A Simple Device for Producing Fluctuating Temperatures, with an Evaluation of the Ecological Significance of Fluctuating Temperatures1

Abstract

Fluctuating temperatures are characteristic of the environment of most organisms, yet constant temperatures are most frequently used for laboratory studies on their life histories. The literature has been reviewed to point out some of the ways in which constant-temperature data for rates of development, developmental thresholds, fertility, and other life-history phenomena could be misleading when an ecologist attempts to model a natural system or to extrapolate to field conditions. To implement the replacement of constant-temperature studies with fluctuating temperature studies, 2 previously reported timer-controlled bimetallic or mercury thermostat devices and a new timer-controlled solid-state controller thresdevice are discussed. With the new device the maximum and minimum temperatures are set with 2 potentiometers, and a synchronous motor timer is used to switch between the 2 potentiometers. The earlier devices have the advantage of controlling the temperature throughout the cycle. However, with the new device the temperature drifts between maximum and minimum temperatures at a rate of 2–5°C per hour, and this rate is similar to the rate of change in the field. The new device has the advantage of a more easily changed temperature program and remote control of the temperature cabinet, with no need to place the entire device within the cabinet.