Population dynamics of large and small mammals

We offer an evaluation of the Caughley and Krebs hypothesis that small mammals are more likely than large mammals to possess intrinsic population regulating mechanisms. Based on the assumption that intrinsic regulation will be manifest via direct density-dependent feedbacks, and extrinsic regulation via delayed density-dependent feedbacks, we fit autoregressive models to 30 time series of abundance for large and small mammals to characterize their dynamics. Delayed feedbacks characterizing extrinsic mechanisms, such as trophic-level interactions, were detected in most time series, including both small and large mammals. Spectral analyses indicated that the effect of such delayed feedbacks on the variability in population growth rates differed with body size, with large mammals exhibiting predominantly reddened and whitened spectra in contrast with predominantly blue spectra for small mammals. Large mammals showed less variance and more stable dynamics than small mammals, consistent with, among other factors, differences in their potential population growth rates. Patterns of population dynamics in small versus large mammals contradicted those predicted by the Caughley and Krebs hypothesis.     

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.     

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.     

Population dynamics of two small cichlid fish species in a tropical man-made lake (Lake Kariba)

The population dynamics of two small cichlid fishes (Pharyngochromis darlingi andPseudocrenilabrus philander) were studied in Lake Kariba, a very large African man-made lake. They are of no economic importance but make up about 14% and 7% respectively of the inshore fish population and are the major components of the diet of fish-eating birds on the lake.P. darlingi isthe larger species (L = 156.5 mm) and is found on both shelving and steep, eroding shores. Its mortality rate differs in each habitat (Z = 0.44 and 0.72 month^–1 respectively), only 0.79% survive for 12 months and its % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamiuaiaac+% cadaqdaaqaaiaadkeaaaaaaa!384D!\[P/\overline B \] ratio is 5.45 (on shelving shores).Ps. philander is smaller (L = 83.9 mm) and is restricted to shelving areas with abundant vegetation. Its monthly mortality rate was high (Z = 7.69), only 0.05% survive to 12 months whilst its % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamiuaiaac+% cadaqdaaqaaiaadkeaaaaaaa!384D!\[P/\overline B \] ratio was very high (7.69). The estimates of growth obtained forP. darlingi differ considerably from those given in an earlier study in Lake Kariba and some possible reasons for this are discussed. In suitable habitats, the combined production of both species could be 40 kg ha^–1 yr^–1 which indicates their potential importance to the ecology of the lake.     

Population dynamics of a generalist rodent in relation to variability in pulsed food resources in a fragmented landscape

1. Pulsed food resources are often considered equivalent in their potential impact on the reproduction and population dynamics of consumers, but differences in the attributes of food pulses and their distribution in the landscape may cause differences in their effects. 2. We tested whether a perishable pulsed resource (periodical cicadas, Magicicada spp.) had similar effects on the population dynamics of a generalist forest rodent, Peromyscus leucopus, as have been reported for a cacheable pulsed resource (acorn mast). 3. Because the availability of periodical cicadas may vary between edge and interior habitat, we also tested whether habitat type (edge vs. interior) and fragment size affected the abundance of cicadas and P. leucopus. 4. Nearly 90% of the variation in the relative population densities of P. leucopus was explained by the variation in the relative densities of periodical cicadas, and fragments with more cicadas tended to have more reproductive female mice and litters. 5. We found more cicadas and more P. leucopus in edge than interior habitat, but no differences in the relative densities of either in relation to fragment size. 6. Data from a non-emergence year revealed no differences other than the presence of periodical cicadas that could explain the 50% higher relative densities of P. leucopus in the emergence year. 7. At the beginning of the emergence of periodical cicadas, the three fragments with the highest numbers of emergence holes had three times more mice than the fragments with the lowest numbers of emergence holes, suggesting that P. leucopus is able to anticipate the emergence of periodical cicadas and increase reproduction prior to the pulse. 8. Hence, despite differences in perishability, seasonal timing and nutritional quality of pulsed food resources in a fragmented landscape, they appear to have similar positive effects on the population dynamics of the generalist rodent, P. leucopus and, in fact, P. leucopus may be able to anticipate resource pulses.     

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.     

How to determine a regional species pool: a study in two Swedish regions

The species pool hypothesis has been proposed as one of the possible explanations for the local species richness of plant communities. For testing and validating this theory, it is of crucial importance to determine the dimension of the regional pool, which is the reservoir of species that are potentially able to exist in a community. The main purpose of this study was to develop and test different methods for the determination of the regional species pool. Two regions in Sweden served as study areas, Öland and Uppland. In both regions, three different vegetation types were treated: dry calcareous grasslands, coastal meadows and deciduous forests. For the determination of the regional pool two main groups of methods are proposed: 1) six ecological approaches, based on Ellenberg species indicator values, and 2) two phytosociological approaches, based on the occurrence of species in different syntaxa in the framework of the Braun-Blanquet system. The different screening methods were tested using Sørensen's index expressing the similarity between the community species pool and the regional species pool. Two types of error were recognized which may result in low index values. For the six ecological methods Sørensen's index values were below 50%. The methods differed considerably from each other in accuracy, due to large differences in errors of both types. The phytosociological methods resulted in higher similarity values of up to almost 70%. The two approaches differed in error type but gave similar results.     

Trophic status of small mammals in the semi-arid Karoo, South Africa

The feeding habits of a community of small mammals from the semi-arid Karoo, South Africa were analysed by microscopic examination of the stomach contents of animals caught during a 13-month snap-trapping study. The community comprised eight rodent species ( Gerbillurus paeba, Mus minutoides, Rhabdomys pumilio, Otomys unisulcatus, Saccostomus campestris, Desmodillus auricularis, Malacothrix typica, Mastomys natalensis ) and a single macroscelid elephant shrew ( Macroscelides proboscideus. ) The rodents were all predominantly herbivorous, while the elephant shrew ate mainly insects. No granivores or omnivores were represented in this community. The results presented here (including the first analysis of the diet of M. typica ) indicate a greater emphasis on herbivory than previously described for these species. Limited dietary overlap was recorded between these species, although some instances of potential dietary competition that deserve further study were identified. The paucity of granivorous small mammals in the semi-arid Karoo contrasts the patterns of trophic specialization for North American and Israeli semi-arid communities, but is similar to that of South American, Australian and other southern African semi-arid communities.     

Geographic and seasonal variability in feeding behaviour of a small herbivorous rodent

Foraging strategies have traditionally been modelled as a result of food selection in response to one factor, as for instance resource availability, deterrent compounds or nutrients. Thus, a trade-off is assumed between plasticity (generalist strategy) and efficiency (specialist strategy). Nevertheless, several studies have demonstrated that animals cope behaviourally with food supply variation. For instance, desert-dwelling rodents partially compensate for nutritional bottlenecks through diet selection. The aim of our study was to test how foraging behaviour matches spatial and temporal variations in the trophic environment and how modelling hypotheses help us to understand the resultant foraging strategy. Our animal study model was the small cavy Microcavia australis, a widely distributed herbivorous rodent. Fieldwork was carried out in four places, in wet and dry seasons. We found significant differences in plant cover, plant diversity and niche breadth, and diet selection revealed a complex foraging strategy. M. australis shows a behavioural repertoire that exceeds single-criterion categories; therefore, we appeal to theoretical models that consider ecological and physiological perspectives. We classified the small cavy as a facultative specialist displaying a thoroughly opportunistic strategy based on the plasticity of the behavioural phenotype. We finally discuss the evolutionary relevance of our results and propose further investigation avenues.     

A comparative study on variability and phylogeny of Triticum species

Summary Interspecific relationship studies between A, S and D genome diploid species, and between AAGG and AABB allotetraploid species of the genus Triticum were conducted using isoenzymatic characters located in dry mature seeds. Data was analyzed by the factorial analysis of correspondences, and dendograms were obtained by two different genetic distances. The discussion of results was based on the limitations of the study, intraspecific variability differences, isoperoxidase frequency differences and chromosomal location of peroxidases in T. aestivum cv. Chinese Spring. The closest relationship was found between dicoccoides and carthlicum. Relationships found between T. turgidum L. and T. timopheevvi Zhuk., both allotetraploid species and boeoticum; this species and speltoides; tauschi and searsii, and the last two species with bicorne, are discussed at the phylogenetic level.     

The Clara cell: a comparative ultrastructural study in mammals.

Clara cells in the terminal bronchoiles of mouse, rat, rabbit, calf and human were compared by light, transmission and scanning microscopy, and species-differences were clearly present. Mouse Clara cells were most numerous and mouse and rabbit Clara cells had large dense mitochondria. Rabbit and calf had glycogen in Clara cells and rat Clara cells had the most variability in secretory granules, some of which had a crystalline structure. Calf Clara cells had deeply indented nuclei. Human Clara cells had the most prominent nucleoli and lacked smooth endoplasmic reticulum, which was a prominent feature of most other species. No evidence of apical extrusion or apocrine secretion of Clara cell secretory granules was observed.     

Space partitioning between two small mammals in a rocky desert

An analysis was made in Augrabies Falls National Park, South Africa of the factors that allow coexistence of two small herbivorous mammals: the rock hyrax Procavia capensis and the dassie rat Petromus typicus. The rocky habitat provides adequate food and living shelters of varying sizes. There appears to be competition for shelters: Petromus occupies only those shelters that are too small for Procavia with the result that the population of Petromus is small and restricted to certain favourable areas whereas Procavia is abundant and widespread.     

Topographic patterns of odorant receptor expression in mammals: a comparative study

In a comparative study, molecular probes for various odorant receptor subtypes were employed in in situ hybridization experiments on tissue sections through the nose from different mammalian species. OR37 reactive neurons were found exclusively in the rodent species, where they were clustered in very similar position within the nasal cavities; an OR37-related receptor subtype was not detectable in the rabbit. All other subtypes tested, hybridized across species borders to neurons that were distributed within distinct zones of the olfactory epithelium. Most receptor types were found in the same zone in all species; however, a few subtypes which are expressed in the medial zone in rat were found in the dorsal zone in guinea pig.     

Reuse potential of agricultural wastes in semi-arid regions: Egypt as a case study

Agricultural wastes represent an important source of bio-energy and valuable products. In Egypt, 18% of the agricultural wastes is used directly as fertiliser. Another 30% is used as animal food. The remainder is burnt directly on the fields or is used for heating in the small villages, using low efficiency burners. These wastes can be used more efficiently as a source of energy and as organic fertiliser. The anaerobic bioconversion of these materials will result in a net energy production. The utilisation of agricultural wastes for the production of energy and compost, combined with using solar energy will save fossil fuel, improve health conditions and the general life quality in the villages. This revised version was published online in June 2006 with corrections to the Cover Date.     

Population dynamics of Panonychus osmanthi (Acari: Tetranychidae) on two Osmanthus species

Panonychus osmanthi is a non-diapausing species of spider mite that superficially resembles P. citri. It infests Osmanthus species, which are evergreen roadside and garden trees. The population dynamics of P. osmanthi were studied on Osmanthus aurantiacus and O.×fortunei during a three-year period. Seasonal changes in P. osmanthi populations were fundamentally the same in each year, although their density differed greatly from year to year. TheP. osmanthi population was bimodal, with one peak in spring (May–June) and another in winter (November–January). Populations abruptly declined after the spring peak. Predators showed a delayed density-dependent response to changes in spider mites from spring to summer, whereas in autumn and winter, predators were few because they had entered diapause. To determine the effect of predators on the rapid decline of spider mites just after the spring peak, the predators were removed by treating the trees with a synthetic pyrethroid. As a result, spider mite density did not decline after the spring peak and remained at a high level during the June-August period when spider mite density is usually very low. This suggests that predators play an important role in the drastic decline of P. osmanthi density just after the spring peak. This revised version was published online in July 2006 with corrections to the Cover Date.     

Population dynamics ofDaphnia rosea in a small eutrophic pond

The population dynamics ofDaphnia rosea were studied in a small, eutrophic fish-free pond during November 1986–November 1987.D. rosea showed two density peaks in 1987, a high peak in spring and a slightly lower one in autumn, but they disappeared in mid- and late summer when a smaller cladoceran,Ceriodaphnia reticulata, dominated. The rapid decline in density ofD. rosea in mid-May and the low density in June/July were preceded by or coincided with a period of increased male density, the appearance of ephippial females, smaller body length of adult females, decreased brood size, and increased frequency of empty brood chambers, all of which indicate a worsening food situation. The rapid density decline ofD. rosea in mid-May was considered attributable neither to increasing water temperature, nor predation by the dipteranChaoborus flavicans, but to insufficient food conditions for the maintenance of stable reproduction. Although edible phytoplankton was abundant in June/July, the general food situation was not suitable forD. rosea due to blooms of the large-celled dinoflagellate,Ceratium hirundinella, which probably inhibited the feeding activity ofD. rosea. TheC. hirundinella blooms might also be important for the shift of the dominant herbivore from the largerD. rosea to the smallerCeriodaphnia reticulata in August/September.     

Population dynamics and harvesting of semelparous species with phenotypic and genotypic variability in reproductive age

We study the evolution of polymorphic life histories in anadromous semelparous salmon and the effects of harvesting. We derive dynamic phenotypic and genetic ESS models for describing the evolutionary dynamics. We show in our deterministic analysis that polymorphisms are not possible in a panmictic random mating population. Instead, genetic or behavioral polymorphisms may be observed in populations with assortative mating systems. Positive assortative mating may be supported and generated by behavioral and phenotypic traits like male mate choice, spawning ground selection by phenotype, or within-river homing-migration-distance by size. In the case of an evolutionarily stable dimorphism, the ESS is characterized by a reproductive ideal free distribution such that at an equilibrium the individuals are indifferent from the fitness point of view between the two life histories of early and late reproduction. Different strategy models - that is, phenotypic and genetic ESS models - yield identical behavioral predictions and, consequently, genetics does not seem to play an important role in the present model. An evolutionary response to increased fishing mortality is obvious and may have resource management implications. High sea fishing mortalities drive the populations toward early spawning. Thus it is possible that unselective harvesting at sea may eliminate, depending on the biological system, behavioral polymorphisms or genetic heterozygozity and drive the population to a monomorphic one. If within-river homing migration distances depend on the size of fish, unselective harvesting at sea, or selective harvesting of spawning runs in rivers, may reduce local population sizes on spawning grounds high up rivers. Finally, harvesting in a population may cause a switch in a dominant life-history strategy in a population so that anticipated sustainable yields cannot be realized in practice.