Measuring floral resource availability for insect pollinators in temperate grasslands – a review

Abstract

1. The relationship between pollinators and flowering plants plays a crucial role in the function of terrestrial ecosystems. Although pollinators use floral nectar and pollen as food resources, no general methodology for floral resource availability estimates exists.2. A brief review is provided on floral resource sampling methods frequently used in pollination studies. The focus is on how representative vegetation samples are both spatially and temporally, and how these are constrained by sampling effort.3. Field studies investigating flowering plant abundance for insect pollinators in temperate grasslands were selected. We categorised the reviewed studies according to aims, sampling units, and count variables used and provide a descriptive summary on methodology. We also searched for trade‐offs between different aspects of sampling investment.4. One hundred and fifty‐eight pollination studies were reviewed. Large methodological differences were found, and vegetation sampling was presented in many studies insufficiently. Sampling covered a small proportion (median: 0.69%) of the study sites, with long intervals (median: 30 days), and most studies lasted only a few years. The most often used count variables were indirect proxies of floral resources. Negative relationships were found in some of the different aspects of sampling, e.g. the proportion of site covered with sampling decreased with increasing site area.5. By tailoring sampling methods to specific research questions, research effort should be optimally allocated to obtain proper spatio‐temporal resolution and data coverage. Guidelines were suggested to design sampling, e.g. to increase coverage and frequency. Further field work on optimising sampling techniques is mandatory.