Transition from Connected to Fragmented Vegetation across an Environmental Gradient: Scaling Laws in Ecotone Geometry

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. abstract: A change in the environmental conditions across spacefor example, altitude or latitude-can cause significant changes in the density of a vegetation type and, consequently, in spatial connectivity. We use spatially explicit simulations to study the transition from connected to fragmented vegetation. A static (gradient percolation) model is compared to dynamic (gradient contact process) models. Connectivity is characterized from the perspective of various species that use this vegetation type for habitat and differ in dispersal or migration range, that is, "step length" across the landscape. The boundary of connected vegetation delineated by a particular step length is termed the " hull edge." We found that for every step length and for every gradient, the hull edge is a fractal with dimension 7/ 4. The result is the same for different spatial models, suggesting that there are universal laws in ecotone geometry. To demonstrate that the model is applicable to real data, a hull edge of fractal dimension 7/4 is shown on a satellite image of a piñon-juniper woodland on a hillside. We propose to use the hull edge to define the boundary of a vegetation type unambiguously. This offers a new tool for detecting a shift of the boundary due to a climate change.

Species richness and diversity across rocky intertidal elevation gradients in Helgoland: testing predictions from an environmental stress model

“…The elevation 9 shore interaction was not significant (Table 2), so no simple effects were calculated predictions. For example, communities in transition areas between two contiguous biotas share species to some extent (Kent et al 1997;Attrill and Rundle 2002;Gastner et al 2009). In rocky intertidal habitats, high elevations are often only occupied by truly intertidal species, which decrease in richness toward the upper intertidal boundary without sharing the substrate with the terrestrial species (e.g., vascular plants) that occur above (Raffaelli and Hawkins 1996).…”

Front structure and dynamics in dense colonies of motile bacteria: Role of active turbulence

“…In the limit D → 0, the front speed is completely determined by turbulent diffusivity the concentration field c(x, t 0 ) at a time instant t 0 . We use the biased random walk algorithm (BRWA) [36] to identify a locus of points (or a hull) h i ≡ (x i , y i ) such that c(h i , t 0 ) = 0.5, where the hull index 0 ≤ i ≤ N h and 0 ≤ (x i , y i ) ≤ L are the Cartesian points in our simulation domain D. Connecting the points of the hull, we get a continuous curve that starts at the bottom of the domain y = 0 and ends at the top y = L. Figure 5(inset) shows a representative plot of the c = 0.5 hull overlaid on the pseudocolor plot of the concentration field.…”

Nonuniversal and anomalous critical behavior of the contact process near an extended defect

“…The contact process is often interpreted as a simple, idealised model of population dynamics. In reality, however, it is not uncommon that the local environmental variables which influence the reproduction rate of a population show some variations with the geographical coordinates [31]. In this respect, our model describes population dynamics in the presence of a special form of spatial inhomogeneity.…”