Dietary plasticity of black rats (Rattus rattus) and its implications for competition with small native mammals in the Andean temperate rainforest of Chile

Exclusion of small mammals and lagomorphs invasion interact with human-trampling to drive changes in topsoil microbial community structure and function in semiarid Chile

Context Small mammals may traverse the urban fringe and use both natural and anthropogenic resources. In Australia, human commensal black rats (Rattus rattus) and native long-nosed bandicoots (Perameles nasuta) are important tick hosts, which can be found persisting at the urban fringe, leading to human–wildlife conflict. Aims We aimed to (1) determine the relative activity of small mammals in yards and associations with yard attributes, (2) compare activity of black rats and long-nosed bandicoots in bushland with activity in yards and (3) determine the proportion of black rats and long-nosed bandicoots that crossed the urban fringe. We predicted that native bandicoots would be more active in bushland habitats and that black rats would be more active in yards. Methods We used camera trapping in 56 residential yards, 18 of which were paired with adjacent bushland to measure small mammal activity in the two habitats. We recorded yard attributes and examined these associations using generalised linear models. We used isodar analysis to investigate black rat preferences of bushland habitat compared with yards, and we used Rhodamine B baiting to investigate movement at the urban fringe. Key results We found that black rats were the most active small mammal in residential yards and were detected in more yards than other small mammals, followed by bandicoots. Black rat activity was greater in yards adjacent to bushland, but no other yard attributes were associated with black rat and bandicoot activity. Overall, activity tended to be higher in bushland than in yards at paired locations. Conclusions Our findings suggest residential yards likely provide high-quality resources for long-nosed bandicoots. Low rates of movement at the urban fringe (6%), and a preference for bushland at low densities suggests that black rats may be synanthropic rather than commensal, occupying an urban niche but not depending on anthropogenic resources as expected. Implications Residential properties located adjacent to bushland may be exposed to increased black rat activity in yards. Future work should consider how introduced rats may be controlled in bushland to assist urban rat control efforts and avoid non-target impacts. Residential yards are likely to be important habitat for the persistence of long-nosed bandicoots in urban environments.

The black rat, Rattus rattus, is an alien rodent in Australian ecosystems where niche overlap with native small mammals may lead to competition for resources and displacement of native species. In coastal habitats surrounding Jervis Bay in south‐eastern Australia, R. rattus co‐occurs with the native bush rat, Rattus fuscipes, and brown antechinus, Antechinus stuartii. Relative distributions and abundances, and fine‐scale space use suggest invasive and native rodents compete for use of space and habitat. Such competitive interactions were not evident between R. rattus and native A. stuartii, which was negatively influenced more by disturbance to habitat. Differences in rodent communities between spatially separate forests forming the northern and southern peninsulas of Jervis Bay potentially reflect symmetrical competition and differences in competitive outcomes. In southern forests, R. rattus was largely restricted to patches of disturbed forest associated with campgrounds. Competitive interference by native rodent populations inhabiting surrounding intact forests may have so far limited R. rattus colonization of these areas. In northern forests, R. rattus was the predominant rodent irrespective of disturbance, while populations of R. fuscipes were unusually low seemingly due to poor juvenile recruitment. Native individuals avoided areas frequented by adult R. rattus and given that species did not partition use of microhabitats, R. rattus most likely precluded R. fuscipes from suitable habitat and in doing so limited native populations. We discuss how natural disturbance of habitat and human activity have potentially facilitated successful invasion by R. rattus of the northern forests. Studies that manipulate rodent populations are required to support these interpretations of observed patterns.

Summary1. Fire is a major driver of ecosystem structure and function worldwide. It is also widely used as a management tool to achieve conservation goals. A common objective is the maintenance of ‘fire mosaics’ comprising spatially heterogeneous patches of differing fire history. However, it is unclear what properties of fire mosaics most enhance conservation efforts. Here we focus on the spatial and temporal properties of fire‐prone landscapes that influence the distribution of small mammals.2. We surveyed small mammals in 28 landscapes (each 12·6 km²) representing a range of fire histories in the Murray Mallee region (104 000 km²) of semi‐arid Australia. Generalised linear mixed models were used to examine the influence of five landscape properties on the capture rate of individual species and the species richness of native small mammals. We investigated the influence of the proportional extent of fire age‐classes, the diversity of fire age‐classes, the extent of the dominant vegetation type, rainfall history and biogeographic context.3. Three of four study species were associated with the spatial extent of fire age‐classes. Older vegetation was found to provide important habitat for native small mammals. Overall, however, rainfall history and biogeographic context were dominant influences: for example, the species richness of native mammals was positively associated with above‐average rainfall. There was little evidence that the diversity of fire age‐classes influenced either the capture rate of individual species or species richness.4. Synthesis and applications.In fire‐prone environments, habitat availability can change markedly over short time‐scales. Sufficient habitat at a suitable seral stage within the landscape is a key requirement for species conservation. In mallee ecosystems, the retention of older vegetation is recommended to create more desirable fire mosaics for native small mammals. In addition to such spatial properties of mosaics that are amenable to manipulation, an understanding of how ecological processes affect the biota (such as variation in rainfall‐driven productivity) is also essential for informed conservation management.

Effective conservation management requires an understanding of the source and direction of the many interactions that occur within ecological communities. Without this understanding, management interventions such as control or eradication of introduced species can have unexpected and undesirable outcomes. One of the challenges for wildlife managers is to garner relevant information for their site of management. In this paper we describe how images of mammals captured on remote cameras can be used to uncover behavioral interactions that can in turn help to identify and prioritize areas for more explicit research or management. Our cameras were set repeatedly at four sites over three years in Tasmania, Australia, and we used a series of generalized linear mixed models to interpret relative changes in count data of three species of small mammals: the introduced black ratRattus rattus, and the native long‐tailed mousePseudomys higginsiand swamp ratRattus lutreolus velutinus. We also included two potential predators, the introduced feral catFelis catusand the native Tasmanian devilSarcophilus harrisii. We found that counts of the two species of native small mammals were correlated positively with each other, that swamp rats had a negative effect on black rats, and that black rats had a negative effect on the long‐tailed mouse. Devils were important effects in most small mammal models. Despite their effect probably being underestimated by the remote camera survey method, feral cats were included in models for the long‐tailed mouse. On the basis of the inclusion of native and both species of introduced mammals in long‐tailed mouse models, we propose that the long‐tailed mouse is a priority for further research. This research should clarify the competitive dominance and predatory pressure exerted by the black rat and feral cat, respectively, on this species, and also the potential for management of either introduced species to increase the impact of the other. We conclude that remote cameras can help to uncover cryptic or unsuspected interactions within ecological communities, and hence provide an informed basis for developing targeted research questions to increase the effectiveness of wildlife management.

Urbanization has paved the way for the spread of commensal rodents at global scale. However, it is largely unknown how these species use tropical anthropogenic landscapes originally covered with forests and inhabited by diverse small mammal assemblages. We surveyed non-flying small mammals in various urban and suburban habitat types and adjacent forest in the tropical town of Kota Kinabalu in Borneo. We used occupancy and polynomial regression models to determine variation in species occurrences along gradients of land-use intensity. Muller’s sundamys (Sundamys muelleri) was the only native small mammal species found in urban and suburban landscapes with a continuous decrease in occurrence probability from forests to urban habitats. The invasive Asian black rat (Rattus rattus species complex) and the invasive Asian house shrew (Suncus murinus) had the highest occurrence probabilities in habitats of intermediate land-use intensity, but Asian black rats are also likely to occasionally invade forested habitats and occupied urban habitats in sympatry with the Norway rat (Rattus norvegicus). In urban and suburban habitats, fallow land possibly favoured the occurrence of S. muelleri and S. murinus. Other native small mammal species (Muridae, Sciuridae, Tupaiidae) were found only in forested areas. Our study shows that native small mammals found in forest are largely replaced by invasive species in urban and suburban habitats. Due to their occurrence in habitats of various land use intensities, S. muelleri and R. rattus comprise central links between forest wildlife and urban species, an association that is important to consider in studies of parasite and disease transmission dynamics.

The composition of small mammal communities in forest, shrub land, grassland and anthropogenic habitats of the Giritale Nature Reserve of north central Sri Lanka was studied from June 2006 to August 2007 to estimate the abundance and diversity of small mammals inhabiting this nature reserve. Live trapping using Sherman traps and Pitfall traps were adopted to catch the small mammals. A total of 71 individuals representing two orders (Insectivora and Rodentia) and three families (Soricidae, Muridae, Scuridae) was captured. Species recorded included Suncus murinus murinus Linnaeus, 1766 (Common Indian Musk Shrew), Mus cervicolor fulvidiventris Blyth, 1852 (Ceylon Field Mouse), Mus mus culuscastaneus Waterhouse, 1843 (Indian Field Mouse), Mus fernandoni Phillips, 1932 (Ceylon Spiny Mouse), Rattus blanfordi Thomas, 1881 (White Tailed Rat), Funambulus palmarum Linnaeus, 1766 (Indian Palm Squirrel) and Rattus rattus. The species Rattus rattus consisted of two subspecies Rattus attusrattus Linnaeus, 1758 (Common House Rat) and Rattus rattus rufescens Gray, 1837 (Indian House Rat). Highest and lowest abundances were recorded in the grasslands (0.08) and shrub lands(0.01), respectively. Highest diversity index was recorded in anthropogenic habitats (1.62), which included paddy fields, home gardens and buildings, while lowest diversity index was recorded in shrub lands (0.67). The number of small mammals captured was significantly different in the four habitat types (χ2 = 22.69, df = 3, p<0.05). This study, which is the first detailed examination of terrestrial small mammals in a dry zone forest of Sri Lanka, indicated that the Giritale Nature Reserve is home to six species of small mammals. Key words: Abundance, Diversity, Evenness, Nature reserve, Small mammals

Urbanization processes are taking place at a very high rate, especially in Africa. At the same time, a number of small mammal species, be they native or invasive, take advantage of human-induced habitat modifications. They represent commensal communities of organisms that cause a number of inconveniences to humans, including potential reservoirs of zoonotic diseases. We studied via live trapping and habitat characterization such commensal small mammal communities in small villages to large cities of Senegal, to try to understand how the species share this particular space. Seven major species were recorded, with exotic invasive house mice (Mus musculus) and black rats (Rattus rattus) dominating in numbers. The shrew Crocidura olivieri appeared as the main and more widespread native species, while native rodent species (Mastomys natalensis, M. erythroleucus, Arvicanthis niloticus and Praomys daltoni) were less abundant and/or more localized. Habitat preferences, compared between species in terms of room types and characteristics, showed differences among house mice, black rats and M. natalensis especially. Niche (habitat component) breadth and overlap were measured. Among invasive species, the house mouse showed a larger niche breadth than the black rat, and overall, all species displayed high overlap values. Co-occurrence patterns were studied at the global and local scales. The latter show cases of aggregation (between the black rat and native species, for instance) and of segregation (as between the house mouse and the black rat in Tambacounda, or between the black rat and M. natalensis in Kédougou). While updating information on commensal small mammal distribution in Senegal, a country submitted to a dynamic process of invasion by the black rat and the house mouse, we bring original information on how species occupy and share the commensal space, and make predictions on the evolution of these communities in a period of ever-accelerating global changes.

Grassland ecosystems globally are being negatively impacted by changes in climate, disturbance regimes, nutrient flux, and consumer guilds. Changes in the trophic ecology of consumers can substantially influence local resources, contributing to shifting diversity, community turnover, and other processes of ecosystem change. Small mammals are diverse and abundant within grasslands and yet the impact of changing ecosystems on small mammals and the role of these mammals as consumers are still both under‐studied. We assessed small mammal resource use within grassland and woodland vegetation types that have resulted from landscape‐scale experimental disturbance through fire treatments within the tallgrass prairie ecoregion of the North American Great Plains. We predicted that resource use would vary significantly among grassland vs. woodland communities, in turn reducing the role of small mammals in contributing to future maintenance of native prairies. We sampled five dominant species of rodents across three years and multiple habitats. Using stable isotope analysis, we investigated isotopic niche area and overlap to infer variation in diet, both within and among species. Resource use shifted in bivariate isotopic space seasonally but not across years when combining all species and habitats. Inferred spring diet (based on fur samples) was highly diverse and overlapping. Summer isotopic values (based on liver tissue) in woody habitat treatments were narrower and overlapped less than within grassland habitats. Consumers generally shifted from C4herbivory to C3herbivory, or greater omnivory, when analyzing grassland, shrubland, and woodland habitats respectively. Within the tallgrass prairie ecosystem, small mammal populations in herbaceous‐dominated habitats use a broader variety of resources than small mammals in proximate woody‐dominated habitats. As native grasslands experience woody encroachment, small mammal assemblages experience turnover of dominant species and associated changes in diet. Ecosystem changes such as cessation of frequent fire resulting in more woody habitats may include reduced roles by native small mammals as consumers/dispersers/propagators of native grassland plants.

The impacts of invasive predators can be amplified by high densities of invasive prey species. In Australia, hyper abundant rabbit populations lead to high densities of feral cats and correspondingly high impact of cats on native species, especially small mammals. Therefore, it would be expected reducing rabbits could also reduce abundance of cats, and thereby alleviate predation on native small mammals. However, cats might respond to the loss of rabbits by prey-switching to native small mammals, resulting in increased predation on those species. Our aim was to understand the short-term effects of an experimental reduction of rabbit abundance on feral cats and their small-mammal prey in arid South Australia. We reduced the rabbit population in a 37 km2 experimental enclosure by ~ 80%, while monitoring an adjacent unmanipulated area as a control. Cat activity and survival of VHF-collared cats in the enclosure decreased by 40% following the rabbit reduction. Surviving cats increased their consumption of reptiles, birds and invertebrates, but they nevertheless evinced hunger by increased intake of experimentally-supplied sausages. There was no change in either the proportion of cat scats that contained remains of small mammals, or the rate at which video-collared cats were recorded killing small mammals, even though the activity of small mammals declined. Our results demonstrate that individual feral cats prey-switch in response to removal of their primary prey. However, we also show that survival and overall activity of cats decreased, which could result in net, long-term benefits for native prey threatened by cats. Management of feral cats using food lures or baits would also be more effective when introduced prey are scarce, as cats are more likely to eat novel food.

Exotic tree diseases have direct impacts on their host and may have indirect effects on native fauna that rely on host tree species. This paper reports on relative preference for European beech Fagus sylvatica (L.) and sugar maple Acer saccharum (Marsh.) seed to small mammals, the direct impacts of beech bark disease (BBD) on seed production of American beech F. grandifolia (Ehrh.), and indirect impacts of this disease complex on native small mammal fauna in the Upper Peninsula of Michigan. We expected these indirect effects to result from altered seed production in American beech, both in the short and long term. If present, a preference for beech could suggest a mechanism for an indirect impact of BBD on native small mammals. Seed production of infected American beech declined throughout the 3 y of the study, while production of trees in healthy stands varied annually. We found that the abundance of Peromyscus spp. were related to seed crop in the previous autumn but that the presence of the disease complex had no detectable effect on mouse populations. Variation in eastern chipmunk Tamias striatus (L.) population sizes were not explained by variation in seed production, although this species tended to be more abundant where beech was present. Finally, southern red-backed voles Clethrionomys gapperi (Vigors) were present in forests that did not contain American beech, apparently absent from forests with healthy beech, and present in low numbers in BBD-infected forests. We found that granivorous small mammals consistently preferred European beech seed over sugar maple seed. In general, our studies were indicative of limited short term impacts of BBD on small mammals but suggest the possibility of greater impacts in the future. © 2010, American Midland Naturalist.

Because of the relatively undisturbed vegetation and litter conditions they provide, fencerows should be important to nongame wildlife in agricultural areas. To understand the value of non-wooded fencerows to nongame mammals in Kansas, we compared use of prairie-cropland fencerows, grazed native prairie, and cropfields by rodents and shrews in Lincoln and Russell counties in north-central Kansas. Small mammals were assessed in fencerows, cropfields, upland prairie, and limestone breaks prairie using two traplines per habitat during each of seven censuses from July 1981 to July 1983. Total abundance and species richness for native small mammals were high in fencerows (22.5 individuals and 3.8 species per trapline per census) as compared to upland prairie (7.8 individuals and 2.8 species), breaks prairie (17.6 individuals and 2.2 species), and cropfields (17.3 individuals and 2.2 species). Prairie-cropland fencerow, especially fallow cropland, was the preferred habitat (of the four habitats studied) of cotton rats (Sigmodon hispidus), Elliot's short-tailed shrews (Blarina hylophaga), western harvest mice (Reithrodontomys megalotis), and prairie voles (Microtus ochrogaster). Deer mice (Peromyscus maniculatus), the most common of the small mammals, were abundant in fencerows as well as breaks prairie and cropfields, whereas northern grasshopper mice (Onychomys leucogaster) reached their greatest abundance in cropfields and fencerows. The introduced house mouse (Mus musculus) was trapped only in cropfields and fencerows. Results indicate that this prairie-cropland ecotone provides suitable habitat for several native small mammals that are uncommon in upland and breaks prairie in the mixed-grass prairie region of north-central Kansas. Species responding favorably to herbaceous vegetation in prairie-cropland fencerows were likely common in lowland mixed-grass prairie which mostly has been converted to cropland during the last 100-125 years.

Australia has a range of native and introduced large herbivores that could affect the abundance of small mammals through direct and indirect effects. Here we study the relationship between occurrence of the introduced rusa deer (Rusa timorensis) and the native swamp wallaby (Wallabia bicolor), and the abundance of four species of native small mammals in coastal heath vegetation with varying fire history. The abundance of two species, the brown antechinus (Antechinus stuartii) and bush rat (Rattus fuscipes), was related to occurrence of large herbivores and was dependent also on fire history. Abundance of swamp rats (R. lutreolus) and New Holland mice (Pseudomys novaehollandiae) was not related to the occurrence of any of the large herbivores, and did not depend on fire history. At sites burned within the last 9 years, captures of brown antechinus were negatively related to both deer and wallaby occurrence, and captures of bush rats were negatively related to deer occurrence. However, at sites that burned more than 15 years ago, captures of brown antechinus and bush rats were not related to large herbivore occurrence. Overall there was either no relationship, or a negative one, between small mammals and the large herbivores. This mensurative study has demonstrated relationships between deer and wallabies and small mammals, with fire as an additional important factor. From the results of the current study we put forward a series of hypotheses that need to be tested by future experiments.

Small mammals and reptiles were surveyed by trapping in uncropped and cropped parts of two dry lakebeds in semi-arid New South Wales, Australia, in spring 1992 and 1993. Four species of native small mammals (18 individuals) were captured in uncropped parts of the lakebeds, compared with two individuals of one species in cropped parts of the lakebeds. A total of 38 reptiles (seven species) was caught at the uncropped sites compared with 10 individuals (four species) at the cropped sites. Small mammals were absent where the soil was scarified and bare between crop cycles. The habitat requirements of small mammals (particularly Planigale gilesi) and reptiles need to be provided for when cropping lakebeds. The most effective way to do this is to leave wide strips of uncropped soil at the edges of lakebeds, and patches of uncropped country that are connected to the strips, on lakebeds.

In recent decades, motion sensor camera traps have revolutionised wildlife monitoring as a cost-effective strategy requiring less time investment than traditional monitoring methods. While medium-to-large body sized mammals are captured at sufficient resolution to permit confident species identifications, small mammal species (mice, voles, and shrews) are difficult to distinguish in conventional camera trap imagery. Since camera traps represent a potential solution for overcoming spatial and temporal constraints of traditional small mammal survey methodologies (live trapping), novel designs have materialised in recent years to adjust camera traps for observing smaller animals. In this research, we further refined an existing design, the Littlewood box, and investigated the optimal bait strategy to maximise small mammal detections in the Northeast of England within the currently known range of the non-native greater white toothed shrew, Crocidura russula . We found no significant difference in the probability of detection of small mammal species by bait type, but there were greater numbers of captures of shrew species at traps baited with mealworms. We conclude that the use of bait is associated with a greater number of captures for all small mammal species observed compared to non-baited traps. Despite the cameras being deployed in the centre of the known range of C. russula in Britain, this species was present at a lower proportion of sites than native small mammals.