If you need an accessible version of this item please contact JSTOR User Support

The Demography of Bromus Tectorum: Variation in Time and Space

Richard N. Mack and David A. Pyke
Journal of Ecology
Vol. 71, No. 1 (Mar., 1983), pp. 69-93
DOI: 10.2307/2259964
Stable URL: http://www.jstor.org/stable/2259964
Page Count: 25
  • Download PDF
  • Cite this Item

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If you need an accessible version of this item please contact JSTOR User Support
The Demography of Bromus Tectorum: Variation in Time and Space
Preview not available

Abstract

(1) Amplitude in the variation of recruitment, survivorship and fecundity was examined for the introduced annual grass Bromus tectorum in three habitat types in eastern Washington (U.S.A.) for three consecutive generations. A total of 18 143 individuals in populations varying from 364 to 5322 members per site were mapped repeatedly from emergence to death with sufficient frequency to detect multiple constituent cohorts varying in age from fewer than 16 to more than 200 days. (2) Recruitment was usually concentrated in late summer and autumn, but occurred at any time until mid-May of the following year. (3) Most of any population experienced low death risk until June, although some cohorts emerging in late summer were devastated (Deevey Type III curve) during periods of drought or extended snow cover. (4) Most plants survived to produce seed. Loss of seed production from devastated autumn-emergent plants was off-set by the reproduction of late winter-spring recruits. Even individuals less than 45 days old often produced at least one viable seed by June. (5) B. tectorum persists under the vagaries of steppe environments by its ability to behave simultaneously on the same site as an ephemeral monocarpic, annual monocarpic and winter annual monocarpic species. (6) Year-to-year variation in environment (weather, predator activity) overrode the intrinsic differences among the three habitat types along a 200 km transect of varying moisture availability often producing considerable amplitude in population attributes (recruitment, survivorship and fecundity). Characterization of any species as a colonizer, etc. on the basis of life history traits alone may be erroneous; knowledge of the variation in such population attributes is also necessary.

Page Thumbnails

  • Thumbnail: Page 
69
    69
  • Thumbnail: Page 
70
    70
  • Thumbnail: Page 
71
    71
  • Thumbnail: Page 
72
    72
  • Thumbnail: Page 
73
    73
  • Thumbnail: Page 
74
    74
  • Thumbnail: Page 
75
    75
  • Thumbnail: Page 
76
    76
  • Thumbnail: Page 
77
    77
  • Thumbnail: Page 
78
    78
  • Thumbnail: Page 
79
    79
  • Thumbnail: Page 
80
    80
  • Thumbnail: Page 
81
    81
  • Thumbnail: Page 
82
    82
  • Thumbnail: Page 
83
    83
  • Thumbnail: Page 
84
    84
  • Thumbnail: Page 
85
    85
  • Thumbnail: Page 
86
    86
  • Thumbnail: Page 
87
    87
  • Thumbnail: Page 
88
    88
  • Thumbnail: Page 
89
    89
  • Thumbnail: Page 
90
    90
  • Thumbnail: Page 
91
    91
  • Thumbnail: Page 
92
    92
  • Thumbnail: Page 
93
    93