Integrating multiple evidence streams to understand insect biodiversity change.

Insects dominate animal species diversity yet face many threats from anthropogenic drivers of change. Many features of insect ecology make them a challenging group, and the fragmented state of knowledge compromises our ability to make general statements about their status. In this Review, we discuss the challenges of assessing insect biodiversity change. We describe how multiple lines of evidence—time series, spatial comparisons, experiments, and expert opinion—can be integrated to provide a synthesis overview of how insect biodiversity responds to drivers. Applying this approach will generate testable predictions of insect biodiversity across space, time, and changing drivers. Given the urgency of accelerating human impacts across the environment, this approach could yield a much-needed rapid assessment of insect biodiversity change. Editor's summary: Reports of declining insect abundance and biodiversity have generated concern, but trends vary across taxonomic groups, locations, and the types of data used. Ideally, trends would be assessed using population time series spanning many taxa and locations, with variation in the strength of drivers such as temperature, land use change, and pesticide use. However, these criteria are not often met, making it difficult to parse drivers and find overall patterns. Cooke et al. reviewed the factors that complicate insect trend detection and the data sources available to do so. The authors propose a model for integrating data sources to predict relationships and the effects of policies aiming to mitigate insect decline rather than waiting for more time series to accumulate. —Bianca Lopez BACKGROUND: Insects are the dominant form of animal life on our planet in terms of species diversity, abundance, and biomass. They perform a plethora of functions that are essential to human health and well-being and occupy central positions in trophic networks. Insects are declining in many regions of the world in response to interacting drivers. Understanding the mechanisms behind these changes is essential if we are to prevent further declines and safeguard populations of insects in the future. Insects are a challenging group to study because they are hyperdiverse, have complex life cycles, are functionally complex, and experience substantial population fluctuations. In addition, the fragmented and unrepresentative available evidence base means that the global state of insect biodiversity remains unclear. In the face of these challenges, new approaches are required to determine the global status of insects and their responses to drivers of change. ADVANCES: Time-series data provide the most direct evidence for biodiversity trends. However, insect time series are typically too short and too variable to show clear trends, and geographic coverage is too patchy for global inference. Increasingly, data from experiments, spatial comparisons, expert elicitation, and other sources are being used to make large-scale assessments of biodiversity change. These alternative evidence types have their own strengths, weaknesses, and gaps. In this Review, we address the grand challenge of understanding insect biodiversity change by using these fragmentary data. We propose an approach for combining multiple evidence types that would allow us to take advantage of the strengths of each while mitigating their weaknesses. This will enable informed assessments of insect responses to drivers of change, acknowledging uncertainty, resulting in better directed conservation action. Although conceived with the challenges of insects in mind, our approach is equally applicable to other taxonomic groups. OUTLOOK: Evidence on the global state of insect biodiversity is incomplete. There is an urgent need to understand how, and crucially why, insect biodiversity is changing. We cannot wait decades for additional data and answers to emerge from new monitoring schemes before acting. We propose an approach to better understand how insects are changing in the context of multiple drivers of global change. To achieve this understanding, we must combine evidence from existing data from a range of sources to enable generalization across space, time, and taxonomy. This will facilitate more robust assessments of insect biodiversity change and improve our confidence in those assessments so that informed conservation and policy recommendations can be made to protect insect biodiversity. Harnessing the breadth of evidence on insect biodiversity change.: By combining data from a range of sources—including from time series, spatial comparisons, expert elicitation, and experiments—we can gain a more complete picture of how insects respond to drivers of change while allowing transparency in uncertainty and data gaps. [ABSTRACT FROM AUTHOR]