关键词： plant colonization   Ficus   endozoochory   bird and bat frugivory   fig wasps   Krakatau   dispersal   avian raptors   island ecology  

摘要： Since the biologically extirpating eruption of Krakatau (Sunda Strait) in 1883, Rakata (Krakatau's remnant) and two closely adjacent islands, Sertung and Panjang, have been colonized by over 200 species of vascular plants. They now carry species-poor mixed tropical forest, including some twenty-three species of Ficus. Data on the sequence of colonization over the last century by twenty-four Ficus species, twenty-three species of volant frugivores, and by agaonid fig-wasps, presumably from the large islands of Java and Sumatra, each some 44km distant, are summarized. The potential of the volant frugivores as dispersers of fig seeds is assessed, the pollination problems involved in the colonization of islands by figs are reviewed and patterns of colonization by fig species and by their bird and bat dispersers are identified and discussed. In 1930 a new island, Anak Krakatau, emerged from Krakatau's submerged caldera. This active volcano suffered a self-sterilizing eruption in 1952/1953 and has been colonized, under considerable constraint from its own volcanic activity, probably largely from the (selected) species pool present on Rakata, Sertung and Panjang, 2-4 km away. Its vegetation is at an earlier successional stage (grassland and Casual ina woodland) than that of the three older islands, and in 1992 the Casuarina woodland was in an early stage of transition to mixed forest. The colonization of Anak Krakatau by Ficus species, agaonid wasps and volant frugivores over a critical decade (1982-92) is reviewed, including preliminary assessments of the effects of pollinator limitation on four pioneer fig species and indications of a possible effect of the presence of avian raptors, particularly the peregrine falcon, on fig colonization and forest diversification.

关键词： Pollinating insects   Trees   Phylogeny   Genera   Seeds   Pollen   Insect pollination   Biogeography  

关键词： biomass allocation   browsers   herbivory   production   spinescence  

摘要： Length, branch production, orientation, spinescence and biomass were measured for current shoots of Acacia tortilis shrubs in a range of habitats in Botswana. All shoot characteristics varied between individuals and between habitats with longer, less spinescent shoots produced in the habitat recently protected from wildlife. Biomass allocated to woody material increased with shoot length at the expense of leaf mass, whilst investment in straight prickles was as much as 6% of shoot dry mass. Shoot length had significant effects on total current shoot mass per shrub which was greatest in the recently protected area but the mean number of shoots per shrub also varied between habitats. Age and history of disturbance, including herbivory, appear to be important determinants of. morphology and growth pattern of individual shrubs. Fitness of A. tortilis individuals and the consequence of flexibility in growth responses for vegetation structure and community organization are discussed.

关键词： habitat use and preference   mixed wild and domestic ungulate community   niche overlap and interspecific competition   southern Africa savanna woodland  

摘要： 1. The spatial distribution of two wild ungulates, impala and kudu, and of domestic cattle, was monitored across seasons in a 9400 ha ranch of the 'highveld' of Zimbabwe. Habitat use, preference, selectivity and overlap were estimated. Predation was negligible and the study concentrated on interspecific competition. 2. Cattle were contained in paddocks, and were moved regularly, while wild ungulates moved freely. Wild ungulate habitat use, preference and selectivity between paddocks with and without cattle were compared, as was the variation in broad diet, group size and densities. 3. All herbivores were selective, with a marked preference for the nutrient-rich Acacia/Dichrostachys vegetation type. Terminalia communities were almost completely avoided. Selectivity increased as the dry season progressed. Habitat overlap was always high. 4. Interspecific competition occurred between cattle and impala, especially during the wet season and the hot dry season. Impala showed a switch in habitat preference and an increase in selectivity and started to concentrate on 'refuge habitat'. Some also switched in their diet composition. During the hot dry season, when resources were at their lowest, most impala stopped using paddocks with cattle. 5. Kudu seemed relatively unaffected by the presence of cattle: the variations observed in kudu spatial behaviour may have been caused by competition with impala.

关键词： testudines   Trachemys scripta elegans   tetrapod phylogeny   molecular evolution   alpha-crystallin  

摘要： The phylogenetic relationships among the major groups of amniote vertebrates remain a matter of controversy. Various alternatives for the position of the turtles have been proposed, branching off either before or after the mammals. To discover the phylogenetic position of turtles in relation to mammals and birds, we have determined cDNA sequences for the eye lens proteins alpha A- and alpha B-crystallin of the red-eared slider turtle (Trachemys scripta elegans). In addition, databases were searched for turtle protein sequences, for which mammalian, avian, and outgroup orthologs were available. All sequences were analyzed by three phylogenetic tree reconstruction methods (neighbor-joining, maximum parsimony, and maximum likelihood). Including the alpha-crystallins, 7 out of 12 proteins support a sister-group relation of turtles and birds with all 3 methods. For each of the other five proteins no topology was consistently preferred by the three approaches. Analyses of the combined amino acid data (1,695 aligned sites) also give extremely strong evidence that turtles are nearer to birds, indicating that mammals branched off before the divergence between turtles and birds occurred.

关键词： Tadpoles   Snakes   Predators   Swimming   Garters   Amphibians   Phenotypic traits   Ecological competition   Predator prey relationships  

摘要： Two experimental approaches were used to determine if burst swimming speed in Pseudacris regilla tadpoles is subject to selection by predatory garter snakes, Thamnophis sirtalis. In eight our of 10 experiments in seminatural arenas, fast tadpoles survived snake predation more often than expected (P < 0.01). In videotaped encounters, tadpoles that escaped attacks swam 1.68 times as fast (P < 0.0001) and nearly four times as evasively (P < 0.05) as those that were captured. Burst swimming speed is clearly important to success at escaping snakes In experimental arenas and, given widespread snake predation on tadpoles is probably subject to predator-mediated selection in nature.

关键词： airways, branching geometry   mammals, dog, hamster, humans, rat   model, branching airways (4 mammals)  

摘要： A diameter-based classification technique, which we have previously used to analyse human bronchial geometry (Phillips et al., Respir. Physiol. 98: 193-217, 1994) is applied also to the partial measurements of the dimensions of dog, rat and hamster conducting airways, made by Raabe et al. (Tracheobronchial Geometry: Human, Dog, Rat, Hamster, 1976). The local branching patterns are characterised by means of three parameters, which reflect the asymmetry and the degree of expansion at each bifurcation, and the ratio of the length of each branch to its diameter. The mean values of these parameters as functions of diameter, calculated from the raw morphometric data, are shown for the four species. A statistical reconstruction technique is then used to estimate from the incomplete measurements of Raabe and coworkers some geometrical properties of the whole system of conducting airways, which are likely to influence transport processes in the lung. These include the distribution of the total airway volume between branches of different diameters, the mean and variance of the total lengths of different pathways through the bronchial tree, and a simple model for the variation of now velocity with airway diameter. Our results show significant differences between the branching structures of all four species. In particular, the human differs from the others in branching much more symmetrically, and in that branches of a given diameter are typically much longer than in the other species;together, these observations imply that the human bronchial tree is geometrically very different from those of the other species.

摘要： There is a lack of research on the effects of logging on Canadian amphibians. We compared the abundance of terrestrial salamanders in old-growth forests with that in young and mature post-harvest stands. We also measured habitat features of amphibians and contrasted these with old-growth and harvested stands to assess the effects of forest harvest. Quadrat searches demonstrated that clearcut harvesting reduces terrestrial amphibian populations by up to 70% in coastal old-growth forests. We suggest that this reduction results from a decrease in availability of moist microhabitats. Salamander densities within 10 meters of streams in managed stands were similar to those near and away from streams in old growth. We recommend that forest managers recognize the needs of terrestrial amphibians and help maintain amphibian populations by preserving cool, moist habitats. This can be accomplished within cutblocks by (1) maintaining an even distribution of logs and snags as stable, moist microhabitats;(2) retaining some understory as sources of shade;and (3) preserving streamside buffers. Managers must also ensure some level of landscape connectivity to enable climate-sensitive amphibians to disperse and recolonize marginal habitats.

关键词： CARBON-NUTRIENT BALANCE   DELAYED INDUCIBLE RESISTANCE   FERTILIZATION   INDUCTION   INSECT GUILDS   LEAF DAMAGE   NUTRIENT AVAILABILITY   PLANT DEFENSES   QUERCUS   TANNINS  

摘要： Previous work has shown that fertilization can mitigate across-year induced resistance among individual Alaska paper birch, supporting the hypothesis that induction results from nutrient deficiency rather than active defense. The present study suggests that fertilization can prevent induction responses in oak within one season, and among leaves within individual trees. Saplings of two oak species, divided among fertilizer treatments within a plantation, were defoliated to varying degrees by a gypsy moth outbreak during spring. We monitored foliage chemistry and insect herbivore distributions during summer and fall of the same year. Damaged leaves within unfertilized Quercus prinus saplings showed increases in foliar astringency and proanthocyanidins. Within fertilized trees, damage did not induce increases in either astringency or proanthocyanidins. Defoliation also induced increases in proanthocyanidins and astringency within Q. rubra saplings, but induction was unaffected by fertilization. On both tree species, the distributions of certain insect guilds were skewed away from damaged leaves on unfertilized trees, but independent of damage on fertilized trees. We suggest that the effects of fertilization on induction can vary among tree species, and can occur at more than one spatial and temporal scale. Our data support the view that nutrient availability may affect phytochemical induction and herbivore responses.