Metapopulations, fragmentation, corridors
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Transcript of Metapopulations, fragmentation, corridors
Metapopulations, fragmentation, corridors
Environment 121Conservation of BiodiversityVictoria Sork, 16 April 2009
I. MetapopulationsGeneral definition:
Population of populations in discrete patches linked by migration and extinction.
Examples of natural metapopulations• Islands (e.g. Caribbean Islands)• Habitat islands: areas which are not islands
– Lakes– Mountain tops (e.g. Sky Islands of Arizona)– Unusual geology (serpentine outcrops)– Desert oases
Examples of anthropogenic metapopulations– Remnant fragments after deforestation
Types of Metapopulations
Source: Harrison and Taylor 1997.
Elements of metapopulation dynamics1. Composed of discrete subpopulations2. Some degree of migration3. If migration is high, the set of
populations will be one large population4. Physical separation of patches5. Models are based on persistence and
existence of patches, not numbers of individuals within patches.
6. Regional or landscape scale
Dynamics of Sources and SinksDefinition: Metapopulation in which some patches have
negative population growth rate at low density and in the absence of immigration (sinks) and other patches have positive growth rate at low density (sources).
Patches vary in good and poor habitat qualitySource populations
– good habitats – population size is growing – emigrants colonize other sites
Sink populations – poor habitats– local populations are headed toward extinction– immigrants may constantly colonize site
California Gnatcatcher: a metapopulation case study
• Federally threatened subspecies inhabiting the coastal sage scrub community in southern California.
• The coastal sage scrub is a distinctive plant community that has declined due to extensive agricultural and urban development in this area.
• Analysis of the dynamics of the California Gnatcatcher in central and coastal Orange County, California.
• Used this habitat model as a basis of a metapopulation model, which included demographic data such as fecundity, survival, as well as variability in these demographic rates.
Example: Habitat suitability model• Patches are
connected• Legend indicates
suitability of habitats for Gnatcatchers
• Does the survival of the species rely on multiple patches?
Answer: They needed to preserve large patch and medium-sized patches OR species is at risk of extinction.
II. Habitat fragmentation• the loss and isolation of natural
habitats.• reduction of the total amount of habitat
type• apportionment of the remaining habitat
into smaller, more isolated patches.• Results in insularization • Often times creates a "shredded"
landscape
Fragmentation & Diversity
1. Initial exclusion 2. Isolation 3. Species-area
effects 4. Edge effects 5. Disruption of
natural processes
Biological consequences of fragmentation
A. Initial exclusion
Important species may not be in preservesB. Barriers and isolation
1. scale of movement patterns2. Roads3. inbreeding and genetic drift4. landscape matrix can increase isolation
C. Crowding effects2. population sinks.
D. Local and regional extinctions1. Metapopulation dynamic
Example of fragmentation: Colombian oak forests
0 500 m
59
42 15
9 21
Source: Fernandez-M, J. F. and V. L. Sork. 2007. Genetic variation in fragmented forest stands of the Andean oak Quercus humboldtii Bonpl. (Fagaceae). Biotropica 39:72-78.
Map of remnant forest patches remaining from once continuous forest.
Question: Does fragmentation affect genetic diversity?
Fragment seedling populations had reduced genetic diversity—Why?
Impact of Fragmentation on Species DiversitySpecies Area
Relationship:• The number of species
in an area is a function of the area.
• Usually, for single taxa or guild
• Uses – predict expected species – Size of a sampling plot
A big consequence of fragmentation is loss of space for species
The Theory of Island Biogeography
Robert H. MacArthur & Edward O. Wilson
“One of Princeton University Press's Notable Centenary Titles”
Components– colonization rate – extinction rate
Prediction of equilibrium number of species based on:• island size (small vs. big) • isolation (near vs. far)
Vulnerable species to fragmentation
1.rare species 2.species with large home range 3.species with limited dispersal 4.species with low reproductive potential 5.species with short life cycles 6.species depending on resources that are
unpredictable in time or space 7.ground nesting birds 8.species of habitats interiors 9.species exploited or persecuted by people
III. Corridors and Connectivity Connectivity: the ease
with which organisms and materials can travel between two points.
Benefits: – Gene flow– Colonization of new
patches– Habitats
Drawbacks:– Edge effects– Disease/predator/
parasite spread– Invasive species
http://www.unl.edu/nac/bufferguidelines/guidelines/2_biodiversity/5.html
Examples of Corridor ProjectsCentral America: www.pasopacifico.org/ home_area_map.htmlGreater Mekong Subregion: www
.adb.org/projects/ gms-biodiversity/
Conservation buffer guidelines• Source:
http://www.unl.edu/nac/bufferguidelines/index.html
• A partnership of USDA and US Forest Service