Browsing by Subject "Disturbance"

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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.
Facilitation of weed seed predation by living mulch and cover crops
(2022) Schumacher, Matthias; Gerhards, Roland
Weed seed predation (WSP) is an important agro‐ecosystem service that naturally suppresses weed populations. Disturbances directly interfere with the activity of the seed predators, for example, harvest and soil tillage during a peak in weed seed availability (around cereal harvest). Plant soil cover and reduced soil tillage are factors that might positively affect WSP. We investigated cover crops and living mulch along with soil disturbance (no‐till and conventional seeding) in comparison to a fallow and repeated stubble tillage with a chisel plough in terms of WSP, activity‐density of carabid beetles and soil cover. A field experiment with a randomised complete block design and four replications was conducted at two sites from 2017 until 2019. WSP rates were assessed with seed cards and exclosure cages from July until November during a period of eight consecutive days each month. Living mulch exhibited the highest WSP rates of 72% with a maximum of 95% immediately following cereal harvest in August and September of 2017 and 2019, while the remainder of the treatments ranged from 2% to 5% WSP. In October and November mustard showed on average twice as high WSP rates compared to the other treatments (50% vs. 10%–25%). Seeding and soil tillage did not significantly influence carabid beetle activity‐density and WSP, except for living mulch. Predator groups (invertebrates and vertebrates) were not influenced by the various treatments, rather year and month determined the predator groups dominance. Besides their weed suppressive effects, living mulches and cover crops also facilitate WSP.