Metabolic dependence of phytoplankton species richness

Abstract

Aim To analyse the dependence of phytoplankton species richness on temperature within the framework of the metabolic theory of ecology (MTE) with explicit consideration of its assumptions and predictions. Location Lakes from the Southern Hemisphere – South America (Argentinean Pampa to Tierra del Fuego) and Antarctica – and Northern Hemisphere – North America (USA) and Europe (Denmark to Spain). Methods The MTE proposes that natural logarithm of species richness and the inverse of temperature are linearly related, with a slope equal to the activation energy. The MTE assumes that the total community abundance, average body size and per species average community productivity are independent of the temperature. These predictions and assumptions are here evaluated using c. 660 phytoplankton lake communities and a literature review of 281 experimental measures of growth rate. Linear, curvilinear and segmented models were contrasted with empirical trends. Results Temperature–richness relationships showed a three‐phase segmented form in two of the three continents. Generally, at temperatures above 17 °C and below 11 °C there was a weak relationship or none. Intermediate temperatures showed the expected positive association with richness, but with steeper slopes (c. 1) than MTE expectations (c. 0.3). Statistical models including total community abundance and average body size explained up to 64% of the variance in richness. Main conclusions In its original formulation the MTE is not a satisfactory model for large‐scale richness patterns in phytoplankton. However, the MTE is able to better explain richness patterns when the temperature dependence of abundances and body size are explicitly accounted for in the model. These temperature dependences improve the performance of MTE predictions but question the interpretation of the richness–temperature slope as a measure of activation energy. The balance among activation energy, abundance and body size produced the observed segmented pattern in temperature–richness relationships for lake phytoplankton.

Morphology-based differences in the thermal response of freshwater phytoplankton

“…We compiled data from 563 experiments from prokaryotes and eukaryotes over nine major phylogenetic groups (see electronic supplementary material, table S1 for original data). The linear model (equation (1.2)) fitted to the whole dataset gives an estimation of activation energy (E[CI-95%]) ¼ 0.31[0.25-0.38]) similar to previous values estimated for freshwater and marine organisms [5,7]. The segmented model improved the fit with respect to the linear model (DAIC ¼ 13.5; figure 1) with a larger estimated activation energy for the rise (E r ¼ 0.51[0.38-0.64]).…”

“…The segmented model improved the fit with respect to the linear model (DAIC ¼ 13.5; figure 1) with a larger estimated activation energy for the rise (E r ¼ 0.51[0.38-0.64]). This suggests that the fitting of a linear model (equation (1.2)) generally underestimates the average activation energy of the rise, as found before [7]. The breakpoint was estimated at 218C (294 Kelvin), and the activation energy after the breakpoint (E f ) was not significantly different from zero (E f [95% CI] ¼ 0 [20.2 to 0.2]).…”

“…A systematic bibliographic search was conducted, aimed at gathering experimental information on how freshwater phytoplankton growth rate changes with temperature. This search covered peer reviewed journals reporting laboratory experiments exploring changes in population growth rate over a broad range of temperatures under nutrients replete and non-limiting light conditions [7].…”

“…Irrespective of the particular formulation, the exponential model is useful to characterize the metabolic response in a wide thermal range. However, it does not describe the sharp decay observed above the optimum temperature (T BK ) [7,8], which is generally included within the biologically relevant temperature ranges (e.g. [9]).…”

A metabolic view of amphibian local community structure: the role of activation energy

“…An important difference between previous analyses of variation in species richness in the MTE framework, and the present analysis focused on the number of calling species, should be highlighted (Allen et al ). The MTE considered the individuals’ energetic demand – standard metabolic rate – and its dependence on temperature to predict trends in species richness (Allen et al , Segura et al ). Here, the metabolic rate affected by temperature also involves the energetic expenditure of calling (Gillooly and Ophir , Ophir et al , Ziegler et al ).…”