Lifting the veil: richness measurements fail to detect systematic biodiversity change over three decades

Abstract

While there is widespread recognition of human involvement in biodiversity loss globally, at smaller spatial extents, the effects are less clear. One reason is that local effects are obscured by the use of summary biodiversity variables, such as species richness, that provide only limited insight into complex biodiversity change. Here, we use 30 yr of invertebrate data from a metacommunity of 10 streams in Wales, UK, combined with regional surveys, to examine temporal changes in multiple biodiversity measures at local, metacommunity, and regional scales. There was no change in taxonomic or functional α-diversity and spatial β-diversity metrics at any scale over the 30-yr time series, suggesting a relative stasis in the system and no evidence for on-going homogenization. However, temporal changes in mean species composition were evident. Two independent approaches to estimate species niche breadth showed that compositional changes were associated with a systematic decline in mean community specialization. Estimates of species-specific local extinction and immigration probabilities suggested that this decline was linked to lower recolonization rates of specialists, rather than greater local extinction rates. Our results reveal the need for caution in implying stasis from patterns in α-diversity and spatial β-diversity measures that might mask non-random biodiversity changes over time. We also show how different but complementary approaches to estimate niche breadth and functional distinctness of species can reveal long-term trends in community homogenization likely to be important to conservation and ecosystem function.

Evenness effects mask richness effects on ecosystem functioning at macro‐scales in lakes

“…Although strong evenness effects on ecosystem functioning have been demonstrated in previous regional studies (e.g. Filstrup et al 2014a;Hodapp et al 2015), our study extends these relationships to continental scales (Figs 2 and 3), thereby echoing recent calls to consider measures of biodiversity beyond richness in BEF relationships (Hillebrand et al 2018;Larsen et al 2018). Evenness has been argued to be more sensitive to environmental change than richness because species tend to become rare in communities before becoming extinct (Hillebrand et al 2008;Hillebrand & Matthiessen 2009).…”

“…Recent debate surrounding interpretation of static or increasing temporal trends in local species richness and studies demonstrating that these trends may not be sensitive indicators of biodiversity change (Cardinale et al 2018;Hillebrand et al 2018;Larsen et al 2018) justify the need for a more complete understanding of BEF relationships. The focus on species richness as the primary measure of biodiversity has resulted in a poor understanding of the effects of other biodiversity metrics on ecosystem functioning (Wilsey et al 2005;Hillebrand et al 2008;Hillebrand & Matthiessen 2009;Hooper et al 2012).…”

No biotic homogenisation across decades but consistent effects of landscape position and pH on macrophyte communities in boreal lakes

“…For example, Winegardner et al (2017) did not find changes in spatial beta diversity of lake diatoms between 1850 and 2007, even though they had a longer time period examined compared with that in our study. Similarly, Larsen et al (2018) did not find signs of biotic homogenisation when they studied stream macroinvertebrates in 10 streams during 30 yr. However, Wengrat et al (2018) found a decreasing trend in spatial beta diversity of diatom assemblages, but only when they studied eutrophic reservoirs instead of the whole set of reservoirs over the past 60-100 yr.…”

The three Rs of river ecosystem resilience: Resources, recruitment, and refugia

“…The trait‐based approaches to appraise the mechanisms behind community resilience can be illustrated using a case study from the Lynn Brianne Stream Observatory (Wales, United Kingdom: see Ormerod & Durance, ). A long‐term time series of benthic invertebrate communities monitored in multiple catchments shows overall stability in taxonomic richness and suggests resilience to environmental changes (Larsen, Chase, Durance, & Ormerod, ). Different responses to environmental change can be inferred from taxonomic and phylogenetic indices (respectively taxonomic richness and taxonomic distinctness, Figure ) because the two metrics show specific variations that can each be linked to specific types of environmental change, involving large flow variations and high temperatures.…”

“…In this case study, a measure of taxonomic richness can indicate the community response in redundancy most clearly, where the phylogenetic diversity provided a strong indicator for recruitment recovery and for selective responses (specialists resistant to heat wave). In conclusion, most studies find that responses are difficult to reveal with single indices and that community‐level aspects of niche breath and specialization often are necessary to analyse over longer time intervals to fully detect and interpret responses of communities to disturbances (Larsen et al, ).…”