Dennis E. Jelinski

The modifiable areal unit problem and implications for landscape ecology

Landscape ecologists often deal with aggregated data and multiscaled spatial phenomena. Recognizing the sensitivity of the results of spatial analyses to the definition of units for which data are collected is critical to characterizing landscapes with minimal bias and avoidance of spurious relationships. We introduce and examine the effect of data aggregation on analysis of landscape structure as exemplified through what has become known, in the statistical and geographical literature, as theModifiable Areal Unit Problem (MAUP). The MAUP applies to two separate, but interrelated, problems with spatial data analysis. The first is the “scale problem”, where the same set of areal data is aggregated into several sets of larger areal units, with each combination leading to different data values and inferences. The second aspect of the MAUP is the “zoning problem”, where a given set of areal units is recombined into zones that are of the same size but located differently, again resulting in variation in data values and, consequently, different conclusions. We conduct a series of spatial autocorrelation analyses based on NDVI (Normalized Difference Vegetation Index) to demonstrate how the MAUP may affect the results of landscape analysis. We conclude with a discussion of the broader-scale implications for the MAUP in landscape ecology and suggest approaches for dealing with this issue.

THE RELATIVE IMPORTANCE OF PATCH AREA AND PERIMETER–AREA RATIO TO GRASSLAND BREEDING BIRDS

Habitat fragmentation has been implicated as a major cause of population decline in grassland birds. We tested the hypothesis that a combination of area and shape determines the use of grassland patches by breeding birds. We compared both species richness and individual species presence in 45 wet meadow grasslands in the floodplain of the central Platte River, Nebraska. Bird data were collected through the use of belt transects and supplemented by walking and listening outside transects. Our data supported our pri- mary hypothesis that perimeter-area ratio, which reflects both the area and shape of a patch, is the strongest predictor of both individual species presence and overall species richness. The probability of occurrence for all six common species (Grasshopper Sparrows, Bobo- links, Upland Sandpipers, Western Meadowlarks, Dickcissels, and Red-winged Blackbirds) was significantly inversely correlated with perimeter-area ratio. The probability of occur- rence of Grasshopper Sparrows, Bobolinks, Upland Sandpipers, and Western Meadowlarks was also correlated with area. We conclude that species richness is maximized when patches are large ( .50 ha) and shaped so that they provide abundant interior areas, free from the impacts of edges.

Multiscale analysis of landscape heterogeneity: Scale variance and pattern metrics

Abstract A major goal of landscape ecology is to understand the formation, dynamics, and maintenance of spatial heterogeneity. Spatial heterogeneity is the most fundamental characteristic of all landscapes, and scale multiplicity is inherent in spatial heterogeneity. Thus, multiscale analysis is imperative for understanding the structure, function and dynamics of landscapes. Although a number of methods have been used for multiscale analysis in landscape ecology since the 1980s, the effectiveness of many of them, including some commonly used ones, is not clear or questionable. In this paper, we discuss two approaches to multiscale analysis of landscape heterogeneity: the direct and indirect approaches. We will focus on scale variance and semivariance methods in the first approach and 17 landscape metrics in the second. The results show that scale variance is potentially a powerful method to detect and describe multiple-scale structures of landscapes, while semivariance analysis may often fail to do so especially if landscape variability is dominant at broad scales over fine scales. Landscape metrics respond to changing grain size rather differently, and these changes are reflective of the modifiable areal unit problem as well as multiple-scale structures in landscape pattern. Interestingly, some metrics (e.g., the number of patches, patch density, total edge, edge density, mean patch size, patch size coefficient of variation) exhibit consistent, predictable patterns over a wide range of grain sizes, whereas others (e.g., patch diversity, contagion, landscape fractal dimension) have nonlinear response curves. The two approaches to multiple-scale analysis are complementary, and their pros and cons still need to be further investigated systematically.

Seasonal trends in energy, water, and carbon dioxide fluxes at a northern boreal wetland

Micrometeorological measurements were made over a northern boreal fen near Thompson, Manitoba, Canada, as part of the Boreal Ecosystem-Atmosphere Study. The measurement period extended from the start of snowmelt until the early fall, at which time senescence was widespread throughout the fen. Data analysis concentrated on identifying seasonal trends in energy, water, and carbon dioxide fluxes and linking them to observed surface cover changes. Albedos (solar and photosynthetically active radiation (PAR)) showed large decreases over the melt period, reaching seasonal lows at the end of melt. Solar albedo increased in the summer in response to vegetation growth on the fen, while PAR albedo remained constant. Incoming and outgoing longwave flux seasonal trends were similar, so seasonal changes in net radiation were driven by the net solar flux. During the spring thaw, the melting of snow and ground ice was equal to about 28% of the daily total net radiation, while the soil heat flux accounted for about 5%. Bowen ratios at this time were above unity. Mean Bowen ratio decreased to 0.70 during the period between spring thaw and leaf-out. As the vascular vegetation cover developed, Bowen ratios decreased to seasonal lows of 0.10-0.20 near midsummer and then increased to above unity during senescence. The daily evaporative fraction (EF) was highest (≥0.80) during midsummer when the vascular vegetation was in full leaf and actively photosynthesizing, and EF decreased to a mean of 0.55 during senescence. Eddy correlation measurements of carbon dioxide flux showed the fen acting as a net sink for CO 2 only while the vascular vegetation was actively photosynthesizing with a daily mean flux of -0.81 g CO 2 -C m -2 d -1 (standard error = 0.16). Before leafing and during senescence the fen was a net source of CO 2 . Integrated over the study period of 124 days, the fen experienced a net loss of 30.4 g CO 2 m -2 to the atmosphere.

WRACK DEPOSITION ON DIFFERENT BEACH TYPES: SPATIAL AND TEMPORAL VARIATION IN THE PATTERN OF SUBSIDY

The onshore deposition of macroalgal and macrophyte wrack provides a potentially significant marine subsidy to intertidal and supratidal herbivore and decomposer communities. Based on the study of daily input loads to beaches, we estimated summer wrack deposition of up to 140 Mg (dry mass)/km shoreline in Barkley Sound, British Columbia. However, input rates were highly variable depending on beach type, nearshore hydrodynamics, and buoyancy characteristics of the wrack. Cobble beaches retained ;10 times and 30 times more wrack than did gravel and sand beaches, respectively. Cobble and gravel beaches also differed in species composition of new (fresh) wrack input, with Ma- crocystis integrifolia being characteristic for the former and Nereocystis luetkeana for the latter, which we attribute to buoyancy characteristics of the floating debris. On sand beaches, Phyllospadix spp. and Enteromorpha spp. were the dominant wrack species. Species com- position of freshly deposited wrack also depended on wave exposure, but predictability based on the species pool within a beachs catchment was restricted. Drift lines of aging wrack differed from freshly deposited wrack in species composition, probably due to wrack decomposition that results in fluxes of nutrients and energy between the adjacent marine and terrestrial habitats. We hold that the characteristics of a given beach, e.g., substratum and wave exposure, and their effects on wrack input, will have important ecological and biogeochemical implications for the marine-terrestrial ecotone.

Image classification of a northern peatland complex using spectral and plant community data

Abstract Ordination and cluster analysis are two common methods used by plant ecologists to organize species abundance data into discrete “associations”. When applied together, they offer useful information about the relationships among species and the ecological processes occurring within a community. Remote sensing provides surrogate data for characterizing the spatial distribution of ecological classes based on the assumption of characteristic reflectance of species and species associations. Currently, there exists a need to establish and clarify the link between theories and practices of classification by ecologists and remote sensing scientists. In this study, high spatial resolution Compact Airborne Spectrographic Imager (CASI) reflectance data were examined and compared to plant community data for a peatland complex in northern Manitoba, Canada. The goal of this research was to explore the relationship between classification of species cover and community data and reflectance values. Ordination and cluster analysis techniques were used in conjunction with spectral separability measures to organize clusters of community-based data that were suitable for classification of CASI reflectance data, while still maintaining their ecological significance. Results demonstrated that two-way indicator species analysis (TWINSPAN) clusters did not correspond well to spectral reflectance and gave the lowest classification results of the methods investigated. The highest classification accuracies were achieved with ecological classes defined by combining the information obtained from a suite of analysis techniques (i.e., TWINSPAN, correspondence analysis (CA), and signature separability analysis), albeit not statistically superior to the classification obtained from the signature separability analysis alone.

Geostatistical analyses of interactions between killer whales (Orcinus orca) and recreational whale-watching boats

Abstract Johnstone Strait in coastal British Columbia, Canada, is a core habitat for seasonal concentrations of killer whales (Orcinus orca), which have attracted considerable attention from commercial whale-watching operators and recreational boaters. Within the Strait lies the Robson Bight–Michael Bigg Ecological Reserve, a marine reserve set aside as critical habitat for killer whales and closed to recreational boat traffic. The geography of encounters between killer whales and seven types of whale-watching vessels (including kayaks, charter and pleasure craft) in and near this reserve was analysed with a suite of geostatistics in a geographic information system (GIS) vector environment. Reserve boundary violation was high among most user groups, with kayakers being the most frequent offenders. Motorized vessels had significantly longer contact times with whales compared to kayaks and sailboats. Motorized vessels showed the travel characteristic of deliberate tracking of whales. The movements of killer whales also appear to be affected by boats. These results have important implications for killer whale conservation and management in areas where they are subject to intensive whale-watching activities, and possible chronic disturbance.

Detrital Subsidy to the Supratidal Zone Provides Feeding Habitat for Intertidal Crabs

Beach-cast wrack of marine origin is considered a spatial subsidy to the marine-terrestrial transition zone. We found that the wrack line on sand and gravel beaches of Vancouver Island was frequented by intertidal purple shore crabs,Hemigrapsus nudus (Dana 1851) and densely colonized by detritivorous talitrid amphipods. Amphipods spend the day buried in sand and forage on beach wrack during the night.H. nudus were found in supratidal wrack putches immediately after nightly high tides in field censuses, but spent most of the day and ebb tides either submerged subtidally or hidden underneath intertidal rocks and boulders. In feeding trials, intertidal shore crabs were capable of preying on talitrid amphipods. We considerH. nudus an omnivore feeding on both fresh and decaying macroalgae as well as animal prey. Although living supratidally, amphipods were significantly preferred over intertidal littorine snails by foraging shore crabs. Handling time of amphipods was significantly shorter than for littorine snails. While amphipods had a reduced risk of predation byH. nudus when buried in the sand, foraging undern eath wrack patches did not reduce predation pressure on amphipods by shore crabs. Rates of amphipod consumption by shore crabs were higher at darkness than daylight. In addition to an apparent day-night rhythm, tidal height and time elapsed since previous high tide had a significant influence on shore crab density wrack. We conclude that beach-cast wrack acts as a spatial subsidy by virtue of providing a valuable food source to talitrid amphipods, which are in turn consumed by shore crabs that ride the nightly high tide into supratidal wrack patches to reduce the risk of passing bare sand on theiry way to a feeding habitat rich in valuable prey.

On a landscape ecology of a harlequin environment: the marine landscape

The marine ‘landscape’, like its terrestrial counterpart, is characterized by a mosaic of resource and environmental patches, that is, a ‘‘harlequin environment’’ (sensu Horn and MacArthur 1972), created by, and embedded in, a matrix of otherwise relatively homogeneous conditions (Levin and Whitfield 1994). The notion of patchiness and heterogeneity in marine landscapes is well known at a range of spatial– temporal scales (Stommel 1963; Longhurst 2006). This notwithstanding, just how the multi-dimensional spatial structure of physical and biological forcing agents in marine environments (e.g., fronts, currents, eddies, prey patches) affect biota and influence key ecological processes lags behind that known for terrestrial environments. The general aim of this paper makes a case for more widespread application of the principles and concepts of landscape ecology to ecological studies of coastal, benthic and, pelagic systems, the latter of which has been especially slow or reluctant to consider the paradigm of landscape ecology. Landscape ecology is fundamentally an interdisciplinary science of heterogeneity (Wu and Hobbs 2002; Wu 2006). Issues of scale, heterogeneity, patchiness and connectivity are widespread in these systems thus making a landscape ecology perspective germane to their study and management. I also argue that we need to overcome more general impediments between marine and terrestrial ecology insofar as sharing of empirical information, methodologies and theory if landscape ecology is to make greater inroads into the marine realm.

Effects of leaf area profiles and canopy stratification on simulated energy fluxes: the problem of vertical spatial scale

Abstract We investigated the effects of the shape of leaf area profiles and the number of canopy layers on simulated sensible and latent heat fluxes using a gradient diffusion-based biometeorological model. Three research questions were addressed through simulation experiments: (1) Given the same amount of cumulative leaf area in the vertical direction, how does the shape of the leaf area profile affect simulation results? (2) For a given leaf area profile, how does the number of layers influence the simulation results? (3) How do these two factors interact with each other in affecting the simulated energy fluxes? Our results demonstrated that the scheme of canopy stratification could substantially affect the simulated energy fluxes, and that the effect exhibited a consistent pattern — an S-shaped response curve. There existed a minimal number of layers for achieving a required degree of accuracy. The turning point of the S-shaped curve represented the optimal number of layers, indicating a desirable balance between the accuracy of the model and demands for computation and data collection. Our results also showed that differences in the shape of leaf area profiles alone could significantly alter the simulated energy fluxes even if the total amount of leaves in the canopy and the values of all other model parameters remained the same. Furthermore, the shape of leaf area profiles interacted with the number of layers in affecting the simulated energy fluxes. While considerable impacts were observed for all leaf area profiles, complex (nonlinear) shapes exacerbated the effects of changing the number of layers.