Ambient UV radiation has substantially increased during the last decades, but its impact on marine benthic communities is hardly known. The aim of this study was to globally compare and quantify how shallow hard-bottom communities are affected by UV during early succession. Identical field experiments in 10 different coastal regions of both hemispheres produced a consistent but unexpected pattern: (i) UV radiation affected species diversity and community biomass in a very similar manner, (ii) diversity and biomass were reduced to a larger extent by UVA than UVB radiation, (iii) ambient UV levels did not affect the composition of the communities, and (iv) any UV effects disappeared during species succession after 2-3 months. Thus, current levels of UV radiation seem to have small, predictable, and transient effects on shallow marine hardbottom communities.

Oviposition preference is considered to be one of the most important factors behind patterns of host use among herbivorous insects. However, preference is defined as host plant choice under equal host abundance and availability, and it is likely that frequency-dependent effects will alter the actual pattern of host use beyond what preference trials reveals. The effects of such alterations are poorly known but could be important for the understanding of specialization and host shifts. We investigated how changes in frequency of a preferred and a less preferred host affected movement patterns and egg deposition within and among patches in a polyphagous butterfly, Polygonia c-album. Two experiments were carried out in large (8 · 30 m) outdoor cages, artificially divided into distinct patches with different frequencies of the two hosts: one that allowed for limited movement between patches and one that did not. There was a clear effect of frequency on patch selection; females spent more time in and laid more eggs in patches with a high frequency of the preferred host, which will potentially have a large effect on host use by modifying encounter rates in favor of the preferred host. However, there was no significant frequency-dependent plant choice within patches in any experiment. Instead, results indicate that females are distributing their eggs among plants species according to specific likelihoods of oviposition, independent of encounter rates, which is compatible with a strategy of risk-spreading.

While the reasons for the prevalence of specialists over generalists among herbivorous insects have been at the focus of much interest, less effort has been put into understanding the polyphagous exceptions. Recent studies have suggested that these exceptions may be important for insect diversification, which calls for a better understanding of the potential factors that can lead to an increased host plant repertoire. Females of the Nymphalid butterfly, Polygonia c-album, were used to test if egg output and/or likelihood of finding a host increased with the addition of a secondary host. There was no effect of prior eggs on the host for willingness to oviposit on a plant. The main experiments were conducted both in small laboratory cages and in large outdoor experimental arenas. No positive effect was found when another oviposition target was added in small cages in the laboratory. On the other hand, in the outdoor arenas the females more often found a host to oviposit on and had a higher egg output when they had access to an additional host, even though the second host was lower in their preference hierarchy. The difference between these experiments was attributed to searching for acceptable host plants within a patch, a factor that was included in the large cages but not in the small. When host availability is limited, adding oviposition targets can potentially act to counterbalance specialization and thus favor the evolution of generalization.