Interactions between initial weed seedling density and postemergence herbicide and mechanical weed control were studied in two field experiments conducted between 1994 and 1996. Increasing seedbank densities of velvetleaf (0 to 500 seed m–2) in soybean or common sunflower (250 to 2,500 seed 1.3 m–2) in corn or soybean were established at Lincoln and Mead, NE, respectively. Emerged seedlings were treated with increasing intensities of weed control from none to bentazon alone or with interrow cultivation. A positive linear relationship between initial seedling density and density of surviving seedlings was consistently observed. As initial seedling density increased, more survivors were present after treatment. As intensity of weed control increased, the number of seedling survivors decreased. Resulting reproductive fitness decreased with increasing management intensity but remained positive when regressed against surviving seedling densities. Weed management outcomes were dependent on initial seedling density, such that the absolute number of survivors increased, while proportion of survivors appeared constant within the density ranges studied. These research findings emphasize the need to account for weed infestation level when assessing efficacy of weed management systems and provide evidence that patchy weed distributions may persist in part because of the need for considerably higher management intensities in high density patch centers.

Primates are important seed dispersers in tropical forests, but they are being lost due to forest fragmentation. We compared post-dispersal seed fate and seedling density for the tree Dialium guianense, in forest fragments in which its main seed disperser, the mantled howler monkey (Alouatta palliata) is present, and in fragments in which it is absent. We also carried out a germination experiment to assess gut-passage effect. Seeds extracted from fruits had very low germination (2%) compared with defecated seeds (70%). Seeds in monkey faeces had a lower probability of being attacked by predators, but a higher probability of being attacked by fungus, when compared with seeds inside fruits. Seed fate was similar in fragments with vs. without monkeys, and in sites under parent trees vs. under monkey sleeping sites. Seedling density was highest under sleeping sites in fragments with monkeys, followed by sites under parent trees in fragments with monkeys, and it was lowest in uninhabited fragments, regardless of deposition site. Our study adds to an increasing line of evidence suggesting that loss of frugivores can have strong consequences for plant recruitment.