Minimum Patch Size Research Articles

Evolution of local adaptations in dispersal strategies

The optimal probability and distance of dispersal largely depend on the risk to end up in unsuitable habitat. This risk is highest close to the habitat's edge and consequently, optimal dispersal probability and distance should decline towards the habitat's border. This selection should lead to the emergence of spatial gradients in dispersal strategies. However, gene flow caused by dispersal itself is counteracting local adaptation. Using an individual based model we investigate the evolution of local adaptations of dispersal probability and distance within a single, circular, habitat patch. We compare evolved dispersal probabilities and distances for six different dispersal kernels (two negative exponential kernels, two skewed kernels, nearest neighbour dispersal and global dispersal) in patches of different size. For all kernels a positive correlation between patch size and dispersal probability emerges. However, a minimum patch size is necessary to allow for local adaptation of dispersal strategies within patches. Beyond this minimum patch area the difference in mean dispersal distance between center and edge increases linearly with patch radius, but the intensity of local adaptation depends on the dispersal kernel. Except for global and nearest neighbour dispersal, the evolved spatial pattern are qualitatively similar for both, mean dispersal probability and distance. We conclude, that inspite of the gene‐flow originating from dispersal local adaptation of dispersal strategies is possible if a habitat is of sufficient size. This presumably holds for any realistic type of dispersal kernel.

Detection of Leafy Spurge (Euphorbia esula) Using Multidate High-Resolution Satellite Imagery

Leafy spurge is a deep-rooted perennial weed that displaces native rangeland vegetation and replaces forage for cattle and other forages used by vertebrate herbivores. Strategic planning to control this weed requires monitoring its distribution and spread. Classical monitoring techniques, which often involve extensive ground survey efforts, can be aided by the synoptic nature of remotely sensed imagery. This research addresses the use of Space Imaging's 4-m multispectral Ikonos imagery for the survey and detection of leafy spurge infestations. Survey data were collected at a site in western North Dakota and used to produce supervised classifications of leafy surge infestations with Ikonos imagery. Multiple image dates per year were combined with each other to assess the added accuracy afforded by multitemporal imagery. Finally, individual patches of leafy spurge were analyzed to determine the minimum patch size and percent cover that were detectable with supervised classification of Ikonos imagery. Under some circumstances, the imagery was effective at detecting leafy spurge, but in areas with a higher forb component, the classification was not as effective. Multidate imagery provided increased accuracy, but improvements were not consistently significant. Leafy spurge infestations of <30% cover and 200 m2were not reliably detected.

Stabilization of cylinder wakes in shallow water flows by means of roughness elements: an experimental study

Shallow wakes that occur in a wide range of natural flows tend to generate instabilities that develop into large, 2D coherent structures (2DCS). We present the results of an experimental study to stabilize shallow wakes by local, enhanced bottom roughness. Two successful stabilization strategies are compared to a base case of an unsteady bubble wake. First, localized bed roughness is placed in the lateral shear layers near the shoulders of the cylinder. Second, a local roughness element is placed at the end of the recirculation bubble, in the downstream region where large-scale vortices would normally shed. Dye visualization is used to assess the qualitative behavior of the wake, and two-component laser Doppler velocimetry (LDV) measurements are made to measure the Reynolds stress distributions and time-averaged velocity profiles. In both stabilization cases, a minimum patch size of the enhanced roughness elements is required for stabilization, which depends on the momentum thickness of the shear layers and the locations of enhanced Reynolds shear stresses. The main effect of the wake stabilization is a reduction in momentum exchange with the ambient flow due to damping of the large 2DCS. This reduction in eddy diffusivity results in a narrower wake and a slower decay of the centerline velocity deficit with downstream distance compared to the base case of an unsteady bubble wake.

Bryophyte community differences between edge and interior environments in temperate rain-forest fragments of coastal British Columbia

The species richness, community composition, and abundance of bryophytes within taxonomic and functional groups were examined in relation to habitat conditions in forest edge and interior habitats of nine old-growth temperate rain-forest patches remaining after logging in the Nimpkish River Valley of Vancouver Island, British Columbia. Bryophytes were sampled at a fine scale using 0.1 m × 0.3 m microplots to examine responses of species abundance on the forest floor, downed logs, and tree bases and at a coarser scale using 10 m × 2 m belt transects to determine changes in patterns of species richness and distribution. Edge habitats, sampled to a depth of 45 m into the forest fragments, were characterized by greater windthrow disturbance. Within the edge zone, increases in the richness of clearing-affiliated functional groups were associated primarily with the location of windthrown trees and tip-up mounds, rather than with distance from the edge per se. Interior habitats had both greater abundance of old-growth-associated functional groups and total bryophyte cover. The extension of the edge zone to at least 45 m into remnant patches carries implications for minimum patch size requirements in the context of variable-retention logging of coastal temperate rain forests.

Linearity of the Earthquake Recurrence Curve to M < -1 from Little Skull Mountain Aftershocks in Southern Nevada

Laboratory and theoretical studies suggest that there is a minimum patch size for rupture on faults, thus limiting observed earthquake sizes to above some moment or magnitude corresponding to this patch dimension. This limit, most likely being at a much lower magnitude than that which can be observed due to background noise of the Earth and to attenuation, is difficult to verify for real earthquakes. We have recorded earthquakes to as small as M -2 (Richter local magnitude) in the aftershock zone of the M 5.6 Little Skull Mountain earthquake of 29 June 1992. The network threshold for location is below M 0. However, by considering all the triggered earthquakes at station LSC, which is just above the aftershock zone, and combining these with the located events, the recurrence curve is extended well below the network threshold. We do this by forming a relation between the trace amplitudes of the LSC recordings and the network magnitudes for larger events and then assigning an estimated M to the smaller triggered events. The recurrence curve plotted for the combined data shows a constant b -value of 0.82 down to roughly M -1.2. We show that this magnitude is somewhat below the detection threshold of LSC. The smallest recorded events are similar in appearance to events larger by as much as 3 magnitude units in the aftershock zone, partly due to the band limitation of the 100-samples/sec data and local attenuation. S -to- P ratios much greater than 1 and broadband signals for these small events are indicative of normal tectonic earthquakes. The seismic moments of the very smallest events near M -2 are approximately 5 × 109 N m, larger than observations in deep mines by at least an order of magnitude. Because the source corner frequency is too high to be seen in the spectrum of the smallest earthquakes, we cannot estimate source radii. Manuscript received 19 February 2003.

The Conversion of Even-Aged Stands to Uneven-Aged Structure in Southern New England

Abstract Partial cutting is common in mature even-aged stands in southern New England because the level of disturbance associated with even-aged regeneration methods is unacceptable to many private owners of small forest properties. This cutting often consists of high-grading, but foresters seeking an alternative generally turn to the selection method to begin the conversion of these stands to uneven-aged structure. However, the single-tree or small-group selection methods used may produce long-term results that are similar to high-grading in shifting stand composition toward shade tolerant species (many of which have low timber value). A review was made of the extensive research on the use of the selection method in northern New England and central Appalachian forest types, as well as of the limited research in the southern New England transition hardwood-white pine (Pinus strobus)-hemlock (Tsuga canadensis) type. Recent management experience in a Massachusetts public watershed forest was also reviewed. These provide general guidelines for using selection cutting in the region to regenerate species of a wide range in shade tolerance: (a) use patch selection (rather than single-tree or group selection) with a minimum patch size of 0.3 ac, and with understory as well as overstory trees removed in the patches; (b) use area control (proportion of stand to be harvested) rather than a target diameter distribution (q-value or other method) to regulate the stand cutting level. This approach is likely to be effective in meeting regeneration goals and in being logistically feasible, given the intensity of management possible on most of these properties. North. J. Appl. For. 20(3):109–116.

A Mixed-Integer Formulation of the Minimum Patch Size Problem

Abstract Forest harvest scheduling models have addressed wildlife habitat concerns in a variety of ways. One way is through minimum patch size constraints specifying that a certain amount of the forest must consist of patches meeting both minimum size and minimum age requirements. Patch size requirements may be necessary because a forest with only small patches of mature habitat may not be able to support populations of some wildlife species. Maximum harvest opening size constraints, which are often imposed for legal or policy reasons, tend to divide forest habitat into small patches. Minimum patch size constraints may be able to help mitigate the negative impact of maximum harvest opening size restrictions. Patch size requirements have been considered elsewhere, but a mixed-integer linear programming (MILP) formulation has never been presented. This article presents such a formulation, which allows minimum patch size problems to be solved using the branch and bound algorithm available through commercial solver packages. An example problem is formulated, solved, and discussed. For. Sci. 49(4):608–618.

Acrylate-Based Transdermal Therapeutic System of Nitrendipine

The objective of the present research investigation was to fabricate an acrylate-based transdermal therapeutic system (TTS) of nitrendipine, which could deliver drug at maximum input rate so as to deliver drug in minimum patch size. Transdermal patches were fabricated using synthesized acrylate pressure-sensitive adhesives (PSAs): PSA1, PSA2, and commercially available PSA3 and PSA4 using d-limonene as permeation enhancer. Effect of concentration of d-limonene on permeation kinetics of nitrendipine in PSAs was studied. Fabricated TTS in mentioned PSAs were evaluated for in-vitro release and permeation kinetics through guinea-pig skin. Cumulative release of drug in PSA1, PSA2, PSA3, and PSA4 was observed to be 45%, 40%, 25%, and 25%, respectively, upto 24 hr. Flux of drug through guinea-pig skin calculated at 48 hr in PSA1, PSA2, PSA3, and PSA4, with and without d-limonene, was observed to be 0.346 ± 0.10, 0.435 ± 0.17, 0.410 ± 0.17, and 0.162 ± 0.06, and 0.625 ± 0.19, 1.161 ± 0.46, 0.506 ± 0.17, and 0.520 ± 0.18 (µg/cm2/hr), respectively. The TTS in PSA2 showed comparatively high flux and could deliver drug at high input rate through transdermal route. PSA2 was found to have good rate-controlling property and could be successfully employed in transdermal delivery of nitrendipine.

Conditional persistence in logistic models via nonlinear diffusion

A nonlinear diffusion process modelling aggregative dispersal is combined with local (in space) population dynamics given by a logistic equation and the resulting growth-dispersal model is analysed. The nonlinear diffusion process models aggregation via a diffusion coefficient, which is decreasing with respect to the population density at low densities. This mechanism is similar to area-restricted search, but it is applied to conspecifics rather than prey. The analysis shows that in some cases the models predict a threshold effect similar to an Allee effect. That is, for some parameter ranges, the models predict a form of conditional persistence where small populations go extinct but large populations persist. This is somewhat surprising because logistic equations without diffusion or with non-aggregative diffusion predict either unconditional persistence or unconditional extinction. Furthermore, in the aggregative models, the minimum patch size needed to sustain an existing population at moderate to high densities may be smaller than the minimum patch size needed for invasibility by a small population. The tradeoff is that if a population is inhabiting a large patch whose size is reduced below the size needed to sustain any population, then the population on the patch can be expected to experience a sudden crash rather than a steady decline.

An Assessment of the Focal‐Species Approach for Conserving Birds in Variegated Landscapes in Southeastern Australia

Abstract: The temperate woodlands of the northern Australian Capital Territory and bordering the New South Wales region of eastern Australia have been extensively disturbed by agriculture and urbanization. Small patches of woodland are now embedded in a pastoral or suburban matrix. Birds within landscapes of this region are threatened by a reduction in habitat area, increased isolation, and declining habitat condition. Within this setting, we assessed Lambeck's (1997)“focal species” approach for its ability to identify the minimum patch size, habitat structural complexity, and landscape connectivity required to accommodate existing woodland birds. Presence/absence data were gathered for 72 woodland remnants that varied in size, isolation, and habitat structural complexity. The Hooded Robin ( Melanodryas cucullata) was identified as the focal species for the threats of area and resource limitation because it had the most demanding requirements for area (>100 ha) and habitat complexity. The eastern Yellow Robin ( Eopsaltria australis) was the species most threatened by isolation of remnants. A landscape designed to meet the habitat requirements of these birds should encompass the requirements of all other woodland bird species that are sensitive to similar threats. A revegetation scenario based on the requirements of these two focal species is not feasible because the majority (>95%) of woodland remnants within the study area are too small, too lacking in habitat structural complexity, and too isolated to meet the requirements of the focal species. If woodland management guidelines concentrate on increasing small remnants to 10 ha in size and on ensuring that these remnants have complex shrub and ground‐layer vegetation and are not isolated by more than 1.5 km from neighboring remnants, the needs of at least 95% of the resident woodland bird species in the region should be accommodated. The focal‐species approach was effective for rapidly developing planning guidelines for the conservation of woodland birds in these variegated landscapes, and the approach is likely to be useful for guiding landscape reconstruction in other environments.

Relationships Between Landscape Structure and Breeding Birds in the Oregon Coast Range

Human—caused fragmentation of forests is increasing, yet the consequences of these landscape changes to vertebrate communities are poorly understood. Although bird community response to forest fragmentation caused by agricultural or urban development has been well studied, we have little understanding of these dynamics in landscapes undergoing intensive forest management, where late—seral forest stands are separated by younger forest stands of varying ages and are part of a spatially and temporally dynamic forest landscape. We investigated the relationship between landscape structure and breeding bird abundance in the central Oregon Coast Range. We sampled vegetation and birds in 30 landscapes (250—300 ha) distributed equally among three basins. Landscapes represented a range in structure based on the proportion of the landscape in a late—seral forest condition and the spatial configuration of that forest condition within the landscape. We computed a variety of landscape metrics from digital vegetation cover maps for each landscape. Using analysis of variance and regression procedures, we quantified the independent effects of habitat area and configuration on 15 bird species associated with late—seral forest. Species varied dramatically in the strength and nature of the relationship between abundance and several gradients in habitat area and configuration at the landscape scale. Landscape structure (composition and configuration) typically explained <50% of the variation in each species' abundance among the landscapes. Species' abundances were generally greater in the more heterogenous landscapes; that is, they were associated with the more fragmented distribution of habitat. Only Winter Wrens showed evidence of association with the least fragmented landscapes. These results must be interpreted within the scope and limitations of our study. In particular, the scale of our analysis was constrained by the lower and upper limits of resolution in our landscapes, as set by minimum patch size and landscape extent, respectively. Thus, our results do not preclude much stronger and different relationships at finer and/or coarser scales. In addition, our community—centered habitat classification scheme and artificially discrete representation of patch boundaries may not have captured the functionally meaningful heterogeneity for each species. Finally, our analysis was limited to relatively common and widespread diurnal breeding bird species. Species sensitive to habitat fragmentation at the scale of our analysis may have been rare already and therefore not subject to the parametrical statistical approach that we employed.

Automatic Mapping of Avian Species Habitat Using Satellite Imagery

The Thematic Mapper is a remote sensing instrument aboard the most recent Landsat satellites that generates digital imagery of the earth with a ground resolution of 30 m. This imagery was digitally processed to produce a habitat classification in a study area located in NE Kansas, USA. In addition, bird counts were done throughout this study area. The two data bases were then combined and processed to obtain habitat suitability estimates and produce maps reflecting the habitat needs of individual species. This processing considered not only the types of habitat present (e.g., rangeland, mesic forest, xeric forest) but also the spatial characteristics of the habitat of a species (e.g. minimum habitat patch size, distance to edge). Using this approach it was possible to automatically generate distribution, suitability and density maps, and make rough estimates of population size.

Forward scattering of underwater sound and its frequency dependence on the medium

In the interference region of forward scattered sound by thermal inhomogeneities, there appears to exist a dominant thermal patch size for scattering at a given frequency. Several published results are examined and it is shown that over a decade of frequencies, the dominant (or effective) scattering patch size shows an f−5/2 frequency dependence. It also appears that a minimum patch size of approximately 1 cm is reached and that the frequency selectivity disappears after this value has been reached.