Fighting over food unites the birds of North America in a continental dominance hierarchy

Abstract

The study of aggressive interactions between species has, to date, usually been restricted to interactions among small numbers of ecologically close competitors. Nothing is known about interspecific dominance hierarchies that include numerous, ecologically varied species. Such hierarchies are of interest because they could be used to address a variety of research questions, e.g. do similarly ranked species tend to avoid each other in time orspace, and what will happen when such species come into contact as climates change?Here, we propose a method for creating a continental-scale hierarchy, and we make initial analyses based on this hierarchy. We quantified the extent to which a dominance hierarchy of feeder birds was linear, as intransitivities can promote local species' coexistence. Using the existing network of citizen scientists participating in Project FeederWatch, we collected the data with which to create a continent-spanning interspecific dominance hierarchy that included species that do not currently have overlapping geographic distributions. Overall, the hierarchy was nearly linear, and largely predicted by body mass, although there were clade-specific deviations from the average mass-dominance relationship. Most of the small number of intransitive relationships in the hierarchy were based on small samples of observations. Few observations were made of interactions between close relatives and ecological competitors like Melanerpes woodpeckers and chickadees, as such species often have only marginally overlapping geographic distributions. Yet, these species' ranksemergent properties of the interaction network-were usually in agreement with published literature on dominance relationships between them.

Urban Bird Feeders Dominated by a Few Species and Individuals

“…Body size frequently determines, or contributes to, the development of dominance hierarchies, outcomes of agonistic interactions, and subsequent resource access (Forrester, 1991;Wojczulanis-Jakubas et al, 2015;Miller et al, 2017). However, there were no obvious patterns in the species co-occurrence matrix to indicate that negative associations were more common between species closest in body size, or that positive associations were more common between species of greater size disparity.…”

Everything you always wanted to know about intransitive competition but were afraid to ask

“…() also show that intransitivity is related to the functional traits not only of the target species but also of those with which it is competing (see also Kunstler et al., ). Interestingly, clear relationships between functional traits and competitive dominance have been observed in a number of taxa when competition is hierarchical (Kunstler et al., ; LeBrun, ; Liouw, Di Martino, Voje, Rust, & Taylor, ; Miller et al., ), but a study in this issue suggests that these relationships may dampen when competition is intransitive (Soliveres et al., ). This opens the question of whether cases where traits fail to predict competitive ability could be indicators of intransitive competition.…”

“…Among these species‐specific traits, mobile organisms seem less likely to compete intransitively than sessile ones (Reichenbach, Mobilia, & Frey, ). Evidence for this idea is mostly indirect, with studies on mobile taxa including protists (Carrara, Giometto, Seymour, Rinaldo, & Altermatt, ), ants (LeBrun, ), flies (Ulrich et al., ), fish (Henriksson et al., ) and birds (Miller et al., ) showing competition to be strongly hierarchical, whereas studies on sessile organisms more often show intransitive competition (Bowker et al., ; Buss, ; Dormann, ; Soliveres et al., ). However, it is easy to find evidence against this apparently general pattern, as shown by the first multi‐taxa experiment testing this notion, published in this issue (Soliveres et al., ).…”

“…Evidence for this idea is mostly indirect, with studies on mobile taxa including protists (Carrara, Giometto, Seymour, Rinaldo, & Altermatt, 2015), ants (LeBrun, 2005), flies (Ulrich et al, 2014), fish (Henriksson et al, 2016) and birds (Miller et al, 2017) showing competition to be strongly hierarchical, whereas studies on sessile organisms more often show intransitive competition (Bowker et al, 2010;Buss, 1980;Dormann, 2007;Soliveres et al, 2015). However, it is easy to find evidence against this apparently general pattern, as shown by the TA B L E 1 Summary of the research gaps and generalities that can be drawn from the contributions in this special issue and those of previous literature on intransitive competition…”

Citizen science and wildlife biology: Synergies and challenges

“…Such observations are probably easier to perform and more reliable than those including the identification of specific behaviours such as patterns of vigilance or agonistic encounters. However, a recent study relied on citizen scientists to record interactions between birds of different species to determine hierarchies or social networks in groups (Miller et al., ). The number of such projects is increasing, which mirrors a growing interest of behavioural scientists in CS and citizens in participating in behavioural research (Hecht & Cooper, ; Stewart et al., ; Williams, Porter, Hart, & Goodenough, ).…”