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HURRICANE DISTURBANCE AND THE POPULATION DYNAMICS OF A TROPICAL UNDERSTORY SHRUB: MEGAMATRIX ELASTICITY ANALYSIS
Author(s) -
Pascarella John B.,
Horvitz Carol C.
Publication year - 1998
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/0012-9658(1998)079[0547:hdatpd]2.0.co;2
Subject(s) - population , understory , shrub , vital rates , leslie matrix , ecology , canopy , disturbance (geology) , population growth , environmental science , biology , demography , paleontology , sociology
The role of environmental variation in the population dynamics of the tropical understory shrub Ardisia escallonioides was explored using single‐environment matrix analysis and dynamic‐environment megamatrix analysis. We investigated how variation in forest‐canopy openness caused by hurricanes affected population dynamics. A 7 × 7 patch‐transition matrix was created to model forest dynamics based on the historical frequency and strength of hurricanes in south Florida. Seven 8 × 8 stage‐classified matrices for plant population dynamics were derived from four field populations and two posthurricane years. These populations spanned a strong gradient of forest‐canopy openness resulting from hurricane disturbance caused by Hurricane Andrew (24 August 1992). The patch‐transition matrix was analyzed for its stable patch distribution. The seven single‐environment matrices were each analyzed for population growth rates and elasticity of stage classes. The 56 × 56 megamatrix was analyzed for population growth rate, reproductive value, stable patch‐stage distribution, and elasticity of both patches and stages. Population growth rate of the single‐environment matrix models (8 × 8) was lowest for the shadiest environment (λ = 1.0), intermediate but variable for intermediate environments, and highest for the most open environment (λ = 1.96). The population growth rate (λ) of the megamatrix model was 1.71. The stable patch‐stage distribution was characterized by a high proportion of seeds in open patches. Reproductive value was highest for very large adults in open patches. Megamatrix elasticity analysis revealed several components of the demography that were not apparent from examination of the single‐environment matrices. Although closed‐canopy patches were the most common type of environment, elasticity analysis of the megamatrix showed that the highest patch elasticity was for the most open environment. We found contrasting predictions for the relative importance of life history stages to population growth rate from single‐environment analysis vs. the megamatrix analysis. In the most common single‐environment patch, very large adults had the highest elasticity. In the megamatrix, small juveniles contributed the most elasticity and all stages contributed some elasticity. For plant species inhabiting temporally varying environments, megamatrix analysis offers new insight into the importance of both patches and stage classes.