Do predators influence the behaviour of bats?

Many aspects of animal behaviour are affected by real‐time changes in the risk of predation. This conclusion holds for virtually all taxa and ecological systems studied, but does it hold for bats? Bats are poorly represented in the literature on anti‐predator behaviour, which may reflect a lack of nocturnal predators specialized on bats. If bats actually experience a world with minimal anti‐predator concerns, then they will provide a unique contrast within the realm of vertebrate ecology. Alternatively, such predator‐driven behaviour in bats may not yet be fully understood, given the difficulties in working with these highly mobile and nocturnal animals. We provide a wide‐ranging exploration of these issues in bat behaviour. We first cover the basic predator‐prey information available on bats, both on potential predators and the ways in which bats might perceive predators and respond to attacks. We then cover work relevant to key aspects of bat behaviour, such as choice of daytime roosts, the nature of sleep and torpor, evening roost departures, moonlight avoidance, landscape‐related movement patterns, and habitat selection. Overall, the evidence in favour of a strong influence of predators on bat behaviour is equivocal, with the picture clouded by contradictory results and a lack of information on potential predators and the perception of risk by bats. It seems clear that day‐active bats run a considerable risk of being killed by diurnal raptors, which are able to capture bats with relative ease. Thus, bats taking advantage of a pulse of insects just prior to sunset are likely taking risks to gain much‐needed energy. Further, the choice of daytime roosts by bats is probably strongly influenced by roost safety. Few studies, however, have directly addressed either of these topics. As a group, insectivorous temperate‐zone bats show no clear tendency to avoid apparently risky situations, such as activity on moonlit nights. However, some observations are consistent with the idea that predation risk affects choice of movement paths and feeding areas by temperate‐zone bats, as well as the timing of roost departures. The behaviour of tropical bats, on the other hand, seems more generally influenced by predators; this is especially true for tropical nectarivores and frugivores, but also for insectivorous bats. Presumably there are more serious predators on bats in the tropics (e.g. specialized raptors or carnivorous bats), but the identity of these predators is unclear. More information is needed to assess fully the influence of predators on bat behaviour. There is much need for work on the ways in which bats perceive predators via auditory, visual, and olfactory cues, and whether bats have some knowledge of the risks posed by different predators. Also needed is information on how predators attack bats and how bats react to attacking predators. Difficult to obtain, but of critical value, will be information on the nature of the predation risk experienced by bats while away from roosts and during the full darkness of night.     

Coexistence of protected avian predators: does a recovering population of White-tailed Eagle threaten to exclude other avian predators?

The processes of competition and predation determine the degree to which species can coexist; the importance of competition in particular has been emphasized at high trophic levels. Competition exclusion will occur when habitat overlap between sympatric species is high. In this study, we investigated nesting habitat overlap between internationally protected diurnal tree-nesting avian predators of central Europe, namely, White-tailed Eagle (Haliaeetus albicilla), Lesser Spotted Eagle (Aquila pomarina), Black Stork (Ciconia nigra), and Osprey (Pandion haliaetus). We found significantly different nesting habitats among the study species and suggest that this could be a consequence of the resource-based segregation, but not a consequence of asymmetrical interspecific competition. The results also show that habitat of the recovering populations of White-tailed Eagle overlapped with the habitat used by the Lesser Spotted Eagle, Black Stork, and Osprey to varying extents with a niche overlap values being below the competition exclusion threshold. Nevertheless, we suggest that competition by White-tailed Eagle at a population level may limit Osprey, though not Lesser Spotted Eagle or Black Stork.     

Sensory ecology: giant eyes for giant predators?

Mathematical models suggest the enormous eyes of giant and colossal squid evolved to see the bioluminescence induced by the approach of predatory whales.     

How do predators cope with chemically defended foods?

Many prey species (including plants) deter predators with defensive chemicals. These defensive chemicals act by rendering the prey's tissues noxious, toxic, or both. Here, I explore how predators cope with the presence of these chemicals in their diet. First, I describe the chemosensory mechanisms by which predators (including herbivores) detect defensive chemicals. Second, I review the mechanisms by which predators either avoid or tolerate defensive chemicals in prey. Third, I examine how effectively free-ranging predators can overcome the chemical defenses of prey. The available evidence indicates that predators have mixed success overcoming these defenses. This conclusion is based on reports of free-ranging predators rejecting unpalatable but harmless prey, or voluntarily ingesting toxic prey.     

Do leaf shelters always protect caterpillars from invertebrate predators?

Abstract 1. All larval instars of Epargyreus clarus , the silver-spotted skipper, construct and inhabit leaf shelters that are presumed to protect them from predator attack.
2. Shelters effectively protected the larvae against foraging Crematogaster opuntiae ants and naive Polistes spp. wasps in laboratory tests, but did not protect them from predators, largely vespid wasps, present in the field.
3. A range of factors, including type of predator, learning ability, and experience level, may determine the effectiveness of leaf shelters as protection from predators.     

Are fleeing ”noisy” lizards signalling to predators?

Many prey signal to predators with the intention of deterring further pursuits. In the lizard Psammodromus algirus, individuals sometimes escape with noisy long runs on dry leaves, whereas on many other occasions they escape quietly and with short flights. We hypothesised that the duration of this noisy display might be considered as an auditory signal of their alertness and ability to escape directed to predators. We examined in the field the escape behaviour of the lizard P. algirus in response to a human observer acting as a predator and tested a series of predictions to analyse this hypothesis. During a noisy escape response, lizards escaped sooner and ran further and for a longer time, while passing potential refuges before hiding. Production of noise was not entirely dependent on environmental factors, such as temperature or microhabitat, and was not directed to warn conspecifics because most individuals were solitary. Lizards still made noise when concealed and in response to successive approaches, which might be interpreted as a signal of alertness to the predator approach. In addition, condition of individuals with noisy responses could be assessed from their ability to run further and for a longer time, and because, in contrast to quiet responses, speed and distance were not positively correlated with environmental temperature. Thus, they might be in a better condition or internal state because they were able to run at high speed under unfavourable conditions. We suggest that lizards with noisy escape responses might be honestly signalling their alertness and ability to escape to avoid being chased. Received: 7 February 2000 / Received in revised form: 25 May 2000 / Accepted: 30 May 2000     

Ecosystem restoration with teeth: what role for predators?

Recent advances highlight the potential for predators to restore ecosystems and confer resilience against globally threatening processes, including climate change and biological invasions. However, releasing the ecological benefits of predators entails significant challenges. Here, we discuss the economic, environmental and social considerations affecting predator-driven ecological restoration programmes, and suggest approaches for reducing the undesirable impacts of predators. Because the roles of predators are context dependent, we argue for increased emphasis on predator functionality in ecosystems and less on the identities and origins of species and genotypes. We emphasise that insufficient attention is currently given to the importance of variation in the social structures and behaviours of predators in influencing the dynamics of trophic interactions. Lastly, we outline experiments specifically designed to clarify the ecological roles of predators and their potential utility in ecosystem restoration.     

Is larger better in sit-and-wait predators? Competitive superiority in Hydra

Contrary to a generalisation arising from many studies, a larger body size is not always the key to competitive superiority amongst animals. An analysis of competition between pairs of Hydra oligactis, Hydra vulgaris and Hydra circumcincta, that simultaneously encountered a single prey item, showed that competitive success in these sessile predators depended on species and clone in inter- and intraspecific competition, respectively. H. oligactis appeared to be competitively superior, even to the larger H. vulgaris individuals. Phenotypic traits important for prey capture, such as the fraction of the nematocyst that penetrates the prey (penetrants), were positively related to success in intraspecific competition. Body size appeared to be a positive key factor in determining foraging success in the competition between pairs of conspecifics from single or different clones. In contrast to the results of the intraspecific competition, body size was not significantly related to the foraging success of competing heterospecifics.     

Signaling by decorating webs: luring prey or deterring predators?

Many organisms convey false signals to mislead their prey orpredators. Some orb-weaving spiders build conspicuous structureson webs called decorations. Web decorations and spider colorationsare both suggested to be important signals involved in interactionsbetween spiders and other organisms. There are several hypothesesabout the functions of signaling by decorations, among whichprey attraction had received much support, but empirical evidenceregarding predator defense is controversial. In this study,we conducted field experiments to investigate the effects ofspider decoration and coloration on insect interception ratesof webs built by Argiope aemula and to evaluate whether presenceof decorations may decrease predation risk of spiders. Decoratedwebs with spiders present had the highest prey interceptionrate, followed by undecorated webs with spiders, and then undecoratedwebs without spiders. Such results indicated that decorationsof Argiope spiders functioned as visual lures, and so did spiders'bright body colorations. In the field, almost all wasp attackevents occurred on medium-sized spiders rather than on largeones. Moreover, medium-sized Arg. aemula on decorated webs receivedfar more attacks than those on undecorated webs. Results ofthis study thus show that the signals conveyed by decorationscan visually lure prey but at the cost of an increased predationrisk. Received 20 March 2007; revised 3 August 2007; accepted 5 August 2007.     

Do native predators benefit from non‐native prey?

Despite knowledge on invasive species’ predatory effects, we know little of their influence as prey. Non‐native prey should have a neutral to positive effect on native predators by supplementing the prey base. However, if non‐native prey displace native prey, then an invader's net influence should depend on both its abundance and value relative to native prey. We conducted a meta‐analysis to quantify the effect of non‐native prey on native predator populations. Relative to native prey, non‐native prey similarly or negatively affect native predators, but only when studies employed a substitutive design that examined the effects of each prey species in isolation from other prey. When native predators had access to non‐native and native prey simultaneously, predator abundance increased significantly relative to pre‐invasion abundance. Although non‐native prey may have a lower per capita value than native prey, they seem to benefit native predators by serving as a supplemental prey resource.     

Must top predators be culled for the sake of fisheries?

If humankind occupies the ecological role of top predator, then within individual ecosystems it must compete with other top predators for valuable food resources. This notion presents a fascinating ecological problem, with tremendous social and economic ramifications. Because of the socioeconomic dimension, the scientific debate has at times been controversial. The recent attention and data gathering resources focused on the problem present a unique opportunity to test and refine ecological theory in the arena of complex, large-scale systems.     

Aversive reactions of two invertebrate predators to European red–black insects

Prey species gain protection by imitating signals of unpalatable models in defensive mimicry. Mimics have been traditionally classified as Batesian (palatable mimic resembling an unpalatable model) or Müllerian (unpalatable mimic resembling a similarly unpalatable model). However, recent studies suggest that rather than discrete categories, the phenomenon of mimicry can be better understood as a continuum. The level of unpalatability of defended prey is a key factor in determining the type of mimetic relationship. Herein, we used insects (ladybugs and true bugs) from a putative European “red–black” mimetic complex as experimental models of defended species and crickets as a control prey. We offered the prey to two species of sympatric invertebrate predators (praying mantis and spider) and video recorded the interactions. We tested three alternative hypotheses, namely (i) the three red–black species tested are similarly defended against both predators; (ii) some red–black species are better defended than others against both predator species, and (iii) the effectiveness of the red–black species defenses is predator dependent. Both predators attacked all prey types with a similar frequency. But while all three red–black species similarly elicited aversive behaviors in spiders, the mantises' aversive reactions varied depending on the prey species. Our results provide support to the third hypothesis, suggesting that the same prey species can fall into different parts of the spectrum of palatability–unpalatability depending on the type of predator.     

Plant–insect interactions: gentians,seed predators and parasitoid wasps

While studying breeding systems and pollination ecology of nine Gentiana species (G. lutea, G. punctata, G. asclepiadea, G. pneumonanthe, G. cruciata, G. pyrenaica, G. verna, G. utriculosa, and G. nivalis) in the Bulgarian mountains, we recorded number of insects that feed on their maturing seeds. In addition, parasitoid wasps in connection to these seed predators were detected. Insects are identified and the impact on the seed set of afore mentioned Gentiana species is estimated. Fruit capsules of Gentiana spp. from different populations in the mountains in Bulgaria were investigated for the presence or absence of damage by larvae during the period of 16 years. The seed destruction varies among the nine investigated Gentiana species. The insects whose larvae damaged the seed/fruit set belonged mainly to Coleoptera and Diptera. The larvae of lycaenid butterflies, Maculinea spp. (Lepidoptera), were recorded only in seeds of G. asclepiadea, G. pneumonanthe and G. cruciata. Parasitoid wasps from the families Ichneumonidae, Braconidae, and Pteromalidae were identified, some of them new for the fauna of Bulgaria.     

How can automimicry persist when predators can preferentially consume undefended mimics?

It is common for species that possess toxins or other defences to advertise these defences to potential predators using aposematic ("warning") signals. There is increasing evidence that within such species, there are individuals that have reduced or non-existent levels of defence but still signal. This phenomenon (generally called automimicry) has been a challenge to evolutionary biologists because of the need to explain why undefended automimics do not gain such as a fitness advantage by saving the physiological costs of defence that they increase in prevalence within the population, hence making the aposematic signal unreliable. The leading theory is that aposematic signals do not stop all predatory attacks but rather encourage predators to attack cautiously until they have identified the defence level of a specific individual. They can then reject defended individuals and consume the undefended. This theory has recently received strong empirical support, demonstrating that high-accuracy discrimination appears possible. However, this raises a new evolutionary problem: if predators can perfectly discriminate the defended from the undefended and preferentially consume the latter, then how can automimicry persist? Here, we present four different mechanisms that can allow non-trivial levels of automimics to be retained within a population, even in the extreme case where predators can differentiate defended from undefended individuals with 100% accuracy. These involve opportunity costs to the predator of sampling carefully, temporal fluctuation in predation pressure, predation pressure being correlated with the prevalence of automimicry, or developmental or evolutionary constraints on the availability of defence. These mechanisms generate predictions as to the conditions where we would expect aposematically signalling populations to feature automimicry and those where we would not.     

Naiveté and an aquatic-terrestrial dichotomy in the effects of introduced predators

There is much evidence that suggests that freshwater systems are more sensitive to introduced predators than are terrestrial or marine systems. We argue here that this dichotomy reflects widespread naiveté toward introduced predators among freshwater prey. Continental terrestrial animals are seldom naive toward novel predators owing to the homogenizing effects of historical biotic interchanges. Comparable biotic interchanges might have also precluded prey naiveté in most marine systems. By contrast, freshwater systems exhibit persistent large- and small-scale heterogeneity in predation regimes. This heterogeneity promotes naiveté at multiple spatial scales in freshwater prey, thereby producing a systemic vulnerability to introduced predators that is not seen in continental terrestrial or marine systems.