Sedimentary records of accelerated nutrient loading in Florida lakes

Transfer functions relating trophic state (Carlson's TSI_{chlorophyll-a}) to present day accumulation rate of (1) nutrients, (2) cations, and (3) organic sediment, are computed using Binford's ²¹⁰Pb-dilution method. As computed from surficial sediments of 27 lakes, former trophic states are reconstructed for recent (²¹⁰Pb-dated) sedimentary histories of 14 lakes. Of the three kinds of models potentially available, model (3) (TSI vs. organic accumulation) is the weakest statistically, and may be unduly influenced by exceptional deposition and/or preservation of allochthonous organic matter. At present, however, it is the only model applicable to all 14 of the histories tested. Results are encouraging in that model accurately predicts observed TSI's in several mesotrophic and eutrophic lakes. Clearly significant increases (accelerations) are inferred only for a of the most eutrophic lakes of the set, while the model consistently overpredicts TSI's of the 7 most oligotrophic lakes. As Whitmore's diatom-assemblage index is a better predictor of TSI than is model (3) in the one eutrophic lake in which it has been tested, we expect more persuasive results when models (1) and (2) can be tested within a more complete set of analytical data. We were surprised to find 3 severely disturbed lakes among the 12 that show little or no acceleration in rate of eutrophication in recent decades, but we defer attempts at explanation until former nutrient loading can be tested by model (1).     

Musical chairs mortality functions: density-dependent deaths caused by competition for unguarded refuges

Structural refuges within which prey can escape from predators can be an important limiting resource for the prey. In a manner that resembles the childhood game of musical chairs, many prey species rapidly retreat to shared, unguarded refuges whenever a predator threatens, and only when refuges are relatively abundant do all prey individuals actually escape. The key feature of this process is that the per capita prey mortality rate depends on the ratio of prey individuals to refuges. We introduce a new class of mortality functions with this feature and then demonstrate statistically that they describe field mortality data from a well-studied coral reef fish species, the Caribbean bridled goby Coryphopterus glaucofraenum, substantially better than do several mortality functions of more conventional form. J. F. Samhouri and R. R. Vance contributed equally to this work.     

The effect of transfer from low to high light intensity on electron transport in Rhodospirillum rubrum membranes

The effects of transfer from low to high ligh intensity on membrane bound electrontransport reactions of Rhodospirillum rubrum were investigated. The experiments were performed with cultures which did not form bacteriochlorophyll (Bchl) for about two cell mass doublings during the initial phase of adaptation to high light intensity. Lack of Bchl synthesis causes a decrease of Bchl contents of cells and membranes. Also, the cellular amounts of photosynthetically active intracytoplasmic membranes decrease.In crude membrane fractions containing both cytoplasmic and intracytoplasmic membranes the initial activities of NADH oxidizing reactions increase only slightly (about 1.2 times) per protein, but the initial activities of succinate oxidizing reactions decrease (multiplied by a factor of 0.7). On a Bchl basis activities of NADH oxidizing reactions increase 3.4 times while activities of succinate dependent reactions increase 1.9 times. With isolated intracytoplasmic membranes activities of NADH as well as succinate dependent reactions increase to a comparable extent on a Bchl basis (about 1.8 times) and stay nearly constant on a protein basis. Cytochrome c oxidase responds like succinate dependent reactions. The data indicate that in cells growing under the conditions applied NADH oxidizing electron transport systems are incorporated into both, cytoplasmic and intracytoplasmic membranes, while incorporation of succinate oxidizing systems is confined to intracytoplasmic membranes only.Activities of photophosphorylation and succinate dependent NAD⁺ reduction in the light increase per Bchl about 1.8 times. On a Bchl basis increases of the fast light induced on reactions at 422 nm and increases of soluble cytochrome c ₂ levels are comparable to increases of photophosphorylations and succinate dependent activities. But increases of slow light off reactions at 428 nm and of b-type cytochrome levels become three times greater then increases of cytochrome c ₂ reactions and levels. These results infer that although electrontransport reactions of intracytoplasmic membranes change correlated to each other, Bchl, cytochrome c ₂ and b-type cytochromes cellular levels are independent of each other. Furthermore, the data indicate that cytochrome c ₂ rather than b-type cytochrome is involved with steps rate limiting for photophosphorylation.Abbreviations Bchl bacteriochlorophyll - DCIP 2,6-dichlorophenolindophenol     

Ecological theories and Dutch nature conservation

This paper aims to achieve insight into various ecological theories in the Netherlands which have different, and sometimes opposing, views on the conservation of nature. Interviews, publications and archival research brought to light four separate theories: vitalistic/holistic, dynamic, cybernetic and chaos. Diversity is reached through stability according to vitalistic/holistic and cybernetic theories, but through change and instablility according to the dynamic and chaos theories. These two groups are working apart, and continue to have their own ideas. Prediction of the future is only possible with the vitalistic/holistic and cybernetic theories. Ecologists who adhere to these theories feel responsible and able in different ways to change ecological nature towards desirable end goals. The other two theories, dynamic and chaos, appear to be less activist.     

Phenotypic characteristics and composition of rhizobia associated with woody legumes growing in diverse Kenyan conditions

Over 480 rhizobia were isolated from root nodules of woody legume and herbaceous trap host species grown in soils collected from 12 different Kenyan sites. The isolates were differentiated by growth and morphological characteristics, intrinsic antibiotic resistance (IAR) and salt (NaCl) tolerance levels (STL) when grown on yeast mannitol mineral salts agar and broth media.The bulk of the isolates (91%) were watery, milky-translucent and curdled milk types with moderate to copious extracellular polysaccharide (EPS). The rest were creamy or white opaque with little to moderate EPS production. Overall, they showed a wide range of growth rates: very fast-growing (mean generation time 1.6–2.5 h), fast-growing (2.8–4.8 h), intermediate between fast- and slow-growing (5.6–5.7 h) and slow- and very slow-growing (6.4–8.8 h). The isolates were tentatively grouped into Rhizobium spp., to include very fast, fast and intermediate (acid-producing) types; and Bradyrhizobium spp., to include very slow, slow and intermediate (alkali-producing) types.Bradyrhizobium spp. were more sensitive to antibiotics (40 g mL^-1) than Rhizobium spp., contrary to the general opinion which indicates that they are normally resistant. Cluster analysis based on sensitivity responses of IAR and STL could not distinguish Rhizobium spp. from Bradyrhizobium spp., neither was there any association by site nor host of isolation except for those isolates trapped with Phaseolus vulgaris at Kibwezi.Our data demonstrated a high diversity of tropical rhizobia associated with trees.