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DETECTION OF DENSITY DEPENDENCE REQUIRES DENSITY MANIPULATIONS AND CALCULATION OF λ
Author(s) -
Fowler N. L.,
Overath R. Deborah,
Pease Craig M.
Publication year - 2006
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/05-1197
Subject(s) - ecology , density dependence , statistical physics , biology , physics , medicine , environmental health , population
To investigate density‐dependent population regulation in the perennial bunchgrass Bouteloua rigidiseta , we experimentally manipulated density by removing adults or adding seeds to replicate quadrats in a natural population for three annual intervals. We monitored the adjacent control quadrats for 14 annual intervals. We constructed a population projection matrix for each quadrat in each interval, calculated λ, and did a life table response experiment (LTRE) analysis. We tested the effects of density upon λ by comparing experimental and control quadrats, and by an analysis of the 15‐year observational data set. As measured by effects on λ and on N t +1 / N t in the experimental treatments, negative density dependence was strong: the population was being effectively regulated. The relative contributions of different matrix elements to treatment effect on λ differed among years and treatments; overall the pattern was one of small contributions by many different life cycle stages. In contrast, density dependence could not be detected using only the observational (control quadrats) data, even though this data set covered a much longer time span. Nor did experimental effects on separate matrix elements reach statistical significance. These results suggest that ecologists may fail to detect density dependence when it is present if they have only descriptive, not experimental, data, do not have data for the entire life cycle, or analyze life cycle components separately.