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Size‐dependent competitive ability in a deposit‐feeding amphipod, Monoporeia affinis
Author(s) -
Aljetlawi Albashir A.,
Leonardsson Kjell
Publication year - 2002
Publication title -
oikos
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.672
H-Index - 179
eISSN - 1600-0706
pISSN - 0030-1299
DOI - 10.1034/j.1600-0706.2002.970103.x
Subject(s) - functional response , biology , growth rate , amphipoda , competition (biology) , zoology , interference (communication) , ecology , predation , toxicology , mathematics , crustacean , channel (broadcasting) , geometry , electrical engineering , engineering , predator
We investigated the competitive ability in terms of maintenance resource density, C 0 , in relation to body size, of a deposit feeder Monoporeia affinis (Lindström) (Amphipoda). Growth curves were obtained from nine‐day single size‐class experiments with several food densities, consisting of fresh phytoplankton. The functional response and the size‐dependence of attack rate (clearance rate) and handling time were estimated using a dynamic growth model including ingestion and energetic costs. The energetic costs were obtained from treatments without food. C 0 was solved from the growth model by setting growth to zero. The best description of growth was found using a Holling type II functional response. The attack rate was independent of M. affinis body size, while handling time decreased, and C 0 increased with body size.
To investigate the occurrence of intercohort interference and its influence on C 0 , we used the parameter estimates to predict the growth in mixed size‐classes experiments. These experiments were similar to the single size‐class experiments except for the addition of two size‐classes of M. affinis . The observed growth was lower than predicted for all size‐classes. Incorporation of an interference term to the functional response in the growth model improved its fit to the observed data. This indicated that both interference and exploitation competition occurred. The interference increased C 0 for the smallest sizes, and reduced its size‐dependence. C 0 increased most for the largest individuals, but most likely for reasons other than interference. According to predictions by Persson et al. (1998) concerning population dynamic properties, our results indicate that the unstable dynamics commonly found for this species are due to higher competitive ability of juveniles rather than of maturing sub‐adults.