Luís Reino

Introduced alien species are associated with lower taxonomic, functional and phylogenetic diversity of native communities and negative impacts on ecosystem functioning. This is particularly evident in habitats where human disturbance may favour alien species, posing an additional stressor on native communities. Following the community resistance hypothesis (higher diversity promotes higher resistance to invasion), we predicted: 1) higher taxonomic, functional and phylogenetic diversity (TD, FD and PD respectively) in non‐invaded bird communities (i.e. no alien bird species); and 2) higher diversity and resistance to invasion in less human‐disturbed areas. We surveyed bird communities in a modified Mediterranean landscape subject to varying levels of human disturbance. We tested whether TD, FD and PD were significantly different between non‐invaded and invaded bird communities, and assessed the effect of land classes (forest, agriculture, urban), landscape composition and heterogeneity on these metrics. We found that non‐invaded communities retained higher TD and FD, but not PD, than invaded communities. Alien birds occupied marginal niches in invaded communities, and did not fully compensate for the taxonomic and functional diversity loss caused by the absence of native species. These results were consistent across different land classes, suggesting weak environmental filtering of communities. Generally, less human‐modified and more heterogeneous areas supported higher TD regardless of the presence of alien species. FD and PD of invaded communities decreased with increases in human‐modified areas, whereas non‐invaded communities were not affected. Our results suggest that even within a human‐modified landscape, invaded community diversity is more affected by, and thus has a lower resilience to, disturbance. Restoring and protecting natural habitats within human‐modified landscapes is likely to increase the resilience of native species.

Morphology, habitat and various selective pressures (e.g. social and sexual selection) can influence the evolution of acoustic signals, but the relative importance of their effects is not well understood. The order Psittaciformes (parrots, sensu lato ) is a large clade of very vocal and often gregarious species for which large‐scale comparative studies of vocalizations are lacking. We measured acoustic traits (duration, sound frequency, frequency bandwidth and sound entropy) of the predominant call type for >200 parrot species to test: (1) for associations with body size; (2) the acoustic adaptation hypothesis (AAH) (predicting differences between forest and open‐habitat species); (3) the social complexity hypothesis (predicting more complex calls in gregarious species) and (4) influences of sexual selection (predicting correlated evolution with colour ornamentation). Larger species had on average longer calls, lower sound frequency and wider frequency bandwidth. These associations with body size are all predicted by physical principles of sound production. We found no evidence for the acoustic adaptation and social complexity hypotheses, but perhaps social complexity is associated with vocal traits not studied here, such as call repertoire sizes. More sexually dichromatic species had on average simpler calls (shorter, with lower entropy and narrower frequency bandwidth) indicating an influence of sexual selection, namely an evolutionary negative correlation between colour ornamentation and elaborate acoustic signals, as predicted by the transference hypothesis. Our study is the first large‐scale attempt at understanding acoustic diversity across the Psittaciformes, and indicates that body size and sexual selection influenced the evolution of species differences in vocal signals.