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.

本数据集报告了两项实验的研究结果。实验1中，我们评估了白斑狗鱼（pike）在浑浊（棕色）与清澈水体中三种温度梯度下的功能响应。实验2中，我们量化了从完全清澈到极度浑浊的水体梯度下的白斑狗鱼摄食率。本研究已获得马尔默/隆德动物实验伦理审查委员会的许可。

《Analysis.R》包含了用于完成本研究所有分析的R代码。
data_experiment1.csv包含了以白斑狗鱼为捕食者、拟鲤（roach）为猎物的功能响应实验数据，实验设置了三种温度、两种水体视觉条件（清澈与浑浊水体）以及四种猎物密度。其中：Orig.order用于标识单条实验记录；Temp为三种温度处理的水温（单位：摄氏度）；Watercolor为水体视觉条件，分为清澈（420nm处吸光度=0.02）与浑浊（420nm处吸光度=0.097）两类；Nprey为每次24小时试验初始时投放的拟鲤数量；Rep为重复试验编号（1-8）；Pit为每条白斑狗鱼的PIT标签（Pit tag）ID；Time.introduced为白斑狗鱼被放入试验池的时间；Time.started为猎物被投放的时间；Time.ended为白斑狗鱼被取出、试验结束的时间；Day.all为自试验开始起的天数（以天为单位），用作习惯化程度的代理变量；Day.ind为自某条白斑狗鱼首次参与觅食试验起的天数；Trial.N为新试验开始时该个体已参与的连续试验编号；Dec.h为每次试验的持续时长（以十进制小时为单位）；Nsurv为每次试验结束时剩余的猎物数量；Eaten为试验期间被捕食的猎物数量；Outlier用于标记论文中被排除分析的3个个体，因数据显示其在试验期间未在实验室环境中启动捕食行为。

data_experiment2.csv包含了以白斑狗鱼和拟鲤为受试对象的觅食实验数据，实验设置了五种水体浑浊度梯度与两种猎物密度。其中：Date_started为觅食试验启动的日期；Day为自试验开始起的天数；Temp为水温（单位：摄氏度）；Watercolor为水体视觉条件，梯度覆盖从完全清澈到极度浑浊，其因子水平对应目标吸光度[0.01、0.10、0.3、1.0和3.5]，实际测得的吸光度水平分别为0.02±0.01、0.08±0.02、0.24±0.04、0.84±0.10和3.06±0.22（420nm处吸光度均值±1倍标准差）；Nprey为每次24小时试验初始时投放的拟鲤数量；Rep为重复试验编号（1-8）；Pit_tag为每条白斑狗鱼的PIT标签ID；N_survived为每次试验结束时剩余的猎物数量；Eaten为试验期间被捕食的猎物数量。

body_temps.csv包含了6条成年白斑狗鱼体内植入生物传感器后，在三个大型试验池塘中连续12个月记录的体温数据（单位：摄氏度）。

pike_wt.csv包含了本实验中所用白斑狗鱼个体的湿重数据（单位：克），该数据用于分析实验1与实验2的结果。

### 方法总结
#### 实验1
我们量化了白斑狗鱼在三种温度（5℃、9℃和13℃）与两种视觉条件（清澈与浑浊水体）下捕食拟鲤的功能响应。试验在实验室中开展，设置了四种猎物密度（每700升水体投放2、5、10或20条拟鲤）。觅食试验在6个内部尺寸为121cm×104cm（长×宽）的水箱中进行，水箱注水至56cm深度，使用经过过滤与曝气的水（总水体体积：704升）。通过向其中3个水箱添加3.5g腐殖酸（Humintech GmbH，德国）来调控水体视觉条件。清澈水体处理组的420nm处吸光度为0.020±0.007，浑浊水体处理组为0.097±0.012。24种处理组合各重复8次。试验持续23.5小时，包含15分钟的适应期。两次试验之间，白斑狗鱼在9℃环境下禁食4天以统一饥饿水平与捕食动机。本实验共使用24条白斑狗鱼（平均湿重51.8±12.8g，均值±1倍标准差，n=23，范围：34.5g–79.2g），每条个体最多参与10次觅食试验（平均8次）。拟鲤作为猎物使用，其平均湿重为0.91±0.34g（均值±1倍标准差，n=47）。

#### 实验2
我们设置了两种猎物密度（5条与10条拟鲤）与五种水体视觉梯度开展觅食试验。与实验1一致，通过添加腐殖酸调控水体视觉条件。浑浊处理组的吸光度分别为0.02±0.01、0.08±0.02、0.24±0.04、0.84±0.10和3.06±0.22（420nm处吸光度均值±1倍标准差；每组每周测量7次）。试验温度恒定为9℃。实验1与实验2之间，白斑狗鱼禁食12天。觅食试验的流程与实验1完全一致。

#### 体温监测
我们为6条成年白斑狗鱼植入生物传感器，在试验池塘中连续12个月记录其体温。通过电捕鱼法捕获白斑狗鱼，将其转运至三个试验池塘（70m×30m，水深1.5m），并放置于暂养网箱（3×3×1.5m，网孔尺寸1.5cm；Pokorný Sítě, Brloh, 捷克共和国）中进行适应。通过外科手术为白斑狗鱼植入Centi-HRT生物传感器（Star-Oddi，加尔达巴埃尔，冰岛），设置为每30分钟记录一次体温，并于2021年11月23日将其放归池塘。2022年10月初，通过电捕鱼法重新捕获所有白斑狗鱼，取回生物传感器并下载体温数据。