Trade-Offs between the Metabolic Rate and Population Density of Plants

Abstract

The energetic equivalence rule, which is based on a combination of metabolic theory and the self-thinning rule, is one of the fundamental laws of nature. However, there is a progressively increasing body of evidence that scaling relationships of metabolic rate vs. body mass and population density vs. body mass are variable and deviate from their respective theoretical values of 3/4 and −3/4 or −2/3. These findings questioned the previous hypotheses of energetic equivalence rule in plants. Here we examined the allometric relationships between photosynthetic mass (M p) or leaf mass (M L) vs. body mass (β); population density vs. body mass (δ); and leaf mass vs. population density, for desert shrubs, trees, and herbaceous plants, respectively. As expected, the allometric relationships for both photosynthetic mass (i.e. metabolic rate) and population density varied with the environmental conditions. However, the ratio between the two exponents was −1 (i.e. β/δ = −1) and followed the trade-off principle when local resources were limited. Our results demonstrate for the first time that the energetic equivalence rule of plants is based on trade-offs between the variable metabolic rate and population density rather than their constant allometric exponents.

Insights into plant size-density relationships from models and agricultural crops

“…These results offer a different perspective from many studies that have emphasized how competitive and successional processes vary across plant taxa, life forms, and environmental conditions (21,22,(24)(25)(26)(27)(28)(29)(30)(39)(40)(41)(42). They suggest to us that scaling exponents, when measured across orders of magnitude variation in plant size, are relatively independent of phylogenetic affiliation, growth habit, and abiotic environmental features.…”

“…Plot areas were 1 m × 1 m, with 0.3-m-wide buffer zones to avoid edge effects. The local growing conditions were sufficient to ensure vigorous plant growth without water or nutrient stress (21,22). Numbers of stems were counted and above-ground dry plant biomass was measured after harvesting reproductively mature plants on each plot.…”

“…One focuses on theoretical models and empirical measurements of abundance, spacing, survival, mortality, and recruitment as functions of plant size in relatively undisturbed natural populations and communities, especially forests (4)(5)(6)(7)(8)(9)(10)(11), where the thinning process is complicated by effects of shading and other factors on asymmetries in resource supply and resulting growth and mortality rates (11)(12)(13)(14)(15)(16). The second approach focuses on the structure and dynamics of plants in agricultural settings (17)(18)(19)(20)(21)(22), where plants of nearly identical age grow under controlled conditions. Studies of such simplified agricultural systems have led to theoretical and empirical selfthinning relationships that characterize the temporal trajectory of decreasing population density as a function of increasing plant size as stands develop under conditions of resource limitation and competition (17)(18)(19).…”

“…For decades, plant scientists have debated the empirical form of the thinning line and the mechanisms that give rise to it (18,(21)(22)(23)(24)(25)(26)(27). Much of the debate has revolved around the value of the exponent, α.…”

Species Distribution Patterns, Species-Area and Species- Temperature Relationships in Eastern Asian Plants

“…This question has perplexed biogeographers and ecologists for about 100 years, and the diverse theories and hypotheses have been put forward to account for latitudinal gradients in biodiversity (Wright 1983;Rohde, 1992;Waide et al, 1999;Colwell & Lees, 2000;Gaston, 2000;Allen et al 2002;Hawkins et al, 2003;Willig et al 2003;Ricklefs, 2004;Mittelbach et al 2007;Gillooly& Allen, 2007;Storch et al 2007;Cardinale, et al, 2009), Recent decade, the metabolic theory of biodiversity (MTB) is developed and attracting a lot of attentions of ecologists as a novel hypothesis based on metabolic theory of ecology (MTE) and the energeticequivalence rule (West et al 1997(West et al , 1999Enquist et al 1998;Allen et al 2002Brown et al 2004;Deng et al 2006Deng et al , 2008. The MTB is recognized as a general principle that can quantify relationships between the dynamic processes of population and biodiversity patterns in ecosystem, and between species richness and environmental factors (see also Allen et al 2003Gillooly & Allen 2007).…”