Fear and food: Effects of predator-derived chemical cues and stoichiometric food quality on Daphnia

While resource quality and predator‐derived chemical cues can each have profound effects on zooplankton populations and their function in ecosystems, the strength and direction of their interactive effects remain unclear. We conducted laboratory experiments to evaluate how stoichiometric food quality (i.e., algal carbon [C] : phosphorus [P] ratios) affects responses of the zooplankter, Daphnia pulicaria, to predator‐derived chemical cues. We compared growth rates, body P content, metabolic rates, life‐history shifts, and survival of differentially P‐nourished Daphnia in the presence and absence of chemical cues derived from fish predators. We found effects of predator cues and/or stoichiometric food quality on all measured traits of Daphnia. Exposure to fish cues led to reduced growth and increased metabolic rates but had little effect on the body %P content of Daphnia. Elevated algal C : P ratios reduced growth and body %P and increased mass‐specific respiration rates. While most of the effects of predator cues and algal C : P ratios of Daphnia were non‐interactive, reduced survival and relatedly reduced population growth rates that resulted from P‐poor food were amplified in the presence of predator‐derived cues. Our results demonstrate that stoichiometric food quality interacts with antipredator responses of Daphnia, but these effects are largely trait dependent and appear connected to animal life‐history evolution. Given the ubiquity of predators and P‐poor food in lake ecosystems, our results highlight the importance of the interactive responses of animals to predator cues and poor nutrition

Sample histogram separating activity modes in Blanding’s turtles: Terrestrial in-motion from motionless and aquatic in-motion from motionless.

The red vertical line indicates the threshold value determined after testing the accuracy of ΔODBA values within the overlapping regions. These histograms are based on data sampled at 1 Hz. (PDF)</p

Qualitative selection of the most suitable threshold value (vertical line) relative to accuracy, sensitivity and specificity for Blanding’s turtles and Painted turtles, using accelerometer data sampled at 1 Hz.

Qualitative selection of the most suitable threshold value (vertical line) relative to accuracy, sensitivity and specificity for Blanding’s turtles and Painted turtles, using accelerometer data sampled at 1 Hz.</p

Daily activity-budget for Blanding’s (n = 16) and Painted turtles (n = 23) in the South March Highlands, Ottawa.

Shown are mean proportion (± SD) of time spent doing each of the four main states during a 24-hour period.</p

Overall classification performance for the testing data used to classify Blanding’s turtle and Painted turtle activity based on accelerometry and water sensor data, sampled at 1 Hz.

Overall classification performance for the testing data used to classify Blanding’s turtle and Painted turtle activity based on accelerometry and water sensor data, sampled at 1 Hz.</p

S2 Fig -

Accelerometer (left) and VHF transmitter (right) bolted onto the rear carapace margin of a Painted turtle. (PDF)</p

Mean overall dynamic body acceleration (ODBA) as a function of the duration of the smoothing window for Blanding’s and Painted turtle terrestrial and aquatic motion, using accelerometer data sampled at 1 Hz.

Maximum ODBA value (solid line) and 95% of the maximum ODBA value (dashed) are indicated.</p

Optimizing the threshold value (vertical lines) relative to data accuracy, sensitivity and specificity, for Blanding’s turtles and Painted turtles, using acceleration data calculated with smoothing windows of the other species.

(PDF)</p

Classification performance for the testing data used to classify Blanding’s turtle and Painted turtle activity based on accelerometry data, using the other species’ threshold values.

Classification performance for the testing data used to classify Blanding’s turtle and Painted turtle activity based on accelerometry data, using the other species’ threshold values.</p

S3 Fig -

Boxplot of length of recorded states (top panel), and number of occasions each state was observed (bottom panel) across Blanding’s (blue) and Painted turtles (orange). (PDF)</p