The spatial distribution of predators can affect both the distribution and diversity of their prey. Therefore, differences in predator dispersal ability that affect their spatial distribution, could also affect prey communities. Here, we use the microbial communities within pitcher plant leaves as a model system to test the relationship between predator (protozoa) dispersal ability and distribution, and its consequences for prey (bacteria) diversity and composition. We hypothesized that limited predator dispersal results in clustered distributions and heterogeneous patches for prey species, whereas wide predator dispersal and distribution could homogenize prey metacommunities. We analyzed the distribution of two prominent bacterivore protozoans from a 2‐year survey of an intact field of
The leaves of carnivorous pitcher plants harbor diverse communities of inquiline species, including bacteria and larvae of the pitcher plant mosquito (
In this study, we used high throughput sequencing of bacterial 16S rRNA gene amplicons to characterize and compare microbiota diversity in field- and laboratory-derived
This study provides the first information on microbiota acquisition and assembly in
Microbial eukaryotes, critical links in aquatic food webs, are unicellular, but some, such as choanoflagellates, form multicellular colonies. Are there consequences to predator avoidance of being unicellular vs. forming larger colonies? Choanoflagellates share a common ancestor with animals and are used as model organisms to study the evolution of multicellularity. Escape in size from protozoan predators is suggested as a selective factor favoring evolution of multicellularity. Heterotrophic protozoans are categorized as suspension feeders, motile raptors, or passive predators that eat swimming prey which bump into them. We focused on passive predation and measured the mechanisms responsible for the susceptibility of unicellular vs. multicellular choanoflagellates,
Choanoflagellates, unicellular eukaryotes that can form multicellular colonies by cell division and that share a common ancestor with animals, are used as a model system to study functional consequences of being unicellular versus colonial. This review examines performance differences between unicellular and multicellular choanoflagellates in swimming, feeding, and avoiding predation, to provide insights about possible selective advantages of being multicellular for the protozoan ancestors of animals. Each choanoflagellate cell propels water by beating a single flagellum and captures bacterial prey on a collar of microvilli around the flagellum. Formation of multicellular colonies does not improve the swimming performance, but the flux of prey‐bearing water to the collars of some of the cells in colonies of certain configurations can be greater than for single cells. Colony geometry appears to affect whether cells in colonies catch more prey per cell per time than do unicellular choanoflagellates. Although multicellular choanoflagellates show chemokinetic behavior in response to oxygen, only the unicellular dispersal stage (fast swimmers without collars) use pH signals to aggregate in locations where bacterial prey might be abundant. Colonies produce larger hydrodynamic signals than do single cells, and raptorial protozoan predators capture colonies while ignoring single cells. In contrast, ciliate predators entrain both single cells and colonies in their feeding currents, but reject larger colonies, whereas passive heliozoan predators show no preference. Thus, the ability of choanoflagellate cells to differentiate into different morphotypes, including multicellular forms, in response to variable aquatic environments might have provided a selective advantage to the ancestors of animals.
Predators can strongly affect prey communities, but their influence may be difficult to distinguish from bottom‐up and other environmental effects. The problem of assessing predator impact is especially difficult in large systems that do not allow for comparisons across multiple units (e.g., small lakes) that have varying predator density. For instance, the invasion of the predatory zooplankter,
Intraspecific competition influences population and community dynamics and occurs via two mechanisms. Exploitative competition is an indirect effect that occurs through use of a shared resource and depends on resource availability. Interference competition occurs by obstructing access to a resource and may not depend on resource availability. Our study tested whether the strength of interference competition changes with protozoa population density. We grew experimental microcosms of protozoa and bacteria under different combinations of protozoan density and basal resource availability. We then solved a dynamic predator–prey model for parameters of the functional response using population growth rates measured in our experiment. As population density increased, competition shifted from exploitation to interference, and competition was less dependent on resource levels. Surprisingly, the effect of resources was weakest when competition was the most intense. We found that at low population densities, competition was largely exploitative and resource availability had a large effect on population growth rates, but the effect of resources was much weaker at high densities. This shift in competitive mechanism could have implications for interspecific competition, trophic interactions, community diversity, and natural selection. We also tested whether this shift in the mechanism of competition with protozoa density affected the structure of the bacterial prey community. We found that both resources and protozoa density affected the structure of the bacterial prey community, suggesting that competitive mechanism may also affect trophic interactions.
