The role of competition and habitat in structuring small mammal communities in a tropical montane ecosystem in southern India

Small mammals were sampled in two natural habitats (montane stunted evergreen forests and montane grassland) and four anthropogenic habitats (tea, wattle, bluegum and pine plantation) in the Upper Nilgiris in southern India. Of the species trapped, eight were in montane evergreen forests and three were in other habitats. Habitat discrimination was studied in the rodents Rattus rattus and Mus famulus and the shrew Suncus montanus in the montane forest habitat. Multivariate tests on five variables (canopy cover, midstorey density, ground cover, tree density, canopy height) showed that R. rattus uses areas of higher tree density and lower canopy cover. Suncus montanus and M. famulus use habitat with higher tree density and ground cover and lower canopy height. Multivariate tests did not discriminate habitat use between the species. Univariate tests, however, showed that M. famulus uses areas of higher tree density than R. rattus and S. montanus. Rattus rattus was the dominant species in the montane forest, comprising 60.9% of total density, while the rodent Millardia meltada was the dominant species in the grassland. Studies of spatial interaction between these two species in habitats where they coexisted showed neither overlap nor avoidance between the species. Rattus rattus, however, did use areas of lower ground cover than did M. meltada. The analysis of spatial interactions between the species, habitat discrimination and use, and the removal experiments suggest that interspecific competition may not be a strong force in structuring these small mammal communities. There are distinct patterns in the use of different habitats by some species, but microhabitat selection and segregation is weak. Other factors such as intraspecific competition may play a more important role in these communities.

On breaks of the Indian monsoon

For over a century, the term break has been used for spells in which the rainfall over the Indian monsoon zone is interrupted. The phenomenon of 'break monsoon' is of great interest because long intense breaks are often associated with poor monsoon seasons. Such breaks have distinct circulation characteristics (heat trough type circulation) and have a large impact on rainfed agriculture. Although interruption of the monsoon rainfall is considered to be the most important feature of the break monsoon, traditionally breaks have been identified on the basis of the surface pressure and wind patterns over the Indian region. We have defined breaks (and active spells) on the basis of rainfall over the monsoon zone. The rainfall criteria are chosen so as to ensure a large overlap with the traditional breaks documented by Ramamurthy (1969) and De et al (1998). We have identified these rainbreaks for 1901-89. We have also identified active spells on the basis of rainfall over the Indian monsoon zone. We have shown that the all-India summer monsoon rainfall is significantly negatively correlated with the number of rainbreak days (correlation coefficient -0.56) and significantly positively correlated with the number of active days (correlation coefficient 0.47). Thus the interannual variation of the all-India summer monsoon rainfall is shown to be related to the number of days of rainbreaks and active spells identified here. There have been several studies of breaks (and also active spells in several cases) identified on the basis of different criteria over regions differing in spatial scales (e.g., Webster et al 1998; Krishnan et al 2000; Goswami and Mohan 2000; and Annamalai and Slingo 2001). We find that there is considerable overlap between the rainbreaks we have identified and breaks based on the traditional definition. There is some overlap with the breaks identified by Krishnan et al (2000) but little overlap with breaks identified by Webster et al (1998). Further, there are three or four active-break cycles in a season according to Webster et al (1998) which implies a time scale of about 40 days for which Goswami and Mohan (2000), and Annamalai and Slingo'(2001) have studied breaks and active minus break fluctuations. On the other hand, neither the traditional breaks (Ramamurthy 1969; and De et al 1998) nor the rainbreaks occur every year. This suggests that the 'breaks' in these studies axe weak spells of the intraseasonal variation of the monsoon, which occur every year. We have derived the OLR and circulation patterns associated with rainbreaks and active spells and compared them with the patterns associated with breaks/active minus break spells from these studies. Inspite of differences in the patterns over the Indian region, there is one feature which is seen in the OLR anomaly patterns of breaks identified on the basis of different criteria as well as the rainbreaks identified in this paper viz., a quadrapole over the Asia-west Pacific region arising from anomalies opposite (same) in sign to those over the Indian region occurring over the equatorial Indian Ocean and northern tropical (equatorial) parts of the west Pacific. Thus it appears that this quadrapole is a basic feature of weak spells of the intraseasonal,variation over the Asia-west Pacific region. Since the rainbreaks are intense weak spells, this basic feature is also seen in the composite patterns of these breaks. We find that rainbreaks (active spells) are also associated with negative (positive) anomalies over a part of the cast Pacific suggesting that the convection over the Indian region is linked to that over the east Pacific not only on the interannual scale (as evinced by the link between the Indian summer monsoon rainfall and ENSO) but on the intraseasonal scale as well.

Impact of satellite observed microwave SST on the simulation of tropical cyclones

The impact of realistic representation of sea surface temperature (SST) on the numerical simulation of track and intensity of tropical cyclones formed over the north Indian Ocean is studied using the Weather Research and Forecast (WRF) model. We have selected two intense tropical cyclones formed over the Bay of Bengal for studying the SST impact. Two different sets of SSTs were used in this study: one from TRMM Microwave Imager (TMI) satellite and other is the weekly averaged Reynold's SST analysis from National Center for Environmental Prediction (NCEP). WRF simulations were conducted using the Reynold's and TMI SST as model boundary condition for the two cyclone cases selected. The TMI SST which has a better temporal and spatial resolution showed sharper gradient when compared to the Reynold's SST. The use of TMI SST improved the WRF cyclone intensity prediction when compared to that using Reynold's SST for both the cases studied. The improvements in intensity were mainly due to the improved prediction of surface latent and sensible heat fluxes. The use of TMI SST in place of Reynold's SST improved cyclone track prediction for Orissa super cyclone but slightly degraded track prediction for cyclone Mala. The present modeling study supports the well established notion that the horizontal SST gradient is one of the major driving forces for the intensification and movement of tropical cyclones over the Indian Ocean.

A tropical oviparous lizard, Calotes versicolor, exhibiting a potentially novel FMFM pattern of temperature-dependent sex determination

Among squamate reptiles, lizards exhibit an impressive array of sex-determining modes viz. genotypic sex determination, temperature-dependent sex determination, co-occurrence of both these and those that reproduce parthenogenetically. The oviparous lizard, Calotes versicolor, lacks heteromorphic sex chromosomes and there are no reports on homomorphic chromosomes. Earlier studies on this species presented little evidence to the sex-determining mechanism. Here we provide evidences for the potential role played by incubation temperature that has a significant effect (P<0.01) on gonadal sex and sex ratio. The eggs were incubated at 14 different incubation temperatures. Interestingly, 100% males were produced at low (25.5 +/- 0.5 degrees C) as well as high (34 +/- 0.5 degrees C) incubation temperatures and 100% females were produced at low (23.5 +/- 0.5 degrees C) and high (31.5 +/- 0.5 degrees C) temperatures, clearly indicating the occurrence of TSD in this species. Sex ratios of individual clutches did not vary at any of the critical male-producing or female-producing temperatures within as well as across the seasons. However, clutch sex ratios were female- or male-biased at intermediate temperatures. Thermosensitive period occurred during the embryonic stages 3033. Three pivotal temperatures operate producing 1:1 sex ratio. Histology of gonad and accessory reproductive structures provide additional evidence for TSD. The sex-determining pattern, observed for the first time in this species, that neither compares to Pattern I [Ia (MF) and Ib (FM)] nor to Pattern II (FMF), is being referred to as FMFM pattern of TSD. This novel FMFM pattern of sex ratio exhibited by C. versicolor may have an adaptive significance in maintaining sex ratio. J. Exp. Zool. 317:3246, 2012. (c) 2011 Wiley Periodicals, Inc.

Some characteristics of tropical lightning

An integrated and generalized account of the characteristics of lightning flashes observed in the tropics is presented, along with features of tropical lightning which differ from flashes at other latitudes. Several years of lightning recordings were made at two locations in India by using the electromagnetic radiation of the flash in a suitable radio band. The distances of thunder audibility, the number of thunders/hr, the peak flash rate, the flash duration, the time interval between flashes, the duration of flashing activity of a cloud, the number of cells in the lifetime of the cloud, etc. were all found to follow log-normal distributions. Fewer cells were observed to occur in temperate regions, and thunder was found to be associated with ground flashes only.

Vegetative phenology of tropical montane forests in the Nilgiris, South India

Spatial and temporal variation in foliar phenology plays a significant role in growth and reproduction of a plant species. Foliar phenology is strongly influenced by environmental factors such as rainfall. A study on phenology of tropical montane forests was undertaken in three different forest patches of the Nilgiri Mountains in peninsular India above 2000 meters ASL. Since August 2000, 500 trees belonging to 70 species of angiosperms were monitored for both vegetative and reproductive phenologies on a monthly basis. Climate data were collected from nearby weather stations. This paper reports results of the study from August 2000 - August 2003 on foliar phenology. Non-parametric correlations and multiple regressions were performed to analyse the influence of environmental factors such as rainfall, temperature and sunshine on foliar phenology. It was found that moisture related factors had a negative influence on the leaf initiation. Circular statistical analyses were performed to understand the seasonality in different phenophases of foliar phenology. Different phenophases of leafing were not significantly seasonal. Results are discussed and compared among three different forest patches on the Nilgiri plateau and also with other montane forest patches across the globe.

Analysis of residual tropical cemented soil behaviour

In -situ soils in gee-material spectrum might arise due to sedimentation or could be non-sedimentary residual formations. The inherent nature and diversity of geological processes involved in the soil formation stage itself are responsible for a wide variability in the in-situ state of the soil. In this paper the possibility of analyses to arrive at engineering parameters of residual soils with varied degrees of residual or acquired cementation by the use of physical and in-situ parameters normally determined in routine investigations, are examined. An Intrinsic State Line,(ISL), with reference to an intrinsic state parameter (e/e(L)) and its variation with effective stress for reconstituted clays has been developed for residual tropical soils of non-sedimentary origin. In relation to the Intrinsic State Line (ISL), the undisturbed state, e, the potential parameter, e(L), along with the overburden pressure data has been analyzed to identify the dominance of cementation or stress history or both in controlling the compressibility and strength behaviour of natural residual soil. The location of yield stress point in relation to the ISL, pre-, and post- yield stress, compression indices along the e- log sigma(v) path provide a simple means to the analysis of the compressibility characteristics of cemented soils for analysis.