Rodent Assemblages Research Articles

A succession of Miocene rodent assemblages from fissure fillings in southern France: palaeoenvironmental interpretation and comparison with Spain

An Early to Late Miocene sequence of rodent assemblages from southern France has been quantitatively studied. The resulting pattern seems very similar to a contemporary sequence from central Spain (Calatayud–Teruel Basin). The fossil mammal-bearing localities are of different types: mainly karst infills in France and localities situated in sedimentary basins in Spain. In order to interpret the fossil record, a comparison has been made between southern France faunas of similar age but collected in karst infills and in basin deposits. There seems to be no difference between the two kinds of faunas and thus there is no indication that karst infills systematically give a picture of drier and more open environments. Both types of localities may give a similar relative abundance of taxa and when differences exist they can be attributed to local conditions. The comparison between southern France and the Calatayud–Teruel Basin (central Spain) shows that: (1) similar trends occurred in the two areas; (2) differences between spectra were more important during the late Early Miocene than during the Middle Miocene; (3) the shift between the late Early Miocene and the Middle Miocene environments in southern France does not seem to be correlated with a general drop in temperatures as inferred from the analysis of central Spain faunas.

Structure of communities of ground‐dwelling animals at the junction of two phytogeographic zones

Changes in the structure of tenebrionid beetle, lizard and rodent communities along the aridity gradient that determines the position of a phytogeographic province boundary were studied to test: (1) whether there are two different species assemblages on either side of the boundary (2) the extent of their differentiation and (3) if they are composed of different or the same faunal elements. Several ordination methods were tested for their capacity to reflect community structure, and discriminant function analysis was selected as the primary method of ordination. Each of the ordination axes reflected a complex environmental gradient. The latter was different for each taxon. The gradient of productivity cross‐cuts ecological space for each animal group in an individual manner. Revealed spatial assemblages of species were related to the level of productivity. There was one assemblage of species at high productivity and one or two assemblages occurred at low productivity in each taxon. The α–diversity curve of rodents changed weakly along the productivity gradient, whereas those of lizard and beetle communities were distinctly unimodal and had maxima near the middle of the gradient. β–diversity curves of rodents had a concave shape, but those of lizard and beetle communities increased from low productivity values to the middle of the gradient and after that weakly declined to the upper (productive) end of the gradient. Seven types of ranges or areographic groups of species were distinguished. Each species assemblage was composed of different faunal elements. Comparison of the results of ecological and areographic analyses demonstrated that two assemblages of rodents and lizards represent different guilds within the same community rather than different communities. The phytogeographic border for these taxa is an ecological rather than a geographical boundary. The difference between the two tenebrionid assemblages appears to be zoogeographical rather than ecological, and coincides with the phytogeographic boundary.

Ctenodactyloid rodent assemblage from Kargil Formation, Ladakh Molasse Group: Age and palaeobiogeographic implications for the Indian subcontinent in the Oligo-Miocene

Two ctenodactyloid rodents, Fallomus razaeFlynn, Jacobs & Cheema and F. ladakhensis nov. sp., arebeing described from the Kargil Formation of the Ladakh Molasse Group of Kargil area. Fallomus (? Chapattimyidae) is considered an endemic offshoot of the South Asian Eocene ctenodactyloid stock. The new species is relatively larger and more hypsodont with an ectostylid borne on a separate pillar. At Kargil, Iberomeryx (= Cryptomeryx) savagei and Lophiomeryx kargilensis were earlier reported and indicate an Upper Oligocene age for the lower part of the Ladakh Molasse Group. Both these taxa show Eurasian affinity. From the upper part of the Ladakh Molasse Group i. e. Pashkyum Formation, Hyoboops palaeindicus is known and indicates a Lower Miocene age for the lower part of the Pashkyum Formation. The fossil vertebrates suggest an age for the Ladakh Molasse Group extending from Upper Oligocene to Middle Miocene. The incisor enamel ultrastructure of Fallomus is multiserial with average inclination of the Hunter Schreger Bands varying between 30°–35°.

Structure and floristics of habitats associated with five rodent species in an agroecosystem in Central Argentina

Microhabitat use for five rodent species (Calomys musculinus, Calomys laucha, Akodon azarae, Oligoryzomys flavescens and Bolomys obscurus) inhabiting agroecosystems of the central Argentine pampa was investigated for 17 months at six mark‐recapture grids. Thirteen vegetation variables were measured along 748 transects at trap stations where rodents were captured and 252 stations where no captures were made. Principal components analysis was used to describe physiognomic differences among crop and post‐harvest habitats, as well as the less‐disturbed borders of crop fields. Multiple logistic regression was used to assess the significance of principal components in predicting the presence of rodent species. Associations of rodents with plant species in border habitats were explored with Two‐Way‐Indicator‐Species Analysis and correspondence analysis.Aerial coverage by vegetation, as well as ground cover by litter, and graminoid species richness, were important variables in predicting the presence of all rodent species, except C. laucha. Vertical vegetation density and maximum height were also important in determining the presence of C. musculinus in soybean fields. Within border habitats, C. laucha was found in lower quality microhabitats (increased bare ground, decreased vegetative cover, and decreased vertical vegetation density) and was associated with the invasive, introduced grass, Cynodon dactylon. C. laucha was restricted to apparently sub‐optimal areas within border habitats during periods of high rodent density. These data indicate subtle differences in rodent‐plant associations among the members of the rodent assemblage and possible competitive exclusion of C. laucha from stable habitats. Calomys musculinus is the principal reservoir for Junin virus, aetiological agent of Argentine haemorrhagic fever. These results have practical implications in helping define the risk of human disease on a fine scale and provide a theoretical basis for reservoir control and risk reduction.

COMMUNITY STRUCTURE OF SHORTGRASS-PRAIRIE RODENTS: COMPETITION OR RISK OF INTRAGUILD PREDATION?

Local assemblages of rodents in northern shortgrass prairie may reflect either predatory or competitive effects of northern grasshopper mice (Onychomys leucogaster) on other species such as deer mice (Peromyscus maniculatus). In an effort to distinguish these two types of effects, during the summer of 1994 I compared abundances, patterns of microhabitat use, and diets of P. maniculatus on four areas of shrub-dominated prairie in north-central Colorado to these characteristics on four similar sites where 0. leucogaster was removed. The abundance of P. maniculatus decreased during the study on both control and removal sites, but the decline was greater on controls, where numbers of 0. leucogaster increased. Declines in the abundance of P. maniculatus on individual study plots were correlated with abundances and recolonization rates of 0. leucogaster. Only 6% of P. maniculatus present on controls during pre-removal trapping were captured 7 wk later, compared to 32% of those initially present on removal sites. Furthermore, changes in the number of P. maniculatus were inversely related to the amount of shrub cover on sites, suggesting that shrubs may have provided refuge from 0. leucogaster, which rarely uses these microhabitats. Analyses of microhabitat use support this assertion; individual P. maniculatus increased their use of shrubs on control sites when 0. leucogaster was abundant, but there were no shifts in microhabitat use on removal sites. The proportions of arthropods in the diets of the two species were similar prior to Onychomys removals, and although P. maniculatus consumed fewer arthropods as the experiment progressed, diets did not differ between control and removal sites. In addition, Ord's kangaroo rats (Dipodomys ordii) increased slightly in number following removals, and western harvest mice (Reithrodon- tomys megalotis) colonized two removal sites. These results suggest that predatory or aggressive interference by 0. leucogaster, rather than exploitative competition, was re- sponsible for the observed changes in abundance and microhabitat use. Risk of aggression or predatory interference therefore may influence the local abundance and distribution of P. maniculatus and other small rodents on areas of shortgrass prairie where habitat char- acteristics permit coexistence.

Taphonomy and palaeoenvironment of the middle Eocene rodent localities of northwestern Himalaya, India

In northwestern Himalaya, the middle Eocene rodents are known from the Upper Subathu Group in Jammu and Kashmir and Himachal Pradesh (India) and from the coeval Kuldana Formation in Pakistan. Most of the localities in these areas represent more or less the same timeframe but their faunal compositions differ considerably and also some of them are lithologically dissimilar. The bone assemblages from some of the productive middle Eocene rodent localities of Jammu and Kashmir were analysed applying the standard techniques of taphonomic data collection and interpretation to reconstruct their taphonomic histories and palaeoenvironment. The petrography of the rodent-bearing matrix was also studied and used in the taphonomic analysis. The analysis has revealed markedly different taphonomic histories for two of the most prolific localities thereby partly explaining the differences in their faunal composition and demonstrating that taphonomy can be an important aid to biostratigraphic interpretations. The East Babbian Gala (EBGL) rodent assemblage was initially accumulated in the mammalian predator scats. For the accumulation of Sindkhatuti (SKL) bone assemblage, the nonpredator agents are held responsible and a catastrophic mortality is indicated. The taphonomic data from West Babbian Gala (WBGL), Chenpur (CPL), Tattapani (TTPL) and Triyath-Barakh Road (TBRL) localities is inadequate to identify with certainty mode of accumulation of their assemblages, which is best ascribed at present to an attritional mortality and fluvial accumulation. The palaeoenvironmental reconstructions suggest fluvio-deltaic conditions at the time of deposition of the rodent-yielding uppermost part of the Subathu Group. They further indicate that the shoreline of the Tethys Sea was close to the site of deposition of the Middle Eocene rodents and other land mammals. These interpretations are supported by other associated vertebrate groups which also include marine mammals, Cetacea.

Predation on Competing Rodent Species: A Simple Explanation of Complex Patterns

We extend a predator-prey model previously parameterized for voles and weasels to two prey species, a 'Microtus' (field vole) type which is competitively superior to but more vulnerable to predation than a 'Clethrionomys' (bank vole) type. The model explains four patterns in the dynamics of multispecies rodent assemblages in Fennoscandia : a predictable shift in the relative abundances of different prey species during one multiannual population cycle ; long-term (supracyclic) variation in relative prey abundances ; an association between the amplitude of population oscillations and the type of the numerically dominant prey species ; and increasing rodent species number with increasing latitude. The model results illustrate the complex and often unexpected behaviour of strongly connected multispecies assemblages, of which the Fennoscandian rodent-predator community is a prime example. Since the mid 1980s, rodent oscillations in many, though not all, parts of northern Fennoscandia have become distinctly less regular (non-cyclic), a change which is reflected in the entire animal community linked to the keystone species, the arvicoline rodents. We demonstrate that such long-term changes in the amplitude and regularity of rodent oscillations are not unexpected in multispecies prey-predator assemblages.

The relationship among diet, alimentary tract morphology, and life history for five species of rodents from the central Argentine pampa

A suite of characters describing digestive tract structure has been hypothesized to reflect the relative degree of specialization of the digestive system of rodent species along a continuum from a proteinaceous diet of seeds and insects to a cellulosic diet of vegetation. Similarity, it has been proposed that life history traits might reflect diet and digestive tract structure, with the most oppurtunistic species consuming the most energy-rich diets of seeds and insects. The five members of the rodent assemblage of agroecosystems of the Argentine pampa were found to be omnivores and varied in the relative proportions of seeds, insects, and vegetation consumed.

The Role of Predation in Shaping the Behavior, Morphology and Community Organization of Desert Rodents

Predation greatly influences many aspects of the ecology of desert rodents, from foraging behaviour to mechanisms of species coexistence to the evolution of specialised morphologies. Using a foraging-theory approach, we examine consequences of predation for assemblages of desert rodents from North America and the Middle East. In particular, we review experimental evidence that examines the influence of predation on foraging costs and foraging behaviour, explore how predation can act to structure communities, and discuss the role that predation may have played in the evolution of bipedal locomotion. Finally, we compare the importance of predation for the evolution of anti-predator behaviours and morphology, for population dynamics, and for community processes, with its magnitude and heterogeneity. In regard to foraging behaviour, desert rodents treat the risk of predation as a cost of foraging. They combine assessments of food and safety to arrive at foraging decisions, exploiting resource patches less intensively in response to increased predatory risk. The cost of predation can be up to 91% of the foraging costs of desert rodents, but the proportion is greater for Middle Eastern rodents than for North American rodents. In regard to community structure, predation can provide the niche axis as well as the necessary tradeoff for species coexistence. Despite the importance of predation in shaping the foraging behaviour of desert rodents, predation may not always influence species coexistence. Predation contributes to species coexistence at sites in the Sonoran and Great Basin deserts. But in the Negev Desert, where predation costs are the greatest, predation does not provide a mechanism of species coexistence. In regard to bipedal locomotion, predation most likely confers superior ability to avoid predators by improving sprint speed and ability to take evasive action, but at the expense of foraging ability in safe microhabitats. The evolution of bipedality will be favoured by situations where the risk of predation is great: the open microhabitat is riskier than the bush, the richest patches are found in the riskiest places, and rich patches are far apart. The magnitude of predatory risk will affect the evolution of anti-predator behaviour and morphologies. However, the importance of predation in community processes is not determined by its magnitude, but by its heterogeneity in time and space relative to the abilities of potentially coexisting species.

Rainforest fragmentation and the structure of small mammal communities in tropical Queensland

There is a dire need to assess the impacts of habitat fragmentation on tropical forest biotas. In 1986–1987 three live-trapping methods were used to census small mammals at 52 sites in fragmented and unfragmented rainforest in NE Queensland, Australia. Forest structural, floristic, edaphic and landscape data from each site were used to assess patterns of microhabitat use in common species. Trapping censuses yielded 5,784 captures of 15 species of rodents or marsupials. Species encountered in modified habitats surrounding fragments usually remained stable or increased in fragments ( Melomys cervinipes, Rattus leucopus, R. fuscipes, Uromys caudimaculatus, Antechinus flavipes, Hydromys chrysogaster), whereas those that avoided these habitats declined or disappeared ( A. stuartii, A. godmani, Hypsiprimnodon moschatus). Fragments were more heavily disturbed within 200–500 m of forest edges, and mammals that favored disturbed forest or edges ( Melomys, R. leucopus, A. flavipes) increased in many fragments. Assemblages of abundant native rodents appeared more intensively structured in fragments than in unfragmented forest, with strong competitive interactions occurring between ecologically similar species in fragments.

Reproductive Characteristics of Rodent Assemblages in Cultivated Regions of Central Argentina

Small mammals were trapped for 2 years at 16 localities on the central-Argentine pampa. Six species ( Akodon azarae, Calomys musculinus, C. laucha, Bolomys obscurus, Oligoryzomys flavescens and Mus musculus ) accounted for >95% of captures. The major breeding season, as assessed by pregnancies, was September or October through April or May. Mild weather in late autumn and winter of the second season resulted in a relatively longer breeding season during the 2nd year of the study. Females of all six species comprised significantly 50% of captures during the height of the breeding season. For most species, there was a negative correlation between embryo size and embryos per pregnancy; females with large embryos were poorly represented. C. musculinus had the longest breeding season; C. musculinus and Mus had the highest number of embryos per pregnancy; the two species of Calomys and Oligoryzomys had the highest percentages of pregnant females during the breeding season. The predominance of animals of smaller mass classes during the winter is thought to represent seasonal weight loss rather than juvenile recruitment.

Evolution of early-middle miocene rodent faunas in relation to long-term palaeoenvironmental changes

Cluster and principal components analyses have been applied to the composite sequence of 59 rodent assemblages from Ramblian to Lower Vallesian deposits in the Daroca-Calamocha area in the Calatayud-Teruel Basin (North Central Spain). The studied record is thought to represent the interval from the late Aquitanian to the end of the Serravallian (i.e. Early to Middle Miocene, from ca. 22-10.5 Ma ago). The quantitative results are interpreted by using individual rodent taxa as environmental indicators, and by extrapolating the predominant adaptive strategies of recent taxonomic groups, which also seem to form natural groups on a demographic scheme (French et al., 1975). A general warming trend starts in the Rambian (Early Miocene) and continues into the Middle Aragonisn (early Middle Miocene). The cooling in the Middle to Late Aragonian boundary interval is correlated to the middle Miocene cooling phase. Another cooling occurred around the Aragonian-Vallesian boundary (late Middle Miocene). We relate a major increase of aridity in the beginning of the Middle Aragonian (ca. 16.5 Ma) to the spread of low biomass vegetation due to intensification of the subtropical belt (Wolfe, 1985). A notable feature around the Early-Middle Aragonian boundary, indicating a major shift of climatic belts, is the reversal of the relationship between our relative temperature and humidity curves: before the reversal we find a positive correlation, after it a negative correlation. Around the Middle to Late Aragonian boundary humidity increased again, and a further increase of humidity is indicated by the earliest Vallesian faunas. Our data suggest that the nature of favoured adaptive strategy amongst rodents is related, in the end, to the degree of climatic humidity.

Regionally Nested Patterns of Species Composition in Granivorous Rodent Assemblages

Many island communities exhibit a highly non- random pattern of species composition in which smaller biotas contain successive subsets of the species in richer ones. Here, we examine the composition of continental communities to see whether this 'nested subset' pattern holds and, if so, to determine its spatial scale and environ- mental correlates. Granivorous rodent assemblages at 202 sites in Great Basin, Mojave, Sonoran and Chihuahuan deserts were analysed collectively. Separate analyses were also conducted on sites within each desert, habitat (desert scrub, desert grassland, sand dunes, shrub-steppe), and on desert-habitat combinations. Nested subset patterns of species composition were found to characterize the entire assemblage of 202 sites, all Great Basin sites, all Sonoran sites, and various habitat groupings of sites within deserts. However, groupings of sites by habitats among deserts did

Rodent communities associated with three traditional agroecosystems in the San Luis Potosi Plateau, Mexico

This paper analyzes the rodent richness and abundance of the farmed, edge and unfarmed areas of three agroecosystems in the San Luis Potosi Plateau, Mexico. These were studied throughout a year, with visits every 2 months. The conclusions generated were: (a) rodent communities of the agroecosystems behaved in agreement with the heterogeneity-diversity and diversity-stability hypotheses; (b) there was no clear edge effect; (c) no strict “farmland species” could be defined and, although the croplands tended to have distinct rodent assemblages, on a regional scale they remained associated with their unfarmed surroundings; (d) only the consideration of multiple factors, all associated with rainfall pattern, could explain rodent community differences.

House Mice (Mus musculus) in Natural and Disturbed Habitats in Kansas

The relative density of house mice (Mus musculus) was <0.05 individuals/trapline (20 stations with 15 m between stations) in mixed-grass prairie, planted grasslands, woodlands, and crop fields in north-central Kansas and in tallgrass prairie and woodlands in eastern Kansas. The only exception was in crop-field fencerows in north-central Kansas (0.29 individuals/trapline). Percent abundance of Mus in the rodent assemblage also was low (<0.5% of all rodents) in grasslands, woodlands, mowed hayfields, and roadside ditches, but not in crop fields (2.6% for a mixture of types of crop fields) or crop-field fencerows (4.1%). Percent abundance varied significantly (P < 0.05) among different types of crop fields with the highest values in alfalfa fields and lowest values in wheat fields. Our observations suggest that Mus is seldom, if ever, common in grasslands and woodlands, and only infrequently common in crop fields such as sorghum fields with bales containing grain during winter.

Lithostratigraphy, biostratigraphy, and geochronology of the Barstow Formation, Mojave Desert, southern California

Lithostratigraphy, biostratigraphy, and geochronology of the Barstow Formation, Mojave Desert, southern California

Small Mammals of Wheat Fields and Fallow Wheat Fields in North-Central Kansas

Small Mammals of Wheat Fields and Fallow Wheat Fields in North-Central Kansas

Comparative studies on the reproductive biology of three species of laboratory bred Australian conilurine rodents (Muridae: Hydromyinae)

The reproductive biological parameters of laboratory bred and maintained individuals from three species of Australian conilurine rodents, Notomys alexis, Pseudomys australis and P. nanus were determined. Considerable' divergence was found in interbirth intervals (indicative of gestation length) in nonsuckling and suckling mothers, litter size, growth rate of pups, age at weaning, and time of sexual maturity in both males and females. It is concluded that selection has been for rapid production and development of young in P. nanus, whereas in P. australis and, especially N. alexis, litter size has been maximized within the constraints of the mammary formula. These data further emphasize the high degree of plasticity of the reproductive system in this assemblage of old endemic murid rodents of Australasia.

Stratigraphic and taxonomic revision of the fossil vole remains (Rodentia, Microtinae) from the Lower Pleistocene deposits of eastern England

We review the fossil microtine rodent assemblages from the Lower Pleistocene deposits in eastern England, consisting mainly of marine sediments of the Norwich Crag and Cromer Forest-bed Formations. Material from 17 localities, including the ‘Weybourne Crag’ of the Norfolk Coast, the inland ‘Norwich Crag’, and the Crag of the north Suffolk coast has been studied. The taxaMimomys pliocaenicus, M.rex, M.blanci, M.newtoni, M.pitymyoides, M .altenburgensisandClethrionomysare recognized.Mimomys pitymyoidesandM.altenburgensisare described for the first time from Britain. The type material ofMimomys reidiandM.newtoniis redescribed, and we show thatM.newtoniMajor 1902 is a senior synonym ofM.hungaricus(Kormos), thus resolving confusion that has existed in the literature. The prior name for the species described by M. A. C. Hinton (Monograph of the voles and lemmings (Microtnae) living and extinct. London: British Museum (Natural History) 1926) asMimomys newtoniappears to beMimomys blancivan der Meulen 1973. No evidence has been found for mixing of faunas of different age at a single horizon or locality. Differences in crown height are demonstrated between samples ofMimomys pliocaenicusfrom different localities, and differences between localities in the presence and absence of various species are tabulated. This evidence combined with current interpretations of the stratigraphy leads us to recognize three faunal groups. Group 1 faunas containMimomys pliocaenicus, M.reidi(type level),M.newtoni(type level),M.pitymyoides, M.blanciandClethrionomys. They come from coastal deposits previously termed ‘Weybourne Crag’ and currently considered to date from Pre-Pastonianato Pastonian. The faunas are clearly later than group 2 faunas, which containMimomys pliocaenicus, M.reidi, M.newtoni(these three species less advanced than in group 1 faunas),M.rexandM.altenburgensis(these two species lacking in group 1 faunas). Group 2 faunas come from inland ‘Norwich Crag’ localities and crags in Suffolk yielding a Chillesford type pollen assemblage, which are currently considered to date from the Bramertonian stage. Group 3 faunas containMimomys pliocaenicus, M.reidiandM.blanciand are from coastal deposits at Covehithe and Easton Bavents associated with Baventian stage clays. The evidence from the microtine rodents confirms the relative position of the Bramertonian and Pre-Pastonianastages, but does not yet allow conclusions to be drawn on the relative age of group 3 faunas or the deposits in which they occur. The fauna of the Pastonian stage still requires clarification, since it is not possible to allocate unambiguously to this stage any of the material described here. The British Lower Pleistocene assemblages are broadly similar to material from Tegelen, The Netherlands (Tiglian TC4-6) and to material from superimposed loess levels at Stranzendorf, Austria. The British assemblages are characterized by the presence ofMimomys pliocaenicusand the absence of species with unrooted teeth, indicating that they belong to theMimomyssuperzone of the biostratigraphic system of A. J. van der Meulen (Quaternaria17, 1-144, 1973) corresponding to the Villanyian stage. On the basis of microtine evidence we suggest limits to the correlation of the Pre-Pastonian and Bramertonian stages with the Netherlands chronostratigraphy. These limits are earlier than suggested by other lines of evidence. Correlation of the Pre-Pastonian with part of the Eburonian and the Bramertonian with part of the Tiglian is thought to merit consideration.

Palaeoenvironmental and palaeobiogeographical significance of the fossil rodent assemblages of Laetoli (Pliocene, Tanzania)

The study of the Laetoli rodent assemblages and comparison with other extant and fossil communities of Africa by different statistical methods provide new palaeoenvironmental and palaeobiogeographical results. Firstly, it is demonstrated that at 3.7 Myr the Laetoli assemblage belonged to a southern savanna domain and that its modern equivalent is the Kalahari rodent fauna (Namibia—South West Africa). Secondly, these analyses show that the rodent faunas from Laetoli, Hadar, Omo Member B and F (Ethiopia) and Olduvai Bed I (Tanzania), all of which are situated in the Rift Valley, are clearly distinct assemblages. Each fauna is characterized by a strong endemism and seems to have evolved independently. A tentative explanation of this observation is proposed by the examination of the structure of the Rift Valley and its evolution during Plio-Pleistocene times. Moreover, the different phases of speciation and migration of the rodent faunas can also be correlated with the tectonic events related to the formation of the Rift Valley.