Cross-habitat trophic coupling by arboreal predators: Allochthonous inputs follow diverse routes between food webs

Background/Question/Methods

Two prominent areas of food web research include the effect of species diversity on food web function, and allochthonous resource flux in spatially coupling food webs.  Yet, few studies have examined how species diversity might affect food web coupling.  For example, species-specific traits such as diet breadth and habitat use could generate considerable variation in the magnitude and routing of allochthonous inputs.  With this in mind, we provide an empirically derived, community-wide illustration of allochthonous flux between two adjacent food webs.  More specifically, we investigated the differential routing of allochthonous flow between an arboreal and terrestrial habitat in which the dominant consumers were three species of arboreal lizard (knight anole, Anolis equestris; brown anole A. sagrei; and bark anole, A. distichus).  Our goal was to identify interspecific variation in the magnitude of cross-habitat coupling and illustrate the different routes that carbon follows between these two habitats.  Because the dominant vegetation in each habitat differed isotopically due to distinct photosynthetic pathways (arboreal = C₃; terrestrial = C₄), the contribution of each habitat was traced using stable isotopes.  These data were combined with Anolis stomach contents and prey isotopes to infer differential routing of carbon among and within habitat-specific food webs.

Results/Conclusions

Our results show that each Anolis species differed in habitat use and diet and that all species incorporated carbon from terrestrial and arboreal habitats.  However, the proportion of terrestrially derived carbon differed considerably among species with the highest observed in knight anoles, followed by brown and bark anoles (0.38, 0.33, and 0.23, respectively).  More importantly, prey isotopes, stomach contents and habitat use data showed that the routing of allochthonous input into the arboreal habitat differed for each species.  Specifically, prey movement (ants and grasshoppers) into the arboreal habitat from the terrestrial habitat mediated coupling in knight and bark anoles, while foraging in the terrestrial habitat contributed to cross-habitat coupling in brown anoles.  Because Anolis species occupy distinct habitats, and exhibit different diets, the routes that allochthonous inputs follow into the arboreal habitat varies for each species.  Given the various routes of allochthonous inputs elucidated in our study, we suggest that cross-habitat flux can be mediated by species-specific traits, therefore indicating an important role for consumer diversity in allochthonous resource flux.