime refugia and maternity dens in southern Namibia. Further studies should be conducted to determine what den sites are selected in the absence of springhare, and whether localised persecution of springhare impacts the survival of black-footed cats.

Density-Dependent Mortality of the Diving Beetle, Rhantus elevatus (Dytiscidae: Coleoptera) Preyed Upon Culex pipiens Larvae: Effects of Prey and Predator Densities.

Diving beetles (Coleoptera: Dytiscidae) are general predators that feed primarily on mosquito larvae and can control their populations, but the evidence for such an assumption remains weak. Rhantus elevatus is an important predator of this group distributed in Egypt with both larval and adult stages preying on immature mosquito. For determine predator effectiveness, it is requisite to identify the functional response (a = rate of attack and Th = time of handling) and searching efficacy (at = area of discovery and m = mutual interference) as both correlate with biocontrol efficacy. This study assessed the density-dependent mortality of Culex pipiens larvae by eliciting functional responses of third-instar and adult predators at prey density ranging from 100 to 500 larvae per arena. By contrast, a searching efficacy for the same predator stages was examined at densities ranging from one to five predators per 500 prey. Predation rates of third-instar and adult of R. elevatus were fitted by a model of Type II response with coefficients were: third-instar (a = 0.208 h-1 and Th = 2413 h) and adult (a = 0.1191 h-1 and Th = 3723 h). The maximum number of mosquitoes which can be devoured by an individual larva and adult of R. elevatus within 24 h was 99.46 and 64.46 prey, respectively. The area of discovery for the larval stage declined more steeply than the adult stage of the predator as their density increased from one to five individuals, indicating more interference estimated for the larval stage. Considering these characteristics, larvae would seem to be the most effective stage against low mosquito populations due to low predation risk compared to that generated at high predator densities in the same arena from intra-specific interference. Eventually, we suggested a ratio of 1:100 (predator per prey) must be considered in biocontrol plans for mosquitoes.

Assessing the potential of native copepods in Guatemala for Aedes vector control.

In this study we examine the feeding efficiency of copepods locally found in Guatemala on first instar Aedes aegypti larvae. Copepods are a potential tool for Aedes vector control that has shown promising results in the laboratory and in community-based field trials. Four different copepod species from different habitat types were included in the laboratory assays of this study. All four tested copepod species decreased the number of the first instar Aedes larvae that were inserted into the glass vessels compared with controls. However, average predation rates between the tested species were highly different, with Thermocyclops crassus and Mesocyclops longisetus achieving the highest, with 31.0% (standard deviation [SD] 18.9) and 28. 9% (SD 11.2), respectively. The copepod species with identified high predation rates are potential candidates for planned and other future field trials for community-based Aedes vector control with copepods in the region.

A landscape-based approach to design flower blocks may reduce mammalian predator activity and protect ground-nesting farmland birds

High predation rates threaten many ground-nesting farmland birds and are difficult to address through conventional measures such as lethal predator control or fencing. Landscape-based approaches for conservation measures promise an alternative by reducing predator - bird encounters, but require detailed knowledge of landscape effects on predation risk. Different habitat elements attractive to predators could have opposing effects on neighbouring nesting habitats, with implications for conservation: Increased predation risk due to higher predator activity (A) or reduced predation risk by distracting predators (B). Here we focus on the placement of conservation measures using flower blocks targeted at Grey Partridges in a Central European Farmland. Based on a three-year camera trap dataset, we investigated effects of landscape structure and composition on mammalian predator activity within flower blocks at two scales (100 m and 500 m radius around the camera) with generalized linear mixed models. Length of linear edge structures, i.e., field block borders, was most important, with a greater availability of linear edge structures leading to a decrease in predator activity at both scales (hypothesis B). Conversely, predator captures at both scales increased with increasing extensive vegetation area (i.e., permanent grassland, flower blocks and fallows) and in proximity to roads, indicating that these may attract predators and increase predator densities (hypothesis A). Our results suggest that a landscape-based approach can mitigate predation risk for ground-nesting birds in flower blocks and analogous conservation measures. Highly structured, small-scale agricultural landscapes seem to be particularly important for reducing mammalian predator activity in flower blocks.

Ecoepidemic modeling and dynamics of alveolar echinococcosis transmission

Alveolar echinococcosis, transmitted between definitive hosts and intermediate hosts via predation, threatens the health of humans and causes great economic losses in western China. In order to explore the transmission mechanism of this disease, an eco-epidemiological lifecycle model is formulated to illustrate interactions between two hosts. The basic and demographic reproduction numbers are developed to characterize the stability of the disease-free and endemic equilibria as well as bifurcation dynamics. The existence of forward bifurcation and Hopf bifurcation are confirmed and are used to explain the threshold transmission dynamics. Numerical simulations and bifurcation diagrams are also presented to depict rich dynamics of the model. Numerical analysis suggests that improving the control rate of voles will reduce the risk of transmission, while the high predation rate of foxes may also lead to a lower transmission risk, which is different from the predictions of previous studies. The evaluation of three control measures on voles implies that, when the fox’s predation rate is low (high), the chemical (integrated) control will be more effective.

Variable spatiotemporal ungulate behavioral response to predation risk

AbstractPrey must balance resource acquisition with predator avoidance for survival and reproduction. To reduce risk of predation, prey may avoid areas with high predator use, but if they are unable to due to resource acquisition requirements, they may instead change their habitat use or movement speed to mitigate predation risk. Prey risk response may depend on spatially or temporally varying forage availability as well as seasonal variation in prey vulnerability and availability of alternate foods for predators. To quantify how prey respond to spatial and temporal variation in risk of brown bear predation, we examined Roosevelt elk (Cervus canadensis roosevelti) spatiotemporal behavior responses to brown bear (Ursus arctos) habitat use on Afognak and Raspberry islands, Alaska, using Global Positioning System location data during elk parturition (20 May–15 June), summer (16 June–20 September), and autumn (21 September–10 November). During parturition and summer, elk used forest and shrub landcover in areas of higher brown bear probability of use. During parturition, elk used areas with lower forage productivity in areas of higher bear probability of use, and movement speed decreased with higher bear probability of use, especially in shrub landcover. During summer, elk used areas with higher forage productivity in areas of higher brown bear probability of use. During autumn, elk were less likely to use areas with higher bear habitat probability of use across landcover categories and forage productivity. During summer and autumn, elk movement speed increased with higher brown bear probability of use. Elk behavioral response to risk of brown bear predation could increase energy expenditure and decrease their ability to acquire forage, therefore negatively impacting survival and reproduction with spatiotemporal variation in risk response potentially amplifying these impacts.

Low predator and conspecific density lead to larger juveniles

Predation is a key size-selective mechanism structuring juvenile fish populations, given typically greater susceptibility of small juveniles in a population to predation compared to larger individuals. We tested the hypothesis that greater predator abundance selectively removes the smallest age 0 Atlantic cod ( Gadus morhua) in nearshore habitat, truncating their size distribution in nursery habitats. We tested this hypothesis using fifteen years of historical data on nearshore fish abundance in Newman Sound, Newfoundland. Using skewness to estimate size–frequency distribution asymmetry, our analyses showed smaller age 0 cod were least prevalent under low predator and low conspecific densities. In contrast, high predator abundances corresponded to weak, size-selective removal of the smallest juveniles. Age 0 cod reached the largest sizes under lower predator and conspecific densities. Our analyses link size of individual juvenile fish in the wild with their survival, where predator abundance modulates the advantages gained by attaining larger size.

Cushion sea-star removal enhances coral restoration practices and limits background mortality on recovering reefs

The capacity for natural coral reef recovery and the effectiveness of active restoration efforts are often contingent upon uncertain and understudied background variables, such as chronic predation for example. In the Maldives, small coral colonies (< 10 cm), primarily from the genera Pocillopora and Acropora (often found recolonising degraded reefs) are frequently predated on by the spiny cushion sea-star (Culcita schmideliana). Incidentally, these same corals (especially Acroporids) are often prioritised in active reef restoration practices. However, the level of risk these corallivores pose on restoration success has not yet been assessed. Here, we aimed to initially document the population densities of C. schmideliana on a degraded reef system in the Maldives (Kunfunadhoo, Baa Atoll). We then assessed their associated predatory effects on coral recruits and transplants, and explored the benefits of C. schmideliana removal on the survival of these corals. Population densities ranged between 1.2 and 3.3 individuals per 100 m2, which resulted in high predation rates on coral recruits (4 – 20%) and transplants (11 – 43%). Culcita schmideliana predation accounted for the majority of the documented mortality (85%). Where C. schmideliana were removed, a significant increase in survival for recruits (9% higher) and transplants (24% higher) was shown. Further observations linked a cessation of C. schmideliana removal to a significant rise in predation instances for previously protected corals (up to 52%). Our study therefore highlights the severe impacts of C. schmideliana predation and shows Culcita spp. population management as a viable passive solution for effective reef restoration.