Extinction and colonization processes in subpopulations of five neotropical small mammal species

We report the extinction and colonization rates of five sympatric small mammal species at a semiarid locality in north central Chile. We provide information based on 6 years of monitoring on how colonization and extinction rates change according to landscape features (slope aspect) and on their relationship to populations size, population variability, and body size. We found that: (1) for all species in the assemblage, extinction rates of subpopulations from equatorial-facing slopes were significantly lower than those in polar-facing slopes, (2) population size was the most important factor determining extinction rates, (3) colonization rates did not vary between slopes, and were affected by population size only in equatorial-facing slopes, and (4) most species had higher extinction than colonization rates. Persistence of the metapopulation system for all five small mammal species appears to be fueled by repeated colonization events.     

The structure and stability of small mammal faunas

Summary I examined questions about the local and global stability and resilience characteristics of six small mammal faunas and their relationship to connectance, average interaction strength, community covariance, and indirect competitive pathways. Community matrices estimated elsewhere were used in the analyses. The faunas had from three to nine species and represented several habitat types. The following properties were observed: (1) all community matrices were globally stable, (2) return rates to equilibrium were generally maximized, and (3) competitive interactions were strictly hierarchical. Global stability resulted from a reduction in connectance with increasing species and not from structural characteristics (i.e., community covariance). Average interaction strength did not change with the number of species in these faunas. Increased resilience was due largely to reduced community covariance. Two of the six faunas showed some evidence for indirect pathways, but this appeared to be artifactual. Randomizations of the original community matrices showed that indirect pathways have a high probability of occurrence. Monte Carlo simulations indicated that the probability of indirect pathways increases with increasing number of species or magnitude of competition. These results bring into question previous observational studies invoking indirect competitive pathways. Communities without indirect pathways have a special linear hierarchical structure. This structure has greater resilience than when indirect pathways are present. The observed patterns in community structure are discussed with regard to current theories of habitat selection.     

Effects of small mammal and invertebrate herbivory on plant species richness and abundance in tallgrass prairie

Summary A factorial field experiment was designed to test the effects of small mammals and above- and below-ground invertebrates on plant species richness and composition in native tallgrass prairie at Konza Prairie Research Natural Area, northeast Kansas. Over a 4-year period, Microtus ochrogaster densities were maintained by live-trapping in fenced plots, and invertebrate levels were reduced using the pesticides carbaryl for above-ground invertebrates and an organophosphate (isofenphos) for belowground invertebrates. ANOVA according to a split-plot design of plant species biomass data harvested in 1984 and 1986 revealed few significant effects of either small mammal densities or pesticide application. Of 54 species harvested from both sample dates, only 10 were significantly affected by either treatment. Analysis of species richness according to 8 life-form classes provided a clearer pattern of response than did biomass either by species or life-form class. For example, numbers of C4 grasses were reduced by increasing small mammal densities, whereas numbers of C4 annual forbs were lowest when above-ground herbivory was reduced. While consumers have been shown to have strong effects on successional communities, the few significant results observed in this study suggests that the manipulated levels of small mammals and insects had few effects on a mature tallgrass prairie.Deceased May, 1986     

Population dynamics of small mammal species in urbanized areas

Population dynamics of small mammals was monitored in urbanized forest ecosystems on a long-term basis. Urban rodent communities had higher densities due to a large proportion of hemisynanthropic species of Apodemus (Sylvemus) genus. It was found that small mammals displayed similar population dynamics in the park-forests in the same type of forest, but the pattern broke down in the city. Urban stress proved to have a stronger influence on the structure and population dynamics of small mammals than site conditions. Transformation of lower plant layers disturbs habitat of some species and creates favorable conditions for others. Increasing species richness and thickness of shrub layer make site conditions more favorable for the wood mouse and the field mouse—species that do not normally inhabit coniferous forests.     

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.     

云南大理人工松林中小兽群落与生态因子的关系

本文比较了云南大理不同年龄的人工松林(5-8年、10-15年、16-20年)中小兽群落的物种多度、多样性和主要小兽的丰富度,研究了小兽与森林栖境因子(乔木的密度、覆盖度和森林底层灌木和草本植物的覆盖度、密度、物种多度)的关系,探讨了小兽群落在中国西南人工森林的演替,以及地表植物和森林覆盖度对小兽群落的影响。研究结果显示,地表植物的物种多度和丰富度随着森林的年龄增长而增大,但是小兽群落的物种多度和多样性随着森林年龄的增长而变小。小兽与森林栖境因子的回归关系显示小兽群落的物种多度和多样性与地表植物(PC1)成负相关关系。小兽群落的优势物种随着森林的年龄有明显的演替。在年龄最小的森林(5-8年)中,大绒鼠(E.miletu)和齐氏姬鼠(A.chevrieri)是优势物种;在10-15年森林齐氏姬鼠(A.chevrieri)和锡金小鼠(M.pahari)是优势物种;在年龄最大的森林(16-20年)中,贝氏树(T.belangeri)和珀氏长吻松鼠(D.pernyi)成为优势物种     

Multivariate palaeoecological analysis of a late quaternary small mammal succession from North Bulgaria

The basic assumption of the analysis is that the stratigraphical change of relative abundance of the small mammal species is a phenomenon due to a certain number of environmental factors. In order to reveal these factors and to make some palaeoclimatic reconstructions the following approaches have been used: 1. Analysis of intrinsic structure of the initial data by using principal component analysis (PCA)—delimitation of recurrent groups of species and ordination of assemblages; 2. Extension backward in time of known ecological preference of taxa, forming a particular recurrent group; 3. Comparison of the results with the analysis of assemblages from “known”; (Holocene) environment. On the basis of ecological appearance of particular recurrent groups it is assumed that the main factors are temperatures and effective moisture. The reconstructed values for these environmental factors obtained on the basis of the Holocene recurrent groups of small mammals shows similarity to the recent climate in the area.     

Non-invasive genetic identification of small mammal species using real-time polymerase chain reaction

DNA identification of non-invasive samples is a potentially useful tool for monitoring small mammal species. Here we describe a novel method for identifying five small mammal species: wood mouse, bank vole, common shrew, pygmy shrew and water shrew. Species-specific real-time polymerase chain reaction primers were designed to amplify fragments of the mitochondrial cytochrome b gene from hair and scat samples. We also amplified nuclear DNA from scats, demonstrating their potential as a source of DNA for population genetic studies.     

Effects of vertebrate predation on a caviomorph rodent,the degu (Octodon degus), in a semiarid thorn scrub community in Chile

The effects of vertebrate predation have been monitored since 1989 on 16 replicated 0.56 ha study plots in a semiarid thorn scrub community in north-central Chile. Using fences of different heights with and without holes and suspended game netting to alter principal predator (foxes and raptors) and large rodent herbivore (Octodon degus) access, four grids each have been assigned to the following treatments: 1) low fencing and holes allowing free access of predators and small mammals; 2) low fencing without holes to exclude degus only; 3) high fencing and netting with holes to exclude predators only; and 4) high fencing and netting without holes to exclude predators and degus. Small mammal population censuses are conducted monthly using mark-recapture techniques. Degu population trends during 1989 and 1990 showed strongly but nonsignificantly lower numbers in control plots during months when densities were characteristically low (September–November) for this seasonally reproductive species; since March 1991, differences have become persistent and increasingly significant. Predators appear to have greater numerical effects when their prey populations are low. Survival times of degus, particularly established adults, were significantly longer in predator exclusion grids during the 2 1/2 years of observation; thus, predation also affects prey population structure.     

Plant and small mammal richness correlate positively in a biodiversity hotspot

Hotspots of biodiversity are important areas in facilitating an understanding of species richness and its maintenance. Herbivores can increase plant richness by reducing dominant plant species thus providing space for subdominant species. As small mammals are abundant in the Succulent Karoo and therefore might affect plant richness by means of herbivory, we tested if this mechanism might exist in the Succulent Karoo in southern Africa, a biodiversity hotspot due to its extraordinary plant richness. At ten ecologically different study sites we measured plant and small mammal richness and diversity and determined 11 abiotic factors including soil composition, altitude and rainfall. We found positive correlations between plant richness and the number of small mammal species. A general linear model revealed that the number of small mammal species was more important than abiotic factors in explaining variation in plant richness. To test whether small mammals might directly influence plant richness, we studied the influence of the bush-Karoo rat Otomys unisulcatus, a central place forager, on the plant community. The immediate surroundings of occupied O. unisulcatus nests showed significantly higher plant richness than control areas. We conclude that small mammals can have a positive effect on plant richness in the Succulent Karoo. While experimental data are needed to support these correlative results, the results of our study indicate that areas of high small mammal richness should be included in conservation programs of the Succulent Karoo.     

On the problem of trap-response types of small mammal populations

1. So far as the population data thus far amassed go, commensal rats in residential habitats are of type II; house mice may be of type I or III in fields but might show type II in residences, and fieral species or subspecies may range from type I to III. Altogether alloresponsive populations seem to be much commoner than the isoresponsive.
2. It is as yet little disclosed to what degree the differentiation of the type is correlated with speciation or subspeciation, even if only a proof that a subspecific population would hold type III as its fixed feature is given. The response types are supposed to be associated with the levels of population shyness. Hence some characters reflected in those may possibly be connected with sexual isolation provoking speciation.
3. Some awkward respects due to the heterogeneous trappability, depending upon the trap-response type, among a mixed population of marked and unmarked animals have been confirmed regarding the methodology for estimating parameters.

     

Paleoenvironment of Ankilitelo Cave (late Holocene, southwestern Madagascar): implications for the extinction of giant lemurs

Following human arrival, Madagascar suffered well-documented megafaunal extinctions and widespread deforestation. Although humans are widely considered to be the primary cause of the extinctions, the relative contributions of climate change and human activities to this ecological transformation remain uncertain. Reconstructing the habitats of the giant lemurs of Madagascar can provide key information for understanding the evolutionary mechanisms involved in their extinction. In this study, I present a faunal analysis of the subfossil assemblage from Ankilitelo Cave, southwestern Madagascar. This assemblage documents the latest known occurrence of five species of extinct giant lemur, in association with abundant well-preserved small mammal remains. I compared the small mammal fauna at Ankilitelo with 27 extant Malagasy mammal communities spanning the range of Madagascar's habitat types. Similarities in species composition between modern communities and Ankilitelo were assessed using cluster analysis. Ecological similarities were examined by assigning each species to dietary, locomotor, activity pattern, and body size categories. Multiple discriminant analysis was then used to classify Ankilitelo relative to modern habitat types in Madagascar, based on the ecological structure of the subfossil fauna. Results indicate that the habitat surrounding Ankilitelo during the late Holocene was similar to the succulent woodlands of modern southwestern Madagascar. This suggests that approximately 500 yr BP, these semi-arid habitats supported a subfossil lemur community that included the highly-suspensory Palaeopropithecus, and deliberate slow-climber Megaladapis, as well as Archaeolemur, Pachylemur, and Daubentonia robusta. In such environments, these giant lemurs would likely have been highly vulnerable to increasing human pressure in southwestern Madagascar.     

Frugivorous butterfly species in tropical forest fragments: correlates of vulnerability to extinction

Insects exhibit a variety of population-level responses to forest fragmentation, ranging from population increase to extinction. However, the biological attributes that underlie differences in extinction vulnerability among insects have been little-studied. Using the frugivorous butterfly community of tropical dry forest in Venezuela, we studied body size, population density and colonization ability as attributes that might underlie the range of responses of insects to forest fragmentation. The study was carried out in a set of forest fragments in the reservoir Lago Guri, formed by the damming of the Caroni River in eastern Venezuela. Results show that larger butterfly species were more vulnerable to extinction from habitat fragments than smaller ones. Rarer species were not more vulnerable to extinction, showing that rarity may not be an important correlate of vulnerability to extinction amongst insects. Contrary to expectation, faster-flying species were more and not less vulnerable to extinction from small habitat fragments. We speculate on the possible reasons for the observed patterns in extinction vulnerability using additional observations on behavioural patterns and larval host plant distributions of some of the butterfly species.     

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.     

Population dynamics of small mammals at Mlawula, Swaziland

Population density, biomass and composition of a small mammal community in an Acacia nigrescens savanna were studied over 12 months from August 2000. The community consisted of Mus minutoides (A. Smith 1834), Mastomys natalensis (A. Smith 1834), Lemniscomys rosalia (Thomas 1904), Crocidura hirta (Peters 1952), Steatomys pratensis (Peters 1846); and on one occasion, Graphiurus murinus (Desmarest 1822) was caught. M. minutoides was the dominant species in the site. Species richness was found to vary significantly with the time of the year. The density of M. minutoides was significantly high in winter and low in the other seasons, the ratio of males to females was found to be equal, and pregnant females were caught from November to May. The biomass of small mammals in the area (also density and numbers) was generally low (mean biomass 212 g ha^?1). The occurrence of new individuals in catches remained high throughout the study, suggesting a high mortality or emigration rate or a combination of the two.     

二郎山小型兽类区系及分布格局

动物种类和数量在不同的山地或同一山地的不同垂直高度有很大的差异,正因如此,国际上和国内的研究者们一直在努力探讨动物在山地的分布规律和产生差异的原因(Merriam et al.,1890;鲍毅新等,1984;Heaney,2001;Rickart,2001;SánchezCordero,2001;张云智等,2002;李义明等,2003;马俊等,2010).横断山是中国最长、最宽和最典型的南北向山系,位于青藏高原东南部,通常为四川、云南两省西部和西藏自治区东部南北向山脉的总称.横断山是全球25个生物多样性热点地区之一,其生物多样性资源极其丰富(Myers et al.,2000).     

Food web structure and climate effects on the dynamics of small mammals and owls in semi-arid Chile

Population dynamics of small mammals and predators in semi-arid Chile is positively correlated with rainfall associated with incursions of El Niño (El Niño Southern Oscillation: ENSO). However, the causal relationships between small mammal fluctuations, predator oscillations, and climatic disturbances are poorly understood. Here, we report time series models for three species of small mammal prey and two species of owl predators. The large differences in population fluctuations between the three small mammal species are related to differences in their respective feedback structures. The analyses reveal that per capita growth rate of the leaf-eared mouse is a decreasing function of log density and of log barn owl abundance together with a positive rainfall effect. In turn, per capita population growth rate ( R -function) of the barn owl is a negative function of log barn owl abundance and a positive function of leaf-eared mouse abundance, suggesting a predator–prey interaction. The dramatic population fluctuations exhibited by leaf-eared mouse ( Phyllotis darwini ) are caused by climate effects coupled with a complex food web architecture.     

The intake responses of three species of leaf-nosed Neotropical bats

Flower-visiting bats encounter nectars that vary in both sugar composition and concentration. Because in the new world, the nectars of bat-pollinated flowers tend to be dominated by hexoses, we predicted that at equicaloric concentrations, bats would ingest higher volumes of hexoses than sucrose-containing nectars. We investigated the intake response of three species of Neotropical bats, Leptonycteris curasoae, Glossophaga soricina and Artibeus jamaicensis, to sugar solutions of varying concentrations (292, 438, 584, 730, 876, and 1,022 mmol L⁻¹) consisting of either sucrose or 1:1 mixtures of glucose and fructose solutions. Bats did not show differences in their intake response to sucrose and 1:1 glucose–fructose solutions, indicating that digestion and absorption in bat intestines are designed under the principle of symmorphosis, in which no step is more limiting than the other. Our results also suggest that, on the basis of energy intake, bats should not prefer hexoses over sucrose. We used a mathematical model that uses the rate of sucrose hydrolysis measured in vitro and the small intestinal volume of bats to predict the rate of nectar intake as a function of sugar concentration. The model was a good predictor of the intake responses of L. curasoae and G. soricina, but not of A. jamaicensis.     

The trophic impact of small mammals in successional grasslands

The habitat use and diets of small mammals inhabiting grassland plots of different successional ages were investigated by live-trapping and faecal analysis over a period of 16 months. The contribution of the major plant life forms and the structural profile of the vegetation of each plot and the availability of insect prey were assessed. The dominant species of small mammal found on each plot were Sorex araneus, S. minutus, Apodemus sylvaticus and Microtus agrestis . Small mammals were most commonly found in the late and mid-successional stages, reflecting the habitat structure and food availability. A wide range of insects and other invertebrates were eaten by all four species and insects formed 50–62% of the animal prey taken. The incidence of certain prey in the diets differed between plots. The daily consumption rate of invertebrates by shrews and mice was estimated at some 6800 prey per ha. The greatest predatory impact came from shews but A. sylvaticus showed increased consumption of invertebrates in spring. The combined predatory impact of the grassland small mammal community on insect populations alone was estimated to average 0.01% per day and is predicted to be greatest in the mid-successional stages.     

Scaling coexistence and assemblage patterns of desert small mammals

Scaling biodiversity patterns has been recognized lately as a very important issue in the search of global processes; however coexistence and assemblage patterns are typically approached at a single spatial scale. Here, we examined coexistence and co-occurrence patterns of desert small mammal communities across different spatial scales in the search of general community patterns. We sampled small mammals in Monte desert (Argentina, South America) for small spatial scales and reviewed published papers from other worldwide deserts for large spatial scale analyses. We used classic community estimators (Shannon, Richness), rank abundance curves and fitting distributions to analyze species coexistence and co-occurrence patterns. Assemblage patterns were analyzed evaluating nestedness across spatial scales and among deserts. Worldwide desert small mammal assemblages are characterized mainly by low species richness and high variation in species composition. The central Monte desert of Argentina showed a consistent assemblage pattern across spatial scales, with a generalist species being the most abundant and widely distributed, accompanied by other subordinate and more narrowly distributed species. All Monte desert communities were significantly nested, with nestedness increasing with scale from patch to regional. Assemblage and coexistence patterns were similar when comparing worldwide deserts despite differences in total richness and faunal singularity. The degree of nestedness varied among worldwide deserts; however all of them showed a consistent nested pattern. Differences in the degree of nestedness could be a result of different regulating factors depending on the desert and scale. These results highlight the importance of including multiscale approaches when dealing with processes that structure desert communities.