Data from: Sampling beetle communities: trap design interacts with weather and species traits to bias capture rates

Globally, many insect populations are declining, prompting calls
for action. Yet these findings have
also prompted discussion about sampling methods and
interpretation of long-term datasets. As insect
monitoring and research efforts increase, it is
critical to quantify the effectiveness of sampling
methods. This is especially true if sampling
biases of different methods covary
with climate, which is also changing over time. We
assess the effectiveness of two types of
flight intercept traps commonly used for
beetles, a diverse insect group responsible for numerous
ecosystem services, under different climatic
conditions in Norwegian boreal forest. One of these trap
designs includes a device to prevent rainwater from
entering the collection vial, diluting preservatives
and flushing out beetles. This design is compared to a
standard trap. We ask how beetle capture rates vary between these
traps, and how these differences vary based on precipitation levels and
beetle body size, an important species trait. Bayesian mixed
models reveal that the standard and modified traps differ in
their beetle capture rates, but that the magnitude and
direction of these differences change with precipitation levels and beetle
body size. At low rainfall levels standard traps catch more
beetles, but as precipitation increases the catch rates of
modified traps overtake those of standard traps. This effect is
most pronounced for large-bodied beetles. Sampling
methods are known to differ in their
effectiveness. Here, we present evidence for a less
well-known but likely common phenomenon - an interaction between
climate and sampling, such that relative effectiveness of trap
types for beetle sampling differs depending on
precipitation levels and species traits. This highlights
a challenge for long-term monitoring programs, where both climate
and insect populations are changing. Sampling methods
should be sought that eliminate climate
interactions, any biases should be quantified,
and all insect datasets should include detailed
methodological metadata.