The metabolic theory of ecology and algal bloom formation (Reply to comment by López‐Urrutia)

The metabolic theory of ecology and algal bloom formation (Reply to comment by Ló pez-Urrutia) The comment by Ló pez-Urrutia draws attention to the similarity between the temperature–growth rate relationships reported by Rose and Caron (2007) and the metabolic theory of ecology (MTE). Rose and Caron (2007) noted different responses of the maximal growth rates of heterotrophic and phototrophic protists to temperature that provide one potential explanation for massive phyto-plankton blooms that characterize many polar ecosystems. Ló pez-Urrutia has noted that these relationships match quite well some predictions of the MTE, which provides a (potentially) unifying mechanistic theory of the interaction of body size, temperature, and stoichiometry (chemical composition) on biological structure and function at scales ranging from organisms to ecosystems (Brown et al. 2004). We are in strong agreement with Ló pez-Urrutia on the heart of the matter: i.e., there is little doubt regarding the striking similarity between the relationships reported in Rose and Caron (2007) and the MTE visa `-vis the differential effect of temperature on the metabolic processes of phototrophic and heterotrophic organisms. Moreover, we agree that our findings are consistent with the prediction of the MTE that metabolic rate provides an integrating concept linking the diverse activities among the individuals and species across broad scales of observation and measurement. The possibility that a single characteristic could have such a pivotal effect across such a diverse array of species and ecosystems is exciting in its simplicity. We also concur with the assertion of Ló pez-Urrutia that these relationships imply that unique and singular metabolic bottlenecks might result in the generalized (but different) responses to temperature observed for phytoplankton and heterotrophic microbes (a speculation offered by Rose and Caron 2007). The suggestion that a single characteristic can have such a far-ranging controlling influence on a huge diversity of organisms has its detractors, but it is nonetheless consistent with our analyses. As a purely statistical tool, the MTE appears to have great utility for organizing our high-level understanding of these interactions and their outcomes. Questions remain that our data do not address, however, such as whether the MTE represents a truly mechanistic model that explains biological structure, or whether it constitutes a formalized representation of correlations derived from an examination of empirical data (i.e., is phenomenological). There presently does not seem to be general consensus on the mechanisms that give rise to allometric relationships (Cyr and Walker 2004). More …