Tradeoffs in demographic mechanisms underlie differences in species abundance and stability

Lauren M Hallett,Harold A Mooney,Richard J Hobbs,Emily C Farrer,Katharine N Suding

doi:10.1038/s41467-018-07535-w

Abstract

Understanding why some species are common and others are rare is a central question in ecology, and is critical for developing conservation strategies under global change. Rare species are typically considered to be more prone to extinction—but the fact they are rare can impede a general understanding of rarity vs. abundance. Here we develop and empirically test a framework to predict species abundances and stability using mechanisms governing population dynamics. Our results demonstrate that coexisting species with similar abundances can be shaped by different mechanisms (specifically, higher growth rates when rare vs. weaker negative density-dependence). Further, these dynamics influence population stability: species with higher intrinsic growth rates but stronger negative density-dependence were more stable and less sensitive to climate variability, regardless of abundance. This suggests that underlying mechanisms governing population dynamics, in addition to population size, may be critical indicators of population stability in an increasingly variable world.

Highlights

Understanding why some species are common and others are rare is a central question in ecology, and is critical for developing conservation strategies under global change
We find that coexisting species can exhibit similar average abundances through different mechanisms
We find that population stability is more strongly governed by the mechanisms underlying a species’ average abundance— a higher growth rate when rare (GRWR) that may enhance population recovery—than the resultant population size

Summary

Introduction

Understanding why some species are common and others are rare is a central question in ecology, and is critical for developing conservation strategies under global change. This maximum rate of population increase is set by intrinsic reproductive and death rates, and a high growth rate when rare (GRWR) should contribute to a species’ average abundance (Fig. 1b). Theory predicts that NDD and GRWR should be joint determinants of average abundance[9] (Fig. 1c), and integrating these mechanisms is important in understanding species coexistence[14].

Results

Conclusion