Trait adaptation enhances species coexistence and reduces bistability in an intraguild predation module

Disentangling how species coexist in an intraguild predation (IGP) module
is a great step towards understanding biodiversity conservation in complex
natural food webs. Trait variation enabling individual species to adjust
to ambient conditions may facilitate coexistence. However, it is still
unclear how co-adaptation of all species within the IGP module,
constrained by complex trophic interactions and trade-offs among
species-specific traits, interactively affects species coexistence and
population dynamics. We developed an adaptive IGP model allowing prey and
predator species to mutually adjust their species-specific defensive and
offensive strategies to each other. We investigated species persistence,
the temporal variation of population dynamics, and the occurrence of
bistability in IGP models without and with trait adaptation along a
gradient of enrichment represented by carrying capacity of the basal prey
for different widths and speeds of trait adaptation within each species.
Results showed that trait adaptation within multiple species greatly
enhanced the coexistence of all three species in the module. A larger
width of trait adaptation facilitated species coexistence independent of
the speed of trait adaptation at lower enrichment levels, while a
sufficiently large and fast trait adaptation promoted species coexistence
at higher enrichment levels. Within the oscillating regime, increasing the
speed of trait adaptation reduced the temporal variability of biomasses of
all species. Finally, species co-adaptation strongly reduced the presence
of bistability and promoted the attractor with all three species
coexisting. These findings resolve the contradiction between the
widespread occurrence of IGP in nature and the theoretical predictions
that IGP should only occur under restricted conditions and lead to
unstable population dynamics, which broadens the mechanisms presumably
underlying the maintenance of IGP modules in nature. Generally, this study
demonstrates a decisive role of mutual adaptation among complex trophic
interactions, for enhancing interspecific diversity and stabilizing food
web dynamics, arising e.g. from intraspecific diversity.