Does urbanization explain differences in interactions between an insect herbivore and its natural enemies and mutualists?

Urbanization can alter the composition of arthropod communities. However, little is known about how urbanization affects ecological interactions. Using experimental colonies of the black bean aphid Aphis fabae Scopoli reared on Vicia faba L, we asked if patterns of predator-prey, host-parasitoid and ant-aphid mutualisms varied along an urbanization gradient across a large town in southern England. We recorded the presence of naturally occurring predators, parasitoid wasps and mutualistic ants together with aphid abundance. We examined how biotic (green areas and plant richness) and abiotic features (impervious surfaces and distance to town center) affected (1) aphid colony size, (2) the likelihood of finding predators, mutualistic ants and aphid mummies (indicating the presence of parasitoids), and (3) how the interplay among these factors affected patterns of parasitoid attack, predator abundance, mutualistic interactions and aphid abundance. The best model to predict aphid abundance was the number of mutualistic ants attending the colonies. Aphid predators responded negatively to both the proportion of impervious surfaces and to the number of mutualistic ants farming the colonies, and positively to aphid population size, whereas parasitized aphids were found in colonies with higher numbers of aphids and ants. The number of mutualistic ants attending was positively associated with aphid colony size and negatively with the number of aphid predators. Our findings suggest that for insect-natural enemy interactions, urbanization may affect some groups, while not influencing others, and that local effects (mutualists, host plant presence) will also be key determinants of how urban ecological communities are formed

Possible origin of aliphatic moieties in humic substances

2 pages, 11 figures, 1 table, 60 references.Various hypotheses have been put forward concerning the origin of aliphatic moieties in humic substances. In this paper we consider the possibility of a direct contribution of various classes of aliphatic moieties, occurring in extant organisms, to humic substances. On the basis of their resistance against chemical and biological degradation, it is speculated that recently discovered insoluble, non-hydrolyzable aliphatic biopolymers in algal cell walls and the protective layers of higher terrestrial plants are, via a mechanism of selective preservation, major precursors of aliphatic moieties in humic substances.This work was supported by the Netherlands Foundation for Earth Science Research (AWON) with financial aid from the Netherlands Organization for Scientific Research (NWO), and the C.S.I.C. and C.A.I.C.Y.T., Spain (project 781).Peer reviewe