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Comparative life table demography and population growth of Brachionus macracanthus Daday, 1905 and Platyias quadricornis EHRENBERG, 1832 (Rotifera, Brachionidae) in relation to algal (Chlorella vulgaris) food density

Sarma, S.S.S.; Nandini, S.

Acta Hydrochimica et Hydrobiologica 30(2-3): 128-140

2002


DOI: 10.1002/1521-401x(200211)30:2/3<128::aid-aheh128>3.0.co;2-w
Accession: 010352712

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We tested the effect of five different concentrations (0.25cntdot106, 0.5cntdot106, 1.0cntdot106, 2.0cntdot106 and 4cntdot106 cells mL-1) of the green alga Chlorella vulgaris on the life table demography and population growth of two rotifers (Brachionus macracanthus and Platyias quadricornis). Based on the data from life table studies, we calculated selected survivorship and reproduction variables (age-specific survivorship, life expectancy and stable age distribution, gross reproductive rate, net reproductive rate, generation time and the rate of population increase). In general, both the rotifer species had nearly the same response with increasing food levels as regards the survivorship variables but differed in their reproductive variables. Age-specific survivorship curves were broadly rectangular at lower or intermediate food levels for B. macracanthus while these curves were steep for P. quadricornis. At lower food levels both the rotifer species showed a nearly normal distribution pattern of neonate production. With increasing food levels, both rotifer species showed reduced offspring production. The maximum offspring production was 2.5 ind. female-1 d-1 for B. macracanthus, comparable to P. quadricornis. At the lowest algal food density, the generation time of both the rotifer species was different ((7.12+-0.14) d vs (9.87+-0.18) d for B. macracanthus vs P. quadricornis, respectively), while at the highest Chlorella level, this was nearly the same. B. macracanthus had higher gross and net reproductive rates than P. quadricornis at any tested food level. The rate of population increase was higher (0.42 to 0.52 d-1) for B. macracanthus than P. quadricornis (0.17 to 0.28 d-1) at any Chlorella level. Statistical analysis of the selected life history variables revealed significant (p<0.01) influence of food level on all the chosen parameters of both the rotifer species with the exception of rate of population increase of P. quadricornis (p>0.05). Data on the population growth of B. macracanthus and P. quadricornis in relation to the five algal densities have also been presented. In general at any given Chlorella level, both B. macracanthus and P. quadricornis showed increased population abundance with increasing food availability. However, B. macracanthus had lower population abundance than P. quadricornis. The lowest peak population density recorded for B. macracanthus was 4.3+-0.08 ind mL-1 at 0.25cntdot105 cells mL-1, while the highest values (117.3+-2.4 ind mL-1) were for P. quadricornis at 4cntdot106 cells mL-1. The rate of population increase per day increased with food level for both the rotifer species. However, at any given food level, B. macracanthus had lower growth rates than P. quadricornis. The growth rates ranged from (0.059+-0.001) d-1 to (0.11+-0.001) d-1 for B. macracanthus and (0.14+-0.005) d-1 to (0.21+-0.002) d-1 for P. quadricornis. The observed differences in the life history variables of both the rotifer species in relation to food level have been interpreted in terms of species-specific adaptations, based on a combination of life table demography and population growth parameters.

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