Local compositional change and regional stability across 3000 years of coral reef development

Abstract

AimMeasuring changes in ecological diversity over time is core to understanding and managing human impacts on natural systems. Observational data do not capture pre‐modern community states or multiple generations of long‐lived taxa, so interpretation of current diversity trends requires comparison with the past. We aimed to estimate diversity trends over long time periods in a series of fossil coral terraces.LocationHuon peninsula, Papua New Guinea.Time Period9817–6433 years before 1950 AD.Major Taxa StudiedThirty‐five genera of Sceleractinian coral.MethodsWe estimated trends in standing richness (α diversity) and turnover (temporal β diversity) in palaeoecological time series of fossil reef terraces. We compared taxonomic and functional group composition estimates of α diversity, using Hill numbers, and β diversity, measured both sequentially along each time series and to the earliest community.ResultsWe found regional‐scale trends of slowly increasing α diversity and directional turnover driven by increased evenness over time. These regional trends were averages of local‐scale trends in α and β diversity that were largely synchronous, even as coral composition diverged between spatial clusters. Our two β diversity estimates provided opposing, but complementary, reference frames to understand the magnitude and rate of compositional change in ecological time series.Main ConclusionsWe provide evidence that prior to strong anthropogenic influence, natural communities were experiencing directional diversity and compositional change. Our results provide a valuable perspective of diversity dynamics in the recent geological past, including how choices in the measurement of diversity can occlude and influence results.