caa a22 4500 465757073 CHVBK 20180323111850.0 cr unu---uuuuu 170327e19900301xx s 000 0 eng 10.1007/BF00177284 doi (NATIONALLICENCE)springer-10.1007/BF00177284 Waterfowl of a subtropical African floodplain [Elektronische Daten] II. Stability of the grazing system [K. Rogers, C. Breen] The Pongolo River floodplain supports large populations of waterfowl which feed on the vegetative structures of the submerged plant Potamogeton crispus. Maintenance of a stable grazing system is contingent upon the plants having specific life history characteristics to counter the effects of grazing. Feeding waterfowl uproot P. crispus plants and remove approximately 90% of the attached turions, but only 15-25% of the annual turion production is consumed. A hypothesis was developed from exclosure and laboratory experiments to account for this anomaly: while birds preferentially select large turions, uprooted plants rapidly produce many small turions which are energetically unrewarding for the birds but still have high viability. Thus, while grazing depletes the available food supply, it stimulates production of an unavailable reserve growth potential that maintains annual plant standing crop. Waterfowl consume too few fruits of P. crispus to affect the size of the seed bank which ensures persistence of the species over periodic droughts. The stimulation of annual plant net production by grazing is less than 10%, but more important, uprooting of plants by birds can be a crucial factor in determining the timing of inputs to the detrital food web in this system of highly seasonal floods. A comparison of life history characteristics of P. crispus with theoretical models demonstrates that plant life history traits other than growth rate are responsible for maintaining stability of the grazing system, and that changes in environmental conditions (e.g., water depth) must be accounted for in any model of grazing system stability. SPB Academic Publishing bv, 1990 plant-animal interactions nationallicence plant life histories nationallicence Pongolo nationallicence Potamogeton crispus nationallicence water depth regimes nationallicence waterfowl grazing nationallicence white-faced duck nationallicence Rogers K. Pongolo River Research Group, Department of Botany, University of Natal, Pietermaritzburg, South Africa aut Breen C. Pongolo River Research Group, Department of Botany, University of Natal, Pietermaritzburg, South Africa aut Wetlands Ecology and Management Kluwer Academic Publishers 1/2(1990-03-01), 99-109 0923-4861 1:2<99 1990 1 11273 https://doi.org/10.1007/BF00177284 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00177284 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Rogers K. Pongolo River Research Group, Department of Botany, University of Natal, Pietermaritzburg, South Africa aut NATIONALLICENCE 700 1- Breen C. Pongolo River Research Group, Department of Botany, University of Natal, Pietermaritzburg, South Africa aut NATIONALLICENCE 773 0- Wetlands Ecology and Management Kluwer Academic Publishers 1/2(1990-03-01), 99-109 0923-4861 1:2<99 1990 1 11273 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer