Explaining the variation in the soil microbial community: do vegetation composition and soil chemistry explain the same or different parts of the microbial variation?

Aim

To assess whether vegetation composition and soil chemistry explain the same or different parts of the variation in the soil microbial community (SMC).

Method

The above and below-ground communities and soil chemical properties were studied along a successional gradient from moorland to deciduous woodland. The SMC was assessed using PLFAs and M-TRFLPs. Using variance partitioning, Co-Correspondence Analysis (CoCA) and Canonical Correspondence Analysis (CCA), the variation (total inertia) in the SMC was partitioned into variation which was uniquely explained by either plant composition or soil chemistry, variation explained by both soil chemistry and plant composition, and unexplained variation.

Results

Plant community composition uniquely explained 30, 13, 16 and 20% of the inertia and soil chemistry uniquely explained 5, 18, 9 and 9% of the inertia in the archaeal TRFLPs, bacterial TRFLPs, fungal TRFLPs and all PLFAs, respectively.

Conclusion

For the first time, variance partitioning was used to include data from a CoCA; although the current limits of such an approach are shown, this study illustrates the potential of such analyses and shows that soil chemistry and plant composition are, in substantial amounts, explaining different parts of the variation within the SMC. This marks an important step in furthering our understanding of the relative importance of different drivers of change in the SMC.     

Elevational replacement of two Himalayan titmice: interspecific competition or habitat preference?

Elevational species replacement is a widely documented pattern in montane species. Although interspecific competition has been shown to be important in setting species elevational limits in tropical habitats, its effect in species of temperate regions is poorly studied. We tested the role of interspecific competition for space in the breeding season and for food in the non‐breeding season in mediating the distribution of two resident titmice species in the Himalayas. We show that high elevation green‐backed tits Parus monticolus are behaviourally dominant over low elevation cinereous tits Parus cinereus in both song playback and feeder trials. Despite being subordinate, at their elevational upper limit, cinereous tits occur in sympatry in human modified habitats. Our study suggests that the loss of natural habitats in the sympatric zone, not interspecific competition, might be limiting the distribution of the high‐elevation green‐backed tits and facilitating an upward range shift through human association in cinereous tits.     

Kinetic analysis of gill (Na⁺,K⁺)-ATPase activity in selected ontogenetic stages of the Amazon River shrimp, Macrobrachium amazonicum (Decapoda, Palaemonidae): interactions at ATP- and cation-binding sites

We investigated modulation by ATP, Mg²⁺, Na⁺, K⁺ and NH₄ ⁺ and inhibition by ouabain of (Na⁺,K⁺)-ATPase activity in microsomal homogenates of whole zoeae I and decapodid III (formerly zoea IX) and whole-body and gill homogenates of juvenile and adult Amazon River shrimps, Macrobrachium amazonicum. (Na⁺,K⁺)-ATPase-specific activity was increased twofold in decapodid III compared to zoea I, juveniles and adults, suggesting an important role in this ontogenetic stage. The apparent affinity for ATP (K _M = 0.09 ± 0.01 mmol L⁻¹) of the decapodid III (Na⁺,K⁺)-ATPase, about twofold greater than the other stages, further highlights this relevance. Modulation of (Na⁺,K⁺)-ATPase activity by K⁺ also revealed a threefold greater affinity for K⁺ (K _0.5 = 0.91 ± 0.04 mmol L⁻¹) in decapodid III than in other stages; NH₄ ⁺ had no modulatory effect. The affinity for Na⁺ (K _0.5 = 13.2 ± 0.6 mmol L⁻¹) of zoea I (Na⁺,K⁺)-ATPase was fourfold less than other stages. Modulation by Na⁺, Mg²⁺ and NH₄ ⁺ obeyed cooperative kinetics, while K⁺ modulation exhibited Michaelis-Menten behavior. Rates of maximal Mg²⁺ stimulation of ouabain-insensitive ATPase activity differed in each ontogenetic stage, suggesting that Mg²⁺-stimulated ATPases other than (Na⁺,K⁺)-ATPase are present. Ouabain inhibition suggests that, among the various ATPase activities present in the different stages, Na⁺-ATPase may be involved in the ontogeny of osmoregulation in larval M. amazonicum. The NH₄ ⁺-stimulated, ouabain-insensitive ATPase activity seen in zoea I and decapodid III may reflect a stage-specific means of ammonia excretion since functional gills are absent in the early larval stages.     

Spatial variation in species diversity and composition of flea assemblages in small mammalian hosts: geographical distance or faunal similarity?

Aim Spatial variation in the diversity of fleas parasitic on small mammals was examined to answer three questions. (1) Is the diversity of flea assemblages repeatable among populations of the same host species? (2) Does similarity in the composition of flea assemblages among populations of the same host species decay with geographical distance, with decreasing similarity in the composition of local host faunas, or with both? (3) Does the diversity of flea assemblages correlate with climatic variables? Location The study used previously published data on 69 species of small mammals and their fleas from 24 different regions of the Holarctic. Methods The diversity of flea assemblages was measured as both species richness and the average taxonomic distinctness of their component species. Similarity between flea assemblages was measured using both the Jaccard and Morisita–Horn indices, whereas similarity in the composition of host faunas between regions (host ‘faunal’ distance) was quantified using the Jaccard index. Where appropriate, a correction was made for the potentially confounding influence of phylogeny using the independent contrasts method. Results Flea species richness varied less within than among host species, and is thus a repeatable host species character; the same was not true of the taxonomic distinctness of flea assemblages. In almost all host species found in at least five regions, similarity in flea assemblages decreased with increases in either or both geographical and faunal distance. In most host species, the diversity of flea assemblages correlated with one or more climatic variable, in particular mean winter temperature. Main conclusions Spatial variation in flea diversity among populations of the same mammal species is constrained by the fact that it appears to be a species character, but is also driven by local climatic conditions. The results highlight how ecological processes interact with co‐evolutionary history to determine local parasite biodiversity.     

Australian Entomology: isolated, or in touch with the rest of the world?

Abstract   Australia is isolated from the rest of the world geographically but not scientifically: Australian entomology has a long and distinguished record of collaboration with a diversity of other countries. Much of the focus relates to keeping new pests out of Australia (biosecurity and quarantine) and managing those that do get in (biological control and insect pest management). Many projects have cooperated with neighbouring countries, to assist them to control pests and thereby reduce threats to Australia. Biological control projects have also had two-way benefits, and examples are given of various collaborations in these fields.     

Unravelling genetics at the top: mountain islands or isolated belts?

Background and Aims

In mountain plant populations, local adaptation has been described as one of the main responses to climate warming, allowing plants to persist under stressful conditions. This is especially the case for marginal populations at their lowest elevation, as they are highly vulnerable. Adequate levels of genetic diversity are required for selection to take place, while high levels of altitudinal gene flow are seen as a major limiting factor potentially precluding local adaptation processes. Thus, a compromise between genetic diversity and gene flow seems necessary to guarantee persistence under oncoming conditions. It is therefore critical to determine if gene flow occurs preferentially between mountains at similar altitudinal belts, promoting local adaptation at the lowest populations, or conversely along altitude within each mountain.

Methods

Microsatellite markers were used to unravel genetic diversity and population structure, inbreeding and gene flow of populations at two nearby altitudinal gradients of Silene ciliata, a Mediterranean high-mountain cushion plant.

Key Results

Genetic diversity and inbreeding coefficients were similar in all populations. Substantial gene flow was found both along altitudinal gradients and horizontally within each elevation belt, although greater values were obtained along altitudinal gradients. Gene flow may be responsible for the homogeneous levels of genetic diversity found among populations. Bayesian cluster analyses also suggested that shifts along altitudinal gradients are the most plausible scenario.

Conclusions

Past population shifts associated with glaciations and interglacial periods in temperate mountains may partially explain current distributions of genetic diversity and population structure. In spite of the predominance of gene flow along the altitudinal gradients, local genetic differentiation of one of the lower populations together with the detection of one outlier locus might support the existence of different selection forces at low altitudes.     

Niche expansion and the niche variation hypothesis: does the degree of individual variation increase in depauperate assemblages?

The niche expansion and niche variation hypotheses predict that release from interspecific competition will promote niche expansion in depauperate assemblages. Niche expansion can occur by different mechanisms, including an increase in within-individual, among-individual, or bimodal variation (sexual dimorphism). Here we explore whether populations with larger niche breadth have a higher degree of diet variation. We also test whether populations from depauperate lizard assemblages differ in dietary resource use with respect to variation within and/or among individuals and sexual dimorphism. We found support for the niche expansion and niche variation hypotheses. Populations in assemblages with low phylogenetic diversity had a higher degree of individual variation, suggesting a tendency for niche expansion. We also found evidence suggesting that the mechanism causing niche expansion is an increase in variation among individuals rather than an increase in within-individual variation or an increase in bimodal variation due to sexual dimorphism.     

Egg-size variation and reproductive success in the Herring Gull Lams argentatus: adaptive or constrained size of the last egg?

Herring Gull Larus argentatus eggs from a study colony in the Baltic showed a slight but significant variation in egg size within the laying sequence. Last-laid eggs were only about 5% smaller by volume than first eggs. There was no significant difference in dry yolk weight or dry albumen weight, although possible differences were evident. The chicks had nearly equal hatching weights and equally long tarsi. There was no differential mortality in the third chick in the study colony, and there were no indications of egg-size-mediated mortality. The birds in the colony produced an average of 1.45 fledglings per pair. Compared with several other studied colonies, the difference in egg size within a clutch was low, and a comparison of colonies from northwestern Europe suggests that variance within the clutch is negatively correlated with fledging success, so that a large difference in size between first and last eggs is associated with low fledging success. We suggest that the size of the last egg in the clutch reflects the feeding potential in the environment and is mainly a nonadaptive response to poor feeding conditions during laying.     

Nutrient composition,microbial biomass and activity at the air–water interface of small boreal forest lakes

Nutrient contents, microbial biomass and microbial activities werestudied at the air–water interface in the surface microlayer (SM) andsubsurface waters (10 cm depth) in small boreal forest lakes. Two differentsampling techniques were used to evaluate differences in the nutrientcomposition in SM- and subsurface waters and to study their effects onmicrobial biomass and activities of neustonic and planktonic microbialcommunities. Inorganic nutrients were only slightly enriched in the SMcompared to the subsurface water samples. P-PO⁴ variedbetween 6–10 mg P-PO₄ m_™3 in the SM andbetween 1–2 mg P–PO₄ m^-3 in thesubsurface waters. Dissolved inorganic nitrogen (NO₂ ^™+NO₃ ^™+NH₄ ⁺) varied between 12–20 mg Nm^™3 in the SM and between 3–12 mg N m^™3 insubsurface waters. Polymeric organic bound phosphorus and nitrogen wereabout 10 times enriched in the SM compared to the subsurface samples.However, microbial biomass like chlorophyll was by a factor of 8 to 280times enriched in the SM of meso-polyhumic lakes and 2–25 timeenriched in an acidified lake. Bacterioneuston biomass was by a factor of1.5 to 2 times enriched in the SM compared to that of bacterioplankton.However, fungal biomass was 30 to 40 times higher in the SM than in thesubsurface samples. Microbial activities was measured as[¹⁴C]-UL-α-D-Glucose uptake and as microbial biopolymerprocessing measured with 4-methylumbelliferyl-α-D-Glucopyranoside asmodel substrate for tracing the enzymatic cleaving rate of α-glycosidicpolymer bound glucose via microbial α-glucosidase (αGlucAse). [¹⁴C]-UL-α-D-Glucose uptake was about 4–5 timeshigher in bacterioneuston compared to bacterioplankton and varied between4–22 μm m³ h^™1 in bacterioneustoncommunities and between 1.5–2.5 μm m^™3h^™1 in bacterioplankton. αGlucAse was about 1.5 to 8 timeshigher in SM samples and varied between 38–108 μmm^™3 h^™1 in the SM microbial communities comparedto 12–35 μm m^™3 h^™1 in thesubsurface water microbial communities. The ratios between αGlucAseactivities and [¹⁴C]-UL-α-D-Glucose uptake was about3–5 times lower in the bacterioneuston than in the bacterioplanktoncommunities which means a tighter metabolic coupling between biopolymerprocessing and substrate uptake in bacterioneuston than in bacterioplankton.Biofilms in surface microlayers at the air–water interface in smallhumic forest lakes can provide favourable microhabitats for the growth ofneuston communities which may act as important sinks for allochthonousnutrient resources and may then generate new nutrient pools and prey forplanktonic microbial food webs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Marker-based quantitative genetics in the wild?: the heritability and genetic correlation of chemical defenses in eucalyptus

Marker-based methods for estimating heritability and genetic correlation in the wild have attracted interest because traditional methods may be impractical or introduce bias via G x E effects, mating system variation, and sampling effects. However, they have not been widely used, especially in plants. A regression-based approach, which uses a continuous measure of genetic relatedness, promises to be particularly appropriate for use in plants with mixed-mating systems and overlapping generations. Using this method, we found significant narrow-sense heritability of foliar defense chemicals in a natural population of Eucalyptus melliodora. We also demonstrated a genetic basis for the phenotypic correlation underlying an ecological example of conditioned flavor aversion involving different biosynthetic pathways. Our results revealed that heritability estimates depend on the spatial scale of the analysis in a way that offers insight into the distribution of genetic and environmental variance. This study is the first to successfully use a marker-based method to measure quantitative genetic parameters in a tree. We suggest that this method will prove to be a useful tool in other studies and offer some recommendations for future applications of the method.     

Compounds isolated at the institute of microbiology in 1989–2001 and future trends

A total of 307 new compounds, natural, semisynthetic or synthetic, were isolated at theInstitute of Microbiology during the last twelve years. Due to the development of separation (chromatographic) methods and of analytical methods used to determine the chemical structure of these compounds,i.e. NMR, MS and X-ray diffraction, many new metabolites could be described.     

Vegetation composition,structure, and biomass of two unpolluted watersheds in the Cordillera de Piuchué, Chiloé Island,Chile

Research in pristine forests provides a necessary reference of energy and nutrient cycling in absence of anthropogenic influence. Therefore two unpolluted watersheds in the Cordillera de Piuchué of southern Chile (42 °30 S) were chosen for detailed ecosystem analysis. The goals of this study were to quantify the distribution of the living biomass in the research watershed and to document topographic gradients in the vegetation. Across a small spatial gradient from ravine bottom to ridgetop (approximately 60 m in elevation and < 300 m in length) in the Cordillera de Piuchué watersheds, there were significant shifts in vegetation composition, structure, and biomass. Based on sampling in 18, 100 m² plots, we identified three distinct community associations: a Fitzroya forest at the bottom of the watershed, a mid-slope Pilgerodendron-Tepualia transition zone, and a ridgetop moorland community. The Fitzroya forest was dominated by a cohort of approximately 400 year-old Fitzroya cupressoides trees. Both tree basal area (138 m²/ha) and total live biomass (656 Mg ha^–1) reached a maximum in this vegetation type. The Pilgerodendron-Tepualia forest consisted of smaller, shorter, and younger trees with dominance shared by Pilgerodendron uviferum, Tepualia stipularis, and to a lesser extent, F. cupressoides. Basal area and biomass were half that of the Fitzroya forest (69.5 m² ha^–1; 350 Mg ha^–1) but tree density was 65% greater. The moorland can best be described as an open community of mosses and cushion plants that included low stature individuals of P. uviferum, F. cupressoides, and T. stipularis. The size and age structure of F. cupressoides in the bottomland forest suggest that the current cohort of adult trees was established following a catastrophic disturbance and that F. cupressoides is unable to regenerate under its own canopy. In contrast, the size structure of the tree populations in the Pilgerodendron-Tepualia zone indicates that all the constituent tree species, except F. cupressoides, are able to reproduce at least at some microsites in the understory. The watershed-level means for live biomass were 306 Mg ha^–1 of aboveground tree biomass, 25 Mg ha^–1 of large root biomass (diameter ge 1 cm), and 46 Mg ha^–1 of small root biomass (diameter < 1 cm).     

Leptin in energy balance and reward: two faces of the same coin?

Leptin receptors are expressed on mesolimbic dopamine neurons, yet little is known about the functional significance of this anatomical relationship. In this issue of Neuron, Hommel et al. reveal a novel site for leptin's regulation of feeding. In turn, Fulton et al. propose a novel role for leptin in regulating non-feeding-related motivated behaviors.     

Which option best estimates the above-ground biomass of mangroves of Bangladesh: pantropical or site- and species-specific models?

Wetlands Ecology and Management - Bangladesh has the single largest tract of naturally growing mangrove forest as well as the world’s largest manmade mangrove forest on newly accreted land in...     

Latitudinal variation in litter size of polar bears: ecology or methodology?

I used data reported in the scientific literature to examine latitudinal variation in litter size of polar bears in 18 different populations. No relationship was found between litter size and latitude using non-weighted regression. Regression weighted by sample size indicated a negative relationship with latitude. However, sampling biases caused by latitudinal differences in the timing of sampling and cub mortality after den emergence could produce a latitudinal cline. Stratifying analyses by sampling area, at dens or away from dens, revealed no latitudinal trend in litter size. Observed differences in litter size among populations may result from variation in demography and ecosystem productivity that is not simply related to latitude. I conclude that available data do not provide support for a biologically significant latitudinal cline in polar bear litter size. Accepted: 25 May 1999     

Does the width of isolated ravine forests influence moss and liverwort diversity and composition?—A study of temperate forests in South Africa

The evidence of microclimatic edge effects through forest/open area ecotones is firm. How this affects the species composition near edges is less well understood and documented. In south-western South Africa shrub-dominated regularly burnt vegetation (i.e. fynbos) is the most common vegetation with indigenous temperate forests naturally occurring mostly in ravines on mountain slopes. The size and width of these forest patches varies considerably. In order to understand how the width of forest patches affects species composition of mosses and liverworts we investigated 20 forest patches of different width. In each forest patch we compiled a total species list, and collected data on selected environmental variables, for a plot of 10×20 m. No significant relationship was found between patch width and the number of either moss or liverwort species. However, the species composition of mosses (but not liverworts) changed along the gradient of patch width. The variation in number of species was large (8–29 mosses and 11–33 liverworts) among the plots and we propose that factors other than distance to the forest edge may be more important in structuring the bryophyte community of these ravine forests. One such factor that is likely to be important is the climatic difference among the plots. There is variation in features, such as precipitation, summer temperature, cloudiness, and the amount of fog, for which we do not have data but that could overrule the microclimatic differences due to edge effects.     

A fruit in the hand or two in the bush? Divergent risk preferences in chimpanzees and bonobos

Human and non-human animals tend to avoid risky prospects. If such patterns of economic choice are adaptive, risk preferences should reflect the typical decision-making environments faced by organisms. However, this approach has not been widely used to examine the risk sensitivity in closely related species with different ecologies. Here, we experimentally examined risk-sensitive behaviour in chimpanzees (Pan troglodytes) and bonobos (Pan paniscus), closely related species whose distinct ecologies are thought to be the major selective force shaping their unique behavioural repertoires. Because chimpanzees exploit riskier food sources in the wild, we predicted that they would exhibit greater tolerance for risk in choices about food. Results confirmed this prediction: chimpanzees significantly preferred the risky option, whereas bonobos preferred the fixed option. These results provide a relatively rare example of risk-prone behaviour in the context of gains and show how ecological pressures can sculpt economic decision making.     

Ecological observations and biomass proximate composition of the brine shrimp Artemia (Crustacea: Anostraca) from Pichilingue,Baja California Sur,México

The brine shrimp, most probably Artemia franciscana occurs in the solar salt plant (`salina') of Pichilingue (24°15N and 110°20W, total area about 10 ha), Baja California Sur, México. During the periods September 1999 to March 2000 and June 2000 to March 2001, salinity and temperature were determined weekly in selected evaporation ponds, as were the biological parameters of Artemia biomass, size of adult females and males, and monthly the biochemical composition of dried Artemia biomass. An explosive growth of Artemia was observed during moderate salinity levels (80–120 g l^–1), reaching a standing crop level of 300 kg wet weight ha^–1. With increasing salinity, biomass production and the size, especially of the females, decreased drastically, probably due to limited availability of natural food and to environmental stress. Brine shrimp survived up to a salinity of 270 g l^–1. Despite wide variations in the environmental conditions, the proximate analysis of Artemia biomass showed only small differences, with the exception of the crude fibre content.     

Seasonal variation in the metabolic rate and body composition of female grey seals: fat conservation prior to high-cost reproduction in a capital breeder?

Many animals rely on stored energy through periods of high energy demand or low energy availability or both. A variety of mechanisms may be employed to attain and conserve energy for such periods. Wild grey seals demonstrate seasonal patterns of energy storage and foraging behaviour that appear to maximize the allocation of energy to reproduction—a period characterized by both high energy demand and low food availability. We examined seasonal patterns in resting rates of oxygen consumption as a proxy for metabolic rate (RMR) and body composition in female grey seals (four adults and six juveniles), testing the hypothesis that adults would show seasonal changes in RMR related to the reproductive cycle but that juveniles would not. There was significant seasonal variation in rates of resting oxygen consumption of adult females, with rates being highest in the spring and declining through the summer months into autumn. This variation was not related to changes in water temperature. Adults increased in total body mass and in fat content during the same spring to autumn period that RMR declined. RMR of juveniles showed no clear seasonal patterns, but did increase with increasing mass. These data support the hypothesis that seasonal variation in RMR in female grey seals is related to the high costs of breeding.