Interplay of physiology, ecology and the environment: the implications of body size and shape

Abstract

Body size is a key trait that influences organisms’ vital rates. Organisms also differ in their body shape, which may influence the scaling of physiological rates. Metabolic rates commonly scale with body size with a scaling exponent between 2/3 and 1 for reasons still contested. Using meta-analyses, I show that the intraspecific scaling exponents of cephalopods covary positively with metabolic levels (i.e. elevation of the metabolism-mass relationship) across species, contrasting the negative covariation observed in teleost fish. I describe how contrasting energetic and mortality pressures, and the steeper size-scaling of body surface area associated with relative body shape elongation or flattening in epipelagic cephalopods that have rapid, near-exponential growth can explain this difference. I further reveal clear differences in energy use during non-flight activity between insects and spiders. Across species, active metabolic rates scaled more steeply with body mass in insects than spiders, and is associated with greater energetic demands for sustained activity in larger insects, which is accentuated by possessing wings. These findings add to the evidence that metabolic scaling varies systematically with multiple ecological factors. I then show that experimental warming strongly influenced body size of model protist species, while their body shape was affected more by resource availability, indicating their competitive abilities. Finally, an experimental heatwave imposed on freshwater plankton communities reduced the elevation and steepened the slope of the negative relationship between organism abundance and body size, and also decreased total zooplankton abundance. However, using a species introduction treatment, I show that connectivity to the regional species iv pool buffers such changes in the elevation. As changes in the abundance-body size relationship relate to warming effects on trophic efficiency and increased energy use, understanding the interplay between body size, metabolism and temperature is critical for understanding climate change impacts on ecosystem structure and function.