Thermal Biology

Overview

Ectothermic animals depend on environmental temperature for body heat. Every physiological process—locomotion, digestion, growth, reproduction—has a temperature optimum. Performance ramps up as temperature increases toward that optimum, then drops off sharply above it. The result is an asymmetric, hump-shaped thermal performance curve.

As climate change shifts ambient temperatures upward, understanding these curves becomes critical for predicting which species are most vulnerable. A tropical lizard already living near its thermal optimum has a much smaller safety margin than a temperate species with room to warm. This experiment lets you measure those curves and draw your own conclusions.

What You'll Do

Expose simulated ectotherms to a range of controlled temperatures. At each temperature, measure performance metrics—sprint speed, metabolic rate, feeding rate—and record the data. Plot thermal performance curves from your measurements. Identify the critical thermal minimum (CT_min) and critical thermal maximum (CT_max) for each species.

Compare thermal breadth across species from different ecological niches and geographic origins. Calculate thermal safety margins under current and projected climate conditions, and assess which populations face the greatest risk.

Learning Objectives

1. Generate and interpret thermal performance curves from experimental data
2. Determine CT_min, CT_max, and thermal optimum from measured performance values
3. Compare thermal physiology across species with different ecological niches
4. Predict species vulnerability to climate warming based on thermal safety margins

Background

The thermal performance curve concept dates back to the work of physiologists in the mid-20th century, but it took on new urgency with the recognition that climate change would push many ectotherms beyond their thermal limits. Raymond Huey and colleagues formalized the thermal safety margin framework in the 2000s, showing that tropical ectotherms—despite living in warmer environments—are often more vulnerable than temperate species because they operate closer to their thermal optima.

The key insight is that thermal performance curves are asymmetric. Performance increases gradually with temperature up to the optimum, then crashes rapidly above it. This means that even modest warming can push a species from peak performance into dangerous territory if it's already near the top of its curve.

This experiment draws on data from lizards, amphibians, and insects across latitudinal and elevational gradients. You'll see firsthand why a 2°C increase in mean temperature doesn't affect all species equally.