Abstract
Habitat orientation has recently been demonstrated to affect the foraging behavior, growth, and production of plankton grazers. Because the orientation effect may vary with species, we hypothesize that habitat orientation may alter interspecific interactions between animal species. We experimentally investigated how habitat orientation (placing cuboid chambers in three orientations with long, medium, and small side as the chamber height) affected the interaction between two common cladoceran species, Daphnia magna and Moina micrura, which competitively exploited green algae of Chlorella pyrenoidosa at two volume scales (64 and 512 ml). Results show that chamber orientation and volume additively affected the behavior and species performance of the grazers. Specifically, both grazer species generally decreased their average swimming velocity, grazing rate (on algal cells), body size, and survival and reproduction rates with increasing chamber height for both chamber volumes and with decreasing chamber volume regardless of chamber orientation. Nevertheless, the decrease magnitude was greater for M. micrura with increasing chamber height but was greater for D. magna with decreasing chamber volume. Correspondingly, when cocultured, the density ratio of D. magna to M. micrura increased with increasing chamber height but decreased with decreasing chamber volume. At the end of the experiment, none of D. magna individuals survived in the small and short (large‐based) chambers, and few M. micrura individuals survived in large and tall (small‐based) chambers. These results indicate that both habitat orientation and size affect the outcome of interspecific competition between grazer species. We suggest that variation in habitat orientation may improve community coexistence and species diversity in nature.
Highlights
Spatial property is one of the factors affecting species interaction and diversity (Whalen, Aquilino, & Stachowicz, 2016; Yeager, Keller, Burns, Pool, & Fodrie, 2016)
Two-way ANOVAs were used to determine the effect of habitat orientation and chamber volume on swimming behavior, average swimming velocity, and grazing rate, density, and other species performance variables for both grazer species and the cell density of the algal species on a specific day, followed by the Tukey test for multiple comparisons once a significant effect was detected
Our results provide experimental evidence that changes in habitat orientation and size affect species differentially likely because of the difference in their body morphology and body size, which further affected the outcome of interspecies competition
Summary
Given that cladoceran grazers generally have to spend more energy to swim upward the same distance than individuals swimming horizontally as a result of additional costs of overcoming gravity, swimming velocity of these grazers should be lower in tall chambers than in short ones (Pan et al, 2015) Such behavioral responses of cladocerans to habitat orientation would transmit to affect their grazing rate and body growth, and survival and reproduction rates due to the significant positive relationships between swimming velocity and grazing rate (Christensen, Lauridsen, Ravn, & Bayley, 2005; Visser & Kiørboe, 2006) and between grazing rate with body growth, and survival and reproduction rates (Rinke & Vijverberg, 2005; Zhang et al, 2017). We predicted that (1) D. magna would be more appropriate to swimming and grazing in tall chambers than short ones (because it had a higher ratio of body depth to width compared to M. micrura), and (2) the survival, growth and reproduction rates, as well as the competitive ability of D. magna, would be higher in the tall chambers
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