The effects of elephants at low densities and after short occupation time on the ecosystems of the Eastern Cape Province, South Africa
- Authors: Parker, Daniel Matthew
- Date: 2008
- Subjects: Elephants -- South Africa -- Eastern Cape Biotic communities -- South Africa -- Eastern Cape Animal populations -- South Africa -- Eastern Cape Plant communities -- South Africa -- Eastern Cape Mammals -- Ecology -- South Africa -- Eastern Cape Animal-plant relationships -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5678 , http://hdl.handle.net/10962/d1005363
- Description: Elephants (Loxodonta africana, Blumenbach) are recognised as keystone herbivores and ecosystem engineers in African ecosystems due to the noticeable impact they have on plant communities. This impact can influence other animal taxa and ecosystem processes, especially within enclosed systems. I investigated the effects of elephants in four vegetation types and the cascade effect on three associated taxa and two ecosystem processes at five sites with elephants and five paired sites without elephants in the Eastern Cape Province, South Africa, between April 2005 and July 2007. In grassland habitats, the physical structure of the vegetation was neither enhanced nor degraded in the presence of elephants. Within the locally important Thicket Biome, elephant browsing transformed relatively homogeneous stands of vegetation into more heterogeneous units. However, although seeds from thicket plant species were recorded in elephant dung, elephants did not promote the viability and germination success of these plants. In addition, elephant foraging on aloes caused declines in their populations. By contrast, the size of bushclumps was not reduced in the presence of elephants in bushclump savanna. The associated insect, bird and mammal communities appeared to benefit from elephant foraging in all vegetation types assessed, whereas vegetation patch dynamics and soil surface processes were neither enhanced nor degraded in the presence of elephants. I conclude that, at current densities, elephants do not (in most cases) negatively affect plant and animal communities or ecosystem processes in enclosed reserves. However, elephants have only been present at each site for a relatively short period and it is likely that their impact will be cumulative, increasing over time in these closed systems. Thus, future research along a continuum of elephant density and time since re-introduction is recommended.
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- Date Issued: 2008
An assessment of density estimation methods for forest ungulates
- Authors: Ellis, Amanda Morgan
- Date: 2004
- Subjects: Wildlife management -- South Africa -- Eastern Cape Animal populations -- Estimates Wildlife conservation -- South Africa -- Eastern Cape Game farms -- South Africa -- Eastern Cape Ungulates -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5829 , http://hdl.handle.net/10962/d1007830
- Description: The development of conservation and management programs for an animal population relies on a knowledge of the number of individuals in an area. In order to achieve reliable estimates, precise and accurate techniques for estimating population densities are needed. This study compared the use of direct and indirect methods of estimating kudu (Trage/aphus strepsiceras), bush buck (Trage/aphus scriptus), common duiker (Sy/vicapra grimmia), and blue duiker (Philantamba manticala) densities on Shamwari Game Reserve in the Eastern Cape Province, South Africa. These species prefer habitats of dense forest and bush for concealment and are therefore not easily counted in open areas. Herein direct observation counts were compared to indirect sampling via pellet group counts (clearance plots, line transects, variable-width transects, and strip transects). Clearance plots were examined every 2 weeks, while all other methods were conducted seasonally, from August 2002 until August 2003. The strip transect method provided the lowest density estimates (animals per hal ranging from 0.001 for bushbuck to 0.025 for common duiker, while direct observations yielded the highest estimates, ranging from 0.804 for bush buck to 4.692 for kudu. Also, a validation of methods was performed against a known population of kudu during which the DISTANCE method yielded the most accurate results, with an estimated density of 0.261 that was within the actual density of 0.246 to 0.282. In addition, the DISTANCE method was compared to helicopter counts ofkudu and its estimates were found to be approximately 2.6 times greater than the helicopter count results. When the assessment of the methods was made, the cost, manpower and effort requirements, coefficient of variation, and performance against a known population for each method were taken into consideration. Overall, the DISTANCE method performed the best with low cost, minimal manpower and effort requirements, and low coefficient of variation. On Shamwari Game Reserve, the DISTANCE method estimated 0.300 kudu, 0.108 bushbuck, 0.387 common duiker, and 0.028 blue duiker per ha, which, when extrapolated to the total number of animals present within subtropical thicket habitat, estimated 1973 kudu, 710 bush buck, 2545 common duiker, and 184 blue duiker.
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- Date Issued: 2004
The effect of photoperiod on some aspects of reproduction in a Southern African rodent : the pouched mouse (Saccostomus Campestris)
- Authors: Gray, Janine
- Date: 2001
- Subjects: Mice -- Reproduction Antechinus -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5676 , http://hdl.handle.net/10962/d1005361
- Description: The pouched mouse, Saccostomus campestris is widely distributed south of the Sahara, inhabiting both subtropical and tropical latitudes and a number of different biotic zones, where it breeds seasonally. In North temperate latitudes, reproduction in small mammals is controlled by photoperiod however this cue becomes less influential as latitude decreases towards the equator. The aim of the present study is to establish the role of photoperiod in the environmental control of reproduction in a seasonally breeding small mammal at low latitudes in a highly unpredictable environment. Spermatogenesis of domesticated and Fl-generation pouched mice was not inhibited by short daylength while decreasing daylength significantly affected the oestrous cycle of adult domesticated female pouched mice. Photoperiod had little effect on the oestrous cycle of F I-generation females while a possible inherent circannual endogenous rhythm controlled inhibition of reproduction in these females. Body mass of male and female juvenile pouched mice was consistently lower in short daylength and in juvenile female pouched mice the onset of fertility may be weight-dependent. The attainment of sexual maturity of domesticated and FIlF2-generation females was retarded but not halted in short daylength and females in long daylength reached puberty 7.8 - 10.2 days earlier. Short daylength also lengthened the interval between vaginal perforation and first oestrus. Puberty in juvenile females was age-dependent as both domesticated and FIlF2-generation males attained puberty at 50 days of age, although fewer males were fertile in long daylength than short daylength. Although litter size of pouched mice was smaller in short daylength for both domesticated and wildcaught females this was not due to a reduction in the ovulation rate. Domesticated females had significantly larger litters than wild-caught females. Male and female pouched mice have evolved different reproductive strategies as males become sexually mature at the same age irrespective of photoperiod and remain fertile throughout the year. In contrast, females tend to be more complex as juveniles delay reproductive maturity and adults become nonreproductive in short daylength. However, in the presence of a fertile male and if environmental conditions are favourable, in short daylength, females can become reproductively active within approximately 3 days. Thus, although the pouched mouse has adopted a purely opportunistic reproductive strategy, vestiges of photoresponsiveness are still present in the female. The seasonality exhibited in the wild is therefore due to the female. Pouched mice live in a highly unpredictable environment so the sole use of photoperiod to regulate reproduction would be disadvantageous.
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- Date Issued: 2001