关键词： MALE MATING SUCCESS   SEXUAL SELECTION   TREE FROGS   HYLA-VERSICOLOR   BODY-SIZE   BEHAVIOR   ANURAN   TOADS   RISK   BUFO  

摘要： Despite the large amount of work on frog mating systems, the potential role of predators as an agent of selection on breeding adults has received very little study. Here, I use data from multiple populations of Pacific Treefrogs (Pseudacris regilla) to demonstrate that sexual selection from mating success favors larger males, but natural selection from predation by giant water bugs favors smaller males. Additionally, I found no relationship between male body condition and mating success or predation risk. This result demonstrates that predation is a potentially important agent of selection that counteracts sexual selection in anurans.

关键词： bird   corridor   exotic pasture grass   grazing   miner   remnant  

摘要： This study reports on the responses of bird assemblages to woodland clearance, fragmentation and habitat disturbance in central Queensland Australia, a region exposed to very high rates of vegetation clearance over the last two to three decades. Many previous studies of clearing impacts have considered situations where there is a very sharp management contrast between uncleared lands and cleared areas: in this situation, the contrast is more muted, because both cleared lands and uncleared savanna woodlands are exposed to cattle grazing, invasion by the exotic grass Cenchrus ciliaris and similar fire management. Bird species richness (at the scale of a 1-ha quadrat) was least in cleared areas (8.1 species), then regrowth areas (14.6 species), then uncleared woodlands (19.9 species). Richness at this scale was unrelated to woodland fragment size, connectivity or habitat condition;but declined significantly with increasing abundance of miners (interspecifically aggressive colonial honeyeaters). At whole of patch scale, richness increased with fragment size and decreased with abundance of miners. This study demonstrates complex responses of individual bird species to a regional management cocktail of disturbance elements. Of 71 individual bird species modelled for woodland fragment sites, the quadrat-level abundance of 40 species was significantly related to at least one variable representing environmental position (across a rainfall gradient), fragment condition, fragment size and/or connectivity. This study suggests that priorities for conservation management include: cessation of broad-scale clearing;increased protection for regrowth (particularly where this may bolster connectivity and/or size of woodland fragments);control of miners;maintenance of fallen woody debris in woodlands;increase in fire frequency;and reduction in the incidence of grazing and exotic pasture grass.

关键词： artificial waterholes   surface water   water   dependency   grazing heterogeneity   piosphere   Kruger National Park  

摘要： It has been argued that the wide-scale provision of artificial surface water in semi-arid savannas may result in homogenisation of foraging regimes, compromising biodiversity and ecosystem resilience. This is the first landscape-scale study investigating to what degree artificial waterholes and natural rivers influence the distribution of large herbivores, and hence foraging patterns, in the Kruger National Park, South Africa. This is explored by examining consistencies within and differences between distribution patterns of herbivore feeding groups on different geologies. Seven years of dry season aerial census data of thirteen large herbivores were analysed in a GIS. It was found that different herbivores exhibit different distribution patterns around rivers and waterholes. it was found that most grazer species were associated with artificial waterholes, whereas browsers and mixed feeders were indifferent to waterholes and were associated with the main rivers. This has important management implications for artificial water provision in the KNP and potentially for other semi-arid African savanna conservation areas. Man-made waterholes are therefore features in the landscape that can change the distribution of herbivores, even in a landscape where natural water is available, transforming patterns of landscape use. Furthermore, it was also found that the underlying geology interacts with water distribution in shaping herbivore distributions, with artificial waterholes and rivers acting as stronger nodes of herbivore activity on nutrient-rich basaltic soils than nutrient-poor granitic soils. The results from this paper may be useful for designing surface water policies and management plans for Kruger and other savanna reserves in Africa in order to maximise biodiversity conservation. (C) 2006 Elsevier Ltd. All rights reserved.

关键词： corolla length   hummingbird assemblages   hummingbird bill length   Nicotiana glauca   pollination  

摘要： Nicotiana glauca, a hummingbird pollinated plant, exhibits geographical variation in several floral traits. We examined whether geographical differentiation occurred for different flower characters and if this differentiation could be explained, at least in part, by the existence or abundance of different hummingbird species in the respective pollinator assemblages. The comparison between five populations showed significant variation in six floral traits and two female fitness measures. The traits that better discriminated between populations were corolla length and corolla width. There were metric correlations between corolla length and style length in all populations studied and, in four of the five populations, both corolla length and width were also correlated. Among plants in each population, seed weight was correlated positively and significantly with style exertion, suggesting that fruit quality is dependent on the degree of cross pollination. Assemblages of hummingbirds differed between populations in species composition, visitation frequencies, and bill length. Linear regression involving bill length of the more frequent hummingbird pollinators and corolla length yielded positive and significant relationships. Thus, there appears to be an adjustment between pollinators and flowers traits that have high incidence in the among population variation. (c) 2007 The Linnean Society of London.

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.