| 1. |
- Berg, Björn, et al.
(författare)
-
Late stage pine litter decomposition : Relationship to litter N, Mn, and acid unhydrolyzable residue (AUR) concentrations and climatic factors
- 2015
-
Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 358, s. 41-47
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper is to evaluate relationships between decomposition rates of Scots pine (Pinus sylvestris) and lodgepole pine (Pinus contorta var. contorta) needle litter in the late stage of decomposition (>30% accumulated mass loss), and the progressively changing concentrations of manganese (Mn), nitrogen (N), and acid unhydrolyzable residue (AUR), as well as mean annual temperature (MAT) and mean annual precipitation (MAP). Using available long-term decomposition studies on pine needle litter in a climate gradient in Sweden, we calculated annual mass loss and related to concentrations of Mn, N, and AUR at the start of each one-year period as well as to MAT and MAP. We investigated these relationships for (i) all data on annual mass loss combined and (ii) annual mass loss for five different decomposition categories as defined by accumulated mass loss. We found highly significant, negative, and dominant relationships between annual mass loss and N (R2=0.39) and AUR (R2=0.39), a slight but significant positive relationship to Mn (R2=0.08) and a significant negative relationship to MAT (R2=0.06). The relationships were dynamic, and changed with accumulated mass loss. The rate-dampening effect of N decreased to be a rate-enhancing effect at c. 60-80% accumulated mass loss. A similar trend was found for AUR, becoming rate-enhancing at 70-80% accumulated mass loss. For Scots pine needle litter the effect of MAT on mass loss decreased with increasing accumulated mass loss and changed to a rate-dampening effect at c. 50-70% accumulated mass loss. Mn showed a stimulating effect on mass loss rate in all categories whereas MAP showed no effect in this mainly boreal climatic gradient. The current approach indicates a method for detailed studies of rate-regulating factors for litter decomposition.
|
|
| 2. |
- Flykt, Anders, et al.
(författare)
-
Fear of Wolves and Bears : Physiological Responses and Negative Associations in a Swedish Sample
- 2013
-
Ingår i: Human Dimensions of Wildlife. - : Informa UK Limited. - 1087-1209 .- 1533-158X. ; 18:6, s. 416-434
-
Tidskriftsartikel (refereegranskat)abstract
- Human fear is important in wildlife management, but self-reported fear provides only partial information about fear reactions. Thus, eye movements, skin conductance, and changes in heart rate were assessed during picture viewing, visual search, and implicit evaluation tasks. Pictures of bears, wolves, moose, and hares were presented to participants who self-reported as fearful of bears (n = 8), fearful of bears and wolves (n = 15), or not fearful of bears or wolves (n = 14). The feared animal was expected to elicit strong physiological responses, be dwelled upon, and be associated with negative words. Independent of fearfulness, bear pictures elicited the strongest physiological responses, and wolf pictures showed the strongest negative associations. The bear-fearful group showed stronger physiological responses to bears. The bear- and wolf-fearful group showed more difficulty in associating bears with good words. Presence of a feared animal in the search task, resulted in prolonged response time.
|
|
| 3. |
- Grönbladh, Alfhild, et al.
(författare)
-
GH (Growth hormone) improves spatial memory and reverses certain anabolic androgenic steroid-induced effects in intact rats
- 2013
-
Ingår i: Journal of Endocrinology. - 0022-0795 .- 1479-6805. ; 216:1, s. 31-41
-
Tidskriftsartikel (refereegranskat)abstract
- Growth hormone (GH) has previously been shown to promote cognitive functions in GH deficient rodents. In this study we report effects of GH on learning and memory in intact rats pretreated with the anabolic androgenic steroid nandrolone. Male Wistar rats received nandrolone decanoate (15 mg/kg) or peanut oil every third day for three weeks and were subsequently treated with recombinant human GH (1.0 IU/kg) or saline for ten consecutive days. During the GH/saline treatment spatial learning and memory were tested in the Morris water maze (MWM). Also, plasma levels of insulin-like growth factor 1 (IGF1) were assessed and the gene expression of the GH receptor, Igf1, and Igf2 in hippocampus and frontal cortex was analyzed. The results demonstrated a significant positive effect of GH on memory functions and increased gene expression of Igf1 in the hippocampus was found in the animals treated with GH. In addition, GH was demonstrated to increase the body weight gain and was able to attenuate the reduced body weight seen in nandrolone treated animals. In general, the rats treated with nandrolone alone did not exhibit any pronounced alteration in memory compared to controls in the MWM, and in many cases GH did not induce any alteration. Regarding target zone crossings, considered to be associated to spatial memory, the difference between GH and steroid treated animals was significant and administration of GH improved this parameter in the latter group. In conclusion, GH improves spatial memory in intact rats and can reverse certain effects induced by AAS (anabolic androgenic steroid).
|
|
| 4. |
- Johansson, Anders, et al.
(författare)
-
Tuning positive feedback for signal detection in noisy dynamic environments
- 2012
-
Ingår i: Journal of Theoretical Biology. - : Elsevier BV. - 0022-5193 .- 1095-8541. ; 309, s. 88-95
-
Tidskriftsartikel (refereegranskat)abstract
- Learning from previous actions is a key feature of decision-making. Diverse biological systems, from neuronal assemblies to insect societies, use a combination of positive feedback and forgetting of stored memories to process and respond to input signals. Here we look how these systems deal with a dynamic two-armed bandit problem of detecting a very weak signal in the presence of a high degree of noise. We show that by tuning the form of positive feedback and the decay rate to appropriate values, a single tracking variable can effectively detect dynamic inputs even in the presence of a large degree of noise. In particular, we show that when tuned appropriately a simple positive feedback algorithm is Fisher efficient, in that it can track changes in a signal on a time of order L(h)= (vertical bar h vertical bar/sigma)(-2), where vertical bar h vertical bar is the magnitude of the signal and sigma the magnitude of the noise.
|
|
| 5. |
- Ma, Qi, et al.
(författare)
-
A first principles derivation of animal group size distributions
- 2011
-
Ingår i: Journal of Theoretical Biology. - : Elsevier BV. - 0022-5193 .- 1095-8541. ; 283:1, s. 35-43
-
Tidskriftsartikel (refereegranskat)abstract
- Several empirical studies have shown that the animal group size distribution of many species can be well fit by power laws with exponential truncation. A striking empirical result due to Niwa is that the exponent in these power laws is one and the truncation is determined by the average group size experienced by an individual. This distribution is known as the logarithmic distribution. In this paper we provide first principles derivation of the logarithmic distribution and other truncated power laws using a site-based merge and split framework. In particular, we investigate two such models. Firstly, we look at a model in which groups merge whenever they meet but split with a constant probability per time step. This generates a distribution similar, but not identical to the logarithmic distribution. Secondly, we propose a model, based on preferential attachment, that produces the logarithmic distribution exactly. Our derivation helps explain why logarithmic distributions are so widely observed in nature. The derivation also allows us to link splitting and joining behavior to the exponent and truncation parameters in power laws.
|
|
| 6. |
|
|
| 7. |
|
|
