关键词： Cleora scriptaria   Geometridae   Macropiper excelsum   Piperaceae   kawakawa   herbivory   induced defences   abscission   insect-plant interaction  

摘要： The pattern of herbivore damage on the New Zealand pepper tree (kawakawa;Macropiper excelsum) caused by its main insect herbivore (Cleora scriptaria) was investigated in the field and laboratory. In the field, only a small proportion of kawakawa leaves had no herbivore damage and C. scriptaria typically produced a number of small holes in each leaf. Leaves were shed at a rapid rate but leaf shedding was not increased by higher levels of herbivore damage. Some alder leaves had less damage than would be expected for their age, possibly suggesting some variation in leaf susceptibility to herbivory. The effect of previous leaf damage on subsequent herbivory was examined in the field and laboratory. On no occasion did artificial leaf damage, or herbivory by larvae of the same or another species, affect the edibility of leaves to C. scriptaria. The results suggest that leaf shedding by kawakawa was not primarily a response to herbivore damage and induced defences against herbivores could not be demonstrated in this system.

关键词： climax community   diversity   grazing   herbivory   scale   stability   succession   vegetation model  

摘要： Long-term (45-yr) basal area dynamics of dominant graminoid species were analyzed across three grazing intensity treatments (heavily grazed, moderately grazed and ungrazed) at the Texas A&M University Agricultural Research Station on the Edwards Plateau, Texas. Grazing intensity was identified as the primary influence on long-term variations in species composition. Periodic weather events, including a severe drought (1951-1956), had little direct influence on composition dynamics. However, the drought interacted with grazing intensity in the heavily grazed treatment to exacerbate directional changes caused by grazing intensity. Species response to grazing was individualistic and noisy. Three response groups were identified. Taller, more productive mid-grasses were most abundant under moderate or no grazing. Short grasses were most abundant under heavy grazing. Intermediate species were most abundant under moderate grazing and opportunistic to weather patterns. Graminoid diversity increased with the removal or reduction of grazing intensity. The moderately and ungrazed treatments appeared most resistant to short-term weather fluctuations, while the heavily grazed treatment demonstrated significance resilience when grazing intensity was reduced after over 110 yr of overgrazing. Identification of a 'climax' state is difficult. Significant directional change, which took nearly 20 yr, appears to continue in the ungrazed treatment after 45 yr of succession. The observed, relatively linear patterns of perennial glass composition within the herbaceous patches of this savanna were generally explained by traditional Clementsian succession. However, when dynamics of the herbaceous community are combined with the woody component of this savanna, the frequency and intensity of fire becomes more important. Across the landscape, successional changes follow several pathways. When vegetation change is influenced by several factors, a multi-scale model is necessary to demonstrate int

摘要： Aggregations in tadpoles of the West African savanna frog Phrynomantis microps were often observed in their breeding ponds in our study area, situated in Comoe National Park, Ivory Coast. Experiments under seminatural conditions demonstrated that this behaviour was only shown while predators were present. The tadpoles reacted differently to different predators. Factors inducing swarm behaviour were optical (the predator) and/or chemical (liquid from injured tadpoles). Alarm substances are not species-specific. Kinship seems not to play a role in swarm formation.

关键词： aucubin   catalpol   iridoid glycosides   chemical defense   sequestration   tritrophic interactions   diet breadth   host range   predation  

摘要： Recent studies demonstrate that generalist insect herbivores may be more subject to predation than specialists and suggest that this pattern is related to the availability and utilization of plant-derived natural products in diets of the latter. This intuitively attractive hypothesis has seldom been tested under natural conditions, however. A well-described plant-insect system, the buckeye butterfly. Junonia coenia, and its iridoid glycoside-containing host plants, was used to test the hypotheses: (1) that larval sequestration of iridoids reduces predation in the field, and (2) that this protection varies among populations. Fifth-instars reared in the laboratory on leaves of two host-plant species. Kickxia elatine (Scrophulariaceae) or Plantago lanceolata (Plantaginaceae). or on artificial diets were attached to monofilament tethers and set out into four natural populations. Only larvae id on the locally available host plant and artificial diet-fed caterpillars were used at each site. Despite high overall predation, significantly more leaf-fed caterpillars survived than did artificial diet-fed caterpillars in Plantago sites, but the trend was not significant in Kickxia sites. The results reflect the differences in iridoid glycoside availability in these two host-plant species. They indicate that predators exert a strong selective force on this insect, that sequestered iridoid glycosides can be effective deterrents to predation, and that host-plant choices by ovipositing females and feeding larvae have consequences for mortality from natural enemies. This protection. however, is not absolute, and depends on local predator abundance and/or selectivity. The ecological interactions between buckeye caterpillars, their host plants, and their natural enemies are locally variable in nature.

关键词： rumen   protozoa   defamation  

摘要： Samples and extracts of foliage from African multipurpose trees were screened for their effects on rumen protozoa and bacteria with a view to predicting their safety as feed supplements and for identifying species with potential antiprotozoal activity. The species tested were Acacia aneura, Chamaecytisus palmensis, Brachychiton populneum, Flindersia maculosa, Sesbania sesban, Leucaena leucocephala and Vernonia amyedalina. Antimicrobial effects were mild except for S. sesban, which was highly toxic to rumen protozoa in vitro, and A. aneura, which was toxic to rumen bacteria. The antiprotozoal factor in S. sesban was apparently associated with the fraction of the plant containing saponins. When S. sesban was fed to sheep, protozoal numbers fell by 60 % after 4 d, but the population recovered after a further 10 d, in vitro experiments demonstrated that washed protozoa from later times were no more resistant to S. sesban than on initial exposure, suggesting that other micro-organisms, probably the bacteria, adapted to detoxify the antiprotozoal agent. Thus S. sesban may be useful in suppressing protozoa and thereby improving protein how from the rumen, but only if the bacterial metabolism of the antiprotozoal factor can be avoided.

关键词： Ungulates   Herbivores   Primary productivity   Savanna soils   Biomass production   Savannas   Predators   Body size  

关键词： INSECTIVORES (Mammals)   MAMMALS   PHYLOGENY  

摘要： The order Insectivora, including living taxa (lipotyphlans) and archaic fossil forms, is central to the question of higher-level relationships among placental mammals(1). Beginning with Huxley(2), it has been argued that insectivores retain many primitive features and are closer to the ancestral stock of mammals than are other living groups(3). Nevertheless, cladistic analysis suggests that living insectivores, at least, are united by derived anatomical features(4). Here we analyse DNA sequences from three mitochondrial genes and two nuclear genes to examine relationships of insectivores to other mammals. The representative insectivores are not monophyletic in any of our analyses. Rather, golden moles are included in a clade that contains hyraxes, manatees, elephants, elephant shrews and aardvarks. Members of this group are of presumed African origin(5,6). This implies that there was an extensive African radiation from a single common ancestor that gave rise to ecologically divergent adaptive types. 12S ribosomal RNA transversions suggest that the base of this radiation occurred during Africa's window of isolation in the Cretaceous period before land connections were developed with Europe in the early Cenozoic era.

关键词： multipurpose trees   Acacia angustissima   Acacia saligna   Chamaecytisus palmensis   Leucaena pallida   Sesbania sesban   ciliate protozoa   rumen pH  

摘要： The effect of five multipurpose trees (MPTs), Acacia angustissima, Acacia saligna, Chamaecytisus palmensis, Leucaena pallida and Sesbania sesban on ciliate protozoa was investigated in rumen cannulated Ethiopian sheep. Both entodiniomorphs and holotrichs were counted. The protozoa counts from S. sesban supplemented diet were significantly (P < 0.04) higher than from other diets. Maize stover alone and maize stover supplemented with C. palmensis or L. pallida did not have any significant (P > 0.05) effect on the numbers of ciliate protozoa. A. saligna supplemented diet reduced the numbers of protozoa from 1.60 X 10(5) to 0.62 x 10(5) cells ml(-1) rumen fluid. Differences in ciliate numbers among other MPT supplements barely failed to reach significance (P < 0.06). Entodiniomorphs dominated (93.3%) the protozoa population in all diets, with Entodinium species being the most predominant (80.7%). None of the MPTs tested eliminated protozoa. Effect of eating S. sesban and placing it in the rumen on protozoa was tested. Protozoa numbers decreased in the sheep in which S. sesban was placed in the rumen while they remained high in the sheep that were allowed to eat the supplement. Relationships between protozoal numbers and in sacco fibre degradation and neutral detergent fibre (NDF) digestibility were also examined. Degradation rate (c) increased with increase in protozoa numbers. NDF digestibility was significantly (P<0.01) lower in A. saligna supplemented diet than in others. No significant relationship was observed between ruminal pH and protozoal numbers with all diets. The animals on A. angustissima died after 9 and 21 days of the experiment. (C) 1997 Elsevier Science B.V.

关键词： Foraging   Herbivory  

摘要： We evaluated palatability of winter dormant tree twigs to the mountain hare Lepus timidus and the grey-sided vole Clethrionomys rufocanus with captive animals. We tested differences among trees within sites, among sites, and between two tree species (the mountain birch Betula pubescens ssp. czerepanovii and the tea-leaved willow Salix phylicifolia). In one of the sites, we also measured growth rates of autumnal moth Epirrita autumnata larvae on the same trees that were used in preference trials with the hares and voles. The differences in palatability to hares and voles were greatest al the level of tree species;both hares and voles preferred birches over willows, but with the hare there was some overlap in palatability between the tree species. There were also large and significant differences among sites and among trees within sites. Within sites, variation in tree palatability seemed to be larger among willows than among birches. Hares and voles may select willows at least partly on the same basis, but there was no correlation between palatability of the trees to the mammals and the growth rate of the larvae of the autumnal moth on the same trees. Variation in twig palatability to the hares and voles was so large at all levels (among trees within sites, among sites and between tree species) that we suggest it also has implications for food selection of these mammalian herbivores under natural conditions.

关键词： Savannas   Beetles   Species diversity   Sampling methods   Arthropod communities   Grassland fires   Prairies   Prescribed burning  

摘要： We investigated the effects of prescribed burning on the composition, abundance, species richness and diversity of oak savanna arthropod communities in a replicated, large-scale, 30-y experiment We employed four sampling methods over 3 y and caught 11,215 arthropods of 551 species. Species had varied and often negatively correlated short vs. longterm responses to burning. In the years savannas were burned, species richness and abundance of arthropods, especially Homoptera and Lepidoptera, were reduced and species compositions were sometimes more similar. However, despite its major effect on vegetation, frequency of burning did not affect arthropod abundance and species richness, but sometimes caused savannas to be similar in species or taxonomic order composition. The Shannon diversity index was unaffected by burning. On the whole, prescribed burns necessary to maintain grasslands and savannas do not appear to be harmful to, or to greatly impact, the arthropod fauna.