Urban animals and birds in particular are able to cope with diverse novel threats in a city environment such as avoiding novel, unfamiliar predators. Predator avoidance often includes alarm signals that can be used also by hetero-specifics, which is mainly the case in mixed-species flocks. It can also occur when species do not form flocks but co-occur together. In this study we tested whether urban crows use alarm calls of conspecifics and hetero-specifics (jackdaws, Corvus monedula) differently in a predator and a non-predator context with partly novel and unfamiliar zoo animal species. Birds were tested at the Tiergarten Schönbrunn in the city of Vienna by playing back con- and hetero-specific alarm calls and control stimuli (great tit song and no stimuli) at predator (wolf, polar bear) and non-predator (eland antelope and cranes, peccaries) enclosures. We recorded responses of crows as the percentage of birds flying away after hearing the playback (out of those present before the playback) and as the number of vocalizations given by the present birds. A significantly higher percentage of crows flew away after hearing either con- or hetero-specific alarm calls, but it did not significantly differ between the predator and the non-predator context. Crows treated jackdaw calls just as crow calls, indicating that they make proper use of hetero-specific alarm calls. Responding similarly in both contexts may suggest that the crows were uncertain about the threat a particular zoo animal represents and were generally cautious. In the predator context, however, a high percentage of crows also flew away upon hearing the great tit control song which suggests that they may still evaluate those species which occasionally killed crows as more dangerous and respond to any conspicuous sound.
In aquatic systems, chemical cues are one of the major sources of information through which animals can assess local predation risk. Non-native red-eared sliders (Trachemys scripta elegans) have the potential to disrupt aquatic ecosystems in Central Europe because of their superior competitive abilities and omnivorous diets. In this study, we examined whether continuous predator-borne cues are tied to changes in the developmental rates, growth rates and sizes at metamorphosis of common frog tadpoles (Rana temporaria). Our results show rather rarely documented types of amphibian prey responses to caged predators. The presence of turtles shortened the time at metamorphosis of tadpoles from 110 ± 11.7 days to 93 ± 13.0 days (mean ± S.D.). The first metamorphosed individuals were recorded on the 65th day and on the 80th day from hatching in the predator treatment and in the control group, respectively. The froglets were significantly smaller (12.8 ± 0.99 mm) in the presence of the predator than in the control treatment (15.2 ± 1.27 mm). The growth rate trajectories were similar between the predator treatment and the control. Thus, predator-induced tadpole defences were evident in higher developmental rates and smaller sizes at metamorphosis without significant changes in growth.
- MeSH
- Biological Evolution MeSH
- Metamorphosis, Biological * MeSH
- Ecosystem MeSH
- Cues * MeSH
- Predatory Behavior * MeSH
- Anura physiology MeSH
- Turtles physiology MeSH
- Animals MeSH
- Check Tag
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
BACKGROUND: Many animals rely on their escape performance during predator encounters. Because of its dependence on body size and temperature, escape velocity is fully characterized by three measures, absolute value, size-corrected value, and its response to temperature (thermal sensitivity). The primary target of the selection imposed by predators is poorly understood. We examined predator (dragonfly larva)-imposed selection on prey (newt larvae) body size and characteristics of escape velocity using replicated and controlled predation experiments under seminatural conditions. Specifically, because these species experience a wide range of temperatures throughout their larval phases, we predict that larvae achieving high swimming velocities across temperatures will have a selective advantage over more thermally sensitive individuals. RESULTS: Nonzero selection differentials indicated that predators selected for prey body size and both absolute and size-corrected maximum swimming velocity. Comparison of selection differentials with control confirmed selection only on body size, i.e., dragonfly larvae preferably preyed on small newt larvae. Maximum swimming velocity and its thermal sensitivity showed low group repeatability, which contributed to non-detectable selection on both characteristics of escape performance. CONCLUSIONS: In the newt-dragonfly larvae interaction, body size plays a more important role than maximum values and thermal sensitivity of swimming velocity during predator escape. This corroborates the general importance of body size in predator-prey interactions. The absence of an appropriate control in predation experiments may lead to potentially misleading conclusions about the primary target of predator-imposed selection. Insights from predation experiments contribute to our understanding of the link between performance and fitness, and further improve mechanistic models of predator-prey interactions and food web dynamics.
- MeSH
- Larva anatomy & histology physiology MeSH
- Tail anatomy & histology physiology MeSH
- Swimming MeSH
- Food Chain * MeSH
- Salamandridae anatomy & histology growth & development physiology MeSH
- Temperature MeSH
- Odonata growth & development physiology MeSH
- Body Size MeSH
- Animals MeSH
- Check Tag
- Animals MeSH
- Publication type
- Journal Article MeSH
The ability to modify phenotypes in response to heterogeneity of the thermal environment represents an important component of an ectotherm's non-genetic adaptive capacity. Despite considerable attention being dedicated to the study of thermally-induced developmental plasticity, whether or not interspecific interactions shape the plastic response in both a predator and its prey remains unknown. We tested several predictions about the joint influence of predator/prey scents and thermal conditions on the plasticity of preferred body temperatures (T (p)) in both actors of this interaction, using a dragonfly nymphs-newt larvae system. Dragonfly nymphs (Aeshna cyanea) and newt eggs (Ichthyosaura alpestris) were subjected to fluctuating cold and warm thermal regimes (7-12 and 12-22°C, respectively) and the presence/absence of a predator or prey chemical cues. Preferred body temperatures were measured in an aquatic thermal gradient (5-33°C) over a 24-h period. Newt T (p) increased with developmental temperature irrespective of the presence/absence of predator cues. In dragonflies, thermal reaction norms for T (p) were affected by the interaction between temperature and prey cues. Specifically, the presence of newt scents in cold regime lowered dragonfly T (p). We concluded that predator-prey interactions influenced thermally-induced plasticity of T (p) but not in a reciprocal fashion. The occurrence of frequency-dependent thermal plasticity may have broad implications for predator-prey population dynamics, the evolution of thermal biology traits, and the consequences of sustaining climate change within ecological communities.
- MeSH
- Phenotype MeSH
- Larva MeSH
- Population Dynamics MeSH
- Food Chain MeSH
- Salamandridae growth & development MeSH
- Body Temperature MeSH
- Models, Theoretical MeSH
- Odonata growth & development MeSH
- Eggs MeSH
- Animals MeSH
- Check Tag
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Due to the extensive use of copper (Cu) in various commercial products, its existence in aquatic bodies (freshwater and marine) is not unusual. Cu is well known for its effect on the olfactory physiology of fish. However, there are limited studies on the effect of Cu on important ecological functions in fish (predator-prey dynamics) that are primarily influenced by olfaction. In a series of experiments, we studied the effect of Cu exposure on the chemoreceptive behavior of the prey fish, Lepidocephalichthys thermalis. Prey fishes were exposed to an environmentally relevant concentration (5 μg/L) of Cu for 3 h and the anti-predator responses against native (Channa gachua) and alien predatory fish (tilapia) were quantified using an ethological assay. Cu exposed prey fishes did not recognize the native predator and had a lower survival rate than control (unexposed) fishes in predation trials. Cu exposed prey fishes have failed to learn associatively to detect a non-native predator resulting in higher mortality in prey population in direct encounters with tilapia. However, such a lack of predator recognition was found to be short-term and the treated prey fishes recovered anti-predator responses within 72 h. In addition, Cu inactivated the alarm cue which acts as a signal for the presence of predators and ensures associative learning and therefore it was considered to be an 'info-disruptor' in the present study. These outcomes together demonstrate that even at low concentration, Cu influences ecological decisions and survival against predators. Owing to the ubiquitous occurrence of Cu in water bodies, the present investigation will contribute to the knowledge of how environmental stressors alter the crucial ecological decisions of prey individuals in aquatic ecosystems. In addition, we suggest that freshwater reservoirs containing high levels of Cu could be unsuitable for the long-term survival of prey fishes and freshwater biodiversity.
- MeSH
- Ecosystem MeSH
- Humans MeSH
- Cypriniformes * MeSH
- Copper * toxicity MeSH
- Predatory Behavior MeSH
- Fishes MeSH
- Fresh Water MeSH
- Animals MeSH
- Check Tag
- Humans MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Predatory aquatic insects are a diverse group comprising top predators in small fishless water bodies. Knowledge of their diet composition is fragmentary, which hinders the understanding of mechanisms maintaining their high local diversity and of their impacts on local food web structure and dynamics. We conducted multiple-choice predation experiments using nine common species of predatory aquatic insects, including adult and larval Coleoptera, adult Heteroptera and larval Odonata, and complemented them with literature survey of similar experiments. All predators in our experiments fed selectively on the seven prey species offered, and vulnerability to predation varied strongly between the prey. The predators most often preferred dipteran larvae; previous studies further reported preferences for cladocerans. Diet overlaps between all predator pairs and predator overlaps between all prey pairs were non-zero. Modularity analysis separated all primarily nectonic predator and prey species from two groups of large and small benthic predators and their prey. These results, together with limited evidence from the literature, suggest a highly interconnected food web with several modules, in which similarly sized predators from the same microhabitat are likely to compete strongly for resources in the field (observed Pianka's diet overlap indices >0.85). Our experiments further imply that ontogenetic diet shifts are common in predatory aquatic insects, although we observed higher diet overlaps than previously reported. Hence, individuals may or may not shift between food web modules during ontogeny.
- MeSH
- Insecta physiology MeSH
- Hydrobiology methods MeSH
- Food Chain MeSH
- Predatory Behavior physiology MeSH
- Animals MeSH
- Check Tag
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Despite the encountering of a predator always being extremely threatening, there is a significant plasticity among individuals in how they cope with such a situation. In laboratory experiments with wild-caught great tits (Parus major), we tested the effect of exploratory behaviour (performance in novel food, object and environment test, startle test) on the ability of individual birds to assess the threat represented by a predator. We presented a wooden dummy of the European sparrowhawk (Accipiter nisus), an extremely dangerous predator, and its visual modifications (chimeras), changing the beak or head to be non-threatening (those of a pigeon - Columba livia f. domestica). We showed that the differences between 'slow' and 'fast explorers' are not very distinct, but that 'slow explorers' generally tended to be more cautious in the presence of an unmodified sparrowhawk dummy, while the 'fast explorers' tended to observe the dummy. On the contrary, 'slow explorers' tended to treat both chimaeras (and the pigeon dummy as well) as less-threatening than 'fast explorers'. Since 'slow explorers' are usually considered to be more sensitive to environmental cues, it came as no surprise that most of them correctly assessed the unmodified sparrowhawk dummy as threatening, while they probably subjected the chimeras to a detailed inspection and were not confused by the presence of sparrowhawk features and assessed them as non-threatening.
- MeSH
- Behavior, Animal physiology MeSH
- Passeriformes physiology MeSH
- Exploratory Behavior physiology MeSH
- Cues * MeSH
- Visual Perception physiology MeSH
- Animals MeSH
- Check Tag
- Animals MeSH
- Publication type
- Journal Article MeSH
Insecticides usually present in low concentrations in streams are known to impair behaviour and development of non-target freshwater invertebrates. Moreover, there is growing awareness that the presence of natural stressors, such as predation risk may magnify the negative effects of pesticides. This is because perception of predation risk can by itself lead to changes on behaviour and physiology of prey species. To evaluate the potential combined effects of both stressors on freshwater detritivores we studied the behavioural and developmental responses of Chironomus riparius to chlorantraniliprole (CAP) exposure under predation risk. Also, we tested whether the presence of a shredder species would alter collector responses under stress. Trials were conducted using a simplified trophic chain: Alnus glutinosa leaves as food resource, the shredder Sericostoma vittatum and the collector C. riparius. CAP toxicity was thus tested under two conditions, presence/absence of the dragonfly predator Cordulegaster boltonii. CAP exposure decreased leaf decomposition. Despite the lack of significance for interactive effects, predation risk marginally modified shredder effect on leaf decomposition, decreasing this ecosystem process. Shredders presence increased leaf decomposition, but impaired chironomids performance, suggesting interspecific competition rather than facilitation. C. riparius growth rate was decreased independently by CAP exposure, presence of predator and shredder species. A marginal interaction between CAP and predation risk was observed regarding chironomids development. To better understand the effects of chemical pollution to natural freshwater populations, natural stressors and species interactions must be taken into consideration, since both vertical and horizontal species interactions play their role on response to stress.
- MeSH
- Chironomidae drug effects growth & development physiology MeSH
- Insecta drug effects growth & development physiology MeSH
- Insecticides toxicity MeSH
- Larva drug effects growth & development physiology MeSH
- Plant Leaves MeSH
- Nymph drug effects growth & development physiology MeSH
- Alnus MeSH
- ortho-Aminobenzoates toxicity MeSH
- Food Chain * MeSH
- Predatory Behavior * MeSH
- Feeding Behavior drug effects MeSH
- Odonata growth & development physiology MeSH
- Animals MeSH
- Check Tag
- Animals MeSH
- Publication type
- Journal Article MeSH
Genetically engineered (GE) crops with stacked insecticidal traits expose arthropods to multiple Cry proteins fromBacillus thuringiensis(Bt). One concern is that the different Cry proteins may interact and lead to unexpected adverse effects on non-target species. Bi- and tri-trophic experiments with SmartStax maize, herbivorous spider mites (Tetranychus urticae), aphids (Rhopalosiphum padi), predatory spiders (Phylloneta impressa), ladybeetles (Harmonia axyridis) and lacewings (Chrysoperla carnea) were conducted. Cry1A.105, Cry1F, Cry3Bb1 and Cry34Ab1 moved in a similar pattern through the arthropod food chain. By contrast, Cry2Ab2 had highest concentrations in maize leaves, but lowest in pollen, and lowest acquisition rates by herbivores and predators. While spider mites contained Cry protein concentrations exceeding the values in leaves (except Cry2Ab2), aphids contained only traces of some Cry protein. Predators contained lower concentrations than their food. Among the different predators, ladybeetle larvae showed higher concentrations than lacewing larvae and juvenile spiders. Acute effects of SmartStax maize on predator survival, development and weight were not observed. The study thus provides evidence that the different Cry proteins do not interact in a way that poses a risk to the investigated non-target species under controlled laboratory conditions.
- MeSH
- Bacillus thuringiensis MeSH
- Bacterial Proteins genetics MeSH
- Arthropods * MeSH
- Endotoxins genetics MeSH
- Plants, Genetically Modified genetics MeSH
- Hemolysin Proteins genetics MeSH
- Zea mays genetics MeSH
- Larva MeSH
- Food Chain * MeSH
- Animals MeSH
- Check Tag
- Animals MeSH
- Publication type
- Journal Article MeSH
The role of generalist predators in biological control remains controversial as they may not only reduce pest populations but also disrupt biocontrol exerted by other natural enemies. Here, we focus on spiders as a model group of generalist predators. They are among the most abundant and most diverse natural enemies in agroecosystems. We review their functional traits that influence food-web dynamics and pest suppression at organisational levels ranging from individuals to communities. At the individual and population levels, we focus on hunting strategy, body size, life stage, nutritional target, and personality (i.e., consistent inter-individual differences in behaviour). These functional traits determine the spider trophic niches. We also focus on the functional and numerical response to pest densities and on non-consumptive effects of spiders on pests. At the community level, we review multiple-predator effects and effect of alternative prey on pest suppression. Evidence for a key role of spiders in pest suppression is accumulating. Importantly, recent research has highlighted widespread non-consumptive effects and complex intraguild interactions of spiders. A better understanding of these effects is needed to optimize biocontrol services by spiders in agroecosystems.
