关键词： Acacia drepanolobium   Africa   Laikipia   Kenya   landscape of fear   optimal foraging   predator avoidance   structural equation modeling   tree-grass interactions   ungulates   woody encroachment  

摘要： Herbivores choose their habitats both to maximize forage intake and to minimize their risk of predation. For African savanna herbivores, the available habitats range in woody cover from open areas with few trees to dense, almost-closed woodlands. This variation in woody cover or density can have a number of consequences for herbaceous species composition, cover, and productivity, as well as for ease of predator detection and avoidance. Here, we consider two alternative possibilities: first, that tree density affects the herbaceous vegetation, with concomitant "bottom-up'' effects on herbivore habitat preferences;or, second, that tree density affects predator visibility, mediating "top-down'' effects of predators on herbivore habitat preferences. We sampled sites spanning a 10-fold range of tree densities in an Acacia drepanolobium-dominated savanna in Laikipia, Kenya, for variation in (1) herbaceous cover, composition, and species richness;(2) wild and domestic herbivore use;and (3) degree of visibility obstruction by the tree layer. We then used structural equation modeling to consider the potential influences that tree density may have on herbivores and herbaceous community properties. Tree density was associated with substantial variation in herbaceous species composition and richness. Cattle exhibited a fairly uniform use of the landscape, whereas wild herbivores, with the exception of elephants, exhibited a strong preference for areas of low tree density. Model results suggest that this was not a response to variation in herbaceous-community characteristics, but rather a response to the greater visibility associated with more open places. Elephants, in contrast, preferred areas with higher densities of trees, apparently because of greater forage availability. These results suggest that, for all but the largest species, top-down behavioral effects of predator avoidance on herbivores are mediated by tree density. This, in turn, appears to have cascading effects o

关键词： Quercus alba   Quercus velutina   carbon distribution   root starch   tannins   herbivory  

摘要： This study was developed to experimentally determine whether the differential mortality of white oak versus black oak observed following defoliation events in the oak-dominated forests of the central hardwoods region of the eastern USA may be due to differences in carbon allocation between the two species. Black oak and white oak growing in a common garden were artificially defoliated (90%) using scissors in two consecutive years. Concurrent with the second defoliation event, herbivore performance and phytochemical characteristics were measured, followed immediately by measures of tree growth. In the dormant season following the second defoliation event, roots were sampled to assess tree vigor. Species-specific differences in foliar chemistry and herbivory were evident, regardless of defoliation. Defoliation-induced changes in above-ground biomass were evident in white oak, but not black oak. Defoliation-induced changes in foliar chemistry were more evident in black oak;these were reflected in greater differences in herbivore suitability. Herbivore consumption was correlated with depressed foliar C:N ratios and elevated foliar nitrogen. White oak root starch concentrations were markedly lower in defoliated trees, suggesting that white oak vigor is especially sensitive to resource limitations in the form of photosynthate loss. The implications of these results with respect to defoliation events and white oak mortality, as well as potential phylogenetic differences in response to severe defoliation between the red and white oak groups, are discussed. (C) 2008 Elsevier B.V. All rights reserved.

摘要： The zooplankton of 23 small salmon rivers of the White Sea and Barents Sea basins in the Kola Peninsula were studied. The species composition and quantitative indices in juvenile salmonids habitats are characterized. The maximum species diversity and abundance of planktonic fauna were recorded in lake-regulated rivers and places with large quantities of water. The quantitative development of zooplankton in rivers is low, which testifies to its minor role as a food resource for salmonid juveniles. The assessment of the ecological state of the river water is presented.

关键词： cohorted recruitment   competition   deep-rooted species   Kalahari   sapling growth rates   savanna  

摘要： Acacia species in arid environments are thought to only establish in years of above-average rainfall, so should exhibit cohorted or pulsed recruitment. I studied population demography of Acacia erioloba Meyer in semi-arid savanna in the Kimberley area (mean annual precipitation = 425 +/- 132 mm), South Africa, to establish whether they recruit episodically. This species was found to have a sapling bank at the sites, indicating that even though cohorted recruitment probably occurs, it is not the primary factor limiting recruitment to larger size classes. A. erioloba saplings given supplementary water and protection from herbivory showed significantly less height growth than saplings given water but not protected from herbivores, and grass within exclusion plots was taller and denser than outside of exclusion plots. The generalized linear model, although finding a significant difference between watered and protected and watered and unprotected saplings, explained only 16% of variation in growth, demonstrating the importance of factors other than competition from grass when rainfall is above-average. Average height increase across all treatments for a growing season was small (43.1 +/- 30.81 mm), suggesting most investment is belowground. A. erioloba sapling below surface stem diameter correlated positively with aboveground growth, indicating larger, and presumably older, individuals grow faster. When grass was removed around saplings, growth rates were not significantly greater than for saplings surrounded by grass, over a growing season. Thus, in these study sites, pulsed events allow seedlings to establish, and then saplings slowly accumulate over many growing seasons within the grass sward, owing to slow aboveground growth combined with competition from grass in absence of grazers. Release events, e.g., heavy grazing combined with good rainfall, may allow mass release, giving the impression of cohorted or pulsed recruitment.

关键词： Sediments   Taxa   Ribosomal DNA   Species diversity   Keys   Salt marshes   Phylogenetics   Phylogeny   Mud flats   Benthos  

摘要： Foraminiferal species distribution and richness have traditionally been assessed through examination of the shells (tests) built by most of the described species, but molecular surveys indicate that this approach likely underestimates true foraminiferal diversity. We use a series of targeted DNA-based surveys and focused morphological searches to document the diversity of allogromiid foraminiferans, which have less distinctive tests, at selected locations along the U.S. eastern seaboard. These sites, although well studied by previous foraminiferal researchers, have not been reported to host large numbers or diverse assemblages of allogromiids. Both survey methods revealed the presence of many new allogromiid taxa and documented striking differences in the allogromiid assemblages between the three locations. The assemblage at a given site as determined by morphological criteria also differed substantially from that determined by molecular surveys. Combined with information from other locales, our data strongly suggest that allogromiid diversity is underestimated;indeed, allogromiids may actually dominate many benthic foraminiferal assemblages. This finding has significant implications for benthic trophodynamics and for the reconstruction of paleoenvironments because the morphological inconspicuousness and taphonomic fragility of allogromiid foraminiferans may lead to underestimates of total foraminiferal diversity and abundance.

关键词： above-belowground relationship   litter quality   macrofauna   nutrients   single-tree influence circles   tropical mountain cloud forest  

摘要： This paper tests whether individual trees in a mature forest stand influence the process of litter decomposition and the macroinvertebrate communities in the soil underneath their canopies, as a result of species-specific characteristics. A field decomposition experiment was performed in a mature forest stand of tropical montane cloud forest in Mexico. The areas under the canopies of Quercus laurina Humbl. & Bompl., Oreopanax xalapensis (Kunth) Decne. & Planchon and Beilschmedia ovalis (Blake) C. K. Allen trees were used as experimental units. The natural soil and litter macroinvertebrate communities were monitored and compared to the community that invaded decomposition boxes with reciprocally transplanted leaf litter. The abundances of four macroinvertebrate taxa in natural litter differed among tree species independently of season. No differences were found in the soil community. The response to experimental litter by macroinvertebrate taxa suggests that the production of a specific quality of litter is an important mechanism by which a tree influences the litter macroinvertebrate community that develops under its canopy. However, not all differences in community composition naturally found between tree species can be explained by differences in litter quality during the first year of decomposition. Differences in nutrient release that occur after the first year, and physical properties of litter also probably play an important role. Independently of the canopy tree, the initial chemical quality (N, P, Ca, Mg and lignin) of experimental litter largely determined the decomposition rate and nutrient dynamics of decomposing leaves. However, it was found that under O. xalapensis trees the breakdown of lignin from the litter produced by the same species of tree was particularly effective. This suggests that a feedback has developed between this tree species and the decomposer community prevailing under its canopy.

关键词： Acacia drepanolobium savanna   associational resistance   Cynodon plectostachyus   facilitation   grasslands   herbivory   indirect effects   Kenya   Pennisetum stramineum   succession  

摘要： Empirical and theoretical evidence suggests that facilitation between plants, when it occurs, is more likely during periods of abiotic stress, while competition predominates under more moderate conditions. Therefore, one might expect the relative importance of competition vs. facilitation to vary seasonally in ecosystems characterized by pronounced dry (abiotically stressful) and wet (benign) seasons. Herbivory also varies seasonally and can affect the net outcome of plant-plant interactions, but the interactive effects of seasonality and herbivory on the competition-facilitation balance are not known. I experimentally manipulated neighboring plants and herbivory during wet and dry periods for two species of grass: Cynodon plectostachyus and Pennisetum stramineum, in the semiarid Laikipia District of Kenya. These experiments indicate that Pennisetum was competitively dominant during the wet season and that it responded negatively to grazing, especially during the dry season. Cynodon showed more complex season- and herbivore-dependent responses. Cynodon experienced facilitation that was simultaneously dependent on presence of herbivores and on dry season. During the wet season Cynodon experienced net competition. These results illustrate how herbivory and seasonality can interact in complex ways to shift species-species competition-facilitation balance. Additionally, because Cynodon and Pennisetum are key players in a local successional process, these results indicate that herbivory can affect the direction and pace of succession.

关键词： MULTIPLE SEQUENCE ALIGNMENT   PHYLOGENETIC-RELATIONSHIPS   HISTORICAL BIOGEOGRAPHY   MAXIMUM PARSIMONY   SUPPORT VALUES   FROGS ANURA   PERU   DIVERSIFICATION   SALAMANDERS   BUFONIDAE  

摘要： Wiens (2007, Q. Rev. Biol. 82, 55-56) recently published a severe critique of Frost et al.'s (2006, Bull. Am. Mus. Nat. Hist. 297, 1-370) monographic study of amphibian systematics, concluding that it is "a disaster" and recommending that readers "simply ignore this study". Beyond the hyperbole, Wiens raised four general objections that he regarded as "fatal flaws": (1) the sampling design was insufficient for the generic changes made and taxonomic changes were made without including all type species;(2) the nuclear gene most commonly used in amphibian phylogenetics, RAG-1, was not included, nor were the morphological characters that had justified the older taxonomy;(3) the analytical method employed is questionable because equally weighted parsimony "assumes that all characters are evolving at equal rates";and (4) the results were at times "clearly erroneous", as evidenced by the inferred non-monophyly of marsupial frogs. In this paper we respond to these criticisms. In brief: (1) the study of Frost et al. did not exist in a vacuum and we discussed our evidence and evidence previously obtained by others that documented the non-monophyletic taxa that we corrected. Beyond that, we agree that all type species should ideally be included, but inclusion of all potentially relevant type species is not feasible in a study of the magnitude of Frost et al. and we contend that this should not prevent progress in the formulation of phylogenetic hypotheses or their application outside of systematics. (2) Rhodopsin, a gene included by Frost et al. is the nuclear gene that is most commonly used in amphibian systematics, not RAG-1. Regardless, ignoring a study because of the absence of a single locus strikes us as unsound practice. With respect to previously hypothesized morphological synapomorphies, Frost et al. provided a lengthy review of the published evidence for all groups, and this was used to inform taxonomic decisions. We noted that confirming and reconciling all morpholo

关键词： herbivory   large aninial exclosure   riparian ecotone   sodic area   herbaceous species richness   plant biodiversity  

摘要： Herbivory is a major driver of ecosystem functioning in semi-arid African savannas, yet its impact on herbaceous biomass dynamics has been poorly understood. Using a 72 ha animal exclosure established 3 years prior, we measured the distribution of herbaceous biomass and species composition in the presence and absence of herbivory in a semi-arid savanna toposequence along the Sabie River in Kruger National Park, South Africa. We found that, in the presence of large herbivores in the reference site, the biomass of herbaceous plant species generally increased from the hillcrest to the lower, wetter riparian zone, while species richness did not change. However, after only 2 and 3 years of herbivore exclusion, the annual maximum biomass in the riparian area increased threefold to similar to 600 g m(-2). Simultaneously, plant species richness declined by 55% and 64% from 10.2 to 9.2 species per m(2) in 2004 and 2005, respectively. In the absence of herbivores, fast-growing grasses overtopped and shaded out forbs of lower stature, resulting in a reduction in the richness of herbaceous species. We conclude that large herbivores are essential in reducing herbaceous competition and maintaining species diversity and ecosystem functioning in African savanna ecosystems, especially in riparian corridors. Published by Elsevier Ltd.

关键词： sensors   herds   animal behavior   cattle production   neck   estimation   mathematical models   prediction   geographic information systems   velocity   speed   cattle production   herd   animal behaviour   Sensors   Neck   angle of pitch   sort tree structure  

摘要： An in-depth study of wireless sensor networks applied to the monitoring of animal behaviour in the field is described. Herd motion data, such as the pitch angle of the neck and movement velocity, were monitored by an MTS310 sensor board equipped with a 2-axis accelerometer and received signal strength indicator functionality in a single-hop wireless sensor network. Pitch angle measurements and velocity estimates were transmitted through a wireless sensor network based on the ZigBee communication protocol. After data filtering, the pitch angle measurements together with velocity estimates were used to classify the animal behaviour into two classes;as activity and inactivity. Considering all the advantages and drawbacks of classification trees compared to neural network and fuzzy logic classifiers a general classification tree was preferred. The classification tree was constructed based on the measurements of the pitch angle of the neck and movement velocity of some animals in the herd and was used to predict the behaviour of other animals in the herd. The results showed that there was a large improvement in the classification accuracy if both the pitch angle of the neck and the velocity were employed as predictors when compared to just pitch angle or just velocity employed as a single predictor. The classification results showed the possibility of determining a general decision rule which can classify the behaviour of each individual in a herd of animals. The results were confirmed by manual registration and by GPS measurements. (c) 2008 IAgrE. Published by Elsevier Ltd. All rights reserved.