Wolves adapt territory size, not pack size to local habitat quality.

1. Although local variation in territorial predator density is often correlated with habitat quality, the causal mechanism underlying this frequently observed association is poorly understood and could stem from facultative adjustment in either group size or territory size. 2. To test between these alternative hypotheses, we used a novel statistical framework to construct a winter population-level utilization distribution for wolves (Canis lupus) in northern Ontario, which we then linked to a suite of environmental variables to determine factors influencing wolf space use. Next, we compared habitat quality metrics emerging from this analysis as well as an independent measure of prey abundance, with pack size and territory size to investigate which hypothesis was most supported by the data. 3. We show that wolf space use patterns were concentrated near deciduous, mixed deciduous/coniferous and disturbed forest stands favoured by moose (Alces alces), the predominant prey species in the diet of wolves in northern Ontario, and in proximity to linear corridors, including shorelines and road networks remaining from commercial forestry activities. 4. We then demonstrate that landscape metrics of wolf habitat quality - projected wolf use, probability of moose occupancy and proportion of preferred land cover classes - were inversely related to territory size but unrelated to pack size. 5. These results suggest that wolves in boreal ecosystems alter territory size, but not pack size, in response to local variation in habitat quality. This could be an adaptive strategy to balance trade-offs between territorial defence costs and energetic gains due to resource acquisition. That pack size was not responsive to habitat quality suggests that variation in group size is influenced by other factors such as intraspecific competition between wolf packs.

Space-use behaviour of woodland caribou based on a cognitive movement model.

Movement patterns offer a rich source of information on animal behaviour and the ecological significance of landscape attributes. This is especially useful for species occupying remote landscapes where direct behavioural observations are limited. In this study, we fit a mechanistic model of animal cognition and movement to GPS positional data of woodland caribou (Rangifer tarandus caribou; Gmelin 1788) collected over a wide range of ecological conditions. The model explicitly tracks individual animal informational state over space and time, with resulting parameter estimates that have direct cognitive and ecological meaning. Three biotic landscape attributes were hypothesized to motivate caribou movement: forage abundance (dietary digestible biomass), wolf (Canis lupus; Linnaeus, 1758) density and moose (Alces alces; Linnaeus, 1758) habitat. Wolves are the main predator of caribou in this system and moose are their primary prey. Resulting parameter estimates clearly indicated that forage abundance is an important driver of caribou movement patterns, with predator and moose avoidance often having a strong effect, but not for all individuals. From the cognitive perspective, our results support the notion that caribou rely on limited sensory inputs from their surroundings, as well as on long-term spatial memory, to make informed movement decisions. Our study demonstrates how sensory, memory and motion capacities may interact with ecological fitness covariates to influence movement decisions by free-ranging animals.

Phase shift keyed systems based on a gain switched laser transmitter.

Return-to-Zero (RZ) and Non-Return-to-Zero (NRZ) Differential Phase Shift Keyed (DPSK) systems require cheap and optimal transmitters for widespread implementation. The authors report on a gain switched Discrete Mode (DM) laser that can be employed as a cost efficient transmitter in a 10.7 Gb/s RZ DPSK system and compare its performance to that of a gain switched Distributed Feed-Back (DFB) laser. Experimental results show that the gain switched DM laser readily provides error free performance and a receiver sensitivity of -33.1 dBm in the 10.7 Gbit/s RZ DPSK system. The standard DFB laser on the other hand displays an error floor at 10(-1) in the same RZ DPSK system. The difference in performance, between the two types of gain switched transmitters, is analysed by investigating their linewidths. We also demonstrate, for the first time, the generation of a highly coherent gain switched pulse train which displays a spectral comb of approximately 13 sidebands spaced by the 10.7 GHz modulation frequency. The filtered side-bands are then employed as narrow linewidth Continuous Wave (CW) sources in a 10.7 Gb/s NRZ DPSK system.

Optimization of a 42.7 Gb/s wavelength tunable RZ transmitter using a linear spectrogram technique.

The optimization of a wavelength tunable RZ transmitter, consisting of an electro-absorption modulator and a SG DBR tunable laser, is carried out using a linear spectrogram based characterization and leads to 1500 km transmission at 42.7 Gb/s independent of the operating wavelength. We demonstrate that, to ensure optimum and consistent transmission performance over a portion of the C-band, the RF drive and bias conditions of the EAM must be varied at each wavelength. The sign and magnitude of the pulse chirp (characterized using the linear spectrographic technique) is therefore tailored to suit the dispersion map of the transmission link. Results achieved show that by optimizing the drive and DC bias applied to the EAM, consistent transmission performance can be achieved over a wide wavelength range. Failure to optimize the EAM drive conditions at each wavelength can lead to serious degradation in system performance.

Reducing stem bending increases the height growth of tall pines.

The hypothesis was tested that upper limits to height growth in trees are the result of the increasing bending moment of trees as they grow in height. The increasing bending moment of tall trees demands increased radial growth at the expense of height growth to maintain mechanical stability. In this study, the bending moment of large lodgepole pine (Pinus contorta Dougl. Ex Loud. var. latifolia Engelm.) was reduced by tethering trees at 10 m height to counter the wind load. Average bending moment of tethered trees was reduced to 38% of control trees. Six years of tethering resulted in a 40% increase in height growth relative to the period before tethering. By contrast, control trees showed decreased height growth in the period after tethering treatment. Average radial growth along the bole, relative to height growth, was reduced in tethered trees. This strongly suggests that mechanical constraints play a crucial role in limiting the height growth of tall trees. Analysis of bending moment and basal area increment at both 10 m and 1.3 m showed that the amount of wood added to the stem was closely related to the bending moment produced at these heights, in both control and tethered trees. The tethering treatment also resulted in an increase in the proportion of latewood at the tethering height, relative to 1.3 m height. For untethered control trees, the ratio of bending stresses at 10 m versus 1.3 m height was close to 1 in both 1998 and 2003, suggesting a uniform stress distribution along the outer surface of the bole.

A unified nomenclature for quantification and description of water conducting properties of sapwood xylem based on Darcy's law.

The literature dealing with the water conducting properties of sapwood xylem in trees is inconsistent in terminology, symbols and units. This has resulted from confusion in the use of either an analogy to Ohm's law or Darcy's law as the basis for nomenclature. Ohm's law describes movement of electricity through a conductor, whereas Darcy's law describes movement of a fluid (liquid or gas) through a porous medium. However, it is generally not realized that, in their full notation, these laws are mathematically equivalent. Despite this, plant physiologists have failed to agree on a convention for nomenclature. As a result, the study of water movement through sapwood xylem is confusing, especially for scientists entering the field. To improve clarity, we suggest the adoption of a single nomenclature that can be used by all plant physiologists when describing water movement in xylem. Darcy's law is an explicit hydraulic relationship and the basis for established theories that describe three-dimensional saturated and unsaturated flow in porous media. We suggest, therefore, that Darcy's law is the more appropriate theoretical framework on which to base nomenclature describing sapwood hydraulics. Our proposed nomenclature is summarized in a table that describes conventional terms, with their formulae, dimensions, units and symbols; the table also lists the many synonyms found in recent literature that describe the same concepts. Adoption of this proposal will require some changes in the use of terminology, but a common rigorous nomenclature is needed for efficient and clear communication among scientists.

Stem sapwood permeability in relation to crown dominance and site quality in self-thinning fire-origin lodgepole pine stands.

Stem sapwood hydraulic permeability, tree leaf area, sapwood basal area, earlywood to latewood ratio of annual rings, radial variation in hydraulic permeability and stem hydraulic capacity were examined in dominant (D), codominant (CD) and suppressed (SP) lodgepole pine (Pinus contorta Dougl. ex Loud.) trees growing on medium and poor sites. Hydraulic permeability on a sapwood area basis (ks) was lower in suppressed trees (0.71 x 10(-12) m2) compared to dominants (1.97 x 10(-12) m2) and codominants (1.79 x 10(-12) m2), and higher on medium than on poor sites. The leaf/sapwood area ratio (S) varied with crown dominance position (D > CD > SP) but not by site type. Leaf specific conductivity (kL) did not vary between crown classes or site types. The relationship between leaf area and stem hydraulic supply capacity (Q*) was strong, but differed among crown classes. Dominant trees and trees from the medium sites had a greater proportion of earlywood in outer rings of sapwood than suppressed trees. Sapwood permeability declined from the cambium to the sapwood-heartwood boundary in all samples, but the decline was more gradual in dominant trees compared to codominant and suppressed trees; differences in the radial variation in sapwood permeability may be related to differences in S. Sapwood permeability is positively related to crown dominance, whereas subdominant (CD and SP) trees have greater Q* in relation to leaf area, leading us to propose that this may give subdominant trees a survival advantage, slowing self-thinning.