Biological barriers to restoration: testing the biotic resistance hypothesis in an upland stream recovering from acidification

Jessica L Frame,Mark E Ledger,Steve J Ormerod,J Iwan Jones,Jonathan P Sadler

doi:10.1007/s10750-016-2772-0

Jessica L Frame, Mark E Ledger + Show 3 more

Open Access

https://doi.org/10.1007/s10750-016-2772-0

Copy DOI

Abstract

The biotic resistance hypothesis provides one of several explanations for the limited biological recovery of streams recovering chemically from acidification. The hypothesis proposes that acidification has changed the presence, abundance and interactions among species in acidified streams to the extent that acid-sensitive colonists cannot re-invade even where acidity has ameliorated. As a first step in testing for biotic resistance in streams, we conducted a field experiment to determine whether the success (growth rate) of acid-sensitive recolonists (mayfly nymphs, Baetis rhodani) is reduced by competition with abundant acid-tolerant residents (stonefly nymphs, Leuctra inermis) in a chemically recovering Welsh stream (UK). Gut contents analysis revealed a marked overlap in resource use between the two species. However, when Baetis was exposed to several (0, 0.25, 0.5 and 1 times ambient) densities of its putative competitor, Leuctra, growth rates of the colonist were not affected by the residents at any of the densities tested. These results do not support the hypothesis that resident species constrain colonist populations by affecting growth rates through competition for limited resources or interference. Further work is required to assess whether independent and/or interactive ecological effects of other common residents might affect colonists in ecosystems recovering from past stressors.

Highlights

Declining acid deposition across the northern hemisphere over recent decades has led to widespread improvements in the water quality of formerly acidified surface waters (Battarbee et al, 2014; Monteith et al, 2014)
Abiotic resistance may limit the persistence of recolonists where continued acid episodicity arises after heavy rainfall or snowmelt (Lepori et al, 2003; Kowalik & Ormerod, 2006), but episodes may not be a straightforward explanation for limited biological recovery where acidity is ameliorating (Monteith et al, 2014)
We examine the potential for biotic resistance to recovery within the benthic macroinvertebrate community of a chemically recovering stream in mid-Wales, UK

Summary

Introduction

Declining acid deposition across the northern hemisphere over recent decades has led to widespread improvements in the water quality of formerly acidified surface waters (Battarbee et al, 2014; Monteith et al, 2014). We do not know whether changes in the presence and abundance of species, and biotic interactions, which occur under acid conditions in turn influence the invasibility of riverine communities as acidity ameliorates (Ledger & Hildrew, 2005; Murphy et al, 2014). Acidified streams in the catchments of the River Wye are improving chemically, both through declining acid deposition and restoration projects (liming), but to date evidence for biological recovery is scarce, with limited persistence of many acid-sensitive invertebrates, especially mayflies One of the untested mechanisms of community resistance to reinvasion in streams is competition with residents, and it could be that changes in species abundances and interactions occurring as streams acidified place tight constraints upon the subsequent return of sensitive species when acidity ameliorates (Ledger & Hildrew, 2005; Layer et al, 2013). Consistent with the biotic resistance hypothesis, we predicted that the growth of Baetis would be constrained by Leuctra and that mayfly growth rates would decrease with the increasing abundance of the stonefly resident

Methods

Results

Discussion