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.
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.
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.
The critically endangered African forest elephant (Loxodonta cyclotis) plays a vital role in maintaining the structure and composition of Afrotropical forests, but basic information is lacking ...regarding the drivers of elephant movement and behavior at landscape scales. We use GPS location data from 96 individuals throughout Gabon to determine how five movement behaviors vary at different scales, how they are influenced by anthropogenic and environmental covariates, and to assess evidence for behavioral syndromes-elephants which share suites of similar movement traits. Elephants show some evidence of behavioral syndromes along an 'idler' to 'explorer' axis-individuals that move more have larger home ranges and engage in more 'exploratory' movements. However, within these groups, forest elephants express remarkable inter-individual variation in movement behaviours. This variation highlights that no two elephants are the same and creates challenges for practitioners aiming to design conservation initiatives.
Elephant populations are in peril everywhere, but forest elephants in Central Africa have sustained alarming losses in the last decade 1. Large, remote protected areas are thought to best safeguard ...forest elephants by supporting large populations buffered from habitat fragmentation, edge effects and human pressures. One such area, the Minkébé National Park (MNP), Gabon, was created chiefly for its reputation of harboring a large elephant population. MNP held the highest densities of elephants in Central Africa at the turn of the century, and was considered a critical sanctuary for forest elephants because of its relatively large size and isolation. We assessed population change in the park and its surroundings between 2004 and 2014. Using two independent modeling approaches, we estimated a 78–81% decline in elephant numbers over ten years — a loss of more than 25,000 elephants. While poaching occurs from within Gabon, cross-border poaching largely drove the precipitous drop in elephant numbers. With nearly 50% of forest elephants in Central Africa thought to reside in Gabon 1, their loss from the park is a considerable setback for the preservation of the species.
Poulsen et al. estimate the loss of elephants from poaching in an African national park to represent over 70% of the population, more than 25’000 individuals, in one decade.
•Complete defaunation is not a prerequisite to alter the strength of plant-animal interactions.•Hunting reduced the mean seed dispersal distances of mammal-dispersed tree species.•Hunted forest had ...reduced rates of seedling herbivory and lower above-ground biomass.•Modification of plant-animal interactions could compromise forest carbon storage potential.
Unprecedented rates of logging and hunting threaten to transform the remaining primary tropical forest into a degraded mosaic, emptied of wildlife. Defaunation is expected to interrupt plant–animal interactions with cascading effects for forest structure, composition, and ecosystem services. In a Central African forest first logged 35years ago, we evaluated this process of ecological erosion in 30 study sites distributed across forest disturbed by logging and hunting, logging alone, and neither logging nor hunting. Both logging and hunting tended to reduce abundances of large mammals, together shifting the relative abundance of the animal community towards squirrels and small birds. Through a series of experiments, we evaluated the effects of logging and hunting on seed dispersal, seed predation and herbivory. We demonstrate that complete defaunation is not necessary to significantly alter the strength of plant-animal interactions. Hunting reduced the mean dispersal distances of nine mammal-dispersed tree species by 22%. Rates of seed predation were similar among forest types, but hunted forest had significantly lower rates of herbivory that we attribute to the lower abundance of meso-herbivores. Hunted forest also had significantly lower above-ground biomass (301Mgha−1) than the logged only (358Mgha−1) and undisturbed (455Mgha−1) forest types, but similar numbers of tree species and individuals. Lower biomass in hunted forest is likely attributable to significantly lower wood densities at small tree size classes (<40cm). We hypothesize that over time the human-mediated modification of plant-animal interactions can alter the composition of the forest to have a higher proportion of fast-growing, low wood density tree species, diminishing the long-term potential for carbon storage.
Quantifying the relative importance of the multiple processes that limit recruitment may hold the key to understanding tropical tree diversity. Here we couple theoretical models with a large-scale, ...multi-species seed-sowing experiment to assess the degree to which seed and establishment limitation shape patterns of tropical tree seedling recruitment in a central African forest. Of five randomly selected species (Pancovia laurentii, Staudtia kamerunensis, Manilkara mabokeensis, Myrianthus arboreas, and Entandophragma utile), seedling establishment and survival were low (means of 16% and 6% at 3 and 24 months, respectively), and seedling density increased with seed augmentation. Seedling recruitment was best explained by species identity and the interaction of site-by-species, suggesting recruitment probabilities vary among species and sites, and supporting the role of niche-based mechanisms. Although seed augmentation enhanced initial seedling density, environmental filtering and post-establishment mortality strongly limited seedling recruitment. The relative importance of seed and establishment limitation changed with seed and seedling density and through time. The arrival of seeds most strongly affected local recruitment when seeds were nearly absent from a site (∼ 1 seed m(2)), but was also important when seeds arrived in extremely high densities, overwhelming niche-based mortality factors. The strength of seed limitation and density-independent mortality decreased significantly over time, while density-dependent mortality showed the opposite trend. The varying strengths of seed and establishment limitation as a function of juvenile density and time emphasize the need to evaluate their roles through later stages of a tree's life cycle.
Aim
Large trees ≥ 70 cm diameter at breast height (DBH) contribute disproportionately to aboveground carbon stock (AGC) across the tropics but may be vulnerable to changing climate and human ...activities. Here we determine the distribution, drivers and threats to large trees and high carbon forest.
Location
Central Africa.
Time period
Current.
Major taxa studied
Trees.
Methods
Using Gabon's new National Resource Inventory of 104 field sites, AGC was calculated from 67,466 trees from 578 species and 97 genera. Power and Michaelis–Menten models assessed the contribution of large trees to AGC. Environmental and anthropogenic drivers of AGC, large trees, and stand variables were modelled using Akaike’s information criterion (AIC) weights to calculate average regression coefficients for all p
ossible models.
Results
Mean AGC for trees ≥ 10 cm DBH in Gabonese forestlands was 141.7 Mg C/ha, with averages of 166.6, 171.3 and 96.6 Mg C/ha in old growth, concession and secondary forest. High carbon forests occurred where large trees are most abundant: 31% of AGC was stored in large trees (2.3% of all stems). Human activities largely drove variation in AGC and large trees, but climate and edaphic conditions also determined stand variables (basal area, tree height, wood density, stem density). AGC and large trees increased with distance from human settlements; AGC was 40% lower in secondary than primary and concession forests and 33% higher in protected than non‐managed areas.
Main conclusions
AGC and large trees were negatively associated with human activities, highlighting the importance of forest management. Redefining large trees as ≥ 50 cm DBH (4.3% more stems) would account for 20% more AGC. This study demonstrates that protecting relatively undisturbed forests can be disproportionately effective in conserving carbon and suggests that including sustainable forestry in programs like reduced emissions for deforestation and forest degradation could maintain carbon dense forests in logging concessions that are a large proportion of remaining Central African forests.
Most plant species have a range of traits that deter herbivores. However, understanding of how different defences are related to one another is surprisingly weak. Many authors argue that defence ...traits trade off against one another, while others argue that they form coordinated defence syndromes.
We collected a dataset of unprecedented taxonomic and geographic scope (261 species spanning 80 families, from 75 sites across the globe) to investigate relationships among four chemical and six physical defences.
Five of the 45 pairwise correlations between defence traits were significant and three of these were tradeoffs. The relationship between species' overall chemical and physical defence levels was marginally nonsignificant (P = 0.08), and remained nonsignificant after accounting for phylogeny, growth form and abundance. Neither categorical principal component analysis (PCA) nor hierarchical cluster analysis supported the idea that species displayed defence syndromes.
Our results do not support arguments for tradeoffs or for coordinated defence syndromes. Rather, plants display a range of combinations of defence traits. We suggest this lack of consistent defence syndromes may be adaptive, resulting from selective pressure to deploy a different combination of defences to coexisting species.
Within the last decade the study of phenology has taken on new importance because of its contribution to climate-change research. However, phenology data sets spanning many years are rare in the ...tropics, making it difficult to evaluate possible responses of tropical communities to climate change. Here we use two data sets (1970–1983 and 1990–2002) to describe the fruiting patterns of the tropical tree community in Kibale National Park, Uganda. To address variation in spatial patterns, we describe fruiting over 2–3 y among four sites each separated by 12–15 km. Presently, the Kibale region is receiving c. 300 mm more rain than it did at the start of the century, droughts are less frequent, the onset of the rainy season is earlier, and the average maximum monthly temperature is 3.5 °C hotter than it was 25 y ago. The 1990–2002 phenology data illustrated high temporal variability in the proportion of the populations fruiting. Interannual variation in community-wide fruit availability was also high; however, the proportion of trees that fruited has increased over the past 12+y. At the species level a variety of patterns were exhibited; however, a number of the most common species currently rarely fruit, and when they do, typically <4% of the individuals take part in fruiting events. Combining the data set from 1990 to 2002 with that from 1970 to 1983 for specific species again reveals an increase in the proportion of trees fruiting between 1990 and 2002; however, the proportion of the populations fruiting decreased during the earlier period. When one examines particular species over this whole period a variety of patterns are evident. For example, Pouteria altissima exhibited a relatively regular pattern of fruiting during the 1970s; however, it rarely fruited in the 1990s. Contrasting phenological patterns at four sites revealed that at the community level the fruiting patterns of only one of the six pair-wise site combinations were correlated. Relationships between rainfall and fruiting were variable among sites. Contrasting changes in fruiting patterns over the 30 y with differences among the four sites varying in rainfall, suggests that the changes observed in fruiting may be due to climate change. Responses to this climate change are likely complex and will vary among species. However, for some species, current conditions appear unsuitable for fruiting.
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