104
period of time for the water in the pan to evaporate (20
days in this case), assuming that the pan is not affected
by groundwater movement.
The highly variable interannual and intraseasonal
rainfall patterns in the region of pan abundance (Figs
4 and 8) belie the fact that one cannot develop a useful
model of inundation. The inundation pattern derived
from the model turned out to be remarkably stable
between years. Over the ten years studied, the model
predicted an average of 5.8 inundations per year, varying between four and eight in anyone year, while the
mean period of inundation of 18.8 days with a Standard
Deviation of 16.6 days (Table 4) implies a degree of
intraseasonal predictability that can be used as a base
for a life history strategy.
Among the organisms from the pan (Branchipodopsis tridens, Leptestheriella inermis and Triops granarius) and the organism that was more common where
inundations were longer (Streptocephalus macrourus)
it was clear that all reached maturity within the first
week of inundation and produced a store of eggs within the mean inundation period of about 19 days. All
four species were iteroparous so, once egg production
had begun, it continued until death of the organism,
usually as a result of desiccation. T. granarius is a ubiquitous species in temporary waters of the Orange Free
State (Seaman & Kok, 1987) and is therefore not solely
from waters with inundations as short as 19 days, consequently it cannot be expected to show specialisations
for such short inundations. While not enough is known
of the pan habitat of L. inermis and while S. macrourus seems to be similar to T. granarius, it is clear that
B. tridens is adapted to short inundations of maximum
about two weeks (Figs 14 to 16). B. tridens grows
rapidly to maximum length within eight days, most
individuals are dead by two weeks and egg-production
occurs within six and 14 days. Therefore the shorter
the inundation the better for this species and the worse
for the other anostracan S. macrourus.
The simplistic r and K life history strategy continuum (MacArthur & Wilson, 1967; Pianka, 1970) is
not appropriate to these organisms. It is more appropriate to look at the combination of traits which make
each population successful (Stearns, 1976, 1993), and
the two most relevant ones are probably time taken to
maturity and iteroparity which firstly allow the organism to reproduce while the aquatic habitat is available
and secondly to keep putting eggs into the 'egg-bank'
as long as the habitat allows.
Acknowledgments
The University of the Orange Free State is acknowledged for facilities and running costs. Marie Watson,
Annetjie Botha, Sonja van Niekerk and Birgit Seaman
are thanked for their technical contributions.
References
Anderson, G. & S-Y. Hsu, 1990. Growth and maturation of a North
American fairy shrimp, Streptocephalus seali (Crustacea; Anostraca): a laboratory study. Freshwat. BioI. 24: 429-442.
Brendonck, L., 1991. Contributions to the study of the reproductive
biology of Streptocepha/us proboscideus (Anostraca, Streptocephalidae). Crustaceana 60: 145-162.
Geldenhuys, J. N., 1982. Classification of pans in the western Orange
Free State according to vegetation structure, with reference to
avifaunal communities. S. Afr. J. Wildi. Res. 12: 55-62.
Goudie, A. S. & D. S. G. Thomas, 1985. Pans in southern Africa
with particular reference to South Africa and Zimbabwe. Z. Geomorpho N.F. 29: 1-19.
Le Roux, J. S., 1978. The origin and distribution of pans in the
Orange Free State. S.A. Geogr. 6: 167-176.
MacArthur, R. H. & E. O. Wilson, 1967. The Theory of Island
Biogeography. Princeton University Press, Princeton, N.J.
Mitchell, S. A., 1991. The growth rate and growth efficiency of
Streptocephalus macrourus (Crustacea, Anostraca) cultured on
microalgae. Hydrobiologia 212 (Dev. Hydrobioi. 64): 1-10.
Pianka, E. R., 1970. On r- and K-selection. Am. Nat. 104: 592-597.
Seaman, M. T., D. J. Kok, B. J. von Schlichting & A. J. Kruger, 1991.
Natural growth and reproduction in Triops granarius (Lucas)
(Crustacea: Notostraca). Hydrobiologia 212: 87-94.
Seaman, M. T. & D. J. Kok, 1987. Ecological diversity in Orange
Free State pans. In R. D. Walmsley & L. Botten (eds), Symposium
on the ecology and diversity of wetlands in South Africa, Foundation for Research Development, CSIR, Pretoria, Occasional
Report Series 28: 260-273.
Steams, S. C., 1976. Life-history tactics: a review of the ideas. Q.
rev. BioI. 51: 3-47.
Steams, S. C., 1993. The Evolution of Life Histories. Oxford University Press, Oxford and New York, 249 pp.
Department of Water Affairs, 1986. Management of the Water
Resources of the Republic of South Africa. Department of Water
Affairs, Pretoria, South Africa.
period of time for the water in the pan to evaporate (20
days in this case), assuming that the pan is not affected
by groundwater movement.
The highly variable interannual and intraseasonal
rainfall patterns in the region of pan abundance (Figs
4 and 8) belie the fact that one cannot develop a useful
model of inundation. The inundation pattern derived
from the model turned out to be remarkably stable
between years. Over the ten years studied, the model
predicted an average of 5.8 inundations per year, varying between four and eight in anyone year, while the
mean period of inundation of 18.8 days with a Standard
Deviation of 16.6 days (Table 4) implies a degree of
intraseasonal predictability that can be used as a base
for a life history strategy.
Among the organisms from the pan (Branchipodopsis tridens, Leptestheriella inermis and Triops granarius) and the organism that was more common where
inundations were longer (Streptocephalus macrourus)
it was clear that all reached maturity within the first
week of inundation and produced a store of eggs within the mean inundation period of about 19 days. All
four species were iteroparous so, once egg production
had begun, it continued until death of the organism,
usually as a result of desiccation. T. granarius is a ubiquitous species in temporary waters of the Orange Free
State (Seaman & Kok, 1987) and is therefore not solely
from waters with inundations as short as 19 days, consequently it cannot be expected to show specialisations
for such short inundations. While not enough is known
of the pan habitat of L. inermis and while S. macrourus seems to be similar to T. granarius, it is clear that
B. tridens is adapted to short inundations of maximum
about two weeks (Figs 14 to 16). B. tridens grows
rapidly to maximum length within eight days, most
individuals are dead by two weeks and egg-production
occurs within six and 14 days. Therefore the shorter
the inundation the better for this species and the worse
for the other anostracan S. macrourus.
The simplistic r and K life history strategy continuum (MacArthur & Wilson, 1967; Pianka, 1970) is
not appropriate to these organisms. It is more appropriate to look at the combination of traits which make
each population successful (Stearns, 1976, 1993), and
the two most relevant ones are probably time taken to
maturity and iteroparity which firstly allow the organism to reproduce while the aquatic habitat is available
and secondly to keep putting eggs into the 'egg-bank'
as long as the habitat allows.
Acknowledgments
The University of the Orange Free State is acknowledged for facilities and running costs. Marie Watson,
Annetjie Botha, Sonja van Niekerk and Birgit Seaman
are thanked for their technical contributions.
References
Anderson, G. & S-Y. Hsu, 1990. Growth and maturation of a North
American fairy shrimp, Streptocephalus seali (Crustacea; Anostraca): a laboratory study. Freshwat. BioI. 24: 429-442.
Brendonck, L., 1991. Contributions to the study of the reproductive
biology of Streptocepha/us proboscideus (Anostraca, Streptocephalidae). Crustaceana 60: 145-162.
Geldenhuys, J. N., 1982. Classification of pans in the western Orange
Free State according to vegetation structure, with reference to
avifaunal communities. S. Afr. J. Wildi. Res. 12: 55-62.
Goudie, A. S. & D. S. G. Thomas, 1985. Pans in southern Africa
with particular reference to South Africa and Zimbabwe. Z. Geomorpho N.F. 29: 1-19.
Le Roux, J. S., 1978. The origin and distribution of pans in the
Orange Free State. S.A. Geogr. 6: 167-176.
MacArthur, R. H. & E. O. Wilson, 1967. The Theory of Island
Biogeography. Princeton University Press, Princeton, N.J.
Mitchell, S. A., 1991. The growth rate and growth efficiency of
Streptocephalus macrourus (Crustacea, Anostraca) cultured on
microalgae. Hydrobiologia 212 (Dev. Hydrobioi. 64): 1-10.
Pianka, E. R., 1970. On r- and K-selection. Am. Nat. 104: 592-597.
Seaman, M. T., D. J. Kok, B. J. von Schlichting & A. J. Kruger, 1991.
Natural growth and reproduction in Triops granarius (Lucas)
(Crustacea: Notostraca). Hydrobiologia 212: 87-94.
Seaman, M. T. & D. J. Kok, 1987. Ecological diversity in Orange
Free State pans. In R. D. Walmsley & L. Botten (eds), Symposium
on the ecology and diversity of wetlands in South Africa, Foundation for Research Development, CSIR, Pretoria, Occasional
Report Series 28: 260-273.
Steams, S. C., 1976. Life-history tactics: a review of the ideas. Q.
rev. BioI. 51: 3-47.
Steams, S. C., 1993. The Evolution of Life Histories. Oxford University Press, Oxford and New York, 249 pp.
Department of Water Affairs, 1986. Management of the Water
Resources of the Republic of South Africa. Department of Water
Affairs, Pretoria, South Africa.