Functional similarity affects similarity in partner composition in flea-mammal networks

Abstract

Functional signal in an interaction network is a phenomenon in which species resembling each other in their traits interact with similar partners. We tested the functional signal concept in realm-specific and regional flea-host networks from four biogeographic realms and asked whether the species composition of (a) host spectra and (b) flea assemblages is similar between functionally similar flea and host species, respectively. Analogously to testing for phylogenetic signal, we applied Mantel tests to investigate the correlation between flea or host functional distances calculated from functional dendrograms and dissimilarities in sets of interacting partners. In all realm-specific networks, functionally similar fleas tended to exploit similar hosts often belonging to the same genus, whereas functionally similar hosts tended to harbour similar fleas, again often belonging to the same genus. The strength of realm-specific functional signals and the frequency of detecting a significant functional signal in the regional networks differed between realms. The frequency of detecting a significant functional signal in the regional networks correlated positively with the network size for fleas and with the number of hosts in a network for hosts. A functional signal in the regional networks was more frequently found for hosts than for fleas. We discuss the mechanisms behind the functional signal in both fleas and their hosts, relate geographic functional signal patterns to the historic biogeography of fleas and conclude that functional signals in the species composition of host spectra for fleas and of flea assemblages for hosts result from the interplay of evolutionary and ecological processes.

Keywords: Fleas; Functional dendrogram; Mammals; Mantel test; Traits.

Fig. 1

Results of the branch-specific analyses of functional signals (see text for explanation) in species interactions for fleas (A) and hosts (B) in the Afrotropics. The nodes of a functional dendrogram (A fleas, B hosts) are coloured according to the results of the Mantel test of the correlation (R) between functional dissimilarity and dissimilarity in sets of interacting partners

Fig. 2

Results of the branch-specific analyses of functional signals (see text for explanation) in species interactions for fleas (A) and hosts (B) in the Nearctic. The nodes of a functional dendrogram (A fleas, B hosts) are coloured according to the results of the Mantel test of the correlation (R) between functional dissimilarity and dissimilarity in sets of interacting partners

Fig. 3

Results of the branch-specific analyses of functional signals (see text for explanation) in species interactions for fleas (A) and hosts (B) in the Neotropics. The nodes of a functional dendrogram (A fleas, B hosts) are coloured according to the results of the Mantel test of the correlation (R) between functional dissimilarity and dissimilarity in sets of interacting partners

Fig. 4

Results of the branch-specific analyses of functional signals (see text for explanation) in species interactions for fleas (A) and hosts (B) in the Palearctic. The nodes of a functional dendrogram (A fleas, B hosts) are coloured according to the results of the Mantel test of the correlation (R) between functional dissimilarity and dissimilarity in sets of interacting partners

Fig. 5

Relationships between the probability to detect a significant functional signal (see text for explanation) in a regional flea-mammal network for A fleas and network size and B hosts and the number of host species

Fig. 6

Relationship between the strength of the functional signal (value of the Mantel correlation; see text for explanation) in a regional flea-mammal network and the number of host species