Data and code from: Effects of temperature and browning on the functional response of a freshwater top predator

This dataset reports results from two experiments. In Experiment 1, we estimate pike functional responses in brown and clear water at three temperatures. In Experiment 2, we quantify feeding rates along a gradient from completely clear to extremely brown. This study was performed under permission from the Malmö/Lund authority for ethics of animal experimentation.Analysis.R contains R code for performing all analyses in the MS.data_experiment1.csv contains data from a functional response experiment with pike as predator and roach as prey in clear and brown water at three temperatures and four prey densities. Orig.order is used to identify individual records. Temp is the water temperature (in degrees Celsius) for the three temperature treatments. Watercolor is the visual conditions, either Clear (Absorbance at 420nm = 0.02) or Brown (Absorbance at 420nm = 0.097) water. Nprey is the number of roach added at the beginning of each 24h trial. Rep is the replicate number (1-8). Pit is the individual Pit tag ID for each individual pike. Time.introduced is the time when the pike was introduced to the arena. Time.started is the time when prey were introduced. Time ended is the time when the pike was removed and the trial ended. Day.all represents the time (in Days since the experiment started), used as a proxy for habituation. Day.ind is the number of days since the first time an individual pike was used in a foraging essay. Trial.N is the sequential number of trials an individual has experienced at the start of a new trial. Dec.h is the duration (in decimal hours) of each trial. Nsurv is the number of prey remaining at the end of each trial. Eaten is the number of prey eaten during the trial. Outlier identifies three individuals that were excluded from the analysis in the paper as the data indicate that they had not started eating in the laboratory during the trial.data_experiment2.csv contains data from a foraging experiment with pike and roach at five levels of browning and two food densities. Date_started is the day when the foraging trial was initiated. Day is the time in days since the experiment started. Temp is the water temperature (in degrees Celsius). Watercolor represent the visual conditions, ranging from entire clear to extremely brown. The factor levels represent the target levels of absorbance [0.01, 0.10, 0.3, 1.0 and 3.5]. The actual (measured) absorbance levels were 0.02±0.01, 0.08±0.02, 0.24±0.04, 0.84±0.10 and 3.06±0.22 (mean Abs420/5 +-1SD) . Nprey is the number of roach added at the beginning of each 24h trial. Rep is the replicate number (1-8). Pit_tag is the individual Pit tag ID for each individual pike. N_survived is the number of prey remaining at the end of each trial. Eaten is the number of prey eaten during the trial.body_temps.csv contain data from surgically implanted biosensors in six adult pike that recorded body temperatures (in degrees Celsius) for 12 months in three large experimental ponds.pike_wt.csv constains data on the wet weights (in gram) of pike individuals used in the experiment. This data is used for analyzing the results of both Experiment 1 and 2.<br>Methods summaryExperiment 1.We quantified functional responses of pike foraging on roach at three temperatures (5°C, 9°C and 13°C) and two levels of visual condition (clear and brown water). We performed the foraging trials in<i> </i>the laboratory at four prey densities (2, 5, 10 or 20 roach per 700L). Foraging trials were performed in six tanks with an interior dimension of 121cm x 104 cm (length x width) filled to 56cm with filtered and aerated water (total water volume: 704L). Visual conditions were manipulated by adding 3.5g humic acid (Humintech GmbH, Germany) to three tanks. The clear water treatment had an absorbance (Abs_420/5) of 0.020±0.007 and the brown water treatment 0.097±0.012. Each of the 24 treatment combinations was replicated eight times. The trials lasted 23.5h with a 15-minute acclimation period. Pike were starved for 4 days at 9°C between trials to standardize hunger levels and motivation. A total of 24 pike were used (mean wet weight 51.8±12.8g (mean ±1SD), n=23, range: 34.5g – 79.2g). Pike were used for up to 10 foraging trials (average=8). Roach were used as prey (wet weight = 0.91±0.34g (mean ±1SD), n=47).Experiment 2.We performed foraging trials at two prey densities (5 and 10 roach) and five visual levels. As before, visual conditions were modified by adding humic acid. The absorbance in the browning treatments was 0.02±0.01, 0.08±0.02, 0.24±0.04, 0.84±0.10 and 3.06±0.22 (mean Abs_420/5± 1 SD; 7 weekly measurements per treatment). The temperature was kept constant at 9°C. Pike were fasted for 12 days between Experiment 1 and 2. Foraging trials were performed exactly as in Experiment 1.Body TemperatureWe equipped six adult pike with biosensors and recorded their body temperature for 12 months in experimental ponds. Pike were captured by electrofishing and transported to three experimental ponds (70m x 30m, depth 1.5m) where they were placed in keep nets (3 x 3 x 1.5 m, 1.5 cm mesh size; Pokorný Sítě, Brloh, Czech republic) for acclimation. Pike were surgically implanted with Centi-HRT biosensors (Star-Oddi, Garðabær, Iceland) set to record body temperatures at 30 minute intervals and released into the ponds on November 23, 2021. In early October 2022, all pike were recaptured by electrofishing, biosensors retrieved, and body temperature data downloaded.