The effects of cyanobacterial toxins on herbivorous zooplankton depend on cyanobacterial strains, zooplankton species and environmental conditions. To explore the relationship between zooplankton and cyanobacteria, we investigated the effects of Planktothrix agardhii extracts on Daphnia magna population dynamics. We designed an experiment where individuals were grown in the presence of extracts of two P. agardhii strains. We monitored daily life-history parameters of D. magna individuals subjected to microcystin-RR (MC-RR), intracellular and extracellular extracts of a microcystin-producing strain (MC-strain, PMC 75.02) and a microcystin-free strain (MC-free strain, PMC 87.02) of P. agardhii. Measured life-history parameters of D. magna were used to build population dynamics models and compute expected population growth rate, replacement rate, generation time and proportion of adult and juveniles at demographic equilibrium. Results show that MC-RR tends to slow the life history (reduced growth rate and larger proportion of adults). In contrast, intracellular extracts of the two strains tend to accelerate the life history (increased growth rate, decreased generation time and lower proportion of adults). Extracellular extracts produce the same trends as the intracellular extracts but to a lesser extent. However, the MC-strain has stronger effects than the MC-free strain. Interestingly, extracellular extracts of the MC-free strain may have effects comparable to pure MC-RR. Moreover, in the presence of MC-RR and both cyanobacterial extracts, the daily fecundities present a cyclic pattern. These results suggest that MC-RR and unknown metabolites of cyanobacterial extracts have negative effects on D. magna reproduction processes such as those observed with endocrine-disruptive molecules.

A demographic study was carried out on Bertholletia excelsa, the Brazil nut tree, in two primary forest sites in Northern Bolivia where Brazil nuts have been harvested for several decades. In spite of the large proportion (93%) of seeds that are harvested, reasonable densities of recently emerged seedlings were found. Seeds of Bertholletia are contained in woody fruits that are primarily opened by agoutis. Most fruits are left untouched on the forest floor for 1–2 y before they are opened, possibly due to high energetic costs of fruit opening just after fruit fall. However, the proportion of viable seeds is strongly reduced in older fruits.

Growth in diameter at breast height (dbh) was low for pole-sized trees (< 15 cm dbh) and adult trees (> 100 cm dbh) and peaked for intermediate-sized trees (30–60 cm). These trees often attained a growth rate of > 1.5 cm y−1, which is high compared with other non-pioneer tropical trees. This, and the strong growth response to increased light availability found for seedlings and saplings, suggest that Bertholletia excelsa can be classified as a gap-dependent species. Matrix population models were constructed for both study populations. Population growth rates (λ) were close to one, and were most sensitive to persistence in one size category. Age estimates revealed that age at first reproduction (at dbh > 60 cm) amounts to over 120 y, and age in the last category (dbh > 160 cm) to almost 300 y. Given the continuous rejuvenation of the population, the stable population size, the high age at maturity and the long reproductive period, it is concluded that current levels of Brazil nut extraction may be sustained at least for several decades and perhaps for even longer periods.

Borassus aethiopum is a dioecious palm tree of African savannas. A stage-classified matrix population model has been parametrized with field data (Lamto reserve, Ivory Coast). It enabled the study of the persistence of the population, and analysis of its sensitivity to different vital rates. Age of palms in each stage were estimated to complete the description of the palm life-history. The main results are: (1) The studied populations are very close to the equilibrium but the stable stage distribution (predicted by the model) and the observed distribution are significantly different indicating a former change in the vital rates. (2) Reproduction seems to be highly delayed (first reproduction on average at 114 y), while the estimated duration of the reproductive part of the life-cycle is relatively short (22 y).

The population dynamics of perennial crop plants are influenced by numerous factors, including management practices. Conditions in the field vary from year to year, and matrix population models are useful for evaluating population behaviour in relation to environmental variability. In Missouri, the stand persistence of birdsfoot trefoil (Lotus corniculatus), a perennial legume, is often limited by disease and poor seed production. A stage-based, matrix population model was developed to evaluate the population dynamics of birdsfoot trefoil in relation to clipping treatment. The plant growth stages represented in the model were seeds, seedlings, mature vegetative and reproductive plants. Two phases of population growth were evaluated in clipped and unclipped stands. Establishment-phase populations were characterized by relatively high mortality and low reproduction. Elasticity analysis indicated that growth of these populations was most sensitive to the survival of vegetative plants. Mature vegetative plants and seeds comprised the majority of surviving individuals in clipped and unclipped populations, respectively; however, establishment-phase populations under both management treatments tended toward extinction. Populations in the post-establishment phase of growth were characterized by relatively low mortality and high reproduction. Population growth in this phase of growth was most sensitive to seed production, and most individuals in these populations were at the seed stage.