Diversity-stability cascade in pond plankton experiments

This collection of files consists of freshwater plankton biomass data from a laboratory microcosm experiment and an accompanying field mesocosm experiment in which we manipulated the presence of two heteropteran predators. In the laboratory experiment, we incubated 20 large microcosms with phytoplankton and zooplankton, fully crossing a 1x vs. 2x zooplankton density treatment with presence or absence of a single Notonecta undulata adult. Two of these microcosms were lost, resulting in data for 18 of these large microcosms. Concurrently, we incubated 20 small microcosms with a smaller amount of the same plankton mix, which similarly were fully crossed with the 1x vs. 2x zooplankton density treatment and presence or absence of a single Neoplea striola adult. After five days we collected the zooplankton remaining in each microcosm for identification and biomass estimation. For the field experiment, we established 20 mesocosms (cattle tanks) with phytoplankton and zooplankton collected from the same sources, and added six Notonecta adults to five mesocosms, 90 Neoplea adults to another five, and three Notonecta and 45 Neoplea to another five, with the remaining five mesocosms acting as no-predator controls. We sampled both the phytoplankton and zooplankton once per week for six weeks for identification and biomass estimation.

Methods
We collected phytoplankton, zooplankton, Notonecta undulata adults, and Neoplea striola adults from small freshwater bodies in Austin, TX.

For the laboratory experiment, we filled 20 microcosms with 1.5 L of a mixture of the plankton, doubling the concentration of zooplankton in 10 of the microcosms, and adding a Notonecta individual to half (5) of the microcosms with each zooplankton density. We then set up 20 smaller microcosms the same way, except with 100 mL plankton mixture and Neoplea individuals. After 5 days we filtered and preserved the zooplankton. Finally we used microscopy to identify, count, and measure the zooplankton, allowing us to estimate the biomass of each zooplankton taxon in each microcosm using length-mass regressions.

For the field experiment, we used the same plankton to establish pond communities in 20 cattle tanks at Brackenridge Field Laboratory in Austin, TX. We added 6 Notonecta to 5 tanks, 90 Neoplea to 5 tanks, 3 Notonecta and 45 Neoplea to 5 tanks, and added no insects to the other 5. Then every week for 6 weeks we used tube samplers to take several whole water column zooplankton and phytoplankton samples from each tank and pool them into a composite zooplankton and a composite phytoplankton sample for each tank. We filtered and preserved the zooplankton samples, and preserved the phytoplankton samples. Then we used microscopy to identify, count, and measure the plankton, which allowed us to estimate the biomass of each zooplankton taxon in each sample using length-mass regressions, and to estimate the biovolume of each phytoplankton morphospecies in each sample using geometric formulas.

See the corresponding article for more details.