arXiv subjects

Brian J. Enquist

Publications and source records attributed to Brian J. Enquist.

4 recordsLinked to original sources

arXiv2022

Global city densities: re-examining urban scaling theory

Understanding scaling relations of social and environmental attributes of urban systems is necessary for effectively managing cities. Urban scaling theory (UST) has assumed that population density scales positively with city size. We present a new global analysis using a publicly available database of 933 cities from 38 countries. Our results showed that (18/38) 47% of countries analyzed supported increasing density scaling (pop ~ area) with exponents ~5/6 as UST predicts. In contrast, 17 of 38 countries (~45%) exhibited density scalings statistically indistinguishable from constant population densities across cities of varying sizes. These results were generally consistent in years spanning four decades from 1975 to 2015. Importantly, density varies by an order of magnitude between regions and countries and decreases in more developed economies. Our results (i) point to how economic and regional differences may affect the scaling of density with city size and (ii) show how understanding country- and region-specific strategies could inform effective management of urban systems for biodiversity, public health, conservation and resiliency from local to global scales.

physics.soc-ph↗

arXiv2020

Branching principles of animal and plant networks identified by combining extensive data, machine learning, and modeling

Branching in vascular networks and in overall organismic form is one of the most common and ancient features of multicellular plants, fungi, and animals. By combining machine-learning techniques with new theory that relates vascular form to metabolic function, we enable novel classification of diverse branching networks--mouse lung, human head and torso, angiosperm and gymnosperm plants. We find that ratios of limb radii--which dictate essential biologic functions related to resource transport and supply--are best at distinguishing branching networks. We also show how variation in vascular and branching geometry persists despite observing a convergent relationship across organisms for how metabolic rate depends on body mass.

q-bio.QM↗

arXiv2015

Scaling from traits to ecosystems: Developing a general Trait Driver Theory via integrating trait-based and metabolic scaling theories

The rise of trait-based ecology has led to an increased focus on the distribution and dynamics of traits in communities. However, a general theory of trait-based ecology, that can apply across different scales (e.g., species that differ in size) and gradients (e.g., temperature), has yet to be formulated. While research focused on metabolic and allometric scaling theory provides the basis for such a theory it does not explicitly account for differences traits within and across taxa, such as variation in the optimal temperature for growth. Here we synthesize trait-based and metabolic scaling approaches into a framework that we term Trait Drivers Theory or TDT. It shows that the shape and dynamics of trait distributions can be uniquely linked to fundamental drivers of community assembly and how the community will respond to future drivers. To assess predictions and assumptions of TDT, we review several theoretical studies, recent empirical studies spanning local and biogeographic gradients. Further, we analyze how the shift in trait distributions influences ecosystem productivity across an elevational gradient and a 140-year long ecological experiment. We argue that our general TDT provides a baseline for (i) recasting the predictions of ecological theories based on species richness in terms of the shape of trait distributions; and (ii) integrating how specific traits, including body size, and functional diversity scale up to influence the dynamics of species assemblages across climatic gradients and how shifts in functional composition influences ecosystem functioning. Further, it offers a novel framework to integrate trait, metabolic/allometric, and species-richness based approaches in order to build a more predictive functional biogeography to show how assemblages of species have and will respond to climate change.

q-bio.PE↗

arXiv2002

Red herrings and rotten fish

A longstanding problem in biology has been the origin of pervasive quarter-power allometric scaling laws that relate many characteristics of organisms to body mass (M) across the entire spectrum of life from molecules and microbes to ecosystems and mammals. In particular, whole-organism metabolic rate, B=aM^b, where a is a taxon-dependent normalisation constant and b is approximately equal to 3/4 for both animals and plants. Recently Darveau et al. (hereafter referred to as DSAH) proposed a "multiple-causes model" for B as "the sum of multiple contributors to metabolism", B_i, which were assumed to scale as M^(b_i). They obtained for average values of b: 0.78 for the basal rate and 0.86 for the maximally active rate. In this note we show that DSAH contains serious technical, theoretical and conceptual errors, including misrepresentations of published data and of our previous work. We also show that, within experimental error, there is no empirical evidence for an increase in b during aerobic activity as suggested by DSAH. Moreover, since DSAH consider only metabolic rates of mammals and make no attempt to explain why metabolic rates for other taxa and many other attributes in diverse organisms also scale with quarter-powers (including most of their input data), their formulation is hardly the "unifying principle" they claim. These problems were not addressed in commentaries by Weibel and Burness.

physics.bio-ph↗