关键词： indirect effects   megafauna   pollination   species interactions   trophic cascade   ungulate  

摘要： Pollination by animals is a key ecosystem service(1,2) and interactions between plants and their pollinators are a model system for studying ecological networks,(3,4) yet plant-pollinator networks are typically studied in isolation from the broader ecosystems in which they are embedded. The plants visited by pollinators also interact with other consumer guilds that eat stems, leaves, fruits, or seeds. One such guild, largemammalian herbivores, are well-known ecosystem engineers(5-7) and may have substantial impacts on plant-pollinator networks. Although moderate herbivory can sometimes promote plant diversity,(8) potentially benefiting pollinators, large herbivores might alternatively reduce resource availability for pollinators by consuming flowers,(9) reducing plant density,(10) and promoting somatic regrowth over reproduction.(11) The direction and magnitude of such effects may hinge on abiotic context-in particular, rainfall, which modulates the effects of ungulates on vegetation.(12) Using a long-term, large-scale experiment replicated across a rainfall gradient in central Kenya, we show that a diverse assemblage of native large herbivores, ranging from 5kg antelopes to 4,000-kg African elephants, limited resource availability for pollinators by reducing flower abundance and diversity;this in turn resulted in fewer pollinator visits and lower pollinator diversity. Exclusion of large herbivores increased floral-resource abundance and pollinator-assemblage diversity, rendering plant-pollinator networks larger, more functionally redundant, and less vulnerable to pollinator extinction. Our results show that species extrinsic to plant-pollinator interactions can indirectly and strongly alter network structure. Forecasting the effects of environmental change on pollination services and interaction webs more broadly will require accounting for the effects of extrinsic keystone species.

关键词： ants   drought   grasshoppers   rainfall   savanna   termite mounds  

摘要： Global climate change is predicted to increase the frequency of droughts, with major impacts on tropical savannas. It has been suggested that during drought, increased soil moisture and nutrients on termite mounds could benefit plants but it is unclear how such benefits could cascade to affect insect communities. Here, we describe the effects of drought on vegetation structure, the cascading implications for invertebrates and how termite mounds influence such effects. We compared how changes in grass biomass affected grasshopper and ant diversity on and off Macrotermes mounds before (2012) and during a drought (2016) at two locations that experienced large variation in drought severity (Skukuza and Pretoriuskop) in the Kruger National Park, South Africa. The 2013-2016 drought was not ubiquitous across the study site, with rainfall decreasing at Skukuza and being above average at Pretoriuskop. However, grass biomass declined at both locations. Grasshopper abundance decreased at droughted Skukuza both on and off mounds but decreased on mounds and increased off mounds at non-droughted Pretoriuskop. Ant abundance and species richness increased at Skukuza but remained the same on mounds and decreased off mounds at Pretoriuskop. Our results demonstrate the spatially extensive effects of drought. Despite above average rainfall in 2016 at Pretoriuskop, grass biomass decreased, likely due to an influx of large mammalian herbivores from drought-affected areas. This decrease in grass biomass cascaded to affect grasshoppers and ants, further illustrating the effects of drought on invertebrates in adjoining areas with higher rainfall. Our grasshopper results also suggest that increased drought in savannas will contribute to overall declines in insect abundance. Moreover, our recorded increase in ant abundance was primarily in the form of increases in dominant species, illustrating how drought-induced shifts in relative abundance will likely influence ecosystem structure and func

关键词： Acorn size   Forest fragmentation   Seed dispersal   Seedling mortality   Seedling recruitment  

摘要： The local extinction or reduction of a species or even a small functional group as a result of forest fragmentation may have different consequences on the sympatric plants. Here, we investigated acorn dispersal and seedling recruitment, along with the mortality of two oak species, Quercus variabilis with large acorn and Quercus chenii with small acorn, in an isolated forest patch in Wuhan city, central China, where rodents are rare, but birds (e.g., Eurasian jay) are present. We hypothesized that a reduction of rodents would induce greater threats to the regeneration of oaks with large acorn than that with small acorns because bird dispersers may prefer to disperse small acorns. The results showed that, for both of the oak species, very few acorns were dispersed on the ground surface, leading to a clustered distribution of newborn seedlings underneath adults, which was followed by a high mortality in the next year. However, due to the existing Eurasian jay preferring to harvest small acorns, more small Q. chenii acorns were dispersed than large Q. variabilis acorns, resulting in a less clustering and a lower mortality of Q. chenii seedlings than Q. variabilis in the experimental patch. These results suggest that the loss of granivorous rodents in urban forests may result in low regeneration of rodent-dispersed species, but this degradation of ecological function can be partially buffered by bird dispersers (e.g., Eurasian jay) for smallseeded trees. Ecological-based management of rodents and birds are needed in urban forests to ensure their sustainability.

关键词： camera traps   monitoring   Mozambique   multi‐   species modeling   Africa   wildlife recovery   species richness   restoration  

摘要： As local and global disturbances reshape African savannas, an understanding of how animal communities recover and respond to landscape features can inform conservation and restoration. Here, we explored the spatial ecology of a wildlife community in Gorongosa National Park, Mozambique, where conservation efforts have fostered the recovery of large mammal populations after their near-extirpation during Mozambique's civil war. We deployed a grid of 60 camera traps and used a hierarchical, multi-species occupancy modeling approach to examine patterns of occupancy and its environmental and anthropogenic correlates for different functional groups and species. Our survey provides strong evidence that wildlife in Gorongosa is recovering. Throughout the study area, modeled species richness was comparable to richness in less-disturbed savanna systems in Tanzania and Botswana, and exceeded estimates of richness from a mixed-use landscape outside the park and from postwar (1997-2002) aerial surveys. However, the mammal community in Gorongosa differs from prewar conditions and from those of more intact systems, with few large carnivores, low occupancy probabilities for large ungulate species that were dominant prior to the war, and high occupancy for other ungulates that are now ubiquitous. Associations with tree cover varied among species and guilds. Contrary to our expectation, there was no effect of lake proximity on community and group-level occupancy, and previously dominant floodplain ungulate species now occupy more wooded areas. Mammals were more likely to occupy areas that burned frequently, as post-fire vegetation regrowth provides high-quality forage, highlighting the importance of Gorongosa's fire regime. Occupancy was lower in areas with more illegal hunting, and higher closer to roads, potentially because roads were established in areas of high wildlife density and facilitate animal movement. Continued multi-species monitoring in Gorongosa can shed light on the di

关键词： Afromontane   Biological invasions   Ecological interactions   Microhabitats  

摘要： Invasive alien trees transform landscapes and subsequent ecosystem function. For grassland ecosystems, fragmentation following invasion by alien woody species is of concern. In this study, we examined how an invasive alien tree, Robinia pseudoacacia L. (Fabaceae) impacts grassland microclimates and the subsequent assemblages of endemic arthropods. The phenological trajectory of R. pseudoacacia, temperature and light intensity, as well as arthropod abundances in both invaded and uninvaded habitats, were monitored. Results showed that R. pseudoacacia significantly lowers average understory temperatures and light penetration in grassland ecosystems. Average temperatures were at least 2 degrees C lower in understory habitats than open grasslands while light intensity was lower by more than 1200 lumens/ft(2). In addition, arthropod communities differed between invaded and uninvaded habitats. The most affected taxa were Acridids from the order Orthoptera as they were excluded from understory habitats while Coleopterans were more abundant under R. pseudoacacia. Apart from absence of main host plants, invasion mediated differences in microenvironments appeared to be the main driver of this shift in affected arthropod taxa. Implications for insect conservation These results highlight the need to sustainably manage R. pseudoacacia invasions especially in grassland ecosystems. In addition to their conservation value due to their role in nutrient cycling, grassland arthropods also serve as important indicators of ecosystem health. Hence, they can be used to monitor ecosystem recovery post invasive alien tree management.

关键词： Ecoacoustics   Ecological disturbances   Cerrado   Biophony   Passive acoustic monitoring  

摘要： Wildfire is a natural process in Brazilian savannas, but human activities alter fire regimes and threaten biodiversity. In this study, we used an ecoacoustics approach to assess fauna responses and recovery after wildfire in a Brazilian savanna Six passive acoustic monitoring devices were used to record soundscapes before and after a wildfire a at burned and non-burned sites for one year and one month (September 2012 to September 2013). Power Spectral Density and the Acoustic Complexity Index were used to track biophony. Before the fire, the two sites had similar biophonic patterns (PSD: T = 1136, Z = 1.52, P = 0.12;ACI: T = 1117, Z = 1.10, P = 0.26) and soniferous species richness (Site 1 = 52 and Site 2 = 49). However, in the first two sessions of recordings after the tire, biophony became higher at the burned site during the day (PSD: T = 211 and 233;Z = 4.13 and 6.41;ACI: T = 120 and 469, Z = 5.14 and 7.07;all P < 0.00). During the night, biophony was usually higher at the non-burned site until May 2013 (PSD: T = 0 to 453;Z = 3.30 to 5.90;ACI: T= 333 to 491, Z = 3.80 to 4.93;all P < 0.00). Biophony became similar (P = 0.17 to 0.38) at the two sites or higher (P = 0.00 to 0.01) at the burned site from July to September 2013 (PSD: T = 55 to 1167;Z = 1.35 to 6.89;ACI: T = 719 to 1365, Z = 0.87 to 3.04). After the fire, a reduction of soniferous species at the burned site was observed for insects and bats. Both biophonic activity and soniferous species showed a tendency to recover one year after the fire, but there were still less species in September 2013 (non-burned = 43 and burned = 37) when compared to September 2012 at both sites (Site 1 = 52 and Site 2 = 49). Our results showed that changes in the natural regimes of fire can negatively impact the biodiversity and reinforce the need for monitoring protocols and inspection of wildfires. (C) 2021 Elsevier B.V. All rights reserved.

关键词： allometry   herbivory   recruitment   saplings   seedlings  

摘要： Conspicuously absent from plant allometric models are insect herbivores, despite their ubiquity in pantropical forests as well as the importance of gauging their impact on plant growth for understanding tree regeneration dynamics. Conceivably, the scaling relationships of plant populations with and without exposure to insects could be compared to gain insight, but this has yet to be tried. Here, I examined the size allometry of three canopy-statured species (Fabaceae) by fitting standard major axis regressions of stem height, number of leaves, and maximum area per leaf against stem diameter (root collar) of their juveniles (seedlings/saplings) in 41 canopy gaps after ca. 2 years of herbivore exclusion (using mesh cages with mesh-rooftop controls), in a central African forest. Herbivores did not change the slope or intercept, nor shift the location of Tetraberlinia bifoliolata and T. korupensis populations, whose seedlings tolerate shade well. In stark contrast, all three size allometries were altered in the faster-growing Microberlinia bisulcata, whose seedlings cannot tolerate shade indefinitely. More pronounced than either an altered slope (scaling exponent) or intercept was the strong rightward shift in location (to larger sizes) of protected M. bisulcata, whereas its normal (control) population was left stunted, with fewer and smaller leaves. Nevertheless, all species had higher than theoretically predicted scaling exponents, even in the absence of herbivores, suggesting a convergent response early in tree ontogeny across the shade-tolerance spectrum prioritizing height gain over mechanical stability in forest gaps. But insect herbivores were able to significantly strengthen this deviation in M. bisulcata, and perhaps in T. korupensis. These results demonstrate an allometric approach may prove useful for revealing how insects differentially impact trees' growth and form (slenderness) when they are most vulnerable to herbivory.

关键词： biodiversity conservation   cattle stocking rate   ecological restoration   elephant   grazing intensity   livestock–   wildlife interactions   savanna ecosystems   spatio‐   temporal heterogeneity  

摘要： Cattle and other livestock graze more than a quarter of the world's terrestrial area and are widely regarded to be drivers of global biodiversity declines. Studies often compare the effects of livestock presence/absence but, to our knowledge, no studies have tested for interactive effects between large wild herbivores and livestock at varying stocking rates on small-bodied wild vertebrates. We investigated the effects of cattle stocking rates (none/moderate/high) on the diversity of wildlife 0.05-1,000 kg using camera traps at a long-term exclosure experiment within a semi-arid savanna ecosystem in central Kenya. In addition, by selectively excluding wild 'mesoherbivores' (50-1,000 kg) and 'megaherbivores' (>1,000 kg;elephant and giraffe), we tested whether the presence of these two wild herbivore guilds (collectively, 'larger wild herbivores') mediates the effect of cattle stocking rate on habitat use and diversity of 'smaller wildlife' (mammals ranging between 10 and 70 cm shoulder height and birds). Our results show that cattle enhance alpha diversity of smaller wildlife (with or without larger wild herbivore presence) and of all wildlife 0.05-1,000 kg (with or without megaherbivore presence), by altering vegetation structure. However, for smaller wildlife, this effect is less pronounced in the presence of larger wild herbivores, which also shorten grass. In the absence of cattle, mesoherbivore-accessible sites showed higher alpha diversity of smaller wildlife than sites excluding mesoherbivores. Smaller wildlife habitat use was increased by high cattle stocking rates and wild mesoherbivores more in the presence of the other. Synthesis and applications. Our findings imply that grazing, whether by livestock or wildlife, can enhance local savanna wildlife diversity. The biodiversity benefits of localised increases in herbivory are likely to be due to shortened grass and associated visibility improvements (for predator avoidance/foraging). This suggests that land ma

关键词： African herbivores   browser   faeces   grazer   nitrogen fixation   nutrient limitation   phosphorus   tree–   grass balance  

摘要： The balance between trees and grasses is a key aspect of savanna ecosystem functioning, and so far, believed to be regulated by resource availability, fire frequency and consumption by mammalian herbivores. Herbivores, however, also impact plant communities through the deposition of growth-limiting nutrients in their dung and urine. Little attention has been paid to the fact that savanna herbivores produce dung containing different concentrations of nutrients and it remains unknown what the effect of this variation is on tree-grass interactions. Here, we investigate if stoichiometric differences in dung from browsers and grazers from an African savanna are large enough to influence competitive interactions between N-2-fixing trees and grasses. We performed a competition experiment with seedlings of three common N-2-fixing tree species and three common C-4 grass species from a Kenyan savanna. Plants were grown in mesocosms as monocultures or mixtures with dung from either zebra (grazer) or giraffe (browser). We show that variation in dung nitrogen (N) to phosphorus (P) ratio between these herbivores was large enough to drive the competitive outcome between tree seedlings and grasses. Under zebra dung with a low N:P ratio (3.5), tree seedlings had an advantage due to increased nodulation and N-2 fixation. Under giraffe dung with a high N:P ratio (6.4), grasses suppressed nodulation and tree seedling growth. Synthesis. We identify another potentially important mechanism by which mammalian herbivores can stimulate ecosystem stability, namely through the N:P ratio of their dung. This illustrates how connected browsing and grazing herbivores are in African savannas, through the forage quality they consume, the N:P stoichiometry of their dung and subsequent effects on plant competition.

关键词： fire experiments   fire frequency   fire intensity   fire management   fire‐   prone biomes   monsoonal tropics  

摘要： Aim Fire is particularly frequent, complex and contentious in the vast tropical savannas of northern Australia, where declines in many threatened species are associated with fire, and substantial areas are under fire management for greenhouse gas abatement. Controlled field experiments are crucial for understanding biodiversity responses, and here I present key insights into faunal responses to fire that have been revealed by them, along with their lessons for fire management. Location Australian monsoonal tropics. Methods Results are synthesized from six replicated fire experiments that have been conducted in Australian savannas and include multispecies assessments of fauna. The synthesis also draws on other fire studies and is presented in the form of five key insights into faunal responses. Results The key insights are as follows: (a) most faunal groups are extremely resilient to fire, with highly contrasting fire regimes often having little or no detectable impact on species abundances, at least in the medium term;(b) the most important effects of fire are typically indirect through habitat modification, even when there is substantial direct mortality;(c) fire intensity is not as important a factor as is widely thought;rather, fire frequency is particularly important;(d) there will always be winners and losers with any fire;and (e) fire is required for the maintenance of diversity. Main conclusions These insights have important implications for conservation management in Australian savannas: management needs to focus on fire-induced changes to habitat suitability, and to consider faunal outcomes at the landscape scale;a combination of frequently (every 2-3 years) and less frequently (every >= 5 years) burned habitat may adequately conserve the great majority of animal species without a need for complex fire mosaics;special management attention is required for frequent-fire losers because of an extremely low representation of longer-unburnt habitat;and fire needs