Aim: On islands, species richness is reduced and interspecific competition relaxed in relation to the mainland, allowing species to use broader ecological niches. These factors are known to affect diet and morphology, but can also affect communication and acoustic signalling in particular. However, no study has ever compared insular and continental soundscapes to determine to which extent islands present reduced acoustic richness (number of co-vocalizing species) and fewer constraints for vocalizing species.Location: São Tomé Island, Mount Cameroon, Madeira Island, Southern France.Taxon: Birds. Methods:We compared two pairs of insular and continental soundscapes: one in a temperate zone, the other in the tropics. We recorded sounds produced in similar types of primary forests and measured acoustic richness and ambient noise profiles.We then assessed acoustic niche organization by computing, for each community, species turnover, temporal and frequency overlaps, and acoustic avoidance. Results:We found fewer species co-vocalizing on islands compared to mainland and in temperate compared to tropical region. Ambient noise was louder in the tropics and occupied a wider frequency range, especially on the mainland, thereby revealing a reduction in available acoustic space for tropical mainland birds. In this more crowded and noisy soundscape, species presented a higher acoustic turnover, overlapped less in time and in frequency with each other and acoustically avoided each other more when compared to the three other communities.Main conclusions: Soundscapes differed and imposed fewer constraints on vocalizing species along the species diversity gradient from tropical mainland to temperate island. Acoustic niche partitioning increased with species richness and was associated with increased levels of acoustic interference. Results set a scene for an effect of relaxed competition on song evolution on islands, especially in the tropics.

When they detect a predator, many species emit antipredator vocalizations. In some cases, they emit mobbing calls, which are associated with the caller approaching and harassing the predator while attracting others to join it. Surprisingly, although mobbing has been widely reported in adults of numerous species, there has been no test of the role of learning in mobbing call recognition, especially during ontogeny. Here, we exposed wild great tit (Parus major) nestlings to playbacks of an unthreatening, novel sound either associated with conspecific mobbing calls (experimental treatment) or with another unthreatening novel sound (control treatment). We then tested them as nestlings and fledglings to see how responses to the novel sound compared to conspecific mobbing calls. Results revealed that fledglings in the experimental treatment behaved similarly to conspecific mobbing calls and the novel sound associated with conspecific mobbing calls. Because mobbing efficiency is often linked to interspecific communication, associative learning should be used by heterospecifics as a mobbing calls recognition mechanism. Regardless of treatment during the nestling phase, fledglings always were sensitive to the playback of conspecific mobbing calls.However, fledglings from the control group were more likely to approach the loudspeaker than those from the experimental group when mobbing calls were played, suggesting that overexposure during the nestling phase altered mobbing learning. Overall, these results suggest that learning could play a role in the recognition of calls, like heterospecific mobbing calls, when paired with conspecific mobbing, and that mobbing is perceived as a threatening stimulus from a very young age.

Photoperiod is a major factor regulating biological rhythms in animals and plants. At low latitudes, annual variation in daylength is low and species are expected to strongly rely on photic cues to reset their circadian clocks. A corollary is that individuals should be strongly affected by sudden changes in the photic regime as those generated by artificial light at night (ALAN). We tested this hypothesis in an anuran in Costa Rica (10°N). Using an outdoor experimental design, we exposed adult cane toads Rhinella marina, a broadly distributed tropical anuran species to two ALAN intensities (0.04 and 5 lx). Locomotor activity was reduced at the lowest intensity, and the activity pattern shifted from crepuscular to nocturnal. Contrary to humans and mice in which ALAN favor obesity, toads from the two exposed groups did not gain mass whereas controls did. Corticosterone was reduced at the highest intensity, a possible consequence of the reduced activity of toads or the altered regulation of their circadian pattern. Thus, the behavioral and physiological disruption that we observed supports the hypothesis of the strong reliance on photic cues to regulate circadian rhythms and control homeostasis in this intertropical anuran. Furthermore, our results suggest that the negative effects of ALAN on physiology, in particular body mass regulation, may differ between vertebrate groups, thus preventing anticipated generalization before more comparative studies have been carried out. We stress the importance of considering the impact of the changing nocturnal environment in the intertropical zone which host the largest fraction of biodiversity.

Secondary dispersal of terrestrial plant species through watercourses increases the dispersal range of floating seeds but their exposure to water may also challenge their viability and colonisation potential. Many terrestrial invasive species benefit from watercourses to extend their invasive range because water exposure can favour seed germination and early survival of seedlings for species sensitive to dry conditions and water flow enhances their dispersal distance downstream. Floatability, germination rate and survival after water exposure are seed traits involved in water dispersal and their variability may lead to different dispersal strategies. To address the question of the variability of achene traits involved in dispersal, we experimentally measured these three traits for Fallopia × bohemica achenes collected from 10 different stands. The floatability of achenes varied between stands from 2.5 to 5 days and their germination in water extended this period to 20 days through the emergence of floating seedlings. Germination proportions also differed between stands from 0.3 to 0.95 and were negatively related to the median germination time. Seedling survival after planting in soil was affected by their exposure time. This effect differed between stands, but a short germination time did not explain a better survival of some stands. These results show that achenes may differ in their dispersal potential in terms of floatability, as well as tolerance of seedlings to water exposure during dispersal. This study also highlights the fact that achenes of some stands present a combination of traits particularly adapted to long distance dispersal through watercourses, which can contribute to the extension of the invaded area.