Alan A. Berryman

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The bark anatomy of Norway spruce clones that were resistant or susceptible to Ceratocystis polonica, a bark-beetle-vectored fungal pathogen, was compared. The major difference concerned the axial parenchyma cells, called polyphenolic parenchyma (PP cells) because of their vacuolar deposits. The phenolic nature of the deposits was indicated by(More)
Hypotheses for the causes of regular cycles in populations of forest Lepidoptera have invoked pathogen-insect or foliage-insect interactions. However, the available data suggest that forest caterpillar cycles are more likely to be the result of interactions with insect parasitoids, an old argument that seems to have been neglected in recent years.
Several commentaries have appeared recently on the status of ecology as a science, with some being quite pessimistic when comparing ecology to the hard sciences like physics. For example, some ecologists wonder if we will ever have general laws and theories (Roughgarden 1998, Lawton 1999) or become a predictive science (McIntosh 1985, Peters 1991). The(More)
Is population regulation a ‘‘bankrupt paradigm’’ (Krebs 1991) and ‘‘a monumental obstacle to progress’’ (Krebs 1995). Is it just a mindset, a dogma, a faith? (White 2001). Is there a ‘‘consensus emerging’’ (Turchin 1999) or is there still no ‘‘widespread evidence that populations are regulated’’ (White 2001). Ecology may be cursed by many contentious(More)
Chaotic dynamics emerge when positive/negative feedback systems are dominated much of the time by positive feedback growth processes. Although all ecological systems contain the seeds of chaos (positive feedback), empirical evidence and evolutionary/ecological reasoning support the view that ecosystems do not normally behave chaotically. They may, however,(More)
A central problem in ecology is explaining the causes of population fluctuations, and an important step in the solution is determining the structure of the negative feedback (density dependent) process regulating population dynamics. The conventional way to determine the dimension or order of density dependence in a time series is to calculate the partial(More)
Wolda (1989), in the title of his commentary on the concepts of equilibrium and density-dependence, asks " W h a t does it all mean?" This note attempts to answer his question. In his paper, Wolda concludes that, because the concept of density-dependent population regulation rests on the a priori assumption that "populations fluctuate in size around an(More)
From basic principles of positive/negative feedback control and classical density-dependent/independent population theory we outline a general explanation for the regulation of herbivore populations in forested ecosystems. We identify three fundamental patterns of behavior; (i) populations regulated close to equilibrium (“tight” regulation) by fast-acting(More)