Figure 5. Two hypothetical scenarios of how stressor effects
can propagate across trophic levels leading to complex community
outcomes and disruption of species interactions. (Scenario A)Stressor A may disproportionately affect a single functional level (e.g.
a keystone predator) which has positive indirect benefits for a consumer
and negative
indirect benefits on a producer. Stressor A, for example, may cause high
physiological stress in the predator leading to reduced activity and
hunting, thus releasing the consumer from density and trait mediated
effects of the predator. Even though stressor A also has a physiological
cost on the consumer, this cost is exceeded by the benefits associated
with lower predation risk and increased foraging opportunities.
Conversely, the direct negative effects of stressor A combined with
increased top-down effects from consumers, may lead to negative
synergistic effects on producers. (Scenario B) Stressor B
disrupts the sensory capability of a specialist pollinator leading to
decreased foraging activity and pollination of ‘plant A’. A key seed
disperser which prefers a diet of ‘plant A’, switches their primary diet
to fruits of ‘plant B’ due to a reduction in the availability of ‘plant
A’. ‘Plant B’ now benefits both from increased seed dispersal and
decreased space competition from ‘plant A’ leading to a fundamental
shift in the composition of the plant community. Line thickness denotes
size of the stressor effect. Positive/negative symbols represent
stressor net effects on each trophic node.