Food-related determinants of Kudu carrying capacity in a semi-arid savanna

[摘要] English: A comparative study was conducted in order to investigate the relationship betweenforage availability and parameters of kudu populations thought to have a bearing onkudu carrying capacity in a semi-arid savanna. This involved eight game-fenced studyunits. The leaf production and standing crop of woody and forb species weredetermined. Woody species were classified according to rainfall season acceptance tobrowsers, the presence and absence of physical deterrents and foliage retention periodinto the dry season. Ungulate densities were determined during the late dry season of1999 by helicopter census.The leaf dry mass production below a height of 2 m, the mean browsing height of kudu,ranged from 362 kg ha' to 695 kg ha' (mean = 516 kg ha') between study units. Theforb standing crop (dry mass) ranged from 83 kg ha' to 376 kg ha' (mean = 214 kg ha')between study units.Large-scale kudu mortalities were reported in the dry season of 1998 in the study area.Below average rainfall received during the preceding rainfall season probablycontributed to these mortalities, which were further aggravated by a prolonged cold spellexperienced at the time. The lack of late dry season woody foliage was significantlyrelated to mortalities. Relationships between kudu mortalities and kudu density or studyunit size were insignificant.Kudu faecal nitrogen concentration was determined at regular time intervals during thedry season of 1999. This was preceded by a normal rainfall season. Kudu faecalnitrogen concentration declined during the dry season and reached a minimum duringthe dry hot season (August - October). Kudu faecal nitrogen concentration peakedduring the month of November. Mortalities and poor physical condition of kudupopulations were linked to low dry hot season kudu faecal nitrogen concentrations.Variation in kudu faecal nitrogen concentration was significantly explained by theavailability of woody species' foliage, excluding the contribution of early deciduousspecies. It is hypothesised that kudu survival is largely dependent on the nutritional status of theanimals. Animals with a low nutritional status are more susceptible to diseases and theeffect of physical exposure during adverse weather. The nutritional status of kudupopulations is apparently dependent on the availability of dry season foliage resources,which is again dependent on the preceding rainy season's rainfall. During droughts,forage resources available during the late dry season, the critical period, are important.During average rainfall years, kudu appear to be less dependent on critical resources,and the availability of dry season resources before the critical period is entered becomesincreasingly important.Different strategies to optimise kudu production, given the variation in forage resourcesbetween years, are discussed. It is proposed that kudu carrying capacity in semi-aridsavanna is based on the availability of forage resources during the dry season, takinginto account the effect of rainfall on resource availability/quality.

[发布机构] University of the Free State