I. Edge Habitat & Species. Dividing a large patch into two smaller ones creates an additional edge habitat (inbetween the two new smaller patches), leading to higher population sizes and a slightly greater number of edge species, which are often common or widespread in the landscape.

II. Interior Habitat & Species. Dividing a large patch into two smaller ones removes the interior habitat of that patch, leading to reduced population sizes and number of interior species, which are often of conservation importance.

III. Local Extinction Probability. A larger patch normally has a larger population size for a given species than a smaller patch, making it less likely that the species (which fluctuates in population size) will go locally extinct in the larger patch.

IV. Extinction. The probability of a species becoming locally extinct is greater if a patch is small, or of low habitat quality.

V. Habitat Diversity. A large patch is likely to have more inhabitants present, and therefore contain a greater number of species than a small patch.

VI. Barrier to Disturbance. Dividing a large patch into two smaller ones creates a barrier to the spread of some disturbances (such as fire).

VII. Large Patch Benefits. Large patches of natural vegetation are the only structures in a landscape that protect aquifers and interconnected stream networks, sustain viable populations of most interior species, provide core habitat and escape cover for most large-home-range vertebrates, and permit near-natural disturbance regimes.

VIII. Small Patch Benefits. Small patches that interrupt extensive stretches of matrix act as stepping-stones for species movement. They also contain some uncommon species where large patches are absent, or, in unusual cases, are unsuitable for a species. Therefore small patches provide different and supplemental ecological benefits than large patches.

I. Metapopulation Dynamics. Removal of a patch reduces the size of a metapopulation (i.e., an interacting population subdivided among different patches), thereby increasing the probability of local within-patch extinctions, slowing down the recolonization process, and reducing stability of the metapopulation.

II. Number of Large Patches. Where one large patch contains almost all the species for that patch type in the landscape, two larges patches may be considered the minimum for maintaing species richness. However, where one patch contains a limited portion of the speties pool, up to four or five large patches are probably required.

III. Grouped Patches as Habitat. Some relatively generalist species can, in the absence of a large patch, survive in a number of nearby smaller patches, which although individually inadequate, are together suitable.

IV. Extinction. The probability of a species going locally extinct is greater in an isolated patch. Isolation is a function not only of distance, but also of the characteristics (i.e., resistance) of the intervening matrix habitat.

V. Recolonization. A patch located in close proximity to other patches or the "mainland" will have a higher chance of being colonized or re-colonized, than a more isolated patch.

VI. Patch Selection for Conservation. The selection of patches for conservation should be based on their:

A. Contribution to the overall system, i.e., how well the location of a patch relates or links to other patches within the landscape or region; and

B. Unusual or distinctive characteristics, e.g., whether a patch has any rare, threatened, or endemic species present.

I. Edge Structural Diversity. Vegetative edges with a high structural diversity are richer in edge animal species.

II. Edge Width. Edge width differs around a patch, with wider edges on sides facing the predominant wind direction and solar exposure.

III. Administrative and Natural Ecological Boundary. Where the administrative or political boundary of a protected area does not coincide with a natural ecological boundary, the area between the boundaries often becomes distinctive, and may act as a buffer zone, reducing the influence of the surroundings on the interior of the protected area.

IV. Edge as Filter. Patch edges normally function as filters, which dampen infliences of the surroundings on the patch interior.

V. Edge Abruptness. Increased edge abruptness tends to increase movement along an edge, whereas less edge abruptness favors movement across an edge.

I. Natural and Human Edges. Most natural edges are curvilinear, complex, and soft, whereas humans tend to make straight, simple, hard edges.

II. Straight and Curvilinear Boundaries. A straight boundary tends to have more species movement along it, whereas a convoluted boundary is more likely to have movement across it.

III. Hard and Soft Boundaries. Compared with a straight boundary between two areas, a curvilinear "tiny-patch" boundary may provide a number of ecological benefits, including less soil erosion and greater wildlife usage.

IV. Edge Curvilinearity and Width. Curvilinearity and width of an edge combine to determine the total amount of edge habitat within a landscape.

V. Coves and Lobes. The presence of coves and lobes along an edge provides greater habitat diversity than along a straight edge, thereby encouraging higher species diversity.

I. Edge and Interior Species. A more convoluted patch will have a higher proportion of edge habitat, thereby slightly increasing the number of edge species, but sharply decreasing the number of interior species, including those of conservation importance.

II. Interaction With Surroundings. The more convoluted the shape of a patch, the more interaction, whether positive or negative, there is between the patch and the surrounding matrix.

III. Ecologically "Optimum" Patch Shape. An ecologically optimum patch provides several ecological benefits, and is generally "spaceship shaped," with a rounded core for protection of resources, plus some curvilinear boundaries and a few fingers for species dispersal.

IV. Shape and Orientation. A patch oriented with its long axis parallel to the route of dispersing individuals will have a lower probability of being colonized or re-colonized than a patch perpendicular to the route of dispersers.

I. Corridors on Corridor Functions. Width and connectivity are the primary controls on the five major functions of corridors, i.e., habitat, conduit, filter, source, and sink.

II. Corridor Gap Effectiveness. The effect of a gap in a corridor on movement of a species depends on length of the gap relative to the scale of species movement, and contrast between the corridor and the gap.

III. Structural Versus Floristic Similarity. Similarity in vegetation structure and floristics (plant species) between corridors and large patches is preferable, though similarity in structure alone is probably adequate in most cases for interior species movement between large patches.

I. Stepping Stone Connectivity. A row of stepping stones (small patches) is intermediate in connectivity between a corridor and no corridor, and hence intermediate in providing for movement of interior species between patches.

II. Distance Between Stepping Stones. Fore highly visually-oriented species, the effective distance for movement between stepping stones is determined by the ability to see each successive stepping stone.

III. Loss of a Stepping Stone. Loss of one small patch, which functions as a stepping stone for movement between other patches, normally inhibits movement and thereby increases patch isolation.

IV. Cluster of Stepping Stones. The optimal spatial arrangement of a cluster of stepping stones between large patches provides alternate or redundant routes, while maintaining an overall linearly-oriented array between the large patches.

I. Roads and Other "Trough" Corridors. Road, railroad, powerline, and trail corridors tend to be completely connected, relatively straight, and subject to regular human disturbance. Therefore, they commonly serve as barriers that subdivide populations of species into metapopulations; conduits mainly for disturbance-tolerant species; and sources of erosion, sedimentation, exotic species, and human effects on the matrix.

II. Wind Erosion and Its Control. Modest winds reduce soil fertility by selectively removing and blowing fine particles long distances, whereas heavier winds often move mid-sized particles only tends of meters. Wind erosion control reduces field size in the preponderant wind direction, and maintains vegetation, furrows, or soil clods, especially in spots susceptible to vortices, turbulence, or accelerated streamline airflow.

I. Stream Corridor and Dissolved Substances. Dissolved substances, such as nitrogen, phosphorus, and toxins, entering a vegetated stream corridor are primarily controlled from entering the channel and reducing water quality by friction, root absorption, clay, and soil organic matter; these in turn are most effectively provided by a wide corridor of dense natural vegetation.

II. Corridor Width for Main Stream. To maintain natural processes for a stream, maintain an interior or upland habitat on both sides, which is wide enough to control dissolved-substance inputs from the matrix; provide a conduit for upland interior species; and offer a suitable habitat for floodplain species displaced by beaver flooding or lateral channel migration.

III. Corridor Width for a River. To maintain natural processes, a river corridor maintains an upland interior on both sides, as a conduit for upland interior species and species displaced by lateral channel migration. In addition, maintaining at least a "ladder pattern" of large patches crossing the floodplain provides a hydrologic sponge, traps sediment during floods, and provides soil organic matter for the aquatic food chain, logs for fish habitat, and habitats for rare floodplain species.

IV. Connectivity of a Stream Corridor. Width and length of a vegetated stream corridor interact or combine to determine stream processes. However, a continuous stream corridor, without major gaps, is essential to maintain aquatic conditions such as cool water temperature and high oxygen content. Without these, plus other physiological conditions, viable populations of certain fish species, such as trout, will not be maintained.

I. Network Connectivity and Circuitry. Network connectivity (the degree to which all nodes are linked by corridors), combined with network circuitry (the degree to which loops or alternate routes are present), indicates how simple or complex a network is, and provides an overall index of the effectiveness of linkages for species movement.

II. Loops and Alternatives. Alternative routes or loops in a network reduce the negative effects of gaps, disturbances, predators, and hunters within corridors, thus increasing efficiency of movement.

III. Corridor Density and Mesh Size. As mesh size of a network decreases, the probability of survival drops sharply for a species that avoids or is inhibited by corridors.

IV. Intersection Effect. At the intersection of natural-vegetation corridors, commonly a few interior species are present, and species richness is higher than elsewhere in a network.

V. Species in a Small Connected Patch. A small patch or node connected to a network of corridors is likely to have slightly more species and a lower rate of local extinction than an equal-sized patch separated from the network.

VI. Dispersal and Small Connected Patch. Small patches or nodes along an existing network are effective in providing habitat in which individuals pause and/or breed, resulting in a higher survival rate for dispersing individuals, and, hence, more dispersing individuals in the network.

I. Loss of Total Versus Interior Habitat. Fragmentation decreases the total amount of a particular habitat type, but proportionally causes a much greater loss of interior habitat.

II. Fractal Patches. Fractal configuration is a natural reaction to transition, with isolated patches often reacting similarly to a disturbance as a group. As these patches either become smaller or larger, their structural relationships or pattern stay essentially the same, until an unusually strong disturbance occurs.

III. Suburbanization, Exotics, and Protected Areas. In landscapes undergoing Suburbanization and consequent invasion of exotic species, a biodiversity or nature reserve may be protected against damage by invaders using a buffer zone with strict controls on exotic species.

IV. Grain Size of Mosaics. A coarse-grained landscape containing fine-grained areas is optimum to provide for large-patch ecological benefits, Multihabitat species including humans, and a breadth of environmental resources and conditions.

I. Animal Perception of Scale of Fragmentation. A finely-fragmented habitat is normally perceived as continuous habitat by a wide-ranging species, whereas a coarsely fragmented habitat is discontinuous to all species, except the most wide-ranging large animals.

II. Specialists and Generalists. Specialist species are more likely to be negatively affected by fine-scale fragmentation than are generalist species of similar size.

III. Mosaic Patterns for Multihabitat Species. Multihabitat species are favored by convergency points (junctions where three or more habitats converge), adjacencies (different combinations of adjoining habitat types), and habitat interspersion (habitats scattered rather than aggregated).