Predation in the presence of decoys: an inhibitory factor on pathogen control by bacteriophages or bdellovibrios in dense and diverse ecosystems

Several attempts have been made at the removal of specific pathogens from the intestinal microflora using either bacteriophages or "predatory" bacteria such as Bdellovibrio spp. To date these attempts have had mixed success. A mechanism explaining these findings based on competitive hindrance by non-prey, or decoy species is put forward. It is shown that this hindrance tends to damp out predator-prey oscillations, and therefore reduces the probability of prey extinction. Possible experiments to verify this theory are discussed. The decoy effect may play a role in any system with high densities of bacteria or other particulate matter, such as activated sludge or biofilms.     

Arrival date and microorganisms in barn swallows

Migration between breeding sites and winter quarters constitute a major life history strategy in birds. The benefits of such migrations must at least equal the costs for such behavior to evolve and be maintained. We tested whether there was a relationship between abundance and diversity of microorganisms on nest lining feathers and timing of arrival by barn swallows Hirundo rustica. Nest lining feathers are chosen and transported by adult barn swallows to their nests just before and during egg laying, at a time when barn swallows have arrived weeks earlier, implying that any heterogeneity in abundance and diversity of microorganisms on feathers in nests must arise from feather preferences. There was a negative relationship between arrival date and the total number of fledglings showing that early arrival is advantageous. The arrival date of adult barn swallows was significantly positively correlated with the abundance of specific bacteria (Bacillus licheniformis) and positively correlated with the abundance of the fungus Trichoderma reesei and negatively correlated with the abundance of the fungus Mucor circinelloides. Moreover, we found a significant positive relationship between arrival date and mean total number of bacterial colonies in TSA medium. There was a significant negative relationship between arrival date and mean total number of bacterial colonies in FMA medium, and Simpson's diversity index of the abundance of bacteria in FMA medium. Such heterogeneity may arise from some microorganisms being beneficial, others detrimental and yet others benign and of no significant importance. In contrast, there was no significant relationship between arrival date and age of individuals. These findings are consistent with the hypothesis that early arriving barn swallows differ in abundance and diversity of microorganisms from late arriving conspecifics, and that they choose feathers for their nests that differ in terms of microorganisms from those chosen by late arrival individuals.     

Microorganisms Associated with Feathers of Barn Swallows in Radioactively Contaminated Areas Around Chernobyl

The Chernobyl catastrophe provides a rare opportunity to study the ecological and evolutionary consequences of low-level, environmental radiation on living organisms. Despite some recent studies about negative effects of environmental radiation on macroorganisms, there is little knowledge about the effect of radioactive contamination on diversity and abundance of microorganisms. We examined abundance patterns of total cultivable bacteria and fungi and the abundance of feather-degrading bacterial subset present on feathers of barn swallows (Hirundo rustica), a colonial migratory passerine, around Chernobyl in relation to levels of ground level environmental radiation. After controlling for confounding variables, total cultivable bacterial loads were negatively correlated with environmental radioactivity, whereas abundance of fungi and feather-degrading bacteria was not significantly related to contamination levels. Abundance of both total and feather-degrading bacteria increased with barn swallow colony size, showing a potential cost of sociality. Males had lower abundance of feather-degrading bacteria than females. Our results show the detrimental effects of low-level environmental radiation on total cultivable bacterial assemblage on feathers, while the abundance of other microorganism groups living on barn swallow feathers, such as feather-degrading bacteria, are shaped by other factors like host sociality or host sex. These data lead us to conclude that the ecological effects of Chernobyl may be more general than previously assumed and may have long-term implications for host–microbe interactions and overall ecosystem functioning.     

Predation against birds with low immunocompetence

Differences in the phenotypic characteristics between individuals falling prey to predators and conspecifics avoiding predation will reflect the intensity of selection on prey. If prey are generally in poor condition, we predicted that they should have an inferior health status in comparison to individuals dying for other reasons. We investigated this prediction for prey and conspecifics that did not die from predation by comparing the size of the spleen, which is an important immune defence organ reflecting one component of immunocompetence, using 18 species of passerine birds and domestic cat Felis catus predators as a model system. Prey had consistently smaller spleens than non-prey, implying that they had weak immune systems. The data set did not indicate that sex or age, month of death, body mass, body condition, liver mass, wing length or tarsus length differed significantly between prey and non-prey. Thus there was little evidence of confounding factors affecting the results. These observations indirectly suggest that disease and parasitism may play an important role in predator-prey interactions. Received: 4 August 1999 / Accepted: 7 October 1999     

Insect herbivores and the nutrient flow from the canopy to the soil in coniferous and deciduous forests

Phytophagous insects can have severe impacts on forested ecosystems in outbreak situations but their contribution to flows of energy and matter is otherwise not so well known. Identifying the role of phytophagous insects in forested ecosystems is partly hindered by the difficulty of combining results from population and community ecology with those from ecosystem ecology. In our study we compared the effects of aphids and leaf-feeding lepidopterous larvae on the epiphytic micro-organisms in the canopies of spruce, beech and oak, and on the vertical flow of energy and nutrients from the canopies down to the forest floor. We particularly searched for patterns resulting from endemic herbivory rather than outbreak situations. Excreta of lepidopterous larvae and aphids promoted the growth of epiphytic micro-organisms (bacteria, yeasts, filamentous fungi) on needles and leaves, which suggests that micro-organisms were energy limited. Leachates from needles and leaves of infested trees contained higher concentrations of dissolved organic C and lower concentrations of NH₄-N and NO₃-N, relative to uninfested trees. The seasonal abundance of herbivores and micro-organisms significantly affected the dynamics of throughfall chemistry; for instance, concentrations of inorganic N were lower underneath infested than uninfested trees during June and July. There was little difference between the chemistry of soil solutions collected from the forest floor beneath infested and uninfested trees. Thus, under moderate to low levels of infestation the effects of above-ground herbivory seems to be obscured in the soil through buffering biological processes.     

Fungi,feather damage,and risk of predation

Predation is a powerful selective force with important effects on behavior, morphology, life history, and evolution of prey. Parasites may change body condition, health status, and ability to escape from or defend prey against predators. Once a prey individual has been detected, it can rely on a diversity of means of escape from the pursuit by the predator. Here we tested whether prey of a common raptor differed in terms of fungi from nonprey recorded at the same sites using the goshawk Accipiter gentilis and its avian prey as a model system. We found a positive association between the probability of falling prey to the raptor and the presence and the abundance of fungi. Birds with a specific composition of the community of fungi had higher probability of falling prey to a goshawk than individual hosts with fewer fungi. These findings imply that fungi may play a significant role in predator–prey interactions. The probability of having damaged feathers increased with the number of fungal colonies, and in particular the abundance of Myceliophthora verrucos and Schizophyllum sp. was positively related to the probability of having damaged feathers. In addition, we found a significant correlation between the rate of feather growth of goshawk prey with birds with more fungi being more likely to be depredated. These findings are consistent with the hypothesis that survival and feather quality of birds are related to abundance and diversity of fungi.     

Use of prey and non-prey food by the ladybird beetle Eriopis connexa (Coleoptera: Coccinellidae) under laboratory-rearing conditions

Prey for predators can fluctuate in abundance and in quality over time requiring predator strategies to cope with food shortage. Coccinellinae are often associated with sap-sucking pests that exhibit high population unpredictability such as aphids and psyllids. Eriopis connexa (Germar) (Coleoptera: Coccinellidae) is a predator with potential for biological control, especially a well-studied population which is resistant to pyrethroids used to control insect defoliators. Both larvae and adult E. connexa were provided ad libitum prey and non-prey foods (pollen and honey water solution) at increasing intervals from 1 to 10 days. Neonate larvae of E. connexa required eating prey daily to develop into adults. However, non-prey food such as honey water solution did prolong larval and adult survival but neither fulfilled larval development nor adult reproduction. Honey water solution promoted 100% adult survival up to 25 days in the adult stage without prey with oviposition returning after daily feeding on prey. Females subjected to increased feeding intervals over four days reduced oviposition and lived longer, but 10-day feeding intervals correlated with risk to adult survival. These results indicate the importance of non-food sources in E. connexa maintenance and the ability of larvae and adult females to compensate for prey scarcity.     

The bigger they come, the harder they fall: body size and prey abundance influence predator-prey ratios

Large carnivores are highly threatened, yet the processes underlying their population declines are still poorly understood and widely debated. We explored how body mass and prey abundance influence carnivore density using data on 199 populations obtained across multiple sites for 11 carnivore species. We found that relative decreases in prey abundance resulted in a five- to sixfold greater decrease in the largest carnivores compared with the smallest species. We discuss a number of possible causes for this inherent vulnerability, but also explore a possible mechanistic link between predator size, energetics and population processes. Our results have important implications for carnivore ecology and conservation, demonstrating that larger species are particularly vulnerable to anthropogenic threats to their environment, especially those which have an adverse affect on the abundance of their prey.     

Pathogenic bacteria and timing of laying

Pathogenic bacteria constitute a serious threat to viability of many organisms. Because growth of most bacteria is favored by humid and warm environmental conditions, earlier reproducers in seasonal environments should suffer less from the negative consequences of pathogenic bacteria. These relationships, and the effects on reproductive success, should be particularly prominent in predators because they are frequently exposed to pathogenic microorganisms from sick prey. Here, we presented and tested this hypothesis by sampling bacteria on adult and nestling goshawks Accipiter gentilis. We predicted that early breeders and their offspring should have fewer bacteria than those reproducing later during the breeding season. Adult goshawks with a high abundance of Staphylococcus on their beak and claws were easier to capture and their laying date was delayed. Moreover, goshawks that laid their eggs later had offspring with more Staphylococcus on their beaks and claws. The strength of the association between laying date and bacterial density of nestlings was stronger during the warm spring of 2013, when nestlings suffered from a higher abundance of pathogenic bacteria. Hatching failure and fledging failure were more common in nests with a higher abundance of Staphylococcus independently of the number of years occupied, laying date, and age of the female nest owner. These findings imply that timing of reproduction may be under the influence of pathogenic bacteria. Because early breeding goshawks produce more recruits than later breeders, our results suggest a role for pathogenic bacteria in the optimal timing of reproduction.     

Frequency of fault bars in feathers of birds and susceptibility to predation

Fault bars are transparent bands in the feathers of birds produced under stressful and adverse conditions. The frequency of feathers with fault bars is highly heterogeneous among species. We predicted that prey had a higher frequency of fault bars than individuals from the general population, and that a high susceptibility to predation would be associated with a low frequency of fault bars among species of birds because such species would suffer particularly high costs of producing fault bars. The frequency of fault bars in prey was almost three-fold higher than in the general population, based on a database on the frequency of fault bars and susceptibility to predation by the goshawk Accipiter gentilis L., implying intense natural selection against fault bars. A high susceptibility to predation by the sparrowhawk Accipiter nisus L. and the goshawk, relative to what would be expected from their abundance, was associated with a low frequency of fault bars across species, with long distance migration also being negatively associated with frequency of fault bars. Feathers with fault bars were more likely to break than feathers without fault bars, thereby potentially affecting the flight ability of individuals. These findings are consistent with the hypothesis that susceptibility to factors that cause production of fault bars can be modified by natural selection, as illustrated by the impact of predation on the frequency of fault bars.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 334–345.     

Feather micro-organisms and uropygial antimicrobial defences in a colonial passerine bird

1.  The relationship between the composition of communities of micro-organisms and their hosts remains poorly understood. We conducted extensive field studies of feather-degrading bacteria, other cultivable bacteria, and fungi on the plumage of a migratory bird, the barn swallow Hirundo rustica Linnaeus, to understand the association between micro-organisms, host sociality and host antimicrobial defences, as reflected by the size of the uropygial gland.
2.  The abundance of feather-degrading bacteria, but not other cultivable bacteria or fungi, decreased with increasing size of the uropygial gland.
3.  Females had more feather-degrading bacteria than males.
4.  Barn swallows living in larger colonies had more feather-degrading bacteria than less social conspecifics.
5.  These findings suggest that the uropygial gland plays a specific role in regulating the abundance of feather-degrading bacteria that furthermore depends on the social environment of the host.     

Effects of potential food sources on biological and demographic parameters of the predatory mites Kampimodromus aberrans, Typhlodromus pyri and Amblyseius andersoni

Kampimodromus aberrans, Typhlodromus pyri and Amblyseius andersoni are generalist predatory mites important in controlling tetranychid and eriophyoid mites in European vineyards. They can persist by exploiting various non-prey foods when their main prey is absent or scarce. A comparative analysis of the effects of various prey and non-prey foods on the life history of these predators is lacking. In the laboratory, predatory mites were reared on herbivorous mites (Panonychus ulmi, Eotetranychus carpini and Colomerus vitis), a potential alternative prey (Tydeus caudatus) and two non-prey foods, i.e. the pollen of Typha latifolia and the mycelium of Grape downy mildew (GDM) Plasmopara viticola. Developmental times, survival, sex ratio and fecundity as well as life table parameters were estimated. Kampimodromus aberrans developed faster on E. carpini, C. vitis or pollen than on P. ulmi and laid more eggs on pollen than on prey. Low numbers of this predator developed on GDM infected leaves. Tydeus caudatus was not suitable as prey for any of the three predatory mites. Kampimodromus aberrans showed the highest intrinsic rate of population increase when fed on pollen. Developmental times of T. pyri on prey or pollen were similar but fecundity was higher on pollen than on P. ulmi. Typhlodromus pyri had higher intrinsic rates of population increase on C. vitis and pollen than on P. ulmi; E. carpini showed intermediate values whereas GDM resulted in the lowest r ( m ) values. Development of A. andersoni females was faster on pollen and C. vitis than on P. ulmi and GDM. Fecundity was higher on pollen and mites compared to GDM. Life table parameters of A. andersoni did not differ when predators were fed with prey or pollen while GDM led to a lower r ( m ) value. On a specific diet A. andersoni exhibited faster development and higher fecundity than T. pyri and K. aberrans. These findings improve knowledge on factors affecting the potential of predatory mites in controlling phytophagous mites in European vineyards.     

Feather corticosterone reveals stress associated with dietary changes in a breeding seabird

Changes in climate and anthropogenic pressures might affect the composition and abundance of forage fish in the world's oceans. The junk‐food hypothesis posits that dietary shifts that affect the quality (e.g., energy content) of food available to marine predators may impact their physiological state and consequently affect their fitness. Previously, we experimentally validated that deposition of the adrenocortical hormone, corticosterone, in feathers is a sensitive measure of nutritional stress in seabirds. Here, we use this method to examine how changes in diet composition and prey quality affect the nutritional status of free‐living rhinoceros auklets (Cerorhinca monocerata). Our study sites included the following: Teuri Is. Japan, Middleton Is. central Gulf of Alaska, and St. Lazaria Is. Southeast Alaska. In 2012 and 2013, we collected “bill loads” delivered by parents to feed their chicks (n = 758) to document dietary changes. We deployed time–depth–temperature recorders on breeding adults (n = 47) to evaluate whether changes in prey coincided with changes in foraging behavior. We measured concentrations of corticosterone in fledgling (n = 71) and adult breeders' (n = 82) feathers to determine how birds were affected by foraging conditions. We found that seasonal changes in diet composition occurred on each colony, adults dove deeper and engaged in longer foraging bouts when capturing larger prey and that chicks had higher concentrations of corticosterone in their feathers when adults brought back smaller and/or lower energy prey. Corticosterone levels in feathers of fledglings (grown during the breeding season) and those in feathers of adult breeders (grown during the postbreeding season) were positively correlated, indicating possible carryover effects. These results suggest that seabirds might experience increased levels of nutritional stress associated with moderate dietary changes and that physiological responses to changes in prey composition should be considered when evaluating the effect of prey quality on marine predators.     

Why eat extrafloral nectar? Understanding food selection by Coleomegilla maculata (Coleoptera: Coccinellidae)

Methods of increasing predator abundance within a habitat include the incorporation of non-prey food items, yet the influence of this on predation intensity toward herbivores remains unknown. In order to gain an understanding of nectar feeding in the predaceous beetle, Coleomegilla maculata (DeGeer), laboratory studies were conducted evaluating prey consumption in the presence of extrafloral nectaries. The physiology of beetles with access to prey only and a mixed diet were compared. To elucidate results of beetle physiology, Y-tube olfactometer studies were conducted and preferences between food types evaluated. Coleomegilla maculata females consumed 9 % fewer aphids when nectar was available. Lipid and glycogen content, as well as oocyte volume were not increased upon consumption of a mixed diet. Evaluation of predator behavior when offered both food resources together and separately demonstrated that extrafloral nectaries are attractive.     

Nonlinear effects of an aquatic consumer: causes and consequences

The assumption that per capita consumer effects on prey density are independent of consumer and prey density is examined with a large-scale manipulation of an aquatic herbivore (Daphnia). A gradient of consumer removal was maintained long enough to allow the abundances of both consumer and prey (phytoplankton) to equilibrate to the manipulation. Strong and unequivocal nonlinearities were found in the effect of Daphnia on total phytoplankton abundance and the abundance of most of the common phytoplankton species. Daphnia's suppression of phytoplankton was strong between 0 and approximately 400 microg Daphnia L(-1) but essentially nil from approximately 400 to 900 microg Daphnia L(-1). The sharp deceleration in Daphnia's effect was not caused by a shift within the phytoplankton community toward consumption-resistant forms. The most likely explanation for the deceleration was a reduction in Daphnia's filtering effort at low phytoplankton abundance, that is, a Type III functional response. A review of experimental literature suggested that decelerating effects of consumers are the norm in aquatic systems. Nonlinear effects present problems for the estimation of interaction strength and the building of community interaction models from the results of predator manipulations. It is suggested that the role of field experiments in community ecology should be to test rather than to parameterize models.     

Defensive larval secretions of leaf beetles attract a specialist predator Parasyrphus nigritarsis

1. Noxious larval secretions of leaf beetles, which repel generalist predators, do not deter specialist syrphid fly predators (genus Parasyrphus ). These flies cause considerable mortality to the beetles, but little is known about their foraging behaviour.
2. Larvae of Parasyrphus nigritarsis were attracted to the volatile larval secretions produced by two prey species Phratora vitellinae and Linaeidea aenea. Parasyrphus nigritarsis feeds on both beetles in nature. Phratora vitellinae feeds on willows and utilizes host plant compounds for secretion production, while the alder-feeding L. aenea produces an autogenous secretion.
3. Fly larvae were strongly attracted to pieces of filter paper treated with larval secretion of the beetles. They attempted to feed on them for up to 7 min, and were equally attracted to the secretions of Ph. vitellinae and L. aenea . Fly larvae were also attracted to pure salicyl aldehyde, the main component of the secretion of Ph. vitellinae .
4. Fly larvae searched extensively for prey on leaves that had been damaged by beetle larvae. They also followed trails made with solutions containing faecal matter of prey larvae. They showed no differential preference for Ph. vitellinae or L. aenea , but always rejected larvae of the non-prey leaf beetle Agelastica alni .
5. Beetle secretions thus play an important, but unexpected, role in the feeding behaviour of P. nigritarsis . This predator uses the beetle secretion to locate its prey. The implications of these results for three trophic level interactions are discussed.     

Changes in digestive rate of a predatory beetle over its larval stage: Implications for dietary breadth

Prey and non-prey foods differ substantially in their suitability for zoophytophagous omnivores, but the relative quality of these foods depends on the stage-specific digestive capabilities of the organism in question. Quantitative (or real-time) PCR was used to amplify food-specific DNA and measure consumption rates and digestion efficiencies of four foods - two prey (Aphis glycines and Leptinotarsa decemlineata eggs) and two non-prey (Zea mays pollen and the yeast Saccharomyces cerevisiae) species - over different larval stages of Coleomegilla maculata. The amount of Z. mays pollen consumed increased as larvae aged, but not proportionately with larval size, such that consumption rates decreased uniformly with insect age. While aging larvae fed A. glycines had a similar pattern in their diminishing consumption rates, they consumed similar amounts of A. glycines regardless of age, suggesting a negative feedback mechanism for consumption of this species of aphids. Older larvae digested three of the four foods significantly more efficiently than younger larvae, the exception being larvae fed A. glycines which was digested at a similar rate throughout the larval stage. There was a significant effect of time on food quantity detected for all four species of food. We conclude that C. maculata expands its physiological capacity for digesting prey and non-prey foods as they age in order to better accommodate the increased nutritional needs of the older larvae. This strategy has important implications for the life history strategies of zoophytophagous insects and how they function within foods webs.     

Interactions between Bdellovibrio and like organisms and bacteria in biofilms: beyond predator–prey dynamics

Bdellovibrio and like organisms (BALOs) prey on Gram-negative bacteria in the planktonic phase as well as in biofilms, with the ability to reduce prey populations by orders of magnitude. During the last few years, evidence has mounted for a significant ecological role for BALOs, with important implications for our understanding of microbial community dynamics as well as for applications against pathogens, including drug-resistant pathogens, in medicine, agriculture and aquaculture, and in industrial settings for various uses. However, our understanding of biofilm predation by BALOs is still very fragmentary, including gaps in their effect on biofilm structure, on prey resistance, and on evolutionary outcomes of both predators and prey. Furthermore, their impact on biofilms has been shown to reach beyond predation, as they are reported to reduce biofilm structures of non-prey cells (including Gram-positive bacteria). Here, we review the available literature on BALOs in biofilms, extending known aspects to potential mechanisms employed by the predators to grow in biofilms. Within that context, we discuss the potential ecological significance and potential future utilization of the predatory and enzymatic possibilities offered by BALOs in medical, agricultural and environmental applications.     

Predator personality structures prey communities and trophic cascades

Intraspecific variation is central to our understanding of evolution and population ecology, yet its consequences for community ecology are poorly understood. Animal personality – consistent individual differences in suites of behaviours – may be particularly important for trophic dynamics, where predator personality can determine activity rates and patterns of attack. We used mesocosms with aquatic food webs in which the top predator (dragonfly nymphs) varied in activity and subsequent attack rates on zooplankton, and tested the effects of predator personality. We found support for four hypotheses: (1) active predators disproportionately reduce the abundance of prey, (2) active predators select for predator‐resistant prey species, (3) active predators strengthen trophic cascades (increase phytoplankton abundance) and (4) active predators are more likely to cannibalise one another, weakening all other trends when at high densities. These results suggest that intraspecific variation in predator personality is an important determinant of prey abundance, community composition and trophic cascades.     

The effect of small zooplankton on the microbial loop and edible algae during a cyanobacterial bloom

SUMMARY 1. We studied the effect of the small crustacean zooplankton on heterotrophic micro-organisms and edible phytoplankton in a eutrophic lake during a cyanobacterial bloom.
2. Small (15 L) enclosures were filled with natural or screened (100 μm) lake water and incubated for 5 days in the lake. Screening removed crustacean zooplankton but the initial density of rotifers and phytoplankton remained the same in control and removal treatments. Changes in the abundance and biomass of bacteria, autotrophic picoplankton (APP), heterotrophic nanoflagellates (HNF) and ciliates were measured daily.
3. The crustacean zooplankton, dominated by the small cladoceran Chydorus sphaericus , did not affect cyanobacteria, the main phytoplankton group during the experiment.
4. The removal of the crustacean zooplankton induced a higher abundance of ciliates and reduced that of the HNF, indicating the importance of ciliates in controlling HNF in this system.