Do predators limit the abundance of alternative prey? Experiments with vole‐eating avian and mammalian predators

Predation has been invoked as a factor synchronizing the population oscillations of sympatric prey species, either because predators kill prey unselectively (the Shared Predation Hypothesis; hereafter SPH), or because predators switch to alternative prey after a density decline in their main prey (the Alternative Prey Hypothesis; APH). A basic assumption of the APH is that the impact of predators on alternative prey depends more on the density of main prey than on the predator/alternative prey ratio. Both SPH and APH assume that the impact of predators on alternative prey is at least periodically strong enough to depress prey populations. To examine these assumptions, we utilized data from replicated field experiments in large areas where we reduced the breeding densities of avian predators during three years and the numbers of least weasels (Mustela nivalis) in two years when vole populations declined. In addition, we reduced the breeding densities of avian predators in two years when vole populations were high. The reduction of least weasels increased the abundance of their alternative prey, small birds breeding on the ground, but did not affect the abundance of common shrews (Sorex araneus). In years when vole populations declined, the reduction of avian predators increased the abundance of their alternative prey, common shrews and small birds. Therefore, vole‐eating predators do at least periodically depress the abundance of their alternative prey. At high vole densities, the reduction of avian predators did not increase the abundance of common shrews, although the ratio of avian predators to alternative prey was similar to years when vole populations declined, which supported APH. In contrast, the abundance of small birds increased after the reduction of avian predators also at high vole densities, which supported SPH. The manipulations had no obvious effect on the number of game birds, which are only occasionally killed by these small‐sized predators. We conclude that in communities where most predators are small or specialize on a single prey type, the synchronizing impact of predation is restricted to a few similar‐sized species.     

A short-lived herbivore on a long-lived host: tree resistance to herbivory depends on leaf age

Short-lived insect herbivores should be able to adapt to the resistance mechanisms of their long-lived woody hosts because the life span of a single host will encompass numerous generations of herbivores. However, adaptation may be slowed down if host genotypes can create, in a single genotype, such large phenotypic variation in traits relevant for the herbivore that it matches variance among host genotypes. We tested this hypothesis by measuring leaf consumption by, and growth of, half-sibs of the geometrid moth Epirrita autumnata on individual birch trees, during three instars. The instar×tree interaction, rather than tree identity alone, was a significant variance component for both consumption and growth, indicating that different larval instars ranked individual trees differently. Both consumption and growth varied most between the 3rd and the later (4th and 5th) instars, coinciding with rapid seasonal changes in numerous nutritive and phenolic traits of maturing leaves. Thus, developmental variance in the leaf quality of individual trees may reduce the likelihood of E. autumnata genotypes adapting to the defenses of their host trees. We did not find evidence of in the ability of different half-sibs to utilize individual trees or leaf stages, indicating that E. autumnata larvae are generalists over a wide variety of host traits.     

Phenotypes and functional effects caused by various viral RNA silencing suppressors in transgenic Nicotiana benthamiana and N. tabacum

RNA silencing suppressor genes derived from six virus genera were transformed into Nicotiana benthamiana and N. tabacum plants. These suppressors were P1 of Rice yellow mottle virus (RYMV), P1 of Cocksfoot mottle virus, P19 of Tomato bushy stunt virus, P25 of Potato virus X, HcPro of Potato virus Y (strain N), 2b of Cucumber mosaic virus (strain Kin), and AC2 of African cassava mosaic virus (ACMV). HcPro caused the most severe phenotypes in both Nicotiana spp. AC2 also produced severe effects in N. tabacum but a much milder phenotype in N. benthamiana, although both HcPro and AC2 affected the leaf tissues of the two Nicotiana spp. in similar ways, causing hyperplasia and hypoplasia, respectively. P1-RYMV caused high lethality in the N. benthamiana plants but only mild effects in the N. tabacum plants. Phenotypic alterations produced by the other transgenes were minor in both species. Interestingly, the suppressors had very different effects on crucifer-infecting Tobamovirus (crTMV) infections. AC2 enhanced both spread and brightness of the crTMV-green fluorescent protein (GFP) lesions, whereas 2b and both P1 suppressors enhanced spread but not brightness of these lesions. P19 promoted spread of the infection into new foci within the infiltrated leaf, whereas HcPro and P25 suppressed the spread of crTMV-GFP lesions.     

Risk induced by a native top predator reduces alien mink movements

1. Nonlethal predation effects may have stronger impacts on prey populations than direct predation impacts, and this should also apply to intraguild predation. The consequences of such interactions become especially important if invasive, and potentially destructive alien predators act as intraguild prey. 2. We studied the predation-risk impacts of a re-colonizing native top predator, Haliaeetus albicilla (white-tailed sea eagle), on the movements of Mustela vison (American mink), an alien predator in Europe. We radiocollared 20 mink in two study areas in the outer archipelago of the Baltic Sea, South-west Finland, during 2004 and 2005. In the archipelago, mink home ranges incorporate many islands, and mink are most predisposed to eagle predation while swimming between islands. Observed swimming distances of mink were compared to distances expected at random, and deviations from random swimming were explained by mink distance from nearest eagle nest, number of eagle observations near mink location, and mink home-range size. 3. Mink reduced their swimming distances with increasing sea eagle predation risk: for females, the reduction was 10% for an increase of 10 eagle observations, and 5% for each kilometre towards an eagle nest. Conclusions for males were restricted by their small sample size. 4. Our results suggest that female mink modify their behaviour according to eagle predation risk, which may reduce their population growth and have long-term cascading effects on lower trophic levels including bird, mammal and amphibian populations in the archipelago. Ecosystem restoration by bringing back the top predators may be one way of mitigating alien predator effects on native biota.     

The Effect of Personality on Daily Life Emotional Processes

Personality features are associated with individual differences in daily emotional life, such as negative and positive affectivity, affect variability and affect reactivity. The existing literature is somewhat mixed and inconclusive about the nature of these associations. The aim of this study was to shed light on what personality features represent in daily life by investigating the effect of the Five Factor traits on different daily emotional processes using an ecologically valid method. The Experience Sampling Method was used to collect repeated reports of daily affect and experiences from 104 healthy university students during one week of their normal lives. Personality traits of the Five Factor model were assessed using NEO Five Factor Inventory. Hierarchical linear modeling was used to analyze the effect of the personality traits on daily emotional processes. Neuroticism predicted higher negative and lower positive affect, higher affect variability, more negative subjective evaluations of daily incidents, and higher reactivity to stressors. Conscientiousness, by contrast, predicted lower average level, variability, and reactivity of negative affect. Agreeableness was associated with higher positive and lower negative affect, lower variability of sadness, and more positive subjective evaluations of daily incidents. Extraversion predicted higher positive affect and more positive subjective evaluations of daily activities. Openness had no effect on average level of affect, but predicted higher reactivity to daily stressors. The results show that the personality features independently predict different aspects of daily emotional processes. Neuroticism was associated with all of the processes. Identifying these processes can help us to better understand individual differences in daily emotional life.     

Evolution of Strategies to Stay in the Game

Life-history evolution is a complexprocess. Life-history theory covers the fundamentallevel of the process, the evolution of life-historytraits. Life-history traits interact; thosecoevolving as a response to the same selectionpressure form life-history tactics. Top level of thehierarchy, life-history strategy, is formed bygenetically interconnected tactics. Our aim is toexpand the traditional view to life-history evolutionby considering what boundary conditions a successfullife-history strategy has to fulfil. We claim thatthe most fundamental condition successful strategieshave to meet is to minimize the risk of evolutionaryfailure. Here the risk of failure refers to failurein transferring practitioners of the strategy to thenext time point, either through survival, or byreproduction. We make an attempt to classify types ofrisks as they lead to evolutionary failure, anddiscuss how risk minimization ideas may be approachedempirically. We conclude that understanding howtraits evolve may not cover all aspects of howstrategies evolve. We emphasize that bookkeeping ofthe actual causes of failure might help in developinglife-history theory that uses causes of selection topredict responses to selection.     

Parental effort of kestrels (Falco tinnunculus) in nest defense: effects of laying time, brood size, and varying survival prospects of offspring

We studied the nest defense behavior of Eurasian kestrels (Falcotinnunculus) towards a stuffed pine marten (Martes martes) througha 3-year vole cycle (1990–92) in western Finland. Survivalprobability of offspring decreases with a later start of breeding,and, therefore, early breeders should protect their offspringmore than late ones. We found this true for males during theincubation period, but not for females. In addition, we expectedthe nest defense intensity to increase with offspring number.During the incubation period, this was true for females, butnot for males. During the nestling phase, parents did not adjusttheir defense effort to natural or manipulated (by one to twoyoung) brood size. Survival prospects of kestrel offspring werehighest in the increasing vole year 1991 and lowest in the decreasingvole year 1992, and, therefore, we expected the defense activityof kestrels to follow the same trend. However, the oppositeresult appeared true for females with a similar tendency formales. Most hypotheses predicting avian nest defense behaviorwere not supported by our data. Temporally heterogeneous environmentand low degree of nest-site tenacity of migratory kestrels maymake them unfamiliar with environmental variation and survivalprospects of their offspring. Therefore, fitness benefits ofparental care are not predictable, and kestrels may thus adjusttheir parental effort to their own future reproductive potential(i.e., number of future breeding attempts), rather than to somecurrent investment indicator, like offspring age and number.     

C and N storage in living trees within Finland since 1950s

Living biomass contains 45 to 60% carbon and 0.05 to 3% nitrogen, in dry weight. Like throughout Europe, the amount of living biomass in Finnish forests has increased on average over the last decades, largely because of changes in forest management. The storage of organic C and N in biomass has also increased.Changes in biomass vary between regions. Data were analysed on changes in the last 30–40 years in C and N storage in living trees in Finland, subdivided into 20 regions. Tree biomass increased in 17 regions, and decreased in 3 regions. The storage rate varied between -170 and +480 kg C ha^-1 a^-1, and between –0.5 and +1.2 kg N ha^-1 a^-1.Nitrogen accumulation in trees was less than 15% of atmospheric N deposition in all regions. Although the eventual increase of the nitrogen concentration in tree tissues was omitted, it is not possible that living biomass has been the major sink for atmospheric N deposition to forests. A hypothesis is presented that the main sink is litter layer and organic soil. Carbon can also be accumulating in soils essentially faster than hitherto estimated in analyses of carbon budgets of European forests.Died on September 2, 1994.     

Habitat-mediated impact of alien mink predation on common frog densities in the outer archipelago of the Baltic Sea

Alien predators have been recognised as one possible cause for amphibian declines around the world, but little is known of habitat-mediated predation impacts especially on adult amphibians. We studied common frog Rana temporaria under American mink Mustela vison predation in the outer archipelago of the Baltic Sea, south-western Finland. Using egg batches as an index of breeding frog female numbers we compared frog numbers and densities between a large, long-term mink-removal area and a comparable control area. Frog numbers in the removal area were at least 2.7-fold higher than those in the control area. In the presence of mink, frog densities increased with the amount of vegetation cover on the islands, indicating that mink predation affected frog densities especially on less-vegetated islands. An opposite trend appeared to be true for frogs in the mink-removal area, where other predators like snakes could induce a decline of frog densities on more vegetated islands. Shrub or grass vegetation seems to provide frogs shelter against alien mink predation. Our result highlights the importance of landscape-level habitat management as a conservation tool for amphibian populations.     

Functional characterization of fingers subdomain-specific monoclonal antibodies inhibiting the hepatitis C virus RNA-dependent RNA polymerase

The hepatitis C virus (HCV) RNA-dependent RNA polymerase (RdRp), encoded by nonstructural protein 5B (NS5B), is absolutely essential for the viral replication. Here we describe the development, characterization, and functional properties of the panel of monoclonal antibodies (mAbs) and specifically describe the mechanism of action of two mAbs inhibiting the NS5B RdRp activity. These mAbs recognize and bind to distinct linear epitopes in the fingers subdomain of NS5B. The mAb 8B2 binds the N-terminal epitope of the NS5B and inhibits both primer-dependent and de novo RNA synthesis. mAb 8B2 selectively inhibits elongation of RNA chains and enhances the RNA template binding by NS5B. In contrast, mAb 7G8 binds the epitope that contains motif G conserved in viral RdRps and inhibits only primer-dependent RNA synthesis by specifically targeting the initiation of RNA synthesis, while not interfering with the binding of template RNA by NS5B. To reveal the importance of the residues of mAb 7G8 epitope for the initiation of RNA synthesis, we performed site-directed mutagenesis and extensively characterized the functionality of the HCV RdRp motif G. Comparison of the mutation effects in both in vitro primer-dependent RdRp assay and cellular transient replication assay suggested that mAb 7G8 epitope amino acid residues are involved in the interaction of template-primer or template with HCV RdRp. The data presented here allowed us to describe the functionality of the epitopes of mAbs 8B2 and 7G8 in the HCV RdRp activity and suggest that the epitopes recognized by these mAbs may be useful targets for antiviral drugs.