The origin of the debate

Building on the ideas of Robert MacArther, E.O. Wilson (The Theory of Island Biogeography, 1967), Harper (1970) framed the seed yield tradeoff concept in 1970, drawing on Erik Pianka's r/K terminology:

Tradeoff 1: Reproductive effort vs. longevity; seeds vs. "persistent vegetative organs"

"There is evidence that plant species differ in the proportion of their net annual assimilated income which is devoted to reproductive effort (2, 3). Crude generalizations about the reproductive effort of different types of plant are summarized in Table 1.

"It appears that species occupying early phases in succession (colonizing species) have a high reproductive effort, usually in the form of a large number of seeds, and a correspondingly high intrinsic rate of natural in- crease. These would be r species in the sense of MacArthur & Wilson (4). Perennials, and particularly woody species with low values of reproductive effort, seem to fit into the category of K species, which have stable habitats in later phases of succession. A greater part of their available energy resource is devoted to persistent vegetative organs; this confers advantages in a long-term intensive struggle for existence in crowded, resource-limited stable environments.

Tradeoff 2: Average seed mass (size) vs. number of seeds per plant

"Just as the resources available to a plant during development are partitioned between seed production and other ends, so the allocation to seeds is itself partitioned between numbers and size. Thus, the number of seeds borne by a plant is determined by 1. the size of the annual assimilated income, 2. the proportion of this devoted to seeds, and 3. the size of the seed units in which it is invested. It is a central thesis of this essay that seed numbers and seed size represent alternative strategies in the disposition of reproductive resources.

Sources:
J. L. Harper, P. H. Lovell, K. G. Moore (1970) The Shapes and Sizes of Seeds Author(s): Source: Annual Review of Ecology and Systematics, Vol. 1 (1970), pp. 327-356
MacArthur, R. and Wilson, E.O. (1967). The Theory of Island Biogeography, Princeton University Press (2001 reprint), ISBN 0-691-08836-5M.
Pianka, E.R. (1970). On r and K selection. American Naturalist 104, 592-597.