Insect biomass decline scaled to species diversity: General patterns derived from a hoverfly community

Area of Science:

• Ecology
• Entomology
• Conservation Biology

Background:

• Global flying insect biomass declines are reported, raising concerns about biodiversity.
• The relationship between biomass reduction and actual biodiversity loss remains unclear.

Purpose of the Study:

• To analyze hoverfly (Diptera: Syrphidae) abundance and species richness changes over time.
• To model the impact of varying decline rates on common versus rare species.
• To assess if insect biomass declines predict biodiversity loss.

Main Methods:

• Analyzed 19,604 hoverfly individuals across 162 species from six German nature reserves in 1989 and 2014.
• Developed a model to generalize decline rates for common and rare species.
• Used a theoretical null model to explore changes in rank-abundance curves and species persistence.

Main Results:

• Observed isometric decline rates between total insect biomass and hoverfly abundance.
• Documented scale-dependent declines in hoverfly species richness (-23% seasonally, -82% daily).
• Found lower-than-expected persistence rates for intermediate-abundance species; rarest species showed random decline/appearance rates.

Conclusions:

• Large insect biomass declines are strong predictors of insect diversity declines.
• Common hoverfly species are increasingly threatened, necessitating a reevaluation of conservation approaches.
• Current conservation strategies may need expansion beyond targeting only rare and endangered species.