关键词： Savanna ecosystems   Cause and effect mechanisms   Complex systems   Fires   Loop analysis   Positive feedback  

摘要： The dynamics of savanna ecosystems depends on the interplay between multiple factors such as grazing, browsing, fires, rainfall regime and interactions between grass and woody vegetation. In most modelling applications this interplay may not be fully understood because some of these drivers enter the models as dynamically independent factors. In this paper we consider such factors as dynamic variables. To analyze their interplay we focus on the structure of the interactive network of variables and exploit the properties of signed digraphs using the algorithm of Loop Analysis. Qualitative signed digraphs for the savanna ecosystem are developed and their predictions used to interpret patterns of abundance observed in case studies selected from the literature. The outcomes of this exercise unveil that: 1) the structure of the interactions is appropriate locus for the explanation of patterns observed in savannas;2) signed digraph can help disentangling causative mechanisms by linking correlation patterns, source of change and network structure. This study highlights that central to the understanding of savanna dynamics is our ability to diagram the important relationships and understand how they interrelate with sources of variations to cause ecosystem change. (C) 2016 Elsevier B.V. All rights reserved.

关键词： amphibians   areas of endemism   biodiversity   biotic elements   distributional patterns   Neotropical region   open areas   regionalization   reptiles  

摘要： Aim To analyse ranges of endemic squamates and anurans in the Cerrado hotspot, searching for coincident distributional patterns in two ecologically distinct clades, and proposing a testable and comprehensive regionalization scheme for the richest and most threatened savanna on the planet. Location Cerrado region, central South America. Methods We updated previous point-locality compilations for endemic species of the Cerrado herpetofauna, gathering 4588 unique occurrence records. Using a 1 degrees grid cell, we compared regionalization results of biotic element ( BE) and endemicity analyses. To search for a unified regionalization pattern, we compared analyses with a combined dataset ( anurans + squamates) with those obtained in single-group analyses. Results The analysis with the combined dataset recovered more complete results than those in taxon-specific analyses. We found 13 main biogeographical units formed by anurans and squamates that were recovered in both analyses with the combined dataset, and formed our general regionalization scheme. In general, biogeographical units defined by BEs correspond to those recovered by endemicity analysis with the combined dataset. Most recovered biogeographical units were formed both by anurans and squamates, with fewer areas determined solely by one group. Main conclusions Common regionalization processes operated on both anurans and squamates, shaping general biogeographical patterns for the Cerrado. The general regionalization pattern recovered with anurans and squamates may be valid for other taxa, and should be tested in future studies. As in previous results, most biogeographical units are found over ancient plateaus, separated by peripheral depressions. These major topographical barriers may explain major coincident patterns, linking the evolution of Cerrado biotas to the geomorphological history of the Brazilian shield.

关键词： Eastern Amazon   Connectivity   Patch size   Landscape ecology   Conservation  

摘要： Patch-size and connectivity effects on organisms are usually strong, but may be positive or negative, depending on the landscape context. A binary habitat/non-habitat perspective that fails to consider matrix heterogeneity often explains these inconsistent results, as matrix influences patch quality and connectivity differently for different species. Here we tested the effects of patch size, connectivity and matrix type on non-volant small-mammal assemblages in an eastern-Brazilian Amazonian forest-savanna mosaic. We sampled 14 forest-patches and 2 continuous-forest plots, using 60 baited live traps and 8 pitfall traps (60 L) per plot in 3 field expeditions. We estimated connectivity using the Proximity Index and matrix type as the proportions of savanna or regrowth forest around patches. We used one-dimensional NMDS, ANCOVA and multiple regression to test the relationships among species composition, species traits and predictor variables. We captured 178 individuals of 16 small-mammal species and an NMDS ordination showed a pattern of assemblage change that was strongly related to matrix type. Connectivity and patch size had no statistically significant effect on assemblage composition. Species associated with patches in regrowth-forest matrix were mostly rodents, relatively large and mainly frugivorous, while species associated with savanna-matrix patches were smaller, mostly insectivorous, marsupials. This may be related to how matrix is used by small mammals and affects patch quality, rather than how it limits animal movements. Composition of small-mammal assemblages in patches depended on the type of surrounding matrix, so matrix heterogeneity enhances small-mammal assemblage diversity in this landscape and should be taken into consideration in regional conservation-unit management plans. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： connectors   hubs   network theory   phenophase length   restoration  

摘要： The Neotropical region harbors the world's most diverse terrestrial plant communities. A key component of this diversity is a range of plant-animal interactions involving frugivory, nectarivory, and insectivory. Millions of Neotropical hectares subjected to human land-use systems contain trees that are either planted by land managers or retained from the pre-existing forests. Biodiversity-conservation approaches in these systems are often ineffective because of the unfounded assumption that all plants provide equal benefits for consumers. We propose criteria for tree-species selection based on plant-animal interaction research that could guide decisionmakers. We show that tree-species identity is key for enhancing biodiversity and recommend that selection be guided by the structure of plant-animal interaction networks. We also recommend that selection practices consider the timing of resource production, because the year-round availability of food resources in the Neotropics plays an important role in the adaptive radiation of nectar-and fruit-eating vertebrates.

关键词： Forest ecology   Insects   Spiders   Biodiversity conservation   Veteran trees   Conservation management  

摘要： Temperate open woodlands are recognized as biodiversity hotspots. They are characterised by the presence of scattered, open-grown, often old and large trees (hereafter referred to as "solitary trees"). Such trees are considered keystone ecological features for biodiversity. However, the ecological role of solitary trees and their importance for woodland communities are still not fully understood. Communities of arthropods in temperate forests are often structured not only by the horizontal openness of the stand, but also by vertical stratification. Thus there is a need for comparisons among communities associated with solitary trees and different forest strata. In this study, we analysed the diversity, conservation value, and nestedness of four taxonomic groups (beetles (Coleoptera), bees and wasps (aculeate Hymenoptera), ants (Formicidae), and spiders (Araneae)) on (i) solitary trees in open woodlands, and four habitat types in adjacent closed-canopy forests: (ii) edge-canopy, (iii) edge-understorey, (iv) interior-canopy, and (v) interior-understorey. Across the focal insect groups, solitary trees harboured the greatest number of species, whilst spider communities were also equally rich in forest edge canopies. The conservation value of communities was highest in solitary trees for beetles, and in solitary trees and edge-canopy habitats for bees and wasps. For spiders, the conservation value was similar across all habitat types, but ordination analysis revealed general preferences for solitary trees among threatened species. We also found that communities from the forest interior were mostly only nested subsets of the communities found on solitary trees. Our results show an important and irreplaceable role that open-grown trees have in maintaining temperate woodland biodiversity. Therefore, preservation and maintenance of open-grown trees should be a primary concern in biological conservation. (C) 2016 Elsevier B.V. All rights reserved.

关键词： Acanthus pubescens   elephants   Lantana camara   logged forest   primates   restoration ecology   tropical rain forest  

摘要： Tropical landscapes are changing rapidly as a result of human modifications;however, despite increasing deforestation, human population growth, and the need for more agricultural land, deforestation rates have exceeded the rate at which land is converted to cropland or pasture. For deforested lands to have conservation value requires an understanding of regeneration rates of vegetation, the rates at which animals colonize and grow in regenerating areas, and the nature of interactions between plants and animals in the specific region. Here, we present data on forest regeneration and animal abundance at four regenerating sites that had reached the stage of closed canopy forest where the average dbh of the trees was 17 cm. Overall, 20.3 percent of stems were wind-dispersed species and 79.7 percent were animal-dispersed species, while in the old-growth forest 17.3 percent of the stems were wind-dispersed species. The regenerating forest supported a substantial primate population and encounter rate (groups per km walked) in the regenerating sites was high compared to the neighboring old-growth forests. By monitoring elephant tracks for 10 yr, we demonstrated that elephant numbers increased steadily over time, but they increased dramatically since 2004. In general, the richness of the mammal community detected by sight, tracks, feces, and/or camera traps, was high in regenerating forests compared to that documented for the national park. We conclude that in Africa, a continent that has seen dramatic declines in the area of old-growth forest, there is ample opportunity to reclaim degraded areas and quickly restore substantial animal populations.

关键词： Diet breadth   Body mass   Browser   Grazer   Competition   Coexisting  

摘要： Understanding the mechanisms of species coexistence within local assemblages can play a crucial role in conservation of a species. There is little understanding of how large mammalian bovid species from West Africa partition diet resources, and to what extent they may vary their diet and habitat selection seasonally in order to coexist. Here we studied an assemblage of eleven bovid species in Pendjari Biosphere Reserve, West Africa and used faecal stable isotopes of carbon (delta C-13) and nitrogen (delta N-15) to test the impact of body mass diet partitioning at a seasonal scale. We found a significant positive relationship between isotopic niche similarity and body size similarity both in dry (p < 0.001) and wet (p < 0.001) season. Partitioning of carbon isotope niches is at least partly due to interactions amongst species rather than historical effects. Our findings also show numerous patterns in resource partitioning amongst the 11 bovid species studied, suggesting that different species used dietary resources in contrasting ways. In practice, actual resource competition between bovid species is difficult to demonstrate, but there exists much overlap in diet along the stable carbon isotope axis for most of the studied species. However we conclude that in our study area, especially in the wet season, niche breadth and diet overlap remain large. Abundant resources and low herbivore densities mean there is no need for herbivores to specialize, because they do not have to compete over scarce resources. (C) 2016 Deutsche Gesellschaft fur Saugetierkunde. Published by Elsevier GmbH. All rights reserved.

关键词： Elevate nitrogen inputs   Conifers   Broadleaves   Meta-analysis   Plant-insect interaction   Insect performance  

摘要： Increasing atmospheric nitrogen (N) inputs have the potential to alter terrestrial ecosystem function through impacts on plant-herbivore interactions. The goal of our study is to search for a general pattern in responses of tree characteristics important for herbivores and insect herbivorous performance to elevated N inputs. We conducted a meta-analysis based on 109 papers describing impacts of nitrogen inputs on tree characteristics and 16 papers on insect performance. The differences in plant characteristics and insect performance between broadleaves and conifers were also explored. Tree aboveground biomass, leaf biomass and leaf N concentration significantly increased under elevated N inputs. Elevated N inputs had no significantly overall effect on concentrations of phenolic compounds and lignin but adversely affected tannin, as defensive chemicals for insect herbivores. Additionally, the overall effect of insect herbivore performance (including development time, insect biomass, relative growth rate, and so on) was significantly increased by elevated N inputs. According to the inconsistent responses between broadleaves and conifers, broadleaves would be more likely to increase growth by light interception and photosynthesis rather than producing more defensive chemicals to elevated N inputs by comparison with conifers. Moreover, the overall carbohydrate concentration was significantly reduced by 13.12% in broadleaves while increased slightly in conifers. The overall tannin concentration decreased significantly by 39.21% in broadleaves but a 5.8% decrease in conifers was not significant. The results of the analysis indicated that elevated N inputs would provide more food sources and ameliorate tree palatability for insects, while the resistance of trees against their insect herbivores was weakened, especially for broadleaves. Thus, global forest insect pest problems would be aggravated by elevated N inputs. As N inputs continue to rise in the future, forest ecosys

关键词： HERBIVORES   PLANT communities   SAVANNAS   GNUS   PLANT diversity   AFRICA  

摘要： In areas with diverse herbivore communities such as African savannas, the frequency of disturbance by fire may alter the top-down role of different herbivore species on plant community dynamics. In a seven year experiment in the Kruger National Park, South Africa, we examined the habitat use of nine common herbivore species across annually burned, triennially burned and unburned areas. We also used two types of exclosures (plus open access controls) to examine the impacts of different herbivores on plant community dynamics across fire disturbance regimes. Full exclosures excluded all herbivores > 0.5 kg (e.g. elephant, zebra, impala) while partial exclosures allowed access only to animals with shoulder heights 0.85 m (e.g. impala, steenbok). Annual burns attracted a diverse suite of herbivores, and exclusion of larger herbivores (e.g. elephant, zebra, wildebeest) increased plant abundance. When smaller species, mainly impala, were also excluded there were declines in plant diversity, likely mediated by a decline in open space available for colonization of uncommon plant species. Unburned areas attracted the least diverse suite of herbivores, dominated by impala. Here, herbivore exclusion, especially of impala, led to strong declines in plant richness and diversity. With no fire disturbance, herbivore exclusion led to competitive exclusion via increases in plant dominance and light limitation. In contrast, on triennial burns, herbivore exclusion had no effect on plant richness or diversity, potentially due to relatively little open space for colonization across exclosure treatments but also little competitive exclusion due to the intermediate fire disturbance. Further, the diverse suite of grazers and browsers on triennial burns may have had a compensating effect of on the diversity of grasses and forbs. Ultimately, our work shows that differential disturbance regimes can result in differential consumer pressure across a landscape and result in heterogeneous patterns

关键词： Animals   Botswana   Conservation of Natural Resources   Ecosystem   Ecosystem   Elephants/growth & development   Geographic Information Systems   Population Density   Surveys and Questionnaires  

摘要： Accurate counts of animals are critical for prioritizing conservation efforts. Past research, however, suggests that observers on aerial surveys may fail to detect all individuals of the target species present in the survey area. Such errors could bias population estimates low and confound trend estimation. We used two approaches to assess the accuracy of aerial surveys for African savanna elephants (Loxodonta africana) in northern Botswana. First, we used double-observer sampling, in which two observers make observations on the same herds, to estimate detectability of elephants and determine what variables affect it. Second, we compared total counts, a complete survey of the entire study area, against sample counts, in which only a portion of the study area is sampled. Total counts are often considered a complete census, so comparing total counts against sample counts can help to determine if sample counts are underestimating elephant numbers. We estimated that observers detected only 76% +/- SE of 2% of elephant herds and 87 +/- 1% of individual elephants present in survey strips. Detectability increased strongly with elephant herd size. Out of the four observers used in total, one observer had a lower detection probability than the other three, and detectability was higher in the rear row of seats than the front. The habitat immediately adjacent to animals also affected detectability, with detection more likely in more open habitats. Total counts were not statistically distinguishable from sample counts. Because, however, the double-observer samples revealed that observers missed 13% of elephants, we conclude that total counts may be undercounting elephants as well. These results suggest that elephant population estimates from both sample and total counts are biased low. Because factors such as observer and habitat affected detectability of elephants, comparisons of elephant populations across time or space may be confounded. We encourage survey teams to incorpor