Beetle ecological indicators – A comparison of cost vs reward to understand functional changes in response to restoration actions

Abstract

• Reduced grazing affects abundance-, richness- and biomass-based ecological indicators differently. • Richness and abundance indicators are less informative than biomass-based ones. • Family-based functional groups are useful ecological indicators for functional change. • Abundance- and biomass-based indicators offer different functional insights. • Abundance indicators of the most common family groups are the most cost-effective indicators. Ecosystem restoration can play a vital role in conserving biodiversity, but its effectiveness can be difficult to assess for hyperdiverse biota such as insects. Species traits of insects can be used to understand their functional responses to restoration, but their use often requires considerable effort, and few studies have examined what additional insight can be gained from this approach. We used a spatially and temporally controlled restoration experiment to examine beetle species, grouped by flight ability, family membership and feeding guild, as indicators of ecosystem functional change. We tested for the effects of reduced vertebrate grazing on beetle assemblages sampled from two different microhabitats (next to log and in open ground) one year prior and two years after a vertebrate grazing treatment was applied. We compared the responses of the different beetle functional groupings, and then related these to the effort involved in employing these indicators. We found that beetle species traits gave several functional insights into their responses to reduced grazing, including responses to changes in vegetation structure and biomass. Species richness indicators and abundance indicators of beetle functional groups showed similar responses in many cases, whereas biomass indicators gave additional insights related to the extra biomass of vegetation and detritus resulting from the reduction in grazing. We found that most results were revealed by using family groups as indicators for functional change. This is because the traits that often define beetle families, such as size, flight ability and feeding guilds each have distinctive functional roles, allowing a link from family to function, and supporting the idea that phylogeny is often a useful shortcut to species ecology. We conclude that in our study system, the least-cost approach to identifying functional responses of beetles to reduced vertebrate grazing, and possibly other restoration actions, is to use abundance indicators of the most common family groups.