Waterfowl of a subtropical African floodplain

Autor: K. H. Rogers, C. M. Breen
Rok vydání: 1990
Předmět:
Zdroj: Wetlands Ecology and Management. 1:99-109
ISSN: 1572-9834
0923-4861
Popis: 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.
Databáze: OpenAIRE
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