Occurrence of bees along grazing and agricultural gradients in Northern Tanzania

Study Extent

The study was carried out in a set of study sites established in agricultural (transformed), grazing (degraded) and natural savannah (conserved) lands to represent different land-use categories.   

Sampling

Data were collected in 40 study sites distributed along grazing and agricultural gradients in the study area intermittently from August to December 2018. Study sites were pre-selected using remote sensing techniques in the Google Earth Engine (GEE), followed by ground-truthing to confirm the sites basing on the level of land use and vegetation cover. A paired patch study design was adopted in each site whereby two 50 x 50 m plots were established for bee sampling. The two plots were placed at an interval of 300 m in the opposite direction and a GPS coordinate of each site was recorded at the midpoint between the two plots using a hand-held device (Garmin; GPSMAP64s, Garmin Ltd, Taiwan). We sampled bees using a combination of pan traps and sweep-netting techniques which have successfully been used for sampling bees in the Kilimanjaro region and other parts of the world. In each plot, four UV-reflecting pan trap clusters (each with yellow, white, and blue) traps were set and left in the field for 48 hours. To increase the chances of collecting bees foraging on shrubs in each plot, we installed two clusters with a 120 cm pole and the remaining two had a 35 cm pole for capturing bees foraging herbaceous plants. The traps were consistently checked for captures at 8:00 am and 16:00 pm everyday. The total trapping effort was 1,152 hours per site. We also conducted a transect walk with sweep nets to sample bee faunal whereby, two researchers were actively collecting bees for two hours per site. This method summed to a sampling effort of 4 man-hours per study site.

Quality Control

Bees data collected from each study site were enriched with other information such as location (coordinates and elevation) and habitat type. The coordinates and elevation of localities were derived from a hand-held Garmin GPS (Model: GPSMAP64s; resolution ±3 m; Garmin Ltd, Taiwan). Also, for each study site, information on weather parameters (temperature and precipitation) and forage resources were recorded. The specimens collected were preserved in 70% ethanol before they were dried, pinned, and later identified by bee taxonomists. The reference bee collections are available at the College of African Wildlife Management, Mweka.

Method steps

1. As per the description provided in the sections on geographic coverage, temporal coverage, project data and sampling methods

Data on bee occurrence were collected from Northern Tanzania in Kilimanjaro, Arusha and Manyara regions. The study regions are located between latitude 3°30’ S and 4°45’ S and longitude 4°30' E to 5°45’ E. The study areas have two rainy seasons: a long rainy season which starts from March to May, and a short rainy season in November and December. Average annual rainfall ranges geographically between 1300 mm and 2400 mm. The annual mean maximum temperature (hottest season) is 25.4 °C between July and September, and the minimum temperature (cold season) is 12.8°C between May and June.