Rethinking trophic niches: Speed and body mass colimit prey space of mammalian predators

1. Realized trophic niches of predators are often characterized along a one‐dimensional range in predator–prey body mass ratios. This prey range is constrained by an “energy limit” and a “subdue limit” toward small and large prey, respectively. Besides these body mass ratios, maximum speed is an additional key component in most predator–prey interactions.
2. Here, we extend the concept of a one‐dimensional prey range to a two‐dimensional prey space by incorporating a hump‐shaped speed‐body mass relation. This new “speed limit” additionally constrains trophic niches of predators toward fast prey.
3. To test this concept of two‐dimensional prey spaces for different hunting strategies (pursuit, group, and ambush predation), we synthesized data on 63 terrestrial mammalian predator–prey interactions, their body masses, and maximum speeds.
4. We found that pursuit predators hunt smaller and slower prey, whereas group hunters focus on larger but mostly slower prey and ambushers are more flexible. Group hunters and ambushers have evolved different strategies to occupy a similar trophic niche that avoids competition with pursuit predators. Moreover, our concept suggests energetic optima of these hunting strategies along a body mass axis and thereby provides mechanistic explanations for why there are no small group hunters (referred to as “micro‐lions”) or mega‐carnivores (referred to as “mega‐cheetahs”).
5. Our results demonstrate that advancing the concept of prey ranges to prey spaces by adding the new dimension of speed will foster a new and mechanistic understanding of predator trophic niches and improve our predictions of predator–prey interactions, food web structure, and ecosystem functions.

     

Demonstration of subcomponents of PIII in the ERG of isolated rabbit retina using sodium asparaginate]

Experiments on the sum potential to dark flashes after eliminating the positive components by low temperature (25 degrees C) and low content of plasma (10% instead of 50%) in the perfusion fluid have shown that the cornea-negative component PIII is extensively reduced by application of 10 mM sodium aspartate. The existence of an aspartate sensitive PIII-subcomponent, which was first discovered by intraretinal records, is not in agreement with the opinion that the whole PIII represents receptor activity. Fast and slow PIII-subcomponents are also discernible in the cornea-negative PIII - recorded with cross-electrodes - by their time course without and with adding sodium aspartate. The fast subcomponents are demonstrable in a rough approximation by condenser-coupling the amplifier (t = 0.3 sec). Changing the temperature from 22 degrees C to 27 degrees C the temperature quotient amounts to 1,3 for the fast subcomponents, and to 2.1 for the whole PIII including the slow subcomponents.     

Euthanasia and the active-passive distinction

The author examines various claimed differences between active and passive euthanasia and, if there are differences, whether they are morally significant. He refutes arguments based on acting vs. not acting, intention, double effect, cause of death, and natural law theory. Reichenbach proposes that the most helpful distinction is the one between intentional killing (active euthanasia) and appropriate treatment for the dying or terminally ill (passive euthanasia). Significant moral difference, however, rests on the contention that intentional killing is always wrong and that, all else being equal, dying by natural means is intrinsically good, whereas dying by unnatural means is not.     

Structural studies on cyanobacterial photosystem I

The cyanobacterial photosystem, I complex from Synechococcus sp. PCC6301 contains polypeptides of apparent M_r of 70,000, 18,000, 17,700, 16,000 and 10,000. Procedures were developed for the purification of the M_r 17,700 and 10,000 polypeptides. Amino acid analyses showed the absence of cystine and cysteine from these polypeptides. Amino-terminal sequences of 98 residues for the M_r 17,700 polypeptide and of 42 residues for the M_r 10,000 polypeptide were determined. Studies of pigment distribution within the photosystem I complex indicated that the binding of chlorophyll a and -carotene is in part dependent on the presence of these polypeptides.Abbreviations PSI photosystem I - P700 reaction center of PSI - SDS sodium dodecylsulfate - TBS tris-buffered saline - TTBS TBS containing Tween-20     

Effect of noradrenaline chronic administration on brown fat phospholipids

Chronic cold exposure of rats (9 days at 5°C) induces an alteration of the fatty acid composition of phospholipids in brown adipose tissue. The alteration is due to an increase of the unsaturation degree of these lipids. The phenomenon can be reproduced by 10^–7 mole. h^–1 administration of noradrenaline for 9 days in rats kept at 25°C. Thus, phospholipid alteration in brown fat of cold exposed rats is most probably a consequence of the increase of sympathetic tone which occurs in this tissue during exposure to cold.     

Utilization of IncP-1 plasmids as vectors for transposon mutagenesis in myxobacteria

No free plasmid has ever been found in the myxobacterium Myxococcus xanthus, but IncP-1 plasmids are able to integrate into the chromosome of this bacterium. The frequency of integration depends greatly upon the structure of the IncP-1 plasmid used. This property has been used to devise new delivery systems for transposon mutagenesis in this species. Plasmids with low integration efficiencies have proved to be efficient donors of Tn5, while plasmids with very high frequencies of integration could be used directly to generate mutations. These vectors have also proved efficient for Tn5 transfer into other species of myxobacteria, which have not so far been susceptible to genetic analysis.     

2- and 8-azido photoaffinity probes. 1. Enzymatic synthesis, characterization, and biological properties of 2- and 8-azido photoprobes of 2-5A and photolabeling of 2-5A binding proteins

The 2- and 8-azido trimer 5'-triphosphate photoprobes of 2-5A have been enzymatically synthesized from [gamma-32P]2-azidoATP and [alpha-32P]8-azidoATP by 2-5A synthetase from rabbit reticulocyte lysates. Identification and structural determination of the 2- and 8-azido adenylate trimer 5'-triphosphates were accomplished by enzymatic hydrolyses with T2 RNase, snake venom phosphodiesterase, and bacterial alkaline phosphatase. Hydrolysis products were identified by HPLC and PEI-cellulose TLC analyses. The 8-azido photoprobe of 2-5A displaces p3A4[32P]pCp from RNase L with affinity equivalent to p3A3 (IC50 = 2 X 10(-9) M in radiobinding assays). The 8-azido photoprobe also activates RNase L to hydrolyze poly(U) [32P]pCp 50% at 7 X 10(-9) M in core-cellulose assays. The 2- and 8-azido photoprobes and authentic p3A3 activate RNase L to cleave 28S and 18S rRNA to specific cleavage products at 10(-9) M in rRNA cleavage assays. The nucleotide binding site(s) of RNase L and/or other 2-5A binding proteins in extracts of interferon-treated L929 cells were investigated by photoaffinity labeling. Dramatically different photolabeling patterns were observed with the 2- and 8-azido photoprobes. The [gamma-32P]2-azido adenylate trimer 5'-triphosphate photolabels only one polypeptide with a molecular weight of 185,000 as determined by SDS gel electrophoresis, whereas the [alpha-32P]8-azido adenylate trimer 5'-triphosphate covalently photolabels six polypeptides with molecular weights of 46,000, 63,000, 80,000, 89,000, 109,000, and 158,000. Evidence that the photolabeling by 2- and 8-azido 2-5A photoprobes was highly specific for the p3A3 allosteric binding site was obtained as follows.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plant oligoadenylates: enzymatic synthesis, isolation, and biological activities

An enzyme that converts [3H, 32P]ATP, with a 3H:32P ratio of 1:1, to oligoadenylates with the same 3H:32P ratio was increased in plants following treatment with human leukocyte interferon or plant antiviral factor or inoculation with tobacco mosaic virus. The enzyme was extracted from tobacco leaves, callus tissue cultures, or cell suspension cultures. The enzyme, a putative plant oligoadenylate synthetase, was immobilized on poly(rI) . poly(rC)-agarose columns and converted ATP into plant oligoadenylates. These oligoadenylates were displaced from DEAE-cellulose columns with 350 mM KCl buffer, dialyzed, and further purified by high-performance liquid chromatography (HPLC) and DEAE-cellulose gradient chromatography. In all steps of purification, the ratio of 3H:32P in the oligoadenylates remained 1:1. The plant oligoadenylates isolated by displacement with 350 mM KCl had a molecular weight greater than 1000. The plant oligoadenylates had charges of 5- and 6-. HPLC resolved five peaks, three of which inhibited protein synthesis in reticulocyte and wheat germ systems. Partial structural elucidation of the plant oligoadenylates has been determined by enzymatic and chemical treatments. An adenylate with a 3',5'-phosphodiester and/or a pyrophosphoryl linkage with either 3'- or 5'-terminal phosphates is postulated on the basis of treatment of the oligoadenylates with T2 RNase, snake venom phosphodiesterase, and bacterial alkaline phosphatase and acid and alkaline hydrolyses. The plant oligoadenylates at 8 X 10(-7) M inhibit protein synthesis by 75% in lysates from rabbit reticulocytes and 45% in wheat germ cell-free systems.(ABSTRACT TRUNCATED AT 250 WORDS)     

An unusual pattern of carbohydrate utilization in Corallococcus (Myxococcus) coralloides (Myxobacterales)

The myxobacterium, Corallococcus (Myxococcus) coralloides strain Cc c127, could not utilize mono- and disaccharides, but maltotriose and the polysaccharides starch, amylose, amylopectin, and pullulan stimulated growth. Radioactive CO₂ was set free from ¹⁴C-labeled starch. When starch was degraded, small amounts of maltose and glucose accumulated in the culture supernatant. Maltotriose, however, appeared only temporarily. Outside the cells, the trisaccharide could not be split into glucose and maltose. Pullulan was hydrolyzed exclusively into a trisaccharide which during growth was immediately consumed. Hexokinase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and phosphoglucomutase could readily be demonstrated in cell extracts, but fructose-1,6-diphosphate aldolase was present with low activity only. The data suggest that intracellular glucose is metabolized mainly via the pentose phosphate pathway.Prof. Dr. Gerhard Drews gratefully dedicated to his 60th birthday