Thermal and energetic constraints on ectotherm abundance: a global test using lizards

Area of Science:

• Ecology
• Bioenergetics
• Zoology

Background:

• Endotherm population densities are constrained by metabolic rates and body mass.
• Ectotherm metabolic rates increase with temperature, suggesting temperature also constrains their population densities.
• Lizards are an ecologically significant group of ectothermic vertebrates.

Purpose of the Study:

• To test bioenergetic models for lizard populations.
• To investigate factors constraining ectotherm population densities.
• To compare constraints on ectotherm and endotherm population densities.

Main Methods:

• Examined 483 lizard populations.
• Analyzed relationships between population density, body mass, environmental productivity, and temperature.
• Utilized simple bioenergetic models.

Main Results:

• Lizard population densities decrease with body mass following a power law.
• Environmental productivity positively affects lizard density, strengthening the density-body mass relationship.
• Environmental temperature has a weak effect on lizard density, likely due to behavioral thermoregulation and thermal evolution.

Conclusions:

• Energy availability, influenced by environmental productivity, is a key constraint on lizard population densities.
• Unlike endotherms, environmental temperature is a less significant factor for lizard population density.
• These findings offer insights into differential constraints on ectotherm and endotherm population densities across broad spatial scales.