Microcosm experimental evidence that habitat orientation affects phytoplankton-zooplankton dynamics

Abstract

Although spatial ecology has achieved a great success in the passing decades, the importance of habitat orientation has not been well studied, especially for its effects on prey-predator dynamics. Here, we examined the responses of zooplankton activity and grazing rate to habitat orientation and their consequences on the stability of phytoplankton-zooplankton system in a two-factor factorial experiment involving habitat orientation (three levels; small, medium, and large base area, respectively) and habitat size (64 ml and 512 ml) using two algal-grazer systems (Chlorella pyrenoidosaDaphnia magna and C. pyrenoidosa-Moina micrura). In both systems, grazer density increased with increasing base area for a given chamber volume and with increasing chamber volume for a given orientation in the first 6 days, followed by a dramatic decrease, which corresponded to increasing the amplitude of density fluctuations in both zooplankton and phytoplankton species. Such an algal-grazer dynamics could be accounted for by the greater average swimming ability and grazing rate observed in large-based and large-volumed chambers. Our results demonstrate that habitat orientation affects the zooplankton behavior and population dynamics of both zooplankton and phytoplankton species, which further influences the stability of phytoplankton-zooplankton systems.In natural ecosystems, species habitats may be placed in space with different orientations. For example, either a two-dimensional (e.g. forest patches to bird species; but not a circular habitat) or three-dimensional (e.g. waters for aquatic species; but not a spherical habitat) habitat may be placed in space at different orientations (e.g. angles relative to light direction for two-dimensional habitats and different sides as chamber base for three-dimensional habitats, see Supplementary Fig. S1), even if the habitat size and shape hold constant. Habitat orientations are diverse in natural ecosystems, particularly under human-induced disturbances that often break up a single continuous habitat into several pieces of fragments.Changes in habitat orientation can affect many environmental conditions (e.g. light, water current, heat, wind, nutrients, Earth's gravity and magnetic field) 1, 2 and thus might have consequences on various ecological processes. For example, van Kleunen & Fischer 3 found that habitat orientation (relative to the light direction) plays an important role in determining the morphology of stoloniferous rosette species by varying light intensity in different directions. Community composition of migrating organisms can also be affected by habitat orientation (relative to their moving directions). Generally, habitats oriented perpendicular to the dispersal paths of migrating organisms intercept more species (birds or fishes) and individuals than comparable habitats oriented parallel to the line of travel in both terrestrial 2, 4 and aquatic ecosystems 5 . However, the mechanisms underlying the habitat orientation effects have scarcely been explored, particularly in t...

Habitat orientation alters the outcome of interspecific competition: A microcosm study with zooplankton grazers

“…Additionally, body size, reproduction, and survival rates of D. magna and M. micrura were estimated on day 6 when the size differences between the parental and neonatal grazers were most obvious and when the first‐generation offspring of the grazers had not begun producing new neonates according to previous studies (e.g., Pan et al., ; Zhang et al., ). Body size of each grazer species was determined using all (<5) survived adult females in small chambers and five randomly chosen adult females in large chambers following Zhang et al.…”

“…Body size of each grazer species was determined using all (<5) survived adult females in small chambers and five randomly chosen adult females in large chambers following Zhang et al. () as the length from top of the head to tip of the abdomen, which was measured using an inverted light microscope at ×40 magnification. Body size was averaged for each chamber before data analyses because the number of grazer individuals differed largely among chambers.…”

“…Similarly, narrow aquatic plant patches could be situated perpendicular or parallel to water current (Tanner, ), harboring different levels of fish abundance and diversity. Recent studies provide direct experimental evidence that habitat orientation affects the foraging rate (Pan & Sun, ), survival, growth, and reproduction, as well as population dynamics of zooplankton grazers (Zhang, Pan, Chen, Hu, & Sun, ), showing its ecological consequences at the individual and population level.…”

“…Recent studies provide direct experimental evidence that habitat orientation affects the foraging rate (Pan & Sun, 2016), survival, growth, and reproduction, as well as population dynamics of zooplankton grazers (Zhang, Pan, Chen, Hu, & Sun, 2017), showing its ecological consequences at the individual and population level.…”

“…Such behavioral responses of cladocerans to habitat orientation would transmit to affect their grazing rate and thus 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). Importantly, cladoceran grazers may have differential responses to habitat orientation among species that coexist in the same aquatic community.…”