Synchrony in small mammal community dynamics across a forested landscape

Long‐term studies at local scales indicate that fluctuations in abundance among trophically similar species are often temporally synchronized. Complementary studies on synchrony across larger spatial extents are less common, as are studies that investigate the subsequent impacts on community dynamics across the landscape. We investigate the impact of species population fluctuations on concordance in community dynamics for the small mammal fauna of the White Mountain National Forest, USA. Hierarchical open population models, which account for imperfect detection, were used to model abundance of the most common species at 108 sites over a three year period. Most species displayed individualistic responses of abundance to forest type and physiographic characteristics. However, among species, we found marked synchrony in population fluctuations across years, regardless of landscape affinities or trophic level. Across the region, this population synchrony led to high within‐year concordance of community composition and aggregate properties (e.g. richness and diversity) independent of forest type and low among‐year similarity in communities, even for years with similar species richness. Results suggest that extrinsic factors primarily drive abundance fluctuations and subsequently community dynamics, although local community assembly may be modified by species dispersal abilities and biotic interactions. Concordant community dynamics across space and over time may impact the stability of regional food webs and ecosystem functions.     

The population dynamics of small rodents in a tropical African grassland

Monthly estimates were obtained of the density of small rodents in tropical grassland in Rwenzori Park, Uganda between April 1972 and September 1973. Of the 12 species of rodents present, the most numerous were Lemniscomys striatus, Lophuromys sikapusi, Mus triton, Mylomys dybowskii and Praomys natalensis . In a live trapping grid estimates were obtained using direct enumeration, numbers caught, Hayne's Lincoln Index and Jolly's method. Monthly estimates ranged between 16·67 and 63·32 animals per hectare. Intensive removal trappings were also undertaken and these gave estimates of 6·45 to 27·24 per hectare. The inconsistency of the two estimates may be accounted for by small microhabitat and vegetational differences.
Breeding occurs in Lemniscomys and Praomys during the wet season whilen Lophuromys it is more extended but nevertheless seasonal. There is considerable evidence of rapid population turnover as the five species examined in detail had a mean duration of residence between two and three months. Few animals were resident for more than eight months.
The monthly standing crop biomass ranged from 672 to 2221 g/ha on the live trapping grid and from 348 to 1126 g/ha on the intensive removal grids. Estimates of net annual production on the live trapping grid rely on a number of assumptions but are nevertheless relatively high ranging from 5897 to 7072 g/ha.
Fires had a significant indirect effect on the composition of the fauna. Mus triton and Lemniscomys increased their numbers in the five months following the burn to levels not previously attained whereas Mylomys and Lophuromys were less frequent during this period. Several species of avian, reptilian and mammalian predators are recorded.     

Fossil record and dynamics of Late Miocene small mammal faunas of the Vienna Basin and adjacent basins,Austria

The Late Miocene small mammal assemblages of the hinterland of Lake Pannon in Austrian Basins are represented by 99 species-level taxa and 30,400 specimens. The fossil-bearing localities can be grouped into eight intervals spanning about three million years from the Early Vallesian to the Middle Turolian. Each time slice is characterised by the occurrence and/or dominance of certain species. The retreat of Lake Pannon is reflected by a distinct diversification. This pattern may be a regional signal due to increasing habitat availability but may also be taphonomically biased due to a rather poor Earliest Vallesian record. Nevertheless, the overall community structure is quite stable throughout the Vallesian and no indication of a Vallesian Crisis can be detected. Instead, a moderate turnover occurs with the onset of the Turolian, reflected by the increasing abundance of xerophilic taxa.     

The predictive accuracy of population viability analysis: a test using data from two small mammal species in a fragmented landscape

This study examines the predictive accuracy of the population viability analysis package, ALEX (Analysis of the Likelihood of EXtinction). ALEX was used to predict the probability of patch occupancy for two species of small native Australian mammals (Antechinus agilis and Rattus fuscipes) among 13 patches of suitable habitat in a matrix of plantation pines (Pinus radiata). The study was retrospective, running each simulation from 1900 until 1997, and the model parameterised without knowledge of the 1997 observed field data of patch occupancy. Predictions were made over eight scenarios for each species, allowing for variation in the amount of dispersal between patches, level of environmental stochasticity, and size of habitat patches. Predicted occupancies were compared to the 1997 field data of patch occupancy using logistic regression, testing H _random, that there was no relationship between observed and predicted occupancy, and H _perfect, that there was a perfect, 1:1 relationship between observed and predicted occupancies. Rejection of H _random and failure to reject H _perfect was taken as a good match between observed and predicted occupancies. Such a match was found for one scenario with R. fuscipes, and no scenarios with A. agilis. In general, patch occupancy was underestimated, with field surveys finding that 9 of the 13 patches were occupied by R. fuscipes and 10 by A. agilis. Nonetheless, PVA predictions were in the right direction, whereby patches predicted to have a high probability of occupancy were generally occupied, and vice versa. A post hoc search over additional scenarios found few scenarios with a better match than the original eight. The results of this study support the notion that PVA is best thought of as a relative, rather than absolute predictor of the consequences of management actions in threatened populations.     

The behavioural ecology and population dynamics of a cryptic ground‐dwelling mammal in an urban Australian landscape

Urbanization results in widespread habitat loss and fragmentation and generally has a negative impact upon native wildlife, in particular ground‐dwelling mammals. The northern brown bandicoot (Isoodon macrourus; Marsupialia: Peramelidae) is one of relatively few native Australian ground‐dwelling mammals that is able to survive within urbanized landscapes. As a consequence of extensive clearing and urban development within the city of Brisbane, bandicoots are now restricted to the mostly small (<10 ha) bushland fragments scattered across the city landscape. Our study examined the behavioural ecology of northern brown bandicoots within habitat fragments located on a major creek‐line, using mark‐recapture population monitoring and radio telemetry. Bandicoots at monitored sites were found to occur at high densities (typically one individual ha^?1), although one‐third of the populations were transient. Radio tracking revealed that bandicoots had relatively small home ranges (mean 1.5 ± 0.2 ha) comprised largely of bushland/grassland with dense, often weed‐infested ground cover. Bandicoots sheltered by day in these densely covered areas and also spent most time foraging there at night, although they occasionally ventured small distances to forage in adjacent maintained parklands and residential lawns. We suggest that introduced tall grasses and other weeds contribute to high habitat quality within riparian habitat fragments and facilitate the persistence of high density populations, comprised of individuals with small home ranges. The generalized dietary and habitat requirements of northern brown bandicoots, as well as a high reproductive output, undoubtedly facilitate the survival of the species in urban habitat fragments. Further research is required on other native mammal species in urbanized landscapes to gain a greater understanding of how best to conserve wildlife in these heavily modified environments.     

Synchrony in brown trout, Salmo trutta, population dynamics: a 'Moran effect' on early-life stages

Synchrony among populations (i.e. spatial covariation in temporal fluctuations of population size or growth rate) is a common feature to many animals. Both large-scale autocorrelated climatic factors (the 'Moran effect') and dispersal between populations are candidates to explain synchrony, although their relative influence is difficult to assess. Only a few investigations have reported patterns of synchrony among freshwater populations, and even fewer directly related these patterns to an environmental variable. In the present study, we analysed the spatio-temporal patterns of fluctuation of 57 brown trout populations widespread across France, each sampled continuously during 5 years. We compared the respective influence of connectivity and stream distance within basins (i.e. that potentially allow a basin-scale dispersal) and environmental factors (hydrological and air temperature variables, available for 37 sites) on the synchrony of brown trout cohort densities (0+, 1+ and adults). A series of Mantel tests revealed that the degree of synchrony was not related to connectivity or stream distance between sites, suggesting no effect of dispersal at the basin-scale. The degree of synchrony among sites for the 0+ fish was significantly related to the degree of hydrological synchrony (based on high flows during the emergence period). For all three age classes, the synchrony in the temperature patterns did not explain synchrony in trout dynamics. Our results allow us to discuss the respective influence of dispersal and climatic factors on the spatio-temporal patterns of trout dynamics at the basin scale.     

Identification of vertebrate scavengers of small mammal carcasses in a forested landscape

We identified vertebrate scavengers of small mammal carcasses at the 780-km² Savannah River Site during the winter of 2000–2001. Rodent carcasses, differing in size and visual conspicuousness, were placed in upland pine forests and bottomland hardwood forests during six 2-week periods. Sixty-two of the 96 carcasses (65%) were removed by vertebrates. With the aid of remote photography, we identified 11 species of scavengers removing carcasses. RaccoonsProcyon lotor, gray foxesUrocyon cinereoargenteus, and feral pigsSus scrofa scavenged most frequently. The mean elapsed time for carcass removal was 5.6 days. The number of carcasses removed by vertebrates did not differ significantly with respect to carcass size, visual conspicuousness, or habitat type; however, air temperature was strongly correlated (positively) with carcass removal. Our study demonstrates that many mammal species are capable of utilizing small carrion items as a food resource, and suggests that scavenging may account for a higher proportion of the diet of some facultative scavengers than is now widely assumed.     

Untangling the roles of fire,grazing and rainfall on small mammal communities in grassland ecosystems

In grassland systems across the globe, ecologists have been attempting to understand the complex role of fire, grazing and rainfall in creating habitat heterogeneity and the consequences of anthropogenic control of these factors on ecosystem integrity and functioning. Using a South African grassland ecosystem as a model, we investigated the impact of fire and grazing pressure on small mammal communities during three differing periods of a rainfall cycle. Over 2 years, 15,203 trap nights revealed 1598 captures of 11 species (nine rodents, one macroscelid and one insectivore). Results highlighted the importance of the interplay between factors and showed that the role of fire, grazing and rainfall in determining small mammal abundance was species-dependant. While no two species were affected by the same environmental variables, grass cover or height was important to 56% of species. Considered independently, high rainfall had a positive influence on small mammal abundance and diversity, although the lag period in population response was species-specific. High grazing negatively affected overall abundance, but specifically in Mastomys coucha; fire alone had little immediate impact on small mammal diversity. Six months after the fire, vegetation cover had recovered to similar levels as unburned areas, although small mammal diversity and richness were higher in burned areas than unburned areas. Grazing levels influenced the rate of vegetation recovery. In conclusion, low-level grazing and burning can help to maintain small mammal biodiversity, if conducted under appropriate rainfall levels. A too high grazing pressure, combined with fire, and/or fire conducted under drought conditions can have a negative impact on small mammal biodiversity. To maintain small mammal diversity in grassland ecosystems, the combined effects of the previous year’s rainfall and existing population level as well as the inhibition of vegetation recovery via grazing pressure need to be taken into consideration before fire management is applied. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synchrony of spatial populations: heterogeneous population dynamics and reddened environmental noise

Many species exhibit widespread spatial synchrony in population fluctuations. This pattern is of great ecological interest and can be a source of concern when a species is rare or endangered. Moran’s theorem suggests that if two (or more) populations sharing a common linear density-dependence in the renewal process are disturbed with correlated noise, they will become synchronized with correlation matching the noise correlation. In this report, correlation of nonidentical populations that are described by linear and stationary autoregressive processes is analyzed. We show that the expected spatial synchrony between two populations can be decomposed into two multiplicative components. One is the demographic component related to the values of the autoregressive coefficients and the noise color. The other is the spatial correlation of the environmental colored noise. The main results are consistent with the predictions of previous experiments and simulations, and the importance of this report is to provide theoretical support.     

The effect of wildfire on population dynamics for two native small mammal species in a coastal heathland in Queensland,Australia

The influences of wildfire through population dynamics and life history for two species of small mammals in a south-east Queensland heathland on Bribie Island are presented. Trapping results provided information on breeding, immigration and movement of Melomys burtoni (Grassland melomys) and Rattus lutreolus (Swamp rat). We first investigated and optimized the design of trapping methodology for producing mark-recapture population estimates to compare two adjacent populations, one of which was subjected to an extensive wildfire during the two year study. We consider how well rodents survive wildfire and whether the immediate impacts of fire or altered habitat have the greatest impact on each species. We found the R. lutreolus population was far more influenced by the fire than the M. burtoni population both immediately after the fire and over 18 months of vegetation recovery.     

A long term study of small mammal populations in a Brazilian agricultural landscape

Long-term monitoring of small mammal populations is very important to understand the variations in temporal abundance on a large time scale, which are related to ecological, economic and epidemiological phenomena. The aim of this study is to monitor the populations of the marsupials Didelphis aurita and Philander frenatus and the rodents Nectomys squamipes, Akodon cursor and Oligorysomys nigripes in a locality of typical Brazilian rural landscape, Sumidouro Municipality, Rio de Janeiro State, Brazil. A mark-recapture study was conducted during five years. We analyzed the population dynamics, the reproduction and age structure of these species. Both marsupials presented higher population sizes in the end of wet period and beginning of the dry period, which can be explained by the seasonal reproduction which begins in the middle of the dry period and ends in the last months of the wet period. N. squamipes reproduced throughout the year but mostly during rainy periods, due to the close association of this rodent to resources found in the water. Higher survivorship and recruitment rates were in the end of the wet season. The rodent A. cursor had an opportunist reproduction, resulting in high turnover rates. Survivorship increased with the effects of the dry periods. O. nigripes showed a clear annual pattern of population cycle with peaks during the dry season. The rodents did not show potential to present outbreaks and become agricultural pests. The annual population cycles of O. nigripes and the unique peak of A. cursor population during five years highlight attention to their importance as wild reservoirs of the hantavirus disease. Their ecological characteristics associated to their opportunistic behavior make these species prone to be good reservoirs of zoonoses.     

Linking small desert mammal distribution to habitat structure in a protected and grazed landscape of the Monte, Argentina

Interpretation of landscape patterns from the perspective of different species allows knowing the way in which they perceive landscape, and how their perception varies with scale. We examined distribution of four small mammal species at different scales over a landscape including protected and grazed areas, and associated species distribution with landscape structure. The study was conducted in the central Monte Desert (Reserve of Ñacuñán). Trap grids were set in both areas at two scales, varying their grain and extent. To determine whether spatial patterns are random, clumped or regular, we used a point pattern analysis. Logistic regressions were performed to relate the presence-absence of small mammals to environmental variables. Intensity of the point pattern was not constant, either in the Reserve or the grazed area. Small mammal abundance exhibited a heterogeneous distribution, and the existence of a first-order effect was detected for all species. No second-order effects were detected, the point pattern was random for all species in both areas. Both areas were differently perceived by rodent species. Habitat structure in both conditions and its variations with scale appear to be important factors affecting distribution patterns.     

Fire,landscape change and models of small mammal habitat suitability at multiple spatial scales

Fire is an important process in many ecosystems, but inappropriate fire regimes can adversely affect biodiversity. We identified a naturally flammable heathy woodland ecosystem where the use of planned fire had increased the extent of older vegetation, and quantified the abundance of two small native mammals in this landscape (silky mouse Pseudomys apodemoides and heath rat P. shortridgei). We defined four time‐since‐fire (TSF) categories representing a 2‐ to 55‐year post‐fire sequence and, on the basis of a habitat accommodation model, predicted that both species would select younger age‐classes over older ones. We also predicted that (i) much of the variance in vegetation structure would remain unexplained by TSF and (ii) statistical models of mammal abundance and occupancy including structural variables as predictors would be better than models including TSF. Pseudomys apodemoides selected 17‐ to 23‐year‐old sites, while there was no evidence that P. shortridgei selected a particular TSF category, findings that were inconsistent with our predictions. In line with our predictions, relatively large portions of the variance in vegetation structure remained unexplained by TSF (adjustedr² for four structural variables: 0.24, 0.29, 0.35 and 0.57), and in three of four cases there was strong evidence that statistical models of mammal abundance and occupancy including structural variables were better than those including TSF. At the site scale (hectares), P. shortridgei abundance was positively related to the cover of dead material at the base of Xanthorrhoea plants and at the trap scale (metres), the trapability of both species was significantly related to vegetation volume at 0–20 cm. Our findings suggest that TSF may not be a good proxy for either vegetation structure or species abundance/occupancy.     

Benefits of habitat restoration to small mammal diversity and abundance in a pastoral agricultural landscape in mid-Wales

Changes in agricultural practice are predicted across the UK following agricultural reform driven by government policy. The suitability of agri-environment schemes for many species is currently debated because limited quantitative data are collected. In order to understand the changes to biodiversity due to agri-environment schemes, there is a need for studies to not just compare biodiversity and species composition in and out of agri-environment areas, but to factor in the influence of temporal habitat changes. In this study, we investigate the suitability of an agri-environment initiative to support and enhance a small mammal fauna among pastoral hill farms in mid-Wales. Grazed and ungrazed woodlands, riparian habitats, and broadleaf plantations, were compared for small mammal abundance and diversity following a trapping study. Mammal diversity was similar across habitats, though abundance varied significantly. A principle component analysis identified that mammal abundance clustered into three main habitat groups separated by seral stage (early, mid, late). No relationship between mammal abundance and stock grazing was found. A canonical correspondence analysis confirmed that vegetation structure was important in explaining the distribution of captures of mammal species across the landscape. The results for habitat type, and habitat context, suggest that a mix of vegetation seral stages, reflecting a varied vegetation structure, is important to maintain small mammal diversity and abundance across the study area. Heterogeneity in structural diversity at the landscape scale is important to maintain a variety of ground-dwelling mammal species, and particularly because trends in countryside surveys show that woodlands are skewed towards late seral stages. Habitat heterogeneity can be maintained because the hill farms neighbour each other, and the farmers co-operate as a group to manage the landscape. Habitat diversity is therefore possible. These results help us to advocate, and anticipate, the benefits of groups of farms within a landscape.     

The interaction of disturbances and small mammal community dynamics in a lowland forest in Belize

1. Three floods (July 2000, August 2002, September 2003) and a hurricane (October 2001) that occurred in a lowland forest in the southern Maya Mountains of Belize presented an opportunity to evaluate the influence of these disturbances on the structure of a small mammal assemblage. 2. Four terrestrial and four primarily scansorial/arboreal species were trapped July 2000-March 2005 in six grids over 14 irregularly spaced trapping periods. 3. Community dynamics were characterized more by changes in species composition than changes in diversity. The dynamics were driven by species-specific variation in abundance, with changes in composition generally, but not exclusively, due to the occurrence or disappearance of species at low abundance. Despite the disturbances, species richness remained relatively constant. Evenness within the assemblage was consistently low, primarily as a result of dominance by one species, Heteromys desmarestianus. 4. Effects of flooding on community structure were direct but relatively brief (< 1 year), and varied with the duration and intensity of flooding. Effects from the hurricane were indirect but long-lasting and strongly related to severely reduced food resources. 5. This study suggests that long-term dynamics in the structure of many animal communities in the tropics often results from interactions between direct and indirect effects of disturbance. It also suggests that community resistance will depend on variation in disturbance type and regime, but resilience will be determined by the life-history characteristics of each species.     

Effects of mammal and insect herbivory on population dynamics of a native Californian thistle, Cirsium occidentale

We explored consequences of spatial and temporal heterogeneity in herbivory on the survival, growth, and reproduction of the Californian native dune thistle, Cirsium occidentale, in coastal and inland sites, for 2 years. We assessed the relative impacts of insect and mammalian herbivores and compared the relative importance of herbivory in coastal and inland habitats and among locations with different microclimates across a coastal dune. Effects of insect and mammalian herbivores were tested with a combination of insecticidal spray and cage exclusion treatments in a factorial experiment at the coastal site. Mammalian herbivores strongly affected the population dynamics of C. occidentale in both years, and their effects were augmented by fungal infection (1991), herbivory by stem-borers (1990) and, to a lesser extent, by insect seed predators in both years. Mammals caused most plant deaths, but the mammal species responsible differed among sites. Rabbit herbivory altered the vegetative growth of coastal thistles and significantly modified other key aspects of Cirsium demography, including growth rate and timing of reproduction. Small, uncaged plants grazed by rabbits took at least 1 year longer to mature than did caged plants. Larvae of Pyrausta subsequalis were the only insects that killed established plants. In 1990 and 1991, the numbers of insects damaging seed heads before dispersal were low, but were sufficient to cause receptacle and seed damage. The number of mature, undamaged seeds (and percent successful seed production) was reduced significantly only for heads infested by fungi near the ocean in 1991: the fungus occurred in 37% of heads and caused a 77% reduction in mature seeds. Received: 21 October 1996 / Accepted: 27 March 1997     

Biotopic distribution, population structure, and some features of small mammal reproduction in Chisinau City

Comparative analysis of species composition, biotopic distribution, population structure, and reproduction of rodents and insectivores in Chisinau City was performed in October?CNovember 2008 (3029 traps days, 715 animals). Sylvaemus sylvaticus appeared to be the most numerous and widely distributed species, the reproductive strategy of which consisted of intense reproduction in the summer. The second most abundant species was Microtus rossiaemeridionalis, which had a different reproductive strategy, with part of its population continuing to reproduce actively in the autumn. Urban woodlands are the most close to natural biotopes by the species composition. The highest number of animals was defined for meadows and gardens. No rodents and insectivores are found on lawns and waste grounds.