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Summary: Intraspecific variation in the strength of density
dependence in aphid populations
A N U R A G A . A G R A W A L , 1
N O R A U N D E R W O O D 2
and J O H N
R . S T I N C H C O M B E 3 1
Department of Botany, University of Toronto, Canada, 2
Department of Biological
Science, Florida State University, U.S.A., and 3
Department of Ecology and Evolutionary Biology, Brown University,
Providence, Rhode Island, U.S.A.
Abstract. 1. Experimental evidence is presented for positive, negative, and no
density dependence from 32 independent density manipulations of milkweed aphids
(Aphis nerii) in laboratory and field experiments. This substantial variation in intra-
specific density dependence is associated with temperature and host-plant species.
2. It is reported that as population growth rate increases, density dependence
becomes more strongly negative, suggesting that the monotonic definition of
density dependence used in many common population models is appropriate for
these aphids, and that population growth rate and carrying capacity are not
directly proportional.
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