Many plant species rely upon ants to protect against herbivores. In arid
environments, these plants often form stronger bonds with dominant ant
species that, in turn, provide a better anti-herbivory defense than low
aggressive subordinate ants. Dominant ants typically claim the plants
producing more nutritious nectar, commonly leaving less valuable plants
to be guarded by lower-quality bodyguards. As water scarcity increases,
the value of the extrafloral nectar also increases, which can increase
the control of the most valuable plants by dominant ants and of the
displacement of outcompeted ants to less valuable plants, reducing niche
overlap among ant species and, consequently, the generalization of
ant-plant interactions at the community level. To evaluate this
hypothesis, we crossed data from 63 empirical ant-plant networks with
the mean precipitation rate of the sites and period in which the
interactions were sampled. As the environment dries, ant-plant networks
decreased in species richness but maintained other network properties.
Surprisingly, the decline in the number of ant and plant species engaged
in the mutualism along the precipitation gradient increased the
interaction generalization in drier habitats. But this increased
generalization is possible due to the increase in probability of
interaction between all plant and ant species due to the lower richness.
Hence, water availability primarily influences ant-plant interactions
through its impact on ant and plant communities. This has significant
eco-evolutionary consequences, as possibly increasing the persistence of
this networks in drier environments, demonstrating a new pathway through
which environmental factors can impact ecological interactions.