Data and code from: Evaluating baselines for long-term ecological monitoring of biodiversity trends: Insights from the US National Ecological Observatory Network carabid data

Evidence is mounting that rapid environmental change threatens global
insect biodiversity, underscoring the need for informed conservation
strategies that protect both species and the ecosystem services they
provide. Armed with accurate baseline community data, long-term
continental-scale monitoring projects are invaluable for detecting and
predicting responses to ecological change. However, high species diversity
and temporal variability in population sizes can hinder our ability to
establish baselines, and, thus, obscure, exaggerate, or reverse temporal
trends in long-term insect data. With its scale and consistent protocol,
the US National Ecological Observatory Network (NEON) carabid pitfall
trapping data provides an excellent case study for evaluating sampling
effort. We use species incidence-frequencies calculated from more than
200,000 identified carabids across up to 10 years of sampling and 46 field
sites to extrapolate asymptotic richness and diversity metrics. We find
that the completeness of observed species richness and diversity is
negatively related to year-to-year species turnover and diversity metrics
themselves, but improves with increasing sampling duration. While observed
diversity converges to asymptotic estimates within a few years, we find
that NEON’s intensive sampling is unlikely to capture all species, even if
no biodiversity loss occurs over its 30-year span. If the mechanisms
driving these patterns can be understood, they hold important implications
for optimizing sampling designs in studies focused on ecological change
detection, particularly for diverse and temporally variable taxa. Our
findings underscore the critical importance of long-term monitoring and
prompt reconsideration of how we interpret trends in existing biodiversity
data, given the complexity of establishing robust baselines.