The temporal dynamics of resource use by frugivorous birds: a network approach

Abstract

Abstract. Ecological network patterns are influenced by diverse processes that operate at different temporal rates. Here we analyzed whether the coupled effect of local abundance variation, seasonally phenotypic plastic responses, and species evolutionary adaptations might act in concert to shape network patterns. We studied the temporal variation in three interaction properties of bird species (number of interactions per species, interaction strength, and interaction asymmetry) in a temporal sequence of 28 plant-frugivore interaction networks spanning two years in a Mediterranean shrubland community. Three main hypotheses dealing with the temporal variation of network properties were tested, examining the effects of abundance, switching behavior between alternative food resources, and morphological traits in determining consumer interaction patterns. Our results demonstrate that temporal variation in consumer interaction patterns is explained by short-term variation in resource and bird abundances and seasonal dietary switches between alternative resources (fleshy fruits and insects). Moreover, differences in beak morphology are associated with differences in switching behavior between resources, suggesting an important role of foraging adaptations in determining network patterns. We argue that beak shape adaptations might determine generalist and specialist feeding behaviors and thus the positions of consumer species within the network. Finally, we provide a preliminary framework to interpret phylogenetic signal in plant-animal networks. Indeed, we show that the strength of the phylogenetic signal in networks depends on the relative importance of abundance, behavioral, and morphological variables. We show that these variables strongly differ in their phylogenetic signal. Consequently, we suggest that moderate and significant phylogenetic effects should be commonly observed in networks of species interactions.

Connecting Resource Tracking by Frugivores to Temporal Variation in Seed Dispersal Networks

“…Animals with generalized diets have the ability to switch to new food types during times when their preferred resource is limited. Diet switching may make tracking resources across the landscape or through time less necessary and, therefore, create a weak association between the abundance of resources and animals (Carnicer et al, 2009). On the other hand, dietary specialists may be constrained to track resources through space and time.…”

“…Many recent studies have highlighted the need to incorporate temporal dynamics to better understand the assembly and maintenance of plantanimal mutualisms (Yang et al, 2013). Research into the temporal dynamics of plant-animal mutualisms, however, has largely focused on the relationship between plants and pollinators (see Olesen et al, 2008;Traveset et al, 2015), with seed dispersal (SD) mutualisms receiving less attention (see Carnicer et al, 2009;González-Castro et al, 2012;Yang et al, 2013). The complexity of community-level interactions complicates our understanding of frugivore-plant mutualisms (Olesen et al, 2010).…”

“…The abundance hypothesis states that the degree (the number of interacting species) and strength of interspecific interactions (amount of interaction such as, the number of fruits eaten) for a species may be determined by that species' abundance (Carnicer et al, 2009). Several predictions can be derived from the abundance hypothesis.…”

“…The abundance hypothesis only explains the temporal variations of mutualistic networks when there are changes in the abundance and/or identity of species within the network through time. If species presence and/or abundance varies in time, then the number and strength of interactions could also vary in time, giving rise to temporal shifts in network structure (Carnicer et al, 2009;Yang et al, 2013). This idea clearly has important implications for mutualistic networks that occur in areas where species abundances vary seasonally as due to migration, climate, and/or other life history properties of the species involved.…”

“…Resource tracking can create scenarios where local abundances of frugivores increase as certain resources increase, which may, in turn, increase the likelihood of interactions with multiple plant species in the area that are fruiting at the same time; a scenario that is predicted by the abundance hypothesis. Multiple studies have suggested that resource tracking may play a role in the temporal dynamics of SD networks (Krishna et al, 2008;Carnicer et al, 2009;Yang et al, 2013). However, the influence resource tracking has on SD networks has not been explicitly explored, and, therefore, theory of how resource tracking may influence networks is still being developed (Figure 1).…”