Nematodes in a polar desert reveal the relative role of biotic interactions in the coexistence of soil animals

Tancredi Caruso,S Craig Cary,Byron J Adams,Diana H Wall,Bryan C Storey,Uffe N Nielsen,John E Barrett,Charles K Lee,T G Allan Green,Eric M Bottos,Ian D Hogg,David W Hopkins

doi:10.1038/s42003-018-0260-y

Abstract

Abiotic factors are major determinants of soil animal distributions and their dominant role is pronounced in extreme ecosystems, with biotic interactions seemingly playing a minor role. We modelled co-occurrence and distribution of the three nematode species that dominate the soil food web of the McMurdo Dry Valleys (Antarctica). Abiotic factors, other biotic groups, and autocorrelation all contributed to structuring nematode species distributions. However, after removing their effects, we found that the presence of the most abundant nematode species greatly, and negatively, affected the probability of detecting one of the other two species. We observed similar patterns in relative abundances for two out of three pairs of species. Harsh abiotic conditions alone are insufficient to explain contemporary nematode distributions whereas the role of negative biotic interactions has been largely underestimated in soil. The future challenge is to understand how the effects of global change on biotic interactions will alter species coexistence.

Highlights

Abiotic factors are major determinants of soil animal distributions and their dominant role is pronounced in extreme ecosystems, with biotic interactions seemingly playing a minor role
The major goal has been to understand the relative roles of the different processes that structure ecological communities with a special emphasis on the balance between stochastic and deterministic processes[4,9,10,11,12,13,14,15]
The belowground component has received far less attention but there have been studies addressing soil community structure at very broad scales[16,17,18] as well as studies focusing on particular groups at relatively local scales[6,19,20]: soil communities are structured at multiple spatial scales with local communities often consisting of species that are dispersal limited over relatively broad spatial scales[21,22]

Summary

Introduction

Abiotic factors are major determinants of soil animal distributions and their dominant role is pronounced in extreme ecosystems, with biotic interactions seemingly playing a minor role. Species can spatially segregate and coexist at relatively broader scales (i.e., colonise different patches in the same landscape) if competition for resources is incompatible with their coexistence at local scales[12] Falsifying this hypothesis as applied to soil ecosystems is very challenging because of the physical and chemical complexity of the soil habitat and its high biotic diversity, which includes aboveground–belowground linkages. To test for this, ideally one would need to control for all the abiotic, biotic, and historical factors (e.g., dispersal dynamics, biogeographical legacies, etc.) that affect the co-occurrence of species[32] To address this challenge in the present study, we targeted the soil ecosystem of the McMurdo Dry Valleys (MDVs) of Antarctica. In terms of their habitat preferences, Plectus and Eudorylaimus prefer higher levels of soil moisture than Scottnema[35,48]

Objectives

Methods

Results

Conclusion