Impacts of seedling herbivory on plant competition and implications for species coexistence

• Published in: Annals of botany Vol. 103; no. 8; pp. 1347 - 1353
• Main Authors: Hanley, M.E, Sykes, R.J
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 01.06.2009; Oxford Publishing Limited (England)
• Subjects: Biomass; Ecological competition; Forest ecology; Growth-defence trade-off; Helix aspersa; Herbivores; lottery models; Original; Plant communities; Plant ecology; plant size variability; Plants; plant–animal interactions; seedling acceptability; seedling defence; Seedlings; Snails; spatio-temporal niches; Species; Species Specificity; Trifolium; Trifolium - growth & development; Trifolium - physiology; Trifolium pratense; Trifolium repens; plant size variability; lottery models; plant-animal interactions; Growth-defence trade-off; spatio-temporal niches; seedling acceptability; seedling defence
• ISSN: 0305-7364; 1095-8290
• DOI: 10.1093/aob/mcp081

BACKGROUND AND AIMS: Although the causes and consequences of seedling herbivory for plant community composition are well understood, the mechanisms by which herbivores influence plant species recruitment to the established phase remain less clear. The aim was to examine how variation in the intensity of seedling herbivory interacts with growth-defence trade-offs and herbivore feeding preferences to affect plant community development. METHODS: Using 14-d-old seedlings of Trifolium pratense and T. repens, relative growth and susceptibility to herbivory by the snail Helix aspersa was quantified to elucidate putative growth-defence trade-offs for these species. Then mixed assemblages of 14-d-old Trifolium seedlings were exposed to herbivory by zero, two, five or ten snails and determined how variation in the intensity of herbivory affected competitive interactions into the mature phase (as measured by total plant biomass at 120 d old). KEY RESULTS: In the absence of herbivory, communities were dominated by T. pratense; a result expected on the basis that it yielded larger and presumably more competitive seedlings. However, when seedlings were exposed to herbivory, the balance of competition shifted. At low levels of herbivory (two snails), both Trifolium species contributed equally to total plant biomass. More intense herbivory (five snails) resulted in almost total mortality of T. pratense and dominance of the mature community by T. repens. The most intense herbivory (ten snails) effectively removed all seedlings from the experimental community. CONCLUSIONS: The study illustrates a mechanism whereby spatio-temporal fluctuations in seedling herbivory, when coupled with species-specific variation in competitive ability and sensitivity to herbivore attack, can differentially influence plant recruitment into the mature phase. This mechanism may be a key element in our attempts to understand plant species coexistence, since fluctuations in plant recruitment are fundamental to the many theories that view coexistence as a consequence of a spatio-temporal lottery for dominance over regeneration micro-sites.