Time-optimized path choice in the termite-hunting ant Megaponera analis.

Trail network systems among ants have received a lot of scientific attention because of their various applications in problem solving of networks. Recent studies have shown that ants select the fastest available path when facing different velocities on different substrates, rather than the shortest distance. The progress of decision making by these ants is determined by pheromone-based maintenance of paths, which is a collective decision. However, path optimization through individual decision making remains mostly unexplored. Here, we present the first study of time-optimized path selection via individual decision making by scout ants. Megaponera analis scouts search for termite-foraging sites and lead highly organized raid columns to them. The path of the scout determines the path of the column. Through installation of artificial roads around M. analis nests, we were able to influence the pathway choice of the raids. After road installation, 59% of all recorded raids took place completely or partly on the road, instead of the direct, i.e. distance-optimized, path through grass from the nest to the termites. The raid velocity on the road was more than double that on the grass, and the detour thus saved 34.77±23.01% of the travel time compared with a hypothetical direct path. The pathway choice of the ants was similar to a mathematical model of least time, allowing us to hypothesize the underlying mechanisms regulating the behavior. Our results highlight the importance of individual decision making in the foraging behavior of ants and show a new procedure of pathway optimization

Foraging of a hypogaeic army ant: a long neglected majority

Army ants have been studied thoroughly for more than a century. The conduction of column and swarm mass raids, featured by epigacicly active species, is believed to be a central characteristic of army ant behavior. Most army ant species, however, lead a hypogaeic life. Due to the difficulties to observe them, nothing is known about their hypogacic behavior in the field. Using palm oil baits, trail excavations, and laboratory observations, the hypogaeic foraging of Dorylus (Dichthadia) laevigatus was observed in Malaysia. D. laevigatus was found to construct stable hypogaeic trunk trail systems providing quick and easy access to all parts of its foraging area. Small column raids were conducted throughout the ground stratum and above the ground surface. These raids were caste specific, with the smallest workers predominantly following existing cracks and tunnels in the soil. In case of food location, larger workers were recruited from nearby trunk trails. Exploratory trails leading to prey had to be widened before larger workers could gain access and help to process the food. Bulky food sources such as baits or termite mounds could be exploited over several weeks to months. Besides raiding in columns, D. laevigatus came occasionally to the ground surface at night to conduct swarm raids. This combination of swarm and column raids with the use of trunk trails has never been demonstrated for a classical army ant species. The omnipresence of D. laevigatus within its foraging area stands in sharp contrast to epigaeicly active species, characterized by a very localized and temporary presence at foraging sites. D. laevigatus stayed in the same foraging area for several weeks to months. Having a broad diet and the ability to exploit bulky food sources over long periods of time, D. laevigatus seems to follow a sustainable use of the soil fauna. Summing up these particularities demonstrates a remarkable divergence of the hypogacic foraging of D. laevigatus from that of epigacicly foraging army ant species

Exploratories for large-scale and long-term functional biodiversity research

Current changes in biodiversity and their functional consequences for ecosystem processes matter for both fundamental and applied reasons. In most places the most important anthropogenic determinant of biodiversity is land use. The effects of type and intensity of land use are modulated by climate and atmospheric change, nutrient deposition and pollution and by feedback effects of changed biological processes. However, it is not known whether the genetic and species diversity of different taxa responds to land-use change in similar ways. Moreover, consequences of changing diversity for ecosystem processes have almost exclusively been studied in model experiments of limited scope. Clearly, there is an urgent scientific and societal demand to investigate the relationships between land use, biodiversity and ecosystem processes in many replicate study sites in the context of actual landscapes. Furthermore, these studies need to be set up in long-term frameworks. Moreover, because monitoring and comparative observation cannot unravel causal mechanisms they need to be complemented by manipulative experiments. In the ‘Exploratories for large-scale and long-term functional biodiversity research’ (see http://www.biodiversity-exploratories.de), we provide a platform for such successful long-term biodiversity research. The biodiversity exploratories aim at contributing to a better understanding of causal relationships affecting diversity patterns and their change, developing applied measures in order to mitigate loss of diversity and functionality, integrating a strong research community to its full potential, training a new generation of biodiversity explorers, extending the integrated view of functional biodiversity research to society and stimulating long-term ecological research in Germany and globally. Our experience has several implications for long-term ecological research and the LTER network including the necessity of formulating common research questions, establishing a joint database, applying modern tools for meta-analysis or quantitative review and developing standardised experimental and measurement protocols for facilitating future data synthesis