1 / 17

Neutral Models

Neutral Models. Landscape Ecology. Questions/Comments . Purpose of models? . Testing hypotheses Simplest hypothesis: Null – no effect Why are null hypotheses difficult for ecological studies? Complex systems Some effect, but from what?

justus
Télécharger la présentation

Neutral Models

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Neutral Models Landscape Ecology

  2. Questions/Comments

  3. Purpose of models? • Testing hypotheses • Simplest hypothesis: • Null – no effect • Why are null hypotheses difficult for ecological studies? • Complex systems • Some effect, but from what? • Rejecting the Null, often doesn’t tell us anything.

  4. Caswell & Hubbell • Other Neutral Models • Built from Community Ecology • Hubbel – • Unified Neutral Theory of Biodiversity and Biogeography

  5. Neutral T of B and B • Theory about community organization • Constructed on Island Biogeography Theory

  6. IBG

  7. Neutral T of B and B • “the theoretical consequences of assuming that ecological communities are structured entirely by ecological drift, random migration, and random speciation.” • What is neutral in this theory? • treats organisms in the community as essentially identical in their per capita probabilities of giving birth, dying, migrating, and speciating.

  8. Null model for a landscape • A random map…. • Random in what way? • Pattern? • Process? • Number of patches? • Probability of patches?

  9. Why use neutral landscape models? • Determine the extent to which natural properties deviate from a theoretical spatial distribution • To predict how the processes (such as animal movement, seed dispersal, nutrient flow, genes, fire) are affected by landscape patterns.

  10. Simple Random maps. • Habitat vs. non-habitat • 0 or 1 • Determine proportion of landscape to be filled with habitat. • p • Randomly choose cells until reach p.

  11. What attributes exist for our map? • Number of patches • Size of patches • Amount of edge • Largest patch • Ability to percolate

  12. What is percolation? • A cluster is said to percolate when a the cluster connects from one edge of the map to the other. • What rules? • 4 edge rule • 8 edge rule • How do these rules change when percolation happens?

  13. Critical thresholds • Studying percolation gives evidence for important or critical thresholds. • Can an organism move through the system? • Or a nutrient? • Or a fire?

  14. Why would anyone want to use random methods to represent actual landscapes? • Same reason we test a null hypothesis! • Neutral landscape models don’t represent real landscape, but a standard to compare.

  15. Beyond just a value of p with random placement, what else can be done with a neutral landscape model? • Can clusters, patches develop from simple random processes?

  16. General Insights • Simply the amount of habitat changes patterns. • Thresholds exist at small changes of p.

More Related