Biota and ecosystems worldwide are undergoing unprecedented environmental changes. Over the past 100 years, the global temperature has increased 0.6ºC, and is predicted to continue up to 1.8-4ºC. At the same time, anthropogenic perturbations are adding nitrogen (N) and phosphorus (P) compounds, strongly affecting the key biogeochemical cycles. Although their single effects are strongly supported, there is an ample debate on the direction of their joint impacts at each biological level. Hence, we are needed of multifactorial and multilevel approaches that consider them simultaneously to increase the reliability of our predictions for species ecology and evolution.
Ecological/Biological Stoichiometry (ES/BS; the study of the balance of energy and multiple chemical elements in ecological interactions/living systems) and Metabolic Theory of Ecology/Biology (MTE/MTB; the study of metabolism as a driving force for ecological patterns/biological processes) have focused on how altered regimes of nutrients and temperature impact, respectively, on consumer growth. Thus, key concepts such as the knife-edge hypothesis (KEH), reporting unimodal responses of growth to nutrients, have greatly advanced our understanding of energy flow and nutrient cycling in ecosystems. Further, both approaches have been particularly interested in how selective pressures on growth have led to changes in metabolism, elemental composition, genome size and structure, and therefore, species evolution. A cornerstone of BS is the growth rate hypothesis (GRH), which proposes that organisms lacking major P storage capacity have elevated demands for increased P allocation to P-rich ribosomal RNA under rapid growth, driving variation in their P content (and therefore C:P and N:P ratios). In addition to this, P-allocation hypothesis (PAH) states that reduced genomes and P allocation from DNA to RNA is the evolutionary consequence of the strong and sustained selection for fast growth in these organisms undergoing P limitation. Both hypotheses establish close connections among individual growth, ribosomal metabolism, elemental composition, and genome size.
Genome size is, at the same time, strongly correlated with cell and body sizes for a wide range of organisms. Because they scale with growth, metabolic, and developmental rates, factors impinging on these trigger far-reaching consequences on life-history strategies, and therefore, evolutionary and ecological processes. Experimental and empirical evidence indicates smaller genome, cell, and body sizes at higher temperatures due to global warming, consistently with the Bergmann-type temperature-size rule. However, these patterns may be masked by other environmental factors such as higher nutrient availability, inducing expectedly larger “sizes”. Thus, it is fundamental to question (i) if the effects of global warming are more intense than those of higher nutrient availability, or quite the opposite; and (ii) if new responses of “sizes” and “rates” emerge when both stressors interact jointly.
STOICHIOMET aimed at studying single and interactive effects of increased nutrients and temperature in keystone species growth to:
I. Test concurrently central concepts of stoichiometric and metabolic theories (KEH, GRH, PAH, Bergmann’s rule).
II. Model the effects of these factors on GRs and coupled traits to integrate both theoretical frameworks.
