The hairy–downy game revisited: an empirical test of the interspecific social dominance mimicry hypothesis

© 2018 The Association for the Study of Animal Behaviour. Understanding the emergence and persistence of convergent phenotypes is the subject of considerable debate. Species may converge on nearly identical phenotypes for a variety of reasons, including occupying similar environments, exhibiting similar foraging ecologies, and for signalling reasons such as mimicry. Interspecific social dominance mimicry (ISDM) is a hypothesis that states that socially subordinate species evolve a phenotype mimicking a dominant species so as to accrue resources and avoid aggression. A recently proposed test case for this phenomenon asserts that downy woodpeckers, Picoides pubescens, evolved mimetic plumage to avoid attacks from hairy woodpeckers, Picoides villosus. We examined this claim with a large behavioural data set collected by citizen scientists. We employed phylogenetic methods and simulations to test whether downy woodpeckers avoid aggression, and whether downy woodpeckers are more dominant than expected based on body mass. Contrary to the expectations of ISDM, we found that downy woodpeckers were markedly more often the target of hairy woodpecker attacks than expected based on their relative abundances. Our empirical data thus offers no support for the strict ISDM hypothesis as an explanation for downy–hairy woodpecker plumage convergence. However, downy woodpeckers are slightly more dominant than expected based on their body mass, albeit not significantly so. Our data therefore lend weight to previous suggestions that the benefits of mimicry potentially accrue from third-party species mistaking the mimic for the model, rather than the model mistaking the mimic for another model

Evidence for longitudinal migration by a “sedentary” Brazilian flycatcher, the Ash-throated Casiornis

The digitalization of museum collections and concurrent increase in citizen-scienceinitiatives is ushering in an era of unprecedented availability of primary biodiversity data. These changespermit a reappraisal of phenological patterns of tropical species. I examined spatio-temporal variation in thedistribution patterns of an ostensibly sedentary endemic Brazilian flycatcher, the Ash-throated Casiornis(Casiornis fuscus), using both specimen data from museums and sighting records and rich media data fromcitizen-science initiatives. I found compelling evidence for partial intratropical longitudinal migration toAmazonia and the Cerrado biomes from the species’ core range in the semi-desert Caatinga biome andadjacent ecotones. These records from outside of the Caatinga were distributed during the height of the dryseason from April to October, although the Caatinga is not entirely vacated at this time. This pattern ofpartial migration leads to a doubling of the distributional range of Ash-throated Casiornises and stronglysuggests that the species is a breeding near-endemic of the Caatinga biome. This pattern was potentiallypreviously not apparent because of significant biases in specimen collection between biomes, giving a falsesense of abundance in the Brazilian Amazon

On dendrograms, ordinations and functional spaces: Methodo-logical choices or pitfalls?

A number of concerns persist regarding (i) how functional spaces should be quantified, (ii) how phylogenetic richness should be calculated, (iii) and how functional beta diversity should be calculated. Because all current methods have their shortcomings we think that analytical choices are as much a matter of knowing the limitations of the data and knowing the working hypothesis. Only then can one follow their personal choice, weighing up the shortcomings of different methods that, at the end of the day, usually produce qualitatively similar results

Species interactions regulate the collapse of biodiversity and ecosystem function in tropical forest fragments

Competitive interactions among species with similar ecological niches are known to regulate the assembly of biological communities. However, it is not clear whether such forms of competition can predict the collapse of communities and associated shifts in ecosystem function in the face of environmental change. Here, we use phylogenetic and functional trait data to test whether communities of two ecologically important guilds of tropical birds (frugivores and insectivores) are structured by species interactions in a fragmented Amazonian forest landscape. In both guilds, we found that forest patch size, quality, and degree of isolation influence the phylogenetic and functional trait structure of communities, with small, degraded, or isolated forest patches having an increased signature of competition (i.e., phylogenetic and functional trait overdispersion in relation to null models). These results suggest that local extinctions in the context of fragmentation are nonrandom, with a consistent bias toward more densely occupied regions of niche space. We conclude that the loss of biodiversity in fragmented landscapes is mediated by niche-based competitive interactions among species, with potentially far-reaching implications for key ecosystem processes, including seed dispersal and plant damage by phytophagous insects

Avifauna of a structurally heterogenous forest landscape in the Serra dos Caiabis, Mato Grosso, Brazil: a preliminary assesment.

Apresentamos um levantamento preliminar da avifauna da Serra dos Caiabis do município de Alta Floresta, estado de Mato Grosso, Brasil. A região se localiza no extremo centro-norte do estado, na zona de contato entre duas biomas: as florestas húmidas da Amazônia e o cerrado do Brasil central. É caracterizada por solos arenosos de baixa qualidade e marcada por um grande mosaico vegetational rico e diverso, com campinaranas e campinas abertas e florestas altas nas bordas dos rios da formação geológica. A comunidade das aves na Serra dos Caiabis tem uma menor riqueza (362 espécies) em relação à comunidade bem conhecida das florestas húmidas de Alta Floresta, incluindo aves tanto de cerrados e campinaranas como florestais. Foram registradas extensões na ocorrência de algumas espécies e pelo menos duas adendas para Mato Grosso (Cyanocorax chrysops e Tangara varia). O preço da terra na região é baixo devido á qualidade dos solos, o que até recentemente impediu o desenvolvimento agrícola. Porém a região já está sob ameaça de desmatamento para uso agrícola, pois a maioria da terra em áreas vizinhas de Sinop e Alta Floresta está sendo explorada

Introductions do not compensate for functional and phylogenetic losses following extinctions in insular bird assemblages

The ratio of species extinctions to introductions has been comparable for many insular assemblages, suggesting that introductions could have ‘compensated’ for extinctions. However, the capacity for introduced species to replace ecological roles and evolutionary history lost following extinction is unclear. We investigated changes in bird functional and phylogenetic diversity in the wake of extinctions and introductions across a sample of 32 islands worldwide. We found that extinct and introduced species have comparable functional and phylogenetic alpha diversity. However, this was distributed at different positions in functional space and in the phylogeny, indicating a ‘false compensation’. Introduced and extinct species did not have equivalent functional roles nor belong to similar lineages. This makes it unlikely that novel island biotas composed of introduced taxa will be able to maintain ecological roles and represent the evolutionary histories of pre-disturbance assemblages and highlights the importance of evaluating changes in alpha and beta diversity concurrently

Longitudinal variation in O6-alkylguanine DNA-alkyltransferase activity in the human colon and rectum

In a systematic study of O6-alkylguanine DNA-alkyltransferase activity in the human colon and rectum, tumours were found to occur in regions of low activity. These results are consistent with the hypothesis that O6-alkylguanine DNA-alkyltransferase levels and alkylating agent exposure may be important determinants of large bowel tumorigenesis

Using avian functional traits to assess the impact of land-cover change on ecosystem processes linked to resilience in tropical forests

Vertebrates perform key roles in ecosystem processes via trophic interactions with plants and insects, but the response of these interactions to environmental change is difficult to quantify in complex systems, such as tropical forests. Here, we use the functional trait structure of Amazonian forest bird assemblages to explore the impacts of land-cover change on two ecosystem processes: seed dispersal and insect predation. We show that trait structure in assemblages of frugivorous and insectivorous birds remained stable after primary forests were subjected to logging and fire events, but that further intensification of human land use substantially reduced the functional diversity and dispersion of traits, and resulted in communities that occupied a different region of trait space. These effects were only partially reversed in regenerating secondary forests. Our findings suggest that local extinctions caused by the loss and degradation of tropical forest are non-random with respect to functional traits, thus disrupting the network of trophic interactions regulating seed dispersal by forest birds and herbivory by insects, with important implications for the structure and resilience of human-modified tropical forests. Furthermore, our results illustrate how quantitative functional traits for specific guilds can provide a range of metrics for estimating the contribution of biodiversity to ecosystem processes, and the response of such processes to land-cover change