关键词： Traffic accidents   Truck drivers   Truck driving  

摘要： The article focuses on the decision of the Accident Review Committee of the U.S. National Safety Council (NSC) to uphold a preventable ruling imposed by a safety director on a truck driver who met an accident while driving on a zero visibility condition in Kansas. The NSC has argued that the 25 miles per hour speed of the driver was too fast for conditions of zero visibility.

关键词： Lago Guri   rodents   seed predation   seedling herbivory   trophic cascade   Venezuela  

摘要： Sapling mortality exceeds recruitment for many species of trees in the dry forest of 16-y-old islets in Lago Guri, Venezuela. Failure of sapling recruitment is potentially attributable to the aberrant animal communities of these islands. Predators of vertebrates are absent and densities of pollinators and seed dispersers are substantially reduced in comparison to the nearby mainland. In contrast, predators of invertebrates, rodents and generalist herbivores (leaf-cutter ants, howler monkeys, common iguanas) are present at greatly elevated densities. Given these distortions in the animal community, recruitment failure of saplings could potentially be attributable to several causes: deduced pollination or seed dispersal, excessive seed predation or seedling herbivory. Two of these hypotheses are tested herein. The seed predation hypothesis predicts greater seed removal in the presence of hyperabundant rodents, and the seedling herbivory hypothesis predicts reduced seedling survival in the presence of hyperabundant herbivores. Seed removal trials were conducted with 18 species of forest trees, using both exposed and lightly buried seeds. Seed removal was not generally higher on islands supporting hyperabundant rodents, contrary to the seed predation hypothesis. Seedlings exposed to herbivores for 4 mo suffered the highest mortality on small islands supporting hyperabundant rodents and leaf-cutter ants. Saplings survived equally well in cages open to arthropods + rodents as in cages open only to arthropods, suggesting that there was no additive effect of rodents on seedling mortality. Current evidence points to excessive seedling herbivory by arthropods, especially by leaf-cutter ants, as the principal cause of recruitment failure on predator-free Lago Guri islets.

关键词： EVOLUTIONARY DIVERSIFICATION   HERBIVOROUS INSECTS   BAYESIAN-INFERENCE   SEQUENCE ALIGNMENT   PERMUTATION TESTS   COLEOPTERA   BRUCHIDAE   MIMOSOIDEAE   LEGUMINOSAE   CONFIDENCE  

摘要： In this study we use an indirect method to address the issue of the systematics of the large and economically important genus Acacia (Leguminosae, Mimosoideae, Acacieae). We propose the use of host-preference data in closely related insect species as a potentially useful tool to investigate host systematic issues, especially when other approaches yield inconsistent results. We have examined the evolution of host-plant use of a highly specialized group of seed-feeders who predate Acacia - the seed-beetles (Coleoptera, Chrysomelidae, Bruchinae). First, the evolution of host-plant preferences in a large clade of Bruchidius species was investigated using molecular phylogenetics and character optimization methods. Second, the scope of our study was enlarged by critically reviewing the host-plant records of all bruchine genera associated with Acacia. Both morphological and molecular data were used to define relevant insect clades, for which comparisons of host-plant range were performed. Interestingly, the analyses of host-plant preferences from 163 seed-beetle species recovered similar patterns of host-plant associations in the distinct clades which develop within Acacia seeds. Our results clearly support the hypothesis of Acacia being a paraphyletic genus and provide useful insights with reference to the systematics of the whole subfamily as well. This study should also be of interest to those involved in the numerous biological control programs which either already use or aim to use seed-beetles as auxiliary species to limit the propagation of several invasive legume tree species.

关键词： bottom-up   top-down   ecosystem engineers   food webs   trophic cascades  

摘要： Despite conceptual recognition that indirect effects initiated by large herbivores are likely to have profound impacts on ecological community structure and function, the existing literature on indirect effects focuses largely on the role of predators. As a result, we know neither the frequency and extent of herbivore-initiated indirect effects nor the mechanisms that regulate their strength. We examined the effects of ungulates on taxa (plants, arthropods, and an insectivorous lizard) representing several trophic levels, using a series of large, long-term, ungulate-exclusion plots that span a landscape-scale productivity gradient in an African savanna. At each of six sites, lizards, trees, and the numerically dominant order of arthropods (Coleoptera) were more abundant in the absence of ungulates. The effect of ungulates on arthropods was mediated by herbaceous vegetation cover. The effect on lizards was simultaneously mediated by both tree density (lizard micro-habitat) and arthropod abundance (lizard food). The magnitudes of the experimental effects on all response variables (trees, arthropods, and lizards) were negatively correlated with two distinct measures of primary productivity. These results demonstrate strong cascading effects of ungulates, both trophic and nontrophic, and support the hypothesis that productivity regulates the strength of these effects. Hence, the strongest indirect effects (and thus, the greatest risks to ecosystem integrity after large mammals are extirpated) are likely to occur in low-productivity habitats.

关键词： anti-predator adaptation   dispersal   flowering   fruiting   seasonality  

摘要： 1 We examined the factors determining synchrony in reproduction in nine Acacia and six other tree species in the Serengeti ecosystem. 2 We test two hypotheses: (i) an abiotic hypothesis where the primary determinant of synchrony is an adaptation to water availability;and (ii) biotic hypotheses where these adaptations to water can be further refined by additional adaptations to avoid predators, or attract seed and fruit dispersers. 3 Flowering and fruiting were recorded monthly for individually marked trees during 1997-2004. Flowering in different species occurs semi-annually, annually or, in the case of one species, once every 2 years. For most species synchrony of flowering was correlated with seasonal rainfall, with lags related to the mean height of the species;small species flowered during the rains while larger species flowered in the dry season. Fruiting seasons occurred at the end of the rains irrespective of the flowering season. 4 Most species showed flowering synchrony greater than expected from the distribution of rainfall. This may be related to avoidance of insect seed predators through predator satiation. Two Acacias showed multi-annual fruiting (masting), possibly as a predator avoidance mechanism. Acacia tortilis has two flowering seasons: a dry season flowering with early abortion of pods and a wet season flowering producing successful fruits. 5 Two species of Commiphora appeared to be synchronized so as to attract birds that disperse seeds. Acacia tortilis produced indehiscent pods attractive to ungulates, possibly to kill bruchid beetles during digestion and so increase seed viability. 6 Our results suggest that synchrony in these trees is caused by a strong interaction between abiotic and biotic factors. Closely related species have different reproductive patterns of synchrony that seem to be adapted to different combinations of rainfall, predators and dispersers. Rainfall is the primary determinant but the activities of predators and dispersers

关键词： mycelial mats   meso-fauna   soil community structure   underground herbivory  

摘要： Mycelial mats in a tropical rainforest in southern Mexico were more abundant under large buttressed trees than small trees of Brosimum alicastrum. P and K, though not N, concentrations were lower in fine roots from mats than in control samples and complex changes in functional groups of arthropods associated with mats were also evident. (c) 2006 Elsevier Ltd. All rights reserved.

关键词： mcroinvertebrates   abundance   diversity   habitat heterogeneity   biomass  

摘要： We analyzed benthic samples (n = 128) collected from four cypress-tree population areas within a large, shallow Arkansas reservoir over a 2-year period to investigate macroinvertebrate community distribution patterns and their relation to physical and chemical parameters. The calculated biomass, abundance and diversity of the benthic macroinvertebrate community varied significantly both temporally and spatially. Variations of these variables are most likely explained by significant differences in the concentration of carbon and nitrogen in sediments across lake sites, and on a smaller scale, the presence or absence of cypress trees. Benthic macroinvertebrate abundance, biomass, and diversity significantly decreased with distance from tree.

关键词： Australia   Desert Uplands   fauna   fire   grazing   interaction   management   rangelands   vegetation  

摘要： We studied the response of vegetation and vertebrate assemblages to fire and grazing. and their interacting effects, in Eucalyptus woodland in north-eastern Australia. hi this vegetation type, many pastures remain free of cattle grazing due to the occurrence of a native shrub poisonous to livestock. Vegetation (floristic data and 22 habitat variables) and vertebrate fauna (birds. mammals, reptiles) were sampled in 29 standardized 50 x 50-m quadrats in the 2001 wet season. representing Four treatments: sites burnt recently (within 2 y) and grazed by cattle (4-8 ha per livestock unit): sites unburnt (last burnt > 2 y ago) and grazed: sites burnt recently and ungrazed: and unburn and ungrazed sites. Fire and grazing had a significant influence on vegetation: both grazing and fire reduced ground cover (fire in grazed sites 51-23%, tire in ungrazed sites 68-39%)) and increased the cover of forbs (8%, in burnt and grazed sites, 3%, if ungrazed) and tussock grasses (20%) in grazed and unburnt sites and 5%) when ungrazed). Grazing caused a shift in floristic composition from the perennial hummock grass Trioda pungens to tussock grasses (e.g. Aristida spp.. Enneapogon spp.), forbs (e.g. Phyllanthus spp.) and shrubs (e.g. Acacia spp.). Of the vertebrate groups, birds responded more to fire effects (9 species), reptiles to grazing effects (6 species) and mammals to the interaction (2 species). Species reacted to increases in bare ground (e.g. crested pigeon Ocyphaps lophotes, hooded robin Melanodryas cucullatus. Ctenophorus nuchalis) and to the dominant ground cover (e.g. Ctenotus pantherinus) or change in vegetation architecture (e.g. singing honeyeater Lichenostomus virescens, variegated fairy-wren Malurus lamberti). The clearest example of an interacting effect was the cycle of complementary dominance between the rodents Pseudomys delicatulus and P. desertor, the latter's post-fire recovery becoming more muted in sites where cattle grazed (modelled time for population recov

关键词： species diversity   structural diversity   trophic level   shrub encroachment   vegetation structure  

摘要： Shrub encroachment due to heavy grazing has led to dramatic changes in and savanna landscape structure worldwide. It is considered to be one of the most threatening forms of rangeland degradation altering plant diversity. However, possible impacts of shrub encroachment on species diversity at higher trophic levels remain poorly understood. Additionally, indirect effects, such as changes of trophic interactions, are often ignored when trying to understand changes in biodiversity patterns. In this study, conducted in the southern Kalahari, we explored how the diversity of small carnivores and their prey is affected by shrub encroachment. We analysed the relationships between abundance and diversity of small carnivores, the availability of their main prey groups (coleopterans, termites, grasshoppers, rodents) and the structural diversity of the landscape (shrub, grass and herb cover). Eight hundred track surveys were conducted to determine carnivore abundance on 20 rangeland habitats, which represented a gradient of grazing intensity. Prey availability was surveyed for each study site and related to vegetation cover. Results show a significant impact of shrub cover on abundance and diversity of carnivores and their prey. The diversity of both, carnivores and their prey, showed a hump-shaped response to increasing shrub cover whereas relative carnivore abundance decreased. Availability of prey groups was affected differently by shrub cover increase. Diversity of carnivores was best predicted by shrub cover (R-2>0.7, p<0.001) indicating the overriding role of habitat structure as compared to prey availability. We conclude that intermediate shrub cover values enrich structural diversity of savanna landscape and in consequence sustain diversity of small carnivores and their prey in and and semiarid ecosystems. (C) 2006 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved.

关键词： Species Tree   Gene Tree   Additional Data File   Gene Gain   Tree Reconciliation  

摘要： Background: Comparative genomic studies are revealing frequent gains and losses of whole genes via duplication and pseudogenization. One commonly used method for inferring the number and timing of gene gains and losses reconciles the gene tree for each gene family with the species tree of the taxa considered. Recent studies using this approach have found a large number of ancient duplications and recent losses among vertebrate genomes. Results: I show that tree reconciliation methods are biased when the inferred gene tree is not correct. This bias places duplicates towards the root of the tree and losses towards the tips of the tree. I demonstrate that this bias is present when tree reconciliation is conducted on both multiple mammal and Drosophila genomes, and that lower bootstrap cut-off values on gene trees lead to more extreme bias. I also suggest a method for dealing with reconciliation bias, although this method only corrects for the number of gene gains on some branches of the species tree. Conclusion: Based on the results presented, it is likely that most tree reconciliation analyses show biases, unless the gene trees used are exceptionally well-resolved and well-supported. These results cast doubt upon previous conclusions that vertebrate genome history has been marked by many ancient duplications and many recent gene losses.