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

Abstract

We tested the effect of five different concentrations (0.25 · 106, 0.5 · 106, 1.0 · 106, 2.0 · 106 and 4 · 106 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) atany Chlorella level. Statistical analysis of the selected life history variables revealed significant (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 0.25 · 106 cells mL—1, while the highest values (117.3 ± 2.4 ind mL—1) were for P. quadricornis at 4 · 106 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. Vergleichende Lebenstafel-Demographie und Populationswachstum von Brachionus macracanthus DADAY, 1905 und Platyias quadricornis EHRENBERG, 1832 (Rotifera, Brachionidae) in Bezug zur Algen-Futterdichte (Chlorella vulgaris) Untersucht wird der Einfluss von funf verschiedenen Konzentrationen (0.25 · 106, 0.5 · 106, 1.0 · 106, 2.0 · 106, 4.0 · 106 Zellen mL—1) von Chlorella vulgaris auf die Lebenstafel-Demographie und das Populationswachstum der beiden Rotifera Brachionus macracanthus und Platyias quadricornis. Auf Basis der Lebenstafeln werden ausgewahlte Parameter zu Uberleben und Fortpflanzung berechnet (altersspezifische Uberlebensrate, Lebenserwartung und stabile Altersverteilung, Raten der Brutto- und Nettoproduktion, Generationszeit und Rate des Populationswachstums). Im allgemeinen zeigen beide Arten fast die gleiche Reaktion auf die zunehmende Futterkonzentration hinsichtlich der Uberlebens-Parameter, aber unterschiedliche Reaktionen hinsichtlich der Parameter zur Reproduktion. Alterspezifische Uberlebenskurven sind im unteren und mittleren Bereich der Futterdichte fur B. macracanthus nahezu rechtwinklig, fur P. quadricornis steiler. Bei geringer Futterdichte zeigen beide Arten fur die Produktion von Neonaten nahezu das Muster einer Normalverteilung. Beide Arten zeigen bei steigender Futterkonzentration abnehmende Produktion an Nachkommen mit dem Maximum von 2.5 Ind. je Weibchen und Tag. Bei der geringsten Futterkonzentration betrug die Generationszeit (7.12 ± 0.14) d fur B. macracanthus und (9.87 ± 0.18) d fur P. quadricornis, bei der hochsten Futterkonzentration (4.97 ± 0.04) d bzw. (4.94 ± 0.17) d. Die Brutto- und Nettoproduktionsraten waren fur B. macracanthus stets hoher als fur P. quadricornis. Die Rate des Populationswachstums betrug 0.42…0.52 d—1 fur B. macracanthus und 0.17…0.28 d—1 fur P. quadricornis. Die statistische Analyse ausgewahlter Parameter der Lebensgeschichte ergab einen signifikanten Einfluss (p 0.05). Die maximale Populationsdichte zeigt fur beide Arten lineare Regression zur Futterdichte mit generell hoheren Werten fur P. quadricornisy. Die Rate des Populationswachstums zeigt fur B. macracanthus lineare Regression zur Futterdichte, fur P. quadricornis lineare Regression zum Logarithmus der Futterdichte. Die Differenzen in den Parametern der Lebensgeschichte beider Arten im Verhaltnis zur Nahrungsdichte werden als artspezifische Anpassungen interpretiert.