Landscape Ecology
Scale
"...we must regard scaling not just as a bothersome feature of study design
but as a subject meriting study in its own right..." (Wiens 1992)
Terms/people:
scale (colloquial vs. cartographic definitions) grain
extent extrapolation, interpolation
scalingdomains of scale (Krummel et al. 1987)
ecological neighborhoods
Scale in ecology -
"The problem of pattern and scale is the central problem in ecology, unifying population biology and ecosystems science, and marrying basic and applied ecology. Applied challenges ... require the interfacing of phenomena that occur on very different scales of space, time, and ecological organization." (Levin 1992)
Scale usually/traditionally has been ignored for logistical ease until quite recently:
"Kuhn’s concept of a paradigm shift is a useful way to interpret the [1988] annual meeting of the [Ecological Society of America]...Every symposium or session I attended featured, included, or was structured by the concept of scale...I left feeling I had observed one of those rare creatures of the intellectual bestiary, a paradigm shift." (Golley 1989)
Meentemeyer and Box (1987) call for a "science of scale" in which scale is explicitly examined in each study.
Components of scale: definitions -
Any discussion must begin by defining terms. Scale, in particular, has been plagued by imprecise and inconsistent usage of terms. Click here for some basic definitions.
Scale is:
A clarification of terms: "Scale" as used in this class is not the same as "level of organization." Scale refers to the spatial domain of the study, whereas level of organization depends on the criteria used to define the system. For example, population-level studies are concerned with interactions among conspecific individuals, whereas ecosystem-level studies are concerned with interactions among biotic and abiotic components of some process such as nutrient cycling. One could conduct either a small- or large-scale study of either population- or ecosystem-level phenomena.
There are two usages of the term "scale": colloquial (used in ecology) and cartographic, and these are opposites to one another!
Colloquial –
Cartographic –
Scale has two components: grain and extent. Click here for some generalities about each of these components.
Grain –
Extent –
Some properties of scale -
-What is heterogeneous at one scale may be homogeneous at another: therefore, all measures are scale-dependent, and selection of a particular grain and extent may affect your results and conclusions.
-Grain and extent are correlated.
-Information content is often positively correlated with grain.
-Relationships between grain/extent and data variance:
At what spatial scale has most ecological research been conducted? (click here and see Kareiva and Andersen 1988)
And yet the results from these studies are often used to represent global-scale phenomena! It is true that ecological studies can seldom if ever be done at large enough spatial and temporal scales to encompass all of the possible influencing factors and to capture natural variation (for reasons of money, time, and the limited human lifespan [and attention span]). But how well can such smaller scales represent nature? There are certain ecologists who are convinced that extrapolation from small-scaled studies is futile (see e.g. Carpenter 1996 – and there are several subsequent replies and rebuttals to this paper).
Extrapolation –
Interpolation –
Click here for an example of the effects of changing grain and extent.
As one changes scale (and see Table 1 in Wiens 1989): relationships are usually not continuous. Krummel et al. (1987) example of domains of scaleseparated by transition zones: below 70 ha, landscape patterns were driven by individual landowners’ uses of their plots of land (e.g. for cropland, pasture, etc.). Above 70 ha, landscape patterns were driven by topography and presence of streams and rivers. Implication: mechanisms differ within and outside domains (often linear within and nonlinear outside).
Since pattern-process relationships are scale-dependent, what is the "correct" scale to use?
"[T]here is no single natural scale at which ecological phenomena should be studied; systems generally show characteristic variability on a range of spatial, temporal, and organizational scales...[However, the fact that] there is no single correct scale or level at which to describe a system does not mean that all scales serve equally well or that there are not scaling laws" (Levin 1992).
There is no clear way to find “the correct” scale, but there are a few techniques:
1.
2.
An animal's mobility affects its perception of landscape pattern:
e.g. effect of body size: With 1993 (Ph.D. dissertation, Colo. State U.)
grasshoppers, body size, and vagility -
3.
3 components to scale-dependency -
1) environmental scaling (structural) -
2) observational scaling (perceptual) - In German, the term "umwelt" is used to define the surrounding environment as perceived by a person or organism (distinction between perceived world and real world).
3) organism response (functional) - what Farina (2006) calls an "eco-field" perspective, whereby the spatial configuration of objects carries a meaning for a specific function for an organism; must take an organism-centered viewpoint and not a structure- or pattern-centered one
So, what to do?
-recognize that although there may be no single “correct” scale, there are assuredly “wrong” ones
-collect data from multiple scales if possible; these scales should be based on the biology of the organisms or processes being studied rather than logistics
-be explicit in stating your scale (grain and extent)
-generalize with humility
References:
Addicott, J.F., J.M. Aho, M.F. Antolin, D.K. Padilla, J.S. Richardson, and D.A. Soulik. 1987. Ecological neighborhoods: scaling environmental patterns. Oikos 49:340-346.
Carpenter, S.R. 1996. Microcosm experiments have limited relevance for community and ecosystem ecology. Ecology 77:677-680.
Farina, A. 2006. Principles and Methods in Landscape Ecology: Towards a Science of Landscape. Springer, New York, NY.
Golley, F.B. 1989. Paradigm shift. Landscape Ecology 3:65-66.
Kareiva, P., and M. Andersen. 1988. Spatial aspects of species interactions. Pp. 35-50 in: Community Ecology (A. Hastings, ed.). Springer-Verlag, New York, NY.
King, A.W. 1991. Translating models across scales in the landscape. Pp. 479-517 in: Quantitative Methods in Landscape Ecology (M.G. Turner and R.H. Gardner, eds.). Springer-Verlag, New York, NY.
Krummel, J.R., R.H. Gardner, G. Sugihara, R.V. O’Neill, and P.R. Coleman. 1987. Landscape patterns in a disturbed environment. Oikos 48:321-324.
Levin, S.A. 1992. The problem of pattern and scale in ecology. Ecology 73:1943-1967.
Meentemeyer, V., and E.O. Box. 1987. Scale effects in landscape studies. Pp. 15-24 in: Landscape Heterogeneity and Disturbance (M.G. Turner, ed.). Springer-Verlag, New York, NY.
Miller, J.R., M.G. Turner, E.A.H. Smithwick, C.L. Dent, and E.H. Stanley. 2004. Spatial extrapolation: the science of predicting ecological patterns and processes. BioScience 54:310-320.
Peters, D.P.C., J.E. Herrick, D.L. Urban, R.H. Gardner, and D.D. Breshears. 2004. Strategies for ecological extrapolation. Oikos 106:627-636.
Turner, M.G., R.V. O’Neill, R.H. Gardner, and B.T. Milne. 1989. Effects of changing spatial scale on the analysis of landscape pattern. Landscape Ecology 3:153-162.
Wiens, J.A. 1989. Spatial scaling in ecology. Functional Ecology 3:385-397.
With, K.A. 1993. The translation of patterns across scales: analysis of movement patterns in a grassland mosaic. Ph.D. Dissertation, Colorado State University, Fort Collins, CO.