Lecture 19: Neutral Theory and Landscape Ecology (Chapter 23)
• Community Membership: There are three schools of through what controls community diversity:
o Equilibrium theory: ecological and evolutionary compromises lead to resource partitioning.
o Nonequilibrium theory: fluctuating conditions keep dominant species from monopolizing
o Neutral Theory: species do not differ and diversity patterns are a product of dispersal, speciation
and demographic stochasticity.
• Neutral theory can predict diversity patterns even when all species are competitively equivalent and use the
• In 2001, Stephen Hubbell published a book on neutral theory in ecology. It changed how we explain diversity
1. Individual dies at random.
2. Spot is colonized by any other species in community
3. If new species are not introduced, all but one will go extinct
4. New species through immigration and speciation.
• Neutral theory can predict diversity patterns very well in diverse systems. However, we know from detailed
studies that species are not identical. Modern research is working to reconcile niche (resource partitioning)
and neutral theory.
• Scheffer & van Nes (2006) used computer stimulations to show that evolution would produce groups of
Landscape Ecology/Ecosystem Management (Chapter 23)
• Landscape ecology examines spatial patterns and their relationship to ecological processes and changes.
• Landscape ecology is a sub discipline of ecology that emphasizes the causes and consequences of spatial
variation across a range of scales.
• Landscape ecologists document observed spatial patterns including those that occur across broad geographic
regions and study how those patterns affect and are affected by ecological processes. They are interested in
the spatial arrangement of different landscape elements across Earth’s surface. Examples of landscape
elements: o Include patches of forest surrounded by pasture or lakes scattered across a large region of northern
o Biotic: usually plants and animals, could be other
o Abiotic: topography, soil, climate, water…
A landscape is a heterogeneous area composed of dynamic mosaic interacting ecosystems
• Landscape: an area in which at least one element is spatially heterogeneous
o Heterogeneous: displaying a varied composition or a mixture of elements. In ecology, many
difference across space and/or time.
o Homogenous: consisting of elements, which are similar or identical. Few to no differences across
space and/or time.
o A mosaic is composite of heterogeneous elements.
• Landscapes often include multiple ecosystems. The different ecosystems that make up a landscape are
dynamic and continually interacting with one another. These interactions may occur through the flow of
water, energy, nutrients, or pollutants between ecosystems, as from a forest ecosystem into an adjacent lake.
• Figure 23.3: Landscape Heterogeneity: Landscapes can be heterogeneous in many different kinds of
elements, which may be arranged in ways independent of one another.
o (A) An aerial photograph of Michigan’s Upper Peninsula
o (B) A map of six different soil types in the same area
o (C) A map of seven different landscape elements in the same area.
• There is
also a biotic flow between habitat patches in the mosaic as individuals or their gametes. For such movements
to occur, patches of the same habitat types must be connected to one another, or the surrounding the habitat
must be a type through which dispersal is possible.
Geographic Information Systems (GIS)
• Remote sensing satellites now provide images of Earth that vastly expanded the interpretation of largescale
• Geographic information systems (GIS) have become standard for use in landscape planning, for
conservation and urban development.
• GIS are computerbased systems that allow the storage, analysis and display of data pertaining to specific
geographic areas. o The data used in GIS are derived from multiple sources, including aerial photographs, satellite
imagery, and groundbased field studies. (Figure A).
o Examples of such data include rainfall, elevation, and vegetation cover at specific locations.
o Each of these and many other variables could be used in a particular application of GIS but
whatever variables are used, the data are keyed to or referenced by spatial or geographic
coordinates, so that they can be assembled into a multilayered map.
• Layers of mapped data can be put together in ways to help address particular questions.
o GAP refers to the Gap Analysis Program, a US Geological Survey program whose mission is to
help prevent biodiversity decline by identifying species and communities that are not adequately
represented on existing conservation lands.
o The lark bunting is one such species. It depends on prairie habitat for its breeding grounds, but
much of this habitat has been destroying by humans. As a result, populations of the lark bunting
have been declining (1.6% per year over the past 40 years), making it a species of conservation
o For the lark bunting and any other species, gap analysis is a twostep process.
First, input data one vegetation cover (see top GIS layer in figure A) and other
environmental conditions required or preferred by the lark bunting is used to predict its
geographic distribution (the second GIS layer in Figure A).
Next, the lark’s distribution is compared with a third GIS later showing the locations of
By combining these two layers, we can calculate only a small percentage of the bird’s
distribution is protected. (Figure B).
Figure B: A conservation gap:
less than 3% of the lark bunting’s
distribution is in protected areas.
Describing Landscape Heterogeneity
1) The importance of scale:
• Scale cannot be ignored. A landscape may be heterogeneous at a scale important to a tiger beetle, but
homogeneous to a warbler or moose. The scale we chose to study a landscape determines the results we will
• Scale: the spatial or temporal dimension of an object or process, is characterized by both grain and extent.
• Grain: is the size of the smallest homogeneous unit of study (such as a pixel in a digital image) and
determines the resolution at which we view the landscape.
• Extent: refers to the area or time period encompassed by a study. • The selection of grain will affect the quantity of data that must be manipulated in analysis: using a large
grained approach may be appropriate when one is looking at patterns at a regional to continental scale.
• How the extent is defined can change the composition of the landscape being described.
• Figure 23.6: Effects of Grain and Extent:
o (A) Panels 13 show the effect of increasing grain, measured here as a pixel size
o (B) Panels 46 show the effect of increasing extent
2) Land Composition
• Land composition refers to the kinds of elements or patches in landscape, as well as how much of each kind
is present. Example from Yellowstone national park:
o Five kinds of elements lodgepole pine stand age classes
o The five elements were mapped to show structural complexity
• Figure 23.5: Landscape composition and structure:
o In this 1985 map of the lodgepole pine forest in Yellowstone National Park, we can see that the
landscape is composed of five different classes of forest. Structural complexity varies across the
landscape, as seen in the varying degree of natural
Circle 1 (Closer to top): Only remnants of older
forest remain following recent fires.
Circle 2 (Closer to bottom): Large stands of older
trees are found in this unburned region.
fragmentation. • Landscape structure: the physical configuration of the different elements that compose the landscape.
o In figure 23.5, we can see that some parts of the landscape contain large contiguous blocks of older
forest, while other parts are more fragmented and contain smaller patches of forest with a variety of
o Landscape structure is characterized by: (1) Size of patches; (2) Whether the patches are aggregated
or dispersed; (3) Complexity of patch Shape; (4) Degree of Fragmentation
Landscape patterns affect ecological processes
• Landscape structure plays an important role in ecological dynamics.
• It also influences biogeochemical cycling. Ecosystem ecologists have identified biogeochemical “hot spots”
where chemical reaction rates are higher than in surrounding landscape. Many such hot spots are found at the
interfaces between terrestrial and aquatic ecosystems, but other factors may play a part.
• Habitat patches typically vary in both their quality and their resource availability. This variation can affect the
population densities of species inhabiting each patch, the time animals spend foraging in a patch, and the
movement of organisms between patches.
• The shape and orientation of landscape elements can also be very important in physically intercepting
Disturbance both creates and responds to landscape heterogeneity
• Landscapes are dynamic
• Disturbance can create landscape heterogeneity.
• In nature, change sometimes comes to ecosystems suddenly in the form of large disturbances forests and
prairies burn over large areas, or floods bring sudden inputs of sediment into river ecosystems.
• In 1988, forest fires burned nearly one third of Yellowstone. A complex mosaic of patches that burned at
different intensities resulted. This will dictate the landscape composition for decades to centuries.
o Here, a disturbance fire was a primary force shaping the landscape pattern of the future.
• Figure 23.8: Disturbance Can Shape Landscape Patterns:
o The fires that burned through nearly onethird of Yellowstone national park in summer of 1988
resulted in a complex mosaic of burned and unburned patches. Areas that appear black in this aerial
view of Madison Canyon were burned by in