Abstract
Herbivory is an interaction with great impact on plant communities since relationships between herbivores and plants are fundamental to the distribution and abundance of species over time and space. The aim of this study was to monitor the rate of leaf expansion in the tree fern Cyathea phalerata and evaluate the damage caused by herbivores to leaves of different ages and whether such damage is related to temperature and precipitation. The study was performed in a subtropical Atlantic Forest fragment located in the municipality of Caraá, in the northeast hillside of Rio Grande do Sul state, in southern Brazil. We monitored 24 mature individuals of C. phalerata with croziers in a population of approximately 50 plants. Leaf expansion rate, percentage of damaged leaves and leaf blade consumption rate by herbivory were calculated. Monthly means for temperature and accumulated rainfall were calculated from daily data. Croziers of C. phalerata were found to expand rapidly during the first and second months after emergence (3.98 cm day-1; 2.91 cm day-1, respectively). Damage caused by herbivory was observed in all of the monitored leaves, but none of the plants experienced complete defoliation. The highest percentage (57%) of damaged leaves was recorded at 60 days of monitoring, and also the highest monthly consumption rate of the blade (6.04%) occurred with young, newly-expanded leaves, while this rate remained between 1.50 and 2.21% for mature leaves. Rates of monthly leaf consumption and damaged leaves showed positive and strong relationship with each other and with temperature. The rapid leaf expansion observed for C. phalerata can be considered a phenological strategy to reduce damage to young leaves by shortening the developmental period and accelerating the increase of defenses in mature leaves.
Highlights
Herbivory is one the most negative impactful interactions in plant communities (Coley and Barone, 1996), since relationships between herbivores and plants are fundamental to the distribution and abundance of species over time and space (Edwards and Wratten, 1981)
Plants respond in many ways to herbivory, such as regulating consumption by producing substances that change the concentrations of nutrients in tissues (Neuvonen and Haukioja, 1984; Tuomi et al, 1984; Agrawal, 2007; Futuyma and Agrawal, 2009); depositing a thicker cuticle, thickening the epidermis and producing and depositing abundant crystals in leaves; using physical barriers, such as trichomes and leaf fibers (Fernandes, 1994; Mello and Silva-Filho, 2002; Hanley et al, 2007); and employing chemical defenses, such as toxic substances, repellants or compounds that interfere with the digestibility of vegetal tissue (Mello and Silva-Filho, 2002)
Considering that herbivores act on vegetative growth (Crawley, 1989), and that they could harm leaf growth and development of ferns with different intensities according to the climate (Patra and Bera, 2007) and the stage of leaf development (Mehltreter and Tolome, 2003; Mehltreter et al, 2006), this study aimed to monitor C. phalerata plants for leaf expansion and consumption by herbivores and to assess whether they are related to temperature and precipitation
Summary
Herbivory is one the most negative impactful interactions in plant communities (Coley and Barone, 1996), since relationships between herbivores and plants are fundamental to the distribution and abundance of species over time and space (Edwards and Wratten, 1981). Morphological, physical and chemical defenses do not seem as effective at protecting young leaves as they are for mature leaves, with young leaves being damaged more for most species (Feeny, 1970; Coley, 1983; Coley and Aide, 1991; Aide, 1993) This discrepancy could be due to the greater nutritional content, and lower concentration and diversity of defense compounds of expanding young leaves (Crawley, 1983; Lowman, 1985). A still understudied strategy that may explain the preference for mature leaves of ferns is phenological defense Employing such a defense, fern leaves can: (i) expand rapidly; (ii) be produced synchronously at community level to satiate herbivores; and/or (iii) be produced during seasons with low herbivore abundance (Aide, 1988, 1991, 1993; Murali and Sukumar, 1993)
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