Metapopulations, fragmentation, corridors

1. Metapopulations, fragmentation, corridors Environment 121 Conservation of Biodiversity Victoria Sork, 16 April 2009

2. I. Metapopulations General 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

3. Types of Metapopulations Source: Harrison and Taylor 1997.

4. Elements of metapopulation dynamics 1. Composed of discrete subpopulations 2. Some degree of migration 3. If migration is high, the set of populations will be one large population 4. Physical separation of patches 5. Models are based on persistence and existence of patches, not numbers of individuals within patches. 6. Regional or landscape scale

5. Dynamics of Sources and Sinks Definition: 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 quality Source 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

6. 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.

7. 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.

8. 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

9. Fragmentation & Diversity • Initial exclusion • Isolation • Species-area effects • Edge effects • Disruption of natural processes

10. Biological consequences of fragmentation • Initial exclusion Important species may not be in preserves B. Barriers and isolation • scale of movement patterns 2. Roads 3. inbreeding and genetic drift 4. landscape matrix can increase isolation C. Crowding effects • population sinks. D. Local and regional extinctions 1. Metapopulation dynamic

11. Example of fragmentation: Colombian oak forests 42 15 59 9 21 0 500 m 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.

12. Question: Does fragmentation affect genetic diversity?  Fragment seedling populations had reduced genetic diversity—Why?

13. Impact of Fragmentation on Species Diversity Species 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

14. 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)

15. 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

16. 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

17. Examples of Corridor Projects Central America: www.pasopacifico.org/ home_area_map.html Greater Mekong Subregion: www.adb.org/projects/ gms-biodiversity/

18. Conservation buffer guidelines • Source: http://www.unl.edu/nac/bufferguidelines/index.html • A partnership of USDA and US Forest Service