Alan A. Berryman’s research while affiliated with Washington State University and other places

In applied population dynamics the choice of stochastic per capita growth function has implications for population viability analyses, management recommenda-tions, and pest control. This model choice is often based on statistical criteria, mathematical tractability or personal preferences, and general ecological guidelines are either too vague or entirely missing. To identify such guidelines, it is important to understand how exogenous and endoge-nous factors interact at the individual level and re-emerge at the aggregated population level. We therefore study different types of resource competition (contest vs. scramble competition) and different types of exogenous fluctuations (food and weather fluctuations) at the indi-vidual level in a simple individual-based simulation model. We statistically fit the resulting time series to find out (1) which functional form of the growth function ('hyperbolic' or 'exponential') better describes contest and scramble competition and (2) whether the pattern of population fluctuations resulting from the simulations can be assigned to vertical, lateral or nonlinear perturbations in the sto-chastic growth function (a classification scheme suggested by Royama 1992, Analytical Population Dynamics, Chapman and Hall, London). We found that the same type of competition can result in 'hyperbolic' or 'exponential' functional forms, depending on the type of exogenous fluctuations. So it is the interplay between exogenous variability and endogenous resource competition that affects model performance. In contrast to the widespread assumption of vertical (additive) perturbations, our findings highlight the importance of (non-additive) lateral and nonlinear perturbations and their combinations with verti-cal perturbations. The choice of the stochastic growth function should therefore consider not only statistical cri-teria but also ecological guidelines. We derive such eco-logical guidelines from our analysis.

The future number of people inhabiting the planet will influence the impact over natural ecosystems. In consequence, the growth of the human population represents one of the most important challenges for the near future. In this paper we used population dynamic theory to analyze human population growth. The results suggest that human population growth exhibited important fluctuations during the last 2000 years. In particular two different phases during the last 400 years can be distinguished, a positive relationship with population size implying positive feedback processes, followed by a negative relationship with population size – suggesting that negative feedback processes have been operating during the last 45 years. Our results support the view that ecological concepts derived from population ecology can be useful for understanding human dynamics. While cooperation at low densities in animal populations reminds us the Boserupian view that population growth induces economic development and higher standards of living, competition at high densities reconciles ecological theory with the original Malthusian view. We conclude that the present reduction in human per capita growth rates appears to be consequence of different limiting factors operating in combination around the globe in a similar manner, except in Africa where the factors operating appears to be very different. Humans may achieve a stable equilibrium population in the next century but the possibility of a population collapse caused by second-order oscillations should be considered.

The histology of defense reactions in individual pine trees belonging to three species, Pinusponderosa, P. contorta, and P. monticola, to inoculation with Ceratocystisclavigera and injection with chitosan and a proteinase inhibitor inducing factor was investigated after resin fixation with cupric acetate. The synthesis of secondary resins was directly associated with parenchyma cells in the phloem and in the rays of both phloem and sapwood. However, these resins were largely located in the lumen of sieve cells and tracheids. In the case of the fungus and chitosan, resin soaking began in the outer phloem and latewood of the last growth rings, then spread into the inner phloem and earlywood. With the proteinase inhibitor inducing factor, resinosis was similar to that of the buffer control, being much less extensive than with the fungus or chitosan, and occurring mainly in the inner phloem and earlywood. In P. monticola, the reaction was complicated by the appearance of fissures in the phloem, probably caused by tension from resin pressure. Phloem resinosis was accompanied by apparent secretion of phenolic compounds, presumably from parenchyma cells. The possible origin of these secondary resins and the potential mode of action of the chemicals used are discussed.

Changes in phloem phenolic content of Norway spruce (Picea abies (L.) Karst.) clones were followed during the first 12 days of the reaction induced by phloem artificial inoculation with Ceratocystis polonica Siem., a bark beetle (Ips typographus L.) associated fungus. The aim was to confirm our previous results concerning the mechanisms of this reaction and the possible predictors of Norway spruce resistance to bark beetles and their associated fungi. The induced reaction was characterized by a slight decrease of tanning ability and an increase of (+)-catechin concentration, which confirmed our previous observations. The relative resistance of the clones was first predicted using the predictors previously proposed. In addition, the first axis of the principal component analysis describing the phenolic content of all clones was used as a synthetic predictor (resistance axis). Related variables were also tested as predictors. Actual resistance of each clone was then measured, using mass inoculations of C. polonica, and was compared with the predictions. Four predictors were so validated: the resistance axis, tanning ability and isorhapontin concentration in uninoculated phloem, and (+)-catechin concentration in the phloem 6 days after its inoculation. Phloem phenolic composition could thus be used to predict Norway spruce resistance to bark beetles and their associated fungi.

Healthy lodgepole pine trees (Pinuscontorta Dougl. var. latifolia Engelm.) were girdled on the lower trunk in patterns designed to selectively eliminate the influence of materials transported from the roots, lateral tissues, and crown. Titres of soluble sugars and starch observed in areas isolated by girdling were significantly lower than those observed in areas open to the upper bole and crown. Corresponding decreases were observed in the numbers of Dendroctonusponderosae Hopkins attacking those areas.

The effects of induced translocation stress upon heat pulse velocity, reactions to pathogenic fungi, and bark beetle attack dynamics were compared before, during, and after severe cooling of the bole and after girdling of xylem and phloem in Pinus contorta Douglas var. latifolia Engelmann. Cooled trees evidenced a reduction of heat pulse velocity and the elimination of observable wound responses, which returned to normal upon cessation of the stress the following year. A tree naturally attacked and colonized by Dendroctonus ponderosae Hopkins also evidenced reduced heat pulse velocity within 2 weeks of bark beetle attack. Heat pulse velocity in girdled trees did not change. Stress due to drought and (or) bark beetle attack in nature may be analogous to that induced by cooling. Such stress may reduce a tree's ability to resist bark beetle attack and fungus invasion.

Development of lesions in resistant grand fir trees was observed from time of uninoculated- control injury and Trichosporium symbioticum inoculation to wound stabilization. Lesion development was similar in both types of injury, showing a rapid expansion phase followed by expansion reduction and stabilization. However, in fungus-inoculated wounds vertical lesion growth in the first 7days was much more rapid.Microscopic examination and culturing data showed that T. symbioticum generally lags behind the lesion boundary and is confined within the lesion at the time of wound stabilization. Schizogenic traumatic resin cavity formation begins 14–21 days after wounding and is followed by callus formation 14 days later.Reisolation of the fungus from the lesion indicated that resin and phenolic compounds which accumulated within the reaction zone had little effect on the viability or virulence of the pathogen. These results suggest that fungal confinement in the lesion in resistant grand fir is due to degenerative metabolism within the lesion, which robs the medium of nutrients essential to fungal growth and development, and later is due to secondary resin produced by traumatic resin cavities.

The monoterpene hydrocarbons of the cortical blister oleoresin of Abies grandis were compared, using gas chromatography, with those obtained from lesions that formed as a response of the tree to inoculation with cultured Trichosporium symbioticum, a fungus which is transmitted by the fir engraver beetle Scolytus ventralis. The resins from each source differed both quantitatively and qualitatively. Three terpenic compounds (tricyclene, camphene, and bornyl acetate) that are normally present in primary resin were not found in secondary resin. However, resins that formed in response to the inoculation contained higher concentrations of myrcene in three quarters of the trees and delta3-carene in one quarter of the trees that were sampled than resin from pitch blisters, which contained only trace amounts of these two compounds. These results suggest that conifers respond to fungus infection by producing monoterpenes which are more toxic, repellent, and (or) inhibitory to bark beetles and their associated fungi (e.g. myrcene and delta3-carene) at the expense of attractive or less biologically active compounds (e.g. camphene) which are present in the preformed resin system.