关键词： fire   herbivory   N-fixation   N:P stoichiometry   nutrient balances   mineralization  

摘要： Availabilities of nitrogen (N) and phosphorus (P) have a strong influence on plant growth and the species composition of savannas, but it is not clear how these availabilities depend on factors such as fire, N-2-fixation, and activities of wild herbivores and cattle. We quantified soil N and P availabilities in various ways (extractable pools, mineralization, resin adsorption) along vegetation gradients within a recently abandoned cattle ranch and a former game reserve in Tanzania (both areas now part of the Saadani National Park). We also assessed annual N and P balances to evaluate how long-term availabilities of N and P are affected by large herbivores, symbiotic N-2-fixation, and fire. The results show that cattle ranching led to a spatial re-distribution of nutrients, with the local accumulation of P being stronger and more persistent than that of N. In the former game reserve, intensively grazed patches of short grass tended to have elevated soil N and P availabilities;however, because quantities of nutrients removed through grazing exceeded returns in dung and urine, the nutrient balances of these patches were negative. In dense Acacia stands, N-2-fixation increased N availability and caused a net annual N input. Fire was the major cause for nutrient losses from tallgrass savanna, and estimated N inputs from the atmosphere and symbiotic N-2-fixation were insufficient to compensate for these losses. Our results call into question the common assumption that N budgets in annually burned savanna are balanced;rather, these ecosystems are a mosaic of patches with both N enrichment and impoverishment, which vary according to the vegetation type.

关键词： WILDFIRES -- Prevention & control   ROOSTING   BATS   CARBOXYHEMOGLOBIN   SMOKE plumes   CARBON monoxide  

摘要： Faunal injury and mortality in wildland fires is a concern for wildlife and fire management although little work has been done on the mechanisms by which exposures cause their effects. In this paper, we use an integral plume model, field measurements, and models of carbon monoxide and heat effects to explore risk to tree-roosting bats during prescribed fires in mixed-oak forests of southeastern Ohio and eastern Kentucky. Tree-roosting bats are of interest primarily because of the need to mitigate risks for the endangered Indiana bat (Myotis sodalis), our focal species. Blood carboxyhemoglobin concentrations predicted from carbon monoxide data supplemented by model output only approached critical levels just above flames in the most intense fires. By contrast, an ear-heating model driven by plume model output suggested that injury to the bat's thermally thin ears would occur up to heights similar to those of foliage necrosis, an effect for which predictive relationships exist. Risks of heat injury increase with fireline intensity and decrease with both roost height and ambient wind. Although more information is needed on bat arousal from torpor and behavior during fires, strategies for reducing the risk of heat injury emerge from consideration of the underlying causal processes.

关键词： GENETIC research   RODENTS   RESEARCH   SAVANNAS   ARBOREAL animals  

摘要： The article presents a study on genetic differentiation in arboreal rodent Thallomys nigricauda, commonly known as acacia rat or black-tailed tree rat in the Southern African savannas. The study examines the effect of habitat on genetic structure of the species, by analyzing maternally inherited molecular marker mitochondrial control region (D-loop). In the study 16 unique haplotypes, which were found to be caused by transitions and transversions in genes.

关键词： Chromosomes   Sexes   Genetics   Females   Males   Evolutionary biology   Birds   Industrial production  

摘要： The ability to identify genetic markers in nonmodel systems has allowed geneticists to construct linkage maps for a diversity of species, and the sex-determining locus is often among the first to be mapped. Sex determination is an important area of study in developmental and evolutionary biology, as well as ecology. Its importance for organisms might suggest that sex determination is highly conserved. However, genetic studies have shown that sex determination mechanisms, and the genes involved, are surprisingly labile. We review studies using genetic mapping and phylogenetic inferences, which can help reveal evolutionary pattern within this lability and potentially identify the changes that have occurred among different sex determination systems. We define some of the terminology, particularly where confusion arises in writing about such a diverse range of organisms, and highlight some major differences between plants and animals, and some important similarities. We stress the importance of studying taxa suitable for testing hypotheses, and the need for phylogenetic studies directed to taxa where the patterns of changes can be most reliably inferred, if the ultimate goal of testing hypotheses regarding the selective forces that have led to changes in such an essential trait is to become feasible.

关键词： cattle-wildlife interactions   ecological legacies   facilitation   foraging behaviour   landscape heterogeneity   pastoralism   plant-herbivore interactions   rangeland   succession  

摘要： P>1. Through their effects on plant communities, herbivores can exert strong direct and indirect effects on savanna ecosystems and have the potential to create and maintain savanna landscape heterogeneity. Throughout much of sub-Saharan Africa, periodic creation and abandonment of livestock corrals leads to landscape mosaics of long-term ecosystem hotspots that attract both cattle and large ungulate wildlife. 2. The development and maintenance of vegetation in these types of hotspots may be controlled in part by herbivory. Cattle and wildlife may have different, potentially contrasting effects on plant succession and plant-plant interactions. We ask how cattle and wild herbivores affect the maintenance and vegetation development of corral-derived landscape heterogeneity (0.25-1.0 ha treeless 'glades') in Laikipia, Kenya, through their effects on long-term successional and short-term plant-plant dynamics. 3. We used the Kenya Long-term Exclosure Experiment to exclude from glades different combinations of cattle, large ungulate wildlife (i.e. zebras, gazelles and other antelopes), and mega-herbivore wildlife (i.e. giraffes and elephants). We first assessed long-term changes in cover of the dominant grass species, Cynodon plectostachyus and Pennisetum stramineum (the early- and late-dominant species, respectively). We then used a neighbour removal experiment to test the effects of different herbivores on competition and facilitation between the two glade grass species. 4. In the long-term experiment, we found that large ungulate wildlife reinforced landscape heterogeneity over time by helping maintain glades in their early C. plectostachyus-dominated form. Cattle and mega-herbivore wildlife, on the other hand, appeared to reduce the positive effects through forage preference for C. plectostachyus. 5. In the neighbour removal experiment, we found that each grass species benefited from facilitation when it was the preferred forage for the dominant grazer. Facilitation of

关键词： Tree specialization hypothesis   Abundance   Leaf litter   Arthropods  

摘要： Increased tree species diversity in the tropics is associated with even greater herbivore diversity, but few tests of tree effects on litter arthropod diversity exist. We studied whether tree species influence patchiness in diversity and abundance of three common soil arthropod taxa (ants, gamasid mites, and oribatid mites) in a Panama forest. The tree specialization hypothesis proposes that tree-driven habitat heterogeneity maintains litter arthropod diversity. We tested whether tree species differed in resource quality and quantity of their leaf litter and whether more heterogeneous litter supports more arthropod species. Alternatively, the abundance-extinction hypothesis states that arthropod diversity increases with arthropod abundance, which in turn tracks resource quantity (e.g., litter depth). We found little support for the hypothesis that tropical trees are templates for litter arthropod diversity. Ten tree species differed in litter depth, chemistry, and structural variability. However, the extent of specialization of invertebrates on particular tree taxa was low and the more heterogeneous litter between trees failed to support higher arthropod diversity. Furthermore, arthropod diversity did not track abundance or litter depth. The lack of association between tree species and litter arthropods suggests that factors other than tree species diversity may better explain the high arthropod diversity in tropical forests.

关键词： Heterogeneity   Haplodiploid   Pikonema alaskensis   Phenology   Picea mariana  

摘要： Some herbivorous insects enhance their fitness using foraging strategies that allow them to find and colonize the best of available resources within heterogeneous plants. The yellowheaded spruce sawfly, Pikonema alaskensis (Roh.) (Hymenoptera: Tenthredinidae), is a common defoliator that oviposits and feeds on the developing foliage of young open-grown black spruce [Picea mariana (Mills) B.S.P.]. While female and male eggs are both laid throughout the crown, most eggs laid in the upper crown are female, and more female than male late-instar larvae disperse acropetally, from the lower and mid-crown to the upper crown, to complete juvenile development. Here we present results from 4 years of manipulative sleeve-cage experiments that were carried out to evaluate the hypothesis that sex-biased oviposition-site selection and acropetal dispersal by P. alaskensis are adaptive responses to intra-tree variation in foliage quality. Survival and proportion of survivors that were female were either the same (2 years) or significantly higher (2 years) for groups placed in the lower or mid-crown during early instars, and then transferred acropetally during late instars to complete development in the upper crown, compared with those forced to feed exclusively in the lower crown. This suggests that females benefited most from acropetal dispersal. Sex ratios of survivors that had been forced to develop exclusively in the upper crown were usually more female biased than those of survivors that developed exclusively in the lower crown, suggesting higher survival for female than for male larvae emerging from eggs laid in the upper crown. Sex-biased egg allocation and larval dispersal appear to increase the survival of P. alaskensis by accounting for differential effects on male versus female larvae of phenology-independent temporal and spatial variations in the quality of foliage within the heterogeneous crown of black spruce.

关键词： BIRDS   WATERFALLS   ARTHROPODA   LEPIDOPTERA   LARVAE  

摘要： Considerable uncertainty surrounds the conditions under which birds can cause trophic cascades. In a three-year experiment, we studied the direct and indirect effects of insectivorous birds on arthropod abundance, herbivory, and growth of striped maple Acer pensylvanicum saplings in a northern hardwood forest of central New Hampshire, USA. We manipulated bird predation by erecting exclosures around saplings and directly manipulated herbivory by removing herbivores. We also examined how climate modifies these interactions by replicating the experiment at three locations along an elevational gradient. Effects of bird predation were variable. Overall, mean arthropod biomass was 20% greater on saplings within bird exclosures than on controls (p < 0.05). The mean biomass of leaf-chewing herbivores, primarily Lepidoptera larvae, was 25% greater within exclosures but not statistically different from controls. To a lesser degree, mean herbivore damage to foliage within exclosures exceeded that of controls but differences were not significant. We also did not detect significant treatment effects on sapling shoot growth. The high understory vegetation density relative to bird abundance, and low rate of herbivory during the study (mean 5% leaf area removed, controls), may have limited the ability of birds to affect sapling growth. Climate effects operated at multiple scales, resulting in a complex interplay of interactions within the food web. Regional synchrony of climatic conditions resulted in annual fluctuations in herbivore abundance and tree growth that were shared across elevations. At the same time, local environmental variation resulted in site differences in the plant, herbivore, and bird communities. These patterns resulted in a mosaic of top-down strengths across time and space, suggesting an overall pattern of limited effects of birds on plant growth, possibly interspersed with hotspots of trophic cascades.

关键词： Brazilian savanna   Mammal distribution   Habitat use   Landscape ecology   Habitat heterogeneity  

摘要： So Paulo is the most developed state in Brazil and contains few fragments of native ecosystems, generally surrounded by intensive agriculture lands. Despite this, some areas still shelter large native animals. We aimed at understanding how medium and large carnivores use a mosaic landscape of forest/savanna and agroecosystems, and how the species respond to different landscape parameters (percentage of landcover and edge density), in a multi-scale perspective. The response variables were: species richness, carnivore frequency and frequency for the three most recorded species (Puma concolor, Chrysocyon brachyurus and Leopardus pardalis). We compared 11 competing models using Akaike's information criterion (AIC) and assessed model support using weight of AIC. Concurrent models were combinations of landcover types (native vegetation, "cerrado" formations, "cerrado" and eucalypt plantation), landscape feature (percentage of landcover and edge density) and spatial scale. Herein, spatial scale refers to the radius around a sampling point defining a circular landscape. The scales analyzed were 250 (fine), 1,000 (medium) and 2,000 m (coarse). The shape of curves for response variables (linear, exponential and power) was also assessed. Our results indicate that species with high mobility, P. concolor and C. brachyurus, were best explained by edge density of the native vegetation at a coarse scale (2,000 m). The relationship between P. concolor and C. brachyurus frequency had a negative power-shaped response to explanatory variables. This general trend was also observed for species richness and carnivore frequency. Species richness and P. concolor frequency were also well explained by a second concurrent model: edge density of cerrado at the fine (250 m) scale. A different response was recorded for L. pardalis, as the frequency was best explained for the amount of cerrado at the fine (250 m) scale. The curve of response was linearly positive. The contrasting results (P. conco

关键词： conservation planning   inventory   quantified method   species accumulation   temporal effect  

摘要： Invertebrate diversity is seldom included in conservation assessments, primarily because information is lacking. Broad surveys may be too costly, difficult or ineffective. Here we assess a 'shopping basket' approach, targeting 17 taxa using a range of methods. We sampled 43 one-hectare sites stratified within 560 km2 of heterogenous African savanna. We achieved up to 80% sampling completeness for epigaeic fauna, but generally much lower completeness (around 50%) for plant-dwelling and flying taxa. For the former we identified duplication of methods, and for the latter, addition of methods and increased temporal variation rather than effort would improve completeness. Within a taxon, sampling 75% of species present required, on average, about 784 individuals. When considering the local richness, 75% completeness required about 27 individuals per species, but these figures require validation in other areas. About 58 sites were required to achieve 75% sampling completeness, translating to about one site per 10 km2. The percentage of species sampled only in a particular month ranged between 4% and 46%, with greater temporal effects recorded for flying taxa than for epigaeic ones. The trend was similar for species unique to a particular year, with the most extreme case being 67% of the butterfly species sampled one year not previously recorded. We demonstrated and evaluated the feasibility of a simultaneous multi-taxon survey approach to produce data useful for conservation planning and monitoring. We strongly recommend a quantified approach for surveys and inventories, with details such as specific methods decided based on the biome sampled, and taxonomic expertise available for identification.