How do herbivorous insects respond to drought stress in trees?

Increased frequency and severity of drought, as a result of climate change, is expected to drive critical changes in plant–insect interactions that may elevate rates of tree mortality. The mechanisms that link water stress in plants to insect performance are not well understood. Here, we build on previous reviews and develop a framework that incorporates the severity and longevity of drought and captures the plant physiological adjustments that follow moderate and severe drought. Using this framework, we investigate in greater depth how insect performance responds to increasing drought severity for: (i) different feeding guilds; (ii) flush feeders and senescence feeders; (iii) specialist and generalist insect herbivores; and (iv) temperate versus tropical forest communities. We outline how intermittent and moderate drought can result in increases of carbon‐based and nitrogen‐based chemical defences, whereas long and severe drought events can result in decreases in plant secondary defence compounds. We predict that different herbivore feeding guilds will show different but predictable responses to drought events, with most feeding guilds being negatively affected by water stress, with the exception of wood borers and bark beetles during severe drought and sap‐sucking insects and leaf miners during moderate and intermittent drought. Time of feeding and host specificity are important considerations. Some insects, regardless of feeding guild, prefer to feed on younger tissues from leaf flush, whereas others are adapted to feed on senescing tissues of severely stressed trees. We argue that moderate water stress could benefit specialist insect herbivores, while generalists might prefer severe drought conditions. Current evidence suggests that insect outbreaks are shorter and more spatially restricted in tropical than in temperate forests. We suggest that future research on the impact of drought on insect communities should include (i) assessing how drought‐induced changes in various plant traits, such as secondary compound concentrations and leaf water potential, affect herbivores; (ii) food web implications for other insects and those that feed on them; and (iii) interactions between the effects on insects of increasing drought and other forms of environmental change including rising temperatures and CO₂ levels. There is a need for larger, temperate and tropical forest‐scale drought experiments to look at herbivorous insect responses and their role in tree death.     

Do most human populations descend from phylogenetic trees?

Molecular biologists and some population geneticists have recently claimed to be able to reconstruct modern human populations remote history by means of phylogenetic trees. Many objections to this method are discussed in the present paper. The most important are

1. Inter-populations migrations are likely to have been important, even in the remote past. So the “treeness” of this evolution is disputable.
2. There is no reason to believe that actual molecular phylogenies would be convergent between different molecules and would therefore represent populations history.

The various kind of genetic data, their relations to other data and the limits of their possible use in the analysis of our past are then discussed, together with the ideological background of the most common theories and of their publication. It is very likely that the history of different populations was heterogeneous. Small and isolated hunter-gatherers frequently evolving close to a phylogenetic model, while dense and increasing populations, since the Neolithic, were closer to a dynamic network model, structured by isolation by distance. In any case, our present knowledge is obviously insufficient to reconstruct our genetic past, especially on the long term, and we can only hope that the development of the HUGO Genome Diversity project is going to yield the significant information presently lacking.     

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.     

How do trees respond to species mixing in experimental compared to observational studies?

For decades, ecologists have investigated the effects of tree species diversity on tree productivity at different scales and with different approaches ranging from observational to experimental study designs. Using data from five European national forest inventories (16,773 plots), six tree species diversity experiments (584 plots), and six networks of comparative plots (169 plots), we tested whether tree species growth responses to species mixing are consistent and therefore transferrable between those different research approaches. Our results confirm the general positive effect of tree species mixing on species growth (16% on average) but we found no consistency in species‐specific responses to mixing between any of the three approaches, even after restricting comparisons to only those plots that shared similar mixtures compositions and forest types. These findings highlight the necessity to consider results from different research approaches when selecting species mixtures that should maximize positive forest biodiversity and functioning relationships.     

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.     

Can semiochemicals attract both western flower thrips and their anthocorid predators?

Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) (western flower thrips, WFT) is a key pest in a range of crops worldwide. Anthocorid species (Hemiptera) are important natural enemies of thrips. Several experiments were undertaken to determine whether a thrips lure, methyl isonicotinate (MI), affected the behaviour of WFT and anthocorids found in outdoor crops. Currently, this volatile compound is used in conjunction with sticky traps for monitoring thrips predominantly in greenhouses in Northern Europe. In the present study, in a nectarine [Prunus persica (L.) (Rosaceae)] orchard and an outdoor capsicum [Capsicum annuum L. (Solanaceae)] crop in Spain, blue sticky and white water traps with MI caught significantly more WFT than traps without MI. The volatile compound also significantly increased both blue sticky and white water trap capture of anthocorids – predominantly Orius laevigatus (Fieber) (Hemiptera: Anthocoridae) – in the capsicum crop. These results indicate that the behaviour of both WFT and O. laevigatus were altered by the presence of the compound and suggest there is potential to develop novel tools based on MI in conjunction with biological control strategies for thrips management.     

Is dimethylsulfoxide a reliable solvent for extracting chlorophyll under field conditions?

Dimethylsulfoxide (DMSO) appears to be a reliable solvent for extracting chlorophyll (Chl), however, modification of standard methods may be necessary for some species under field conditions. We found that Chl extraction of whole leaf tissue with DMSO incubated at between 25 and 40 °C was generally similar to the 80% acetone method, except for one graminoid species that required maceration. There was little effect of incubation temperature or duration of incubation beyond 7 h on extraction efficiency, but DMSO extracts were less stable than acetone extracts during one week of cold storage, especially if they thawed during this period. Since Chl extraction methods may provide variable results, particularly in the field, studies using different solvents should be compared cautiously unless specific methods have been calibrated. This revised version was published online in August 2006 with corrections to the Cover Date.     

Do anuran larvae respond behaviourally to chemical cues from an invasive crayfish predator? A community-wide study

Antipredator behaviour is an important fitness component in most animals. A co-evolutionary history between predator and prey is important for prey to respond adaptively to predation threats. When non-native predator species invade new areas, native prey may not recognise them or may lack effective antipredator defences. However, responses to novel predators can be facilitated by chemical cues from the predators’ diet. The red swamp crayfish Procambarus clarkii is a widespread invasive predator in the Southwest of the Iberian Peninsula, where it preys upon native anuran tadpoles. In a laboratory experiment we studied behavioural antipredator defences (alterations in activity level and spatial avoidance of predator) of nine anurans in response to P. clarkii chemical cues, and compared them with the defences towards a native predator, the larval dragonfly Aeshna sp. To investigate how chemical cues from consumed conspecifics shape the responses, we raised tadpoles with either a tadpole-fed or starved crayfish, or dragonfly larva, or in the absence of a predator. Five species significantly altered their behaviour in the presence of crayfish, and this was largely mediated by chemical cues from consumed conspecifics. In the presence of dragonflies, most species exhibited behavioural defences and often these did not require the presence of cues from predation events. Responding to cues from consumed conspecifics seems to be a critical factor in facilitating certain behavioural responses to novel exotic predators. This finding can be useful for predicting antipredator responses to invasive predators and help directing conservation efforts to the species at highest risk.     

Do soil enzymes respond to long-term grazing in an arid ecosystem?

Background and aims

Our objective was to assess the effects of long-term continuous grazing on soil enzyme activities in relation to shifts in plant litter attributes and soil resources in an arid ecosystem, considering both spatial and temporal variations.

Methods

We randomly extracted soil samples with the respective litter cover at 5 modal size plant-covered patches (PCP) and the nearest inter-canopy areas (IC) at Patagonian Monte sites with low, medium and high grazing intensity in winter and summer from 2007 to 2009. We analyzed enzyme activities (dehydrogenase, ß-glucosidase, protease, alkaline and acid phosphatase), microbial biomass-C, organic-C, total soil-N, and moisture in soil and mass and quality in plant litter. We assessed faeces density and plant cover in the field.

Results and conclusions

Grazing led to reduced grass cover, decreasing plant litter mass with increasing soluble phenolics, and reduced phosphatases, ß-glucosidase and microbial biomass-C at PCP. A localized nutrient input from animal excreta seems to promote microbial biomass-C, alkaline phosphatase and dehydrogenase activities but only at IC from the site with high grazing intensity. Plant heterogeneous distribution, plant litter quantity and quality, nutrient inputs from grazers and seasonal variation in soil moisture, also affecting soil resources and microbial biomass, modulate soil enzyme responses to long-term grazing in the arid Patagonian Monte.     

Do ammonia-oxidizing archaea respond to soil Cu contamination similarly asammonia-oxidizing bacteria?

Inhibitory experiments were conducted to investigate the responses of the population sizes of ammonia-oxidizing archaea (AOA) and bacteria (AOB) and the potential nitrification rates (PNRs) to Cu contamination in four Chinese soils. PNR was determined using a substrate-induced nitrification (SIN) assay, and the population size of the nitrifiers represented by amoA gene abundances was quantified using a real-time polymerase chain reaction (qPCR) assay. Both population size and PNR of the ammonia oxidizers reduced considerably at high Cu concentrations in all the soils. Bacterial amoA gene abundance was reduced by from 107-fold (Hailun soil) to more than 232-fold (Hangzhou soil) at the highest Cu concentrations (2,400 mg kg^?1 Cu for Hailun, Langfang and Guangzhou soils and 1,600 mg kg^?1 Cu for Hangzhou soil), while reduction in archaeal amoA gene abundance was from 10-fold (Langfang soil) to 89-fold (Hangzhou soil). AOA seemed more tolerant to Cu contamination than AOB. Nitrification rates were inhibited by more than 50% at a Cu concentration of 600 mg kg^?1, and by more than 90% at the highest Cu concentrations in all soils. These results indicated that both AOA and AOB can be inhibited by toxic metals, highlighting the need to consider the role of AOA in nitrification in soils.     

Do Australian small mammals respond to native and introduced predator odours?

Abstract Coevolution is thought to have led to many small mammal species avoiding the scent marks of their main mammalian predators, as they provide a reliable cue to predation risk. Most support for this hypothesis comes from northern hemisphere predator/prey systems, however, it is unclear whether this avoidance of predator faecal odour occurs in Australia's mammalian fauna, which has evolved in relative isolation from the rest of the world, and is dominated by marsupials rather than placentals. We tested this theory for an Australian system with marsupial and placental predators and prey, that share a long‐term (>1 million years) or short‐term (<150 years) exposure to each other. The predators were the native marsupial tiger quoll Dasyurus maculatus and the introduced placental red fox Vulpes vulpes. The potential prey were three native rodent species, the bush rat Rattus fuscipes, the swamp rat Rattus lutreolus, the eastern chestnut mouse Pseudomys gracilicaudatus, and the marsupial brown antechinus Antechinus stuartii. Small mammals were captured in Elliott traps with 1/3 of traps treated with fox faeces, 1/3 treated with quoll faeces and the remainder left untreated. The native rodent species all showed avoidance of both tiger quoll and red fox odours whereas the marsupial antechinus showed no responses to either odour. Either predator odour avoidance has not evolved in this marsupial or their reaction to predator odours may be exhibited in ways which are not recognizable through trapping. The avoidance by the rodents of fox odour as well as quoll odour indicates this response may either be due to common components in fox and quoll odour, or it may be a recently evolved response.     

Do female black field crickets Teleogryllus commodus benefit from polyandry?

Female insects that mate multiply tend to have increased lifetime fitness, apparently because of greater access to male-derived resources (e.g. sperm, nuptial gifts) that elevate fertility/fecundity. Experiments that standardize the number of matings per female also show that polyandry can improve aspects of offspring performance, most notably early embryo survival (egg hatching success). This improvement is widely attributed to genetic benefits which would arise if polyandrous females skew paternity to produce fitter offspring. In two separate experiments with field crickets (Teleogryllus commodus) polyandrous females (two, three or four mates) did not have higher egg hatching success than monandrous females (effect sizes: r = 0.03 and 0.08 for the respective experiments), which is consistent with our finding of no sire effect on hatching success. Polyandry also had no effect on post-hatching offspring survival. Polyandrous females' offspring took significantly longer to mature but their sons were not heavier and their daughters were actually significantly smaller than those of monandrous females. Finally, after controlling for relative male size, monandrous females' sons were more successful when directly competing for a mate.     

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.     

Do incubation-induced changes in a lizard's phenotype influence its vulnerability to predators?

Strong evidence affirms that incubation temperatures can influence the phenotype of hatchling reptiles, but few studies have examined the fitness consequences of such modifications. Vulnerability to predation is one plausible way that phenotypic shifts could affect an organism's fitness. We incubated the eggs of three sympatric lizard species at temperatures similar to the thermal extremes of natural nests, and measured several traits that are likely to influence a hatchling's susceptibility to a natural (snake) predator. We also examined the lizards' actual vulnerability to snake predators in direct encounters in the laboratory. Our results show that incubation temperature can affect an individual's date of hatching, morphology, locomotor performance, chemosensory responses to snake scent, and ability to avoid a snake predator during staged laboratory encounters. Incubation temperature did not modify the hatchling's `attractiveness' to snakes (as measured via chemical cues) or its antipredator tactics (propensity to escape predation through fleeing or caudal autotomy). The magnitude and direction of incubation- induced phenotypic shifts varied among the three species (even those with similar life histories, thermoregulatory preferences, and microhabitat requirements), and depended on body temperatures and hatchling age. We conclude that incubation-induced modifications to a lizard's phenotype affect a suite of traits that are likely to influence its vulnerability, and also its actual ability to escape from a predator. This result suggests that incubation regimes can influence organismal fitness via their effects on predator-prey interactions. Received: 21 December 1998 / Accepted: 23 March 1999     

Do aphids infected with entomopathogenic fungi continue to produce and respond to alarm pheromone?

The response of pea aphids, Acyrthosiphon pisum, to aphid alarm pheromone was not modified by infection with Beauveria bassiana. Approximately 50% of uninfected and infected aphids responded to synthetic alarm pheromone. The simulated attack of aphids infected with B. bassiana did not elicit a response in uninfected aphids. Preliminary air entrainment experiments of both uninfected aphids and aphids at different stages of B. bassiana (generalist pathogen) or P. neoaphidis (obligate pathogen of aphids) demonstrated that B. bassiana infected aphids produced less alarm pheromone than uninfected aphids and, conversely, P. neoaphidis infected aphids produced more alarm pheromone than uninfected aphids. These results are discussed with particular emphasis on the different life history strategies of these two pathogens. We hypothesise that the obligate, specialist pathogen, P. neoaphidis, is under greater selection pressure to increase pathogen transmission and survival resulting in modified host behaviour, than the generalist pathogen, B. bassiana.     

Do damselfly larvae recognize and differentially respond to distinct categories of macroinvertebrates?

Zygopteran larvae normally encounter other aquatic macroinvertebrates that are predators, competitors, and prey and should therefore demonstrate varied responses when faced with different categories of opponent. In a laboratory experiment individual final-instarIschnura posita (Hagen) larvae were observed in interactions with six categories of invertebrate opponents. The opponent categories were a nonconspecific damselfly and a small crayfish, which represented threatening opponents because they were larger than theI. posita subject larva, and a mayfly and a stonefly, which constituted nonthreatening opponents because they were smaller than the subject larva. The levels of threat posed by conspecific larvae of final and penultimate instar were inferred by comparison to the other opponent categories. Multivariate analysis showedI. posita's response differed between the two larger opponents, but responses were statistically indistinguishable between the two smaller opponents. Larvae retreated, moved around the stalk, and struck their opponents with their lamellae more often in the presence of a crayfish than the nonconspecific zygopteran. In contrast, they assumed an S-bend posture frequently with the zygopteran. Responses toward final-instar conspecifics differed from responses toward the larger opponents. Effectively, larvae wagged their abdomens only in the presence of final-instar conspecifics and retreated and moved around the stalk less frequently in these trials. Responses toward the smaller conspecifics differed from the responses to the small opponents. Larvae struck penultimate-instar conspecifics with their lamellae more frequently than the other small opponents. Our results suggest that larval zygopteran behaviors (such as S-bend and SCS) that have previously been described as intraspecific displays are of a more general nature and used toward a variety of opponents, whereas wag is unique to intraspecific interactions inI. posita.     

Circumnutations under free-fall conditions in space?

Regular growth movement, so-called circumnutation, of plants and plant organs is a very general phenomenon. The origin of circumnutations is, however, unclear. Three different types of model are discussed in relation to some experimental results on circumnutations. It is suggested that an experiment in space, under free-fall conditions, should be done on different species showing circumnutations in order to discriminate between the models.