Patch Dispersion Research Articles

Modeling the effects of trap crop attraction strength, patch dispersion, and biological control on pest suppression

Modeling the effects of trap crop attraction strength, patch dispersion, and biological control on pest suppression

Association with humans and seasonality interact to reverse predictions for animal space use

BackgroundVariation in animal space use reflects fitness trade-offs associated with ecological constraints. Associated theories such as the metabolic theory of ecology and the resource dispersion hypothesis generate predictions about what drives variation in animal space use. But, metabolic theory is usually tested in macro-ecological studies and is seldom invoked explicitly in within-species studies. Full evaluation of the resource dispersion hypothesis requires testing in more species. Neither have been evaluated in the context of anthropogenic landscape change.MethodsIn this study, we used data for banded mongooses (Mungos mungo) in northeastern Botswana, along a gradient of association with humans, to test for effects of space use drivers predicted by these theories. We used Bayesian parameter estimation and inference from linear models to test for seasonal differences in space use metrics and to model seasonal effects of space use drivers.ResultsResults suggest that space use is strongly associated with variation in the level of overlap that mongoose groups have with humans. Seasonality influences this association, reversing seasonal space use predictions historically-accepted by ecologists. We found support for predictions of the metabolic theory when moderated by seasonality, by association with humans and by their interaction. Space use of mongooses living in association with humans was more concentrated in the dry season than the wet season, when historically-accepted ecological theory predicted more dispersed space use. Resource richness factors such as building density were associated with space use only during the dry season. We found negligible support for predictions of the resource dispersion hypothesis in general or for metabolic theory where seasonality and association with humans were not included. For mongooses living in association with humans, space use was not associated with patch dispersion or group size over both seasons.ConclusionsIn our study, living in association with humans influenced space use patterns that diverged from historically-accepted predictions. There is growing need to explicitly incorporate human–animal interactions into ecological theory and research. Our results and methodology may contribute to understanding effects of anthropogenic landscape change on wildlife populations.

Influence of prey dispersion on territory and group size of African lions: a test of the resource dispersion hypothesis

Empirical tests of the resource dispersion hypothesis (RDH), a theory to explain group living based on resource heterogeneity, have been complicated by the fact that resource patch dispersion and richness have proved difficult to define and measure in natural systems. Here, we studied the ecology of African lions Panthera leo in Hwange National Park, Zimbabwe, where waterholes are prey hotspots, and where dispersion of water sources and abundance of prey at these water sources are quantifiable. We combined a 10-year data set from GPS-collared lions for which information of group composition was available concurrently with data for herbivore abundance at waterholes. The distance between two neighboring waterholes was a strong determinant of lion home range size, which provides strong support for the RDH prediction that territory size increases as resource patches are more dispersed in the landscape. The mean number of herbivore herds using a waterhole, a good proxy of patch richness, determined the maximum lion group biomass an area can support. This finding suggests that patch richness sets a maximum ceiling on lion group size. This study demonstrates that landscape ecology is a major driver of ranging behavior and suggests that aspects of resource dispersion limit group sizes.

Dispersion in the Yucatan coastal zone: Implications for red tide events

The mechanisms governing dispersion processes in the northern Yucatan coast are investigated using a barotropic numerical model of coastal circulation, which includes wind-generated and large scale currents (i.e. Yucatan Current). This work provides the foundations for studying the dispersion of harmful algal blooms (HABs) in the area. Modelling experiments include effects of climatic wind (from long term monthly mean NCEP reanalysis), short term wind events (from in situ point measurements), and Yucatan Current (YC) characteristics. Its magnitude was approximated from published reports, and its trajectory from geostrophic current fields derived from altimeter data. These provided a range of real and climatic conditions to study the routes in which phytoplankton blooms may travel. The 2-D model results show that a synthetic and conservative bloom seeded in the Cabo Catoche (CC) region (where it usually grows), moves along the coast to the west up to San Felipe (SF), where it can either move offshore, or carry on travelling westwards. The transport to the west up to SF is greatly influenced by the trajectory, intensity and proximity of the YC jet to the peninsula, which enhances the westward circulation in the Yucatan Shelf. Numerical experiments show that patch dispersion is consistently to the west even under the influence of northerly winds. When the YC flows westward towards the Campeche Bank, momentum transfer caused by the YC jet dominates the dispersion processes over wind stress. On the other hand, when it flows closer to Cuba, the local processes (i.e. wind and bathymetry) become dominant. Coastal orientation and the Coriolis force may be responsible for driving the patch offshore at SF if external forcing decreases.

Using spatial analysis to monitor tree diversity at a large scale: a case study in Northeast China Transect

Aims Monitoring and assessing diversity change at a large scale is important for any meaningful biodiversity conservation and management. Spatial analysis techniques can provide information about different aspects of diversity distribution including change. We applied some common spatial analysis methods and additive partitioning of species diversity in the Northeast China Transect as a case study to show how to characterize the distribution and change of tree diversity in this area from different perspectives. Methods The field data were collected from the permanent plots conducted every 4 km. The additive partitioning of species diversity was used to characterize the diversity of tree species at different scales. Moran’s I was used for identifying the spatial scale of autocorrelation, lacunarity was studied for diversity patch contagion and dispersion and spectral entropy was used for assessing the overall spatial distribution. Important findings Datacollectedfrom1986 to1994indicatethat the changeofa diversity was not significant in the study area, but the change of b diversity was significant. The percentage ofa diversity in total diversity (c) increased from 14.2 to 17.2%, and the percentage of b diversity decreased from 85.8 to 82.8%. For botha andb diversities, the scale of spatial autocorrelation decreased at the scale of 25–40 km and increased around 15–20 and 200 km. The lacunarity ofa diversity decreased significantly andtherewasasuddenchangeatthescaleof56–68km,butthelacunarity of b diversity increased across scales. The spectral entropy decreased slightly ina diversity and remained similar forb diversity. By using spatial analysis, we can monitor the diversity change over a large area and also assess the effectiveness of the current conservation strategies.

Effects of cutline density and land-cover heterogeneity on landscape metrics in western Alberta

Forest cutlines are narrow, linear features created in geophysical surveys. In many areas of Canada, forest cutlines are not consistently detected using relatively coarse spatial resolution land-cover maps, such as those produced by classification of Landsat Thematic Mapper (TM) imagery. However, such features may be important in certain wildlife management applications, including those which require an assessment of landscape structure, or forest fragmentation, at various scales. Higher spatial resolution satellite imagery obtained from sensors on platforms such as Satellite Pour l’Observation de la Terre (SPOT) and the Indian Remote Sensing (IRS) system may be used to map forest cutlines for these applications. In this study, a TM-based land-cover map of western Alberta is analyzed with forest cutlines mapped from a TM-IRS fusion image, and the effect of increasing cutline density is quantified on five commonly used landscape metrics used to characterize landscape structure in grizzly bear habitat assessment. The accuracy of the fusion image interpretation was determined to be 88%. Simulated landscapes were tested first, and the study area was divided into 104 hexagon-shaped sample landscapes of about 6 km diameter each. Across these sample landscapes, cutline density and initial landscape heterogeneity were significant parameters in explaining change in three metrics, namely edge density, mean patch size, and patch context (expressed as mean nearest-neighbour distance). Patch size variability (expressed as the coefficient of variation of mean patch size) and patch dispersion (expressed as the coefficient of variation of mean nearest-neighbour distance) required additional information on cutline positioning. Overall, the density of the introduced cutline network and the pre-cutline metric value reliably predicted and quantified the response of landscape metrics of interest to grizzly bear biologists. This study shows the importance of mapping forest cutlines regarding their role in changing landscape structure quantification and points out the necessity of using additional remotely sensed data when the feature responsible for the landscape transformation is of too small a size to appear reliably in common TM-based classified imagery.

Dye dispersion in the surf zone: Measurements and simple models

To examine the spatial and temporal effect of low-volume land-based runoff on beach contamination, discrete batches of dye were released at the shoreline at three beaches in Santa Monica Bay in 2000 (Malibu Creek, Santa Monica Canyon and Pico–Kenter drain). Dye concentration was measured at the shoreline 25, 50 and 100 m alongshore from the dye release point for up to 40 min after dye release. The shoreline concentration time series are characterized either by approximately exponential decay in concentration after passage of the dye patch maximum concentration or by persistent low concentration up to 30 min after passage of the initial dye patch front. In the absence of detailed measurements of physical conditions, several simple advection–diffusion models are used to simulate shoreline concentration time series for an idealized surf zone in order to probe the roles of alongshore current shear and rip currents in producing the observed characteristics in dye concentration time series. Favorable qualitative and quantitative comparison of measured and simulated time series suggest alongshore current shear and rip currents play key roles in generating the observed characteristics of nearshore dye patch dispersion. The models demonstrate the potential effects of these flow features on the extent and duration of beach contamination owing to a continuous contamination source.

Patch evolution and the biogeochemical impact of entrainment during an iron fertilisation experiment in the sub-Arctic Pacific

Abstract An in situ mesoscale iron-fertilisation experiment in the eastern sub-Arctic Pacific (SERIES) was undertaken to test the Iron Hypothesis, that increasing iron supply would stimulate phytoplankton production and particulate organic carbon (POC) export to deep water. Patch dispersion was monitored for 26 days, using an inert tracer (SF6) and biological tracers (chlorophyll-a and fCO2), and we examine the vertical and lateral evolution of the patch, and the influence of dilution on the biological and biogeochemical response to iron addition. Vertical dispersion of the added iron was initially restricted to the upper 12 m by near-surface stratification, although the vertical flux to the lower mixed layer at this time significantly exceeded the unperturbed rate of iron supply. Calculation of vertical diffusion rates (Kz) provided an estimate of the unperturbed Fe flux across the seasonal pycnocline of 0.3–1.5 nmol/m2/d. The iron/tracer patch partially advected around an anticyclonic Haida Eddy that originated off the west coast of Canada in 1999–2000. Lateral patch evolution was initially dominated by current strain, stretching it into a filament of ∼300 km2 by day 11 and reaching a maximum area of 1300 km2 by day 23. Sustained high winds and intrusion of external waters between days 11 and 18 altered patch geometry and advection. Two scenarios for patch evolution are presented of a single exponential dilution at 0.1/d, and a variable dilution in which dilution increased from 0.078/d to 0.16/d (days 11–18) before decreasing to 0.05/d. Dilution rates were used to constrain dissolved iron dynamics, with iron regeneration rates indirectly estimated from biological iron uptake and lateral dilution losses. Lateral entrainment supplied ∼6–7 μmol/L silicic acid and 4.6 μmol/L nitrate to the patch centre by day 20, equivalent to 37% and 45%, respectively, of total biological uptake. Indirect estimates of phytoplankton nitrate uptake from patch dilution indicated a maximum rate of 1.4 μmol/L/d, in agreement with measured rates. The cumulative entrainment of 392–500 mmol dissolved inorganic carbon (DIC)/m2 at the patch centre by day 20 was of the same order as the total biological DIC uptake and POC accumulation. The potential impacts of a mid-experiment increase in dilution were explored; these included elevated entrainment of silicic acid when concentrations in the patch were growth limiting for phytoplankton, and decreased cell aggregation. Both factors could potentially have delayed the onset of bloom termination and export, and increased the longevity of the SERIES phytoplankton bloom.

The influence of habitat patch attributes on coyote group size and interaction in a fragmented landscape

From February 2000 to January 2002, I investigated correlates of landscape fragmentation with coyote (Canis latrans Say, 1823) group size and resulting effects on within-group spatial interaction in west-central Indiana, USA, to determine whether habitat patch dispersion and attributes mediated group maintenance and persistence. Twenty-one radio-collared coyotes were assigned to 15 social groups; group territories were then classified as having dispersed (n = 10) or aggregated (n = 5) resource patches. Group size was larger in territories with aggregated patches and was directly correlated to forest area and inversely correlated to corridor area (top-ranked model: group size = β0 + forest area – corridor area; AICc = –2.12, ΔAICc = 0.0, ωi = 0.67). Territories with aggregated patches had proportionally more forest (mean = 0.41, SE = 0.02) and less corridor (mean = 0.01, SE = 0.002) habitats than territories with dispersed patches (forest area: mean = 0.11, SE = 0.01; corridor area: mean = 0.03, SE = 0.002). Within-group spatial interaction was not influenced by patch dispersion. I suggest that differences in territory and group sizes relative to patch dispersion reflect the complex combination of environmental pressures present in human-dominated landscapes and their potential to perturb canid social organization.

Evaluating empirical scaling relations of pattern metrics with simulated landscapes

Landscape patterns demonstrate scale‐dependent properties that have been parsimoniously described by empirical scaling functions. These functions, derived from multiple‐scale analysis of real landscapes, are evaluated here for their generality and robustness via a series of simulated landscapes with known landscape patterns. A factorial design was used to generate these landscapes, varying the number of classes, class abundance distribution, and patch dispersion. The results confirm that the three types of scaling relations were both general and robust. Type I metrics were predictable with simple scaling functions (e.g. power laws or linear functions); Type II metrics showed stair‐case like response patterns and were essentially not predictable; Type III metrics exhibited erratic response patterns that were unpredictable in most cases. However, significant differences were found between real and simulated landscapes when landscape extent was increased. Systematic changes in grain size show that the predictability of scaling relations increases with the number of classes, the evenness of class abundance distribution, and the aggregation of patch dispersion. However, random patch dispersion seemed to enhance the predictability of scaling relations when changing spatial extent.

Spatial organization, group living and ecological correlates in low‐density populations of Eurasian badgers, Meles meles

Summary 1 Territoriality and group living are described in a low-density population of Eurasian badgers, Meles meles L., by studying the patterns of spatial grouping and territory marking, as well as the differences between individuals in some of their characteristics (body condition and dispersal) and in their space use (seasonally, periods of activity and interaction between pairs of individuals) under strong seasonal fluctuations in the availability of the key resource (young rabbits, Oryctolagus cuniculus L.). Finally, the role of the spatial distribution of the main prey (young rabbits) in the development of sociality was also studied in order to test some of the assumptions and predictions of the resource dispersion hypothesis (RDH). 2 Badgers were territorial, showing a flexible system of territory marking, which includes the marking of the most used areas (sett-latrines at the centres of activity) and additionally, at the smaller territories, a system of border-latrines in the areas of contact between territories. The maximum use of border-latrines was associated with the reproductive season, and that of sett-latrines with the season of food scarcity. 3 In the study area where badgers had rabbits as main prey, territories were occupied by small groups of animals, formed by one adult female who reproduced, one adult male who also showed signs of reproductive activity, the cubs of the year (if there was reproduction) and some animals born during previous years, which remained in their natal territory until their dispersal (normally during the mating season of their third or fourth year of life). This system was not strictly fixed as males, given the opportunity, expanded their territories to encompass additional females. Territories in another study site were occupied by one adult female (marked), plus the cubs of the year and another adult individual (unmarked). 4 In winter and spring dominant females and subordinates used only a small fraction of their territories, moved short distances, at a low speed and covering small areas per night. These seasons corresponded with the reproduction of rabbits (highest food availability). Dominant females were the only individuals using all the territory available in the summer (lowest food availability), when badgers had the worst body condition. Food availability increased again in autumn, as did body condition, while range sizes were again reduced. Dominant males used the same proportion of their territories over all seasons. However, in winter (reproductive season) they moved faster, over longer distances, and covered larger areas per period of activity. These results indicate that use of space by dominant males was affected by different factors from that of dominant females and subordinates. 5 RDH does not seem to explain group living in our populations because: (a) territoriality in each pair of primary animals was driven by different factors (trophic resources for females and females for males); (b) dominant males acted as expansionists; and (c) territory size was related to its richness and not to patch dispersion. 6 We propose an integrative hypothesis to explain not only group formation but also interpopulation variability in the social organization of badgers within ecological, demographic and behavioural constraints and in the light of current theory on delayed dispersal.

Foraminifera may structure meiobenthic communities.

The cosmopolitan benthic foraminiferan, Ammonia beccarii, is a fervent microfloral predator which often forms densely-populated 2-4 cm2 aggregates in the field. Sediments within aggregate patches become extensively pelletized, mucus bound and depleted in microfloral food. On a West German Wattenmeer mudflat, copepodite and naupliar densities of a predominant harpacticoid copepod, Amphiascoides limicola, were significantly depressed in sediments containing>100 A. beccarii·3 cm-2 suggesting a possible foraminiferal: copepod amensalism. Therefore, I cultured A. beccarii and A. limicola separately in sediment microcosms and then tested if A. limicola's seemingly negative reaction to sediments containing A. beccarii occurs under controlled conditions, how various life stages of A. limicola are affected, and what the repulsive mechanisms of A. beccarii may be. In natural field sediments seeded with a latin-square dispersion of sterile sediment patches containing 0 or 100 A. beccarii, mean A. limicola naupliar and copepodite densities were 2 to 6 times lower in Ammonia-rich patches than Ammonia-poor patches (i.e. patches containing <100 A. beccarii·3 cm-2). Choice experiments directly testing potential A. beccarii inhibitory mechanisms were conducted with A. limicola copepodites: Cubic microcosms containing a latin-square patch dispersion of (1) sterile sediments (SS) seeded with 100 A. beccarii (low microflora), (2) SS bound with sterile mucus (0.0001%) (low microflora), (3) SS seeded with pelletized sediments (high microflora), and (4) SS seeded with mucus and pellets (high microflora), showed that copepodites colonized 1≪2 & 3, but 1 & 4 were not significantly different. Mucus addition by itself, in the absence of pelletization and microflora, strongly facilitated colonization-as did addition of microfloral-rich pelletized sediments. Pelletization and mucousbinding combined, but with low microflora, were least attractive to A. limicola. Pelletization and mucous-binding combined, but with high microflora, were more attractive to A. limicola than its complement, but not significantly so. Thus A. beccarii's inhibition of A. limicola is probably not caused by sediment pelletization and simple mucous exudates but by local microfloral depletion within aggregate foraminiferal patches.

Intertidal Mosaics: Patch Size, Propagule Availability, and Spatially Variable Patterns of Succession

Localized disturbances transform most assemblages of sessile organisms into mosaics of patches differing in characteristics such as size and age (time since last disturbed). This mosaic nature of natural communities is especially evident on exposed intertidal shores along the northwest coast of North America, where the competitively dominant mussel, Mytilus californianus, occupies much of the space at mid—tidal levels. Nearly continuous beds of this species are interrupted by patches of open space generated mainly by the shearing forces of winter storm waves. These patches serve as foci for the recruitment, growth, and reproduction of many competitively inferior, fugitive species, including both algae and sessile invertebrates. These species are doomed to local extinction as the lateral encroachment of adult mussels closes the patch and excludes then from the area. This study examined the dynamics of algal succession within experimental patches cleared in mussel beds. In particular, two potentially important sources of variation in successional dynamics were investigated: (1) the size of the patch when first created, and (2) the location of the patch with respect to potential sources of propagules. The size of a cleared patch was found to influence strongly the course of algal succession. This effect was largely indirect, resulting from an interaction between patch size and grazing intensity. Small patches support higher densities of grazers, especially limpets, than do large patches. As a consequence, the assemblages of algae that develop within small and large patches differ markedly. The assemblage in small patches includes grazer—resistance but apparently competitively inferior species, whereas that in large patches is composed of grazer—vulnerable but competitively superior species. Small patches appear to serve as refuges from competition for grazer—resistant species. Recruitment was variable among the experimental patches. Percent cover of several species was found to be highly correlated with the cover of epozoic conspecific adults within 1 m of the edge of the patch. This result suggests that a number of the species inhabiting patches within mussel beds may disperse their propagules over relatively short distances. For such species, patch dispersion may influence the regional dynamics of their populations.

A priori determination of valid control sites: An example using marine meiobenthic nematodes

Proper control sites for nematode abundance, patch size and patch dispersion could not be defined prior to a manipulative oil pollution experiment despite the apparent physical similarity and proximity of two locations. Comparisons of abundance and patch size demonstrated that neither site could serve as a control for the other. Spectral analysis was not useful, in this case, in resolving patch dispersion in the range of 1·2 to 60 cm. These data indicated that in circumstances where a posteriori studies comparing two areas cannot be avoided, it is only with great caution that a single factor should be interpreted as causative of observed densities or distribution of organisms.

Experimental and Mathematical Analyses of Herbivore Movement: Quantifying the Influence of Plant Spacing and Quality on Foraging Discrimination

Using mark—recapture experiments, I studied the foraging movements of two crucifer feeding flea beetles, Phyllotreta cruciferae and P. striolata. To determine the influence of distance between host patches, and their quality, on beetle movement, I released marked beetles in experimental arrays of collards (Brassica oleracea). I quantified and interpreted movement behavior by applying a passive diffusion model and a continuous—time Markov model to recapture distributions. These models provided both a standard protocol for interspecific comparisons and a formal tool for translating movements into steady—state foraging patterns. In homogeneous arrays (all collard patches of similar quality), P. cruciferae and P. striolata moved in accordance with a constant—coefficient diffusion model. The dispersal rates of both beetles increased as the distance between patches declined; thus, patches of collards acted as stepping—stones to accelerate beetle dispersal. Beetle movement was hampered by old—field vegetation; beetles moved along cultivated ground in lieu of entering dense stands of goldenrod. Under all experimental conditions, P. cruciferae was consistently more mobile than P. striolata. By differentially fertilizing and pruning collards, I created "lush" and "stunted" patches of collards, which were arranged alternately along linear arrays. To determine the influence of patch dispersion on foraging selectivity, I varied the distance between these patches of unequal quality. The degree of foraging discrimination exhibited by the beetles was greatest where patches were closest together, and declined as distance between patches increased. At comparable spacings, P. cruciferae consistently exhibited a higher degree of foraging discrimination than did P. striolata. I developed a Markov model of patch—to—patch dispersal in which each flea beetle's probability of movement depends on patch quality and distance to neighboring patches. Using 60—min observations of marked flea beetles to estimate model parameters, I found that the steady states of foraging discrimination predicted by the model matched the discrimination levels exhibited by undisturbed flea beetles in comparable control arrays of collard patches. Thus, simple movement rules were extrapolated into expected foraging behavior; the dependence of that foraging behavior on patch dispersion was shown to be mediated by varying levels of mobility. In particular, proximity between heterogeneous patches affords beetles greater opportunity for nonrandom foraging than when patches are widely scattered. Since movement is the mechanism by which beetles respond to heterogeneous environments, rates and patterns of movement determine each species' ability to concentrate its numbers on the best foodplants. P. cruciferae is more mobile than P. striolata and in turn can better adjust to variation in collard quality. The interplay between beetle movement and plant dispersion may have consequences well beyond the simple distribution of feeding activity among heterogeneous host patches.

DISTRIBUTION AND ABUNDANCE OF THE LAMP URCHINECHINOLAMPAS CRASSA(BELL) 1880 IN FALSE BAY, CAPE

Summary The subtidal distribution and abundance of the burrowing lamp urchin, Echinolampas crassa (Bell) 1880, was studied with respect to the topography of a benthic biogenous macro-ripple train by scuba at a depth of 12–23 m. A polar co-ordinate sampling method enabled study of the patch size (9–12 m2) and dispersion pattern, which varied with density; being regular during high density (1,09 m−2) and contagious at low density (0,24 m−2). A significant preference of urchins for ripple slopes and avoidance of troughs as a marginal habitat was found. The annual growth rate, as estimated from size frequency distributions, was 0,5 cm yr−1.