Effects of Body Size and Temperature on Population Growth

Abstract

For at least 200 years, since the time of Malthus, population growth has been recognized as providing a critical link between the performance of individual organisms and the ecology and evolution of species. We present a theory that shows how the intrinsic rate of exponential population growth, rmax, and the carrying capacity, K, depend on individual metabolic rate and resource supply rate. To do this, we construct equations for the metabolic rates of entire populations by summing over individuals, and then we combine these population-level equations with Malthusian growth. Thus, the theory makes explicit the relationship between rates of resource supply in the environment and rates of production of new biomass and individuals. These individual-level and population-level processes are inextricably linked because metabolism sets both the demand for environmental resources and the resource allocation to survival, growth, and reproduction. We use the theory to make explicit how and why rmax exhibits its characteristic dependence on body size and temperature. Data for aerobic eukaryotes, including algae, protists, insects, zooplankton, fishes, and mammals, support these predicted scalings for rmax. The metabolic flux of energy and materials also dictates that the carrying capacity or equilibrium density of populations should decrease with increasing body size and increasing temperature. Finally, we argue that body mass and body temperature, through their effects on metabolic rate, can explain most of the variation in fecundity and mortality rates. Data for marine fishes in the field support these predictions for instantaneous rates of mortality. This theory links the rates of metabolism and resource use of individuals to life-history attributes and population dynamics for a broad assortment of organisms, from unicellular organisms to mammals.

Effects of elevated CO<sub>2</sub> and temperature on phytoplankton community biomass, species composition and photosynthesis during an experimentally induced autumn bloom in the western English Channel

“…The increased biomass and photosynthetic carbon fixation in this experimental community under elevated pCO 2 is due to the community shift to Phaeocystis spp. The increased biomass in the high-temperature treatment (where microzooplank- ton biomass remained stable between T17 and T36, though lower than the control) may be attributed to enhanced enzymatic activities, since algal growth commonly increases with temperature until after an optimal range (Boyd et al, 2013;Goldman and Carpenter, 1974;Savage et al, 2004). Optimum growth temperatures for marine phytoplankton are often several degrees higher than environmental temperatures (Eppley, 1972;Thomas et al, 2012).…”

Testing Metabolic Theories

“…The WBE-based models are now being applied in general ecological investigations and have been shown to predict numerous broad-scale physiological and ecological phenomena with remarkable accuracy (e.g., Enquist et al 2003Enquist et al , 2007bBrown et al 2004;Savage et al 2004;Gillooly et al 2005;Price et al 2007;Hou et al 2008). However, vociferous debate has ensued on the universality of the empirically observed scaling (Glazier 2005;White et al 2007;Makarieva et al 2008), the empirical and statistical validity of the temperature dependence term (Clarke 2004;Irlich et al 2009), fundamental principles of the models (Makarieva et al 2004;Suarez et al 2004;Kozłowski and Konarzewski 2005;O'Connor et al 2007;Apol et al 2008;Banavar et al 2010), and their predictive capacity (Algar et al 2007).…”

Size-selective fishing drives species composition in the Celtic Sea

“…102 -225 (WCGFS; Froese and Pauly, 2010). Growth and loss rates for model species follow allometric scaling laws derived using data for plankton, invertebrates, and fish (Niklas and Enquist, 2001;Brown et al, 2004;Savage et al, 2004); the gross conversion efficiency for consumers is derived as the average of the efficiencies for herbivores and carnivores (Hendriks, 2007). With this parametrization, a model shelf community was generated with model species encompassing the body mass range from phytoplankton to large fish.…”