Repeated predatory attacks and multiple decisions to come out from a refuge in an alpine lizard

Prey often respond to predator presence by increasing theiruse of refuges. However, because the use of refuges may entailseveral costs, the decision of when to come out from a refugeshould be optimized. In some circumstances, if predators remainwaiting outside the refuge and try new attacks or if predator density increases, the prey may suffer successive repeated attacksin a short time. Successive attacks may represent an increasein the risk of predation, but the costs of refuge use alsomay increase with time spent in the refuge. Thus, prey shouldmake multiple related decisions on when to emerge from the refuge after each new attack. We simulated in the field repeatedpredatory attacks to the same individuals of the lizard Lacertamonticola and specifically examined the variation in successivetimes to emergence from a refuge under different thermal conditions(i.e., different costs of refuge use). The results showed thatrisk of predation but also thermal costs of refuge use affectedthe emergence decisions. Lizards increased progressively theduration of time spent in the refuge between successive emergencetimes when the costs of refuge use were lower, but tended tomaintain or to decrease the duration of time spent in the refugebetween successive emergence times when cost of refuge useincreased. Additionally, lizards that entered the refuge withhigher body temperatures had overall emergence times of longer duration. Optimization of refuge use and flexibility in theantipredator responses might help lizards to cope with increasedpredation risk without incurring excessive costs of refugeuse.     

Historical influence of predation pressure on escape by Podarcis lizards in the Balearic Islands

Island tameness (reduced escape behaviour on islands where prey have experienced prolonged relaxation of predation pressure) is known in several taxa, although the relationships between recent predation pressure and escape on islands are poorly known. We investigated escape by numerous populations exposed to differing predation pressure of two sister species of Podarcis lizards in the Balearic Islands. Our main findings are that flight initiation distance was greater in Podarcis pityusensis than Podarcis lilfordi and increased as predation pressure increased in P. pityusensis. Island tameness led to extinction of P. lilfordi on Menorca and Mallorca following anthropogenic introduction of predators; this species is extant only on nearby islets. The lack of relationship between recent predation pressure and flight initiation distance in P. lilfordi indicates that the historically acquired deficit in the ability to adjust escape behaviour to predation pressure still exists. Podarcis pityusensis, which was exposed to greater natural predation pressure before human introduction of predators, survives on Ibiza and Formentera, as well as on islets. Retention of the ability to respond to predation pressure is consistent with our finding that flight initiation distance increases as predation pressure increases among current populations. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

When to come out from a refuge: risk-sensitive and state-dependent decisions in an alpine lizard

Prey often respond to predator presence by increasing theiruse of refuges. However, unfavorable thermal conditions in refugesmight entail physiological costs for an ectothermic prey. Thus,the decision of when to come out from a refuge should be optimizedby considering the expected fitness effects of diminution ofpredation risk with time, but also by considering the cost of theloss of time spent at optimal body temperature maximizing physiological functions.The model of Ydenberg and Dill describes the trade-off betweenrisk and cost for a prey fleeing to a refuge. We present a specialcase of this model to predict how emergence time from the refugein lizards or other ectotherms should vary as a function ofrisk of predation and thermal costs of refuge use. The analysesof the variation in emergence time from a refuge of Lacertamonticola lizards in the field under two different predation risklevels supported the predictions of the model. As predicted,time spent in the refuge was longer when the threat of the initialattack had been higher, and therefore the subsequent diminutionof risk was slower, but only when lizards emerged at the sameplace where they hid. When initial body temperature was high,some lizards decreased emergence time by emerging from a differentplace. In addition, the effects of thermal costs were more relevant inthe high-risk situation. Time spent in the refuge under highrisk increased when thermal conditions of the refuge were moresimilar to thermal conditions outside (i.e., physiological costsof refuge use were lower). We conclude that optimization ofrefuge-use strategies might help lizards cope with changes in predationrisk without incurring excessive physiological costs.     

European Roe Deer Increase Vigilance When Faced with Immediate Predation Risk by Eurasian Lynx

Prey animals must balance antipredatory behaviour with foraging behaviour. According to the risk allocation hypothesis, prey increase antipredatory behaviour and reduce foraging activity during pulses of high risk, but with continuous risk, other activities must continue and antipredatory behaviour decreases despite the risk. We studied the impact of lynx presence on the vigilance behaviour of wild roe deer under conditions of (i) a pulsed elevated risk by experimentally spreading lynx urine as an olfactory cue, and (ii) continuous risk by comparing an area where lynx was eradicated 160 years ago to an area where lynx has been re‐introduced 30 years ago. Roe deer were extremely vigilant in response to the predator olfactory cue; however, roe deer vigilance did not differ measurably among areas with or without potential lynx presence. Deer were more vigilant before sunset than during the night at both study areas, probably due to long‐term adaptation of roe deer to human hunting during daytime. Vigilance decreased from August to September even though activity of lynx increases in autumn, which may be a result either of increased foraging due to decrease in food quality in autumn, or of changes in social organization of the deer. Our results suggested that the degree of vigilance depends on environmental cues. We found that roe deer respond to lynx urine despite a long absence of lynx in the ecosystem. Our results support the risk allocation hypothesis for responses to pulses of high risk but not for responses to continuous elevated levels of risk.     

Predicted fitness consequences of threat-sensitive hiding behavior

In studies of refuge use as a form of antipredator behavior,where prey hide in response to a predator's approach, factorssuch as foraging costs and the perceived risk in a predator'sapproach have been shown to influence the hiding behavior ofprey. Because few studies of waiting games have focused on mammals,we studied the hiding behavior of the yellow-bellied marmot(Marmota flaviventris), a ground-dwelling rodent. We testedthe prediction that marmots vary hiding time as a function ofpredator approach speed and presence and absence of food outsidetheir refuge and that marmots hide differently depending ontheir relative condition. We conducted "fast approaches" and"slow approaches" in the presence and absence of extra foodand evaluated hiding times. Multiple regression analyses demonstratedthat the interaction between the approach speed and the presenceand absence of food influenced hiding behavior; body conditionhad a smaller, but nonsignificant effect. We then developeda state-dependent dynamic model to explore potential fitnessconsequences of these decisions. The model suggested that theoverall survival of a population is substantially reduced whenindividuals make suboptimal decisions. Our research builds onprevious studies, indicating that animals integrate both costsand benefits of hiding when determining their hiding times.     

Macrophytes as refuge or risky area for zooplankton: a balance set by littoral predacious macroinvertebrates

1. Zooplankton use macrophytes as day-time refuge areas when trying to escape from pelagic predators. But macrophytes can also host a diverse and abundant macroinvertebrate assemblage and zooplankton are also likely to face predacious macroinvertebrates once they enter the littoral zone. This study aimed to elucidate the role of macroinvertebrates in determining the refuge capacity of macrophytes.
2. We conducted a field enclosure experiment using plastic bags and complementary laboratory feeding trials to test how macroinvertebrates counteract the benefits to zooplankton of the macrophyte refuge. The field experiment consisted of three treatments with different macroinvertebrate assemblages: without predators (WP), low abundance and diversity (LAD) and high abundance and diversity of predators (HAD – which represents lake conditions).
3. Populations of Diaphanosoma brachyurum , Bosmina huaronensis and Moina micrura (Cladocera) and of both male and female Notodiaptomus incompositus (Copepoda, Calanoida) declined (by nearly 80%) in the presence of HAD in comparison to WP and LAD treatments.
4. Feeding trials revealed that Buenoa sp. (backswimmer), adults of Palaemonetes argentinus (grass shrimp) and Cyanallagma interruptum (damselfly) had a significant negative impact on cladocerans ( D. brachyurum, B. huaronensis ) and the calanoid copepod population (males, females and copepodites). These predators showed a strong predation effect ranging from 75% to 100% reductions of zooplankton populations.
5. The refuge effect offered by macrophytes to zooplankton depends on and is balanced by the predacious macroinvertebrate assemblage that plants host. The risk of confronting littoral predators is high and macroinvertebrate presence can turn the macrophytes into risky areas for zooplankton.     

Adult blacktip sharks (Carcharhinus limbatus) use shallow water as a refuge from great hammerheads (Sphyrna mokarran)

A refuge can be any space that keeps an organism safe from danger. Prey usually seek protection in the closest refuge available to minimize cost while maximizing survival. Aerial drone footage of blacktip sharks, Carcharhinus limbatus, along the coast of southeast Florida, USA, shows adult blacktips fleeing to the shallow water adjacent to the beach when confronted with or chased by a predatory great hammerhead shark, Sphyrna mokarran. To authors’ knowledge, this is the first evidence of adult C. limbatus using shallow waters as a refuge.     

Predators induce interspecific herbivore competition for food in refuge space

Resource competition among herbivorous arthropods has long been viewed as unimportant because herbivore populations are controlled by predators. Although recently resurrected as an organizing force in arthropod communities on plants, there is still general agreement that resource competition among herbivores is reduced by predators. Here we show the reverse: predators induce interspecific resource competi-tion among herbivores. We found that thrips larvae ( Frankliniella occidentalis ) use the web produced and inhabited by the spider mite Tetranychus urticae as a refuge from predation by the phytoseiid mite Neoseiulus cucumeris . Thrips larvae prefer clean plant parts, but move into the web upon perceiving volatile cues associated with thrips and predators. This behaviour leads to lower predation risk, but also to reduced developmental rate and lower production of thrips larvae due to competition with spider mites. In addition, thrips larvae consume spider-mite eggs. Thus, predators induce interspecific competition and intraguild predation among herbivores within refuge space, even when host plants have an overall green appearance.     

Mortality risk versus food quality trade-offs in ants: patch use over time

Abstract.

• 1 Foragers of the ant species Lasius pallitarsis (Provancher) and Myrmica incompleta Provancher were given access to two food patches that differed in nutritive quality. In about half of the trials, the higher quality patch also had a mortality risk for the foragers in the form of a large Formica subnuda Emery ant located along the trail. Colonies were given access to the food for 4 or 24 h, every second day.
• 2 Use of the higher quality patch by L.pallitarsis foragers was depressed by the mortality risk. In contrast to the predictions of a food stress hypothesis, foragers used the risky patch more in the longer access trials. This appears due to a decline in the activity level of the F.subnuda, which results in a significantly lower mortality risk per trip.
• 3 M.incompfeta also significantly decreased their use of the higher quality patch when a F.subnuda was present. However, the length of time a colony had access to the patches had no effect on the use of the risky patch. M.incompleta foraging behaviour seems relatively insensitive to short-term food stress or changing levels of mortality risk.
• 4 The differences between species in their exploitation of patches and reactions to F.subnuda are discussed in terms of the species’natural history.

     

Enhanced growth at low population density in Daphnia: the absence of crowding effects or relief from visual predation?

1. It has been suggested that chemical information from crowded populations of an animal such as Daphnia carries a cue indicating imminent food limitation, and we suggest that in the presence of fish kairomones, it may also convey a hint of the need to enhance antipredation defences. 2. We performed two‐factorial experiments with Daphnia grown in flow‐through plankton chambers in medium containing high levels of Scenedesmus food plus chemical information on either low or high population density levels and in the presence or absence of fish chemical cues (kairomones) and recorded (i) the effects on Daphnia growth rate and reproduction, and (ii) the effects on Daphnia depth selection. Further depth‐selection experiments were performed to test the reaction of Daphnia to crowding information at different Daphnia concentrations and to test its effect on daytime and night‐time depth selection by different Daphnia instars in the presence of kairomones. 3. The effects of crowding information alone (in the absence of kairomones) were weak and were not significantly strengthened by the addition of kairomones. The effects of kairomones alone (in the absence of crowding information) were much stronger and were increased by the presence of crowding chemicals: Daphnia selected greater depths in daylight (the later the instar and the larger its body size, the greater the depth), their body growth was slower and daily reproductive investment reduced, compared with Daphnia grown in the absence of crowding information. This suggested that crowding chemicals carry a cue indicating the need to invest more into antipredation defences. 4. The adaptive significance of these effects was confirmed by the differential vulnerability to predation of the Daphnia when offered as prey to live roach after being grown for 6 days either in the presence (higher vulnerability) or in the absence (lower vulnerability) of information on high density. 5. The strong interaction between crowding information and fish kairomones may be explained either as the reaction to a cue indicating impending food stress or as the reaction to a signal of increased predation risk. While the former scenario is already known from crowding studies, the latter is a novel idea that stems from the old concept of ‘low‐density anti‐predation refuge’. The two scenarios are not mutually exclusive: each stems from the need to invest in survival rather than in growth and reproduction [Corrections were made to this paragraph after first online publication on 4 April 2012].     

Cotesia kariyai larvae need an anchor to emerge from the host Pseudaletia separata

Mature larvae of the gregarious endoparasitoid Cotesia kariyai construct cocoons for pupation approximately 10 days after parasitization and emerge from their host Pseudaletia separata under a long day photo-regime (16L8D) at 25 +/- 1 degrees C. The parasitoid larvae make capsules in the host hemocoel just prior to their emergence. These capsules function as "anchors," which enable them to press against the host integument from inside the host. It was predicted that this anchor might be composed of silk proteins secreted from the parasitoid larvae, because a previous study showed that the anchor was made up of a glycoprotein and that the silk gland of parasitoid larvae developed from 2nd larval stage. Fibroin-like proteins in C. kariyai larva mainly consist of two proteins with molecular masses of the 300.6 and 46.7 kDa estimated by SDS-PAGE. The fibroin-like proteins with the same molecular mass were detected from the anchor proteins just prior to parasitoid emergence. These results indicate that the anchor was assembled with fibroin-like proteins and was formed just before parasitoid emergence while in the host body cavity. Injection of bovine pancreatic trypsin inhibited the emergence of parasitoid larvae from the host because the anchor was decomposed by trypsin. Trypsin activity in the parasitized host hemolymph increased only after parasitoid emergence.     

Using mitochondrial DNA to test the hypothesis of a European post-glacial human recolonization from the Franco-Cantabrian refuge

It has been proposed that the distribution patterns and coalescence ages found in Europeans for mitochondrial DNA (mtDNA) haplogroups V, H1 and H3 are the result of a post-glacial expansion from a Franco-Cantabrian refuge that recolonized central and northern areas. In contrast, in this refined mtDNA study of the Cantabrian Cornice that contributes 413 partial and 9 complete new mtDNA sequences, including a large Basque sample and a sample of Asturians, no experimental evidence was found to support the human refuge-expansion theory. In fact, all measures of gene diversity point to the Cantabrian Cornice in general and the Basques in particular, as less polymorphic for V, H1 and H3 than other southern regions in Iberia or in Central Europe. Genetic distances show the Cantabrian Cornice is a very heterogeneous region with significant local differences. The analysis of several minor subhaplogroups, based on complete sequences, also suggests different focal expansions over a local and peninsular range that did not affect continental Europe. Furthermore, all detected clinal trends show stronger longitudinal than latitudinal profiles. In Northern Iberia, it seems that the highest diversity values for some haplogroups with Mesolithic coalescence ages are centred on the Mediterranean side, including Catalonia and South-eastern France.     

Heterogeneous landscapes and the role of refuge on the population dynamics of a specialist predator and its prey

How, and where, a prey species survives predation by a specialist predator during low phases of population fluctuations or a cycle, and how the increase phase of prey population is initiated, are much-debated questions in population and theoretical ecology. The persistence of the prey species could be due mainly to habitats that act as refuges from predation and/or due to anti-predatory behaviour of individuals. We present models for the former conjecture in two (and three) habitat systems with a specialist predator and its favoured prey. The model is based on dispersal of prey between habitats with high reproductive output but high risk of predation, and less productive habitats with relatively low risk of predation. We illustrate the predictions of our model using parameters from one of the most intriguing vertebrate predator–prey systems, the multi-annual population cycles of boreal voles and their predators. We suggest that cyclic population dynamics could result from a sequence of extinction and re–colonization events. Field voles (Microtus agrestis), a key vole species in the system, can be hunted to extinction in their preferred meadow habitat, but persist in sub-optimal wet habitats where their main predator, the least weasel (Mustela nivalis nivalis) has a low hunting efficiency. Re–colonization of favourable habitats would occur after the predator population crashes. At the local scale, the model suggests that the periodicity and amplitude of population cycles can be strongly influenced by the relative availability of risky and safe habitats for the prey. Furthermore, factors like intra-guild predation may lead to reduced predation pressure on field voles in sub-optimal habitats, which would act as a refuge for voles during the low phase of their population cycles. Elasticity analysis suggested that our model is quite robust to changes in most parameters but sensitive to changes in the population dynamics of field voles in the optimal grassland habitat, and to the maximum predation rate of weasels.     

Hunger, light level and body size affect refuge use by post-settlement lingcod Ophiodon elongatus

Using experimental methods, body size, nutritional state (hunger) and light level were investigated as possible determinants of the extent to which juvenile lingcod Ophiodon elongatus used structural refuges. In the laboratory, older, larger individuals (134–162 mm total length, L _T) exhibited a higher propensity for structure use than did smaller juvenile fish (78–103 mm L _T). In fish of both body sizes, increasing hunger levels caused fish to emerge more readily from refuges than satiated individuals, with this effect most prominent for smaller fish. Diel patterns of ambient illumination were simulated in the laboratory, and refuge use by large individuals decreased significantly in response to lower nocturnal light levels, a pattern that was not observed in the smaller size class. These results indicate an ontogenetic shift in refuge use. During the summer, as post-settlement fish grew larger, they tended to increase affinity for structurally complex habitat, and also showed divergent patterns of behaviour in relation to hunger and light level.