Changes In Patch Size Research Articles

Seashore disturbance and management of the clonalArctophila fulva: Modelling patch dynamics

AbstractQuestion:What is the population viability of a critically endangered seashore grass,Arctophila fulvavar.pendulina.Location:Liminka Bay, W Finland, 25°21′70 N, 64°51′90 E.Methods:We constructed a matrix population model based on colonization and disappearance events and patch size changes ofA. fulva.Patches were divided into hydric and non‐hydric zones according to proximity to the seashore and intensity of disturbance. Perturbation analyses were carried out in order to identify transitions critical for population growth. Seed bank and seed germination studies provided background information for the model design.Results:A. fulvapatches observed in the more disturbed hydric zone (closest to the sea) increased in number, as did the total number of patches. However, the number of patches in the less disturbed non‐hydric zone decreased.Conclusions:Short‐term dynamics of theA. fulvapopulation at Liminka Bay seem to be determined by environmental fluctuations, which cause annual variation in transition rates between patch size classes. The long‐term dynamics are probably governed by initiation of primary succession by isostatic land uplift. Increased disturbance at the water's edge may promote persistence ofA. fulvathrough reduced interspecific competition. Our results suggest that shoreline disturbance of the hydric zone is sufficient for maintaining a viable population. Competitive exclusion ofA. fulvain the non‐hydric zone may be delayed by management practices, such as mowing.

Scaling exponents and rank-size distributions as indicators of landscape character and change

Abstract I used a rank-size distribution model and its associated scaling exponents to describe the organization of Yellowstone National Park before and after the 1988 fire season using the statistical distribution of patch sizes. Rank-size distributions indicate the relative effect of patch size on landscape structure, and whether the size of patches differs from what is expected from the model. Scaling exponents describe the distribution and magnitude of change in patch size, and may indicate the effect of fire on ecological processes including succession and resource distribution. The results of my analysis suggest that fires during the 1988 fire-season substantially affected the distribution of patch size in Yellowstone National Park, where large patches have a disproportionate effect on landscape character. For example, patches ≥100 ha occupy a majority of the area even though they represent a minority number of patches in the landscape. Additionally, rank-size distributions indicate fractal properties existed over several orders of magnitude, signifying that processes acting at one level of the landscape hierarchy may be acting similarly at other levels of the hierarchy. This has implications for linking the scaling properties of patch size with other scale-based phenomena including allometry. Finally, the distribution of patch sizes in conjunction with fire-return interval may be useful in assessing the likelihood of landscape-level disturbances.

Seashore disturbance and management of the clonal Arctophila fulva: Modelling patch dynamics

Question: What is the population viability of a critically endangered seashore grass, Arctophila fulva var. pendulina. Location: Liminka Bay, W Finland, 25°21'70 N, 64°51'90 E. Methods: We constructed a matrix population model based on colonization and disappearance events and patch size changes of A. fulva. Patches were divided into hydric and nonhydric zones according to proximity to the seashore and intensity of disturbance. Perturbation analyses were carried out in order to identify transitions critical for population growth. Seed bank and seed germination studies provided background information for the model design. Results: A. fulva patches observed in the more disturbed hydric zone (closest to the sea) increased in number, as did the total number of patches. However, the number of patches in the less disturbed non-hydric zone decreased. Conclusions: Short-term dynamics of the A. fulva population at Liminka Bay seem to be determined by environmental fluctuations, which cause annual variation in transition rates between patch size classes. The long-term dynamics are probably governed by initiation of primary succession by isostatic land uplift. Increased disturbance at the water’s edge may promote persistence of A. fulva through reduced interspecific competition. Our results suggest that shoreline disturbance of the hydric zone is sufficient for maintaining a viable population. Competitive exclusion of A. fulva in the non-hydric zone may be delayed by management practices, such as mowing.

Automatic sampling for CMM inspection planning of free-form surfaces

Coordinate measuring machines (CMMs) are used to examine the conformity of the produced parts with the designer's intent. The inspection of free-form surfaces is a difficult process due to their complexity and irregularity. Many tasks are performed to ensure a reliable and efficient inspection using CMMs. Sampling is an essential and vital step in inspection planning. Efficient and reliable approaches to determine the locations of the points to be sampled from free-form surfaces using the CMM were developed. Four heuristic algorithms for sampling based on the NURBS features of free-form surfaces are presented. The sampling criteria are equiparametric, surface patch size and the surface patch mean curvature. An algorithm for automatic selection of sampling algorithms performs complexity checks on NURBS surfaces, including the surface curvature changes and surface patch size changes, and selects the suitable sampling algorithm. Extensive simulations were performed using the developed methodologies to evaluate their performance using free-form surfaces with different degrees of complexity and compared with the uniform sampling pattern. The CMM measurement errors and manufacturing form errors have been simulated in these studies. The developed algorithms provide a useful tool in selecting the effective sampling plans for the tactile CMM inspection planning of free-form surfaces.

Patch Dynamics of Mussels on Rocky Shores: Integrating Process to Understand Pattern

Within any particular landscape, patch structure and dynamics likely will differ among habitat types because of environmental differences influencing the intensity and outcome of biological interactions. We compared the dynamics of natural and experimentally constructed mussel patches (Mytilus trossulus and M. edulis) in two intertidal habitats, tidepools and emergent rock, over a time series (5, 10, 15 mo) and among seasons (three successive 5-mo intervals). In tidepools, mussels naturally occurred in small patches (median <25 cm2). In contrast, mussels on emergent rock formed extensive beds with decimeter-scale gaps, but these beds start as small patches following disturbance such as ice scour. For our experimental patches (15 cm2) in both habitats, we assessed the relative importance of physical (wave disturbance) and biological (predation, growth, recruitment, and immigration) processes in determining patch size and structure. Although individual experimental and natural patches varied greatly in size over time, mean patch area remained relatively constant. In general, mean size of individuals in experimental patches decreased due to the loss of larger mussels while numbers increased due to recruitment. Wave disturbance, which removes and redistributes mussels, appeared to be more important than predation (by the whelk Nucella lapillus) in determining patch structure and dynamics on this shore, although losses due to either process did not differ consistently between habitats over time. Individual growth rates were low (shell length ≤0.4 mm/mo) but greater in tidepools than on emergent rock, whereas recruitment and immigration rates generally did not differ between habitats. Although each process contributed to changes in patch size and structure, collectively they did not result in a marked divergence in mean patch area or biomass between tidepools and emergent rock over the 15-mo experiment. We suggest that the broad patterns of distribution and abundance of mussels develop slowly on this shore largely because of low individual growth rates. Over time scales of years, however, positive relationships between individual growth and recruitment rates and patch size may accelerate the expansion of aggregations on emergent rock. Mussel assemblages at our site differ from those examined in many other studies in terms of the relative importance of wave dislodgment and predation as causes of loss and in the role of growth in offsetting these losses. This study shows how integrative approaches, with monitoring of patches and individuals within patches, can provide detailed mechanistic understanding of patch structure and dynamics.

Phenotypic plasticity in the expression of sexually selected traits: neglected components of variation

There are numerous studies of between-individual variation in the expression of sexually selected traits, but relatively few of variation within individuals. We investigated within-individual variation, both between and within years, in the size of the sexually selected white forehead patch of the male collared flycatcher, Ficedula albicollis. Patch size was determined from direct measurements of maximum height and width and by image analysis of photographs. Measures obtained by the two methods were highly correlated with each other. Male patch size showed significant repeatability both within and between years, but repeatability was lower for patch width than for patch height. Recent reanalysis of published data suggests that sexual selection acts mostly on the width of the patch rather than the height, suggesting that the component of patch size subject to sexual selection is most plastic. We found that, within individuals, forehead patch width changed in a predictable manner within years, becoming significantly smaller later in the breeding season. This effect was more pronounced in males with an initially larger patch. Patch size also changed predictably between years: males whose parental effort we manipulated experimentally showed corresponding changes in patch size between years, confirming an earlier finding from this population. Our results show that the size of sexually selected traits can vary within individuals, both in response to trade-offs with other life history traits, and also over short timescales. Such variation in the expression of sexually selected traits is important not only for the information it may provide about the processes controlling variation in such traits, but also because failure to account for it will reduce the accuracy of any attempt to quantify selection on them.

Habitat patterns in forested landscapes: management practices and the uncertainty associated with natural disturbances

We present the results of a study to examine the effects of management actions and natural disturbances in influencing the evolution of habitat patterns on forested lands. TELSA, a spatially explicit vegetation succession model with the ability to apply user-defined management actions and stochastic wildfires calibrated to local conditions, was used to evaluate changes in several indicators of habitat condition. We assessed seral stage and patch size changes over multiple 200-year simulations under a constant rate of harvest within each of these analyses. In the absence of natural disturbances, old growth habitat and large patches of forest of similar age and tree species composition decreased unless special management practices were applied. Old-growth management area reserves and periodic ‘aggregated cutblock’ harvesting entries helped maintain forest seral stage distribution at the target level, and patch size characteristics similar to the patterns that would have occurred under historic natural disturbances. Adding wildfire to the management scenarios substantially reduced the amount of old-growth habitat in designated old-growth management area reserves, compromising the ability to maintain old-growth at target levels. A 50% increase in the area designated as old-growth management area reserves would be required to offset the loss of old growth due to wildfire. Although the amount of old-growth habitat was diminished by wildfire, the availability of large habitat patches greater than 250 ha increased. We discuss the need to consider the role of management and natural disturbances in landscape planning, and suggest that redundancy is essential to maintain those features vulnerable to stochastic disturbances. Landscape scenario modeling can facilitate the development of risk averse plans, and encourage the development of innovative approaches to achieving timber and non-timber objectives.

Analysis of a reflectarray antenna using microstrip patches of variable size

Microstrip reflectarrays typically use tuning stubs on each element to adjust the phase of the reflected field. The authors describe a new approach in which the need for tuning stubs is eliminated and phase control is achieved simply by adjusting the resonant length of the patch elements. The advantages of this approach are described, as are a full-wave analysis technique for computing the phase of the reflected field as a function of patch size and a design curve giving the change in patch size for a desired reflected field phase shift.< >

Effects of Host Plant Patch Size on Herbivore Density: Underlying Mechanisms

This study was designed to examine the mechanisms underlying the response of herbivores to variation in the size of host plant patches. In order to explain why identical changes in patch size affect closely related herbivores in different ways, I separated the effects of patch size alone from the confounded effects of the surrounding plant community. Further tests determined whether herbivore densities were directly affected by surrounding nonhost plants (via changes in movement patterns) and/or indirectly affected by changes in host plant size/quality caused by the surrounding nonhost plants. Population densities of three closely related insect herbivores, Acalymma vittatum (SCB), Diabrotica undecimpunctata howardi (SCR), and Diabrotica virgifera (WCR), were studied in experimental patches of squash host plants (Cucurbita maxima). Patches varied in size (4, 16, or 64 plants per patch) and in the nature of their edges (no tomato plant edge, an edge of tomato plants growing in the ground [=interacting nonhost plants], and an edge of tomato plants growing in pots [=non—interacting nonhost plants]). This experimental design enabled a comparison of herbivore densities in patches with no nonhosts surrounding patches, patches with interacting nonhost neighbors, and patches with non—interacting nonhost neighbors. The three herbivore species differed in their response to both patch size and edge treatment. Densities of first generation SCB were significantly affected by both patch size and edge treatment, being greatest in the smallest patches. For a given patch size, densities were greatest in the patches with non—interacting tomato neighbors (tomatoes in pots). More second generation beetles emerged per plant in the treatment with non—interacting plants, but the total number of second generation individuals per plant was not affected by either patch size or edge treatment. SCR densities were significantly affected by edge treatment only, with individuals being most abundant in patches with non—interacting tomato neighbors. For both species, differences in densities as a function of edge treatment were of much greater magnitude in small patches than in large patches. In contrast, population densities of WCR were not influenced by either patch size or edge treatment. The growth (number of leaves) and reproduction (number of flowers and yield) of squash plants were significantly affected by edge treatment, with the largest plants occurring in patches with non—interacting tomato plants and the smallest plants in patches with interacting tomato plants. Patch size influenced both number of leaves and yield. Plant longevity was not significantly influenced by either patch size or edge treatment. The role of these differences in plant parameters in influencing beetle population dynamics was investigated for SCB. For a given average plant size per patch, beetle densities were significantly greater in the treatment with non—interacting nonhosts than in the treatment with no tomato plant edge. A mark—recapture study with SCB and SCR revealed that rates of recapture were not affected by either size or edge treatment, for either herbivore species. However, a greater proportion of both SCB and SCR individuals colonized neighboring small patches than neighboring large patches on a per plant basis. In order to test the mechanisms underlying these herbivore responses to patch size, experiments were conducted with SCB to examine effects of neighboring nonhost vegetation on herbivore feeding preferences and movement patterns. When given a choice of potted plants inside cages, beetles preferred a squash plant alone compared to a squash plant growing next to a tomato plant in a separate pot. When given a choice of leaves (but no direct contact with plants), beetles did not distinguish between leaves from plants grown with conspecific vs. tomato neighbors, indicating beetles did not perceive differences in leaf quality as a function of neighbor type. Observations of movement patterns of SCB beetles in small patches with and without surrounding tomato plants showed that a significantly greater proportion of beetles left patches without surrounding tomato plants than patches with an edge of tomato plants. Thus, surrounding nonhost plants act as a reflective boundary, retaining insects within patches. Movement behavior was also influenced by patch size. Comparisons of flight patterns in 4—plant and 16—plant patches surrounded by tomatoes showed that a greater proportion of beetles emigrated from the large patch because beetles had a lower probability of landing on a tomato plant in large patches. Results from this study for SCB support both hypotheses explaining patch size effects. Beetle densities are affected by patch size, even with no confounding nonhost neighbors present, but they are also affected by the surrounding nonhost community. The effect of nonhost neighbors on population densities consists of a direct positive effect mediated by movement patterns, as well as an indirect negative effect mediated by changes in plant size. The relevance of these results to general patterns of herbivore response to plant spatial pattern is discussed.

Defense of Food Supply by Eusocial Colonies

Overdispersion of colonies exists in many eusocial insects. Overdispersion can be generated by direct attack on colonies or founders, by defense of space, by defense of food resources being harvested, or by exploitative competition. When direct competitive interactions lead to colony overdispersion, territoriality is said to occur. Whereas solitary territory holders typically defend space, most eusocial colonies defend resource patches rather than space per se. Also unlike solitary territory holders, colonies with forager communication can simultaneously defend several spatially separated food patches. A model explores optimal numbers of scouts (discoverers of patches) and recruits (followers) needed to maximize net rate of energy intake by the colony. Territorial costs are added to the model by requiring a higher investment of foragers per unit resource collected. According to the model, optimal colony size and percentage scouts are more sensitive to changes in patch size than in patch density. If patch defense is required for resource control, a decline occurs in optimal percentage of scouts; the decline is greatest for small colonies. Colonies that must defend patches in order to harvest from them suffer a loss in net energy intake; the loss is greatest for small colonies. It is predicted that among eusocial insects, those with territorial defense of resources should preferentially visit large patches and have comparatively large colony sizes and relatively few scouts. Ways of testing these predictions are discussed.

Small-scale pattern of a California current zooplankton assemblage

The small-scale vertical (10′s of meters) and horizontal (100′s to 1000′s of meters) distribution of zooplankton in the California Current near Guadalupe Island, Baja California, Mexico was studied. Vertical distributions were sampled using a vertically-towed Longhurst-Hardy Plankton Recorder (LHPR) which gave a sequence of samples, each integrated over about 5 m, from 250 m to the surface. Because of the sampling biases of the LHPR, details in vertical structure of less than 15 to 20 m were not considered. The pattern of the vertical tows and the variability of the integrated counts of species were used to infer horizontal distribution. Four series of 8 tows each were taken around noon and midnight over a 2-day period. Four of the 8 tows in each series were randomly positioned within 2000 m of a parachute drogue (first day) or a fixed geographic position (second day); four were replicate tows taken at the drogue or the fixed position. Sixty-seven taxonomic categories were counted. The replicate tows, separated by no more than a few hundred meters, gave more similar vertical profiles for species than did the random tows, with separations of 100′s to 1000′s of meters. The night replicate tows showed less variability in depth distribution than did either the night random or any of the day tows, leading to the hypothesis that the vertical distributions observed were generated by interactions of the organisms' diel behavior with internal waves. Variability of abundance estimates using the integrated counts was the same for both replicate and random tows, indicating that horizontal patches may be smaller than 100 m. No evidence was found for a day-night change in patch size, or for a consistent overlapping of patches of different species. Replicate tows gave more similar estimates of community structure (relative proportions of species) than did random tows. Overall day community structure was more similar between tows than night structure. Similarities in species' proportions of any random tow to the replicate tows or to other random tows of a series decreased with increasing distance between the tows being compared. This decrease was greater for the night samples, suggesting that community structure is more heterogeneous at night.

A comparison of zooplankton patterns in the California Current and North Pacific Central Gyre

This study compares the small-scale (100's to 1000's of meters) horizontal spatial distribution of zooplankton from stations in the California Current (29°N; 118°W) and in the North Pacific Central Gyre (31°N; 155°W). Patterns were inferred from the spacing of vertical tows and the variability in abundance of 15 taxonomic categories caught in these tows. In the California Current, 4 tows were taken at random positions within 2000 m of a drogue or fixed geographic position and 4 replicate tows were taken at the drougue or the fixed point. Four series of these 8 tows were taken around noon and midnight during two days. At the Central Gyre station, two similar series (one day and one night) were taken while following a drogue. Estimates of the scale of structure based on comparisons of replicate and random tow variability suggest that aggregated patterns in the Central Gyre are larger than a few hundred meters, while the California Current structures may be less than 100 m in size. Day-night changes in patch size were not apparent in either area. Evidence for multispecies patches was found only for the Central Gyre station. Replication samples in both areas gave more consistent measures of community structure (relative proportions of species) than the random tows. Similarity of community structure decreased with increasing distance between tows being compared. The decrease was much greater for the California Current station, a further indication of smaller patch size in this area. Diurnal changes in community structure occurred in both areas.