Sloppy Predators
Perhaps the most iconic predator spreader in the ecological literature
is the “sloppy predator”. The sloppy predator contributes to increased
parasitism by consuming its prey in a way that increases the
transmission or dissemination of parasites as compared to other sources
of prey mortality (Cáceres et al. 2009; Duffy et al.2019). The classic example of this phenomenon is the larvalChaoborus predator which shreds and regurgitates infectedDaphnia dentifera prey (Cáceres et al. 2009; Strausset al. 2016). This predation behavior spreads fungal parasite
spores in the water column where they are ingested by foraging D.
dentifera . In contrast, D. dentifera that die from parasite
virulence rapidly settle out of the water column, limiting onward
transmission of fungal spores. In this system, both prey biology and
environmental stratification contribute to limit transmission after prey
death from virulent effects of the parasite, while prey and predator
behavior increase transmission after predation by the sloppy predator.
In general, predator behaviors that spread prey blood, tissue, or
viscera are likely to contribute to transmission as long as prey
behaviors expose them to these new sources of infection. These prey
behaviors include indiscriminate grazing or filter feeding, as we see in
the D. dentifera example, but also scavenging behaviors which may
lead prey to consume conspecifics post-predation when they would not
otherwise. (Because our focus in this review is on scenarios where the
predator does not become infected, we are not considering cases of
cannibalism.) Similarly, prey biology and the interaction between
environment and prey space-use impact whether prey are more likely to
encounter the parasite after predation or after death from virulent
mortality. If prey shed few parasites during their life and/or if
parasite shedding from live prey is concentrated in areas avoided by
healthy prey, then there is a clear opportunity for sloppy predation to
increase transmission. In fact, questions of spatio-temporal patterns of
predator spreading are likely of broad relevance to this topic (Box 1).
Efforts to discover and experiment on a wider array of sloppy
predator-spreader systems should begin by identifying predatory
behaviors that spread blood, tissue, or viscera. In these systems, field
manipulation of predator presence/absence should be supported and
contextualized with lab or field mesocosm simulation of predator sloppy
eating byproducts to determine whether sloppiness mechanistically
results in transmission.