Interaction networks of avian mixed‐species flocks along elevation in the tropical Andes

Abstract

Ecological communities are comprised of species that interact with each other and those interactions ultimately generate community structure. Network theory provides a useful framework to study communities, by simultaneously considering species composition and the interactions among species. In this study, I use mixed-species flocks as model systems to gain insights on community and network structure. Specifically, I use co-occurrence network analyses to explore if avian mixed-species flocks change in richness and composition and/or in network structure and pair-wise associations, across elevations in the tropical Andes of Bolivia. Networks of flocking species changed both in composition and in the frequency and realization of pair-wise interactions across elevations, but changes in pair-wise associations explained most of network turnover along elevation. Pair-wise interactions changed rapidly, with shared species changing in position and importance within the network. Network dissimilarity was mostly explained by changes in the nature of associations rather than by differences in composition. Altogether, results show that montane mixed-species flocks are composed of loosely connected species and that most species have the potential of switching associations, often increasing in association strength at high elevations (up to 3150 m). Networks increased in connectivity and cohesion with elevation; flocks in lower elevations had more connections and these were less even. Above 3150 m a.s.l., there was rapid decay suggesting that flocks above this critical point are less connected and cohesive. This study exemplifies how combining community, network and pair-wise analyses can provide a more holistic view on the responses of species and assemblages to environmental gradients.

Ecological drivers of avian community assembly along a tropical elevation gradient

“…Code and data used for analyses are available from the Dryad Digital Repository (and in Supporting information) <http://dx.doi.org/10.5061/dryad.fxpnvx0qj> (Montaño‐Centellas et al 2020b).…”

Habitat alteration modifies the structure and function of mixed‐species flocks in an Andean landscape

“…We also found that the identity of species participating in flocks can be influenced by vegetation structure and the presence of exotic trees. Changes in species composition of flocks related to land‐use change have been described in multiple ecosystems (Brandt et al, 2009; Jones & Robinson, 2020; Montaño‐Centellas, 2020; Thomson & Ferguson, 2007). In our study, the variation in species composition among flocks was driven by differences in habitat affinities of a small number of the flocking species.…”

“…The interaction networks were constructed using the “group gambit” method (Franks et al, 2010), which defines all the individuals of a group of animals observed at any given time as associated (Whitehead & Dufault, 1999). This method assumes interactions among all the species that were part of a flock and is a common method employed in networks of mixed‐species flocks (Mokross et al, 2014; Montaño‐Centellas, 2020; Zhou et al, 2019). To build weighted networks, we used the frequency of co‐occurrence of species in flocks within a transect during each sampling period.…”

“…Traditionally, studies on mixed‐species flocks have focused on describing the response of flock structural parameters (i.e., richness, abundance, and composition) to environmental gradients; however, species within flocks are part of functional interactions that can be better studied using network analysis tools (Farine et al, 2012; Mammides et al, 2018; Mokross et al, 2014; Montaño‐Centellas, 2020; Wey et al, 2008). In mixed‐species flock networks, species are treated as nodes, and the connections among species are links based on species co‐occurrences (Farine & Whitehead, 2015; Kay et al, 2018).…”

“…For instance, the exchange of information is a currency that results in increased fitness gains among members of mixed‐species flocks (Sridhar et al, 2009); thus, any disruption in the flow of information among flock members will ultimately alter flock stability. Network metrics give insight into the flow of information in networks by measuring connectivity levels among interacting members and thus characterize the stability of mixed‐species flocks and their responses to environmental change (Goodale et al, 2010; Mokross et al, 2014; Montaño‐Centellas, 2020).…”