关键词： ant-plant interactions   Bruchidius   parasitoid wasps   Pteromalidae   seed predator   stable isotopes  

摘要： Acacia drepanolobium is an obligate ant-plant that bears dehiscent pods exploited by predispersal seed-predators and parasitoids. Fruit set and seed germination in relation to ant-association, bruchid and parasitoid infestation were investigated in a large-scale multi-year study in Kenya. Ant-association had a significant impact on the overall numbers of fruiting trees. 94.8% of Crematogaster mimosae-occupied trees, 25.6% of ***-occupied trees, and 82.2% of Tetraponera penzigi-occupied trees set fruit. Within each tree, ant-association had no significant impact on the amount of seed produced: ***-occupied trees produced 47.5 seeds per branch, ***-occupied trees 44.9 seeds per branch and ***-occupied trees 38.3 seeds per branch. Ant-association did not limit seed-predators or vary significantly by ant. Seeds infested by bruchids germinated in significantly lower proportions (6.2%) compared to uninfested seed (78.6%). Bruchid-infested seed is also exploited by parasitoid wasps. Parasitoids appear to have a moderate but significant rescue' effect on bruchid-infested seed with 18.4% of parasitoid-infested seed germinating. Stable isotopes (15N) revealed the trophic structure of the seed-associated insects, showing clearly that bruchids are seed predators and the parasitoid wasp Dinarmus magnus exploits the dominant Bruchidius sp. ResumeAcacia drepanolobium est une plante a fourmis indispensable qui porte des gousses dehiscentes exploitees par des predateurs et des parasitoides avant leur dispersion. La nouaison et la germination des graines en relation avec l'association avec les fourmis, et l'infestation de bruches et de parasites ont ete etudiees au cours d'une etude a grande echelle de plusieurs annees, au Kenya. L'association avec les fourmis a un impact significatif sur le nombre total d'arbres qui fructifient. 94.8% des Crematogaster mimosae occupes, 25.6% des *** occupes et 82.2% des Tetraponera penzigi occupes produisent des f

关键词： Cavity-nesting birds   Decaying wood   Forest management   Fungal inoculations   Fomitopsis pinicola   Woodpecker foraging  

摘要： Decaying wood plays a vital role in maintaining biological diversity and ecological processes within forest ecosystems. One enhancement that may help to maintain wood-decay processes in managed forests involves the inoculation of healthy trees with fungus to create potential habitat trees to enable excavation for foraging and nesting by primary cavity nesters (i.e., woodpeckers);however, this approach has only received limited evaluation. We evaluated the inoculation of Fomitopsis pinicola into live trees in managed forests in western Washington in 1997 and 1998. In 2006, we revisited trees that were inoculated with live fungus or sterile controls, and inspected each tree for the presence of fungal growth and woodpecker activity. Of 650 trees inoculated with fungus (n = 330) or a sterile control (n = 320), 528 (81.2%) were alive and standing in 2006 (n = 276 with fungus, 83.6%;n = 252 control trees, 78.8%). Trees had been lost to harvest (11.1%), blowdown (3.8%), breakage (2.9%), and had died of undetermined causes (0.9%). A higher proportion of treatment trees displayed F. pinicola conks (0.200) and mycelia (0.073;inferred to be F. pinicola) than did control trees (0.004 conks [unknown species], 0.012 mycelia), although the difference for mycelia was marginally significant. We also found that western hemlock (Tsuga heterophylla) had a higher proportion of conks (0.313) and evidence of any fungal growth (conks or mycelia;0.393) than Douglas-firs (Pseudotsuga menziesii;0.064 and 0.112, respectively). Further, we observed evidence of significantly (P = 0.010) more woodpecker excavations and sapsucker (Sphyrapicus spp.) foraging holes associated with the fungal inoculations (6.2%) than at control trees (1.2%). Although use by woodpeckers was limited, we suggest that this finding is ecologically significant as we observed no woodpecker use, except for limited sapsucker foraging, when we inspected trees in 2002. The fungal inoculations completed 1997-1998, to some extent

关键词： Crop size   Fruiting environment   Phenotypic selection   Predator satiation   Spatial structure  

摘要： Spatio-temporal variability in fruit production (masting) has been regarded as a key mechanism to increase plant fitness by reducing seed predation. However, considerably more effort has been devoted into understanding the consequences of temporal rather than spatial variations in fruit crop for plant fitness. In order to simultaneously evaluate both components, we quantify fruit production and pre-dispersal damage by three arthropod species (mites, chalcid wasps and moths) in the Spanish juniper (Juniperus thurifera) during 3 years in a spatially explicit context. Our aims were to assess (1) the interaction between fruit production and pre-dispersal fruit damage by arthropods, (2) the potential interference or competition between arthropods, and (3) the form of the phenotypic selection exerted by arthropods on fruit traits considering the spatial context. Arthropods damaged a substantial fraction of fruits produced by Spanish juniper with levels of damage showing sharp inter-annual variations. Fruit damage by mites was negatively related to yearly fruit crop and positively correlated at individual trees fruiting in consecutive years. Increased interspecific interference was an additional consequence of reduced fruit availability during small crop years. During a masting year, fruit damage by less mobile species such as mites was negatively affected by tree crop size, and no spatial structure was observed for mite damage. The incidence of chalcid wasps was low, so the spatial pattern of seed predation was unclear, and no preferences for fruit or seed traits were detected. Conversely, moths selected larger fruits and their incidence on trees was spatially aggregated up to 20 m, with predation levels being negatively affected by fruit abundance at the patch level, suggesting a positive density-dependent effect of neighbors on fruit output. These results highlight the importance of including the spatial component to understand complex species interactions at local scal

关键词： Cadaba farinosa   cattle-wildlife interactions   Colotis spp   herbivore exclusion   pollinators   rangeland system   resource webs   ungulate herbivory  

摘要： Indirect interactions driven by livestock and wild herbivores are increasingly recognized as important aspects of community dynamics in savannas and rangelands. Large ungulate herbivores can both directly and indirectly impact the reproductive structures of plants, which in turn can affect the pollinators of those plants. We examined how wild herbivores and cattle each indirectly affect the abundance of a common pollinator butterfly taxon, Colotis spp., at a set of long-term, large herbivore exclosure plots in a semiarid savanna in central Kenya. We also examined effects of herbivore exclusion on the main food plant of Colotis spp., which was also the most common flowering species in our plots: the shrub Cadaba farinosa. The study was conducted in four types of experimental plots: cattle-only, wildlife-only, cattle and wildlife (all large herbivores), and no large herbivores. Across all plots, Colotis spp. abundances were positively correlated with both Cadaba flower numbers (adult food resources) and total Cadaba canopy area (larval food resources). Structural equation modeling (SEM) revealed that floral resources drove the abundance of Colotis butterflies. Excluding browsing wildlife increased the abundances of both Cadaba flowers and Colotis butterflies. However, flower numbers and Colotis spp. abundances were greater in plots with cattle herbivory than in plots that excluded all large herbivores. Our results suggest that wild browsing herbivores can suppress pollinator species whereas well-managed cattle use may benefit important pollinators and the plants that depend on them. This study documents a novel set of ecological interactions that demonstrate how both conservation and livelihood goals can be met in a working landscape with abundant wildlife and livestock.

关键词： Amphibian   Pesticides   Predation   Stress response   Toxic effects  

摘要： Global amphibian declines have many corroborative causes, and the use of pesticides in agriculture is a likely contributor. In places with high pesticide usage, such as Costa Rica, agrochemical pesticides may interact with other factors to contribute to rapid species losses. Classical ecotoxicological studies rarely address the effects of a pesticide in combination with other stressors. The present study investigated the synergistic roles of 2 pesticides (chlorothalonil and endosulfan), predator stress, and environmental regimes (controlled laboratory environments versus ambient conditions) on the survival of red-eyed tree frog larvae (Agalychnis callidryas). No synergistic effects of pesticide mixtures or predator stress were found on the toxicity of either chlorothalonil or endosulfan. Both pesticides, however, were considerably more toxic under realistic ambient temperature regimes than in a climate-controlled laboratory. Overall, endosulfan displayed the highest toxicity to tadpoles, although chlorothalonil was also highly toxic. The median lethal concentration estimated to kill 50% of a tested population (LC50) for endosulfan treatments under ambient temperatures was less than one-half of that for laboratory treatments (3.26 mu g/L and 8.39 mu g/L, respectively). Studies commonly performed in stable temperature-controlled laboratories may significantly underestimate toxicity compared with more realistic environmental regimes. Furthermore, global climatic changes are leading to warmer and more variable climates and may increase impacts of pesticides on amphibians. (c) 2013 SETAC

关键词： 迪翁   努特   学习委员   蹄兔   小鼯鼠   幼鸟   灰树蛙   令人   太远   夜行性  

摘要： 在树栖班,新学期就像学生们内心的一道坎,因为除了不能再尽情享受愉快的假期外,它们还要在开学第一天交上令人头疼的暑假作业。然而,不管同学们多么不乐意,新学期还是如期而至了……"我说过多少次了,迪翁校长布置的作业必须按时完成,而且要精益求精,这学期咱们班绝不能落在其他班级后面!"

关键词： Dispersal limitation   Diversity maintenance   Predation limitation   Seed dispersal   Seed limitation   Seed predation   Small mammals   Tropical forests  

摘要： Recruitment limitation of trees in tropical forests can occur because of high rates of seed predation or low rates of seed dispersal, but the degree to which limitation is influenced by variation in seed predator abundance, and hence variation in seed predation and dispersal, is not well understood. We experimentally reduced the density of a granivorous small mammal (Heteromys desmarestianus) by 90 % to assess the degree to which its rates of seed predation and dispersal limit seed to seedling survival of nine species of trees in a Neotropical lowland forest. Overall, the proportion of seeds that germinated was influenced more by high rates of predation than by limited dispersal. Reduction in density of H. desmarestianus resulted in an order of magnitude decrease in fruit removal rates and an order of magnitude increase in both the absolute and relative numbers of seeds that germinated. However, the proportion of seeds that were cached remained relatively constant across all periods and between control grids and removal plots. In removal plots, H. desmarestianus dispersed and cached about 10 % of the fruits they handled, of which approximately 25 % germinated. This was 2 to 3 times greater than the germination rates of undispersed seeds, and for two species dispersed seeds were the only ones that germinated. The results suggest the simultaneous occurrence of both seed predation and dispersal limitation for trees with animal-dispersed seeds, but there may also be a hierarchy of importance in the relative strength of these two mechanisms that is determined by the dynamics of seed predator populations.

关键词： exclusion   growth   nitrogen   phosphorus   tannin  

摘要： Impacts of large herbivores (>5kg) on woody plants in African savannas are potentially most severe among plants shorter than 1.6m. It is well established that severe browsing leads to longer shoots, yet prevents saplings from recruiting into adult size-classes in African savannas. Increased shoot length, indicating faster shoot growth, is often associated with reduced concentrations of tannins and increased nutrient concentrations, suggesting carbon limitation. We hypothesized that, on average, large herbivores suppress stem height or circumference, but increase shoot length. We also hypothesized that if there were concomitant positive effects on nutrients, or negative effects on tannin concentrations, they would be greatest early in the wet season. We sampled saplings of four deciduous woody species (Acacia grandicornuta, Dichrostachys cinerea, Combretum apiculatum and Grewia flavescens) at different stages of the wet season in a large-scale, long-term herbivore exclusion experiment in Kruger National Park, South Africa. Plant height, shoot length and stem circumference were generally not adversely affected by large herbivores, suggesting C limitation is rarely present among deciduous saplings in semi-arid African savannas, allowing them to tolerate browsing. Time since first rainfall emerged as a predominant factor consistently affecting nutrient and tannin concentrations, rather than large herbivores. Nitrogen and phosphorus generally decreased (by 20-50%), while condensed tannin concentration increased (150-350%) during the wet season, except for one species. We postulate that *** is less prone than other species to accumulating tannins during the wet season because of high investment of C in spines. Although nutrient and tannin concentrations were generally not affected by large herbivores, species-specific responses were evident very early in the wet season, which is when herbivore populations are most likely to be affected by differential forage q

关键词： Constitutive and inducible defences   extrafloral nectar   EFN   juvenile plants   invasion ecology   specialists   generalists   tallow tree   Triadica sebifera   caterpillars   Noctuidae   Limacodidae  

摘要： Invasive plants can be released from specialist herbivores and encounter novel generalists in their introduced ranges, leading to variation in defence among native and invasive populations. However, few studies have examined how constitutive and induced indirect defences change during plant invasion, especially during the juvenile stage. Constitutive extrafloral nectar (EFN) production of native and invasive populations of juvenile tallow tree (Triadica sebifera) were compared, and leaf clipping, and damage by a native specialist (Noctuid) and two native generalist caterpillars (Noctuid and Limacodid) were used to examine inducible EFN production. Plants from introduced populations had more leaves producing constitutive EFN than did native populations, but the content of soluble solids of EFN did not differ. Herbivores induced EFN production more than simulated herbivory. The specialist (Noctuid) induced more EFN than either generalist for native populations. The content of soluble solids in EFN was higher (21 times), with the specialist vs. the generalists causing the stronger response for native populations, but the specialist response was always comparable with the generalist responses for invasive populations. These results suggest that constitutive and induced indirect defences are retained in juvenile plants of invasive populations even during plant establishment, perhaps due to generalist herbivory in the introduced range. However, responses specific to a specialist herbivore may be reduced in the introduced range where specialists are absent. This decreased defence may benefit specialist insects that are introduced for classical biological control of invasive plants.

关键词： ant exclusion   biological control   Ectatomma ruidum   herbivores   indirect resistance   insect-plant interactions   myrmecophilic timber trees  

摘要： Successful reforestation of tropical pastures can be facilitated or impeded depending on the interactions between native timber trees and arthropod communities. We assessed arthropod abundance on Tabebuia rosea (Bignoniaceae), a Central American extrafloral nectary-bearing timber tree, in a plantation of native trees on former pasture in Panama, and we excluded ants from branches of T. rosea to determine ant impact on arthropod assemblages and on leaf damage. The trees' ant fauna was dominated by ground-nesting species and ants were scarce in tree crowns, constituting only 2% of all arthropods collected by branch beating. Leaf damage was principally caused by caterpillars (mainly the pyralid Eulepte gastralis) and by beetles (mainly the chrysomelid Walterianella inscripta). Sugar baits at tree trunks revealed that rewarding food resources recruited high ant numbers to some tree individuals. Activity of the dominant ant, Ectatomma ruidum, at baits was negatively related to leaf damage by E. gastralis, suggesting that trees might be better protected from this herbivore when ant abundance is high. Exclusion of ants resulted in increased beetle diversity. The key herbivore W. inscripta was significantly more abundant on ant-exclusion branches at the beginning, but not towards the end of the rainy season, when beetle density increased. Overall leaf damage and arthropod abundance were not significantly affected by ant exclusion. In conclusion, ant abundance on native timber trees in plantations recently established on former pasture can be low, and ant assemblages may be dominated by ground-nesting generalist species, as shown in this study. This may explain the lacking protection of the timber trees from insect herbivory by ants. Increased protection of establishing timber trees by ants probably requires plantation management measures that increase the abundance of more specialized tree-visiting and tree-nesting ants.