Landscape Ecology Vignette #1 — Theory


>>John Humphreys: Hello, my name is John
Humphreys. I am the Florida Department of Environmental
Protection’s Mitigation Banking and Uniform Mitigation Assessment Method Coordinator. This video is the first in a four part series
dealing with landscape ecology and terms and concepts often discussed as part of the Uniform
Mitigation Assessment Method’s Location and Landscape Support scoring attributes. Concepts covered by this video include, Spatial
Structure and Function, the Species-Area Relationship, and the Species-Distance Relationship. In landscape ecology, “Structure” can be defined
as physical objects that exist in the environment; for example, vegetation, streams, lakes, roads,
buildings, and the like. Often it is beneficial to describe this structure
to a high level of specificity; such as low quality, mixed hardwood forest vegetation,
freshwater less than 5-acre lakes, infrequently traveled, unpaved roads, etcetera. Rather than describing individual objects
located in the environment, it is often beneficial to describe structure in groupings of sufficiently
homogeneous character as to be assessed as a single unit. This concept is comparable to the idea of
an Assessment Area as referenced by the UMAM Rule, and is also similar to the idea of an
“ecological patch.” Patch simply refers to the habitat of focus
for a particular assessment or study. Everything surrounding the patch is commonly
referred to as the “matrix.” To aid in understanding the patch and matrix
relationship, it is useful to think of the example of oceanic islands. Here, mangrove islands representing habitat
can be viewed as patches; whereas, the surrounding marine waters could be described in terms
of a matrix. However, ecological theory tells us that no
patch exists as a completely isolated island, so not only do oceanic islands serve as a
good example of the patch-matrix relationship; but, so do habitats found in terrestrial systems
— including those located in urbanized or developed landscapes. Ecological theory also tells us that no two
patches are identical, each has unique attributes, and rarely is the matrix homogenous in character. So, another way of thinking about structure
is to view it has the “pattern” on a map. For example, this landcover map is color coded
with each color representing a different type of environment. Some of the colored areas represent Residential
Areas, some of the depicted patterns represent Reservoirs, and others represent Natural Communities. Each of these distinct patterns represent
the presence of structure in the landscape and each can be interpreted in terms of the
patch and matrix relationship. Interpreting natural landscapes in terms of
the patch-matrix relationship helps inform us of underlying biological processes. For example, the Theory of Island Biogeography
makes several predictions based on the distance between two given patches and the areal extent
of those patches. One prediction is that the closer a given
patch is to a source of fish, wildlife, or plant propagules, the more likely it is to
be colonized. Island Biogeography also predicts that resource
availability increases in proportion to the areal extent of the patch. Resource availability and immigration rates,
in turn, can be used to predict the probability of species extinction within a given patch,
such that risk of extinction decreases with increased area, and immigration rates decrease
with increased distance from the source patch. The species-area and species-distance relationships
may also serve to buffer a particular patch against extinction risk. For example, imagine that each of these circles
represents an individual patch, each with its own suite of species. If one patch should experience extinction
or genetic erosion, the chance of that degraded patch to be re-colonized from a more distant
patch is decreased. It is deceased because even if propagules
leave the source patch, crossing the intermediary matrix is a difficult and energetically expensive
journey. However, a patch located in closer geographic
proximity may be positioned to better facilitate re-colonization and thereby counter species
decay. This idea is known as the “Rescue Effect.” So, the Rescue Effect also reduces the risk
of extinction and assists in understanding the complex interplay between migration and
immigration as functions of habitat size and spatial dispersion. This idea is known as “Source-Sink Dynamics,”
which simply refers to the analysis of species interactions in a heterogeneous system, with
heterogeneous referring to a diversity of landscape structure. Remember, think of structure as the pattern
depicted on a map. All patterns can be described in terms of
Composition and Configuration. Composition and Configuration collaborate
to either facilitate or inhibit wildlife mobility and energy exchange between patches. Composition and Configuration determine and
quantify the amount of Structural Connectivity in the landscape, and as a result, predict
the underlying Functional Connectivity between fish, wildlife, and plant species. Taken as a whole, these factors define the
Degree of Isolation exhibited at a given patch. Therefore, before one can undertake an evaluation
to determine if a particular species is isolated or at risk, both Structural and Functional
Connectivity must be contemplated. For more information, please visit the Uniform
Mitigation Assessment Method website, thank you.