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THE GENESIS OF SIZE VARIABILITY IN PLANTS AND ANIMALS
Author(s) -
Pfister Catherine A.,
Stevens Forrest R.
Publication year - 2002
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(2002)083[0059:tgosvi]2.0.co;2
Subject(s) - intraspecific competition , biology , ecology , population size , population , autocorrelation , statistics , demography , mathematics , sociology
The changes in the size structure of a cohort of individuals through time can have important population‐level consequences, but the determinants of patterns of variation in individual size are not well understood. We use an individual‐based simulation model to determine what factors can lead to changes in the variability in size among individuals through time, with attention paid to those factors that increase variability. A pattern of increasing size variability over time (i.e., growth depensation) has been documented in a variety of taxa. Size‐dependent growth has generally been advanced as the explanation for its occurrence. We evaluated the independent and interactive effects of size‐dependent growth factors, positive temporal correlates in growth (termed “growth autocorrelation”), and environmental stochasticity in generating growth depensation. In contrast to expectation, our results indicate that size‐dependent growth is not the major contributor to changing variability patterns. Instead, our simulations indicate that growth autocorrelation is often the major determinant causing growth depensation. Data collected from the kelp Alaria nana and the whelk Nucella canaliculata showed evidence for positive correlations in growth (independent of size), while the tidepool sculpin Oligocottus maculosus does not. The changes in size variability in these three species (increasing size variability through time in A. nana only) were consistent with model predictions. Our results emphasize a need to disentangle size‐related processes from other correlates of growth in field populations and to document how these phenomena are affected by environmental stressors and intraspecific interactions.