2 results
Shearing at the end of summer affects body temperature of free-living Angora goats (Capra aegagrus) more than does shearing at the end of winter
- R. S. Hetem, B. A. de Witt, L. G. Fick, A. Fuller, G. I. H. Kerley, S. K. Maloney, L. C. R. Meyer, D. Mitchell
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Angora goats are known to be vulnerable to cold stress, especially after shearing, but their thermoregulatory responses to shearing have not been measured. We recorded activity, and abdominal and subcutaneous temperatures, for 10 days pre-shearing and post-shearing, in 10 Angora goats inhabiting the succulent thicket of the Eastern Cape, South Africa, in both March (late summer) and September (late winter). Within each season, environmental conditions were similar pre-shearing and post-shearing, but September was an average 5°C colder than March. Shearing resulted in a decreased mean (P < 0.0001), minimum (P < 0.0001) and maximum daily abdominal temperature (P < 0.0001). Paradoxically, the decrease in daily mean (P = 0.03) and maximum (P = 0.01) abdominal temperatures, from pre-shearing to post-shearing, was greater in March than in September. Daily amplitude of body temperature rhythm (P < 0.0001) and the maximum rate of abdominal temperature rise (P < 0.0001) increased from pre-shearing to post-shearing, resulting in an earlier diurnal peak in abdominal temperature (P = 0.001) post-shearing. These changes in amplitude, rate of abdominal temperature rise and time of diurnal peak in abdominal temperature suggest that the goats’ thermoregulatory system was more labile after shearing. Mean daily subcutaneous temperatures also decreased post-shearing (P < 0.0001), despite our index goat selecting more stable microclimates after shearing in March (P = 0.03). Following shearing, there was an increased difference between abdominal and subcutaneous temperatures (P < 0.0001) at night, suggesting that the goats used peripheral vasoconstriction to limit heat loss. In addition to these temperature changes, mean daily activity increased nearly two-fold after March shearing, but not September shearing. This increased activity after March shearing was likely the result of an increased foraging time, food intake and metabolic rate, as suggested by the increased water influx (P = 0.0008). Thus, Angora goats entered a heat conservation mode after shearing in both March and September. That the transition from the fleeced to the shorn state had greater thermoregulatory consequences in March than in September may provide a mechanistic explanation for Angora goats’ vulnerability to cold in summer.
11 - Population level dynamics
- Edited by W. Richard J. Dean, University of Cape Town, Suzanne Milton, University of Cape Town
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- The Karoo
- Published online:
- 23 December 2009
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- 24 June 1999, pp 183-207
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Summary
Introduction
Short-term variability in rainfall patterns in hot and cold deserts is thought to be reflected by fluctuations in population sizes of plants and animals (Caughley and Gunn, 1993). The periodicity of these fluctuations is likely to be tied to mobility and life-histories, and therefore to differ greatly among species.
This chapter reviews the patterns and causes of plant and animal population fluctuations in time and space in the arid zone of southern Africa. Wherever possible, we compare the effects of environmental stochasticity and cyclicity on populations with those of competition, disease and predation. We also consider the possible role of refuges and immigration on the resilience and persistence of small populations in a variable environment. The population dynamics of plants, invertebrates, reptiles, birds and mammals is dealt with separately because the resolution and focus of the information available differs among these groups. In conclusion, we indicate research directions that could improve current predictions based on the few autecological studies and limited long-term data series available for arid zone biota.
Structure and dynamics of plant populations
Ephemerals and annuals
The mass flowering of annual plants in the winter-rainfall western karoo is a major tourist attraction, and the prediction of the flowering time and abundance of annual plants is consequently of economic importance (see Van Rooyen, this volume). Namaqualand ephemerals grew larger and produced more flowers when growing at low temperatures (17 °C) than at higher temperatures (22–27 °C). Moisturestressed plants were smaller than well-watered plants, and allocated less biomass to reproduction (Van Rooyen et al., 1991). Flowering in ephemerals may also be depressed by competition and grazing.