The long history of human-mediated species introductions has resulted in a multitude of novel interactions around the globe. Many of these interactions have been to the detriment of native species. In New Zealand, the ship rat (Rattus rattus) is considered culpable for the rapid declines in the populations of numerous bird species. While seed masts have been implicated in rat population booms, alternative food resources, such as floral nectar, may play an underappreciated role in rat-bird interactions.
In many ecosystems food-web dynamics are driven by spatial and temporal variation in the availability of sugar resources, which form the primary or even exclusive dietary constituents for many species. Scale insects (Hemiptera) produce sugar-rich honeydew, which can be a keystone sugar source in honeydew ecosystems worldwide. In New Zealand, most previous research in honeydew ecosystems has been conducted in areas where herpetofauna are heavily suppressed by introduced predators. Consequently, little is known about potential trophic interactions between endemic lizards and scale insects.
We describe a simple gravimetric technique for measuring the standing crop or production of carbohydrate-rich solutions such as honeydew or nectar. Simulated honeydew was sampled by absorbing droplets of solutions of known concentration and volume with dried and weighed pieces of filter paper. The change in mass of the paper after redrying provides an estimate of the total solution carbohydrates. This method was compared with a widely-used technique, whereby the volume and concentration of droplets is measured with microcapillary tubes and a sugar refractometer.
The rapid decline in bumblebee populations within Europe has been linked to habitat loss through agricultural intensification, and a consequential reduction in the availability of preferred forage plants. The successful introduction of four European Bombus species to the South Island of New Zealand from England (in 1885 and 1906) provides an opportunity to determine how important different forage plants (also introduced from the U.K.) are to two severely threatened European bumblebee species (Bombus ruderatus and B. subterraneus).