Browsing by Author "Beirne, C"

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    Climatic and Resource Determinants of Forest Elephant Movements
    (Frontiers in Ecology and Evolution, 2020-04-17) Beirne, C; Meier, AC; Brumagin, G; Jasperse-Sjolander, L; Lewis, M; Masseloux, J; Myers, K; Fay, M; Okouyi, J; White, LJT; Poulsen, JR
    As a keystone megafaunal species, African forest elephants (Loxodonta cyclotis) influence the structure and composition of tropical forests. Determining the links between food resources, environmental conditions and elephant movement behavior is crucial to understanding their habitat requirements and their effects on the ecosystem, particularly in the face of poaching and global change. We investigate whether fruit abundance or climate most strongly influence forest elephant movement behavior at the landscape scale in Gabon. Trained teams of “elephant trackers” performed daily fruit availability and dietary composition surveys over a year within two relatively pristine and intact protected areas. With data from 100 in-depth field follows of 28 satellite-collared elephants and remotely sensed environmental layers, we use linear mixed-effects models to assess the effects of sites, seasons, focal elephant identification, elephant diet, and fruit availability on elephant movement behavior at monthly and 3-day time scales. At the month-level, rainfall, and to a lesser extent fruit availability, most strongly predicted the proportion of time elephants spent in long, directionally persistent movements. Thus, even elephants in moist tropical rainforests show seasonal behavioral phenotypes linked to rainfall. At the follow-level (2–4 day intervals), relative support for both rainfall and fruit availability decreased markedly, suggesting that at finer spatial scales forest elephants make foraging decisions largely based on other factors not directly assessed here. Focal elephant identity explained the majority of the variance in the data, and there was strong support for interindividual variation in behavioral responses to rainfall. Taken together, this highlights the importance of approaches which follow individuals through space and time. The links between climate, resource availability and movement behavior provide important insights into the behavioral ecology of forest elephants that can contribute to understanding their role as seed dispersers, improving management of populations, and informing development of solutions to human-elephant conflict.
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    Conspecific investigation of a deceased forest elephant (Loxodonta cyclotis)
    (PACHYDERM, 2017-07-01) Hawley, CR; Beirne, C; Meier, A; Poulsen, JR
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    Improving population estimates of difficult-to-observe species: A dung decay model for forest elephants with remotely sensed imagery
    (Animal Conservation, 2021-01-01) Meier, AC; Shirley, MH; Beirne, C; Breuer, T; Lewis, M; Masseloux, J; Jasperse-Sjolander, L; Todd, A; Poulsen, JR
    Accurate and ecologically relevant wildlife population estimates are critical for species management. One of the most common survey methods for forest mammals – line transects for animal sign with distance sampling – has assumptions regarding conversion factors that, if violated, can induce substantial bias in abundance estimates. Specifically, for sign (e.g. nests, dung) surveys, a single number representing total time for decay is used as a multiplier to convert estimated sign density into animal density. This multiplier is likely inaccurate if not derived from a study reflecting the spatiotemporal variation in decay times. Using dung decay observations from three protected areas in Gabon, and a previous study in Nouabalé-Ndoki National Park (Congo), we developed Weibull survival models to adaptively predict forest elephant (Loxodonta cyclotis) dung decay based on environmental variables from field collected and remotely sensed data. Seasonal decay models based on remotely sensed covariates explained 86% of the variation for the wet season and 79% for the dry season. These models included canopy cover, cloud cover, humidity, vegetation complexity and slope as factors influencing dung decay. With these models, we assessed sensitivity of elephant density estimates to spatiotemporal environmental heterogeneity, showing that our methods work best for large-scale studies >50 km2. We simulated decay studies with and without these variables in four Gabonese national parks and reanalyzed two previous surveys of elephants in Minkébé National Park, Gabon. Disregarding spatial and temporal variation in decay rate biased population estimates up to 1.6 and 6.9 times. Our reassessment of surveys in Minkébé National Park showed an expected loss of 78% of forest elephants over ten years, but the elephant abundance was 222% higher than previously estimated. Our models incorporate field or remotely sensed variables to provide an ecological context essential for accurate population estimates while reducing need for expensive decay field studies.
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    LED flashlight technology facilitates wild meat extraction across the tropics
    (Frontiers in Ecology and the Environment, 2020-11-01) Bowler, M; Beirne, C; Tobler, MW; Anderson, M; DiPaola, A; Fa, JE; Gilmore, MP; Lemos, LP; Mayor, P; Meier, A; Menie, GM; Meza, D; Moreno-Gutierrez, D; Poulsen, JR; de Souza Jesus, A; Valsecchi, J; El Bizri, HR
    Hunting for wild meat in the tropics provides subsistence and income for millions of people. Methods have remained relatively unchanged since the introduction of shotguns and battery-powered incandescent flashlights, but the short battery life of such flashlights has limited nocturnal hunting. However, hunters in many countries throughout the tropics have recently begun to switch to brighter and more efficient light-emitting diode (LED) flashlights. Such brighter spotlights stimulate the freeze response of many species, and improved battery life allows hunters to pursue game more often and for longer periods of time. Interviews with hunters in African and South American tropical forests revealed that LEDs increase the frequency and efficiency of nocturnal hunting, and subsequently the number of kills made. In Brazil, these findings were supported by harvest data. The marked change in efficiency brought about by LEDs, well known to hunters around the world, poses a major threat to wildlife. Here we consider the implications of the increasing use of LED lights in hunting for communities, governments, wildlife managers, and conservationists.
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    Long Distance Seed Dispersal by Forest Elephants
    (Frontiers in Ecology and Evolution, 2021-12-22) Poulsen, JR; Beirne, C; Rundel, C; Baldino, M; Kim, S; Knorr, J; Minich, T; Jin, L; Núñez, CL; Xiao, S; Mbamy, W; Obiang, GN; Masseloux, J; Nkoghe, T; Ebanega, MO; Clark, CJ; Fay, MJ; Morkel, P; Okouyi, J; White, LJT; Wright, JP
    By dispersing seeds long distances, large, fruit-eating animals influence plant population spread and community dynamics. After fruit consumption, animal gut passage time and movement determine seed dispersal patterns and distances. These, in turn, are influenced by extrinsic, environmental variables and intrinsic, individual-level variables. We simulated seed dispersal by forest elephants (Loxodonta cyclotis) by integrating gut passage data from wild elephants with movement data from 96 individuals. On average, elephants dispersed seeds 5.3 km, with 89% of seeds dispersed farther than 1 km. The longest simulated seed dispersal distance was 101 km, with an average maximum dispersal distance of 40.1 km. Seed dispersal distances varied among national parks, perhaps due to unmeasured environmental differences such as habitat heterogeneity and configuration, but not with human disturbance or habitat openness. On average, male elephants dispersed seeds farther than females. Elephant behavioral traits strongly influenced dispersal distances, with bold, exploratory elephants dispersing seeds 1.1 km farther than shy, idler elephants. Protection of forest elephants, particularly males and highly mobile, exploratory individuals, is critical to maintaining long distance seed dispersal services that shape plant communities and tropical forest habitat.
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    Old growth Afrotropical forests critical for maintaining forest carbon
    (Global Ecology and Biogeography, 2020-10-01) Poulsen, JR; Medjibe, VP; White, LJT; Miao, Z; Banak-Ngok, L; Beirne, C; Clark, CJ; Cuni-Sanchez, A; Disney, M; Doucet, JL; Lee, ME; Lewis, SL; Mitchard, E; Nuñez, CL; Reitsma, J; Saatchi, S; Scott, CT
    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.