Plant Ecology - Chapter 16 Landscape Ecology

Landscape Ecology Study of the spatial distributions of individuals, populations, and communities, and the causes and consequences of those spatial patterns

Island Biogeography Equilibrium theory of island biogeography by MacArthur & Wilson (1967) Island size and isolation both play important roles in determining number of species present on “islands” Number of species is a balance between immigration and extinction, which vary with island size and isolation

Island Biogeography: Predictions Number of species should eventually become constant through time Continual turnover of species, extinction vs. immigration Large islands should support more species than small islands Species number should decline with remoteness (isolation) of an island

Island Biogeography

Island Biogeography Remoteness a strong influence (bird species more impoverished on far rather than near islands)

Island Biogeography But it takes time to establish the species equilibrium (new island being slowly colonized by new species) Local evolution, speciation processes also must be considered (fruit flies on Hawaiian islands - more important than immigration, extinction)

Metapopulation Theory The population size of a species on any “island” is a result of local population dynamics, plus immigration minus emigration The population on an “island” may go extinct, but new immigrants may repopulate

Metapopulation Theory The equilibrium between immigration and extinction determines the number of surviving populations on different islands, their average size, and the total size of the metapopulation

Metapopulation Theory Source and sink populations - some populations may not be self-sustaining

Metapopulation Theory

Metapopulation Theory Do plant populations have high enough rates of migration, extinction to have an impact on distributions and population sizes?

Metapopulation Theory Prediction 1: If extinction rates are dependent on the frequency of occupied patches, those species occurring in many patches will have large populations when present For most plant species, studies show that occupancy and abundance are positively correlated

Metapopulation Theory Prediction 2: If immigration, extinction depend on frequency of occupied patches, patch occupancy by a species should have a bimodal distribution Core species - common; satellite species - rare

Metapopulation Theory Prediction supported at small scales (< 1 km2), but not at larger scales Spatial structure and dispersal OK at small scale, but not at larger scale - immigration and extinction rates of plants too low for model

Metapopulation Theory Konza Prairie Species-time-area relationships Number of species observed in plot each year won’t change, but extinction/immigration will result in new species being observed in plots over the years Larger plots have more species Larger plots contain metapopulations of all species in landscape, small plots do not

Conservation & Reserves Forest fragmentation and species richness? SLOSS - single large or several small reserves Which gives the most protection per area?

Conservation & Reserves Island biogeography Metapopulation theory

Conservation & Reserves Testing concepts in Brazil

Conservation & Reserves Corridors can also be important - connectivity - seeds for dispersal into sink regions

Conservation & Reserves Bigger should be better More species, larger populations, less chance of extinction Reality: take whatever size you can get

Conservation & Reserves Edge effects Higher mortality near edges - wind, pathogens More prone to invasive species - unprotected edges - fewer barriers to seed dispersal