•We examined the effects of defaunation on seed predation of eight timber species.•Vertebrate seed predation was a strong filter on recruitment.•Rodents caused the greatest seed mortality for all ...tree species studied.•Rodent seed removal increased with defaunation, and seedling establishment decreased.•Hunting-induced defaunation may reduce regeneration of commercially important trees.
Human hunting is widespread in tropical forests and can substantially alter the plant-animal interactions that drive tree recruitment. Seed predation is a strong determinant of plant reproductive success, but it remains unclear how defaunation modifies this process. We examined the effects of hunting-induced defaunation on seed predation and seedling establishment, using replicated exclosure treatments at six sites across a defaunation gradient in northeastern Gabon. We monitored 5580 seeds of eight commercially important tree species that varied in seed traits such as size and dispersal mode. Rodents caused the greatest seed mortality for all species, removing ∼60% of accessible seeds. In comparison, invertebrates and fungi together caused just 6% of seed mortality. With protection from rodents, more than twice as many seeds established as seedlings, demonstrating that vertebrate seed predation was a strong filter on recruitment. With increasing defaunation, the proportion of seeds removed by rodents increased significantly, and seedling establishment decreased significantly, for most species. In heavily defaunated sites, with the lowest abundances of large mammals, seed removal by rodents increased by 63% and seedling establishment decreased by 42% compared to sites with intact fauna. Diminished seedling establishment is likely to reduce the regeneration of many tree species – including some with commercial importance – in hunted forests, with detrimental economic consequences. In turn, declines in timber regeneration may increase the likelihood that selectively logged forests are converted to non-forest land uses with little conservation value. Appropriate management could preclude these outcomes, to the benefit of both wildlife and natural timber regeneration.
In Gabon, like elsewhere in Africa, crops are often sources of conflict between humans and wildlife. Wildlife damage to crops can drastically reduce income, amplifying poverty and creating a negative ...perception of wild animal conservation among rural people. In this context, crop-raiding animals like elephants quickly become "problem animals". To deter elephants from raiding crops beehives have been successfully employed in East Africa; however, this method has not yet been tested in Central Africa. We experimentally examined whether the presence of Apis mellifera adansonii, the African honey bee species present in Central Africa, deters forest elephants (Loxodonta Africana cyclotis) from feeding on fruit trees. We show for the first time that the effectiveness of beehives as deterrents of elephants is related to bee activity. Empty hives and those housing colonies of low bee activity do not deter elephants all the time; but beehives with high bee activity do. Although elephant disturbance of hives does not impede honey production, there is a tradeoff between deterrence and the quantity of honey produced. To best achieve the dual goals of deterring elephants and producing honey colonies must maintain an optimum activity level of 40 to 60 bee movements per minute. Thus, beehives colonized by Apis mellifera adansonii bees can be effective elephant deterrents, but people must actively manage hives to maintain bee colonies at the optimum activity level.
Abstract
Anthropogenic pressures are causing the widespread loss of wildlife species and populations, with adverse consequences for ecosystem functioning. This phenomenon has been widely but ...inconsistently referred to as defaunation. A cohesive, quantitative framework for defining and evaluating defaunation is necessary for advancing biodiversity conservation. Likening defaunation to deforestation, we propose an operational framework for defaunation that defines it and related terms, situates defaunation relative to intact communities and faunal degradation, and encourages quantitative, ecologically reasonable, and equitable measurements. We distinguish between defaunation, the conversion of an ecosystem from having wild animals to not having wild animals, and faunal degradation, the process of losing animals or species from an animal community. The quantification of context-relevant defaunation boundaries or baselines is necessary to compare faunal communities over space and time. Situating a faunal community on the degradation curve can promote Global Biodiversity Framework targets, advancing the 2050 Vision for Biodiversity.
How should ecologists and evolutionary biologists analyze nonnormal data that involve random effects? Nonnormal data such as counts or proportions often defy classical statistical procedures. ...Generalized linear mixed models (GLMMs) provide a more flexible approach for analyzing nonnormal data when random effects are present. The explosion of research on GLMMs in the last decade has generated considerable uncertainty for practitioners in ecology and evolution. Despite the availability of accurate techniques for estimating GLMM parameters in simple cases, complex GLMMs are challenging to fit and statistical inference such as hypothesis testing remains difficult. We review the use (and misuse) of GLMMs in ecology and evolution, discuss estimation and inference and summarize ‘best-practice’ data analysis procedures for scientists facing this challenge.
Crop damage by forest elephants (Loxodonta africana cyclotis) and the resulting human-elephant conflict are issues of great concern for both the conservation of the species and the protection of ...rural livelihoods in Central Africa. Addressing these problems requires identifying the factors that facilitate or impede crop-raiding by forest elephants. Yet to date, the environmental or anthropogenic factors that influence the occurrence and intensity of crop-raiding by forest elephants are largely unknown. We used a multivariate approach to investigate conditions under which forest elephants raid some fields and not others in the buffer zone of Monts de Cristal National Park (MCNP), Gabon. We first interviewed 121 farmers from 11 villages situated within 10 km of MCNP regarding the occurrence of elephant crop-raiding of their fields. We then collected data on 39 explanatory variables to characterize the agricultural fields. Of these, the most important predictors of elephant raid occurrence of crop damage were presence of fruit trees, elephant deterrents (scarecrows, fire, wire string fences and empty barrels), and field topography. We secondly assessed the effect of stage of crop growth, presence of fruit trees, field topography and presence of elephant deterrents on crop-raiding occurrence and intensity by counting raids and measuring areas of crop damage every week in 17 plantations over 19 weeks in the most elephant-impacted zone of the study area. We found that fruit presence and stage of crop growth led to more intense damage to crops, whereas local deterrents did not inhibit raiding events and crop damage by elephants. We report a tradeoff between non-timber forest products (NTFP) services and crop-raiding by elephants. We show for the first time that steep topography impedes elephant damage to crops with no raids recorded in fields with surrounding slopes greater than 25%. We discuss whether farming on steep fields could be used as a strategy for mitigating crop-raiding to favor human-elephant coexistence and enhance elephant conservation.
In 2015 and 2016, the AfriSAR campaign was carried out as a collaborative effort among international space and National Park agencies (ESA, NASA, ONERA, DLR, ANPN and AGEOS) in support of the ...upcoming ESA BIOMASS, NASA-ISRO Synthetic Aperture Radar (NISAR) and NASA Global Ecosystem Dynamics Initiative (GEDI) missions. The NASA contribution to the campaign was conducted in 2016 with the NASA LVIS (Land Vegetation and Ice Sensor) Lidar, the NASA L-band UAVSAR (Uninhabited Aerial Vehicle Synthetic Aperture Radar). A central motivation for the AfriSAR deployment was the common AGBD estimation requirement for the three future spaceborne missions, the lack of sufficient airborne and ground calibration data covering the full range of ABGD in tropical forest systems, and the intercomparison and fusion of the technologies.
During the campaign, over 7000 km2 of waveform Lidar data from LVIS and 30,000 km2 of UAVSAR data were collected over 10 key sites and transects. In addition, field measurements of forest structure and biomass were collected in sixteen 1-hectare sized plots. The campaign produced gridded Lidar canopy structure products, gridded aboveground biomass and associated uncertainties, Lidar based vegetation canopy cover profile products, Polarimetric Interferometric SAR and Tomographic SAR products and field measurements. Our results showcase the types of data products and scientific results expected from the spaceborne Lidar and SAR missions; we also expect that the AfriSAR campaign data will facilitate further analysis and use of waveform lidar and multiple baseline polarimetric SAR datasets for carbon cycle, biodiversity, water resources and more applications by the greater scientific community.
•In 2016, the international collaborative air and field campaign AfriSAR took place•The data provides calibration and validation for NASA GEDI, NISAR and ESA BIOMASS•NASA collected coincident L-band SAR (UAVSAR) and waveform Lidar (LVIS) data•We produced SAR- and Lidar derived canopy height, biomass and vertical profile datasets•We provide an overview of the airborne mission, data products and applications
1. Anthropocene defaunation is the global phenomenon of human-induced animal biodiversity loss. Understanding the patterns and process of defaunation is critical to predict outcomes for wildlife ...populations and cascading consequences for ecosystem function and human welfare. 2. We investigated a defaunation gradient in north-eastern Gabon by establishing 24 transects at varying distances (2-30 km) to rural villages and surveying the abundance and composition of vertebrate communities. Distance from village was positively correlated with observations of hunting (shotgun shells, campfires, hunters), making it a good proxy for hunting pressure. 3. Species diversity declined significantly with proximity to village, with mammal richness increasing by roughly 1-5 species every 10 km travelled away from a village. Compared to forest far from villages, the wildlife community near villages consisted of higher abundances of large birds and rodents and lower abundances of large mammals like monkeys and ungulates. 4. Distance to nearest village emerged as a key driver of the relative abundance of five of the six taxonomic guilds, indicating that the top-down force of hunting strongly influences large vertebrate community composition and structure. Several measures of vegetation structure also explained animal abundance, but these varied across taxonomic guilds. Forest elephants were the exception: no measured variable or combination of variables explained variation in elephant abundances. 5. Synthesis and applications. Hunting is concentrated within 10 km around villages, creating a hunting halo characterized by heavily altered animal communities composed of relatively small-bodied species. Although the strongest anthropogenic effects are relatively distance-limited, the linear increase in species richness shown here even at distances 30 km from villages suggests that hunting may have altered vertebrate abundances across the entire landscape. Central African forests store > 25% of the carbon in tropical forests and are home to 3000 endemic species, but roughly 53% of the region lies within the village hunting halo. Resource management strategies should take into account this hunting-induced spatial variation in animal communities. Near villages, resource management should focus on sustainable community-led hunting programmes that provide long-term supplies of wild meat to rural people. Resource management far from villages should focus on law enforcement and promoting industry practices that maintain remote tracts of land to preserve ecosystem services like carbon storage and biodiversity.
Seed predators drive patterns in seed mortality and seedling establishment and are posited to contribute to the maintenance of plant species diversity through several mechanisms. Negative density ...dependence and spatially restricted recruitment are apparently widespread in Neotropical forests, but are little studied in Afrotropical forests, where generalist vertebrates may contribute more to seed mortality than do specialized invertebrates and fungi. We experimentally assessed the roles of seed density and distance from the parent tree for ten tree species in a forest in northeastern Gabon, using exclosures to isolate the effects of different seed predator types. Vertebrates caused greater seed losses than all other mortality agents combined. Unexpectedly, seeds under fruiting conspecific trees had significantly lower removal and higher seedling establishment than those under heterospecific trees or in neutral non-fruiting locations. Seed density did not significantly affect seedling establishment. Vertebrate seed removal ranged from 0 percent to 100 percent among focal species and was positively correlated with seed mass but had no relationship with species commonness (adult tree density). Seed traits strongly affected patterns of seed removal and seedling establishment and may contribute more to the likelihood of success for an individual seed than do its density or distance from parent. Our results highlight an apparent divergence in patterns of seed mortality and seedling establishment between tropical forest regions and emphasize the need for further comparative study.
Poaching of forest elephants (Loxodonta cyclotis) for ivory has decimated their populations in Central Africa. Studying elephant movement can provide insight into habitat and resource use to reveal ...where, when, and why they move and guide conservation efforts. We fitted 17 forest elephants with global positioning system (GPS) collars in 2015 and 2016 in the tropical forest-grassland mosaic of the Wonga Wongué Presidential Reserve (WW), Gabon. Using the location data, we quantified movement distances, home ranges, and habitat use to examine the environmental drivers of elephant movements and predict where elephants occur spatially and temporally. Forest elephants, on average, traveled 2,840 km annually and had home ranges of 713 km2, with males covering significantly larger home ranges than females. Forest elephants demonstrated both daily and seasonal movement patterns. Daily, they moved between forest and grassland at dawn and dusk. Seasonally, they spent proportionally more time in grassland than forest during the short-wet season when grasses recruit. Forest elephants also traveled faster during the short-wet season when fruit availability was greatest, likely reflecting long, direct movements to preferred fruiting tree species. Forest elephants tended to select areas with high tree and shrub density that afford cover and browse. When villages occurred in their home ranges elephants spent a disproportionate amount of time near them, particularly in the dry season, probably for access to agricultural crops and preferred habitat. Given the importance of the grassland habitat for elephants, maintenance of the forest-grassland matrix is a conservation priority in WW. Law enforcement, outreach, and education should focus on areas of potential human-elephant conflict near villages along the borders of the reserve. GPS-tracking should be extended into multi-use areas in the peripheries of protected areas to evaluate the effects of human disturbance on elephant movements and to maintain connectivity among elephant populations in Gabon.
Tropical forests are a key component of the global carbon cycle. Yet, there are still high uncertainties in forest carbon stock and flux estimates, notably because of their spatial and temporal ...variability across the tropics. Several upcoming spaceborne missions have been designed to address this gap. High-quality ground data are essential for accurate calibration/validation so that spaceborne biomass missions can reach their full potential in reducing uncertainties regarding forest carbon stocks and fluxes. The BIOMASS mission, a P-band SAR satellite from the European Space Agency (ESA), aims at improving carbon stock mapping and reducing uncertainty in the carbon fluxes from deforestation, forest degradation, and regrowth. In situ activities in support of the BIOMASS mission were carried out in French Guiana and Gabon during the TropiSAR and AfriSAR campaigns. During these campaigns, airborne P-band SAR, forest inventory, and lidar data were collected over six study sites. This paper describes the methods used for forest inventory and lidar data collection and analysis, and presents resulting plot estimates and aboveground biomass maps. These reference datasets along with intermediate products (e.g., canopy height models) can be accessed through ESA's Forest Observation System and the Dryad data repository and will be useful for BIOMASS but also to other spaceborne biomass missions such as GEDI, NISAR, and Tandem-L for calibration/validation purposes. During data quality control and analysis, prospects for reducing uncertainties have been identified, and this paper finishes with a series of recommendations for future tropical forest field campaigns to better serve the remote sensing community.
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