A Perspective on Body Size and Abundance Relationships across Ecological Communities.

Vojsava Gjoni,Douglas Stewart Glazier

doi:10.3390/biology9030042

Abstract

Recently, several studies have reported relationships between the abundance of organisms in an ecological community and their mean body size (called cross-community scaling relationships: CCSRs) that can be described by simple power functions. A primary focus of these studies has been on the scaling exponent (slope) and whether it approximates −3/4, as predicted by Damuth’s rule and the metabolic theory in ecology. However, some CCSR studies have reported scaling exponents significantly different from the theoretical value of −3/4. Why this variation occurs is still largely unknown. The purpose of our commentary is to show the value of examining both the slopes and elevations of CCSRs and how various ecological factors may affect them. As a heuristic exercise, we reanalyzed three published data sets based on phytoplankton, rodent, and macroinvertebrate assemblages that we subdivided according to three distinctly different ecological factors (i.e., climate zone, season, and trophic level). Our analyses reveal significant variation in either or both the CCSR slopes and elevations for marine phytoplankton communities across climate zones, a desert rodent community across seasons, and saltwater lagoon macroinvertebrate communities across trophic levels. We conclude that achieving a comprehensive understanding of abundance-size relationships at the community level will require consideration of both slopes and elevations of these relationships and their possible variation in different ecological contexts.

Highlights

Since the 1930s, researchers observed that average plant size was inversely related to population density
Most previous studies of abundance-size relationships across ecological communities have focused on the scaling exponent, and whether it is similar to the −3/4 values predicted by Damuth’s rule and the MTE [21,22,23,24,25]
Suspension feeders; In our commentary, we suggest that better understanding of cross-community scaling relationships (CCSR) may be achieved by examining both the slopes and elevations of these relationships, and how they are affected by various ecological factors

Summary

Introduction

Since the 1930s, researchers observed that average plant size was inversely related to population density. This density-dependent effect is observed by comparing several populations of the same species. The common occurrence of this relationship, which often shows a log-log scaling exponent of −3/2, has led to it being considered a rule or law, often called the self-thinning rule (STR), the −3/2 power rule, or Yoda’s law [1]. The STR is so general that it has even been applied to animals, though the scaling exponent may take on other values, such as −4/3. Power functions have been successfully applied at the community level, starting a new wave of analyses of cross-community scaling relationships (CCSR). CCSRs describe negative relationships between the total number or Biology 2020, 9, 42; doi:10.3390/biology9030042 www.mdpi.com/journal/biology

Results

Discussion

Conclusion