Microhabitat use and behavior of voles under weasel and raptor predation risk: predator facilitation?

An example of predator facilitation is that a microhabitat shiftin a prey species induced by one predator increases the probabilityof the prey falling victim to other predators. Least weasels(Mustela nivalis) hunt in dense plant cover, whereas kestrels(Falco tinnunculus) hunt in habitats with sparse plant cover.Field voles (Microtus agrestis), the main food of weasels andkestrels, prefer open country with a high grass layer. We simulateda multipredator environment in an aviary (3.0 x 4.8 x 2.2 m)to find out whether predator facilitation plays a role in theinteractions between voles, small mustelids, and raptors. Ineach replicate, we placed a field vole in a pen including sidesof high and low grass layers (cover and open). In a predator-freesituation, voles preferred cover but shifted to open when aweasel was introduced to cover. In the presence of a kestrel,voles occupied cover and decreased their mobility. In the presenceof a weasel plus a kestrel, voles behaved as under the kestrelrisk alone. Therefore, in these aviary circumstances, volesperceived the kestrel risk as greater than the weasel risk.Predator facilitation in the assemblage of predators subsistingon rodent prey may contribute to the crash of the four-yearvole cycle: microhabitat shift due to an avoidance of weaseljaws may drive voles to raptor talons.     

Low heritability in morphological characters of Tengmalm's owls: The role of cyclic food and laying date?

Summary In parent—offspring regressions, high heritability estimates of characters may simply be due to common environment: the resemblance between the living conditions of parents and their offspring in species showing restricted natal dispersal. In vole-eating Tengmalm's owls (Aegolius funereus), the natal dispersal and breeding dispersal of adult females are wide (up to > 1000 km and > 500 km, respectively), whereas adult males are resident. We found that body measurements of 183 recruits born in western Finland were independent of parental age and vole abundance in the birth year. Early-laid eggs produced longer winged recruits than late-laid eggs. The wing lengths of the daughters showed a significant positive regression on the wing length of their mothers, but the removal of the maternal effect via laying date lowered this relationship. The development time of offspring to the first autumn might also be crucial for morphological characters of females in their later life. Significant regressions were not found between the wing length of the son and his father. The mother—daughter regression was small for laying date, but positive (p = 0.08) for clutch size. These results suggest low heritability in breeding and morphological characters of owls and this low heritability may enable plastic adjustment to optimize fitness at any stage in a fluctuating environment. Nonadditive genetic variance also creates variation between offspring characters that are not genetically correlated with the parents and may explain these low heritability estimates.     

Experimental tests of the role of predation in the population dynamics of voles and lemmings

• 1 Reasons for fluctuating populations of small mammals have been intensively investigated since the early days of modern ecology. Particular interest has been taken in vole populations exhibiting multiannual oscillations. Much empirical and theoretical work has been accomplished to find out the key factor(s) driving these population cycles and many reviews have been written about the results.
• 2 One of the most plausible processes for explaining regular fluctuations in small mammals is predation. Here I review the existing literature on the experimental studies of the role of predation in vole population dynamics in the hope that a critical examination of these studies will help researchers improve the design of future experiments.
• 3 Most predation manipulations have been done in exclosures, but there are also studies that have attempted to reduce or increase predator numbers in non‐fenced areas, islands and enclosures.
• 4 As the number of experimental studies has increased, their quality in terms of replication, use of controls and realistic spatial and temporal scales has also improved.
• 5 Most studies have found population‐level effects of predator manipulations on prey populations. The effects have varied from very weak to very strong, reflecting dissimilar experimental designs and the great variety of predator–prey interactions among different kinds of species in different landscapes. Most of these studies show that predation limits population growth of voles, and in some circumstances even regulate vole population fluctuations, but none of them clearly demonstrates that predation consistently changes fluctuation patterns of voles.
• 6 To be able to assess more reliably the true role of predation on (cyclic) population fluctuations of voles, more competent experiments are still needed not only over the geographical range of cyclic population dynamics, but also in areas of weakly or non‐cyclic populations of voles.

     

Semen quantity and quality correlate with bank vole males’ social status

Laboratory studies reveal that in several rodent species the females prefer dominant males as mating partners. Here we investigate the correlation between bank vole males’ social rank and their sperm quality and quantity. We used agonistic encounters to determine males’ social status. Sperm quality was assessed by its motility, viability, maturity, morphology and sperm tail membrane integrity. Relatively more dominant males were heavier than males of lower social status. The males’ social position affected the testes, seminal vesicles and coagulation gland development. The weights of these reproductive organs were significantly higher in more dominant males than in more subordinate males. Sperm counts and the values of the other parameters describing sperm quality were higher in high-ranking males than in subordinates. Our results suggest that bank vole females benefit from choosing and mating with high-ranking males by obtaining more and better-quality sperm.     

Hantavirus infections in fluctuating host populations: the role of maternal antibodies

Infected females may transfer maternal antibodies (MatAbs) to their offspring, which may then be transiently protected against infections the mother has encountered. However, the role of maternal protection in infectious disease dynamics in wildlife has largely been neglected. Here, we investigate the effects of Puumala hantavirus (PUUV)-specific MatAbs on PUUV dynamics, using 7 years'' data from a cyclic bank vole population in Finland. For the first time to our knowledge, we partition seropositivity data from a natural population into separate dynamic patterns for MatAbs and infection. The likelihood of young of the year carrying PUUV-specific MatAbs during the breeding season correlated positively with infection prevalence in the overwintered parent population in the preceding spring. The probability of PUUV infection varied between seasons (highest in spring, lowest in late summer) and depended on population structure, but was also, in late autumn, notably, negatively related to summer MatAb prevalence, as well as to infection prevalence earlier in the breeding season. Hence, our results suggest that high infection prevalence in the early breeding season leads to a high proportion of transiently immune young individuals, which causes delays in transmission. This suggests, in turn, that MatAb protection has the potential to affect infection dynamics in natural populations.     

棕色田鼠胃的形态与组织学观察

目的研究棕色田鼠胃的适应性特征。方法采用大体解剖、组织学和扫描电镜研究方法,观察棕色田鼠胃部形态学结构特征。结果根据形态特征棕色田鼠胃部可明显的分为2个胃室,根据有无腺体分布可分为有腺区和无腺区,第一胃室及第二胃室的大部分区为无腺区,胃的无腺区表面为角质化复层扁平上皮;有腺区上皮为单层柱状上皮;第一胃室与第二胃室交界处存在有19～21个特殊的瓣膜结构。结论棕色田鼠胃的形态发生了明显的适应性变化特征,出现了两个胃室,胃室之间首次发现有瓣膜结构存在。     

Polyandry enhances offspring survival in an infanticidal species

The adaptive significance of polyandry is an intensely debated subject in sexual selection. For species with male infanticidal behaviour, it has been hypothesized that polyandry evolved as female counterstrategy to offspring loss: by mating with multiple males, females may conceal paternity and so prevent males from killing putative offspring. Here we present, to our knowledge, the first empirical test of this hypothesis in a combined laboratory and field study, and show that multiple mating seems to reduce the risk of infanticide in female bank voles Myodes glareolus. Our findings thus indicate that females of species with non-resource based mating systems, in which males provide nothing but sperm, but commit infanticide, can gain non-genetic fitness benefits from polyandry.     

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.