Spatial Mosaic Research Articles

Modelling territoriality and wolf–deer interactions

WE propose here a mechanism for territorial pattern formation in wolves (Canis lupus) and analyse it using a spatially explicit mathematical model incorporating wolf movement and scent marking. Model results reflect field observations from northeastern Minnesota: buffer zones where wolves are scarce arise between adjacent packs, and near these buffer zones there are increased levels of scent marking1,2. Territories are arranged in a spatial mosaic (Fig. 1) which covers the wolf range. In the model formulation no assumptions are made about actual existence or extent of wolf territory and buffer zones; these arise naturally as stable steady-state solutions to the equations. We show mathematically how reduced predation by wolves in the buffer zones provides a refuge for prey species. Field studies support this; distribution of a primary prey species, white-tailed deer (Odocoileus virginianus), correlates negatively with that of wolves. Deer are found primarily in buffer zones3,4 (Fig. 2).

Lotic Macroinvertebrate Production in Three Dimensions: Channel Surface, Hyporheic, and Floodplain Environments

A three—dimensional spatial perspective was used to determine annual macroinvertebrate production in two low—gradient, first—order stream systems on the Coastal Plain physiographic province of Virginia. Production in predominant habitats was weighted by the proportional areal abundance of each habitat to determine production in the channel surface, hyporheic zone, and floodplains of both blackwater streams. Highest production as dry mass in Buzzards Branch, a sand—bottomed stream, was in debris dams (27.4 g/m2); production on the sand sediment was lower (4.9 g/m2) and decreased with depth into the hyporheic zone, primarily as a function of decreasing oxygen concentration. Production on the floodplain varied with elevation, and hence period of inundation; it was 1.1 and 4.3 g/m2 at high and low elevations, respectively. Production, weighted for habitat abundance, was 1.7 g/m2 on the floodplain and 15.8 g/m2 in the channel (10.2 g/m2 in the hyporheic zone; 5.6 g/m2 on the channel surface). Production in the Buzzards Branch stream system, incorporating the channel and floodplain, was 2.4 g/m,2, 67% of which was on the floodplain, 21% in the hyporheic zone, and 12% on the channel surface. Production in the Colliers Creek system, with a clay and detritus sediment and no hyporheic zone, was only 2.8 g/m2 in debris dams but was 6.1—6.6 g/m2 on channel sediments and floodplain soils. Production in the stream system was 6.1 g/m2, 95% of which was on the floodplain. Primary consumers composed 72—74% of production in the channels and 80—85% on the floodplains. The predominant functional feeding groups differed between habitats, suggesting a spatial mosaic of functioning within the stream systems. The majority of production in debris dams and on the sediment was by shredders (30—46%) and predators (31—48%). Collector—gatherers composed 58% of production in the Buzzards Branch hyportheic zone and 56—61% on the floodplains of both streams. This study further emphasizes the patchy nature of lotic systems and that habitat—specific sampling is required to adequately determine invertebrate production and function in streams. It also shows the need to view streams with a three—dimensional spatial perspective. Both the hyporheic zone and floodplains can contribute a significant proportion of invertebrate production in low—gradient stream systems.

Breeding Seasonality and Reproductive Success of White-Fronted Bee-Eaters in Kenya

AssmAcT.-White-fronted Bee-eaters (Merops bullockoides) at Nakuru, Kenya, reproduce in an environment where food supply for provisioning nestlings is unpredictable and generally scarce. With data from 8 yr of study on three populations of bee-eaters, we examined how these environmental conditions have influenced the timing of breeding and patterns of nesting success. Breeding coincided with the general pattern of rainfall in the Rift Valley. Kenya experiences two rainy seasons per year, and individual bee-eaters bred with either the long or the short rains, but not both. Members of a given population bred colonially and quite synchronously, but members of adjacent populations were often out of phase with one another. As a result, the distribution of longand short-rains breeding populations formed a spatial mosaic. Reproductive success was highly variable but typically low. Mean (?SD) fledging success was 0.57 ? 0.83 young, and only one nest in four produced an independent offspring (6 months of age). Most prefledging mortality (88%) was due to egg losses and the starvation of young. Very little (7%) was attributable to predation. Social factors, primarily intraspecific nest parasitism, were responsible for nearly half of all egg losses, and represent an important cost of group living. Starvation, the single most important source of prefledging mortality, claimed the lives of 48% of all hatchlings. Starvation was greatest at times of low food availability, in nests with large broods, and in nests tended by pairs without helpers. Hatching was asynchronous. This enhanced the ability of older nestlings to monopolize limited food supplies, and resulted in the selective death of the smallest nestling first. Such brood reduction, coupled with the ability of nestlings to slow their development rate in response to food stress, is considered an adaptation for coping with the unpredictable variation in food supply commonly faced by these birds. Received 17 August 1990, accepted 18 January 1991.

Patch-Burning Desert Nature Reserves in Western Australia Using Aircraft

Fire management in desert nature reserves in Western Australia aims to restrict the spread of wildfires and to re-introduce a spatial and temporal mosaic of firecreated patches. Aerial ignition is well suited to patchburning the large, remote and poorly accessible desert reserves. The Weather Factor, a function incorporating wind speed, temperature and relative humidity, dxectly influenced the ignition rate, the range of sizes of burnt patches and the area burnt. During the trials described here, some 140,000 ha of spinifex fuels in the Gibson Desert Nature Reserve were patch-burnt using aircraft at a total cost of A$O.32 ha-1.

Cell-area distributions of planar sections of spatial voronoi mosaics

Planar sections of spatial Voronoi mosaics with respect to Poisson, hard-core, and cluster point processes are considered. The cell-area distribution is determined by the type and the model parameters of the corresponding spatial point process. Monte Carlo methods are used to describe these relations quantitatively. The results are summarized in parameter diagrams. With their help it is possible to characterize a given empirical spatial mosaic by means of planar sections.

Dynamics of ?acute yellowing? in spruce connected with Mg deficiency

The development of “acute yellowing” and spontaneous regreening in spruce was followed by visual observations and by pigment, mineral and soil analyses. Studies of the population dynamics of “acute yellowing” in mapped natural regenerations of spruce (2000 trees) revealed a small-scale spatial and temporal mosaic of yellowing and spontaneously regreening trees, which was reflected in the Mg content of the needles, but not in changes in pH and in the amount of ammonia-exchangeable Mg in soil samples taken from the rooting areas of diseased and of healthy trees. These findings are not compatible with the assumption of cumulative damage by air pollutants and their depositions, which should lead to an irreversible and much more uniform decline within the stands. The findings rather suggest that “acute yellowing” is a syndrome of complex etiology. In extreme cases, it may be caused solely by too little plant-available Mg in the soil, or by severely restricted Mg uptake resulting from root diseases or antagonists of the rhizosphere flora or mycorrhizae. In most cases, probably both determinants are involved. Magnesium fertilizing will be beneficial in any case since it abolishes the soil-born Mg deficiency and compensates the increasing of the threshold for Mg uptake by a biotic factor.

Landscape Ecology: The Effect of Pattern on Process

Consideration of spatial dynamics in many areas of ecology has received increased attention during the past decade. For example, the role of disturbance in creating and maintaining a spatial mosaic in the rocky intertidal zone was studied. Patch size could be predicted very well by using a model based on past patterns of disturbance and on measured patterns of mussel movement and recruitment. The dynamics of many natural disturbances and their effects on the spatial mosaic have received considerable study in a variety of terrestrial and aquatic systems. This paper demonstrates that a long history of ecological studies provides a basis for the study of spatial patterns and landscape-level processes. However, the emphasis previously was on describing the processes that created the patterns observed in the biota. The explicit effects of spatial patterns on ecological processes have not been well studied; the emphasis on pattern and process is what differentiates landscape ecology from other ecological disciplines. Therefore, this review focuses on the characterization of landscape patterns and their effects on ecological processes.

Canopy Gaps and the Two Major Groups of Forest Trees

In all forests there is a cycle initiated by disturbance. We may arbitrarily recognize gap, building, and mature phases (Watt 1947, Cousens 1974, Whitmore 1975, 1978, 1982), thereby designating forests as spatial mosaics of structural phases which change over time as a result of dynamic processes. Gaps, openings in the forest canopy, drive the forest cycle. Very tiny gaps may be filled by lateral ingrowth of surrounding trees. Usually, though, trees grow up from seedlings to form an immature forest of saplings and poles which grow on and develop into mature trees. The mature phase may enter a fourth degenerate phase as trees become senile, but often is destroyed at a stroke by some external factor. Differences in sizes of gaps result in differences in species composition of the next cycle. Present evidence suggests that, in all forests, tree species fall into one or other of two groups. In small gaps seedlings that became established in the shade of the closed forest are released (i.e., commence height growth). By contrast, a quite different group of species colonizes large gaps. Seeds of these species germinate only in the open, so seedlings occur only after formation of gaps. Swaine and Whitmore (1988), while recognizing that there are no universally accepted terms, propose that these groups be called climax (non-pioneer) and pioneer, respectively. Pioneer species only regenerate in large gaps. When a mature canopy of pioneers enters the degenerate phase, small gaps develop, and these are closed by growth of climax species that became established under them. The next cycle is composed of climax species that, unlike the pioneers, can regenerate in situ. The gap phase is thus the most important part of the growth cycle for the determination of floristic composition. Competition among tree species and their different light requirements at the building and mature phases play a lesser role. Intensive study of forest dynamics since the early 1970s suggests this paradigm is applicable to many forests at all latitudes (Whitmore 1988). There are, however, numerous embellishments, as well as many alternatives, and these lead to the great diversity seen even within a single forest biome. A few examples include: clonal spread occurs in some temperate forests; in some tropical rain forests big gaps may be invaded by woody climbers that arrest the next growth cycle; both pioneer and climax species differ in longevity (hence size) and in autecology (e.g., microsite preferences for seedling establishment).

Stratigraphic Condensation of Marine Transgressive Records: Origin of Major Shell Deposits in the Miocene of Maryland

Cyclic stratigraphic sequences in shallow marine records are commonly characterized by a condensed transgressive lag at the base of thicker, shallowing-upward facies. The standard actualistic model for these thin fossiliferous lags, by which most of the shelf is starved owing to coastal trapping of sediment and fossils are suspected of being reworked because of the association with an erosional ravinement, is contradicted by detailed stratigraphic and taphonomic analysis of Miocene examples in the Maryland coastal plain. The four major shell deposits in the Miocene record are condensed (i.e., demonstrably thin relative to coeval strata), transgressive records of intertidal to subtidal environments (to storm wavebase) and are composed of shells produced locally as transgression proceeded. The complex internal stratigraphies of the shell deposits and the mixture of soft- and shell-bottom faunas indicate condensation under a regime of dynamic bypassing rather than complete sediment starvation; bypassed fine sediments accumulated in deeper water environments below storm wavebase. Deeper, even more basinward parts of the shelf were starved of all sediment size fractions and accumulated shell-poor, bone-rich condensed deposits that lie mid-cycle (bracketing the time of maximum water depth). The base-of-cycle shell deposits and mid-cycle bone bed differ not only in composition and in environment and dynamics of condensation, but also in chronostratigraphic value: the onlapping shell deposits must be diachronous to some degree, whereas the mid-cycle bone bed approximates an isochronous marker for correlation. Thus, in some settings at least, transgressive shelves present a spatial mosaic of condensational and depositional regimes. Regardless of origin, all condensed intervals can time-average assemblages and telescope biostratigraphic datums. They otherwise differ widely, however, in paleontologic attributes and are characterized by highly variable and complex stratigraphic anatomies.

The Role of Herbivorous Fishes in the Organization of a Caribbean Reef Community

Experimental manipulations of grazing intensity were used to examine the role of herbivorous fishes in the families Acanthuridae (surgeonfishes) and Scaridae (parrotfishes) in determining distributions and abundances of benthic species within and among shallow tropical reef habitats. A back reef habitat along the Belizean barrier reef was characterized by a diverse benthic assemblage of algal turfs, coralline algae, and the coral Porites astreoides, but by extremely low macroalgal abundance. In contrast, several nearby shallow habitats were dominated by dense stands of several macroalgal species. Experimental reduction of herbivorous fish grazing in the back reef (achieved by constructing exclosures) rapidly and dramatically altered existing patterns of benthic species composition and species abundances. After 10 wk of reduced herbivory, total macroalgal abundance increased significantly in herbivore exclusion areas relative to unmanipulated controls, and was correlated with decreased percent cover of available space, several algal turf species, crustose coralline algae, and Porites. Some macroalgal species were able to directly overgrow and kill portions of Porites colonies within herbivore exclusion treatments. Successful recruitment and growth of several algal species under experimentally reduced herbivory indicated that macroalgal species distributions may be limited by herbivory rather than by lack of spore availability or unsuitable physical conditions. Algal turfs characteristic of many reef habitats appear to represent herbivore—tolerant assemblages, persisting under high grazing intensity but responding rapidly to reduced herbivory with increased abundances, morphological changes, and altered reproductive status. These results suggest that herbivorous fish grazing profoundly influences benthic species distributions and abundances within some tropical reef habitats. Spatial variation in herbivory appears to be of fundamental importance in determining regional patterns of benthic community structure on tropical reefs. The spatial mosaic of benthic community composition among shallow reef habitats was associated with patterns of grazing intensity by herbivorous fishes. Several reef habitats supporting dense macroalgal stands represented spatial refuges from herbivory, with low herbivorous fish densities and reduced grazing intensities. Transplant experiments revealed that algal species characteristic of these low—herbivory habitats were highly susceptible to grazing by herbivorous fishes. Spatial heterogeneity in grazing intensity may contribute to high regional diversity among tropical reef habitats by maintaining different benthic species assemblages under fundamentally distinct selective regimes.

Free-living Plathelminthes in North Sea salt marshes: Adaptations to environmental instability. An experimental study

In the salt marshes on the island of Sylt (North Sea), >100 species of free-living Plathelminthes have been found above mean high tide level. Such a high diversity was unexpected in a harsh and unpredictable environment. In order to resolve this paradox several experiments were conducted. Shortterm physiological resistance is high for variations in salinity and temperature. Vertical movements are performed to escape zones of low oxygen content or decreased water content. Horizontal migrations do not, however, occur and the above adaptations are insufficient to survive the range of conditions in these salt marshes. In sediment cores the moisture conditions, the salinity, and the temperature were manipulated. Different numbers of species were obtained from these treatments because species proved to be capable of encystment when environmental conditions became harsh, and to hatch as soon as conditions improved. At altered salinities and temperatures, different species hatched and became active. Other species endured seasonal desiccation and anoxia by remaining in egg-capsules. High environmental variability in these salt marshes, in spatial mosaics as well as temporarily, allows many species to find periods for activity, and encystment helps them to overcome intermittent harshness.

Census-Based Information Systems for Ethnic Groups: A Study of Leeds and Bradford

"In this paper are explored the problems involved in using Census data as a guide to the evolving ethnic geography of British cities. The relationship between the concept of ethnicity and Census questions on place of birth is traced. The country-of-birth statistics for Small Areas from the 1971 and 1981 Censuses are employed in an attempt to ascertain the influence of technical specifications on the measurement of the residential segregation of ethnic groups in order to distinguish real differences from apparent ones. The attempt is not fully successful, but it does provide clear pointers on how to proceed further in research on the ethnic spatial mosaics that [British] cities now are."

Decision-Making within a Constrained Population

The creation and perpetuation of the social spatial mosaic of a metropolitan area in the United States is a result of thousands of individual migrations. Each of these moves involved a decision-making process that included elements unique to each household. Embodied in each decision were personally unique goals, needs, and aspirations, as well as particular constraints that may have qualified or limited the realization of these desires. Virtually every household is subject to constraints. Income and distance to work, for example, are limitations that are experienced by most households. Households of a few subgroups, however, experience a unique set of constraints. Blacks, for example, have been limited to a particular segment of the city, primarily as a function of race. This limitation still exists, regardless of strong civil rights laws and activities that have occurred during the last decade. Blacks may be termed a constrained population, therefore, because of this unique and influential limitation. Intra-urban migration is a popular topic among the many geographers, sociologists, and other urbanists concerned with the social composition of the American City. The traditional

Primary neuronal inhibitory responses of a chronically isolated slab of auditory cortex to intracortical stimulation in cats

Responses of 579 neurons in a slab of cerebral cortex (3 weeks after its isolation) to intracortical stimulation, with a distance of 0.5, 1.0, and 2.0 mm between recording and stimulating electrodes, were tested intercellularly and histological changes in a similar slab were studied in experiments on cats. Primary IPSPs were shown to develop in the chronically isolated slab in a much larger number of neurons than in the acutely isolated slab. Latent periods of IPSPs in all series of experiments did not exceed 10 msec, and most IPSPs were mono- and disynaptic. The amplitude and duration of the IPSPs were similar to those observed in the acutely isolated slab and intact auditory cortex in cats. It is concluded that local intracortical neuronal chains along which impulses evoking an inhibitory effect in the terminal neuron of the chain are transmitted are of relatively short length. Such chains may participate in local processing of incoming information. Analysis of the distribution of neurons responding by primary IPSPs by duration of their latent periods and depth in the slab in each series of experiments revealed a spatial and temporal mosaic of inhibitory responses in the chronically isolated slab of auditory cortex and showed that this mosaic is due to intracortical mechanisms.

Nitrogen cycling in United Kingdom forests: the relevance of basic ecological research

Following recent reviews on nutrient cycling in temperate and British forests, two aspects of N cycling are selected for examination because of their fundamental importance and their relevance to management—ecosystem research and mobilization of N during decomposition. Despite the early work by J. D. Ovington and P. J. Rennie, only two major forest ecosystem studies have been developed in Britain. Summaries from these ecosystems show that they span the range of temperate forests in the N cycling characteristics. The Pinus nigra plantation on Culbin Sands is functioning on a low capital with low rates of transfer and shows N deficiency after 40 years. In contrast, the mixed deciduous Meathop Wood has a much larger capital of N and higher rates of transfer. The Pinus ecosystem retained a high proportion of added fertilizer N in the biomass and forest floor, and increased growth rates can be explained through N recycling within the trees. Basic concepts of N mineralization are reviewed and it is shown that they need to be modified for application to forests. Uptake by saprophytic and mycorrhizal fungi from the pool of soluble organic N can short-circuit the ammonification pathway and N can be released from substrates with a high C:N ratio by lysis of microbial tissues and faunal feeding. Some examples of evidence of these processes are given, stressing the spatial and temporal mosaic of substrates acting as sinks and sources of N. Management practices can have a marked effect, not only on the quantity of N returned in residues, but on its availability as a result of variation in the associated carbon. However, growth experiments have shown that substrates with C:N ratios above 35 can release significant amounts of N to tree seedlings. A final examination of the recycling processes in the four nutritional stages of a forest emphasizes the importance of the effects of management on the short- and long-term balance of mobilization processes in the forest soil.

Paleogeography and Structural Development of Late Pennsylvanian-Early Permian Oquirrh Basin, Northwest Utah: ABSTRACT

Deposition in the late Paleozoic Oquirrh basin of northwest Utah produced as much as 7.5 km of limestone and sandstone. Study of Upper Pennsylvanian and Lower Permian lithofacies, trace fossils, and body fossils relative to a time framework determined by fusulinid biostratigraphy reveals a spatial mosaic of depositional environments which shifted through time. The Oquirrh basin changed in form from a broad, topographically subdued, shelf area in the Middle Pennsylvanian to a northwest-trending topographic basin in the Late Pennsylvanian. Water depths may have reached 300 to 400 m. Coarse conglomerates, commonly composed of older Oquirrh Group clasts, are common in latest Pennsylvanian and early Wolfcampian deep-water deposits. They record rapid lithification, uplift, and erosion of the margins of the trough, and imply that the Oquirrh basin was bounded by active northwest-trending high angle faults. The faults, with offset rates of about 25 cm/1,000 years, were apparently initiated in the Late Pennsylvanian, and became inactive by the late Wolfcampian. The upper Oquirrh Group records the passive filling of the remnant graben-like trough.The histories of the Oquirrh basin and of basement uplifts and yoked basins throughout the region to the south and east are similar. The northwest trend, high angle fault margins, and rapid structural development in the latest Pennsylvanian and early Wolfcampian demonstrate the Oquirrh basin's tectonic association with the regional deformation responsible for the Ancestral Rocky Mountains. End_of_Article - Last_Page 730------------

Two Sources of Uneven Development Under Advanced Capitalism: Spatial Differentiation and Capital Mobility

Although capitalist penetration results in a certain regional con vergence, uneven development does not disappear under advanced capitalist conditions. Two sources of geographic unevenness are spatial differentiation and capital mobility. Differentiation produces a spatial mosaic in which the pieces are neither equal, autonomous, nor properly considered "underdeveloped." Mobil ity of capital means that capital may use location as a strategy against labor, local development becomes more dependent on outside capital, development comes and goes over time("Boomtownism") and capital generates a permanent reserve of stagnant places — a lumpengeography of capital. These processes of uneven development are not principally owing to flows of surplus value but to the struc turing of places as use-values for capital, nor are the results particularly suscept ible to traditional regional development policies. Labor's appropriate strategies are several, but must be aimed at finding an alternative to capitalist development not toward a misguided effort to redress geographic differences.

Spatial Behavior and Its Alterations: Old and New Concepts

In a normal perceptual situation, the eye not only sees but also moves. This crude evidence seems to have been largely neglected in the classical models of space perception, in which all the retinal information was thought to be gathered while the retina was stationary. There is no doubt, however, that the retina works as a system of polar coordinates, with their origin in the fovea. Each retinal locus can thus be assigned a sign, defined by its position on the polar diagram: distance from the origin and angular distance from one of the axes of reference (vertical or horizontal). Each local sign is assumed to represent a given portion of the physical space, and consequently the retinal image might constitute a reliable two-dimensional spatial mosaic. The point-to-point correspondence between the retinal image and a central copy, caused by the spatial organization of the upper visual centers, is well known. Such a design certainly holds true in the foveal pure cone system, in which each cone-bipolar-cell-ganglion-cell wiring is individual and represents a single spatial unit. But it becomes largely an ideal in the periphery of the fovea itself and in all of the extrafoveal retina, in which the cone size (and the intercone distance) increases and the cone-optic-tract wiring becomes more and more diffuse. Under these circumstances, the spatial retinal map would be better represented in three dimensions, by plotting the spatial resolving power or the spatial reliability on the Z axis; this would show a peak at the center of the fovea and a rapid exponential decrease toward the periphery (see Jones & Higgins, 1947; Polyak, 1941). As a consequence of the nonhomogeneity of the spatial retinal map and of the poor spatial discrimination outside the fovea, the eyes move so as to bring