Open Access

Population dynamics of exploited cultures of calanoid copepods

  • D. R. Heinle1
Helgoländer wissenschaftliche Meeresuntersuchungen20:BF01609913

https://doi.org/10.1007/BF01609913

Abstract

En laboratoire, cultures des copépodes calanoides,Acartia tonsa (Dana) etEurytemora affinis (Poppe) étaient exposées à différents taux de déprédation, allant de 10 à 24% des populations par jour, suivant les espèces et les températures. Les densités des populations variaient considérablement, ce qui provenait probablement des évènements intermittents (la nourriture et les récoltes) habituelles de la procédure en laboratoire. La bibliographie, ainsi que mes propres observations avancent deux mécanismes homéostatiques. Le cannibalisme aide à régulariser la population d'A. tonsa quand la nourriture devient rare par suite de la haute densité des populations. La proportion des femelles adultes augmente durant les densités basses des populations d'A. tonsa. La proportion sexuelle génésique de ces populations était de 1:1. L'augmentation proportionnelle des femelles paraisse provenir de mâles génotypiques changeant en femelles phénotypiques au cours de leur croissance. Cette proportion plus élevée des femelles augmente le taux de la reproduction quand les populations étaient peu denses.

Summary

1. Population densities of calanoid copepods fluctuated in cultures subjected to exploitation rates of from 10 to 24% of the populations per day. The fluctuations were probably caused by the discontinuous events (feeding and harvesting) that were inherent in the laboratory procedure.

2. Birth rates in the cultures were much higher than were necessary to replace the individuals removed by predation except at rates of exploitation that depleted the populations.

3. Cannibalism probably occurred in the cultures ofAcartia tonsa.

4. Population density decreased with increasing rates of predation in cultures ofArcatia tonsa. The same statistic decreased only with excessive predation in cultures ofEurytemora affinis.

5. Sex ratios changed with increasing predation. The proportion of adultArcatia tonsa that were females increased at the highest rates of exploitation. The proportion of female adults in a wild population was inversely proportional to the logarithm of population density. The genetic sex ratio in the same population was unity. There was no indication of early death of males. It thus appeared that genotypic males became phenotypic females during the course of their growth. Males predominated in both wild and laboratory populations ofEurytemora affinis.

6. Changes in sex ratio of the two species appear to be homeostatic mechanisms. Reproductive rates ofArcatia tonsa were increased at low population densities by the higher proportion of females. The increased proportion of males in populations ofEurytemora affinis may be a means for assuring copulation at low population densities.

Notes

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