Stoichiometric Constraints vs. Algal Defenses: Testing Mechanisms of Zooplankton Food Limitation

The nature of resource limitation for zooplankton grazers is strongly debated. We provide a test of stoichiometric constraints and three alternative mechanisms of resource limitation in six lakes that represent a natural gradient in resource quality. Growth assays measured the responses of juvenile...

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Bibliographic Details
Published in:Ecology (Durham) 2002-12, Vol.83 (12), p.3426-3433
Main Authors: DeMott, William R., Tessier, Alan J.
Format: Article
Language:English
Subjects:
Algae
Animal and plant ecology
Animal, plant and microbial ecology
Animals
assimilation efficiency
Autoecology
Biological and medical sciences
C:P ratio
Daphnia
Digestion
digestion-resistant algae
Ecology
energy limitation
food quality
Food security
Freshwater
Fundamental and applied biological sciences. Psychology
Lakes
Limnology
Marine ecology
Natural resources
Phosphates
phosphorus limitation
Physiological assimilation
Plankton
Protozoa. Invertebrata
Seston
stoichiometric theory
Zooplankton
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Summary:The nature of resource limitation for zooplankton grazers is strongly debated. We provide a test of stoichiometric constraints and three alternative mechanisms of resource limitation in six lakes that represent a natural gradient in resource quality. Growth assays measured the responses of juvenile Daphnia to concentrated natural resources and to supplements of phosphate (P), essential fatty acids (EFA), and P-deficient and P-rich algae. Assimilation experiments quantified the digestibility of 32P-labeled resources. Daphnia growth was much lower on resources from deep compared with shallow lakes (0.13 ± 0.01 d-1 and 0.30 ± 0.03 d-1, respectively) but was independent of resource concentration. Growth was negatively correlated with the resource C:P ratio, but the relationship was not causal as responses to the P supplement were very weak. Adding EFA also produced weak responses. In contrast, supplements of readily digested algae stimulated moderate (P-deficient) and strong (P-rich) increases in growth that accounted for growth variation among the lakes. Changes in Daphnia P balance were also contrary to P limitation. In all, our growth assays implicate energy limitation unrelated to food concentration and, therefore, support the digestion resistance hypothesis. Digestion resistance is further supported by a positive correlation between assimilation efficiency and growth. Our results show that stoichiometric theory needs to be integrated with theory on plant and algal defenses against herbivores.
ISSN:0012-9658
1939-9170
DOI:10.1890/0012-9658(2002)083[3426:SCVADT]2.0.CO;2