Native prey distribution and migration mediates wolf (Canis lupus) predation on domestic livestock in the Greater Yellowstone Ecosystem

Little research has evaluated how the migration and distribution of native prey influence patterns of livestock depredation by large carnivores. Previous research suggests that the presence of native prey can increase depredation rates by attracting predators (prey tracking hypothesis). Alternatively, the absence of native prey may facilitate predation on livestock (prey scarcity hypothesis). In this study, we evaluated support for these competing hypotheses through analysis of 4 years of cattle (Bos taurus L., 1758) depredation data (n = 39 kills), 2 years of summer and fall wolf (Canis lupus L., 1758) predation and tracking data (n = 4 wolves), and 3 years of elk (Cervus elaphus L., 1758) movement data (n = 70 elk). We used logistic regression to compare the relative influence of landscape features and elk distribution on the risk of livestock depredation in areas with migratory and resident elk. Cattle depredations occurred in habitats with increased encounter rates between wolves and livestock. In resident elk areas, depredation sites were associated with elk distribution and open roads. In migratory elk areas, depredation sites were associated with wolf dens, streams, and open habitat. Patterns of carnivore–livestock conflicts are complex, and using ungulate distribution data can predict and minimize such instances.

Simultaneously model-unbiased, design-unbiased estimation

This paper proposes a class of inferential procedures (incorporating both design and estimation elements) that yield estimates of means that are simultaneously model unbiased and design unbiased. Classical regression procedures yield conditionally unbiased estimators for the mean (conditioning on the model and choice of observation points). In contrast, design-based methods yield estimators that are unconditionally unbiased on matter what the form of the underlying model. Variance properties of the proposed class are examined, and applications to bioavailability, water quality from mine run-off, and finite population regression estimation are considered. The proposed procedures perform well, especially in the typical case where a model is only approximately correct.

Metabolic defects in lean nondiabetic offspring of NIDDM parents: a cross-sectional study

First-degree relatives of NIDDM patients have an approximately 40% lifetime risk of developing diabetes, and insulin resistance is the best predictor. However, insulin resistance is altered by many other factors, including age, diet, exercise, and medications. To investigate the metabolic and endocrine alterations associated with insulin resistance when all the above confounding factors are excluded, we examined the first phase of insulin secretion and insulin sensitivity in 49 white normoglycemic (4.99 +/- 0.51 vs. 4.95 +/- 0.41 mmol/l) nonexercising lean (BMI, 24 +/- 3 vs. 23 +/- 2 kg/m2; 105 +/- 3 vs. 104 +/- 3% of ideal body weight) offspring of NIDDM patients. These subjects were compared with 29 matched healthy control subjects by means of an intravenous glucose bolus (0.3 g/kg body wt), immediately followed by a euglycemic-hyperinsulinemic (approximately 420 pmol/l) clamp, along with lipid and amino acid profiles. The offspring showed fasting hyperinsulinemia (40.6 +/- 15.8 vs. 30.9 +/- 13.6 pmol/l; P = 0.005) and higher free fatty acid (FFA) levels (582 +/- 189 vs. 470 +/- 140 micromol; P = 0.007), whereas triglycerides, total cholesterol, and HDL and LDL cholesterol levels were comparable with those of control subjects. Alanine (320 +/- 70 vs. 361 +/- 73 micromol/l; P = 0.017), serine (P = 0.05), and glutamine and glycine (P = 0.02) were lower in the offspring than in the control subjects, whereas branched-chain amino acids (343 +/- 54 vs. 357 +/- 54 micromol/l; P = 0.28) were not different. Insulin sensitivity was lower (4.86 +/- 1.65 vs. 6.17 +/ 1.56 mg x kg(-1) x min(-1); P = 0.001), and an inverse correlation with fasting FFAs in the offspring (adjusted R2 = 0.21, P = 0.0005), but not in control subjects (adjusted R2 = 0.03, P = 0.368), was found. Because insulin sensitivity in the offspring appeared to be a mixture of three distributions, they were subdivided into three subgroups: very low, low, and normal insulin sensitivity (20, 47, and 33%, respectively). The same alterations in amino acid and FFA metabolism were observed in the very low and low subgroups but not in the normal subgroup. The first phase of insulin secretion appeared to compensate significantly for insulin resistance in the low subgroup versus the normal subgroup and controls, but was inappropriately low in the subgroup with very low insulin sensitivity considering its degree of insulin resistance. In conclusion, lean insulin-resistant offspring of NIDDM parents showed 1) trimodal distribution of insulin sensitivity, 2) high fasting plasma FFA concentrations, 3) an inverse correlation between insulin sensitivity and FFA concentration, 4) low plasma gluconeogenic amino acid concentrations, and 5) defective insulin secretion when related to insulin sensitivity in the subgroup of very resistant offspring. These results suggest that, in this white population, insulin sensitivity may be determined by a single major gene and that alterations in FFA metabolism may play a role in the pathogenesis of NIDDM.

Increased glucose transport-phosphorylation and muscle glycogen synthesis after exercise training in insulin-resistant subjects

BACKGROUND

Insulin resistance in the offspring of parents with non-insulin-dependent diabetes mellitus (NIDDM) is the best predictor of development of the disease and probably plays an important part in its pathogenesis. We studied the mechanism and degree to which exercise training improves insulin sensitivity in these subjects.

METHODS

Ten adult children of parents with NIDDM and eight normal subjects were studied before starting an aerobic exercise-training program, after one session of exercise, and after six weeks of exercise. Insulin sensitivity was measured by the hyperglycemic-hyperinsulinemic clamp technique combined with indirect calorimetry, and the rate of glycogen synthesis in muscle and the intramuscular glucose-6-phosphate concentration were measured by carbon-13 and phosphorus-31 nuclear magnetic resonance spectroscopy, respectively.

RESULTS

During the base-line study, the mean (+/-SE) rate of muscle glycogen synthesis was 63 +/- 9 percent lower in the offspring of diabetic parents than in the normal subjects (P < 0.001). The mean value increased 69 +/- 10 percent (P = 0.04) and 62 +/- 11 percent (P = 0.04) after the first exercise session and 102 +/- 11 percent (P = 0.02) and 97 +/- 9 percent (P = 0.008) after six weeks of exercise training in the offspring and the normal subjects, respectively. The increment in glucose-6-phosphate during hyperglycemic-hyperinsulinemic clamping was lower in the offspring than in the normal subjects (0.039 +/- 0.013 vs. 0.089 +/- 0.009 mmol per liter, P = 0.005), reflecting reduced glucose transport-phosphorylation, but this increment was normal in the offspring after the first exercise session and after exercise training. Basal and stimulated insulin secretion was higher in the offspring than the normal subjects and was not altered by the exercise training program.

CONCLUSIONS

Exercise increases insulin sensitivity in both normal subjects and the insulin-resistant offspring of diabetic parents because of a twofold increase in insulin-stimulated glycogen synthesis in muscle, due to an increase in insulin-stimulated glucose transport-phosphorylation.

The roles of insulin and glucagon in the regulation of hepatic glycogen synthesis and turnover in humans

To determine the respective roles of insulin and glucagon for hepatic glycogen synthesis and turnover, hyperglycemic clamps were performed with somatostatin [0.1 micrograms/(kg.min)] in healthy young men under conditions of: (I) basal fasting) portal vein insulinemia-hypoglucagonemia, (II) basal portal vein insulinemia-basal glucagonemia, and (III) basal peripheral insulinemia-hypoglucagonemia. Synthetic rates, pathway (direct versus indirect) contributions, and percent turnover of hepatic glycogen were assessed by in vivo 13C nuclear magnetic resonance spectroscopy during [1-13C]glucose infusion followed by a natural abundance glucose chase in conjunction with acetaminophen to noninvasively sample the hepatic UDP-glucose pool. In the presence of hyperglycemia (10.4 +/- 0.1 mM) and basal portal vein insulinemia (192 +/- 6 pM), suppression of glucagon secretion (plasma glucagon, I:31 +/- 4, II: 63 +/- 8 pg/ml) doubled the hepatic accumulation of glycogen (Vsyn) compared with conditions of basal glucagonemia [I: 0.40 +/- 0.06, II: 0.19 +/- 0.03 mumol/(liter.min): P < 0.0025]. Glycogen turnover was markedly reduced (I: 19 +/- 7%, II: 69 +/- 12%; P < 0.005), so that net rate of glycogen synthesis increased approximately fivefold (P < 0.001) by inhibition of glucagon secretion. The relative contribution of gluconeogenesis (indirect pathway) to glycogen synthesis was lower during hypoglucagonemia (42 +/- 6%) than during basal glucagonemia (54 +/- 5%; P < 0.005). Under conditions of basal peripheral insulinemia (54 +/- 2 pM) and hypoglucagonemia (III) there was negligible hepatic glycogen synthesis and turnover. In conclusion, small changes in portal vein concentrations of insulin and glucagon independently affect hepatic glycogen synthesis and turnover. Inhibition of glucagon secretion under conditions of hyperglycemia and basal concentrations of insulin results in: (a) twofold increase in rate of hepatic glycogen synthesis, (b) reduction of glycogen turnover by approximately 73%, and (c) augmented percent contribution of the direct pathway to glycogen synthesis compared with conditions of basal glucagonemia.

Loss of potentiating effect of hypoglycemia on the glucagon response to hyperaminoacidemia in IDDM

IDDM subjects lose the ability to release glucagon during hypoglycemia. Because replacement of basal levels of amino acids enhances the glucagon response to hypoglycemia in healthy subjects, we tested whether raising amino acid levels during hypoglycemia could reverse the defective alpha-cell response in IDDM patients. For this purpose, 11 IDDM patients (HbA1 9.4 +/- 0.6%) and 8 healthy, nondiabetic subjects received two hypoglycemic insulin clamp studies (0.8 mU.kg-1 x min-1) in which plasma glucose was clamped at 55 mg/dl (3.08 mM) for 180 min. During one of the studies, an infusion of amino acids was superimposed between 120 and 180 min (0.3 g.kg-1 x h-1). This dose of amino acids had a small effect on plasma glucagon levels during euglycemic hyperinsulinemia that was comparable in normal and IDDM subjects. In healthy control subjects, plasma glucagon rose by 80% during the initial hypoglycemic phase of the study. The addition of amino acids produced a further sharp (200-250 ng/L, P < 0.02) rise in plasma glucagon, such a change did not occur in the absence of amino acids. In contrast, plasma glucagon in IDDM patients failed to increase during hypoglycemia alone and rose by only 40-50 ng/L (P < 0.05 vs. controls) when amino acid infusion was superimposed, even though plasma amino acid levels rose to the same extent in IDDM and control subjects. More importantly, the rise in glucagon produced by amino acids was comparable during hypoglycemic and euglycemic hyperinsulinemia in the IDDM patients, results strikingly different from those observed in nondiabetic control subjects.(ABSTRACT TRUNCATED AT 250 WORDS)