Ph.D., Faculty of Science, University of the Witwatersrand, 2011 / The loss of global biodiversity is exacerbated by the problem of trying to conserve species
whose biology is not understood. The conservation of African snakes provides a striking
example of this problem as many species remain entirely enigmatic. If we are to effectively
manage or conserve these species, then we need to begin to describe and quantify their
ecology. This project aimed to increase the body of knowledge regarding the ecology of Bitis
schneideri, an arid-adapted African viperid, and as such, provide the basis for an informed
critical assessment of the conservation status of the species. The improved understanding of
the ecology of B. schneideri will contribute to the emerging study of African snake ecology,
allowing scientists to compare and contrast the ecology of African snakes with those from
northern temperate systems on which most of the global understanding of snake ecology is
based.
Bitis schneideri is a species of very small-bodied viperids that grow rapidly and reach sexual
maturity within the first two years. They are sexually dimorphic for several traits, and
evidence suggests that fecundity selection has played an important role in shaping their
morphology. Moreover, I suggest that the selective advantage of being able to bury into
sandy substrates has resulted in the extreme body size displayed in the species. Bitis
schneideri is diurnally active, a state that is probably a derived condition, as B. caudalis (the
sister species to B. schneideri) is reported to be nocturnal. Additionally, B. schneideri shows
seasonal variation in activity, with increased activity during the spring mating season.
Activity during winter is reduced, but not absent, and appears to be governed by the
availability of suitable environmental conditions. Activity in B. schneideri is limited at all
temporal scales by environmental conditions. Radio-telemetry and mark-recapture analysis
showed that B. schneideri is highly sedentary, moving between 0.8 ± 6.5 m.d-1 and 47.3 ± 3.9
m.d-1, inhabiting small homeranges ( : 0.85 ± 0.09 ha; : 0.10 ± 0.09 ha). Moreover,
juveniles show limited dispersal that, when combined with sedentary adult behaviour, could
result in vulnerability to fragmentation by limiting gene-flow. Population densities are high
( 8 ha-1) and survival is low (39% and 56% per annum) compared to viperids from other
parts of the world. Additionally, juveniles have higher survival rates than adults. Small litter
sizes imposed by small-bodies, and low survival, means that B. schneideri must reproduce
frequently, probably annually, in order for populations to persist. Such frequent reproduction
is atypical, even among closely related species, and in B. schneideri, appears to be facilitated
through the capacity to feed year-round in the aseasonal habitat in which they occur. Bitis
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schneideri is a generalist that ambushes prey in proportion to encounter frequency. Also, I
show that the capacity of B. schneideri to capture and consume relatively large prey items
provides snakes with a large energetic advantage. Abundant generalist predatory birds are
likely to be more important predators of B. schneideri than are rare specialist predatory
raptors, although snakes are also vulnerable to other predators that include small mammals,
other reptiles, and large invertebrates.
Small body-size has two important implications for B. schneideri biology – reduced litter
size, and vulnerability to a wide suite of predators. These attributes interact to result in low
survival, reduced movement and dispersal, frequent reproduction, generalist foraging, and
year-round feeding. Bitis schneideri is not at significant risk of facing extinction in the near
future. The primary biological factor that ameliorates against extinction risk is large
population size and high population density.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/11213 |
| Date | 31 January 2012 |
| Creators | Maritz, Bryan |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf, application/pdf |
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