Deforestation weakens social mutualism in Amazonian avian mixed-species flocks

Data from almost 1000 hours of observation reveal the detrimental effects of deforestation on non-trophic interspecies interactions among avian mixed-species flocks. 

Cinereous antshrike is the core of Amazonian avian mixed-species flocks – they rally individuals of other species and perform alarm calls. Photo by Letícia Soares.

Cinereous antshrike is the core of Amazonian avian mixed-species flocks – they rally individuals of other species and perform alarm calls. Photo by Letícia Soares.

Birds that form mixed-species flocks benefit from high efficiency on finding food and avoiding predation. Hence, avian mixed-flocks are cohesive social groups, and the evolutionary success of within-flock interactions is based on the idea that ‘those who remain together thrive together’. In the Amazon forest, flocks are usually composed by 8-10 different insectivorous species that can be represented by a single individual, a mated pair or a family group. Species may present distinguished roles in the flock, and the most remarkable role is played by the Cinereous antshrike (Thamnomanes caesius) that performs alarm calls, as well as calls to gather individuals to flock. This mutualism also thought to contribute to increase local species diversity, since closely related species will more likely  be members of different flocks.

 

Avian mixed-species flocks are cohesive social groups, in which individuals benefit from enhanced high efficiency on finding food and avoiding predation. This figure depicts the network of interaction in a Amazonian mixed flock, with cinereous antshrike in the center, as the core species in the flock.

This figure depicts the network of interaction in an Amazonian mixed-species flock, with cinereous antshrike in the center, as the core species in the flock. Figure by Karl Mokross.

The beauty of this mutualism, and its usefulness in maintaining species diversity are being threatened by deforestation. In a study published last month in Proc B, Mokross & colleagues use network analysis to show that the cohesion and stability of Amazonian avian mixed-flocks are dramatically affected by deforestation. Flocks from small forest fragments and degraded forest patches not only have fewer species, but also present weaker associations, when these are present at all. The study highlights how the structure of ecological communities can be dramatically affected by non-trophic species interactions, and provides the alarming proof of how detrimental deforestation is for such network.

 

“The flocks completely disappeared from the deforested areas. The craziness about this is that even later on, after 30 years of forest regeneration, the interactions remain weak. In other words, there are flocks, but the species spend less time together.” – Karl Mokross

 

Example of networks and habitat configurations for three flocks found in primary forest, 10 ha fragment and secondary forest habitat types in the Brazilian Amazon. Differences in network structure reflect the decay of interspecific interactions in mixed-species flocks across a disturbance gradient. Edge thickness and transparency in each network are proportional to numbers of interactions. Interaction values at the lowest 10% are set to transparent. Nodes sizes are proportional to flock attendance.Figure and adapted caption from Mokross et al, 2014.

Example of networks and habitat configurations for three flocks found in primary forest, 10 ha fragment and secondary forest habitat types in the Brazilian Amazon. Differences in network structure reflect the decay of interspecific interactions in mixed-species flocks across a disturbance gradient. Edge thickness and transparency in each network are proportional to numbers of interactions. Interaction values at the lowest 10% are set to transparent. Nodes sizes are proportional to flock attendance. Figure and adapted caption from Mokross et al, 2014.

Karl Mokross, Thomas B. Ryder, Marina Corrêa Côrtes, Jared D. Wolfe, and Philip C Stouffer. Decay of interspecific avian flock networks along a disturbance gradient in Amazonia. Proc R Soc B 2013 281: 20132599

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