1. Across the vast boreal forests of North America, no population cycles in Clethrionomys species occur. In Eurasia, by contrast, some Clethrionomys populations of the same species undergo regular ...3-5-year cycles. We examined the effects of nutrients, food, competitors, predators and climate on population limitation in the northern red-backed vole (Clethrionomys rutilus Pallas) in the south-western Yukon to determine why this difference occurs. 2. From 1986 to 1996 we added food, reduced large mammal predators and excluded snowshoe hares (Lepus americanus Erxleben) from large plots and found that none of these manipulations affected red-backed vole abundance. Adding nutrients as nitrogen, phosphorus and potassium (NPK) fertilizer had a slight negative effect, probably acting through a reduction in dwarf shrub productivity caused by competition from grasses. 3. We monitored weasel populations directly through trapping and indirectly through snow tracking. Predation by these vole specialists was irrelevant as a limiting factor most of the time because voles in this area do not reach the densities needed to sustain weasel populations. Other boreal forest mammal and bird predators did not focus on red-backed voles. However, when red-backed vole populations increased in the forest and Microtus voles also increased in the meadows, weasel populations increased and may have temporarily depressed red-backed voles in winter. 4. We monitored one major potential food, white spruce seeds, but seed fall was not related to population changes in red-backed voles, even after mast years. 5. We assessed the impact of weather variables, and the average depth of the snow pack during winter (October-March) was correlated directly with vole demography, having both direct effects in that year and delayed effects in the following year. 6. Our long-term trapping data (1973-96) indicate that Clethrionomys populations fluctuated, with peaks following hare peaks by 2-3 years. 7. We propose that the key variable limiting these vole populations is overwinter survival, and this is a function of overwinter food from berries produced during the previous summer by dwarf shrubs. These shrubs may be stimulated by abundant moisture from winter snows or by periodic fertilization from large quantities of pellets produced at snowshoe hare peaks.
•We developed a synthetic framework about how seed size and number interact to predict seed survival-dispersal patterns.•Seed size and number in oil tea vary considerably at both fruit and tree ...scales.•Seed size-number tradeoff in oil tea occurs at the fruit scale, but not at the tree scale.•Seed size and number make contrasting predictions on seed survival and dispersal patterns.
Seed size and number vary greatly both within and among plant individuals, populations or species. However, we know little about how individual variation in seed size and number relates to seed survival and dispersal dynamics in animal-dispersed plants. Based on the large-seed hypothesis and the predator satiation hypothesis, we developed a synthetic framework and testable predictions for how seed size and number interact to predict seed survival-dispersal patterns at the seed and tree scales, and tested for these effects using rodent-dispersed oil tea, Camellia oleifera. Our results showed that seed size and number varied considerably at both fruit and tree scales, and mean seed size for each fruit was negatively correlated with the number of seeds per fruit. We placed groups of individual-weighed seeds in a way that mimicked seed size and number from individual trees and tracked the fate of these seeds. This showed that seed survival in situ at source trees decreased with increasing seed size, but seed dispersal and the subsequent survival of dispersed seeds increased with larger seed size. In addition, seed survival in situ at source trees increased with larger seed number per tree, but the proportion of dispersed seeds decreased as seed number per tree increased. We demonstrate that individual variation in seed size and number have strong but contrasting effects on seed survival and seed dispersal in oil tea. Moreover, these two factors are not independent in their effects on seed survival at the source tree, but after dispersal, the size of individual seeds may be more important in determining seed survival or further handling by scatterhoarding animals.
Abstract Many studies have recently focused on stress as a marker of an animal’s well being. Since animals respond to a stressor by increasing their glucocorticoid (GC) levels there has been much ...interest in measuring these hormones. Fecal GC analyses have been used in a wide range of studies as they are an easily obtained, non-invasive measure of these stress hormones. However, these analyses rest on two major assumptions. First, they assume that fecal GC metabolites reflect free, biologically active levels of GCs in the plasma. Second, they assume that differences in fecal GC metabolite levels among animals are an accurate reflection of their physiological state and thus of their ability to respond to a stressor. We tested these assumptions in a population of free-ranging snowshoe hares ( Lepus americanus ) in the southwestern Yukon, from 2006 to 2008. Both assumptions were verified. Plasma free cortisol levels mirrored bile and fecal cortisol metabolite (FCM) levels, but plasma total cortisol levels did not. Differences in FCM concentrations among hares robustly predicted their response to a hormonal challenge. Hares with higher FCM concentrations showed a greater resistance to the suppression of their free plasma cortisol following a dexamethasone injection and a more marked increase of free plasma cortisol following an ACTH injection. Furthermore, we found that changes in FCM concentrations in autumn and winter over two years reliably tracked changes in plasma free cortisol levels obtained from the hormonal challenge test. These results indicate that both fecal and plasma measures of an animal’s stress physiology are concordant: they tell the same story.
Estimating population densities of small mammals (< 100 g) has typically been carried out by intensive livetrapping, but this technique may be stressful to animals and the effort required is ...considerable. Here, we used camera traps to detect small mammal presence and assessed if this provided a feasible alternative to livetrapping for density estimation. During 2010–2012, we used camera trapping in conjunction with mark-recapture livetrapping to estimate the density of northern red-backed voles (Myodes rutilus) and deer mice (Peromyscus maniculatus) in the boreal forest of Yukon, Canada. Densities for these 2 species ranged from 0.29 to 9.21 animals/ha and 0 to 5.90 animals/ha, respectively, over the course of this investigation. We determined if hit window—the length of time used to group consecutive videos together as single detections or “hits”—has an effect on the correlation between hit rate and population density. The relationship between hit rate and density was sensitive to hit window duration for Myodes with R2 values ranging from 0.45 to 0.59, with a 90-min hit window generating the highest value. This relationship was not sensitive to hit window duration for Peromyscus, with R2 values for the tested hit windows ranging from 0.81 to 0.84. Our results indicate that camera trapping may be a robust method for estimating density of small rodents in the boreal forest when the appropriate hit window duration is selected and that camera traps may be a useful tool for the study of small mammals in boreal forest habitat.
Motion‐sensitive cameras are commonly used to monitor wildlife occupancy rates; however, few studies have assessed whether data from cameras are correlated with density estimates obtained from more ...traditional labor‐intensive methods such as those based on capture‐mark‐recapture. We used data from a boreal forest community to test whether camera data were correlated with densities estimated from independent monitoring methods. We placed 72 covert cameras in the forest around Lhù'ààn Mân' (Kluane Lake), Yukon, Canada, for 7 years and tracked changes in population densities by camera hit rates. We independently estimated population densities of snowshoe hares (Lepus americanus) and red squirrels (Tamiasciurus hudsonicus) using capture‐mark‐recapture via live trapping, and Canada lynx (Lynx canadensis), coyotes (Canis latrans), and moose (Alces americanus) by snow track transects. Density estimates obtained from conventional aerial surveys were also periodically available for moose. Except for red squirrels, camera hit rates were highly correlated with population density estimates obtained by traditional methods, including across a large range of estimated densities corresponding to cyclic population dynamics in several species. Accordingly, we infer that motion‐sensitive cameras could supplement or replace traditional methods for monitoring key species in boreal forest food webs. Using cameras to monitor population change has several advantages; they require less effort in the field, are non‐invasive compared to live‐trapping, include multiple species at the same time, and rely less on weather than either aerial surveys or snow track transects. Tracking changes across the vast boreal forest is becoming increasingly necessary because of climate and landscape change and our data validate the use of motion‐sensitive cameras to provide a useful quantitative method for state‐of‐the‐environment reporting.
We used data from a Yukon boreal forest community to test whether motion‐sensitive camera data were correlated with density estimated from independent monitoring. Camera hit rates were highly correlated with capture‐mark‐recapture density estimates for snowshoe hares and were highly correlated with snow track transect density estimates for lynx and coyotes. Camera hit rates were not correlated with independent density estimates for red squirrels.
Crucial to the success of studies based on capture-mark-recapture (CMR) designs is the retention (permanency) and recognition (readability) of marks to identify individuals. Several marking methods ...for small mammals (< 60 g) are available, but their efficacy and use is not well known. We implemented a targeted survey of experts to gather their experiences and opinions regarding marking small mammals. Respondents (n = 114) stated their beliefs, perceptions, and current and future use, of marking methods, as well as factors influencing their choices, based on Likert and rank order scale questions. We compared responses based on where researchers' studies occurred, their level of experience, and their subfield of mammalogy. Most respondents (73%) had > 5 years experience marking small mammals, with 60% each marking > 1,000 individuals. Respondents believed that ear-tagging was most preferable in terms of efficiency, impact to affected animals (survival, pain), and personal ethics, whereas passive integrated transponder (PIT)-tagging was the most preferable with regard to retention and recognition, and toe-clipping with respect to cost. Most respondents plan to use ear-tagging (78%) or PIT-tagging (70%) in the future. PIT- and genetic-tagging are expected to increase, and toe-clipping to decline, in the future. The factors influencing which marking method respondents used were ranked—in order of decreasing preference—as impact, retention, recognition, cost, efficiency, and ethics. There were few differences in the mean response or consensus among respondents, regardless of their experience, location, or subfield. Most respondents (66%) agreed that additional studies on the performance and impact of various marking methods are needed to assess their costs and benefits for CMR-based studies. Ultimately, choice of marking method will depend on the species, research question, available resources, and local legislation and permitting. Our study, however, illustrates that collective insights by experienced mammalogists may aid individual researchers in deciding on study designs and protocols, particularly early career scientists.
Knowing the outcome(s) of management efforts in applied ecology is topical and useful. The effort–outcomes principle states that there is a cause-and-effect relationship between the desired outcomes ...of management and the effort applied (the inputs) but with diminishing returns. A question addressed by this relationship is the following: How much management effort is enough to achieve a desired outcome? We evaluate the relationship—namely, how it is described or estimated—give empirical examples, and outline a novel and explicit conceptual framework that connects management efforts to outcomes. We conclude that the relationship has been described three ways previously: in stylized graphs, from computer algorithms, and in observational studies. We recommend a fourth way employing manipulative experiments carried out as part of an adaptive management program and designed explicitly to estimate the relationship’s parameters.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Scavenging by vertebrates can have important impacts on food web stability and persistence, and can alter the distribution of nutrients throughout the landscape. However, scavenging communities have ...been understudied in most regions around the globe, and we lack understanding of the biotic drivers of vertebrate scavenging dynamics.
In this paper, we examined how changes in prey density and carrion biomass caused by population cycles of a primary prey species, the snowshoe hare Lepus americanus, influence scavenging communities in the northern boreal forest. We further examined the impact of habitat and temperature on scavenging dynamics.
We monitored the persistence time, time until first scavenger, and number of species scavenging experimentally‐placed hare carcasses over four consecutive years in the southwestern Yukon. We simultaneously monitored hare density and carrion biomass to examine their influence relative to temperature, habitat, and seasonal effects. For the primary scavengers, we developed species‐specific scavenging models to determine variation on the effects of these factors across species, and determine which species may be driving temporal patterns in the entire community.
We found that the efficiency of the scavenging community was affected by hare density, with carcass persistence decreasing when snowshoe hare densities declined, mainly due to increased scavenging rates by Canada lynx Lynx canadensis. However, prey density did not influence the number of species scavenging a given carcass, suggesting prey abundance affects carrion recycling but not necessarily the number of connections in the food web. In addition, scavenging rates increased in warmer temperatures, and there were strong seasonal effects on the richness of the vertebrate scavenging community.
Our results demonstrate that vertebrate scavenging communities are sensitive to changes in species’ demography and environmental change, and that future assessments of food web dynamics should consider links established through scavenging.
This paper demonstrates that population cycles of snowshoe hares can influence the efficiency of carrion recycling by impacting vertebrate scavenging communities. Carrion persistence decreased when snowshoe hare densities declined, likely through increased scavenging by Canada lynx. Vertebrate scavenging rates in the boreal forest also increased in warmer temperatures.
Perceived predation risk alters prey behaviour and physiology, but few studies have examined downstream consequences on prey demography in wild populations. Perceived predation risk could alter adult ...reproductive performance via reduced investment in offspring quality and post-birth care. We manipulated perceived predation risk in snowshoe hare ( Lepus americanus Erxleben, 1777) by exposing pregnant mothers to chases by a domestic dog ( Canis familiaris Linnaeus, 1758). Litter size was comparable between risk-augmented and control groups, but treated females had more stillbirths and gave birth to leverets of lower body condition. Leverets from risk-augmented females had 88% higher 40-day mortality rate. Maternally preventable causes of death like starvation or predation by red squirrel ( Tamiasciurus hudsonicus (Erxleben, 1777)) caused this difference, particularly during the nursing period. Risk-augmented mothers were always more active than controls, but the difference was greatest during the nursing period. We found that perceived predation risk reduces maternal productivity pre- and post-partum, implying downstream consequences to populations. Because our treatment ended before parturition, we can link offspring performance such as survival and behaviour specifically to maternal life-history trade-offs, which has not been shown in a wild mammal.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Mast seeding involves the episodic and synchronous production of large seed crops by perennial plants. The predator satiation hypothesis proposes that mast seeding maximizes seed escape because seed ...predators consume a decreasing proportion of available seeds with increasing seed production. However, the seed escape benefits of masting depend not only on whether predators are satiated at high levels of seed production, but also on the shape of their functional response (type II vs. type III), and the actual proportion of available seeds that they consume at different levels of seed production. North American red squirrels (
Tamiasciurus hudsonicus
) are the primary vertebrate predator of white spruce (
Picea glauca
) mast seed crops in many boreal regions because they hoard unopened cones in underground locations, preempting the normal sequence of cone opening, seed dispersal, and seed germination. We document the functional response of cone-hoarding by red squirrels across three non-mast years and one mast year by estimating the number of cones present in the territories of individual red squirrels and the proportion of these cones that they hoarded each autumn. Even though red squirrels are not constrained by the ingestive and on-body (fat reserves) energy reserve limitations experienced by animals that consume seeds directly, most squirrels hoarded <10% of the cones present on their territories under mast conditions. Cone availability during non-mast years also reached levels that satiated the hoarding activity of red squirrels; however, this occurred only on the highest-quality territories. Squirrels switched to mushroom-hoarding when cone production was low and mushrooms were abundant. This resulted in type III functional response whereby the proportional harvest of cones was highest at levels of cone availability that were intermediate within non-mast years. Overall, more cones escaped squirrel cone-hoarding during a mast event than when cone production was low in non-mast years, which supports the predator satiation hypothesis. However, the highly variable seed escape in non-mast years may help to explain why all spruce cone production is not concentrated into fewer, larger, mast years.
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