Organisms and Landscape Pattern Landscape Ecology
Spatial distribution of resources in heterogeneous landscapes: • What impacts? • Growth • Reproduction • Dispersal
Conservation • “…maintenance of biodiversity … requires a landscape perspective”
Population vs. landscape ecologists – Different foci • Pop’n • How interactions generate patterns • LE • How composition and configuration of landscape affect pop’n of interest.
Relationship between organisms and space – How to model? • Diffusion • REM: Dispersal lecture • Island Biogeography Theory • Metapopulation Theory
Criticisms of IBG • Assumption of equilibrium. • Time period to reach equilibrium • What about non-equilibrium dynamics? • Such as distrubance • Assumption of equal dispersal abilities • Despite criticisms • Richness increases with area
Metapopulation models • In a fragmented system, any population has a probability of extinction. • However, a patch may also be recolonized. • Levins (1969) model:
Where, • p = proportion of patches colonized at any point in time. • c = colonization prob. • m = extinction prob.
What is the equilibrium condition? • Solve for p
What kind of questions can be addressed with metapopulation models? • Impact of fragmentation. • Habitat destruction • Limits on dispersal
What is missing from Levins model? • Levin’s model is spatially implicit… • Which means? • Does not account for location • Patch quality • Which influences? • Reproduction, growth, etc. • A good patch can become a source.
Mass effects • occur when local interactions operate slowly relative to the speed at which species disperse • local patches maintain populations that would otherwise go extinct without immigration • Means two things: • dispersal is generally thought to increase habitat • this effect varies with changes in the rate of dispersal.
Habitat quality • IBG and Metapopulation models assume equivalent suitable habitat. • How to determine if habitat is good? • Species are there • Have resources • Shelter • Populations reproduce • Are their indicators of habitat quality?
Density as a misleading indicator of habitat quality. • Author: Bea Van Horne • Journal of Wildlife Management • Vol. 47, No. 4, Oct., 1983 • Why would habitat quality by a misleading indicator? • Seasonal habitat is critical • Summer surveys don’t tell you much about the over winter survival of large migratory herbivores (for example). • Multi-annual cycles • Snowshoe hare and lynx • Social interactions may prevent subdominant animals from entering what is actually the high-quality habitat • This is really important when thinking about rare species.
Habitat quality • We also often simplify descriptions of habitat when thinking about large scales. • “The same landscape may be very different for different species”
What is missing from Levins model? • Matrix quality • Boundaries • Connectivity through matrix
Scale-dependent nature of organism responses • Why do appropriate scales differ among taxa? • Attributes of species • Dispersal characteristics • Body mass • Allometric relationships