Effects of invasion of fire‐free arid shrublands by a fire‐promoting invasive alien grass (Pennisetum setaceum) in South Africa

Arid shrublands in the Karoo (South Africa) seldom accumulate sufficient combustible fuel to support fire. However, as a result of invasion by an alien perennial grass (Pennisetum setaceum), they could become flammable. This paper reports on an experiment to assess the effects of fire following invasion by P. setaceum. We established 10 plots (5 × 10 m) separated by 2.5 m, and added grass fuel to five plots (5 and 10 tons ha^?1 to alternate halves of the plot) leaving the remaining five plots as interspersed controls. Plots with fuel added were burnt, and fire behaviour was measured during the burns. Rates of fire spread were generally low (0.01–0.07 m s^?1) and did not differ significantly between burn treatments. Mean fireline intensities were higher in the high compared with the low fuel treatments (894 and 427 kW m^?1, respectively). We recorded plant species and their cover before and after burning on each of the plots. After 15 months of follow‐up monitoring in the burn plots, only two species, the dwarf shrub (Tripteris sinuata) and the perennial herb (Gazania krebsiana) resprouted. Most individuals of other species were killed and did not reseed during the 15‐month study. The mass of added fuel load (high or low) did not influence vegetation recovery rates after fire. Should future invasions by P. setaceum lead to similar fuel loads in these shrublands, inevitable fires could change the vegetation and may favour spread of the flammable grass. Our results have important implications for predicting the effects of invasive alien plants (especially grasses) on fire‐free ecosystems elsewhere. The predicted impacts of fire may alter species composition, ultimately affecting core natural resources that support the Karoo economy.     

Arsenic release and attenuation in low organic carbon aquifer sediments from West Bengal

High arsenic concentrations in groundwater are causing a humanitarian disaster in Southeast Asia. It is generally accepted that microbial activities play a critical role in the mobilization of arsenic from the sediments, with metal‐reducing bacteria stimulated by organic carbon implicated. However, the detailed mechanisms underpinning these processes remain poorly understood. Of particular importance is the nature of the organic carbon driving the reduction of sorbed As(V) to the more mobile As(III), and the interplay between iron and sulphide minerals that can potentially immobilize both oxidation states of arsenic. Using a multidisciplinary approach, we identified the critical factors leading to arsenic release from West Bengal sediments. The results show that a cascade of redox processes was supported in the absence of high loadings of labile organic matter. Arsenic release was associated with As(V) and Fe(III) reduction, while the removal of arsenic was concomitant with sulphate reduction. The microbial populations potentially catalysing arsenic and sulphate reduction were identified by targeting the genes arrA and dsrB, and the total bacterial and archaeal communities by 16S rRNA gene analysis. Results suggest that very low concentrations of organic matter are able to support microbial arsenic mobilization via metal reduction, and subsequent arsenic mitigation through sulphate reduction. It may therefore be possible to enhance sulphate reduction through subtle manipulations to the carbon loading in such aquifers, to minimize the concentrations of arsenic in groundwaters.     

OVARIAN DEVELOPMENT AND OOSORPTION IN AUTOGENOUS FEMALES OF THE BLOWFLY,LUCILIA CUPRINA (WIED.)

Nearly 90% of nulliparous females of a laboratory selected autogenous strain of the sheep blowly, Lucilia cuprina, developed mature oocytes when fed only sucrose and water. The mean number of oocytes matured by those females which reached maturity was about 100. In the few females which did not reach maturity, ovarian development ceased early in vitellogenesis. Females had approximately 250 ovarioles, and when given ad libitum access to sheep liver, matured virtually all their primary oocytes. Flies given limited amounts of protein-rich material matured more oocytes than individuals given only sucrose and water; the apparent efficiency of conversion of ingested protein to ovary protein was of the order of 50%.

In females fed only sucrose and water or limited amounts of protein-rich material, the reduction in the number of oocytes resulted from oosorption initiated early in vitellogenesis. Oosorption was initiated earlier in females fed only sucrose and water, which were destined to resorb of the order of 150 oocytes, than in females which resorbed about 65 oocytes after having consumed a limited amount of protein-rich material.

Mating increased slightly both the proportion of females expressing autogeny and the number of oocytes matured.     

Identification of hypervariable single locus minisatellite DNA probes in the blue tit Parus caeruleus

We report the isolation of a set of hypervariable minisatellite DNA sequences from a blue tit Parus caeruleus genomic DNA library. In our strategy, we cloned a minisatellite-rich DNA fraction into a charomid vector. The resulting cosmid library was screened with the two minisatellite DNA probes 33.6 and 33.15 for recombinants containing a minisatellite DNA insert. A total of 233 positive clones were isolated. Of 37 clones that have been analysed, nine gave polymorphic signals and can be used as single locus probes (SLPs). Four of the SLPs were investigated in more detail. The number of alleles, the heterozygosity and the mutation rate were estimated. Linkage analysis revealed that two of these loci were linked. The SLPs are of value to studies of the mating system and reproductive success in the blue tit, and may also be useful in population genetic studies.     

Seasonal changes on two different spatial scales： response of aquatic invertebrates to water body and microhabitat

Knowledge about the spatial and temporal scales of both habitat use and the functional significance of different adaptations is essential for an understanding of the population dynamics of invertebrate assemblages. This fundamental knowledge is not only interesting from an academic point of view, but is sorely lacking and needed in the field of restoration ecology. Many species are threatened due to degradation. Knowing what environmental conditions are needed dtLring the life cycle of these species is important in the design of restoration measures which aim to lift existing bottlenecks for threatened species. To assess the relative importance of water type and microhabitat in structuring the invertebrate assemblage during different seasons, invertebrates were sampled in three water bodies differing in trophic level and acidity. Different parts within a water body （microhabitats） were sampled separately and each water body was sampled in all four seasons. Results show that water body is an important factor structuring the invertebrate assemblage early in the season, whereas microhabitat became more important later in the season. Structural complexity of microhabitats was related to the type of locomotion employed by invertebrates. Seasonal differences could be related to population dynamics （reproduction, mortality）. Moreover, fluctuations in resource availability were expected to differ between the water bodies, with highest fluctuations in the eutrophic water body and with fluctuations becoming less predictable later in the season. This was confirmed by the data： species synchronization to pulses in food availability was strongest in the eutrophic water body. Moreover, synchronization was strongest in summer, while in autumn waters were invaded by dispersive species. Based on these results a synthesis is presented on the functioning of the different waters during the different seasons.     

Challenges of DNA-Based Mark-Recapture Studies of American Black Bears

Abstract: We explored whether genetic sampling would be feasible to provide a region-wide population estimate for American black bears (Ursus americanus) in the southern Appalachians, USA. Specifically, we determined whether adequate capture probabilities (p > 0.20) and population estimates with a low coefficient of variation (CV < 20%) could be achieved given typical agency budget and personnel constraints. We extracted DNA from hair collected from baited barbed-wire enclosures sampled over a 10-week period on 2 study areas: a high-density black bear population in a portion of Great Smoky Mountains National Park and a lower density population on National Forest lands in North Carolina, South Carolina, and Georgia. We identified individual bears by their unique genotypes obtained from 9 microsatellite loci. We sampled 129 and 60 different bears in the National Park and National Forest study areas, respectively, and applied closed mark-recapture models to estimate population abundance. Capture probabilities and precision of the population estimates were acceptable only for sampling scenarios for which we pooled weekly sampling periods. We detected capture heterogeneity biases, probably because of inadequate spatial coverage by the hair-trapping grid. The logistical challenges of establishing and checking a sufficiently high density of hair traps make DNA-based estimates of black bears impractical for the southern Appalachian region. Alternatives are to estimate population size for smaller areas, estimate population growth rates or survival using mark-recapture methods, or use independent marking and recapturing techniques to reduce capture heterogeneity.     

Plant community diversity relative to human land uses in an Amazon forest colony

We examined numbers of plant species and individuals relative to land use in an agricultural settlement in the Brazilian Amazon. Land uses were forest, cropped after forest, fallows, cropped after fallow, and pasture. These corresponded roughly to farmers' land-use changes over time. Numbers of species and diversity indices were generally highest in forest, but we found quite similar values in older fallows as a result of both survival/re-establishment of forest species and emergence of plants not encountered in forest. The dominant species in fallows, however, were different from those in forest. Lands cropped using slash-and-burn maintained moderate numbers of species–both forest and non-forest. Trends in plant density (individuals per unit ground area) on cropped lands were mainly related to invasion of weedy species (increasing in time after slash-and-burn) and shifts in crop species (replacement of small-sized rice by larger-sized maize and cassava). Useful forest plants (e.g. for construction purposes, food and medicines) decreased with land conversion, although new species also appeared. The fewest species, tree species, and useful plants, and the greatest losses of the forest flora, were encountered in pastures. Consequently, conversion to pasture rather than slash-and-burn agriculture per se led to high biodiversity loss.