Modeling scavenging in food webs: effects of scavenger trophic position and specialization on carrion stages

Background/Question/Methods

Scavenging plays an important role in ecological communities, and the carrion upon which these species feed represents a higher quality resource than is often appreciated.  It has been shown that most carnivores and omnivores scavenge at some point in their life history, and (contrary to some former assumptions) inputs of carrion are often predictable.  There is also evidence suggesting that species' use of carrion varies with their position within a food web: higher trophic level species tend to specialize on fresh carrion, whereas low trophic level species specialize on the more decayed stages of carrion.  Food web models rarely consider scavenging, despite reasons to suspect that it may impact system stability.  Carrion may be more difficult to overdeplete, available at different times, and be shared by different competitors than live prey. 

We examine the effects of scavenging, as well as scavenger specialization on different stages of carrion, on the stability of simple (four to eight species) food web models.  We compared species persistence across a gradient of carrying capacities for one producer, which in the no-scavenging model generated a range of behaviors from persistence of all species with little oscillation to extinction of most or all species in the web.

Results/Conclusions

Scavenging generally reduced system stability and persistence in our models.  However, communities were more stable when scavenging was added in ways that corresponded to empirically observed patterns.  In treatments with scavengers in multiple trophic levels, stability tended to be greater when the higher-trophic-level scavenger specialized on early-stage carrion and the lower-trophic-level scavenger specialized on late-stage carrion.  When only high-level consumers scavenged, stability was generally higher if those scavengers specialized on early-stage carrion compared to when they were either generalists or late-stage specialists.  The opposite occurred when low-level species scavenged: early-stage specialization tended to lead to greater stability than generalization or late-stage specialization.  This suggests that the positions of scavengers in food webs and partitioning of carrion as a resource by scavengers could have important interactive consequences for system stability, and highlights the need for further study of how scavenging is structured in ecological communities.