Small Mammal Assemblages Research Articles

The taphonomy and palaeoenvironmental implications of the small mammals from Karain Cave, Turkey

The small mammal accumulations in the Pleistocene deposits of Karain Cave are investigated to identify the predators and possible biases in the fossil assemblages. Seven small mammal assemblages are studied in chronological order from two chambers of the cave, the main chamber E and the side chamber B. The lowermost level within the whole sequence is Proto-Charentien, which corresponds to an early stage of the Middle Palaeolithic. The main part of the material belongs to Middle Palaeolithic layers. The most important aspect of the fossil record in the cave is the human occupation without any interruption through the Pleistocene to Holocene. The small mammal fossil evidence in the cave denotes the presence of opportunistic predators throughout the sequence with one exception, and these produce balanced samples of small mammal faunas in the habitat. The lack of bias in the small mammal faunas allow the interpretation of local environments, showing that partial steppe and arid conditions existed during deposition of the lowermost levels of the Middle Palaeolithic in Karain Cave and that these shifted into more temperate and wooded habitat in the upper levels. Evidence from the side chamber indicates some differences, with a more open grassy environment. In the Mediterranean part of Anatolia the temperate and moist conditions in the Middle Palaeolithic were superseded by more arid conditions in the Upper Palaeolithic, followed by a decrease in steppe conditions during the Epi-Palaeolithic period.

Small mammal community structure in West Africa: a meta-analysis using null models

Peer-reviewed studies on the community structure of small mammals (Rodentia and Soricomorpha) from the Gulf of Guinea region of West Africa were reviewed. To detect nonrandom patterns in the various assemblages under study, the original datasets were re-analysed using null models [two independent randomization algorithms (RA) for niche overlap] and Monte Carlo simulations. The total species richness in the countries considered in this review was 45 species for soricomorphs and 101 for rodents, and the studies reviewed here reported data for 53.3% of these soricomorph species and for 76.2% of these rodent species. Nonrandom habitat niche partitioning was rarely observed in both rodents and soricomorphs. Instead, aggregated use of habitat resources was frequently detected in both groups. Forest habitat was generally selected as aggregating resource type by small mammal assemblages. Thus, contrary to expectations, our review revealed little evidence for interspecific competition along the habitat niche axis in West African small mammals. However, it is possible that the aggregated use of the forest resource by small mammal species may be apparent, but that the various species partitioned space at a lower scale, for instance selecting different microhabitats. Interspecific competition appeared to be stronger in altered habitats, as predicted by previous studies on other forest organisms in West Africa. Des études révisées par les pairs sur la structure de la communauté de petits mammifères (Rongeurs et Soricomorphes) de la région du Golfe de Guinée, en Afrique de l’Ouest, ont été relues. Afin de déceler des schémas non aléatoires dans les différents assemblages étudiés, les sets de données originaux ont été analysés de nouveau en utilisant des modèles nuls (deux algorithmes de randomisation indépendants pour le recouvrement des niches) et des simulations de Monte-Carlo. La richesse totale en espèces des pays concernés par cette étude était de 45 espèces de soricomorphes et de 101 espèces de rongeurs, et les études révues ici rapportaient des données pour 53,5% de ces espèces de soricomorphes et pour 76,2% des espèces de rongeurs. On a rarement observé un partage aléatoire des niches de l’habitat, aussi bien pour les soricomorphes que pour les rongeurs. On a, au contraire, souvent décelé une utilisation groupée des ressources de l’habitat dans les deux groupes. L’habitat forestier était généralement choisi comme type de ressources rassembleur par des assemblages de petits mammifères. Donc, contrairement aux attentes, notre revue a révélé qu’il y avait peu de preuves d’une compétition interspécifique sur l’axe « niche de l’habitat » chez les petits mammifères d’Afrique de l’Ouest. Il est pourtant possible que l’utilisation groupée des ressources forestières par des espèces de petits mammifères semble évidente, mais que les différentes espèces se répartissent l’espace à plus petite échelle, par exemple en sélectionnant différents micro-habitats. La compétition interspécifique semble plus forte dans des habitats altérés, comme le prédisaient des études antérieures d’autres organismes forestiers en Afrique de l’Ouest.

Artificial nests as an alternative to studies of arboreal small mammal populations: a five-year study in the Atlantic Forest, Brazil

Despite the great diversity of Brazilian Atlantic forest small mammals, natural history of most species is unknown due to their cryptic and nocturnal habits, but also due to the inadequacy of methods to capture some species, especially those of arboreal habits. A new technique, based on the use of artificial nests (AN) to record arboreal marsupials, is presented. Artificial nests were combined with traditional live traps to study the population ecology of four didelphid marsupial species. After 62 months of monitoring, 119 individuals were recorded 243 times (total success = 5.2%). Only 26 individuals (22%) were recorded by both AN and live trap methods, and two of the four species were never captured by live traps, only by AN. Live traps alone would have provided biased data of the structure of small mammal assemblages, creating artificial tendencies in population dynamics of many species. Detectability estimates based on mark-recapture data could correct bias resulting from the use only live traps, but these estimates require that at least some individuals of each age class or stage are captured. Only the combination of AN and live traps can produce more accurate data on population dynamics and assemblage structure. This study demonstrates that artificial nests represent a new method that should be combined with live traps in studies of small mammal assemblages and populations.

Small-mammals from the Middle Pleistocene layers of the Sima del Elefante (Sierra de Atapuerca, Burgos, northwestern Spain)

The Sima del Elefante site, located in the Sierra de Atapuerca (Burgos, Spain), is an important Pleistocene archaeopalaeontological locality that has been excavated every year since 1996. At least two main infill phases have been identified: a first (TELRU) early Pleistocene phase that has provided a rich faunal assemblage, various stone tools and the earliest human remains from western Europe; and a second phase (TEURU) attributed to the Middle Pleistocene. In this paper, for the first time we present a description of the TEURU small-mammal assemblage and its subsequent biochronological, palaeoenvironmental and palaeoclimatic implications. The small-mammal assemblage is highly diverse and comprises at least 17 species: 3 insectivores (cf. Erinaceus sp., Crocidura sp. and Sorex sp.); 4 chiropters (Rhinolophus ferrumequinum, Rhinolophus gr. euryale-mehelyi, Myotis gr. Myotisoxygnathus and Miniopteurs schreibersii); 9 rodents (Myodes glareolus, Microtus arvalis, Microtus agrestis, Iberomys brecciensis, Terricola cf. atapuerquensis, Arvicola sp., Apodemus sylvaticus, Eliomys quercinus and Allocricetus bursae) and 1 lagomorph (Oryctolagus sp.). Such an association suggests a late Middle Pleistocene age (ca. 250-350 ka), a patchy landscape dominated by humid meadows and woodland areas, and mild climatic conditions. These results are compared with other proxies, such as the herpetofauna, malacofauna, large-mammals and charcoals, providing a new scenario for the climatic and environmental conditions that prevailed during the latest Middle Pleistocene in the Sierra de Atapuerca.

Paleozoogeography of the Wine Mouse (Akodon oenos) & Late Holocene Paleoenvironments in South-Central Mendoza, Argentina

Cranial remains of the wine mouse ( Akodon oenos ) are documented from an archaeological site in south-central Mendoza, Argentina (Agua de La Mula, 35o22' S, 68o15' W), which dates to the end of the late Holocene (1610 ± 60; 1260 ± 60; 1000 ± 50 C 14 yr B.P.). The taxonomic status of this small rodent is currently being assessed, but these remains represent the first fossil record for the morphotaxon A. oenos. The species’ present distribution is restricted to a few records from Mendoza province. Analysis of the remains supports paleoenvironmental reconstruction using the small mammal assemblage recovered from this site. From the late Holocene into modernity temperature decreased and winter precipitation increased, resulting in advance of Patagonian steppe grading with altitude into Monte desert. Holocene climatic conditions may explain the relatively late human occupation of ecologically marginal environments in this region, which probably favored effective human occupation of the Payunia region at sites such as Agua de La Mula between 1600 and 1000 years B.P.

Paleozoogeography of the Wine Mouse (Akodon oenos) & Late Holocene Paleoenvironments in South-Central Mendoza, Argentina

Cranial remains of the wine mouse (Akodon oenos) are documented from an archaeological site in south-central Mendoza, Argentina (Agua de La Mula, 35º22' S, 68º15' W), which dates to the end of the late Holocene (1610 ± 60; 1260 ± 60; 1000 ± 50 C14 yr B.P.). The taxonomic status of this small rodent is currently being assessed, but these remains represent the first fossil record for the morphotaxon A. oenos. The species’ present distribution is restricted to a few records from Mendoza province. Analysis of the remains supports paleoenvironmental reconstruction using the small mammal assemblage recovered from this site. From the late Holocene into modernity temperature decreased and winter precipitation increased, resulting in advance of Patagonian steppe grading with altitude into Monte desert. Holocene climatic conditions may explain the relatively late human occupation of ecologically marginal environments in this region, which probably favored effective human occupation of the Payunia region at sites such as Agua de La Mula between 1600 and 1000 years B.P.

Palaeoenvironmental and palaeoclimatic proxies of the Gorham’s cave small mammal sequence, Gibraltar, southern Iberia

Gorham’s cave is located in the British territory of Gibraltar in the southernmost end of the Iberian Peninsula. The cave was discovered in 1907 and first excavated in the 1950s by John Waechter of the Institute of Archaeology in London. New excavations, which started in 1997, have exposed 18 m of human occupation in the cave, spanning the Late Pleistocene, as well as including brief Phoenician, Carthaginian and Neolithic occupations. The Late Pleistocene levels consist of two Upper Palaeolithic occupations, attributed to the Solutrean and Magdalenian technocomplexes (Level III), and which are dated, by AMS radiocarbon, to between 18,000 and 10,000 years ago. The underlying Mousterian layer (Level IV), dated by AMS radiocarbon to between 23,000 and 33,000 years ago, is separated from Level III by an archaeologically sterile layer, which spans some 4000 years. This paper presents previously unpublished palaeoenvironmental and paleoclimatic reconstructions of Gorham’s cave, during these Pleistocene occupations, using the small mammal assemblage. The small mammal assemblage at Gorham’s cave comprises of at least 12 species: 4 insectivores ( Crocidura russula, Sorex gr. coronatus-araneus, Sorex minutus and Talpa occidentalis); 3 chiropters ( Myotis myotis, Myotis nattereri and Miniopterus schreibersii); and 5 rodents ( Microtus ( Iberomys) cabrerae, Microtus ( Terricola) duodecimcostatus, Arvicola sapidus, Apodemus sylvaticus and Eliomys quercinus). The presence of these small mammal species indicates that the landscape surrounding the Rock of Gibraltar was predominantly an open habitat, with the presence of woodland and water stream meadows, as well as the presence of larger bodies of water. These results are then compared with pollen and charcoal analysis as well as other faunal proxies, such as the herpetofauna, bird and large mammal assemblages, providing an accurate reconstruction of the climatic and environmental conditions that prevailed during the Late Pleistocene in the southernmost of the Iberian Peninsula.

Small mammal remains recovered from two archaeological sites in the middle and lower Negro River valley (Late Holocene, Argentina): Taphonomic issues and paleoenvironmental implications

This paper presents the results of a taphonomic and paleoenvironmental analysis of small mammal remains recovered from the Negro Muerto and Angostura 1 archaeological sites. These sites (ca. 0.5 and 0.95 ka BP, respectively), are located in the middle and lower Negro River valley in northern Patagonia, Argentina. Based upon the presence of several types of evidence (cut marks, bone tools, and thermal alteration), it is proposed that Holochilus brasiliensis and cavies were acumulated by humans. At the Angostura 1 site, some remains also show evidence of having been generated by carnivores (digestion, breakage patterns, and relative skeletal element abundances). This indicates that carnivores (e.g., Puma concolor) could have contributed to the formation of the small mammal assemblages. Other small mammal species recovered at both sites (e.g., Galea leucoblephara, Microcavia australis, Akodon molinae, and Graomys griseoflavus) suggest semi-desert environmental conditions, similar to those found today. The presence of Reithrodon auritus and Oligoryzomys sp. indicate the development of open herbaceous steppe environments in proximity to bodies of water. However, the discovery of H. brasiliensis at both sites, an orizomyine of amphibious habitats and subtropical origin, and which is now absent in the area, suggests warmer and wetter conditions during this period.

Influences of pine plantations on small mammal assemblages of the Patagonian forest-steppe ecotone

The management of forested landscapes for biodiversity conservation is increasingly recognized as an important objective in Argentina. However, pine plantations are being established replacing native pristine or human modified vegetation and there is a lack of information of its impact on biodiversity. To understand the effect of this activity on small mammal assemblages, we compared its composition and abundance in pine plantations and native vegetation dedicated to traditional cattle production and studied the habitat structure that could explain the differences between habitat types. Additionally, we evaluated the role of firebreaks as corridors in forested landscapes. We found lower abundance and fewer species in plantations. Firebreaks showed a lower abundance and number of species than native vegetation, suggesting that they do not function effectively as corridors. Abrothrix longipilis was the most frequently captured species and abundance of this species was best explained by herbaceous cover and shrub richness. Our results suggest that pine plantations negatively impacts small mammal assemblages and that the decline is strongly associated with decreased understory cover and plant species richness. Management practices targeting conservation objectives such as maintaining lower tree densities and retention of native understory could enhance the value of forest plantations as habitat for small mammal species.

Nestedness of small mammal assemblages and role of indicator species in isolated marshland habitats

The concept of nestedness has important role in community ecology of fragmented habitats that measures the order in presence-absence matrices of species in different communities, and the vulnerability of species to habitat change can be quantified. We have been examining the composition of small mammal assemblages of Kis-Balaton Landscape Protection Area since 1999 within the framework of Hungarian Biodiversity Monitoring System Programme. Our basic question was how much the species turnover processes and the water-level increase following bountiful precipitation as a natural disturbance predominate in directing the composition of small mammal assemblages and in the nestedness pattern in human disturbed habitat patches. Our investigation was based on nestedness analysis and the IndVal method. The results of nestedness analysis showed that the small mammal assemblages of the isolated Kis-Balaton marshland habitat patches are ordered contrary to the random pattern and showed nested pattern. The endangered habitat-specialist root vole appeared as an asymmetrical indicator species regarding its optimal habitat patch, and we evaluated it as an idiosyncratic species in the nestedness analysis. These results proved admittedly that the root vole – as a habitat specialist species – is very sensitive to habitat fragmentation and human disturbance, so the pattern of its presence influences considerably the nestedness of small mammal assemblages of the examined marshlands.

Some small mammal fossils of Üçağızlı Cave (Hatay, Turkey)

Small mammal assemblages of Üçağızlı Cave, 2 from the early Upper Paleolithic and 1 from the Epipaleolithic, spanning a period from 41 to 17 kya, are described. The remains are referred to as Chionomys nivalis, Microtus guentheri, Apodemus mystacinus, Apodemus flavicollis, Apodemus witherbyi, Mus macedonicus, Mesocricetus brandti, Glirulus sp., Crocidura sp., Pipistrellus cf. kuhlii, and Myotis sp. The rodent fauna of Üçağızlı suggests the dominance of open country and rocky ground with a woodland component. There does not seem to have been any essential environmental changes during the deposition of these layers. However, the poor sample of the Epipaleolithic hampers environmental conclusions. The rodent assemblages of Üçağızlı contain European, local, and Asiatic elements. All of the rodent taxa from Üçağızlı, except for Glirulus, are also known from the contemporaneous levels of Karain B and the extant fauna of the Hatay region. This shows that the rodent fauna of the eastern Mediterranean has not changed much since the Late Pleistocene.

Preliminary small mammal taphonomy of FLK NW level 20 (Olduvai Gorge, Tanzania)

The Bed-I series of Olduvai Gorge (Tanzania) is a reference site in human evolution, having yielded the holotypes of Paranthropus boisei and Homo habilis, together with manufactured artefacts and abundant large and micro-fauna. Excavations in Olduvai Gorge have been recently resumed, with new aims and new results. This paper presents the results of the taphonomic analysis carried out on a fossil small-mammal assemblage recovered from FLK NW level 20, a layer overlying Tuff C, dated from 1.84 Ma. The analysis provides good evidence of a category 1 predator, most likely a barn owl, as the predator of the bone assemblage. Trampling and sediment compression might influence postdepositional breakage of the bones. This study is especially relevant since previous taphonomic analyses carried out at levels above and below this sample led to inconclusive results due to a low number of fossils ( Fernández-Jalvo et al., 1998). The new sample provides new information to reconstruct the paleoenvironmental context in which early hominins inhabited.

The influence of fire and livestock grazing on the assemblage of non-flying small mammals in grassland-Araucaria Forest ecotones, southern Brazil

Grazing and fire, used in pasture regeneration practices, are inter-related activities in livestock management. Both activities affect habitat characteristics by changing the structure of the herbaceous and shrubby vegetation, reducing their biomass and litter cover. This study evaluated the effect of fire and livestock grazing on the assemblage of non-flying small mammals in grassland-Araucaria forest ecotones in southern Brazil. We compared four areas frequently affected by livestock management with four protected areas. Surveys were carried out in four sampling periods, one in each season of 2004. We captured a total of 325 individuals from 12 species of rodents - Akodon montensis Thomas, 1913, Akodon paranaensis Christoff, Fagundes, Sbalqueiro, Mattevi e Yonenaga-Yassuda, 2000, Akodon sp. 1, Akodon sp. 2 (2n = 34), Brucepattersonius iheringi (Thomas, 1896), Delomys dorsalis (Hensel, 1872), Oligoryzomys flavescens (Waterhouse, 1837), Oligoryzomys nigripes (Olfers, 1818), Oxymycterus nasutus (Waterhouse, 1837), Scapteromys sp. (2n = 34), Sooretamys angouya (Fischer, 1814) and Thaptomys nigrita (Lichtenstein, 1829) - and two species of marsupials - Monodelphis dimidiata (Wagner, 1847) and Philander frenatus (Olfers, 1818) -, in a total effective effort of 5254 traps.day-1. The abundance, biomass and diversity of non-flying small mammals were significantly higher in the protected areas than in those affected by fire and livestock grazing. Species strictly associated with grassland habitats were not found in the impacted area. These results indicate that the presence of herds of domestic ungulates negatively affect the assemblage of non-flying small mammals in grassland and Araucaria forest areas in southern Brazil.

Resource pulses and mammalian dynamics: conceptual models for hummock grasslands and other Australian desert habitats

Resources are produced in pulses in many terrestrial environments, and have important effects on the population dynamics and assemblage structure of animals that consume them. Resource-pulsing is particularly dramatic in Australian desert environments owing to marked spatial and temporal variability in rainfall, and thus primary productivity. Here, we first review how Australia's desert mammals respond to fluctuations in resource production, and evaluate the merits of three currently accepted models (the ecological refuge, predator refuge and fire-mosaic models) as explanations of the observed dynamics. We then integrate elements of these models into a novel state-and-transition model and apply it to well-studied small mammal assemblages that inhabit the vast hummock grassland, or spinifex, landscapes of the continental inland. The model has four states that are defined by differences in species composition and abundance, and eight transitions or processes that prompt shifts from one state to another. Using this model as a template, we construct three further models to explain mammalian dynamics in cracking soil habitats of the Lake Eyre Basin, gibber plains of the Channel Country, and the chenopod shrublands of arid southern Australia. As non-equilibrium concepts that recognise the strongly intermittent nature of resource pulsing in arid Australia, state-and-transition models provide useful descriptors of both spatial and temporal patterns in mammal assemblages. The models should help managers to identify when and where to implement interventions to conserve native mammals, such as control burns, reduced grazing or predator management. The models also should improve understanding of the potential effects of future climate change on mammal assemblages in arid environments in general. We conclude by proposing several tests that could be used to refine the models and guide further research.

Relative impacts of cattle grazing and feral animals on an Australian arid zone reptile and small mammal assemblage

AbstractThe effect of different levels of cattle grazing on an arid Australian small terrestrial mammal and lizard assemblage was assessed in a long‐tem series of cross‐fence comparisons. Cross‐fenced sites were closely matched for edaphic and vegetation characteristics and experienced near identical weather patterns, to ensure that cattle grazing pressure was the principal determinant of any differences in fauna assemblages. In addition, the effects of removal of cattle, cats, foxes and rabbits from three of these long‐term monitoring sites were assessed to determine the relative impacts of cattle grazing and feral animals. Small mammal captures, with the exception of Mus musculus, revealed a significant negative response to cattle grazing pressure but this response was of a considerably lower magnitude than the dramatic increase in rodent captures and species richness within the feral animal‐proof Arid Recovery Reserve. Higher kangaroo numbers in ungrazed controls, compared with treatments grazed by cattle, possibly negated the benefits to small mammals of removing cattle grazing. No reptile species responded significantly to the grazing treatments although reptile richness and captures of geckos and skinks were the lowest and agamid captures were the highest at heavily grazed sites. Nephrurus levis was the only reptile species to increase significantly, while captures of some smaller geckoes declined, within the feral‐proof treatment. Feral predation exerted a more significant effect on most small mammal species than the levels of cattle grazing assessed in this study, yet reptile responses to grazing or feral animals were less apparent and were likely primarily driven by changes in vegetation cover or secondary trophic impacts.

Spatial variation in keystone effects: small mammal diversity associated with black‐tailed prairie dog colonies

Species with extensive geographic ranges may interact with different species assemblages at distant locations, with the result that the nature of the interactions may vary spatially. Black‐tailed prairie dogs Cynomys ludovicianus occur from Canada to Mexico in grasslands of the western Great Plains of North America. Black‐tailed prairie dogs alter vegetation and dig extensive burrow systems that alter grassland habitats for plants and other animal species. These alterations of habitat justify the descriptor “ecological engineer,” and the resulting changes in species composition have earned them status as a keystone species. We examined the impact of black‐tailed prairie dogs on small mammal assemblages by trapping at on‐ and off‐colony locations at eight study areas across the species' geographic range. We posed 2 nested hypotheses: 1) prairie dogs function as a keystone species for other rodent species; and 2) the keystone role varies spatially. Assuming that it does, we asked what are the sources of the variation?Black‐tailed prairie dogs consistently functioned as a keystone species in that there were strong statistically significant differences in community composition on versus off prairie dog colonies across the species range in prairie grassland. Small mammal species composition varied along both latitudinal and longitudinal gradients, and species richness varied from 4 to 11. Assemblages closer together were more similar; such correlations approximately doubled when including only on‐ or off‐colony grids. Black‐tailed prairie dogs had a significant effect on associated rodent assemblages that varied regionally, dependent upon the composition of the local rodent species pool. Over the range of the black‐tailed prairie dog, on‐colony rodent richness and evenness were less variable, and species composition was more consistent than off‐colony assemblages.

Small mammal diversity along an elevational gradient in northern Luzon, Philippines

A faunal survey conducted along an elevational gradient in Balbalasang-Balbalan National Park in northern Luzon Island, Philippines, revealed 15 species of non-flying small mammals. Thirteen, including 1 shrew and 12 murid rodents, are native species endemic to the Philippines, 7 of which are endemic to northern Luzon. Two species are non-native murid rodents that were restricted to disturbed habitats. As seen elsewhere in the Philippines, species richness was greatest in montane and mossy forest habitats at mid to high elevations. Although species-rich, the Balbalasang gradient does not include the full diversity of species known from the Central Cordillera region. Comparative data from sites elsewhere on Luzon reveal that total species richness is a function of local elevation, with more species present in areas with higher mountain peaks. These patterns reflect the fact that diversity of non-flying small mammals is concentrated in highland areas where local assemblages include species that differ in diel activity, spatial habitat use, and diet. Numerically dominant species are members of a single murid clade, and several of these are specialized predators of earthworms. Similarly structured communities in the highlands of Mindanao include species that are only distantly related to those of Luzon. Community convergence is thought to reflect the influence of similar habitat structure, food resource availability, and trophic partitioning in shaping small mammal assemblages.

Intrinsic and extrinsic factors in the dynamics of local small-mammal populations

We studied dynamics of local small-mammal assemblages consisting of shrews, voles, and mice by small-scale snap trapping in each spring and autumn from 1981 to 2006 in southern Finland. Our aim was to search for relative roles of possible regulatory associations within and between species, as well as to find reflections of the effects of large-scale climatic phenomena on local populations. Preceding intraspecific densities had a dominating role in seasonal changes in small-mammal numbers. Their relationships with weather-related factors indicated by the indices of the North Atlantic Oscillation (NAO) were most pronounced during winter. Relationships with the NAO indices, increasing values of which indicate milder weather in the north, were negative in voles but positive in shrews and mice. Spring densities were governed by the largely compensatory effects of the growth rate of the preceding summer and subsequent population decline during winter in the field vole ( Microtus agrestis (L., 1761)) and mice, while the effects of winter decline dominated in shrews. The bank vole ( Myodes glareolus (Schreber, 1780) = Clethrionomys glareolus (Schreber, 1780)) showed decreasing winter decline, which had a considerable positive effect on population densities.

Small-mammal species richness and abundance along a tropical altitudinal gradient: an Australian example

Abstract:This study examined patterns in the species richness and abundance of small non-volant mammals along a tropical altitudinal gradient in north-eastern Australia. We investigated whether a mid-altitudinal peak in diversity was apparent, and if it occurred, whether it was determined by particular environmental conditions. We sampled a small-mammal assemblage at 17 sites distributed along an altitude-environmental gradient from savanna (350 m) to rain-forest vegetation (1000 m). Over four separate occasions (5100 trap-nights) we recorded 17 species of mammal with 416 captures. A positive non-linear relationship between altitude and mammal species richness and abundance was observed, peaking at the 800–900 m range. Many species were distributed across a range of altitudes, while others were strongly associated with particular habitat conditions. There was a distinct reduction in abundance and species richness at low altitudes associated with the less complex vegetation, lower productivity and possible anthropogenic effects. Key findings were: that small-mammal richness peaked towards the summit of the gradient and not at one-half the maximum altitude predicted by the mid-domain effect; contrasting conditions and greatest vegetation juxtaposition had the greatest influence on the patterns recorded; and that local idiosyncratic influences such as habitat factors, land management and historical biogeography are significant.

Species Richness of Nonvolant Small Mammals Along Elevational Gradients in Northwestern Argentina

ABSTRACTThe Nevados del Aconquija (5500 m) and Cumbres Calchaquíes (4600 m) are isolated mountain ranges that contain at least three physiognomic units in their eastern slopes: Neotropical rainforests, Andean grasslands and High Andean Steppes. Despite phytogeographical similarities, the two ranges differ in the amount and spatial distribution of rainfall over the elevation gradient. We studied terrestrial small mammals by direct trapping in two altitudinal transects on the eastern slope of the two mountain ranges. We recorded the changes in richness and species composition, as well as the relationships between species and microhabitats at each altitudinal level. The results show a similar structure of the small mammal assemblage in the two ranges. The largest differences, in terms of species composition, were registered at lower elevation forests, and faunal affinities increased with elevation to the point of finding identical species composition at the top of the mountains. Species richness showed a clear curvilinear pattern with a peak at the upper limit of the forests. Our findings suggest that total rainfall has an important influence on the composition and abundance of small mammal species but apparently not on the species richness along the elevation gradient. The highest values of species richness were observed at the sites where a contact between two different physiognomic units exists. These results indicate that habitat heterogeneity plays an important role in allowing the juxtaposition of small terrestrial mammal assemblages of the highlands and lowlands at a given point, contributing significantly to the considerable diversity of species observed in intermediate altitudinal sites.