Rodent Predation Research Articles

Rat-bite Fever, Canada

Rat-bite Fever, Canada

Large‐scale spatial and temporal patterns in population dynamics of the stoat, Mustela erminea, and the least weasel, M. nivalis, in Finland

The stoat and the least weasel are specialist predators of small rodents, and therefore their numbers are likely to depend on the availability of voles. These small predators are ecologically alike, but they differ somewhat in their diet. The stoat is larger in size than the least weasel and therefore capable of using a wider variety of prey species, while the least weasel is more restricted to small mammals. Voles in northern Fennoscandia exhibit cyclic dynamics of 3–5 years with large‐scale spatial synchrony and geographical trends in cycle length and amplitude. We predicted that the cyclic dynamics of voles are reflected in the dynamics of their predators with slight differences between the stoat and the least weasel. In this study we use snow‐tracking data to characterize the dynamics of small mustelids. The data were collected from different parts of Finland using permanent triangle‐shaped census routes of 12 km in 1989 to 2003. Population fluctuations of small mustelids were generally multiannually periodic and in synchrony over large areas, but we did not find any clear geographical gradient in the attribute of small mustelid dynamics comparable to those observed in vole population fluctuations. Instead, we found a similar decreasing temporal trend in the abundances of both species as has been recently reported for voles.

Growth behavior ofPhyllostachys nigra var.henonis (Bambusoideae) in Central China

In the Shennongjia National Nature Reserve of Central China, the vegetative growth behavior of henon bamboo (Phyllostachys nigra var.henonis (Mitford) Stapf. ex Rendle) was studied from shoot recruitment to culm establishment. In May, bamboo shoots emerging from the ground achieved an average density of 2.7 shoots m−2 during the sprouting phase of 16 days. However, about 32% of the new shoots died back before maturity. Insect damage, withering death and rodent predation were responsible for 57%, 29% and 14% of the total shoot mortality, respectively. From May to June, the shoots attained 400±23 cm during the height growth phase of 34 days, with a daily rate varying from 1 to 56 cm. All branches and leaves unfolded during the branch spreading phase from June to August. Shoot production was positively related to the density of standing culms, but negatively to both coverage and height of herb layers.

Mortality factors and predators of Spotted Towhee nests in the Sacramento Valley, California

Nest predation was the main nest mortality factor for Spotted Towhees (Pipilo maculatus) along the Sacramento River, California, during 1993–2003, followed by cowbird parasitism. From 2001 to 2003, I monitored 161 Spotted Towhee nests and filmed 24 nests using miniature infrared video cameras to identify predators. Daily survival rate was 0.928 for this period. I detected no difference in nest survival between the incubation and nestling stages. Nests with cameras had marginally higher survival rates than those without. I filmed nine nest predation events in 2002 and 2003. Eight of these were upon nestlings, while one was upon eggs. Predators were birds, mammals, and a snake, including the Red-shouldered Hawk (Buteo lineatus), Brown-headed Cowbird (Molothrus ater), Western Scrub-Jay (Aphelocoma californica), a raccoon (Procyon lotor), black or Norway rats (Rattus sp.), two unidentified rodents, and a racer (Coluber constrictor). Many of these predators are associated with agriculture and/or human habitation. I documented two multi-predator events. In both instances, a diurnal partial predation by a bird was followed by a nocturnal rodent predator. Two predation events occurred at the very end of the nestling period. I advise investigators engaged in nest success studies to consider the possibility of partial predation that may reduce a female's overall reproductive output and note that a nest should only be considered successful when direct evidence of fledglings is observed near the nest. I recommend more detailed studies of nest predator composition and the compound effects of Brown-headed Cowbird nest parasitism and “infanticide.”

Short‐term changes affecting regeneration of Fagus crenata after the simultaneous death of Sasa kurilensis

Abstract. Question: The aim of the present study is to determine whether seed/seedling predation will increase and Fagus survival will decline with the recovery of the Sasa cover.Methods: We examined Fagus crenata regeneration for seven years in an old‐growth Fagus‐Sasa forest near Lake Towada, northern Japan, by examining the effects of simultaneous death of Sasa, tree canopy gap formation, mast seeding of Fagus and seed and seedling predation by rodents on the survival of Fagus seeds and current year seedlings. We established four types of sites differing in forest canopy (closed or gap) and Sasa status (dead or alive) following the simultaneous flowering and death of Sasa kurilensis (dwarf bamboo) in 1995.Results: Fallen Fagus seed was abundant in 1997 and 2000 (mast years). In sites with alive Sasa, survival from the first growing season was low due to high seed and seedling predation. In sites with dead Sasa, seed survival under the canopy was high for both mast years, but in gaps it varied between years. Seedling survival was highest in canopy gaps with dead Sasa (gap‐dead) in 1998, because of higher light levels and lower predation by rodents. However, seedling survival in these plots was low in 2001, apparently because rapid Sasa recovery favoured rodent predation. In both mast years, Sasa die‐back had significant positive effects on seed and seedling survival under closed canopies because the seedlings there were more successful in escaping predation.Conclusion: The change in successful sites for the early stage of regeneration of Fagus appears to reflect the combined effects of canopy gap, seed/seedling predation and revegetation of Sasa.

Short-term changes affecting regeneration of Fagus crenata after the simultaneous death of Sasa kurilensis

Question: The aim of the present study is to determine whether seed/seedling predation will increase and Fagus survival will decline with the recovery of the Sasa cover. Methods: We examined Fagus crenata regeneration for seven years in an old-growth Fagus-Sasa forest near Lake Towada, northern Japan, by examining the effects of simultaneous death of Sasa, tree canopy gap formation, mast seeding of Fagus and seed and seedling predation by rodents on the survival of Fagus seeds and current year seedlings. We established four types of sites differing in forest canopy (closed or gap) and Sasa status (dead or alive) following the simultaneous flowering and death of Sasa kurilensis (dwarf bamboo) in 1995. Results: Fallen Fagus seed was abundant in 1997 and 2000 (mast years). In sites with alive Sasa, survival from the first growing season was low due to high seed and seedling predation. In sites with dead Sasa, seed survival under the canopy was high for both mast years, but in gaps it varied between years. Seedling survival was highest in canopy gaps with dead Sasa (gap-dead) in 1998, because of higher light levels and lower predation by rodents. However, seedling survival in these plots was low in 2001, apparently because rapid Sasa recovery favoured rodent predation. In both mast years, Sasa die-back had significant positive effects on seed and seedling survival under closed canopies because the seedlings there were more successful in escaping predation. Conclusion: The change in successful sites for the early stage of regeneration of Fagus appears to reflect the combined effects of canopy gap, seed/seedling predation and revegetation of Sasa.

Impacts of scatter-hoarding rodents on restoration of oil tea Camellia oleifera in a fragmented forest

Few studies have evaluated the role of seed dispersal by animals (especially scatter-hoarding rodents) in natural restoration in fragmented forests. In order to assess the potential benefits of oil tea from natural dispersal by seed-caching rodents, we tracked the individual seeds with coded tin tags of oil tea Camellia oleifera (Theaceae), an economically important evergreen shrubs, by establishing artificial seed sources (mimicking natural seed rain) in a secondary stand (i.e. Camellia-poor stand, where no oil tea shrubs grow) in a fragmented forest in the Dujiangyan Region of Sichuan Province, China. Our results indicate that the total survival of the released seeds was zero, which confirms the hypothesis that poor seeding regeneration may be caused by poor seed sources and subsequent high rodent predation in fragmented secondary forests. As small rodents repeatedly handled the tagged seeds, the proportions of seed consumption (i.e. eaten) and removal were constant in both Dispersal I and Dispersal II, but the caching proportion significantly decreased and the missing proportion significantly increased. Our results also indicate that seed-caching rodents are important in promoting natural regeneration of oil tea through scatter-hoarding seeds in soil: (1) seed removal was high (91.2%); (2) many removed seeds were found to be cached (48.2% for the relocated seeds); (3) dispersal distances of the cached seeds ranged from 0 to 38 m (mean, 7.9 m); (4) 81.3% of the caches (including primary and secondary caches) contained only one seed. Therefore, seed-caching rodents could have the potential to help restore natural populations of oil tea if we increase oil tea seed sources in the Camellia-poor stands.

Impacts of scatter-hoarding rodents on restoration of oil tea Camellia oleifera in a fragmented forest

Few studies have evaluated the role of seed dispersal by animals (especially scatter-hoarding rodents) in natural restoration in fragmented forests. In order to assess the potential benefits of oil tea from natural dispersal by seed-caching rodents, we tracked the individual seeds with coded tin tags of oil tea Camellia oleifera (Theaceae), an economically important evergreen shrubs, by establishing artificial seed sources (mimicking natural seed rain) in a secondary stand (i.e. Camellia-poor stand, where no oil tea shrubs grow) in a fragmented forest in the Dujiangyan Region of Sichuan Province, China. Our results indicate that the total survival of the released seeds was zero, which confirms the hypothesis that poor seeding regeneration may be caused by poor seed sources and subsequent high rodent predation in fragmented secondary forests. As small rodents repeatedly handled the tagged seeds, the proportions of seed consumption (i.e. eaten) and removal were constant in both Dispersal I and Dispersal II, but the caching proportion significantly decreased and the missing proportion significantly increased. Our results also indicate that seed-caching rodents are important in promoting natural regeneration of oil tea through scatter-hoarding seeds in soil: (1) seed removal was high (91.2%); (2) many removed seeds were found to be cached (48.2% for the relocated seeds); (3) dispersal distances of the cached seeds ranged from 0 to 38 m (mean, 7.9 m); (4) 81.3% of the caches (including primary and secondary caches) contained only one seed. Therefore, seed-caching rodents could have the potential to help restore natural populations of oil tea if we increase oil tea seed sources in the Camellia-poor stands.

CRYPTIC CONSEQUENCES OF A DISPERSAL MUTUALISM: SEED BURIAL, ELAIOSOME REMOVAL, AND SEED-BANK DYNAMICS

In moving seeds from one location to another, dispersers define the ecological context that a plant will experience throughout its lifetime. Because seed deposition sites may benefit one plant life cycle stage but not others, dispersal may give rise to a conflict between a plant's dispersal needs (e.g., predator escape) and its requirements for successful establishment (e.g., suitable habitat). In this study, we assessed the effects of two com- ponents of seed dispersal by ants (seed burial depth and elaiosome removal) at several stages during the recruitment of Leucospermum truncatulum, an ant-dispersed plant from the fynbos shrublands of South Africa. A seed-predator exclusion experiment revealed that the removal of elaiosomes significantly reduced rodent predation on seeds buried 1 cm deep and increased the viability of seeds that were not consumed. In contrast, we found that elaiosomes had no effect on the probability of a living seed emerging as a seedling. In a seed burial depth experiment in which predators were not excluded, deeper burial significantly enhanced seed survival, but this benefit came at the expense of reduced seedling emergence, delayed emergence, and smaller cotyledon size. Despite the potential importance of these seedling characteristics, elaiosomes and burial depth had no significant effect on seedling survival through the first year of this study. In contrast, burial depth had strong positive effects on the fraction of seeds that persisted in the seed bank. Although dormant individuals may die before germinating and reproducing, those that persist at greater soil depths can play a crucial role in rescuing populations from local extinction in unpredictable environments. Given the extreme variability in fire frequency in fynbos, the net effect of seed dispersal by ants on plant populations will depend on how temporal fluctuations in fire regimes influence cost-benefit thresholds related to seed dormancy and seed mortality.

Scent marking by voles in response to predation risk: a field-laboratory validation

Predators use scent to locate their prey, and prey animals often alter their behavior in response to predation risk. I tested the hypothesis that voles would decrease their frequency of scent marking in response to predation risk. I conducted trials in which prairie voles, Microtus ochrogaster, and woodland voles, M. pinetorum, were allowed to scent mark ceramic tiles placed in their runways in the field. The tiles were subjected to one of three treatments: scented with odor from mink, Mustela vison (a rodent predator); rabbit, Oryctolagus cuniculus (a nonpredator mammal control); and no odor (control). No significant differences were found in the frequency of scent marking in response to the three treatments for either species. To validate that voles did not decrease their scent marking in response to predation risk, I brought male prairie voles from the field site into the laboratory and allowed them to scent mark white paper substrate treated with mink odor, rabbit odor, or no odor. No significant differences were found in the frequency of scent marks in response to the three treatments. These results differ from what was predicted based on laboratory studies with other species of rodents that show avoidance, reproductive suppression, decreased activity, and reduced scent marking in response to odors of predators. Voles appear to scent mark different substrates and under a wide variety of social and environmental situations, and this is not influenced by the presence of odor from a predator. Key words: mink, predation risk, scent marking, vole. [Behav Ecol 15:286–289 (2004)]

Breeding behaviour and performance of the Knysna Warbler Bradypterus sylvaticus on the Cape Peninsula, South Africa

Three pairs of Knysna Warblers were monitored on the south-eastern slopes of Table Mountain during the 2000 breeding season. Males displayed alone on territories until the second half of August, when females arrived. Nest-building (8 days) and incubation (16 days) were undertaken entirely by the female, who was not fed on the nest by the male. Chick provisioning was done mainly by the male. Arachnids and terrestrial amphipods were the most common prey brought to chicks. The fledging period was 12 days. Modal clutch size was three eggs, and depredation rates of eggs and chicks were high. After losses, replacement clutches were laid on average 19 days later, after a new nest was built. A maximum of three clutches per pair was recorded. Of 18 eggs monitored, 28% hatched and 17% fledged, equating to a production of one fledgling per pair per year. Ten days after fledging, the entire family leaves the territory, males probably returning once young are independent. The main threats to the local populations are clearing of riparian undergrowth and management practices that impact the predators of rodents.

Effect of rodents on acorn dispersal and survival of the Liaodong oak ( Quercus liaotungensis Koidz.)

We used a new method of labeling seeds with small pieces of coded tin-tags to investigate the effect of rodent on the seed fate of Liaodong oak ( Quercus liaotungensis) in a mountainous area (40°00′N, 115°30′E) of Beijing, China. In the fall of 1999 and 2000, a total of 1994 and 660 acorns were released and then seed loss was checked. Both sides of the 50 m wide transect were extensively checked to locate the tagged seeds or their fragments. The results indicated that Apodemus speciosus, Rattus confucianus and A. agrarius were potential Liaodong oak acorn predators. Nearly all acorns were consumed by small rodents within 10 days after acorn placement, demonstrating that seed predation was very heavy and that rodent predation contributes to the poor seed regeneration of the oak. The dispersal distances of most seeds were within 20 m. The dispersal distance of the buried seeds was the longest and it was in favor of seed survival and seedling recruitment. Rodents preferred to eat tagged seeds under dense shrub. This is mostly related to predation risk in different micro-environments. Rodents tended to bury the tagged seeds under dense shrub. This burial place of rodent does not favor the seedling recruitment of the oak. The rodents preferred to move seeds to the horizontal and down directions of a slope and this tendency would save energy for rodents. The seeding regeneration rate of tagged acorns were very low in 2 years. Rodent predation is the causative factor of low regeneration of Liaodong oak in the study region.

Frugivory at Juniperus communis depends more on population characteristics than on individual attributes

Summary We investigated the spatio‐temporal variation in the interactions between the juniper Juniperus communis and its vertebrate frugivores (avian dispersers of Turdus spp. and predatory rodents Apodemus sylvaticus) in the Mediterranean mountains of south‐east Spain. Frugivore activity was evaluated at six sites and for 3 years, in relation to both plant reproductive traits (plant size, cone crop and cone size) and characteristics of the immediate environment (distance to the nearest female, abundance of perches, fruiting environment and habitat). Plant characteristics and levels of frugivory varied strongly among the six populations. Cone production, cone size and frugivory also differed significantly among years for the same population. Avian frugivory was only occasionally affected by density of cones per plant, abundance of perches or abundance of other fruiting species, or by habitat. Rodent predation was positively related only to the density of cones per plant and then only in two sites. Levels of both avian frugivory and rodent predation significantly increased in populations with higher cone production. Both groups of vertebrate frugivores responded to the spatio‐temporal variation in cone abundance at a regional scale, discriminating more between juniper populations than between individual plants within a population. The outcome of interactions with frugivores at the individual plant level thus proved more dependent on the whole‐population characteristics than on individual attributes.

Notes on Beech (Fagus crenata Blume) Seed and Seedling Mortality Due to Rodent Herbivory in a Northernmost Beech Forest, Utasai, Hokkaido

We investigated the mortality of post-dispersal seeds and current-year seedlings of a beech species (Fagus crenata Blume) at the northernmost extent of its geographical range at Utasai (Kuromatsunai), Hokkaido, Japan. Introduced seeds that were protected from rodent predation by wire cages had a higher survival rate from winter to the following spring (mean ± SD: 84 ± 16.7%,n = 10) than controls without cages (mean ± SD: 12 ± 17.9%,n = 10). Unprotected transplanted current-year seedlings with almost fully opened primary leaves never survived more than three days (0%,n = 30), while more than 80% (n = 30) of seedlings within cages survived to the end of the growing season. These results indicate that rodent herbivory is a major mortality factor that strongly prevents the establishment of beech seedlings. In a natural population, we observed that 90% of seedlings (n = 197) disappeared within 10 days after their emergence and rodent herbivory caused this heavy mortality. A herbivorous rodent, the gray-backed vole, Clethrionomys rufocanus bedfordiae, was remarkably abundant in late June (101.5 voles/ha), suggesting that this species strongly affects the formation of the seedling bank. The presence of C. rufocanus bedfordiae may be one of the reasons for the scarcity of beech seedlings and saplings and the rarity of recruitment in this northernmost beech forest.

Ecological benefits of myrmecochory for the endangered chaparral shrub Fremontodendron decumbens (Sterculiaceae)

Fremontodendron decumbens grows in a single county in central California, USA. Prior research showed that its elaiosome-bearing seeds are dispersed by the harvester ant Messor andrei. I tested several hypotheses regarding the positive role of ant-mediated dispersal to F. decumbens: (1) Does ant-mediated seed dispersal facilitate seed escape from rodent predation?; (2) Does ant processing of seeds stimulate germination?; (3) Are ant middens more suitable microsites for seed or seedling survival in unburned chaparral areas?; and (4) Do survival benefits of dispersal occur post-fire in the form of differences in seedling survival probabilities and, if so, why? Results of tests of each hypothesis were: (1) similar percentages of seeds placed on ant middens and under F. decumbens shrub canopies were destroyed by rodents, but seeds from which elaiosomes had been removed were more likely to escape rodent predation; (2) seeds processed by ants did not germinate more readily than seeds removed directly from shrub branches; (3) seedling predation was a major cause of mortality in unburned chaparral on both ant middens and under shrubs, and overall seedling survival did not differ between the two microsites; (4) post-burn seedling survival was significantly greater for seedlings dispersed away from F. decumbens shrub canopies, because dispersed seedlings were both less likely to be killed by predators and more likely to be growing in a gap created by the fire-caused death of an established shrub. I concluded that the major ecological benefit to F. decumbens of ant-mediated seed dispersal was elevated post-fire seedling survival resulting from enhanced escape by dispersed seedlings from both predation and competition.

Investigations in plant commonness and rarity: a comparison of seed removal patterns in the widespread Jatropha standleyi and the endemic J. chamelensis (Euphorbiaceae)

During early August to late September 1998 we examined seed dispersal in the tree species Jatropha standleyi (widespread) and J. chamelensis (endemic; Euphorbiaceae) at the Estación de Biologı́a Chamela, Jalisco, México. Using general linear models, we found that seed removal from beneath the parental canopy did not differ between the two species and that seed removal was correlated with both seed availability on the ground and rodent predation. We inferred that seed removal was largely mediated by rodents and determined that if a seed was not removed within 4 d (approx. 16% chance), it was highly unlikely to be removed at all (approx. 3.5% chance) for both species. We note that although differences in patterns of seed removal may not explain the observed differences in range size, differences between the two species in seed crop size are similar to patterns found in other endemic/widespread species pairs.

Investigations in plant commonness and rarity: a comparison of seed removal patterns in the widespread Jatropha standleyi and the endemic J. chamelensis (Euphorbiaceae)

During early August to late September 1998 we examined seed dispersal in the tree species Jatropha standleyi (widespread) and J. chamelensis (endemic; Euphorbiaceae) at the Estacion de Biologia Chamela, Jalisco, Mexico. Using general linear models, we found that seed removal from beneath the parental canopy did not differ between the two species and that seed removal was correlated with both seed availability on the ground and rodent predation. We inferred that seed removal was largely mediated by rodents and determined that if a seed was not removed within 4d (approx. 16% chance), it was highly unlikely to be removed at all (approx. 3.5% chance) for both species. We note that although differences in patterns of seed removal may not explain the observed differences in range size, differences between the two species in seed crop size arc similar to patterns found in other endemic/widespread species pairs.

Circadian modulation of Fos responses to odor of the red fox, a rodent predator, in the rat olfactory system

We have previously shown that neuronal responses to a biologically neutral odor, cedar wood oil, in the olfactory system are greater in the subjective night compared to subjective day. In the present study, we confirm these results and extend them to a biologically relevant odor, the urine of the red fox, a rodent predator. Fos induced by exposure of rats to fox urine or a neutral odor, mineral oil, was markedly enhanced during the subjective night compared to subjective day in the main olfactory bulb, primary olfactory cortex, and other structures related to olfaction. These results show that neuronal responses to an ethologically relevant odor follow a circadian rhythm similar to biologically neutral odors. Fos responses induced by fox urine were observed to be of greater magnitude than a neutral odor in brain areas involved in fear responses, suggesting that fox urine activates fear circuitry.

Seed production of western larch in seed-tree systems in the southern interior of British Columbia

A series of surveys and experiments were conducted on four sites to identify constraints to seed production and natural regeneration in western larch seed-tree systems in the southwestern interior of British Columbia, Canada. These surveys included pollen monitoring, a cone analysis to evaluate seed production potential, seed trapping to estimate seed rain and the installation of field germination trials to assess the effects of germination substrate and seed losses due to bird and rodent predators. Pollen shedding was found to be adequate for moderate seed production with filled seed counts ranging from 9 to 30 per cone (10–34% of all seeds/cone). No significant differences in seed yields per cone and cone characteristics were observed between uncut control stands and seed-tree stands. Seed rain was generally good in 1995, ranging from 70,000 to 4.6 million seed/ha. For the four seed-tree stands, the average filled seed percentage of the trapped seeds ranged from 9–30%. Seed rain and seed quality were much reduced in 1996. Field germination trials showed western larch seeds germinated and survived best (15–70%) on mineral soil but rodent and/or bird predation reduced germination success significantly. Germination/germinant survival on undisturbed forest floor, covered with predator exclusion screens, was intermediate.

Fast wave activity in the rat rhinencephalon: elicitation by the odors of phytochemicals, organic solvents, and a rodent predator

Recent research has shown that bursts of ≈20 Hz fast waves are elicited in rhinencephalic cortex in rats by the odors of a number of different organic solvents and of components of the secretions of predators such as the weasel and the fox. We now show that a number of phytochemicals (benzyl alcohol, carvacrol, eucalyptol, and salicylaldehyde) will elicit fast wave bursts of about 20 Hz in the rat pyriform cortex. Additional organic solvents (carbon tetrachloride, chloroform, diethyl ether, 1,2-dimethoxyethane, n-heptane, mesitylene, methylcyclohexane, and commercial gasoline and kerosene, but not N, N-dimethylformamide or dimethyl sulfoxide) and another component of fox secretions (isopentenylmethyl sulfide) were also effective. Many of these compounds will also elicit fast wave bursts of about 20 Hz in the dentate gyrus. The effectiveness of benzyl alcohol, camphor, carvacrol, eucalyptol, isopentenylmethyl sulfide, 2-propylthietane, salicylaldehyde, toluene, and trimethylthiazoline (all of which elicit rhinencephalic fast waves in rats) in suppressing feeding in various small herbivores suggests that the recording of odor-induced rhinencephalic fast waves may provide an easy means of identifying new antifeedants. We found no evidence that the bursts of 20-Hz activity seen in the rat rhinencephalon were kindling-induced seizure-like reactions of the olfactory brain to the vapors of toxic chemicals.