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    This database contains bibliographic descriptions of all Wageningen University PhD theses from 1920 onwards. It is updated on a daily basis by WUR Library.

    Author abstracts and/or summaries are added to all descriptions. A link to the full text dissertation is added to the bibliographic description. In a few cases, no electronic version is available, mostly because of copyright issues.

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    mail icon WUR Library, 9 july 2012

     

Record number 2002632
Title Living on the edge: physiological and behavioural plasticity of African antelopes along a climatic gradient
show extra info.
Anil Kumar Shrestha
Author(s) Shrestha, A.K.
Publisher [S.l. : s.n.]
Publication year 2012
Description 135 p fig., tab
Notes Proefschrift Wageningenshow all notes
Met lit. opg. - Met samenvatting in het Engels en Nederlands
Tutors Prins, Prof. dr. H.H.T. ; Bie, Prof. dr. S. de ; Wieren, Dr. S.E. van
Graduation date 2012-09-18
Dissertation no. 5302
Author abstract show abstract

Climate change, habitat loss and fragmentation individually or synergistically force species to
live in a sub-optimal condition in terms of climate and resource posing threat to fitness and
survival of the species. Hence, a very pressing issue for biodiversity conservation at present is
to understand if species are able to keep pace with these rapidly changing environment
conditions. To persist with these changes, phenotypic plasticity of behaviour and physiology
may be the most likely response for long-lived endothermic species because of their longer
generation times. Therefore, the central aim of this thesis is to investigate intra- and intervariability
of behavioural and physiological adaptation of range of African antelopes along
spatio-temporal scales in their natural habitats.
With the aim to understand the behavioural plasticity of African antelopes to the climatic
stress, in Chapter 2, I investigated effect of heat stress on diurnal activity pattern of three
species of antelopes of different body size and feeding types namely, eland Taurotragus oryx
(≈ 420 kg; mixed feeders), blue wildebeest Connochaetes taurinus (≈180 kg; grazer) and
impala Aepycerus melampus (≈ 50 kg; mixed feeder) across season and extreme climatic
condition as indicated by the 10 hottest days. During summer when the heat stress was its
highest, the heat stress negatively influenced diurnal activity of all the three species.
However, they shifted the timing of their activity more to the early morning (eland) or late in
the evening, or both (wildebeest and impala) to avoid heat stress and maximize intake of food
in a season when forage is abundant. During the spring and the 10 hottest days over the entire
study period, only the diurnal activity of the larger antelopes (eland and wildebeest) was
negatively influenced by the heat stress whereas the smaller impala was unaffected.
Therefore, these large African antelopes apparently suffer from heat stress during spring and
the extreme hottest days due to their limited capacity to dissipate heat.
In chapter 3, to understand possible behavioural adaptation of the largest African antelope
eland against the thermal stress, I investigated the daily and seasonal selection of
microhabitats based on altitude and microclimate at the southern limits of its distributional
range. Eland actively selected lower altitudes with warm microclimates during the winter and
the five coldest days when the ambient conditions were below its thermal neutral zone. In
contrast, eland did not select higher altitudes or cooler climate when it was warm in the
summer. However, selection of cooler microhabitats was only evident in the three extremely
hottest days when the heat stress was close to the upper end of its thermal neutral zone.
Hence, the eland was able to use diverse topography as a thermal refuge to buffer the adverse
effect of both cold and very hot condition.
In the fourth chapter, to study behavioural response of African antelopes to variation in food
resources which is predicted to exacerbate due to climate change and habitat loss and
fragmentation, I investigated adaptation of home range sizes of eland, impala (both mixed
feeders) and wildebeest (a grazer) over time (seasons) and between two climatically
contrasting areas in South Africa, taking Mapungubwe National Park as the core area and
Asante Sana Game Reserve as the edge area. This comparative study not only showed the
home range size of wildebeest in Mapungubwe was larger during the resource-poor dry
season compared to the resource-rich wet season but their home range size in the core area
was also a four to seven times larger in the dry season than those in the edge area. In contrast,
the home range size of impala was 3-14 times larger in the edge area than those in the core
area. Surprisingly, the home range size of eland neither differs across any season within study
areas nor between Asante Sana and Mapungubwe, while their average year-round home
range size in core area was larger than that in edge area. These results suggest that the home
range size of these African antelope is most likely a response to resource quality and
availability specific to the local habitat.
With an attempt to investigate physiological plasticity of African antelopes over a spatiotemporal
context, in Chapter 5, I compared intraspecific variation of body temperature, as
measured by amplitude, of the eland, blue wildebeest and impala in the two climatically
contrasting areas: one with a less seasonal pattern and a mild winter (Mapungubwe National
Park) and the other with a more seasonal pattern and a long and cold winter (Asante Sana
Game Reserve). The 24-hour amplitude of body temperature of both mixed feeder (eland and
impala) did not differ between the study sites, regardless of season. In contrast, the grazer
(wildebeest) at a less seasonal site exhibited not only a higher variability in the 24-hour
amplitude of body temperature (Tb)(~4ºC) but also a lower daily minimum body temperature
by ~2 ºC compare to the normothermic level during the dry season than the wildebeest at a
seasonal site. Further, the variation in Tb amplitude were influenced both by temperature
(positive effect) and rainfall (negative effect), a proxy for food availability only among the
wildebeest from less seasonal site. This suggest that these physiological response of higher
variability of Tb amplitude and reduced minimum Tb among the wildebeest in Mapungubwe
is a response to nutritional stress rather than a response to cold climate.
These behavioural (home range) and physiological (body temperature) response of African
antelopes to stressful conditions are specific for species and habitats. The smallest impala,
which is a mixed feeder, maintained homeothermy even though they were exposed to
stressful habitats by selecting the most productive habitat, i.e., riparian habitat in
Mapungubwe. In Asante Sana, impala maintained homeothermic status by extending their
dry season home range size when their principle food Acacia Karoo was not available. The
largest antelope (eland) maintained homeostasis by ranging over large areas to track
heterogeneously distributed resources, which is only possible due to their large size and
ability to cope with lower quality food. Eland in Mapungubwe had larger home range sizes
compared to Asante Sana which was most probably due to the poor quality of the habitat in
Mapungubwe. Interestingly, the wildebeest in Mapungubwe did not maintain homeothermy
particularly in dry season. Not only their amplitude of Tb was much larger (~4ºC) and
Minimum Tb lowered by 2 ºC compared to normothermic level, they also extended their
home range size four to seven folds compared to the wildebeest in Asante Sana. This failure
to maintain homeothermy and extension of home range size was due to nutritional stress and
therefore these antelopes are living in a physiologically stressful environment. With the
predicted increase in the frequency and intensity of drought periods in southern Africa due to
climate change, wildebeest, and other grazers, will likely experience greater nutritional stress
in the future.
To conclude, this thesis shows importance of studying behavioural and physiological traits
among a range of species along temporal and spatial scales in their natural habitats to
understand the adaptive capacity, therefore sensitivity of animal species. Apparently,
homeothermic mammals cannot cope well with heat stress, which negatively influence the
larger ones more than the smaller ones. However, mammals can overcome these stresses by
shifting time of their activity to cooler parts of the day or by selecting optimal microhabitats
that minimize absorption of heat at high temperatures or that maximize the absorption of heat
at low temperatures. The behavioural (larger home range size) and physiological (reduced
body temperature) response of wildebeest, a grazer to dry season but not that of the mixed
feeder emphasizes that grazers will become more nutritionally stressed than mixed feeders at
times of low rainfall. With the predicted increase in low rainfall events in many parts of the
world and changes in vegetation structure in savannas due to climate change, browsers and
mixed feeders will be likely to benefit more in future than the ruminant grazers.
 

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Keyword(s) antelopes / taurotragus oryx / connochaetes taurinus / aepyceros melampus / climatic change / microclimate / animal behaviour / thermoregulation / microhabitats / heat stress / adaptation physiology
Categories Environmental Physiology, Stress Physiology
Publication type PhD thesis
Language English
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