“Toward a More Dynamic Metabolic Theory of Ecology to Predict Climate Change Effects on Biological Systems”
Keila A. Stark, Tom Clegg, Joey R. Bernhardt, Tess N. Grainger, Christopher P. Kempes, Van Savage, Mary I. O’Connor, and Samraat Pawar: Read the article
The metabolic theory of ecology explains macroecological patterns in biological rates and states from individuals to ecosystems through fundamental constraints on metabolism. In order to apply it to climate change questions, some of its original assumptions need to be revisited.
All living organisms have a range of temperatures in which they can survive and function optimally, yet altered thermal regimes under climate change are rapidly perturbing biological systems. A tractable framework for predicting the response of living organisms to rising temperatures is essential. This requires mapping changes in temperature to corresponding changes in biological processes, which could occur at levels ranging from individual organisms to ecosystems.
One theory that attempts this is the metabolic theory of ecology (MTE), which links the biology of individual organisms to the ecology of populations, communities, and ecosystems. It posits that metabolic rate is the fundamental limiting process of all biological processes, and that variation in biological rates and conditions at a given time can be explained in terms of organism mass and temperature. The classical MTE is a macroecological theory because it describes variation among broad taxonomic groups spanning orders of magnitude in body size. Over time, however, empirical tests of MTE's temperature predictions have extended from the original macroecological approach to tests in finer-scale systems. In these scenarios, MTE can be misapplied due to assumptions invoked in the macroecological approach, such as metabolic steady state (an even ratio of inputs and outputs, like the energy flux of a biological system staying constant) and negligible temperature variation. For instance, when there is a change in temperature or resource availability, the total energy flux for an individual changes along with how the energy is allocated to processes such as growth, survival, and reproduction. Such changes mean the system is no longer in a metabolic steady state and the classic MTE cannot be applied. Under climate change, perturbations from steady state in natural systems are more likely.
Stark et al. demystify each of classical MTE's assumptions and summarize existing efforts to accommodate violations of these assumptions in systems experiencing variability during the study window. They provide a decision tree to help identify necessary modifications to classical MTE depending on the research question and system conditions. In a situation where temperature and resource supply are constant, the classical MTE can be used. However, for questions centered around changes in metabolic allocation, temperature-dependent community dynamics, or evolutionary or plastic changes in thermal responses, MTE models have to be adjusted to capture these dynamics. The authors list key empirical and theoretical gaps to be filled in a more dynamic MTE for addressing climate change problems; read the full article to learn more!
Shubha Govindarajan is a PhD student with Deepa Agashe at the National Centre for Biological Sciences, Bengaluru, Karnataka, India. She is working on understanding how the age and density experienced by founding individuals affects adaptation in a novel habitat using flour beetles. Her additional interests include classical dance, music and literature.
