Gardening in the desert changes bee communities and pollination network characteristics

Conversion of natural habitats to human settlements creates an alternative habitat with different bio-physical characteristics such as micro-climatic conditions and resource availability. Deserts are especially sensitive to such effects due to generally low nutrient levels and water availability. Gardens in human settlements in the desert are often a main source of alien plant species that provide ample foraging resources year round. These changes in floral composition and availability may alter pollinator community composition and foraging behaviour, as well as pollination network characteristics. We investigated the effects of desert gardening on pollinator communities and pollination networks in the Jordan Rift Valley (Israel), an arid agro-natural landscape south of the Dead Sea. We studied seasonal diversity patterns of plants and wild bees in natural habitats and in gardens in settlements. Wild bees and blooming plants were sampled from February to July in 2007 and in 2008. We constructed plant pollinator networks and compared bee communities between the two habitat types along the season. We found that bee abundance was greater in the gardens, and that rarefied bee species richness was greater in the natural habitat. Bee species richness and abundance exhibited contrasting seasonal patterns between habitats. Bee community composition also differed greatly between habitats, and species in the gardens had a generally wider geographical range in comparison to species in the natural habitat. We also found a higher level of generalisation of the pollination network in the gardens compared to the natural habitat, which may indicate a response to a disturbed and unstable environment. We conclude that gardening in deserts although promoting overall bee abundance, negatively affects species richness and changes community composition and network characteristics, with possible implications on the composition of native flora in the natural habitat surrounding the gardens.