Box 1: Space and Time
Predator-prey and parasite-host interactions both require temporal and
spatial overlap between the victim and the natural enemy. Hosts must
encounter other infected hosts or parasite transmission stages to allow
transmission, while predators must encounter their prey to kill and eat
them. Predator-prey-parasite interactions can increase parasitism in
prey by increasing the spatio-temporal overlap between prey and their
parasites. In heterogeneous landscapes where parasites are deposited
unequally across space, predator interference can increase the extent to
which parasite deposition overlaps with areas of prey space-use through
both sloppy predation and parasites passing through predators (Cácereset al. 2009; Strauss et al. 2016; Duffy et al.2019; Lopez & Duffy 2021); facilitation of prey-parasite
spatio-temporal overlap by the predator generally requires strong
spatio-temporal overlap between that predator and infected prey.
However, the presence of predators can influence parasitism in prey even
without regular spatio-temporal overlap between prey and predators
(Clinchy et al. 2013). If prey and predators occupy the same
areas at different times, then predator cues can have profound
behavioral and physiological effects on parasitism in the prey even
without any direct interactions. However, the extent of these effects is
typically limited by the spatial scale and temporal duration of predator
cues and the duration of parasite persistence in the environment. Highly
localized predator cues (such as feces in terrestrial systems) may
require far finer scale spatial overlap between prey and predator than
more diffusible cues (such as predator kairomones in an aquatic system).
Likewise, durable predator signals (such as a strong chemical cue)
require less temporal overlap between prey and predator than more
ephemeral signals (such as auditory cues). These behavioral effects of
predators, themselves, may alter the space-use of prey in ways that
result in increased spatiotemporal overlap with parasites or infected
prey. Similarly, parasites which persist longer in the environment are
more likely to be encountered by prey than those with limited
environmental viability, making predator spreader effects persist longer
for these parasites.
The flexibility in the extent of spatiotemporal overlap required for
predator-prey-parasite interactions — as well as the way in which the
interaction itself alters spatiotemporal patterns of both prey and
parasites — may make detecting patterns and inferring causal
mechanisms challenging in some systems. Therefore we recommend careful
study of the locations and time periods during which contact between
prey and parasites occur both to improve predictions about the potential
effect of predators on those spatio-temporal overlaps and to aid in
measuring mechanistic intermediary factors between predator presence and
parasite outcomes.