How to efficiently obtain accurate estimates of flower visitation rates by pollinators |
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| Institution: | 1. The New Zealand Institute for Plant & Food Research Limited, Private Bag 4704, Christchurch, New Zealand;2. The New Zealand Institute for Plant & Food Research Limited, Private Bag 3230, Hamilton, New Zealand;1. Department of Entomology, Michigan State University, East Lansing, MI 48824, USA;2. Department of Entomology, University of California, Davis, CA 95616, USA;3. Department of Entomology and Nematology, University of Florida, Gainesville, FL 32643, USA;4. USDA-ARS Pollinating Insects Research Unit, Logan, UT 84322, USA;5. Swedish University of Agricultural Sciences, Department of Ecology, SE-75007 Uppsala, Sweden;6. Xerces Society for Invertebrate Conservation, Portland, OR 97232, USA;1. Biological and Environmental Sciences, School of Natural Sciences, University of Stirling, FK9 9LA, United Kingdom;2. Department of Geography & Sustainable Development, University of St Andrews, St Andrews KY16 9AL, United Kingdom;3. School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, United Kingdom;1. School of Environmental and Rural Science, University of New England, Armidale, 2350, NSW, Australia;2. Laboratorio Ecotono, INIBIOMA-CONICET and Centro Regional Bariloche, Universidad Nacional del Comahue, Quintral 1250, 8400 San Carlos de Bariloche, Río Negro, Argentina;3. Fenner School of Environment and Society, The Australian National University, Canberra Australian Capital Territory 2601, Australia;4. The University of Queensland, School of Biological Sciences, Brisbane, Queensland 4072, Australia |
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| Abstract: | Regional declines in insect pollinators have raised concerns about crop pollination. Many pollinator studies use visitation rate (pollinators/time) as a proxy for the quality of crop pollination. Visitation rate estimates are based on observation durations that vary significantly between studies. How observation duration relates to the accuracy of the visitation rate estimate is, however, unknown. We studied this relationship using six day-long observations (06:00 h–19:00 h) in leek-seed production fields (totalling 78 h). We analysed beyond which point in time observing longer did not significantly improve the accuracy of the visitation rate estimate (minimum observation duration). We furthermore explored the relationship between the minimum observation duration and visitation rate, time of day and temperature. We found that the minimum observation duration (mean ± SD: 24 ± 11.9 min) was significantly related to visitation rate, where the observation time required to obtain accurate estimates decreased with increasing visitation rate. Minimum observation duration varied greatly between days and between fields but not within days. Within days, the visitation rates differed significantly only between the hour-intervals 06:00 h–07:00 h (lowest visitation rate) and 09:00 h–11:00 h (highest rate). Minimum observation duration decreased up to around 22 °C beyond which it remained fairly stable. Surprisingly, even after three day-long observations on the same plant we found new pollinator species visiting the flowers, suggesting that species-richness estimates based on plant observations alone probably underestimate true species richness. Because especially between-day variation in visitation rate on single plants can be large, reliable estimates of the pollinator visitation rate during the plant’s flowering time require observations on multiple days. Standardising the number of pollinators rather than the time to observe (standardised pollinator timing approach: time to n-pollinator visits) may provide more consistent accurate assessments of visitation rate, especially for studies that use gradients in visitation rates to examine the contribution of pollinators to crop pollination. |
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| Keywords: | Minimum observation duration Visitation rate Pollination Crop systems Observation protocol Time of day Weather Species richness |
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