Small Mammalian Herbivores Research Articles

Experimental herbivore exclusion, shrub introduction, and carbon sequestration in alpine plant communities

BackgroundShrub cover in arctic and alpine ecosystems has increased in recent decades, and is predicted to further increase with climate change. Changes in shrub abundance may alter ecosystem carbon (C) sequestration and storage, with potential positive feedback on global C cycling. Small and large herbivores may reduce shrub expansion and thereby counteract the positive feedback on C cycling, but herbivore pressures have also changed in the alpine-arctic tundra; the increased shrub cover together with changes in herbivore pressure is leading to unpredictable changes in carbon sequestration and storage. In this study we investigate the importance of herbivory and shrub introduction for carbon sequestration in the short term. We measured standing biomass and daytime mid-growing season carbon fluxes in plots in a full factorial design where we excluded small and large mammalian herbivores and introduced Salix by planting Salix transplants. We used three study sites: one Empetrum-dominated heath, one herb- and cryptogam-dominated meadow, and one Salix-dominated shrub community in the low-alpine zone of the Dovre Mountains, Central Norway.ResultsAfter 2 years, significant treatment effects were recorded in the heath community, but not in the meadow and shrub communities. In the heath community cessation of herbivory increased standing biomass due to increased biomass of dwarf shrubs. Cessation of herbivory also reduced biomass of bryophytes and ecosystem respiration (ER). Except for an increase in biomass of deciduous shrubs caused by the Salix introduction, the only effect of Salix introduction was an increase in biomass of graminoids in the heath.ConclusionsOur short-term study demonstrated that herbivore exclusion had small but still significant effects on heath vegetation, whereas such effects were not apparent in the herb-and cryptogam-dominated meadow and the Salix-dominated shrub community. Following the treatments over more years is needed to estimate the long-term effects on community structure and the consequences for C sequestration in the three plant communities. Such data are important for predicting the impact of shrub expansion on C budgets from alpine regions.

Interacting effects of ambient temperature and food quality on the foraging ecology of small mammalian herbivores

Both temperature and diet quality play an important role in the time and energy budgets of small mammalian herbivores. However, little is known about how temperature and diet quality interact to influence diet selection, nutrient extraction, and energetics, and how these effects might differ among species. Therefore, we examined the effects of diet quality and temperature on aspects of the foraging ecology of two species of lagomorphs, pygmy rabbits (Brachylagus idahoensis), which are small dietary specialists, and mountain cottontail rabbits (Sylvilagus nuttallii), which are larger dietary and habitat generalists. In a series of feeding experiments, we investigated 1) the effects of temperature on selection of plant fiber and the plant secondary metabolite 1,8 cineole in their diets, 2) effects of temperature and plant fiber on daily intake, digestion, and passage of food, 3) effects of plant fiber and 1,8 cineole on resting metabolic rate, and 4) how these interactions differ between the rabbit species. Both species chose to eat more total food and a greater proportion of high fiber food that passed more quickly through the digestive system in colder temperatures. However, temperature did not affect how much 1,8 cineole the rabbits consumed nor how thoroughly they digested food. Food quality affected how well they digested the dry matter in the food, but not their resting metabolic rate. Understanding how the interactions between ambient temperature and food quality affect selection of diets and intake by small mammalian herbivores, and the physiological mechanisms governing these choices, is useful for predicting how these species might respond to changes in both temperature and food quality and inform conservation and restoration strategies.

Defaunation and habitat disturbance interact synergistically to alter seedling recruitment

Vertebrate granivores destroy plant seeds, but whether animal-induced seed mortality alters plant recruitment varies with habitat context, seed traits, and among granivore species. An incomplete understanding of seed predation makes it difficult to predict how widespread extirpations of vertebrate granivores in tropical forests might affect tree communities, especially in the face of habitat disturbance. Many tropical forests are simultaneously affected by animal loss as well as habitat disturbance, but the consequences of each for forest regeneration are often studied separately or additively, and usually on a single plant demographic stage. The combined impacts of these threats could affect plant recruitment in ways that are not apparent when studied in isolation. We used wire cages to exclude large (elephants), medium, (sambar deer, bearded pigs, muntjac deer), and small (porcupines, chevrotains) ground-dwelling mammalian granivores and herbivores in logged and unlogged forests in Malaysian Borneo. We assessed the interaction between habitat disturbance (selective logging) and experimental defaunation on seed survival, germination, and seedling establishment in five dominant dipterocarp tree species spanning a 21-fold gradient in seed size. Granivore-induced seed mortality was consistently higher in logged forest. Germination of unpredated seeds was reduced in logged forest and in the absence of small to large-bodied mammals. Experimental defaunation increased germination and reduced seed removal but had little effect on seed survival. Seedling recruitment however, was more likely where logging and animal loss occurred together. The interacting effects of logging and hunting could therefore, actually increase seedling establishment, suggesting that the loss of mammals in disturbed forest could have important consequences for forest regeneration and composition.

Tree Diversity Drives Forest Stand Resistance to Natural Disturbances

Forests are frequently exposed to natural disturbances, which are likely to increase with global change, and may jeopardize the delivery of ecosystem services. Mixed-species forests have often been shown to be more productive than monocultures, but it is unclear whether this results from mixed stands being in part more resistant to various biotic and abiotic disturbance factors. This review investigates the relationships between tree diversity and stand resistance to natural disturbances and explores the ecological mechanisms behind the observed relationships. Mixed forests appear to be more resistant than monocultures to small mammalian herbivores, soil-borne fungal diseases and specialized insect herbivores. Admixing broadleaves to conifers also increases the resistance to fire and windstorms when compared to pure conifer stands. However, mixed forests may be more affected by drought depending on the species in the mixture. Overall, our findings suggest that mixed forests are more resistant to natural disturbances that are relatively small-scale and selective in their effect. However, benefits provided by mixtures are less evident for larger-scale disturbances. Higher tree diversity translates into increased resistance to disturbances as a result of ecological trait complementarity among species, reduction of fuel and food resources for herbivores, enhancement of diversion or disruption processes, and multi-trophic interactions such as predation or symbiosis. To promote resistance, the selection of tree species with different functional characteristics appears more important than increasing only the number of species in the stand. Trees with different levels of susceptibility to different hazards should be intermixed in order to reduce the amount of exposed resources and to generate barriers against contagion. However, more research is needed to further improve associational resistance in mixed forests, through a better understanding of the most relevant spatial and temporal scales of species interactions and to optimize the overall provision of ecosystem services.

Small mammal activity alters plant community composition and microbial activity in an old‐field ecosystem

AbstractHerbivores modify their environment by consuming plant biomass and redistributing materials across the landscape. While small mammalian herbivores, such as rodents, are typically inconspicuous, their impacts on plant community structure and chemistry can be large. We used a small mammal exclosure experiment to explore whether rodents in a southeastern old field directly altered the aboveground plant species composition and chemistry, and indirectly altered the belowground soil community composition and activity. In general, when rodents were excluded, C3 graminoids increased in cover and biomass, contributing toward a shift in plant species composition relative to plots where rodents were present. The plant community chemistry also shifted; plant fiber concentration and carbon : nitrogen were higher, whereas plant nitrogen concentration was lower in exclosure plots relative to access plots. While microbial community enzyme activity increased when rodents were excluded, no significant changes in the fungal : bacterial or potential nitrogen mineralization occurred between treatments. Our results show that rodents can rapidly influence aboveground plant community composition and chemistry, but their influence on belowground processes may require plant inputs to the soil to accumulate over longer periods of time.

Digesta retention patterns in geese (Anser anser) and turkeys (Meleagris gallopavo) and deduced function of avian caeca

Although it is well-known that retrograde transport of urine fills the caeca of birds with fluid and small particles, the function of avian caeca is still not fully understood. We measured mean retention times (MRT) of solute (cobalt-EDTA, Co), small particle (<2mm, chromium-mordanted fibre, Cr) and large particle (8mm, cerium-marked fibre, Ce) markers in geese (Anser anser) and turkeys (Meleagris gallopavo) fed alfalfa pellets ad libitum. Intake did not differ between species. Turkeys had longer MRT for all markers (Co: 10.4 vs. 3.2h; Cr 23.3 vs. 2.9h; Ce 9.5 vs. 2.1h), achieved a higher fibre digestibility, and had a higher calculated dry matter gut fill. Thus, geese and turkeys correspond to the typical dichotomy of good fliers vs. poor fliers/flightless species in avian herbivores. Because uric acid is fermented much faster by microbes than fibre, the ultimate cause of short-MRT digesta retention in avian caeca as in geese is possibly rather uric acid than fibre fermentation. The numerical differences between marker MRT in geese correspond to a colonic separation mechanism that delays the excretion of fluids more than small and again more than large particles. In contrast to geese, turkeys excreted solid and liquid (caecal) faeces. Liquid faeces contained less fibre and more crude protein than solid faeces and accounted for the excretion of 7, 25 and 34% of Ce, Co and Cr markers. Marker excretion patterns and MRT for liquid faeces (Co 15 vs. Cr 50h) suggest that small particles did not simply move in parallel to fluids, but were retained selectively by being trapped in colonic digesta upon expulsion from caeca, with subsequent repeated retrograde transport into caeca with the next batch of urine. Given the absence of coprophagy in birds (in contrast to small mammalian herbivores), such a delay of small (microbial) particle escape from the caeca appears reasonable.

Soil conditions moderate the effects of herbivores, but not mycorrhizae, on a native bunchgrass

Herbivores, microbial mutualists, and soil nutrients can affect plant survival, growth, and reproduction, demographic parameters that are essential to plant restoration. In this study we ask: 1) whether native plants that form early associations with mycorrhizal fungi are more tolerant of mammalian grazers, and 2) how early plant associations with mycorrhizal fungi influence mammalian grazing across gradients in soil nutrients. In eight grassland sites in California (USA), we transplanted seedlings of a native bunchgrass, Stipa pulchra, that were or were not pretreated with mycorrhizal fungi in exclosures designed to exclude different guilds of vertebrate grazers. Pretreated plants had greater establishment eight months after transplantation than untreated plants. Mycorrhizal inoculation resulted in twofold greater biomass and fourfold greater seed production when plants were protected from herbivores; inoculation with mycorrhizae resulted in twofold greater biomass and seed production when plants were accessible by all herbivores. Soil phosphate and potassium concentrations influenced herbivory: vertebrate grazing had less effect on transplant biomass and seed production at sites with high phosphate – low potassium soils, but the effects of grazing were more severe in low phosphate – high potassium soils. Pretreatment with mycorrhizal fungi can result in greater survival, growth, and reproduction of transplanted seedlings of native bunchgrass S. pulchra. Our results also illustrate that soil conditions may influence the extent to which the vertebrate herbivore community limits restoration of S. pulchra: the effects of some small mammalian herbivores (e.g., voles) was little affected by soil conditions, but grazing by larger herbivores had a greater effect on S. pulchra performance at sites with low phosphate – high potassium soils. In helping identify the contribution of soil nutrients, herbivores, and mycorrhizae to establishment and performance, our work has implications for the restoration of a species that is likely a fundamental component of pristine California grassland ecosystems.

Linkages among canopy tree neighbourhoods, small mammal herbivores and herbaceous communities in temperate forests

AbstractQuestionSmall mammals are important consumers of tree seeds in forests worldwide. Few studies, however, have addressed the impacts of small mammals as consumers of herbaceous species in the forest understorey. Local neighbourhood‐scale variation in canopy tree composition has strong effects on resource availability for understorey plants, but can also influence the distribution, abundance and foraging behaviour of small mammals, primarily through spatial and temporal variation in seed rain. In this study we examine the direct and indirect effects of canopy tree neighbourhoods and herbivory by small mammals on the diversity, abundance and flowering of herbaceous species in a temperate forest.Location and MethodsIn 1994 we established 36 1 m × 2 m fenced small mammal exclosures, paired with similar‐sized control plots, under the major canopy tree species found at Great Mountain Forest, in Norfolk, CT, US.ResultsWhen re‐sampled in 2005, after 10 yrs of small mammal exclusion, the abundance of herbaceous plants had increased inside the exclosures (F = 5.005, df = 1,38, P = 0.031), as did the proportion of plants flowering (t = −2.11, df = 60, P = 0.039). However, species richness and Shannon–Wiener diversity (H′) were similar inside and outside of exclosures. At one site the identity of the canopy tree species did impact species richness (F = 4.494, df = 5,18, P = 0.008), independent of exclosure. Plots under Fraxinus americana (white ash) had the highest species richness (average number of species = 7.5) while the lowest diversity was found in plots under Tsuga canadensis (Eastern hemlock; average number of species = 2.25) and Quercus rubra (northern red oak; average number of species = 1.5).ConclusionsThe results demonstrate that small mammal herbivores can directly affect the abundance and reproduction of herbaceous species, and that local conditions (such as the surrounding canopy tree neighbourhood) can also play direct and indirect roles in the maintenance of the herbaceous layer in temperate deciduous forests.

Interactive Effects of Black-Tailed Prairie Dogs and Cattle on Shrub Encroachment in a Desert Grassland Ecosystem.

The widespread encroachment of woody plants throughout the semi-arid grasslands in North America has largely resulted from overgrazing by domestic livestock, fire suppression, and loss of native large and small mammalian herbivores. Burrowing-herbivorous mammals, such as prairie dogs (Cynomys spp.), help control shrub encroachment through clipping of shrubs and consumption of their seedlings, but little is known about how this important ecological role interacts with and may be influenced by co-existing large herbivores, especially domestic livestock. Here, we established a long-term manipulative experiment using a 2 × 2 factorial design to assess the independent and interactive effects of black-tailed prairie dogs (Cynomys ludovicianus) and cattle (Bos taurus) on honey mesquite (Prosopis glandulosa) abundance and structure. We found that, after five years, mesquite abundance was three to five times greater in plots where prairie dogs were removed compared to plots where they occurred together or alone, respectively. While both prairie dogs and cattle reduced mesquite cover, the effect of prairie dogs on reducing mesquite abundance, cover, and height was significantly greater than that by cattle. Surprisingly, cattle grazing enhanced prairie dog abundance, which, in turn, magnified the effects of prairie dogs on mesquite shrubs. Mesquite canopy cover per hectare was three to five times greater where prairie dogs and cattle were absent compared to where they occurred together or by themselves; whereas, cumulative mesquite height was two times lower on sites where prairie dog and cattle occurred together compared to where they occurred alone or where neither occurred. Data from our experimental study demonstrate that prairie dogs and moderate grazing by cattle can suppress mesquite growth, and, when their populations are properly managed, they may interact synergistically to significantly limit mesquite encroachment in desert grasslands.

Novel grass–endophyte associations reduce the feeding behaviour of invasive European rabbits (Oryctolagus cuniculus)

Context Small mammalian herbivores, such as European rabbits (Oryctolagus cuniculus), can have significant unwanted impacts on agriculture and horticulture and can attract birds of prey and avian scavengers to airports, increasing the risk of bird strike. Sustainable wildlife management tools that have high efficacy and animal welfare are needed to mitigate these impacts. Aim We assessed perennial ryegrass (Lolium perenne) and tall fescue (Festuca arundinacea) cultivars associated with selected Epichloë endophytes, originally developed for bird management at airports, to determine their feeding-deterrent properties towards invasive rabbits. Methods A pellet feed trial using caged domestic rabbits and a pen trial using wild rabbits were conducted to assess rabbit responses to food pellets with novel endophyte-infected or uninfected grass seed and to plots planted with endophyte-infected or uninfected grasses, respectively. Key results Caged rabbits ate significantly less food pellets containing endophyte-infected grass straw than pellets containing endophyte-free grass straw. Wild rabbits consumed significantly less herbage from plots planted with endophyte-infected grasses than those of the equivalent endophyte-free grass cultivars. Temporal patterns of rabbit feeding behaviour support the hypothesis that deterrence in rabbits resulted from post-ingestion feedback associated with grass–endophyte secondary metabolites. Conclusions Although more research is required on the exact mechanism of action in rabbits, our results suggest novel endophyte-infected grass associations may substantially reduce rabbit feeding behaviour and possibly rabbit numbers in areas where these grasses are sown. Implications Novel grass–endophyte associations have great potential for deterring problem wildlife at airports and other amenity areas.

Rainfall, microhabitat, and small mammals influence the abundance and distribution of soil microorganisms in a Chilean semi-arid shrubland

Patterns in rainfall and soil water availability are considered to be the main drivers governing arid and semiarid ecosystems. While the mechanisms by which water limits aboveground net primary production has been widely explored, few long-term studies have examined interactions between precipitation, soil resources, plant communities, and soil microbial communities; these may be critical to understanding soil biogeochemical cycles and above- and belowground interactions. We capitalized on a long-term biotic manipulation (exclusion of small mammal herbivores from replicate plots) and long-term variation in rainfall to assess how precipitation, small mammals, and shrub cover act directly and interactively to influence the spatial and temporal distribution of soil microorganisms, a key first step to understanding soil biogeochemical cycles. We measured the abundance of arbuscular mycorrhiza (AM), soil fungi, soil bacteria, and soil physicochemical characteristics over 10 consecutive years in a semiarid thorn scrub community in north–central Chile; we sampled two microhabitats (under shrub cover, and in open spaces between shrubs colonized by ephemeral plants), and in plots with or without the presence of native small mammals, the main herbivores in this environment. Annual rainfall ranged widely (11–356 mm) in this period and was the primary factor affecting abundance of AM root colonization and soil microbes. While the percentage of root length with AM was higher in dry compared to wet years, free-living soil bacteria and fungi were more abundant during wet years. All microorganisms were more abundant in the resource islands beneath the shrubs compared to open microhabitat between shrubs, although the relation between soil biota and the concentration of some particular nutrients was negative. These patterns were modulated by the presence of small mammals, which enhanced root colonization by AM fungi, particularly for ephemeral plants, but which were negatively associated with soil fungi abundance. The abundance of soil bacteria showed a more complex response to the presence of small mammals and was dependent on microhabitat and year. The spatial and temporal heterogeneity of soil resources and the activity of small mammals are important modulators of subterranean biotic responses to rainfall, the primary factor affecting soil microbiota abundance in this semiarid ecosystem.

Effects of plateau pika activities on seasonal plant biomass and soil properties in the alpine meadow ecosystems of the Tibetan Plateau

AbstractThe foraging and burrowing activities of small mammalian herbivores may have either detrimental or beneficial effects on grassland ecosystems; the direction of the effect is determined by the species, population abundances and fluctuations. Twelve survey sites with active burrow of plateau pika were classified into four degrees of density: approximately zero‐density, low‐density, medium‐density and high‐density, to evaluate the impact of different pika densities on vegetation, plant biomass, soil organic carbon and nutrients in a whole growing season. We show that pika as a main supplement to livestock activities contributed to a decrease in the number of plant species, vegetation cover, plant height and seasonal mean biomass, while values at medium‐density site except above‐ground biomass were the lowest. With the exception of available potassium, soil organic carbon, nitrogen, total phosphorus and soil water content, zero‐density areas were significantly higher than those of pika occupied areas. However, there were slight or no differences in vegetation characteristics and soil properties between medium‐and high‐density sites. Our study suggests pika activities with high‐density made palatable forage less and soil carbon and nitrogen more than low‐density, moreover, plateau pika had greater impacts on above‐ground vegetation than on root system.

Microsite affects willow sapling recovery from bank vole (Myodes glareolus) herbivory, but does not affect grazing risk.

Large herbivores are often removed or reduced as part of vegetation restoration programmes, but the resultant increase in vegetation biomass and changes in vegetation structure may favour small mammals. Small mammals may have large impacts on plant community composition via granivory and sapling herbivory, and increased small mammal populations may reduce any benefits of large herbivore removal for highly preferred species. This study tested the impacts of small mammal herbivory, microsite characteristics and their interaction on growth and survival of three montane willow species with differing chemical compositions, Salix lapponum, S. myrsinifolia and S. arbuscula. In two separate years, 1-year-old saplings were planted within a 180 ha, large-mammal scrub regeneration exclosure, and either experimentally protected from or exposed to small mammals (bank voles). Saplings were planted in one of two microsite treatments, vegetation mown (to mimic a grazed sward) or disturbed (all above- and below-ground competition removed), and monitored throughout the first year of growth. Approximately 40 % of saplings planted out in each year were damaged by bank voles, but direct mortality due to damage was very low (<2 %). There were no strong species differences in susceptibility to vole damage. Microsite treatment had no impact on the proportion of saplings attacked, but in 2004 saplings in mown microsites were more severely damaged and had smaller increases in size than those in disturbed microsites. In 2003, saplings in mown microsites had smaller increases in stem diameter following attack than those in disturbed microsites. Planting 1-year-old willow saplings into disturbed microsites may aid growth, reduce the severity of small mammal damage and improve recovery following sub-lethal small mammal damage. Restoration management of montane willow scrub should therefore consider manipulating the planting site to provide disturbed areas of soil.

Disproportionate effects of non‐colonial small herbivores on structure and diversity of grassland dominated by large herbivores

The response of semiarid grasslands to small, non‐colonial herbivores has received little attention, focusing primarily on the effects of granivore assemblages on annual plant communities. We studied the long‐term effects of both small and large herbivores on vegetation structure and species diversity of shortgrass steppe, a perennial semiarid grassland considered marginal habitat for small mammalian herbivores. We hypothesized that 1) large generalist herbivores would affect more abundant species and proportions of litter‐bare ground‐vegetation cover through non‐selective herbivory, 2) small herbivores would affect less common species through selective but limited consumption, and 3) herbivore effects on plant richness would increase with increasing aboveground net primary production (ANPP). Plant community composition was assessed over a 14‐year period in pastures grazed at moderate intensities by cattle and in exclosures for large (cattle) and large‐plus‐small herbivores (additional exclusion of rabbits and rodents). Exclusion of large herbivores affected litter and bare ground and basal cover of abundant, common and uncommon species. Additional exclusion of small herbivores did not affect uncommon components of the plant community, but had indirect effects on abundant species, decreased the cover of the dominant grass Bouteloua gracilis and total vegetation, and increased litter and species diversity. There was no relationship between ANPP and the intensity of effects of either herbivore body size on richness. Exclusion of herbivores of both body sizes had complementary and additive effects which promoted changes in vegetation composition and physiognomy that were linked to increased abundance of tall and decreased abundance of short species. Our findings show that small mammalian herbivores had disproportionately large effects on plant communities relative to their small consumption of biomass. Even in small‐seeded perennial grasslands with a long history of intensive grazing by large herbivores, non‐colonial small mammalian herbivores should be recognized as an important driver of grassland structure and diversity.

Shifting bottom-up and top-down regulation of oak recruitment across a regional resource gradient

Aim Questions about the relative importance of top-down and bottom-up regulation of populations have long occupied ecologists. Recent work has explored how the strength of consumer- versus resourced-based limitation can shift in strength across both time and space, and indicates the need for larger scales of study across spatial resource gradients. A better understanding of how climate gradients affect population regulation is integral to conservation ecology, particularly in the context of global change. Location California. Methods We examined the effects of bottom-up (water limitation) and top-down (small mammal herbivory) forces on valley oak (Quercus lobata) sapling recruitment. We used existing literature on valley oak planting experiments and field data on natural populations at 26 sites across the species' distribution to explore how the factors regulating oak populations shift along a regional precipitation gradient. This approach allowed us to study time-integrated ecological processes in a long-lived system that would be impossible to manipulate in a strictly experimental setting. Results We found that the relative importance of top-down and bottom-up forces in limiting oak recruitment shifted across the precipitation gradient, with small mammalian herbivory (top-down) more important as long-term mean site precipitation increased, and factors related to moisture stress (bottom-up) increasingly important at lower precipitation levels. Main conclusions Our findings emphasize the importance of expanding the spatial scale of studies on population and community dynamics in order to better understand patterned variation in the multiple factors regulating them across resource gradients.

Emergency Presentations of the Exotic Small Mammalian Herbivore Trauma Patient

Trauma is a common complaint by owners of small exotic mammalian herbivores (e.g., rabbits, rodents) presented to veterinary hospitals. The term “trauma” is a broad disease category applied to patients with physical debilitation associated with injury often classified as “blunt,” “penetrating,” or “burn” in origin. Because many small exotic mammalian herbivores are prey animals, clinical signs of trauma may be masked until the effects of the injury outweigh the innate nature to survive. Small exotic mammalian herbivores are disproportionately sensitive to stress; thus, pain management and supportive care are extremely important during the initial stages of trauma management. Small exotic mammals differ slightly from other companion animals (e.g., dogs, cats) in regard to common trauma presentations. However, with a few therapeutic modifications (e.g., antibiotic selection, avoidance of corticosteroids, preventing self-trauma), treatment of small exotic mammalian herbivore trauma cases follows the same conventional guidelines used for other companion animals.

Shrub facilitation increases plant diversity along an arid scrubland–temperate rain forest boundary in South America

AbstractAimTheoretical models predict nurse plant facilitation enhances species richness by ameliorating stressful environmental conditions and expanding distributional ranges of stress‐intolerant species into harsh environments. We studied the role of nurse facilitation on the recruitment of perennial plants along an arid scrubland–temperate rain forest boundary to test the following predictions: (1) nurse shrub canopy increases seedling abundance and species richness along the rain forest–scrubland boundary; (2) scrubland species are less dependent on facilitative interactions than temperate rain forest species, especially at the moister, upper end of the gradient.LocationBosque Fray Jorge National Park, north‐central Chile, South America (30° 39′ S – 71° 40′ W).MethodsWe examined seedling abundance and species richness of perennial plants in the open and under different types of patches that may facilitate species recruitment (living shrubs, dead shrubs, perennial grasses and trees) along an arid scrubland–temperate rain forest boundary. To assess whether the potential role of the shrub canopy on seedling survival in the scrubland and forest differs, we designed a 2 × 2 factorial field experiment with shrub canopy (under shrub or open patch) and small mammal herbivory (access or closed) as factors. At both sides of the scrubland–forest gradient, we planted young seedlings of scrubland (Senna cumingii) and forest (Myrceugenia correifolia and Griselinia scandens) species under the four treatment combinations.ResultsNurse living shrubs increased seedling abundance and diversity. Under living shrubs, the number of recruiting species was 100% and 30% larger than in open patches of the arid scrubland and temperate rain forest patches, respectively. Seedling abundance was 60% and 300% larger under living shrubs compared to open patches of the scrubland and the temperate rain forest, respectively. Despite their low cover, dead shrubs were particularly important for recruitment of young seedlings in the scrubland. Seedlings of forest species were extremely rare. The field experiment demonstrated the importance of nurse plant facilitation for the survival of the forest species at both sides of the boundary. In contrast, scrubland species were less dependent on nurse plants than forest and intermediate forest–scrubland species.ConclusionsOur results show that facilitative interactions increase seedling abundance and species richness along an arid scrubland–temperate rain forest boundary, notably by enhancing seedling establishment of forest species. Despite increasing nurse shrub–seedling competition in the arid scrubland, shrubs have a net positive effect on plant community diversity.

Rapid, landscape scale responses in riparian tundra vegetation to exclusion of small and large mammalian herbivores

Productive tundra plant communities composed of a variety of fast growing herbaceous and woody plants are likely to attract mammalian herbivores. Such vegetation is likely to respond to different-sized herbivores more rapidly than currently acknowledged from the tundra. Accentuated by currently changing populations of arctic mammals there is a need to understand impacts of different-sized herbivores on the dynamics of productive tundra plant communities. Here we assess the differential effects of ungulate (reindeer) and small rodent herbivores (voles and lemmings) on high productive tundra vegetation. A spatially extensive exclosure experiment was run for three years on river sediment plains along two river catchments in low-arctic Norway. The river catchments were similar in species pools but differed in species abundance composition of both plants and vertebrate herbivores. Biomass of forbs, deciduous shrubs and silica-poor grasses increased by 40–50% in response to release from herbivory, whereas biomass of silica-rich grasses decreased by 50–75%. Hence both additive and compensatory effects of small rodents and reindeer exclusion caused these significant changes in abundance composition of the plant communities. Changes were also rapid, evident after only one growing season, and are among the fastest and strongest ever documented in Arctic vegetation. The rate of changes indicates a tight link between the dynamics of productive tundra vegetation and both small and large herbivores. Responses were however not spatially consistent, being highly different between the catchments. We conclude that despite similar species pools, variation in plant species abundance and herbivore species dynamics give different prerequisites for change.

Impacts of non-native plant and animal invaders on gap regeneration in a protected boreal forest

In balsam fir (Abies balsamea)-dominated boreal forests of Gros Morne National Park, Newfoundland (Canada), non-native Cirsium arvense (Canada thistle) has invaded forest gaps. Its management is complicated by the lack of viable control techniques and an overarching issue of gap regeneration failure attributed to browsing by non-native moose (Alces alces). This study identifies the impacts of thistle invasion on balsam fir regeneration and explores protocols to re-establish fir in gaps invaded by thistle and moose. Fir seeds were planted into ten gaps (five natural; five anthropogenic) and the emergence, growth, herbivory damage, and survival of fir was determined for 2 years amongst five treatments (n = 50 plots; 32 seeds/plot): (1) thistle monocultures in gaps; (2) where aboveground thistle biomass was removed; (3) where above- and below-ground thistle biomass was removed; (4) non-invaded areas in gaps; and, (5) adjacent uninvaded forest edges. In addition, 432 fir seedlings (aged 15 months) were transplanted into four forest gaps within the above treatments and followed for 1 year. Results indicate that invasion of C. arvense negatively affects fir emergence and early survival, and may further contribute to continued balsam fir regeneration failure independent of future moose densities. However, older fir seedlings transplanted into thistle monocultures experienced a positive facilitative effect due to the protection thistle provided against small mammal herbivory. Restoration actions that combine moose density reductions with the planting of fir seedlings offers the most viable long-term strategy to re-establish the native forest canopy in thistle-invaded gaps and would likely lead to the eventual decline of shade-intolerant C. arvense.

The use of gross dental wear in dietary studies of extinct lagomorphs

Studies of paleoenvironments have commonly focused on large mammalian herbivores such as ungulates. Many localities, however, have yielded large numbers of small mammalian herbivores, including lagomorphs and rodents. These fossils represent an untapped paleoecological resource. However, the fossils are often in the form of isolated teeth, and microwear analysis cannot be used due to taphonomic alteration. As a result, we use ungulate gross dental wear as a model. The dental wear features of extant western Canadian lagomorphs are identified and used to create dietary categories that can be applied to make predictions about the diets of extinct forms. The Horse Local Fauna of the Cypress Hills Formation of Saskatchewan has yielded approximately 2,500 fossil specimens, of which nearly 300 are lagomorphs. Two leporid species (rabbits and hares) are present in the Horse Local Fauna, Palaeolagus temnodon and Megalagus brachyodon. Qualitative analysis of the gross dental wear of the lagomorphs of the Horse Local Fauna indicates that M. brachyodon was mainly folivorous and P. temnodon was primarily frugivorous, suggesting that the contemporaneous ecosystem was tree dominated. Gross dental wear analysis allows the use of small herbivores and isolated teeth in paleoecological studies. Studying the diets of small herbivorous mammals will allow more nearly complete reconstructions of past environments and will become increasingly important as more detailed reconstructions are required by paleontologists.