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 timeContinual turnover of species, extinction vs. immigrationLarge islands should support more species than small islandsSpecies 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 emigrationThe 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 sinkpopulations

- 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 presentFor 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 distributionCore species - common; satellite species - rare

Metapopulation Theory

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

Metapopulation Theory

Species-time-area relationshipsNumber of species observed in plot each year won’t change, but extinction/immigration will result in new species being observed in plots over the yearsLarger plots have more speciesLarger plots contain metapopulations of all species in landscape, small plots do not

Konza Prairie

Conservation & Reserves

Forest fragmentation and species richness?SLOSS - single large or several small reservesWhich gives the most protection per area?

Conservation & Reserves

Island biogeographyMetapopulation 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 betterMore species, larger populations, less chance of extinctionReality: take whatever size you can get

Conservation & Reserves

Edge effectsHigher mortality near edges - wind, pathogensMore prone to invasive species - unprotected edges - fewer barriers to seed dispersal