Small mammal populations of an agroecosystem in the Atlantic Forest domain, southeastern Brazil.

This study reports 2 years of the population dynamics and reproduction of a small mammal community using the removal method. The study was conducted in a rural area of the Atlantic Forest, in Sumidouro, Rio de Janeiro State, Brazil. The population sizes, age structure and reproduction were studied for the four most common species in the study area. The overall diversity was 1.67 and ranged between 0.8 to 1.67. The species richness was 13 considering the whole study. The most abundant species were the rodents Nectomys squamipes (n = 133), Akodon cursor (n = 74), Oligoryzomys nigripes (n = 25) and the marsupials Didelphis aurita (n = 58) and Philander frenatus (n = 50). Seven other rodents were captured once: Necromys lasiurus, Akodon montensis, Sooretamys angouya, Oecomys catherine, Oxymycterus judex, Euryzygomatomys spinosus and Trinomys iheringi. There were higher peaks for diversity and species richness during the winter (dry) months, probably due to higher food availability. The marsupials had a seasonal reproduction with highest population sizes at the end of the rainy seasons. Nectomys squamipes reproduced mostly during rainy periods. Akodon cursor reproduced predominantly in the winter with the highest population peaks occurring during this season. The analysis of the population dynamics of the rodent species indicated that no species behaved as an agricultural pest, probably due to the heterogeneous landscape of high rotativity of vegetable cultivation. Rodent populations were more susceptible to the removal procedure than marsupial ones.     

Small mammal abundance in relation to microhabitat in a dry sub-humid grassland in Kenya

Six species of rodents and two species of insectivores, live-trapped on a 1 ha grid over a 27 month period, were studied in relation to microhabitat factors in a dry sub-humid grassland in Kenya. Wet season peaks of small mammal species were followed by low numbers trapped during the dry seasons. Species distributions were correlated with different microhabitat parameters, and the separation of species with apparently similar environmental requirements could be explained largely in terms of current knowledge of the biology of the species. Correlation analyses indicated an ecological separation of two closely-related Mus species and of two Crocidura shrews. Overlap indices were extremely high, ranging from 0.556 to 0.877 for all combinations of pairs of species. It seems likely that neither food nor micro-habitat partitioning completely explains the coexistence of the small mammal species and it is suggested that populations are highly transient, moving from refuge areas into temporarily favourable areas during the wet season.     

Small mammal assemblages in a disturbed tropical landscape at Pozuzo,Peru

Deforestation in the Peruvian pre-montane forests has increased alarmingly in recent years. Particularly, fragmentation in these forests takes place against a background of very extensive continuous forest. Until now, no studies have detailed how Peruvian small mammals responded to forest fragmentation. In this paper, we report the results of an assessment of nonvolant small mammal fauna in forest remnants (one large fragment and one small fragment) and cattle pasture in a disturbed landscape at Pozuzo, formerly a pre-montane tropical forest in central Peru. In each forest remnant, we quantify habitat parameters and identified small mammals to know if there is a relationship between forest remnant size or microhabitat structure and small mammal assemblages. In addition, we investigated the influence of habitat structure on the presence of small mammal species. We did not find any evidence that habitat structure in large fragment was greater than small fragment. Actually, both forest remnants presented habitat features typical of forests subject to higher levels of disturbance. We found that abundance of small trees (10 - 19 cm DBH) was positively associated with the presence of Marmosops noctivagus, but negatively with the presence of Oecomys bicolor. Likewise, the presence of the arboreal Rhipidomys leucodactylus was associated with the abundance of larger trees (DBH > 50 cm). We recorded 12 small mammal species in large fragment, 9 in small fragment and 3 in cattle pasture. No significant differences were found in species richness between both fragments, but marsupial abundance in the small fragment was greater than large fragment. At Pozuzo, we recorded 9 species restricted to forest habitat and 3 to forest and cattle pastures. However, it is necessary to assess more fragments to improve our knowledge about species survival in this landscape.     

Linking changes in small mammal communities to ecosystem functions in an agricultural landscape

Global increases in agricultural production have significant implications for biodiversity and ecosystem processes. In southern Africa, sugarcane production has converted native vegetation into agricultural monocultures. We examined functional group abundance along a conservation-agriculture gradient in the Lowveld of Swaziland. We captured small mammals representing 4 functional groups: omnivores, insectivores, granivores, and herbivores and found evidence of distinct changes in small mammal functional groups across the conservation-agriculture boundary. Granivores declined with increasing distance into the sugarcane and were completely absent at 375 m from the boundary while omnivores increased in the sugarcane. Insectivores and herbivores showed no differences between the two land uses; however, during the dry season, there were significantly more insectivores at the conservation-agriculture interface than in the conservation lands. Shifts in small mammal communities have clear implications for ecosystem processes as the removal of granivores from savannah systems can drastically alter vegetative structure and potentially lead to shrub encroachment via reduced levels of seed predation, while abundant omnivorous small mammals can cause significant crop damage and increase the prevalence of vector borne diseases in the environment.     

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.     

Degree of landscape fragmentation influences genetic isolation among populations of a gliding mammal

Forests and woodlands are under continuing pressure from urban and agricultural development. Tree-dependent mammals that rarely venture to the ground are likely to be highly sensitive to forest fragmentation. The Australian squirrel glider (Petaurus norfolcensis) provides an excellent case study to examine genetic (functional) connectivity among populations. It has an extensive range that occurs in a wide band along the east coast. However, its forest and woodland habitat has become greatly reduced in area and is severely fragmented within the southern inland part of the species' range, where it is recognised as threatened. Within central and northern coastal regions, habitat is much more intact and we thus hypothesise that genetic connectivity will be greater in this region than in the south. To test this we employed microsatellite analysis in a molecular population biology approach. Most sampling locations in the highly modified south showed signatures of genetic isolation. In contrast, a high level of genetic connectivity was inferred among most sampled populations in the more intact habitat of the coastal region, with samples collected 1400 km apart having similar genetic cluster membership. Nonetheless, some coastal populations associated with urbanisation and agriculture are genetically isolated, suggesting the historic pattern observed in the south is emerging on the coast. Our study demonstrates that massive landscape changes following European settlement have had substantial impacts on levels of connectivity among squirrel glider populations, as predicted on the basis of the species' ecology. This suggests that landscape planning and management in the south should be focused on restoring habitat connectivity where feasible, while along the coast, existing habitat connectivity must be maintained and recent losses restored. Molecular population biology approaches provide a ready means for identifying fragmentation effects on a species at multiple scales. Such studies are required to examine the generality of our findings for other tree-dependent species.     

Habitat structure and disturbance affect small mammal populations in Mediterranean forests

Habitat structure, the physical arrangement of objects in space, affects animal populations, ecological interactions, species diversity, and ecosystem functioning. Conventional forest management practices that reduce habitat structural complexity are thus under reappraisal, and there are increasing efforts to understand how habitat structure affects functionally important species. We investigate here the effect of habitat structures on small mammal dens and their interactions with widespread antagonistic species (wild boars). Among habitat structures we considered tree dimension (diameter), shrub cover, rock cover, dead wood volume, and stump area. Ground cover with rooting signs measured wild boar disturbance. The number of small mammal dens was related positively to rock cover and tree diameter, and negatively to wild boar disturbance. Additionally, a positive interaction between wild boar disturbance and tree diameter emerged, showing that the effect of big trees on small mammal nesting was more evident with higher levels of disturbance. This study suggests that habitat structures that can be affected by forest management provide effective refuges for functionally important species. The effect of habitat structure on species survival and interactions thus needs to be addressed to understand ecosystem management and functioning.     

The changing relation of landscape patterns and jack pine budworm populations during an outbreak

The influence of landscape patterns on ecological processes is generally acknowledged, but often difficult to quantify. The objective of our study was to quantify the relation of jack pine budworm ( Choristoneura pinus pinus ) population levels to both the abundance of jack pine ( Pinus banksiana ) and of jack pine stand edges in the landscape. The 450 000 ha Pine Barrens region, located in northwestern Wisconsin, USA, experienced a severe jack pine budworm outbreak from 1990 to 1995. We calculated landscape indices on a landcover map derived from Landsat TM satellite imagery. Landscape indices were calculated on circular buffers (0.5, 0.75, 1, 1.5, and 2.5 km radius) centered on 143 budworm population sampling points for which annual budworm counts were available. Edge density was normalized for the proportion of jack pine in the landscape using random maps as a standard. Correlations between landscape patterns and budworm populations varied over time: proportion of jack pine showed strongest positive correlation with budworm population levels up to the peak of the outbreak (1993). Edge density exhibited positive correlation up to the peak of the outbreak, but negative correlation in the subsequent years as the outbreak declined. This may suggest that pollen-bearing male cones, which are more abundant along edges, support higher budworm populations in the initial phase of the outbreak, but stronger predation on budworm along edges subsequently reduces populations. We provide insight into previously inconclusive results on the relation of jack pine budworm population density to jack pine stand edges. The effects of landscape patterns, such as edge density, may vary not only in magnitude, but also in direction, being positive and negative during different phases of an insect outbreak. Therefore, caution should be taken in relating landscape patterns to process at either a single scale or point in time.     

Seasonal regulation in fluctuating small mammal populations: feedback structure and climate

We studied fluctuating populations of six small mammal species in the Appalachian Plateau of Pennsylvania, USA for 20 yr. We analyzed the feedback structure of these species using statistical time series models for spring and autumn abundances. All species showed a seasonal density-dependent structure, and in five of them first-order feedbacks were dominant in winter and summer. Instead, southern red-backed voles ( Clethrionomys gapperi ) showed a different feedback structure during winter and summer. In three species ( C. gapperi , Napaeozapus insignis and Peromyscus maniculatus ), environmental factors were more important during summer, while the opposite pattern was found in Blarina brevicauda and Tamias striatus . Snowfall influenced positively the winter population growth rates of southern red-backed voles, white-footed mice, woodland jumping mice and eastern chipmunks. We found seasonal differences in the effects of the small mammals assemblage on population growth rates of the two Peromyscus species. The common feedback structure between seasons observed in most of the species, particularly among voles and mice, points to a different feedback structure from northern cyclic small mammals. We conclude that a seasonal feedback structure dominated by intra- and inter-specific competitive interactions may be at the basis of the population dynamics of these species.     

High gene flow promotes the genetic homogeneity of arable weed populations at the landscape level

To determine whether weed populations growing in neighbouring fields were genetically isolated, we investigated the genetic contamination of Alopecurus myosuroides populations in organic fields by populations in conventional fields. Herbicide resistance was used as a marker for gene flow to organic populations, which are not under herbicide selective pressure. Organic fields contained on average 74.5% herbicide-resistant plants (80.1% in conventional fields). Identical resistance alleles were found in neighbouring organic and conventional fields. AFLP analysis revealed that populations from organic and conventional fields had similar neutral genetic diversity. Massive pollen flow from conventional fields is likely chiefly responsible for the genetic makeup of A. myosuroides populations from organic fields. Using a demo-genetic model, we propose that demographic collapses of populations due to effective weed control enhance gene flow towards these populations. Fields with a low weed density could act as ‘genetic sinks’ that would facilitate the diffusion of genes from neighbouring, dense weed populations. Populations of allogamous wind-pollinated weed species like A. myosuroides occurring in neighbouring fields are therefore clearly not independent units. Adaptive evolution and management of such weeds should thus be considered on a scale broader than the field.     

农业景观步甲多样性时间格局及其与景观结构的关系

于2009年5-9月在北京密云县采用陷阱法对玉米地、花生地、果园和林地4种生境中步甲群落进行取样,并采用逐步线性回归分析了景观中优势生境类型——玉米地中步甲群落及其捕食性步甲功能群多样性的季节分布,及其与周围100、250和500 m半径范围内景观格局指数的关系.结果表明:不同生境下,8月步甲群落、捕食性步甲类群的个体数和物种数均达到最大;5月玉米地中步甲群落的物种数与取样点100 m半径范围内的景观连接度呈正相关,8月步甲群落个体数和500 m半径范围内的景观连接度呈负相关;5月玉米地中捕食性步甲群落不论是个体数还是物种数均与取样点100 m半径范围内景观连接度呈正相关,而8月捕食性步甲的物种数则与100 m尺度范围内的半自然生境的类型数呈负相关.可见,景观连接度、半自然生境的类型数对步甲及其中捕食性步甲群落动态的关键季节的多样性状况有显著影响,合理规划农田半自然用地类型组成、增加景观连接度可促进步甲群落多样性保护及其害虫生物控制功能的发挥.     

Production efficiency in small mammal populations

Summary The data used to analyse the relationship between production (P) and respiration (R) in small mammals (Grodziski and French 1983) are reanalysed and different conclusions are drawn. Differences in production efficiency cannot be attributed to any particular trophic classe, but in the higher taxonomic categories the murids have higher production effeciency than the rest. However examination of numerous populations of the same species shows that production efficiencies of congeneric species sometimes differ significantly and show differences which exceed those between higher taxa. The same applies to trophic classes. The low slope described for the regression of P on R for Insectivora is due to an aberrant set of data for Sorex araneus. Production efficiency is directly related to litter size in rodents and inversely to survival of adults. This result conflicts with much earlier work and is discussed at length.     

Inner-ear structure in Morganucodon, an early Jurassic mammal

The shapes and dimensions of the cochlear cavities from four petrosals of the genus Morganucoden obtained through sectioning and reconstruction. Morganucodon dates from the early Jurassic and represents many of the earliest known mammal specimens. Each Morganucodon petrosal fossil was embedded in Araldite and shaved with an ultramicrotome to expose the internal structure. Line drawings of the exposed cross-sections were digitized and used to produce three-dimensional reconstructions. The reconstructed Monganucodon cochlear cavities differ from extant mammalian cochleas in several respects: they are uncoiled, shorter in length, and lack the bony lamina which supports the basilar membrane. These three features ar characteristic of extant Aves and Reptilia.     

Small mammal responses to moose supplementary winter feeding

Supplementary feeding of wild large herbivores is a widespread practice in North America and Europe. The presence of feeding stations may have ecological consequences through changes to animal distributions, patterns of herbivory and a net nutrient input into the ecosystem. In Fennoscandia, supplementary feeding of moose in winter (Alces alces) is increasing. Although it has been shown to affect bird communities, its effects on small mammal communities were unknown. Here, we studied the effects of moose supplementary feeding stations on plants and on abundance, reproduction, and biomass of small mammals in years with low and high vole abundance. We sampled small mammals with snap traps and conducted surveys of the field layer vegetation, at varying distances from moose supplemental feeding stations. Due to the vegetation changes induced by feeding stations, abundance of common shrews (Sorex araneus) and Microtus voles were positively affected by long-term moose winter feeding, while bank voles (Myodes glareolus) were not affected. Moose feeding stations did not affect reproduction, individual body mass, or the total biomass of small mammals. Moose winter-feeding stations have impacts on nontarget species, providing islands of preferred grass and forb habitat for Microtus spp. and common shrews, allowing them to penetrate into a matrix of less preferred forest habitat.     

Small mammal responses to pyric successional changes in eucalypt forest

Sixteen 1-ha study plots covering five regeneration stages were simultaneously trapped five times over a 20-month period to provide data on small mammal response to vegetation changes following fire. Areas regenerating after fires from 9 years to 1 month before the investigation were sampled in a uniform open forest on a coastal sand plain. Two types of understorey were recognized: one dominated by true forest shrubs with which Rattus fuscipes, Antechinus stuartii and Sminthopsis murina were associated, and another dominated by heath elements where the addition of Pseudomys novaehollandiae and Mus musculus produced a significantly more diverse small mammal community. The two communities exhibited different responses to post-fire vegetation changes. Rattus fuscipes was the most abundant species and showed a logistic growth in biomass. No resident populations were established in the first 3 years, but a rapid increase in biomass occurred from 3 to 5 years to plateau after 8 years. Regeneration age had the greatest effect on R. fuscipes biomass mediated through the amount of accumulated leaf litter with additional variation being attributed to several vegetation structure variables and plant species diversity. A replacement sequence in time was observed for species reaching their maximum abundance (P. novaehollandiae and/or M. musculus → S. murina → A. stuartii → R. fuscipes) and was interpreted as species occupying stages in the succession when their optimal habitat requirements were fulfilled. These results have important implications for the design of management policies using fire or fire regimes as tools for habitat maintenance or alteration. A mosaic of forest patches of adequate size covering the entire range of seral stages is necessary to meet the optimum requirements of all the above species.     

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.