DOI: 10.5061/dryad.tdz08kq12
title: Life history strategy and extinction risk in the warm desert perennial spring ephemeral Astragalus holmgreniorum (Fabaceae)

description: This study of Astragalus holmgreniorum examines its adaptations to the
 warm desert environment and whether these adaptations will enable it to
 persist. Its spring ephemeral hemicryptophyte life history strategy is
 unusual in warm deserts. We used data from a 22-year demographic study
 supplemented with reproductive output, seed bank and germinant survival
 studies to examine the population dynamics of this species using
 discrete-time stochastic matrix modeling. The model showed that A.
 holmgreniorum is likely to persist in the warm desert in spite of high
 dormant-season mortality. It relies on a stochastically varying
 environment with high inter-annual variation in precipitation for
 persistence, but without a long-lived seed bank, environmental
 stochasticity confers no advantage. Episodic high reproductive output and
 frequent seedling recruitment along with a persistent seed bank are
 adaptations that facilitate its survival. These adaptations place its life
 history strategy further along the spectrum from ‘slower’ to ‘faster’
 relative to other perennial spring ephemerals. Extinction risk for small
 populations is relatively high even though mean λs &gt;1 because of
 high variance in year quality. This risk is also strongly dependent on
 seed bank starting values, creating a moving window of extinction risk
 that varies with population size through time. Astragalus holmgreniorum
 life history strategy combines the perennial spring ephemeral life form
 with features more characteristic of desert annuals. These adaptations
 permit persistence in the warm desert environment. A promising conclusion
 is that new populations of this endangered species can likely be
 established through direct seeding.
description: This is a long-term demographic data set (22 years) for a
 federally endangered plant. It was collected via yearly visits to the
 field study plot, where marked plants were monitored once in late
 spring for survival, size, and flower number and new recruits were marked
 and measured. These raw demographic data were processed along with
 supplementary data on seed bank persistence and reproductive output per
 flower as described in thepublished paper to arrive at 39 vital rates to
 be used to parameterize the resulting population matrix model. This data
 set includes yearly values over the 22 years of the study for the 19 vital
 rates in the model that are variable, to show how the means and variances
 for these variable vital rates were calculated. These means and variances
 along with values for the invariant vital rates are included in the
 published paper.
description: We used the Matlab code provided by Morris and Doak in their 2002
 book Quantitative Conservation Biology to construct the population matrix
 model for Astragalus holmgreniorum. In order to use their procedure, we
 needed means for all vital rates, variances for variable vital rates, and
 statistical distributions for each variable vital rate. We also
 needed within-year and between-year correlations among variable vital
 rates. Because of missing data and low sample numbers in some years, we
 used the procedure in Morris and Doak (2002) for producing valid,
 corrected correlation matrices that were usable for subsequent matrix
 algebraic calculations. All the values needed to parameterize and run the
 model are included either in these data sets or in the published
 paper.