关键词： BIOLOGICAL INVASIONS   PHEIDOLE-MEGACEPHALA   RAIN-FOREST   ANT   HOMOGENIZATION   CONSEQUENCES   IMPACT  

摘要： Palmyra Atoll, in the Line Islands of the equatorial Pacific, supports one of the largest remaining native stands of Pisonia grandis forest in the tropical Pacific Ocean. In 2003, we surveyed terrestrial arthropods to document extant native and introduced species richness, compare these lists with historical records, and assess potential threats to native species and ecosystem integrity. In total, 115 arthropod taxa were collected, bringing the total number of taxa recorded since 1913 to 162. Few native species were collected;most taxa were accidental introductions also recorded from the Hawaiian Islands, the presumed main source of introductions to Palmyra. The overlap with previous historical Surveys in 1913 and 1948 was low (<40%), and new species continue to establish, with one species of whitefly reaching pest status between 2003 and 2005. We observed numerous dead or dying large Pisonia grandis, and the green scale Pulvinaria. urbicola (Coccidae) was particularly abundant on trees of poor health. Abundant introduced ants, particularly Pheidole megacephala, tended this and other hemipterans feeding on both native and introduced plants. We hypothesize that the Pheidole-Pulvinaria facultative mutualism is causing the decline of Pisonia grandis. Because of the unique properties of Pisonia grandis forest on oceanic atolls, its importance for nesting seabirds, and its alarming global decline, immediate conservation efforts should be directed at controlling introduced Hemiptera and disrupting their mutualisms with normative ants on Palmyra Atoll.

关键词： bagging   biomonitoring   boosting   decision tree   ecological modelling   habitat suitability   river assessment   tree-pruning  

摘要： In this study, decision tree models were induced to predict the habitat suitability of six macroinvertebrate taxa: Asellidae, Baetidae, Caenidae, Gammaridae, Gomphidae and Heptageniidae. The modelling techniques were applied on a dataset of 102 samples collected in 31 sites along the river Axios in Northern Greece. The database consisted of eight physical-chemical and seven structural variables, as well as the abundances of 90 macroinvertebrate taxa. A seasonal variable was included allowing the description of potential temporal changes in the macroinvertebrate taxa. Rules relating the presence/absence of six benthic macroinvertebrate taxa with the 15 physical-chemical and structural river characteristics and the seasonal variable were induced using the J48 algorithm. In order to improve the performance and the interpretability of the induced models, three optimisation techniques were applied: tree-pruning, bagging and boosting. The predictive performance of the decision tree models was assessed on the basis of the percentage of Correctly Classified Instances (CCI) and the Cohen's kappa statistic. The results of the present study demonstrated that although the models had a relatively high predictive performance, noise in the dataset and inappropriate input variables prevented to some extent, the models from making reliable predictions. Although tree-pruning did not improve significantly the reliability of the induced models, it reduced considerably the tree complexity and in this way increased the transparency of the trees. Consequently, the induced models allowed for a correct ecological interpretation. The effect of bagging and boosting on the other hand varied considerably between the different models, as well as within different repetitions of 10-fold cross-validation in an individual model. In some cases the predictive performance was improved, in others stable or even worsened. The effect of bagging and boosting seemed to be strongly dependent on the dataset o

关键词： embryo behaviour   hatching   inducible defence   phenotypic plasticity   predation  

摘要： Risk-sensitive hatching is adaptive for species facing a trade- off between egg-stage and post-hatching risks, and environmental variation in one or both stages. Such plasticity has been found in amphibians, fishes, reptiles and spiders, with red-eyed treefrogs (Agalychnis callidryas) being the best-studied case. We assessed hatching plasticity and egg- and larval-stage risks in a closely related, syntopic species, the gliding leaf-frog (Agalychnis spurrelli). We found a lower hatching response to egg-eating snakes in A. spurrelli (9-28% of embryos escaped) than in A. callidryas (59-80% escaped). Levels of snake predation were similarly high for clutches of both species monitored at a pond in Costa Rica, and in fish predation experiments early-hatched A. spurrelli tadpoles were more vulnerable than later hatchlings, as has been shown for A. callidryas. A. spurrelli thus face a risk trade-off similar to A. callidryas, and likely would benefit from predator-nduced hatching;their lower responsiveness to snakes appears nonadaptive. A. spurrelli embryos showed a stronger hatching response (57% hatched in 1 h) to submergence underwater than to snake attacks even though submergence is a less frequent risk. This suggests they have a greater capacity for early hatching than is expressed in the context of snake attacks, but have much lower sensitivity to snake cues than to flooding cues. Development in A. spurrelli is accelerated compared to syntopic A. callidryas, and spontaneous hatching is earlier and more synchronous. This is congruent with predictions based on selection by egg predators in the absence of a strong escape hatching response.

关键词： carnivore   faeces   hair   herbivore   Kruger Park  

摘要： This paper characterizes predator - prey interactions amongst African mammals from C-4 savanna environments using stable carbon and nitrogen isotope proxies for diet. Stable carbon (delta C-13) and nitrogen (delta N-15) isotope data from hair and faeces of large African mammal carnivores, and herbivores as potential prey, are presented for a diverse range of taxa. Carbon- isotope data imply that most carnivores from the "lowveld" savanna of South Africa form part of C-4 grass-based food webs. Nitrogen isotope data show clear differences between trophic levels, although it appears that the magnitude of these differences varies between predators feeding on invertebrates and vertebrates, respectively. Whilst the number of carnivore samples for which data are available is relatively few, and data for prey are restricted mainly to large ungulate herbivores, results clearly demonstrate the potential for future applications of this technique to predator-prey food webs in African savannas. In tandem with traditional approaches, stable isotopes can help elucidate patterns of predator impacts on prey populations, domestic livestock, and resolving similar food webs in palaeoenvironmental contexts.

关键词： Africa   wildlife   monitoring   conservation   non-protected areas  

摘要： Ecosystem processes in African savannas can be better conserved if management is based on a mechanistic understanding of wildlife dynamics in livestock-dominated landscapes. For Laikipia District, a non-protected savanna region in northern Kenya, we used spatially explicit estimates of density to characterize factors influencing the dynamics of large herbivores on three land-use types: commercial ranches that favor wildlife, communal 'group ranches' practicing pastoralism, and the remainder ('transitional' properties). For 21-year time series of nine wild and two domestic species, linear model selection was used to ascribe between 45% (Grant's gazelle) and 95% (plains zebra) of observed variation in biomass density to land use, rainfall-dependence, density-dependence, and trends over time. Strongly opposing patterns of variation across the landscape in wildlife and livestock densities affirmed the primacy of land use among factors influencing wildlife abundance in non-protected areas. Rainfall limited densities of only the dominant grazing species throughout the monitoring period (plains zebra and cattle), and of most other species while their densities were high. Regulating effects of density were detected only for the dominant wild grazing and browsing species (zebra and giraffe). All but two wild species (zebra and Grant's gazelle) declined on at least one land-use type, for reasons that varied among land uses. Where favored, diverse and abundant wild herbivores (mean of 1.7 t km(-2) on pro-wildlife ranches) can thrive even when sharing the landscape with a slightly higher biomass density of livestock (mean of 2.7 t km-(12)). Where not favored, only a few resilient wild species (e.g. gazelles and plains zebra) persist with high densities of livestock (mean of 4.6 t km(-2) on transitional ranches). Maintaining higher wild species diversity in the landscape will depend on the creation of a network of unfenced conservation areas in which livestock densities are pers

关键词： Sorbus aucuparia   autumnal senescence   pigments   co-evolution   photoinhibtion   handicap signal  

摘要： We explored two mutually nonexclusive hypotheses on autumnal leaf colouration. The co-evolutionary hypothesis states that autumnal leaf colouration functions as a handicap signal to herbivorous insects, whereas the photoprotection hypothesis posits that plant pigments primarily protect the plant against cold-induced photoinhibition and enhance nutrient transfer. To contrast both hypotheses, we compared yellow and red leaf colouration in three groups of mountain ash (Sorbus aucuparia L.). Two montane groups of different age were characterised by low aphid numbers and low temperature, and a lowland group by high aphid numbers and high temperature. There were no consistent altitudinal differences in leaf colouration. Compared to young trees, adult trees developed fewer red but more yellow leaves at high altitude. In the lowland population, the development of red leaf colour was related to decreasing daytime temperature, whereas the appearance of yellow leaf colouration corresponded to the decreasing photoperiod. This is consistent with the photoprotection hypothesis. Individual differences in red and yellow leaf colouration were inversely correlated to the number of fruits, which might be interpreted as a trade-off between reproductive and protective commitment. Temperature effects explained variation in aphid numbers over time and leaf colouration explained aphid distribution on a given day. As predicted by the co-evolutionary hypothesis, strongly coloured individuals harboured fewer aphids than green or dull-coloured ones. Since decreasing temperature reduced the number of migrating aphids but induced red leaf colouration, these processes are not mutually fine-tuned, which likely restricts the potential for co-evolution between mountain ash and aphids.

关键词： Austrocedrus   climate change   disturbances   fire   livestock   Nothofagus   Patagonia   seedling survival   tree regeneration  

摘要： 1. Wildfires are predicted to increase in many ecosystems in relation to globally increasing temperatures but future patterns of post-fire vegetation change are largely unknown, particularly when there are synergistic effects from introduced biota. In the late 1990s northern Patagonia, Argentina, experienced extreme droughts which led to severe wildfires affecting a range of Andean ecosystems. 2. We experimentally examined how variations in moisture, temperature and herbivory by livestock affect post-1999 fire patterns of the three main tree species. Over two years we monitored, in three forest types, the survival and growth of tree seedlings in a factorial warming (+2 degrees C)/livestock exclosure/watering experiment. 3. Seedling survival in the warmed treatments and in the controls was nil for the evergreen Nothofagus dombeyi and the conifer Austrocedrus chilensis at the two low-elevation experimental sites. Survival of the subalpine Nothofagus pumilio in the warmed treatments at high elevation tended to be lower than in the control;for all treatments of warming alone there were no significant differences compared with the controls. 4. In all three forest types, increased water availability was essential for higher rates of tree seedling survival. Doubling water availability during the growing season resulted in up to fourfold increases in seedling survival and up to threefold increases in seedling biomass. 5. In the subalpine forest, livestock reduced seedling survival by c. 30% in non-watered treatments compared with watered treatments, probably due mainly to soil desiccation and to consumption of or damage to facilitating plants. In contrast, at lower elevation, where livestock pressure was lower, seedling survival of N. dombeyi and A. chilensis tended to be higher in unfenced sites, possibly due to reduced competition from highly palatable shrub species. 6. General circulation models predict a warming-drying trend in northern Patagonia during the twenty-first

关键词： wildlife   rainfall   predation   competition   apparent competition   non-protected area  

摘要： Conserving African wildlife in human-occupied landscapes requires management intervention that is guided by a mechanistic understanding of how anthropogenic factors influence large-scale ecological processes. In Laikipia District, a dry savanna region in northern Kenya where wildlife share the landscape with humans and livestock, we examined why five of nine wild ungulate species suffered protracted declines on properties receiving the greatest conservation investment. Of 10 alternative causes examined, only an increase in predation, interacting with brief periods of high and low rainfall, was consistent with the timing, synchrony, duration and species composition of observed ungulate declines. The principal factor causing predation to increase was a shift in land use from cattle ranching, under which predators and plains zebras were severely suppressed, to wildlife conservation and ecotourism. This prompted a 5-fold increase in plains zebra abundance, and created a demand for living predators. Plains zebras ultimately comprised more than half the available prey biomass, and supported a substantial predator community, but were not limited by predators. We infer that increasing predation pressure caused predator-susceptible prey species to decline, via mechanisms that included apparent competition. Herbivore dynamics in Laikipia shared features with previously reported responses by prey communities to predator manipulation in Kruger and Serengeti National Parks. All featured one or a few numerically dominant herbivore species, which were primarily limited by rainfall and density, supporting a predator community that in turn limited the abundance of other prey species. In each case, predation had a profound effect, but on only a subset of prey species, reducing the evenness component of prey diversity. The presence of cattle in the landscape may affect predator-prey dynamics in both direct and indirect ways, depending on rainfall. In extreme years (floods or drought),

关键词： carbon uptake   ecosystem productivity   herbivory   modelling   photosynthesis  

摘要： 1. Through its effect on plant productivity and fitness, herbivory can regulate forest diversity and ecosystem productivity. We used the interaction between phloem-feeding scale insects [Ultracoelostoma assimile (Homoptera: Coelostomidiidae)] and the beech trees [Nothofagus solandri var. solandri (Hook f.) Oerst.] they feed on to estimate directly the carbon costs of herbivory for a forest tree species over two consecutive years. The scale insects live on the bark of tree trunks and branches, and excrete readily collected droplets of carbon-rich honeydew - this allows us to make an estimate of the carbon cost of herbivory that is not complicated by feeding damage to leaves and buds. 2. Canopy photosynthesis (A) was estimated with an environmentally driven process-based model, developed with parameters derived from measurements of photosynthesis on trees with (HD+) and without (HD-) honeydew scale insects during year 1. Honeydew dry matter production (P-HD) was estimated from values for air temperature and humidity, and accounting for variation in honeydew production due to host-tree diameter. The carbon cost of scale insect herbivory, C-HD, was estimated as P-HD/A(HD+) x 100%, where A(HD+) is canopy photosynthesis for trees with scale insects. 3. Over the two years annual canopy photosynthesis at the site was 1720 g C m(-2) ground area. In spring-summer, values for parameters describing photosynthesis (V-cmax, the maximum rate of rubisco-catalysed RuBP carboxylation, and J(max), the rate of electron transport when irradiance is saturating) were 44% and 66% higher, respectively, in infested, as opposed to uninfested, trees. Consequently, for equivalent basal area, annual canopy photosynthesis was 4% greater for infested trees. 4. Assuming that honeydew dry matter was 42% carbon by mass, annual honeydew production was 59 g C m(-2) ground area, which represents 4% of infested-tree gross photosynthesis (c. 8% of net photosynthesis). Daily values of honeydew production w

关键词： Senna racemosa   Fabaceae   dihydroxyanthraquinones   cassine   antigiardial   antiamoebic  

摘要： Methanol extracts of leaves, roots and bark of Senna racemosa (Mill.) H.S. Irwin & Barneby (syn. Cassia racemosa Mill.) were tested for antiprotozooal activity against Giardia intestinalis and Entainoeba histolytica. All of the tested extracts showed good activity against both protozoa species. Extracts from stem bark and leaves were most active, with an IC50 of 2.10 mu g/mL for Giardia intestinalis and 3.87 mu g/mL for Entainoeba histolytica. Of the previously isolated compounds from Senna racemosa, the piperidine alkaloid cassine had greater activity against Giardia intestinalis with an IC50 of 3.28 mu g/mL and chrysophanol, a 1,8-dihydroxy-anthraquinone, was the most active agent against Entamoeba histolytica, with an IC50 of 6.21 mu g/mL. (c) 2007 Elsevier Ireland Ltd. All rights reserved.