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Predators affect prey by killing them directly (lethal effects) and by inducing costly antipredator behaviours in living prey (risk effects). Risk effects can strongly influence prey populations and cascade through trophic systems. A prerequisite for assessing risk effects is characterizing the spatiotemporal variation in predation risk. Risk effects research has experienced rapid growth in the last several decades. However, preliminary assessments of the resultant literature suggest that researchers characterize predation risk using a variety of techniques. The implications of this methodological variation for inference and comparability among studies have not been well recognized or formally synthesized. We couple a literature survey with a hierarchical framework, developed from established theory, to quantify the methodological variation in characterizing risk using carnivore-ungulate systems as a case study. Via this process, we documented 244 metrics of risk from 141 studies falling into at least 13 distinct subcategories within three broader categories. Both empirical and theoretical work suggest risk and its effects on prey constitute a complex, multi-dimensional process with expressions varying by spatiotemporal scale. Our survey suggests this multi-scale complexity is reflected in the literature as a whole but often underappreciated in any given study, which complicates comparability among studies and leads to an overemphasis on documenting the presence of risk effects rather than their mechanisms or scale of influence. We suggest risk metrics be placed in a more concrete conceptual framework to clarify inference surrounding risk effects and their cascading effects throughout ecosystems. We recommend studies (i) take a multi-scale approach to characterizing risk; (ii) explicitly consider 'true' predation risk (probability of predation per unit time); and (iii) use risk metrics that facilitate comparison among studies and the evaluation of multiple competing hypotheses. Addressing the pressing questions in risk effects research, including how, to what extent and on what scale they occur, requires leveraging the advantages of the many methods available to characterize risk while minimizing the confusion caused by variability in their application.

Two million tonnes of pesticides are currently used globally to improve crop production, yet these pesticides induce adverse effects on soil quality and biodiversity. Moreover, less than 1% of pesticides reach the target pests, while the rest contaminate the surrounding environment. In particular, earthworms are exposed to pesticides and are thus an ideal biological model for ecotoxicological research. Here, we review acute and sub-lethal effects of pesticides on earthworms. We found that pesticides alter growth, reproduction, behaviour, essential enzymes, and DNA of earthworms, even at low pesticide concentrations. These sub-lethal biomarkers allow to evaluate the overall response of an earthworm to pesticides, and to identify the risk for other non-target organisms.

Although pesticide-free techniques have been developed in agriculture, pesticides are still routinely used against weeds, pests, and pathogens worldwide. These agrochemicals pollute the environment and can negatively impact human health, biodiversity and ecosystem services. Acetamiprid, an approved neonicotinoid pesticide in the EU, may exert sub-lethal effects on pollinators and other organisms. However, our knowledge on the scope and severity of such effects is still incomplete. Our experiments focused on the effects of the insecticide formulation Mospilan (active ingredient: 20% acetamiprid) on the peripheral olfactory detection of a synthetic floral blend and foraging behaviour of buff-tailed bumblebee ( Bombus terrestris ) workers. We found that the applied treatment did not affect the antennal detection of the floral blend; however, it induced alterations in their foraging behaviour. Pesticide-treated individuals started foraging later, and the probability of finding the floral blend was lower than that of the control bumblebees. However, exposed bumblebees found the scent source faster than the controls. These results suggest that acetamiprid-containing Mospilan may disrupt the activity and orientation of foraging bumblebees. We hypothesize that the observed effects of pesticide exposure on foraging behaviour could be mediated through neurophysiological and endocrine mechanisms. We propose that future investigations should clarify whether such sub-lethal effects can affect pollinators’ population dynamics and their ecosystem services.

Many species of devastating insect pests have acquired a high degree of resistance to insecticides in the field during the last few decades. Spodoptera exigua , for example, is the most damaging pests of economic crops with a worldwide spread. In a present study, the comparative growth, reproduction, and detoxification enzyme activity were evaluated along with exposure to three insecticides at low lethal doses of lufenuron, indoxacarb, and spinosad as compared to the control. Results indicate that the larval developmental time was significantly extended on lufenuron (21.5 ± 29 days) followed by indoxacarb (20.28 ± 0.24 days) and spinosad (19.74 ± 0.23 days) as compared to that on the control (18.13 ± 0.13 days). Similarly, the lowest number of eggs of S. exigua females were recorded on lufenuron (328.75 ± 50.81 eggs) followed by spinosad (367 ± 36.4 eggs) and indoxacarb (411.58 ± 42.38 eggs) as compared to that on the control (560.2 ± 13.47). Interestingly, the lowest intrinsic rate of increase ( r ) (0.121 ± 0.009) and highest mean generation time ( T ) (36.2 ± 0.35 days) were observed when larvae were treated to a low lethal concentration (LC 20 ) of lufenuron as compared to that of indoxacarb, spinosad, and control. In addition, considerably lower activity of all detoxification enzymes in larvae was recorded on lufenuron after control as compared to that on indoxacarb and spinosad. Our study serves as a reference and basis for the toxicity and low lethal evaluation of lufenuron, indoxacarb, and spinosad on life table parameters and enzymatic properties in S. exigua , which may contribute to identifying targets for effective control of S. exigua .

Predators play an extremely important role in natural communities. In freshwater systems, fish can dominate sorting both at the colonization and post-colonization stage. Specifically, for many colonizing species, fish can have non-lethal, direct effects that exceed the lethal direct effects of predation. Functionally diverse fish species with a range of predatory capabilities have previously been observed to elicit functionally equivalent responses on oviposition in tree frogs. We tested this hypothesis of functional equivalence of non-lethal effects for four predatory fish species, using naturally colonizing populations of aquatic beetles. Among taxa other than mosquitoes, and with the exception of the chemically camouflaged pirate perch, Aphredoderus sayanus, we provide the first evidence of variation in colonization or oviposition responses to different fish species. Focusing on total abundance, Fundulus chrysotus, a gape-limited, surface-feeding fish, elicited unique responses among colonizing Hydrophilidae, with the exception of the smallest and most abundant taxa, Paracymus, while Dytiscidae responded similarly to all avoided fish. Neither family responded to A. sayanus.Analysis of species richness and multivariate characterization of the beetle assemblages for the four fish species and controls revealed additional variation among the three avoided species and confirmed that chemical camouflage in A. sayanus results in assemblages essentially identical to fishless controls. The origin of this variation in beetle responses to different fish is unknown, but may involve variation in cue sensitivity, different behavioral algorithms, or differential responses to species-specific fish cues. The identity of fish species occupying aquatic habitats is crucial to understanding community structure, as varying strengths of lethal and non-lethal effects, as well as their interaction, create complex landscapes of predator effects and challenge the notion of functional equivalence.

Emerging infectious disease is a major cause of wildlife decline around the world. Understanding the impacts of disease even in non‐declining populations is important for understanding population‐level health and resilience to other emerging threats. In this study, we explored the sublethal impacts of the fungal pathogen Batrachochytrium dendrobatidis, Bd, and a novel intestinal nematode on the non‐declining Australian frog, Litoria lesueuri. We collected male animals that were either infected with the fungal parasite, infected with a nematode parasite, infected with both parasites, or uninfected and brought them into the lab and monitored their morphology and fungal pathogen load over a 7‐week trial. At the end of the experiment, we dissected the animals, collected the testes, and identified their nematode prevalence and burden. We morphologically and molecularly characterised the intestinal nematode as belonging to the genus Parathelandros within the order Oxyuridae. We found that this Parathelandros sp. infection was beneficial to the adult frogs, where infected animals were larger and had larger forearm width (an important trait for mating) when we accounted for animal size. The exact mechanisms of this improved condition are unknown and require additional research. However, in the Bd‐infected animals, we found an overall negative impact of infection, including reduced forearm width and sperm production. Bd infection is prevalent in this species, and there are tangible sublethal impacts of Bd infection, indicating that this species is affected even if mortality due to disease is low. Understanding the impacts of disease even in non‐declining populations is important for understanding population level health and resilience to other emerging threats. In this study we explored the impacts of co‐infection of the fungal pathogen and a novel nematode parasite on a common Australian frog species. We found that this novel nematode actually confers a benefit to the frogs, where they were larger and had larger forearms while the fungal parasite had overall a negative effect on the frogs.

Predator mediation of sea urchin grazing pressure may occur via lethal removal of individual sea urchins or non-lethal modification of sea urchin behaviour. Several studies have shown that predation-related cues can affect sea urchin movement and grazing rates, but generalisations about the types of cues that prompt responses and the magnitude of those responses will require further research on a wider variety of species. We examined the effects of potential alarm cues on behaviour of the habitat-forming sea urchin Evechinus chloroticus (Echinometridae) on fished rocky reefs in northeastern New Zealand, where predators are uncommon and the sea urchins form barrens. Exposed E. chloroticus (i.e. those not in crevices) rapidly fled from injured conspecifics within a 1 m radius of the cue, but showed no apparent reaction to injured sea urchins belonging to another family (Centrostephanus rodgersii, Diadematidae), diced pilchards or the disturbance caused by fish attracted to the cues. Densities of exposed sea urchins in an area containing injured conspecifics did not return to control values for at least 20 h, while cryptic individuals remained crevice-bound when injured conspecifics were nearby. Injured conspecifics thus provide a strong, albeit localised, cue for E. chloroticus. By restricting sea urchins to crevices where they have a reduced impact on living kelp, this non-consumptive effect may complement the lethal effects of predation in marine reserves where populations of predators such as rock lobsters and large fish are allowed to recover from overharvesting by humans, thereby reinforcing the trophic cascade initiated by those predators.

Environmental toxicants are pervasive in nature, but sub-lethal effects on non-target organisms and their parasites are often overlooked. Particularly, studies on terrestrial hosts and their parasites exposed to agricultural toxicants are lacking. Here, we studied the effect of sequence and timing of sub-lethal exposures of the pyrethroid insecticide alpha-cypermethrin on parasite establishment using the tapeworm Hymenolepis diminuta and its intermediate insect host Tenebrio molitor as a model system. We exposed T. molitor to alpha-cypermethrin (LD 20 ) before and after experimental H. diminuta infection and measured the establishment success of larval tapeworms. Also, we conducted in vitro studies quantifying the direct effect of the insecticide on parasite viability. Our results showed that there was no direct lethal effect of alpha-cypermethrin on H. diminuta cysticercoids at relevant concentrations (LD 10 to LD 90 of the intermediate host). However, we observed a significantly increased establishment of H. diminuta in beetles exposed to alpha-cypermethrin (LD 20 ) after parasite infection. In contrast, parasite establishment was significantly lower in beetles exposed to the insecticide before parasite infection. Thus, our results indicate that environmental toxicants potentially impact host-parasite interactions in terrestrial systems, but that the outcome is context-dependent by enhancing or reducing parasite establishment depending on timing and sequence of exposure.

Severe weather events are more frequently impacting wildlife, especially in climate‐sensitive ecosystems like coastal habitats. A particularly vulnerable stage for migratory species is juvenile movement between natal and non‐breeding habitats. Globally, coastal habitats represent critical stopover or staging sites during postbreeding migration for many shorebird species. At these sites, individuals must accumulate necessary energy stores (i.e., fats and proteins) to fuel what are often long‐distance, over‐water flights to reach their final destination. Inexperienced juvenile shorebirds in unfamiliar habitats may be particularly susceptible to extreme weather events that alter habitat structure and resource availability, with potential implications for refueling efficiency and migration success. However, few studies have addressed the effects of extreme weather at staging sites, limiting our understanding of the capacity of birds to respond to or recover from acute disturbances. We used a before–after framework to investigate how Hurricane Fiona affected the staging behavior of juvenile semipalmated plovers (Charadrius semipalmatus) in Atlantic Canada during southbound migration. We combined morphometric analyses, automated radiotelemetry tracking, and invertebrate sampling to assess storm effects on relative fuel load, bivalve prey availability, and length of stay in the region. Birds captured poststorm lost an estimated 78% of their relative fuel load compared to prestorm birds, coinciding with an estimated 70% decline in bivalve availability. Individuals who experienced the storm approximately doubled their length of stay. Given that juvenile shorebirds undertake southbound migration later in the season than adults, we predict juveniles will be impacted disproportionately by late‐season tropical storm patterns, with potentially substantial impacts on shorebird populations. We emphasize the need for a greater research focus on extreme weather during vulnerable life‐history stages, like migration, for a broader understanding of how species will respond to increasingly intense storm events.

Predator fear effects influence reproductive outcomes in many species. In non‐urban systems, passerines often respond to predator cues by reducing parental investment, resulting in smaller and lighter nestlings. Since trophic interactions in urban areas are highly altered, it is unclear how passerines respond to fear effects in human‐altered landscapes. Nestlings of passerines in urban areas also tend to be smaller and lighter than their rural counterparts and are often exposed to high densities of potential predators yet experience lower per capita predation—the predation paradox. We suggest fear effects in urban habitats could be a significant mechanism influencing nestling condition in birds, despite lowered predation rates. We manipulated exposure of nesting birds to adult‐consuming predator risk in residential yards across a gradient of urbanization to determine the relative influence of urbanization and fear on nestling condition. We found nestlings had reduced mass in nests exposed to predator playbacks as well as in more urban areas. Despite lower per capita predation rates in urban areas, fear effects from increased predator densities may influence passerine fitness through reduced nestling condition. As urban development expands, biodiversity conservation hinges on a deeper mechanistic understanding of how urbanization affects reproductive outcomes.