At the landscape level species persistence is threatened by:

1. habitat loss

2. Habitat fragmentation

3. Matrix quality

Fragmentation (which is a the most common form of habitat loss)

• "Traditional" fragmentation: habitat is converted and patches remain.

• Perforation: Openings are created within continuous habitat (e.g., the transformed habitat is the patch and the natural habitat is the matrix)

• Internal fragmentation: Linear paths of habitat are transformed.

Fragmentation causes:

• Loss of area
• Increase in edge
• Increased isolation of remaining patches

The "species-area relationship" for a given habitat states that the number of species increases as the area of the habitat increases. The text also uses the idea of "ecosystem" size, that is, a defined area with different habitats, so we’ll discuss the difference between habitat size and "ecosystem" size.

In some sense this is a probabilistic (or stochastic) argument: more area is just more likely to have more species even though it is more area of the same habitat (because there are lots of habitat generalists out here, for one reason). But think about why this might not always be true, and where does it end? If you define an ecosystem as a larger geographical area –and not as a specific habitat----it is likely to encompass more different habitats, or variations within a general habitat type (e.g., brackish marsh; wetland; etc.)..

Area-sensitive species: If we define the area as a geographical range, then we can imagine some species who can use different habitats but need a large area to thrive. Examples: Rocky Mt elk; birds in Amazonia. Also: grassland birds in Missouri.

The "edge effect" had various definitions, so, as above, we need to be careful what terms we’re using and how. My definition of the "edge effect" is the effects (or processes and resulting morphologies) that make the edge of a habitat patch different than the rest of the habitat.

The text authors speak in terms of the effect on species, who, if they are ‘edge sensitive" don’t do as well in that edge zone of the habitat.

Abiotic edge effects: wind, insolation, etc.

Biotic edge effects: some species are edge-generalists, and evolved in edge niches. They do better and can out-compete or prey on core species (which the ext calls "edge sensitive species").

Human Effects: edge effects from human development and behavior: noise, light, pets, and hosting edge-generalists. (e.g., robins in Pitkin County, Colo. They out-compete other songbirds for nests because they are aggressive, larger, and more likely to be present year-round.). See Figs. 8.9 and 8.10.

Each edge effect has a different penetration distance into the patch. This cannot be generalized: raccoons may be able to prey further into a wooded patch than can coyotes.

Result: the edge affected area can vary depending on your species of interest and effects of interest (e.g., how far into the forest from an edge do winds strong enough to knock over oak saplings penetrate?).

The geometry of patches can also make a large difference in edge effects. On the whole, more circular patches have less edge per unit of area than do rectalineal patches (Fig. 8.11, and see the family of perimeter-to-area curves in Fig. 8.13). We can even posit habitats of the same area that have some core or no core (Fig. 8.12).

The third major effect of habitat fragmentation is that remaining patches become increasingly isolated form one another. That is, the mean distance from the edge of one patch the next nearest edge of another patch increases with landscape transformation.

The effectiveness of isolation is related to species dispersal mechanisms and behaviors. Dispersal-sensitive species are those who may have trouble getting across the matrix or linear barriers between patches. The case offered in coyotes vs. tortoises, or small wind-dispersed plant seeds vs. larger, animal- or even-gravity dispersed seeds. These are morphological limits. Physiological limits can include biological sensitivity to sunlight, wind, etc. Finally, many species have behavioral limits on dispersion.

Read the case of the white-breasted nuthatch (p. 182).

The landscape mosaic is the full assemblage of habitat patches and matrices. The mosaic at a given time is always in transition, for example as open patches are colonized by trees and as openings are created in forest stands by human (e.g., swidden agriculture) or natural processes (e.g., blow down).

Moreover, the elements of a mosaic, both matrices and patches, interact via flows of mass, energy, individuals and species.

Matrix: is the landscape’s most extensive, most connect land cover. It is obvious then that qualities of the matrix affect what happens in the patches it surrounds. The text offers agricultural and urban matrices. Clearly, the authors write, you can probably more successfully manage for the persistence of human-sensitive species if your matrix is agricultural land rather than subdivisions. What patch species, or what sensitivities of species, might actually thrive better in a patch surrounded by houses rather than by agricultural lands?

Fragmentation and the [HUMANIZED] landscape matrix: The last section in this chapter describes the inevitable result of human development: whole ecosystems are transformed so that human-created and dominated landscapes become the matrix rather than the patches. Natural patch size decreases, edge effect grows to cover larger proportion of remaining patches, and patch isolation increases. Eventually the qualities of the humanized matrix comes to dominate the hole landscape. A general set of results is that: weedy, generalist, and human adapted species come to dominate the landscape.