Positive effects of an invasive shrub on aggregation and abundance of a native small rodent (original) (raw)
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Native seed dispersal by rodents is negatively influenced by an invasive shrub
Animal Biodiversity and Conservation, 2021
Refuge–mediated apparent competition is the mechanism by which invasive plants increase pressure on native plants by providing refuge for generalist consumers. In the UK, the invasive Rhododendron ponticum does not provide food for generalist seed consumers like rodents, but evergreen canopy provides refuge from rodent predators, and predation and pilferage risk are key factors affecting rodent foraging and caching behaviour. Here we used a seed removal/ seed fate experiment to understand how invasion by an evergreen shrub can alter seed dispersal, seed fate and early recruitment of native trees. We used seeds of four species, small and wind–dispersed (sycamore maple Acer pseudoplatanus and European ash Fraxinus excelsior) and large and animal–dispersed (pedunculate oak Quercus robur and common hazel Corylus avellana), and monitored seed predation and caching in open woodland, edge habitats, and under Rhododendron. In the open woodland, wind–dispersed seeds had a higher probability ...
NeoBiota, 2020
Monospecific stands of invasive plants can dramatically restructure habitat for fauna, thereby elevating population densities or promoting foraging of consumer species who benefit in the altered habitat. For example, dense stands of invasive plants may protect small mammals from predators, which in turn could increase foraging pressure on seeds that small mammals feed upon. We used a before-after, control-impact experimental design to test whether small mammal capture rates were higher and giving-up densities (GUDs) lower beneath dense stands of Berberis thunbergii, an invasive shrub with a rapidly expanding range throughout eastern North America. Our experimental design included three plot categories: 1) plots heavily invaded by B. thunbergii, 2) control plots lacking invasive shrub cover, and 3) invaded plots where we eradicated B. thunbergii midway through the study. Although our overall small mammal capture rate was low, small mammal captures were 65% higher in B. thunbergii inv...
Ecological Monographs, 2015
Understanding the long-term impacts of invasive mammalian browsers and granivores in mixed forests is difficult due to the many processes potentially affecting the demography of long-lived trees. We constructed individual-based spatially explicit simulation models of two mixed conifer-angiosperm forests, growing on soils of contrasting phosphorus (P) availability, to investigate how browsing by invasive red deer (Cervus elaphus scoticus) and granivory by invasive rodents (primarily house mouse Mus musculus) might alter forest dynamics. Models were parameterized with field data. Seedling growth and survival rates were estimated inside and outside deer exclosures. Seed predation rates were estimated at high and low rodent densities in mast and non-mast seeding years. For the alluvial terrace forest, which grew on P-rich soil, our model contained 15 tree species dominated by angiosperms; our model of the P-poor marine terrace forest contained seven species dominated by conifers. The two forest models were used to explore four 500-year scenarios: deer and rodents present, deer present and rodents absent, deer absent and rodents present, and deer and rodents absent.
LONG-TERM EFFECTS OF RODENT HERBIVORES ON TREE INVASION DYNAMICS ALONG FOREST–FIELD EDGES
Ecology, 2001
Despite many observations of herbivores and granivores influencing the survival of tree seeds and seedlings, the net effects of these consumers on plant succession remain unclear. We used both experimental herbivore manipulations and observations of changes in vegetation cover to evaluate the longer-term impacts of small-mammal herbivores and granivores on woody plant invasion into old fields in New York State. Over a 5-yr period, we manipulated the density of meadow voles (Microtus pennsylvanicus) within partial enclosures replicated at five study sites. Average vole activity in enclosures with high vole density was significantly greater than that in enclosures with low vole density. In contrast, activity of competitively inferior white-footed mice (Peromyscus leucopus) was significantly greater within enclosures designated as low vole density. Colonization by tree seedlings, as well as shrubs and vines, was significantly greater in enclosures under the low vole density treatment. Further, tree seedling abundance was higher in shrub-dominated enclosures with low vole, but high mouse, activity. Five years of contrasting mouse and vole activity within adjacent enclosures revealed that seedling predation by voles had a greater net effect on changes in woody vegetation cover in old fields than did seed predation by mice, despite studies reporting higher rates of seed vs. seedling predation in these areas. We conclude that short-term measures of predation intensity may not accurately predict the longer-term effects of small-mammal herbivores on vegetation dynamics and suggest that voles may be a keystone herbivore in old-field succession.
Restoration Ecology
One potential, unintended ecological consequence accompanying forest restoration is a shift in invasive animal populations, potentially impacting conservation targets. Eighteen years after initial restoration (ungulate exclusion, invasive plant control, and out planting native species) at a 4 ha site on Maui, Hawai'i, we compared invasive rodent communities in a restored native dry forest and adjacent non-native grassland. Quarterly for 1 year, we trapped rodents on three replicate transects (107 rodent traps) in each habitat type for three consecutive nights. While repeated trapping may have reduced the rat (Black rat, Rattus rattus) population in the forest, it did not appear to reduce the mouse (House mouse, Mus musculus) population in the grassland. In unrestored grassland, mouse captures outnumbered rat captures 220:1, with mice averaging 54.9 indiv./night versus rats averaging 0.25 indiv./night. In contrast, in restored native forest, rat captures outnumbered mouse captures by nearly 5:1, averaging 9.0 indiv./night versus 1.9 indiv./night for mice. Therefore, relatively recent native forest restoration increased Black rat abundance and also increased their total biomass in the restored ecosystem 36-fold while reducing House mouse biomass 35-fold. Such a community shift is worrisome because Black rats pose a much greater threat than do mice to native birds and plants, perhaps especially to large-seeded tree species. Land managers should be aware that forest restoration (i.e. converting grassland to native forest) can invoke shifts in invasive rodent populations, potentially favoring Black rats. Without intervention, this shift may pose risks for intended conservation targets and modify future forest restoration trajectories.
Biological Invasions, 2014
The impact of invasive bank vole (Myodes glareolus) and greater white-toothed shrew (Crocidura russula) on indigenous Irish small mammals, varies with season and habitat. We caught bank voles in deciduous woodland, young coniferous plantations and open habitats such as rank grass. The greater white-toothed shrew was absent from deciduous woods and plantations but did use open habitats with low level cover in addition to field margins. Numbers of both invasive species in field margins during summer were higher than in the previous spring. The indigenous wood mouse (Apodemus sylvaticus) and pygmy shrew (Sorex minutus), differed in degrees of negative response to invasive species. Wood mice with bank voles in hedgerows had reduced recruitment and lower peak abundance. This effect was less extreme where both invasive species were present. Wood mice numbers along field margins and open habitats were significantly depressed by the presence of the bank vole with no such effect in deciduous woodland or coniferous plantations. Summer recruitment in pygmy shrews was reduced in hedgerows with bank voles. Where greater white-toothed shrew was present, the pygmy shrew was entirely absent from field margins. Species replacement due to invasive small mammals is occurring in their major habitat i.e. field margins and open habitats where there is good ground cover. Pygmy shrew will probably disappear from these habitats throughout Ireland. Wood mice and possibly pygmy shrew may survive in deciduous woodland and conifer plantations. Mitigation of impacts of invasive species should include expansion of woodland in which native species can survive.
Effects of forest management on density and survival in three forest rodent species
Forest Ecology and Management, 2016
Several studies have shown that small mammal communities are influenced by silvicultural activities, possibly because these affect the quality of wildlife habitats. Previous research mainly focused on community parameters and abundance of target species, however the most robust way to study the impacts of forestry on wildlife is to follow a demographic-response approach. Investigating multiple demographic measurements is essential to understand how populations respond to forest management, nevertheless studies focusing on multiple demographic parameters are lacking. Our analyses targeted individual survival and population density, to understand the demographic mechanisms by which forest management exerts its effects on small mammals. We focused on the populations of Apodemus flavicollis, A. sylvaticus and Myodes glareolus, constituting the guild of forest-and ground-dwelling rodents in central Italy. Populations were monitored for three years in a continuous forest subject to different management practices (mainly coppicing activities and conifer afforestation). We identified four forest management types (three coppice stands logged in different years and a conifer plantation) where we selected 12 sampling areas. We sampled a total of 31,752 trap-nights capturing more than 1350 individuals. We also gathered quantitative data on the amount of trophic and cover resources in each area to better interpret the response of populations to silvicultural activities. For all the three species, coppicing activities had strong positive effects on population density, which were, in some cases, matched by similar effects on individual survival whereas afforestation of conifer plantations negatively affected populations of A. flavicollis and M. glareolus. We found that different types of forest management, such as the recently coppiced stands, did not create high-density sinks but, rather, enhanced the carrying capacity of the habitats by increasing the availability of cover and food resources. On the contrary, the high forest resulted to be less preferred habitat for A. sylvaticus and M. glareolus, possibility due to its lack of food and cover resources. Our analyses encompassing multiple population parameters allowed us to highlight the mechanisms by which forest management affects small mammal populations.
PloS one, 2012
Over the past century, increases in both density and distribution of deer species in the Northern Hemisphere have resulted in major changes in ground flora and undergrowth vegetation of woodland habitats, and consequentially the animal communities that inhabit them. In this study, we tested whether recovery in the vegetative habitat of a woodland due to effective deer management (from a peak of 0.4-1.5 to ,0.17 deer per ha) had translated to the small mammal community as an example of a higher order cascade effect. We compared deer-free exclosures with neighboring open woodland using capture-mark-recapture (CMR) methods to see if the significant difference in bank vole (Myodes glareolus) and wood mouse (Apodemus sylvaticus) numbers between these environments from 2001-2003 persisted in 2010. Using the multi-state Robust Design method in program MARK we found survival and abundance of both voles and mice to be equivalent between the open woodland and the experimental exclosures with no differences in various metrics of population structure (age structure, sex composition, reproductive activity) and individual fitness (weight), although the vole population showed variation both locally and temporally. This suggests that the vegetative habitat -having passed some threshold of complexity due to lowered deer density -has allowed recovery of the small mammal community, although patch dynamics associated with vegetation complexity still remain. We conclude that the response of small mammal communities to environmental disturbance such as intense browsing pressure can be rapidly reversed once the disturbing agent has been removed and the vegetative habitat is allowed to increase in density and complexity, although we encourage caution, as a source/sink dynamic may emerge between old growth patches and the recently disturbed habitat under harsh conditions. Citation: Bush ER, Buesching CD, Slade EM, Macdonald DW (2012) Woodland Recovery after Suppression of Deer: Cascade effects for Small Mammals, Wood Mice (Apodemus sylvaticus) and Bank Voles (Myodes glareolus). PLoS ONE 7(2): e31404.
Effects of Amur honeysuckle invasion and removal on white-footed mice
The Journal of Wildlife Management, 2014
Amur honeysuckle (Lonicera maackii) is an exotic shrub that has invaded many forests throughout the United States. Although effects on native plants and birds have been documented, little is known about the influence of Amur honeysuckle on small mammals. We examined the short-term effects of removing Amur honeysuckle and other exotic shrubs on the abundance of white-footed mice (Peromyscus leucopus; a generalist rodent species found throughout North America), in 6 hardwood forests of Indiana. We cut and removed exotic shrubs from treatment (removal) areas in fall and winter of 2010-2011. We used mark-release-recapture (MRR) methods by trapping mice for 6 nights in the summer of 2010 and 4 nights in the fall of 2010 (before exotic shrub removals), and again during the summer and fall of 2011 (after removals). For both trapping seasons, mean abundance of mice increased from 2010 to 2011 in both removal and reference areas, but the magnitude of increase within removal areas was substantially greater (permutation P 0.05 for removal areas). For the feasible subset of mice, we calculated mean squared distance (MSD) as an index of space use and investigated how environmental variables influenced space use by individuals. For mice captured in the summer, percent cover of leaf litter was the most important predictor (relative variable importance ¼ 0.94) of MSD, whereas canopy cover and mouse abundance were the most important predictors of MSD for mice captured in the fall (canopy cover relative variable importance ¼ 0.71, mouse abundance relative variable importance ¼ 0.74). Our results indicate that management efforts to control the spread of Amur honeysuckle and other exotic shrubs may lead to short-term increases in the abundance of generalist rodents such as white-footed mice. Furthermore, factors such as leaf litter cover, canopy cover, and abundance may influence space use by individual mice within invaded habitats. Ó
Behavioral consequences of plant invasion: an invasive plant alters rodent antipredator behavior
Behavioral Ecology, 2010
Antipredator behavior is an important aspect of predator-prey dynamics and prey survival, and invasive species are becoming an increasing threat to ecosystems worldwide. Although these 2 concepts are frequently connected in terms of invasive predators and naïve prey, other effects of invasive species, such the creation of novel habitats by invasive plants, may also have indirect effects on animal behavior and community dynamics. We used giving-up densities to examine foraging behavior of Peromyscus leucopus in forest habitats that were invaded or uninvaded by the exotic invasive shrub, Lonicera maackii, which forms a novel shrub layer in hickory-oak forests in Missouri. We experimentally manipulated the presence or absence of an artificial cover over foraging trays and predicted that rodents would have less of a preference for artificial cover in invaded sites with high densities of invasive shrub cover. We found that the invasive shrub decreased perceived predation risk, but this effect was contingent on other environmental correlates of predation risk (i.e., clear, moonlit nights) and foraging cost (i.e., warm temperatures). Our results demonstrate that invasive plants can change animal behavior, which may benefit the invasive species by causing apparent competition and promoting further invasion. Our results have implications for further behavioral changes that could affect multiple trophic levels and suggest that plant invasions can have cryptic, interactive effects on animal behavior, aside from their commonly studied effects on other plant species.