Browsing by Person "Worden, Jeffrey S."

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    Comparative ungulate diversity and biomass change with human use and drought: implications for community stability and protected area prioritization in African savannas
    (2025) Bartzke, Gundula S.; Ogutu, Joseph O.; Piepho, Hans‐Peter; Bedelian, Claire; Rainy, Michael E.; Kruska, Russel L.; Worden, Jeffrey S.; Kimani, Kamau; McCartney, Michael J.; Ng'ang'a, Leah; Kinoti, Jeniffer; Njuguna, Evanson C.; Wilson, Cathleen J.; Lamprey, Richard; Hobbs, Nicholas Thompson; Reid, Robin S.; Bartzke, Gundula S.; Biostatistics Unit, Faculty of Agricultural Sciences, Institute of Crop Science, University of Hohenheim, Stuttgart, Baden‐Württemberg, Germany; Ogutu, Joseph O.; Biostatistics Unit, Faculty of Agricultural Sciences, Institute of Crop Science, University of Hohenheim, Stuttgart, Baden‐Württemberg, Germany; Piepho, Hans‐Peter; Biostatistics Unit, Faculty of Agricultural Sciences, Institute of Crop Science, University of Hohenheim, Stuttgart, Baden‐Württemberg, Germany; Bedelian, Claire; Danish Institute for International Studies, Copenhagen, Capital Region of Denmark, Denmark; Rainy, Michael E.; International Livestock Research Institute, Nairobi, Nairobi County, Kenya; Kruska, Russel L.; International Livestock Research Institute, Nairobi, Nairobi County, Kenya; Worden, Jeffrey S.; World Wildlife Fund, Nairobi, Nairobi County, Kenya; Kimani, Kamau; International Livestock Research Institute, Nairobi, Nairobi County, Kenya; McCartney, Michael J.; Campfire Conservation, Nairobi, Nairobi County, Kenya; Ng'ang'a, Leah; International Livestock Research Institute, Nairobi, Nairobi County, Kenya; Kinoti, Jeniffer; Department of Infrastructure, Lands and Urban Development, County Government of Laikipia, Rumuruti, Laikipia, Kenya; Njuguna, Evanson C.; International Livestock Research Institute, Nairobi, Nairobi County, Kenya; Wilson, Cathleen J.; International Livestock Research Institute, Nairobi, Nairobi County, Kenya; Lamprey, Richard; Department of Natural Resources, Faculty of Geo‐Information Science and Earth Observation, University of Twente, Enschede, Overste, the Netherlands; Hobbs, Nicholas Thompson; Natural Resource Ecology Laboratory, Department of Ecosystem Science and Sustainability, Colorado State University, Fort Collins, Colorado, USA; Reid, Robin S.; International Livestock Research Institute, Nairobi, Nairobi County, Kenya
    Drought and human use may alter ungulate diversity and biomass in contrasting ways. In African savannas, resource‐dependent grazers such as wildebeest (Connochaetes taurinus) and zebra (Equus quagga) may decline or disperse as resources decline, opening space for more drought‐tolerant species such as gazelles (Eudorcas and Nanger) and impala (Aepyceros melampus). This shift can increase species richness, evenness, and overall ungulate diversity. Although higher diversity may stabilize ungulate communities, it may be associated with lower biomass (the total body mass of all individuals in a community), which in turn affects vegetation structure and composition, nutrient cycling, energy flows, and other organisms in savannas. While ungulate biomass often declines during drought or in areas of intense human use, the effects on diversity changes under low‐to‐moderate human use remain less clear. Our fine‐scale censuses in the Maasai Mara National Reserve and adjacent pastoral lands in Kenya showed that ungulate biomass declined more than diversity in the 1999 drought year. In the normal rainfall year of 2002, diversity peaked along the reserve boundary, but species richness leveled off in the drought year. Biomass peaked in the reserve in both census years, and migratory ungulates moved further into the reserve in the drought year, where diversity declined. These findings suggest that core protected areas are crucial for maintaining ungulate biomass, while transition zones from protected and pastoral lands support higher diversity unless drought reduces species richness.
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    Increasing anthropogenic disturbance restricts wildebeest movement across east African grazing systems
    (2022) Stabach, Jared A.; Hughey, Lacey F.; Crego, Ramiro D.; Fleming, Christen H.; Hopcraft, J. Grant C.; Leimgruber, Peter; Morrison, Thomas A.; Ogutu, Joseph O.; Reid, Robin S.; Worden, Jeffrey S.; Boone, Randall B.
    The ability to move is essential for animals to find mates, escape predation, and meet energy and water demands. This is especially important across grazing systems where vegetation productivity can vary drastically between seasons or years. With grasslands undergoing significant changes due to climate change and anthropogenic development, there is an urgent need to determine the relative impacts of these pressures on the movement capacity of native herbivores. To measure these impacts, we fitted 36 white-bearded wildebeest (Connochaetes taurinus) with GPS collars across three study areas in southern Kenya (Amboseli Basin, Athi-Kaputiei Plains, and Mara) to test the relationship between movement (e.g., directional persistence, speed, home range crossing time) and gradients of vegetation productivity (i.e., NDVI) and anthropogenic disturbance. As expected, wildebeest moved the most (21.0 km day–1; CI: 18.7–23.3) across areas where movement was facilitated by low human footprint and necessitated by low vegetation productivity (Amboseli Basin). However, in areas with moderate vegetation productivity (Athi-Kaputiei Plains), wildebeest moved the least (13.3 km day–1; CI: 11.0–15.5). This deviation from expectations was largely explained by impediments to movement associated with a large human footprint. Notably, the movements of wildebeest in this area were also less directed than the other study populations, suggesting that anthropogenic disturbance (i.e., roads, fences, and the expansion of settlements) impacts the ability of wildebeest to move and access available resources. In areas with high vegetation productivity and moderate human footprint (Mara), we observed intermediate levels of daily movement (14.2 km day–1; CI: 12.3–16.1). Wildebeest across each of the study systems used grassland habitats outside of protected areas extensively, highlighting the importance of unprotected landscapes for conserving mobile species. These results provide unique insights into the interactive effects of climate and anthropogenic development on the movements of a dominant herbivore in East Africa and present a cautionary tale for the development of grazing ecosystems elsewhere.