Size-dependent herbivore attack and the demography of an arid grassland shrub
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Authors: M. A. Parker
Date: 1985
Journal: Ecology
Volume: 66
Number: 3
Pages: 850-860
Summary of Methods: The relationship of plant size and age to herbivory and the effects of herbivory of two different insect species (grasshoppers and a root boring beetle) that feed on threadleaf snakeweed plants were examined on the Bernalillo watershed in New Mexico. These insects typically invade the southwest from May through September. Age structure and root borer damaged was measured by extraction of all threadleaf snakeweed plants (excluding seedlings) in 2, 8 x 8 m plots, canopy size (six size-classes), and presence of root borer damage were recorded. Mortality due to root boring beetle was measured by comparing live stems on 20 protected and 20 non-protected mature plants for a three year period. Juvenile plant mortality due grasshopper herbivory was determined by recording plant status (alive vs. dead) and presence or absence of herbivory on protected and unprotected plants. Mature protected and unprotected plants were examined for grasshopper herbivory, plant vigor and number of flower heads per plant was recorded.
Article Summary / Main Points: Large plants had a higher mortality and senescence rate, these increased rates were highly correlated to beetle damage. Juvenile threadleaf snakeweed plants hat a higher mortality rate due to grasshopper herbivory than intermediately sized mature plants. Canopy cover of threadleaf snakeweed creased by 40%. Severe grasshopper herbivory can depress and almost eliminate snakeweed flowering in a given year.
Vegetation Types: Mountain Shrublands Pinyon-Juniper Woodlands (includes juniper woodlands)
MLRA Ecoregions: 36 Southwestern Plateaus, Mesas, and Foothills 39 Arizona and New Mexico Mountains
Agrovoc Control Words: Weeds Rangelands Grasshoppers
Article Review Type: Refereed
Article Type: Experimental Research
Keywords: age structure, grasshopper herbivory, gutierrezia microcephala, crossidius pulchellus, hesperotettix viridis, plant demography, plant mortality, seed pools
Annotation: This study examined insect herbivory and not ungulate herbivory.
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