Allocating species in Grime’s strategy space: an alternative to trait-based approaches

Background: The three primary-strategy theory proposed by Grime identifies stress and disturbance as key environmental factors leading to the emergence of distinct plant strategies. These are defined by a combination of stress and disturbance tolerance. Plant strategies are usually inferred from sets of traits, but this may lead to circular reasoning and artificial restrictions to species’ distribution in strategy space. Question: Can measurements of stress and disturbance tolerance be used to estimate the position of different species relative to each other in Grime’s strategy space? Data description: Stress, disturbance, and abundances for 50 species at 25 0.5 ha sites. Study site and dates: Semiarid grassland, Oaxaca, Mexico, 2014. Methods: Species’ tolerance to stress and disturbance were inferred from abundances, and used to allocate species in Grime’s space. We tested if some attributes of our study species changed over the strategy space according to theoretical expectations. Results: Most species were allocated towards high disturbance and low stress intensities. Species attributes were in line with the trends expected from their position in the strategy space. Discussion: Perhaps because of a long grazing history, most species were tolerant to disturbance. The allocation of species in the strategy space using stress and disturbance measurements seemed correct based on their attributes. Thus, our measurements seem to reflect the basic principles proposed by Grime. Our method provides relative positions in the strategy space, and (as previous work) requires defining somewhat arbitrary limits to such space if we wish to label species as ruderals, competitors or stress-tolerant.

A Comprehensive Study of Orchid Seed Production Relative to Pollination Traits, Plant Density and Climate in an Urban Reserve in Western Australia

The pollination of 20 common terrestrial orchids was studied in a 60-ha urban banksia and eucalypt dominated woodland in Western Australia. Five years of data (24,000 flowers, 6800 plants) measured fruit set relative to floral areas, capsule volumes, climate, phenology, pollination mechanisms, disturbance tolerance and demography. Pollination varied from 0–95% of flowers, floral displays from 90–3300 mm2 and capsules from 15–1300 mm3 per spike. Pollination traits strongly influenced outcomes, with self-pollination highest (59—95%), followed by sexually deceptive autumn or winter-flowering (18–39%), visual deception (0–48%) and sexually deceptive spring-flowering (13–16%). Pollination was limited by drought in autumn or spring and cool winter temperatures. Some orchids were resilient to drought and one formed seed after the leaves withered. Plant density had the greatest impact on fruit set for orchids forming large groups, especially for sexually deceptive pollination. Consequently, small group average (SGA) pollination was up to 4× greater than overall averages and peak seed production occurred in the best locations for genetic exchange and dispersal. SGA rates and seedpod volumes were strongly linked to clonality, but not to demographic trends. Resource competition limited flowering at higher plant densities and competition within spikes resulted in smaller, later-forming seedpods. Pollination data from co-occurring common orchids identified five evolutionary trade-offs linked to pollination, provided baseline data for rare species and revealed impacts of changing climate.

Finite-Time Regulation of Two-Spool Turbofan Engines With One Shaft Speed Control

Nonlinear control of aircraft engines has attracted much attention in consideration of the inherent nonlinearity of the engine dynamics. Most of the nonlinear design techniques, however, require the information from the rotational speeds of both high-pressure compressor and fan. This is not desirable from engine health management perspective, and this paper proposes a single sensor measurement and single actuator control approach. The proposed method can provide fast regulation of engine speed in a finite-time in comparison with conventional infinite time stability. Important results are obtained on both controller design and disturbance tolerance. Numerical examples are provided for validation of the proposed finite-time controller, demonstrating fast regulation property and remarkable disturbance tolerance capability.

Robust H-Infinity Stabilization and Resilient Filtering for Discrete-Time Constrained Singular Piecewise-Affine Systems

This paper is concerned with the problem of designing robust H-infinity output feedback controller and resilient filtering for a class of discrete-time singular piecewise-affine systems with input saturation and state constraints. Based on a singular piecewise Lyapunov function combined with S-procedure and some matrix inequality convexifying techniques, the H-infinity stabilization condition is established and the resilient H-infinity filtering error dynamic system is investigated, and, meanwhile, the domain of attraction is well estimated. Under energy bounded disturbance, the input saturation disturbance tolerance condition is proposed; then, the resilient H-infinity filter is designed in some restricted region. It is shown that the controller gains and filter design parameters can be obtained by solving a family of LMIs parameterized by one or two scalar variables. Meanwhile, by using the corresponding optimization methods, the domain of attraction and the disturbance tolerance level is maximized, and the H-infinity performanceγis minimized. Numerical examples are given to illustrate the effectiveness of the proposed design methods.

Fast Sampling Control of Singularly Perturbed Systems with Actuator Saturation andL2Disturbance

We will consider the problem of fast sampling control for singularly perturbed systems subject to actuator saturation andL2disturbance. A sufficient condition for the existence of a state feedback controller is proposed. Under this controller, the boundedness of the trajectories in the presence ofL2disturbances is guaranteed for any singular perturbation parameter less than or equal to a predefined upper bound. To improve the capacity of disturbance tolerance and disturbance rejection, two convex optimization problems are formulated. Finally, a numerical example is presented to demonstrate the effectiveness of the main results of this paper.