Effect of tall-grass invasion on the flowering-related functional pattern of submediterranean hay-meadows

Several studies demonstrated that abandonment changes the functional composition of grasslands; nevertheless, little is known about the effects of grassland abandonment on the flowering-related functional pattern. We hypothesized that invasion by tall grasses affects this pattern. We counted the number of flowering shoots per species at five times during the growing season, in 80 plots placed in mown and in abandoned grasslands (central Apennines), and assessed the differences in the trait composition of flowering species between the two treatments. The selected traits were linked to resource acquisition and stress tolerance strategies. Our results indicated that abiotic environmental control is prevalent in determining the phenological pattern in both conditions and in accordance with the phenological “mid-domain hypothesis”. We demonstrated that when the dominant species is a tall grass with competitive behaviour, the magnitude of this phenomenon is amplified due to the abiotic changes yielded by the tall grass invasion. Indeed, in the central and late phases of the growing season (when invasive tall grasses are growing and blooming), abandoned grasslands were marked by a set of traits devoted to stress tolerance or underlying a long reproductive cycle or linked to competition for light.     

A quantitative estimation of sequential foliage development and fertility inDryopteris crassirhizoma

The foliage development ofDryopteris crassirhizoma Nakai was quantitatively estimated by measurements of shape and size of leaves from different developmental stages of sporophytes, to lead to an understanding of the life history characteristics of the species. The number of midrib branches (NV, number of veins) of the leaf corresponds to the leaf-shape complexity (DI, dissection index; shape complexity from a circle) and length of leafblade (BL). Some quantitative characters, such as leaf uniformity (decrease in NV variation), changes in shape and increase in number of leaves, vary progressively during foliage formation. The sequence of foliage development can be quantified using the parameter NV: for example, 15-NV for leaf uniformity, 30-NV for leaf-shape change from triangular to oblanceolate, 60-NV for increase in leaf number and leaf fertility in the course of sporophyte ontogeny. Contribution No. 3297 from the Institute of Low Temperature Science, Hokkaido University.     

Identification of a 3.7-Mb region for a marbling QTL on bovine chromosome 4 by identical-by-descent and association analysis

QTL mapping for growth and carcass traits was performed using a paternal half-sib family composed of 325 Japanese Black cattle offspring. Nine QTL were detected at the 1% chromosome-wise significance level at a false discovery rate of less than 0.1. These included two QTL for marbling on BTA 4 and 18, two QTL for carcass weight on BTA 14 and 24, two QTL for longissimus muscle area on BTA 1 and 4, two QTL for subcutaneous fat thickness on BTA 1 and 15 and one QTL for rib thickness on BTA 6. Although the marbling QTL on BTA 4 has been replicated with significant linkages in two Japanese Black cattle sires, the three Q (more marbling) haplotypes, each inherited maternally, were apparently different. To compare the three Q haplotypes in more detail, high-density microsatellite markers for the overlapping regions were developed within the 95% CIs (65 markers in 44–78 cM). A detailed haplotype comparison indicated that a small region (<3.7 Mb) around 46 cM was shared between the Qs of the two sires, whose dams were related. An association of this region with marbling was shown by a regression analysis using the local population, in which the two sires were produced and this was confirmed by an association study using a population collected throughout Japan. These results strongly suggest that the marbling QTL on BTA 4 is located in the 3.7-Mb region at around 46 cM.     

Structural and functional measures of leaf-associated invertebrates and fungi as predictors of stream eutrophication

Eutrophication is a major threat to freshwater ecosystems worldwide that affects aquatic biota and compromises ecosystem functioning. In this study, we assessed the potential use of leaf decomposition and associated decomposer communities to predict stream eutrophication. Because leaf quality is expected to affect leaf decomposition, we used five leaf species, differing in their initial nitrogen concentration. Leaves of alder, chestnut, plane, oak and eucalyptus were placed in coarse-mesh bags and immersed in six streams along an eutrophication gradient to assess leaf decomposition and the structure of associated decomposer communities. A hump-shaped relationship was established between leaf decomposition and the eutrophication gradient for all leaf species, except for eucalyptus. Invertebrate biomass and density as well as fungal biomass and sporulation were lowest at the extremes of the gradient. Leaf-associated invertebrate and fungal assemblages were mainly structured by stream eutrophication. The percentage of shredders on leaves decreased, whereas the percentage of oligochaeta increased along the eutrophication gradient. The Iberian Biological Monitoring Working Party Index (IBMWP) applied to benthic invertebrates increased from oligotrophic to moderately eutrophic streams and then dropped sharply at highly and hypertrophic streams. Overall, leaf decomposition was a valuable tool to assess changes in stream water quality, and it allowed the discrimination of sites classified by the IBMWP within class I and class IV. Moreover, decomposition of most leaf species responded in a similar way to eutrophication when decomposition was normalized by the quality of leaves.     

Power of QTL detection by either fixed or random models in half-sib designs

The aim of this study was to compare the variance component approach for QTL linkage mapping in half-sib designs to the simple regression method. Empirical power was determined by Monte Carlo simulation in granddaughter designs. The factors studied (base values in parentheses) included the number of sires (5) and sons per sire (80), ratio of QTL variance to total genetic variance (λ = 0.1), marker spacing (10 cM), and QTL allele frequency (0.5). A single bi-allelic QTL and six equally spaced markers with six alleles each were simulated. Empirical power using the regression method was 0.80, 0.92 and 0.98 for 5, 10, and 20 sires, respectively, versus 0.88, 0.98 and 0.99 using the variance component method. Power was 0.74, 0.80, 0.93, and 0.95 using regression versus 0.77, 0.88, 0.94, and 0.97 using the variance component method for QTL variance ratios (λ) of 0.05, 0.1, 0.2, and 0.3, respectively. Power was 0.79, 0.85, 0.80 and 0.87 using regression versus 0.80, 0.86, 0.88, and 0.85 using the variance component method for QTL allele frequencies of 0.1, 0.3, 0.5, and 0.8, respectively. The log₁₀ of type I error profiles were quite flat at close marker spacing (1 cM), confirming the inability to fine-map QTL by linkage analysis in half-sib designs. The variance component method showed slightly more potential than the regression method in QTL mapping.     

New method for rapid assessment of the functional composition of herbaceous plant communities

Abstract We propose a rapid sampling method to assess the functional composition of herbaceous plant communities without prior knowledge of the floristic composition. To determine the community‐level value of traits (‘aggregated trait values’) for a plant community, a standardized population‐centred method exists, but requires substantial manpower and reliable botanical knowledge. We tested an alternative method, the trait transect, using four subalpine pastures in the Beaufortain region (Northern French Alps) selected along a fertility gradient. We applied both methods to measure five commonly used ‘soft traits’ known to be responsive to soil nutrient availability: plant vegetative and reproductive height, specific leaf area, leaf dry matter and nitrogen contents. We tested whether the variation of these traits along the gradient detected with the population‐centred method was also detected with the trait transect. Both methods detected expected trends in the traits in response to the fertility gradient. The trait transect method was as efficient as the population‐centred method and is recommended as an appropriate tool for monitoring ecosystem changes in response to environmental conditions and management, especially in species‐rich communities.     

Body size but not colony size increases with altitude in the holarctic ant,Leptothorax acervorum

1. Bergmann's rule states that organisms inhabiting colder environments show an increase in body size or mass in comparison to their conspecifics living in warmer climates. Although originally proposed for homoeothermic vertebrates, this rule was later extended to ectotherms. In social insects, only a few studies have tested this rule and the results were ambiguous. Here, ‘body size’ can be considered at two different levels (the size of the individual workers or the size of the colony). 2. In this study, data from 53 nests collected along altitudinal gradients in the Alps were used to test the hypotheses that the worker body size and colony size of the ant Leptothorax acervorum increase with increasing altitude and therefore follow Bergmann's rule. 3. The results show that the body size of workers but not the colony size increases with altitude. Whether this pattern is driven by starvation resistance or other mechanisms remains to be investigated.     

Understanding seagrass resilience in temperate systems: the importance of timing of the disturbance

Temperate seagrass meadows form valuable ecosystems in coastal environments and present a distinct seasonal growth. They are threatened by an increasing amount of stressors, potentially affecting their capacity to recover from disturbances. We hypothesized that their resilience to disturbances is affected by seasonal dynamics. Hence, we investigated the effect of the timing of the disturbance on seagrass Leaf Area Index (as a proxy for presence, or ‘visible’ status), recovery from disturbance (as a proxy for meadow resilience), and rhizome carbohydrates (as a proxy for longer term resilience) by a series of four disturbance-recovery field experiments spread over the growing season at two sites in Shandong Province, China. During the course of the growing season, we found the highest recovery at the start of the growing season, lowest recovery when Leaf Area Index peaked around mid-growing season, and intermediate recovery when Leaf Area Index decreased at the end of the growing season. Rhizome carbohydrates were not affected by disturbances during any of the four experimental periods and could not explain the low recovery during mid-growing season. The two sites differed in exposure and in the occurrence of incidents like a green tide and storms, which affected recovery. However, general patterns were similar; timing strongly influenced the indicator of meadow resilience and its correlation with presence during the two main seagrass growth phases. Our results emphasize the importance of carefully considering timing in the evaluation of seagrass resilience in temperate systems. Furthermore, our study implies that, to effectively protect seagrass beds, conservation management should aim at avoiding disturbances particularly during the peak of the growing season, when resilience is lowest.     

Trait‐divergence assembly rules have been demonstrated: Limiting similarity lives! A reply to Grime

The recent Forum contribution by Grime (2006) contrasts the MacArthur/Diamond assembly‐rule approach to studying plant communities with the study of environmental trait gradients. Both are valid and useful. In doing so, Grime declares that the assembly rules model, in which negative interactions between plants act with limiting similarity to cause local trait divergence, is “not supported by empirical study of plant communities”. This is, he says, the agony of community ecology. I show that there is now abundant evidence for assembly rules, and no agony.     

Structural and physiological responses of two invasive weeds, <Emphasis Type="Italic">Mikania micrantha</Emphasis> and <Emphasis Type="Italic">Chromolaena odorata</Emphasis>, to contrasting light and soil water conditions

To better understand the requirement of light and soil water conditions in the invasion sites of two invasive weeds, Mikania micrantha and Chromolaena odorata, we investigated their structural and physiological traits in response to nine combined treatments of light [full, medium and low irradiance (LI)] and soil water (full, medium and low field water content) conditions in three glasshouses. Under the same light conditions, most variables for both species did not vary significantly among different water treatments. Irrespective of water treatment, both species showed significant decreases in maximum light saturated photosynthetic rate (P _max), photosynthetic nitrogen-use efficiency, and relative growth rate under LI relative to full irradiance; specific leaf area, however, increased significantly from full to LI though leaf area decreased significantly, indicating that limited light availability under extreme shade was the critical factor restricting the growth of both species. Our results also indicated that M. micrantha performed best under a high light and full soil water combination, while C. odorata was more efficient in growth under a high light and medium soil water combination.