Dataset: Warming Determines Predation

Sampling Description 

Organisms were collected from two locations on San Cristóbal, the easternmost island of the Galápagos Archipelago. Vasula melones, Heliaster cumingi, and Tribulus planospira were collected in Tijeretas (-0°53'18.0", -89°36'28.0''), a small bay on the southwest side of San Cristóbal.

H. cummingi were collected, and the experiment was conducted in July 2021. V. melones, and T. planospira were collected and experiments were conducted in July 2023. Hexaplex princeps was collected from La Barcaza (-0° 46' 41.7", -89° 31' 06.9"), a small islet located off the island's northwest coast, during morning periods during June 2021. 

 

Experimental Methods

In the predation experiment, Tribulus, Hexaplex, and Heliaster were fed barnacles (Megabalanus peninsularis), while Vasula were fed small herbivorous snails (Columbella haemastoma and Engina pyrostoma). Although the largest Vasula typically consume barnacles, those used in the experiment were smaller and thus fed the smaller prey. Barnacles were collected at an 8 m depth from La Barcaza and intertidally at Kicker Rock (0° 46' 41.7" S, 89° 31' 06.9" W). The herbivorous snails used as prey were collected from Tijeretas. 

We measured predator feeding rates inside 16 L glass aquaria during May, June, and July of 2021 and 2023. Throughout the predation experiments, individuals were exposed to 12 hours of both light and darkness. Experimental temperatures were maintained with a thermostat control system (Inkbird ITC-308 Digital Temperature Controller 2-Stage Outlet Thermostat Heating and Cooling). Once the temperature inside a given aquarium deviated by ± 0.3°C from the desired experimental temperature, the system activated a centralized chiller (AquaEuroUSA Max Chill-1/13 HP Chiller) or an individual submersible heater (Tetra HT30 Submersible Aquarium Heater & Electronic Thermostat, one per aquarium), respectively, to bring the temperature back to the experimental temperature

The selection of experimental temperatures varied among predators based on field observations and pilot studies, which indicated that some species could not tolerate higher temperatures. Due to space and other resource limitations in the laboratory, all temperature incubations and experiments across the four predator species were conducted asynchronously.

For the predation experiments with Tribulus, Hexaplex, and Heliaster, barnacle prey were epoxied (Z SPAR Splash Zone 2-Part Epoxy Compound) to small stones and placed in the aquaria. For the Vasula treatment, five herbivorous snails were added to each aquarium. Predation was monitored daily by checking for the presence of consumed prey, and any consumed prey was replaced within 24 hours. Additionally, we took note of the predator's position in the aquarium, and we used this to estimate a proxy of movement rate (number of position changes in the aquaria per day). To assess the effect of temperature on prey mortality, one control aquarium was included for each temperature incubation, where prey were exposed to the same conditions as the experimental trials but without predators. No significant effect of temperature on prey mortality was observed; no prey died in the control aquarium at any temperature.