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United States Department of Agriculture

Agricultural Research Service

Research Project: MANAGEMENT TECHNOLOGIES FOR CONSERVATION OF WESTERN RANGELANDS

Location: Range Management Research

Title: Life form influences survivorship patterns for 109 herbaceous perennials from six semi-arid ecosystems

Authors
item Chu, Chengjin -
item Havstad, Kris
item Kaplan, Nicole -
item Lauenroth, William -
item Mcclaran, Mitchell -
item Peters, Debra
item Vermeire, Lance
item Adler, Peter -

Submitted to: Journal of Vegetation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 3, 2013
Publication Date: N/A

Interpretive Summary: We compiled six long-term datasets from western North America to test for ecosystem-dependent demographic responses for forbs and grasses. Based on these data, we characterized 123 survivorship curves for 109 species. We examined three demographic parameters: survival rate at age 1, life expectancy at age 1, and a parameter describing the shape of the survivorship curve. We compare differences in demographic parameters between life forms (forbs or grasses) and among ecosystems with mean annual precipitation and mean annual temperature as explanatory variables. Grasses had higher survival and longer life expectancy than forbs at one year of age. Both forbs and grasses followed Type III survivorship curves. While mean annual precipitation had no effect on any demographic parameter, mean annual temperature had a significantly negative effect on both first year survival rates and life expectancy for forbs. Our results demonstrate that life form exerts a strong influence on demographic parameters and their response to temperature variation among ecosystems

Technical Abstract: We compiled six long-term datasets from western North America to test for ecosystem-dependent demographic responses for forbs and grasses. Based on these data, we characterized 123 survivorship curves for 109 species. Three demographic parameters were extracted from these survivorship curves: survival rate at age 1, life expectancy at age 1, and a parameter describing the shape of the survivorship curve. We used a mixed-effects model to compare the differences in demographic parameters between life forms (forbs or grasses) and among ecosystems with mean annual precipitation and mean annual temperature treated as explanatory variables. Grasses had higher survival and longer life expectancy than forbs at one year of age. Both forbs and grasses followed Type III survivorship curves, though forbs were closer to Type II compared to the grasses. Averaging across species, hazard ratios for whole survivorship curves differed among most ecosystems. While mean annual precipitation had no effect on any demographic parameter, mean annual temperature had a significantly negative effect on both first year survival rates and life expectancy for forbs. Our results demonstrate that life form exerts a strong influence on demographic parameters and their response to temperature variation among ecosystems. This unprecedented information on the age-specific demography of herbaceous plants has implications for population modeling and research on life history evolution and senescence.

Last Modified: 8/27/2014
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