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Landscape Ecology
Landscape elements (patches, corridors, boundaries)
Terms/people:
Patch
corridor
boundary hardness/softness
Ecotone
10% rule
edge effect
Composition
configuration
homogeneous
Heterogeneous
area, perimeter, shape (for patches)
Ecological trap
Alexander von Humboldt
matrix
Geometric module
“rescue effect”
landscape composition,
configuration, & connectivity
“contagious catastrophes”
“ecological fire escape”
species-area relationship
Darlington’s rule
But first, some background:
landmarks
“positional awareness”
geometric module (Cheng and Spetch 1998)
“sense of place”
Most organisms can recognize "landmarks" (which may be visual, olfactory, auditory,
chemosensory, magnetic, or tactile), indicating that they recognize that the world is
heterogeneous and can identify landscape structure. In this way they become oriented
and consequently know where they are (Healy 1998). But in addition to landmarks, most
other organisms also have an instinctive “positional awareness.” Experiments on rats,
for example, have shown that they utilize geometric space more than other cues like
odors in orientation. This trait has also been found in domestic chicks and in human
children and is called a geometric module (Cheng and Spetch 1998). This "sense of
place" is a strong instinctive response in many animals, including humans. These facts
indicate that animals recognize that they exist within a spatial context–in other words,
they recognize that they exist within a landscape.
The features that are recognized/used as landmarks and to reinforce the geometric module
are patches, corridors, and boundaries. These to be embedded in a matrix, the
background land-use type, characterized by extensive cover, high connectivity, and/or
control over dynamics that occur within patches and corridors and along boundaries.
The matrix can have a PROFOUND effect on pattern-process relationships happening
within patches (much more in future lectures); see recent review by Prevedello and Vieira
2010 for more info.
What is a landscape?
Consider these varied definitions:
"the total spatial entity of human living space" (Troll 1968)
"[the] physical, ecological and geographical entities [that integrate] all natural and human
(‘caused’) patterns and processes" (Naveh 1987)
"heterogeneous land area composed of clusters of interacting ecosystems [that] is
repeated in similar form throughout" (Forman and Godron 1986)
"a particular configuration of topography, vegetation cover, land use and settlement
patterns which delimits some coherence of natural and cultural processes and activities"
(Green et al. 1996)
A landscape, by the way, need not be terrestrial. It can also be aquatic.
Alexander von Humboldt From what are landscapes made?
Landscapes are (usually) heterogeneous in composition (vs. homogeneous, which would
be rather boring). Landscapes are comprised of three main elements: patches,
corridors, and boundaries (all embedded in a matrix). Different landscapes differ in the
configuration of these elements. Recall that landscape ecology is the study of the effect of
pattern on process. Therefore, it is important to describe landscape structure in terms of
its pattern of patches, corridors, and boundaries:
for comparative purposes, to quantify the differences between or among study
areas; &
to infer underlying agents (causal mechanisms) of pattern formation.
Of course, this latter goal is fundamental to much of landscape ecology as it is to ecology
in general. As we shall see, the task of attributing causal mechanism (process) to
observed pattern is a daunting task.
Patches Patches are defined as regions that are more or less internally homogeneous with respect
to a measured variable (a set of spatially proximate homogeneous units). There are
several approaches to defining specifically what a patch is:
Simple aggregation of like-valued regions: A straightforward method of defining
patches is simply to aggregate all adjacent areas that have the same (or similar) value of
the variable of interest.
Contrast methods: An alternative approach is to define patches by finding the
edges around patches, which contrasts the patch from its surroundings. In some cases,
this is easy to do; in other cases, edges can be subtle (more later in the course). An edge
in this case is an area where a variable (e.g. canopy height) changes abruptly (will have
high variance).
Patch Characteristics
A patch (once found/defined) is usually quantified (described) by its:
Area - the size of the patch, in units of map scale (e.g., m2) or as a proportion of
the total map area. Actually very difficult to measure. Often crucially important to
organisms (species-area relationship).
Perimeter - patch circumference
Shape - often summarized in terms of edge/area ratio. In many instances, this ratio
is normalized to take on a value of 1.0 for the most compact shape possible (e.g. a square
for raster data)
Type - usually a categorization of some internal patch attribute, such as "forest,"
"urban," etc.
Components of Landscape Structure
There are three main components of landscape structure (O'Neill et al. 1988):
composition configuration connectivity Corridors – see book Corridor Ecology by Hilty et al. (2006) & recent review by
Gilbert-Norton et al. (2010)
Various definitions of corridor (some structural, others functional):
“narrow strips of land which differ from the matrix on either side” (Forman and
Godron 1986, p. 123)
“a linear landscape element that provides for movement between habitat patches”
(Rosenberg et al. 1997, p. 678)
“routes that facilitate movement of organisms between habitat fragments” (Hilty
et al. 2006, p. 5)
“a landscape element that plays a key role in connectivity” (Anderson and Jenkins
2006, p. 3)
Corridors have been of especial concern in conservation with respect to reserve design to
combat fragmentation-induced habitat isolation (“bandages for wounded landscapes”
according to Laurance and Laurance 2003). They are presumed to decrease extinction
risk by boosting connectivity (click here for a modeling example). Why would
connectivity be important for this?
Click here for some properties of corridors.
There are:
benefits of corridors (Noss 1987) -
deleterious aspects of corridors (Simberloff and Cox 1987, Simberloff et al.
1992) -
But see a recent review by Haddad et al. 2014 - No evidence that corridors increase
unwanted disturbances or invasives, and there were as many positive as negative edge
effects…
Although the value of corridors has been debated (Hobbs 1992), there is a growing body
of empirical work of corridor use, although many studies have been on small mammals
that aren’t in need of reserves (see, for example, Coffman et al. 2001) and short-term.
More good data/studies on how corridors affect large, endangered organisms are needed
(although some work has been done on Florida panthers, Australian marsupials, plants,
insects, birds, Iberian lynx, and gray wolves). As a great example of some empirical
work, check out the following news link (from Scientific American) that discusses a
study of how corridors affect animals, plants, and processes such as pollination:
http://www.sciam.com/article.cfm?articleID=00039786-33B9-1D86B3B9809EC588EEDF .
(The paper cited in the article won the 2002 Best Paper in Landscape Ecology award.)
Other empirical examples:
-bat species richness increased in patches linked by forested corridors in French
Guiana (Brosset et al. 1996)
-small mammal species richness increased in patches of Atlantic forest in Brazil
that were linked by corridors compared to isolated patches (Pardini et al. 2005)
Gilbert-Norton et al. (2010) conducted a meta-analysis of corridor use and effectiveness
in 78 experiments from 35 studies; you should know what their key findings were (from
assigned reading).
Keep in mind that something that is a corridor to one species may not be perceived or
used as such by another species (i.e., corridors [and, thus, connectivity] are taxondependent). And corridors may have both positive and negative effects on the same
species at different life stages (Orrock and Damschen 2005). And the landscape matrix
surrounding a corridor may influence its use (Pearson 1993; see Turner et al. text pp.
236-238 for more details).
How wide does a corridor need to be? Too narrow and it may expose organisms to
adverse weather conditions, predation risk, etc. Too wide and it may cause animals to
wander around in it, spending energy without finding a suitable territory. A “10% rule”
has been proposed (see Laurance and Laurance 2003): the corridor’s width should be
10% of the area of the patches it is connecting.
Boundaries The transition zone between two distinct landscape elements (e.g. patch and matrix) is
variously called:
• an edge
• an ecotone
• a boundary
This transition area possesses some characteristics of both landscape elements but is
neither completely one nor the other. Therefore, some people refer to an ecotone as a
landscape element (habitat type) unto itself. Edges are often drier and hotter, with more
weedy species, than the patches of which it is an edge. Others recognize that although it
may have some emergent properties, an edge/ ecotone/boundary’s primary function is as
a barrier (permeable or impermeable) to ecological flows (movement of matter [including
organisms] and energy). The transition may be subtle (a "soft" boundary, e.g. edge
between mixed oak-beech stand to pure oak stand) or quite sharp ("hard," e.g. edge
between forest and clear-cut), with implications for movement of matter and energy
across the landscape. Soft boundaries may be traversed with relative ease, whereas a hard
boundary may hinder, slow, or even deflect ecological flows. Edge effects create a "patch
within a patch" situation (i.e., interior patch within patch as a whole). For example,
Wilcove (1985) showed that nesting birds suffer greater predation the closer to forest
edges they nested.
Similar deleterious edge effects have been found for plant growth and seed dispersal.
Although certain taxa may be favored by ecotonal conditions (such as nest predators),
boundaries can act as ecological traps: because they often have more sunlight, edges
favor growth of weeds, which have lots of seeds and insects that songbirds feed upon;
songbirds may be fooled by apparent high habitat quality and nest there, unwittingly
exposing themselves (literally) to increased nest predation. See Battin (2004) for a nice
review of the topic of ecological traps.
Determining boundary "hardness" (or "softness") is extremely difficult because it is more
a posteriori than a priori: difficult to predict whether, when, and how a particle
(especially an animal) will actually flow from one element to the other. Closed
boundaries create a patch.
See Johnston et al. (1992) for quantitative methods for studying boundaries. One oftenused technique is "sliding windows" (e.g. along a transect or within a quadrat), which is
used to detect areas where variance changes suddenly (i.e., a boundary). Compare
variances between one window position and the next using squared Euclidian distance
(SED). Click here for an example of how changing the window size changes the results.
An alternative to detecting boundaries involves variance. Click here for an example.
We will discuss movement in greater depth later in the course, for movement is a key
ecological process with implications for conservation biology, wildlife management, pest
management, and many other areas.
How do these landscape elements affect ecological processes?
The composition, configuration, and connectivity of these landscape elements, singly
and interactively, determine the abundance and distribution of organisms, where dispersal
and flows occur, and the rates of biogeochemical reactions (Dunning et al. 1992, Taylor
et al. 1993). These 3 descriptors should always be at the back (if not the front!) of your
mind throughout this course.
References:
Anderson, A., and C.N. Jenkins. 2006. Applying Nature’s Design: Corridors as a
Strategy for Biodiversity Conservation. Columbia University Press, New York, NY.
Battin, J. 2004. When good animals love bad habitat: Ecological traps and the
conservation of animal populations. Conservation Biology 18:1482-1491.
Brosset, A., P. Charles-Dominique, A. Cockie, J.C. Cosson, and D. Masson. 1996. Bat
communities and deforestation in French Guiana. Canadian Journal of Zoology 74:19741982.
Cheng, K., and M.L. Spetch. 1998. Mechanisms of landmark use in mammals and birds.
Pp. 1- 17 in: Spatial Representation in Animals (S. Healy, ed.). Oxford University Press,
New York, NY.
Coffman, C.J., J.D. Nichols, and K.H. Pollock. 2001. Population dynamics of Microtus
pennsylvanicus in corridor-linked patches. Oikos 93:3-21.
Dunning, J.B., B.J. Danielson, and H.R. Pulliam. 1992. Ecological processes that affect
populations in complex landscapes. Oikos 75:169-175.
Forman, R.T.T., and M. Godron. 1986. Landscape Ecology. Wiley and Sons, New York,
NY.
Gilbert-Norton, L., R. Wilson, J.R. Stevens, and K.H. Beard. 2010. A meta-analytic
review of corridor effectiveness. Conservation Biology 24:660-668.
Green, B.H., E.A. Simmons, and I. Woltjer. 1996. Landscape Conservation: Some Steps
Towards Developing a New Conservation Dimension. A draft report of the IUCN-CESP
Landscape Conservation Working Group. Dept. Agriculture, Horticulture and
Environment, Wye College, Ashford, Kent, UK.
Haddad, N.M., L.A. Brudvig, E.I. Damschen, D.M. Evans, B.L. Johnson, D.J. Levey, J.L.
Orrock, J. Resasco, L.L. Sullivan, J.J. Tewksbury, S.A. Wagner, and A.J. Weldon. 2014.
Potential negative ecological effects of corridors. Conservation Biology 28:1178-1187.
Healy, S., ed. 1998. Spatial Representation in Animals. Oxford University Press, New
York, NY.
Hilty, J.A., W.Z. Lidicker Jr., and A.M. Merenlender. 2006. Corridor Ecology: The
Science and Practice of Linking Landscapes for Biodiversity Conservation. Island Press,
Washington, D.C.
Hobbs, R.J. 1992. The role of corridors in conservation: solution or bandwagon? Trends
Ecol. Evol. 7:389-392.
Johnston, C.A., J. Pastor, and G. Pinay. 1992. Quantitative methods for studying
landscape boundaries. Pp. 107-125 in: Landscape Boundaries: Consequences for Biotic
Diversity and Ecological Flows (A.J. Hansen and F. di Castri, eds.). Springer-Verlag,
New York, NY.
Laurance, S.G.W., and W.F. Laurance. 2003. Bandages for wounded landscapes: faunal
corridors and their role in wildlife conservation in the America. Pp. 313-325 in: How
Landscapes Change: Human Disturbance and Ecosystem Fragmentation in the Americas
(G.A. Bradshaw and P.A. Marquet, eds.). Springer, New York, NY.
Legendre, P., and M.J. Fortin. 1989. Spatial pattern and ecological analysis. Vegetatio
80:107- 138.
Li, H., and J. F. Reynolds. 1995. On definition and quantification of heterogeneity.
Oikos 73:280-284.
Mech, S.G., and J.G. Hallett. 2001. Evaluating the effectiveness of corridors: a genetic
approach. Conserv. Biol. 15:467-474.
Naveh, Z. 1987. Biocybernetic and thermodynamic perspectives of landscape functions
and land use patterns. Landscape Ecol. 1:75-83.
Noss, R.F. 1987. Corridors in real landscapes: a reply to Simberloff and Cox. Conserv.
Biol. 1:159-164.
O'Neill, R.V., J.R. Krummel, R.H. Gardner, G. Sugihara, B. Jackson, D.L. DeAngelis,
B.T. Milne, M.G. Turner, B. Zygmunt, S.W. Christensen, V.H. Dale, and R.L. Graham.
1988. Indices of landscape pattern. Landscape Ecol. 1:153-162.
Pardini, R., S.M. Souza, R. Braga-Neto, and J.P. Metzger. 2005. The role of forest
structure, fragment size and corridors in maintaining small mammal abundance and
diversity in an Atlantic forest landscape. Biol. Conserv. 124:253-266.
Pielou, E.C. 1984. The Interpretation of Ecological Data. Wiley, New York, NY.
Prevedello, J.A., and M.V. Vieira. 2010. Does the type of matrix matter? A quantitative
review of the evidence. Biodiversity Conservation 19:1205-1223.
Rosenberg, D.K., B.R. Noon, and E.C. Meslow. 1997. Biological corridors: form,
function, and efficacy. BioScience 47:677-687.
Simberloff, D., and J. Cox. 1987. Consequences and costs of conservation corridors.
Conserv. Biol. 1:63-71.
Simberloff, D., J.A. Farr, J. Cox, and D.W. Mehlman. 1992. Movement corridors:
conservation bargains or poor investments? Conserv. Biol. 6:493-504.
Taylor, P.D., L. Fahrig, K. Henein, and G. Merriam. 1993. Connectivity is a vital
element of landscape structure. Oikos 68:571-572.
Troll, C. 1968. Landschaftsokologie. Pp. 1-21 in: Pflanzensoziologie und
Landschaftsokologie (R. Tuxen, ed.). Berichte das Internalen Symposiums der
Internationalen Vereinigung fur Vegetationskunde. Stolzenau/Weser, The Hague, The
Netherlands.
Wiens, J.A. 1992. Ecological flows across landscape boundaries: a conceptual overview.
Pp. 217-235 in: Landscape Boundaries: Consequences for Biotic Diversity and
Ecological Flows (A.J. Hansen and F. di Castri, eds.). Springer-Verlag, New York, NY.
Wiens, J.A., N.C. Stenseth, B. Van Horne, and R.A. Ims. 1993. Ecological mechanisms
and landscape ecology. Oikos 66:369-380.
Wilcove, D.S. 1985. Nest predation in forest tracts and the decline of migratory
songbirds. Ecology 66:1211-1214.
Wu, J., D.E. Jelinski, M. Luck, and P.T. Tueller. 2000. Multiscale analysis of landscape
heterogeneity: scale variance and pattern metrics. Geographic Information Sciences 6:619.