Evaluating grazing response strategies in winter annuals: A multi-trait approach
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Date
2021
Journal Title
Journal ISSN
Volume Title
Publisher
Wiley
Abstract
Plants minimize fitness losses through grazing by three fundamental strategies:
tolerance, avoidance and escape. Annual species have been traditionally assumed
to escape grazing through their short life cycle and seed dormancy; however, their
grazing response strategies remain almost unexplored. How traits and their coordination
affect species' grazing responses, and whether the generalized grazing
model, which posits convergent filtering by grazing and drought, is applicable to
this ecologically and economically important species group thus remain unclear.
2. We used a trait-based
approach to evaluate grazing response strategies of winter
annuals from the Middle East. Across 23 species, we examined the coordination
of 16 traits hypothesized to be relevant for grazing responses, and linked them to
species' fecundity responses, as proxy for fitness responses, to simulated grazing
in controlled conditions, to species' abundance responses to grazing in the field
and to species' distribution along a large-scale
rainfall gradient.
3. Winter annuals exhibited both grazing escape and to a lesser extent tolerance
indicated by (a) independent coordination of escape and tolerance traits, and (b)
maintenance of higher fecundity in species with more pronounced escape or tolerance
traits under simulated grazing. In the natural habitat, species with a more
pronounced escape but not tolerance strategy maintained higher abundance
under grazing in dry habitats, indicating convergent favouring of escape by both
grazing and drought. However, this finding at the local scale was not mirrored by
a strategy shift along a large-scale
rainfall gradient.
4. Synthesis. The convergent favouring of escape traits by grazing and drought in
annuals is consistent with the generalized grazing model. This model, which has
been developed for perennials based on the avoidance strategy, can thus be extended
to annuals based on escape, a finding that should facilitate projecting consequences
of global change in drylands dominated by annuals.
Description
Keywords
annual species, ecological filtering, escape, plant–herbivore interaction, rainfall gradient, semi-arid rangelands, tolerance, trait coordination