by Carl Strang
Soon we’ll have flowers blooming and bees buzzing. Here are some studies of interactions between plants and their insect pollinators from last year:
Burkle, Laura A., John C. Marlin, and Tiffany M. Knight. 2013. Plant-pollinator interactions over 120 years: loss of species, co-occurrence, and function. Science 339:1611-1615. They studied forest understory pollinators around Carlinville, IL, not far from St. Louis, comparing present-day species to those documented by a researcher in the late 1800’s. They found that 50% of bee species have gone extinct there. Changes have included the conversion of most forest and prairie land to agriculture, and an increase of 2°C in spring and fall temperatures which has resulted in phenological mismatches. Focusing on the interactions of forest floor forbs and bees, they found that only 24% of the original interactions had survived, though this was compensated in part by new ones, “such that the absolute difference of interactions lost was 46%.” All 26 species of forbs have persisted. The lost bees were predominantly specialists, parasites, cavity-nesters and those whose interactions with the plants were weak because of limited phenological overlap. They found a reduction in pollinator visits per flower, and expressed concern about this, about the loss of stabilizing redundancy in the entire network, and the continued weakening of phenology matches.
Rasmussen, C, et al. 2013. Strong impact of temporal resolution on the structure of an ecological network. PLoS ONE 8(12): e81694. doi:10.1371/journal.pone.0081694 They looked at day-to-day changes in pollinator-plant connections in a Greenland tundra ecosystem, and compared them to the season-wide summary typical of past studies. They found that the difference is significant. Many indirect links between species that had been implied by the static network proved to be impossible in the dynamical ones because the species are active at different points in the season. The nature of generalist vs. specialist species also becomes transformed because of the limited phenological availabilities of the various species. Their methods involved a focus on a 500m x 500m study area, with randomly selected plants (or 5x5cm clusters where individual plants were difficult to separate), observed for 40-minute intervals.
Eggs, B., and D. Sanders 2013. Herbivory in spiders: the importance of pollen for orb-weavers. PLoS ONE 8(11): e82637. doi:10.1371/journal.pone.0082637 They looked at the diets of juveniles in two species of orb-weavers, and found that pollen, ingested when the spiders recycled their webs, made up 25% of their diet. Flying insects (flies and hymenoptera) made up most of the rest. The pollen ingestion was not incidental, as the spiders deliberately use an external digestive process to consume pollen grains too large to be eaten without such treatment. They regard these spiders as omnivores rather than carnivores.
Clarke, Dominic, Heather Whitney, Gregory Sutton, and Daniel Robert. 2013. Detection and learning of floral electric fields by bumblebees. Science 340:66-69. They showed experimentally that bumblebees can read electrical information from flowers. The bees themselves transfer electrons that quickly can change flowers’ electrical fields, so that bees can read which flowers have or have not been visited recently by others. Intrinsic electrical qualities also can be added to color and shape to help bees identify flower species and suitability for visits.