Morphological adaptation of a palatable plant to long-term grazing can shift interactions with an unpalatable plant from facilitative to competitive

Abstract

Unpalatable plants can protect palatable neighbor plants from grazing pressure, but morphological evolution of a palatable species might change its interactions with unpalatable plants. We predicted that when a palatable species has locally adapted to grazing by expressing a dwarf phenotype that reduces grazer accessibility, the dwarf plants experience relatively more competitive effects than facilitative effects from large, well-defended, unpalatable species. We used a transplant experiment, in which both dwarf and large ecotypes of a palatable annual species, Persicaria longiseta, were transplanted outside and inside the canopy of an unpalatable nettle, Urtica thunbergiana, in a long-term deer grazing habitat of Nara Park, Japan. The dwarf ecotype of Persicaria has adapted to the grazing environments of the park by exhibiting inherently short shoots and small leaves, whereas the large ecotype is found in habitats with no grazing history. A previous common-garden study suggested that the phenotypic differences were genetically based and that phenotypic plasticity contributed little to the morphological difference. The large-phenotype of Persicaria experienced significantly increased morphological size, survival, and reproductive output under the Urtica canopy compared to outside the canopy, whereas these traits of the dwarf phenotype were reduced under the Urtica canopy compared to outside. These results indicate that the net effects of Urtica on Persicaria were positive for the large ecotype and negative for the dwarf ecotype. Thus, the morphological adaptation of a palatable species to avoid grazing altered its interactions with a large, well-defended neighbor.

Interference of allelopathic wheat with different weeds

“…These contradictory effects may be explained by the biochemical plasticity and below‐ground complementary interactions between allelopathic wheat and these weeds. Plants can modulate their growth and the production of secondary metabolites in response to competitors and other environmental conditions, resulting in morphological and chemical plasticity . The plant interactions within a mixed‐species system are a balance of negative and positive interactions among the component species.…”

Moving forward on facilitation research: response to changing environments and effects on the diversity, functioning and evolution of plant communities

“…Besides abiotic conditions, the evolutionary grazing history is also an important determinant of the outcome of plant–plant interactions. The ‘naïve’ (without grazing history) phenotype of the palatable Persicaria longiseta strongly benefits from protection against browsing, while its grazing‐adapted phenotype does not (Suzuki & Suzuki, ). Interestingly, this study suggests that adaptations to grazing can occur within a relatively short time span (decades to centuries), which is much faster than assumed in the classical studies on evolutionary grazing history (>10000 years; Mack & Thompson, ; Milchunas, Sala & Lauenroth, ).…”

“…Ecologists generally agree on the existence of multiple factors driving the outcome of pairwise plant-plant interactions. For example, the performance measure used (Goldberg et al, 1999;Maestre et al, 2005), the nature of the stress factor involved (resource or non-resource; Maestre et al, 2009b), the ontogenetic stage of the interacting species (Sthultz, Gehring & Whitham, 2007;Soliveres et al, 2010;Smit & Ruifrok, 2011), the ecological requirements of the interacting plants (Liancourt, Callaway & Michalet, 2005;Chu et al, 2008) or the evolutionary relationships of the species involved (Suzuki & Suzuki, 2012;Soliveres, Torices & Maestre, 2012c), are known to interact with the environment to define such an outcome. Added to this complexity is the fact that multiple environmental stressors, both biotic and abiotic, often co-occur in nature, and jointly shape the response of pairwise plant-plant interactions across environmental gradients (Baumeister & Callaway, 2006;Kawai & Tokeshi, 2007;Smit et al, 2009;le Roux & McGeoch, 2010;Soliveres et al, 2012a).…”

Demographic responses of rare forest plants to multiple stressors: the role of deer, invasive species and nutrients

“…Furthermore, individuals already stressed by effects of one agent are likely to become more vulnerable to additional stresses. For example, plant responses to deer herbivory include the development of dwarf growth forms (Knight ; Suzuki & Suzuki ), which may lack the necessary storage resources to withstand desiccation or nutrient limitation as a result of earthworm invasion (Frelich et al . ; Hale, Frelich & Reich ).…”