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Network Biology, 2027, 17(1): 76-101
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Article

Decline rate estimations and functional extinction time predictions for major terrestrial insect taxa: An integrated framework of critical network decoupling and multidimensional functional thresholds

WenJun Zhang
School of Life Sciences, Sun Yat-sen University, Guangzhou, China

Received 11 February 2026;Accepted 26 May 2026;Published online 8 June 2026;Published 1 March 2027
IAEES

Abstract
Global declines in insect populations have attracted attention, yet most assessments focus on counts and species richness rather than the erosion of ecological functions. Here, I ask when major terrestrial insect taxa (butterflies, bees, and ants) will cease to perform their roles at levels sufficient for ecosystem integrity. I synthesize data from 73 historical reports, 166 long-term surveys across 1676 sites, 40 additional studies, and systematic reviews of global change impacts. Using a Bayesian hierarchical approach that accounts for spatial and taxonomic heterogeneity, I estimate annual declines of 1.5-2.5% for butterflies, 1.8-3.5% for wild bees, and highly variable ant trajectories from local stability to 42-54% functional collapse in invaded areas. I introduce a multidimensional functional extinction threshold integrating three dimensions: minimum functional population, a network decoupling index quantifying keystone connectivity loss, and a functional performance baseline at 30% of historical levels. Building on critical slowing down theory, I propose the Critical Network Decoupling Hypothesis, in which ecological networks initially compensate via interaction redundancy, then enter a decoupling phase with rising variance and loss of synchrony among keystone species, culminating in abrupt functional collapse. I further propose the Life History Buffer Hypothesis to explain taxon-specific differences in decline timing based on generation time, dietary specialization, and sociality. Our models predict that specialized pollination by long-tongued wild bees will reach functional extinction thresholds between 2030 and 2050 in temperate regions, butterfly-mediated networks around 2060, and native ant seed dispersal in tropical forests between 2050 and 2080. I introduce the Functional Loss Acceleration index as a more sensitive early warning metric than conventional population trends. These findings call for a paradigm shift from species-counting to network function protection, providing a science-based early warning framework to prevent irreversible ecosystem function collapse.

Keywords insect decline;butterflies;wild bees;ants;functional extinction;rate heterogeneity;critical decoupling;network robustness;extinction debt;ecological network resilience;conservation early warning.


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