Abstract
AbstractZooplankton exhibit different small‐scale motile behaviors related to feeding and mating activities. These different motile behaviors may result in different levels of predation risk, which may partially determine the structure of planktonic communities. Here, we experimentally determined predation mortality associated with (1) feeding activity (ambush feeders vs. feeding‐current vs. cruising feeders) and (2) mate‐finding behavior (males vs. females). The copepods Oithona nana, O. davisae (ambush feeders), Temora longicornis (feeding‐current feeder), and Centropages hamatus (cruising feeder) were used as prey for different predatory copepods. Copepods with “active” feeding behaviors (feeding‐current and cruising feeders) showed significantly higher mortality from predation (~2–8 times) than similarly sized copepods with low motility feeding behavior (ambush feeders). Copepod males, which have a more active motile behavior than females (mate‐seeking behavior), suffered a higher predation mortality than females in most of the experiments. However, the predation risk for mate‐searching behavior in copepods varied depending on feeding behavior with ambush feeders consistently having the greatest difference in predation mortality between genders (~4 times higher for males than for females). This gender‐specific predation pressure may partially explain field observations of female‐biased sex ratios in ambush feeding copepods (e.g., Oithonidae). Overall, our results demonstrate that small‐scale motile behavior is a key trait in zooplankton that significantly affects predation risk and therefore is a main determinant of distribution and composition of zooplankton communities in the ocean.
Highlights
More than 90% of the biological processes in the ocean are due to planktonic organisms, and attempts to understand ocean biogeochemistry and predict responses to climate change and other stressors require a mechanistic understanding of the biological processes in plankton food webs (Parsons and Takahashi 1973, Hays et al 2005, Kiørboe 2008a)
Predation risk associated with feeding behavior We found substantial differences in predation rates depending on feeding behavior of the prey
In the context of trait-based approaches (Bruggeman and Kooijman 2007, Litchman et al 2013), and in light of our results, small-scale motile behavior must be considered a key trait in zooplankton due to its strong influence on feeding, reproduction, and predation risk
Summary
More than 90% of the biological processes in the ocean are due to planktonic organisms, and attempts to understand ocean biogeochemistry and predict responses to climate change and other stressors require a mechanistic understanding of the biological processes in plankton food webs (Parsons and Takahashi 1973, Hays et al 2005, Kiørboe 2008a). Knowledge of zooplankton predator–prey interactions is essential for understanding the factors regulating the structure and dynamics of marine food webs Most animals are both predator and prey and have to face the challenge of feeding and evading predators simultaneously (Lima and Dill 1990, Tiselius et al 1997, Kiørboe et al 2010, Kiørboe 2013). Survival (fitness) of most organisms is determined by their ability to find food and mates and avoid predation These vital missions depend on encounter rates with prey, mate, and predators and, for most zooplankters, encounters rates are directly influenced by its small-scale motile behavior (Gerritsen and Strickler 1977, Visser 2007, Kiørboe 2008a). There is a conflict (trade-off) between maximizing prey and mate encounter rates and simultaneously minimizing encounter rates with predators (Lima and Dill 1990, Tiselius et al 1997, Kiørboe et al 2010, Lasley-Rasher and Yen 2012)
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