Announcements

• Added a README file re: VORTEX

• HW3 due Wednesday

• First draft due April 16 (Changed from April 13)!

Optional Part of HW

• What IS the MVP?– How low can it go?

• What life-history parameters are most important for the persistence of your population.

Details of “First Draft” (due 4/16)• Introduction

– Outline (B,C,D,E)• Natural history

• Population demography

• Population ecology

• Population genetics

– Preliminary list of sources (H).

• Simulation Results– Parameter list (not the same as input sheet from HW) with

justification (I)

– Output sheet (same as output sheet from HW) for base analysis (F)

• Note: Letters correspond to sections on assignment sheet

From VORTEX “Readme”

• “It is . . . incumbent upon the user to specify those parameters that can be estimated reasonably, to leave out of the model those that are believed not to have a substantial impact on the population of interest, and to explore a range of possible values for parameters that are potentially important but very imprecisely known.”

A Defense of PVA

Brook, B. W., J. J. O'Grady, A. P. Chapman, M. A. Burgman, H. R. Akçakaya, and R. Frankham. 2000. Predictive accuracy of population viability analysis in conservation biology. Nature 404:385-387.

Conceptual Utility of PVA

• It identifies the population, not land, as the critical unit for conservation purposes.

• The term “viability” stresses long term population persistence and emphasizes self-sustainability.

• The idea of “minimum” emphasizes that there may be a threshold below which a population is doomed to extinction.

Assumptions of Previous Models

• Nt+1 = B-D

• Ignores I and E– i.e., assumes a closed population

Spatial Ecology

• Addresses movement of individuals• Dispersal

– “The spreading of individuals away from each other.” Begon et al.

• Migration– “The movement of individuals or . . . populations from

one region to another.” Begon et al.

– Immigration and emigration

Metapopulation: Population of Populations

Classic Metapopulation Model

• Habitat occurs in discrete patches

• All populations have a substantial risk of extinction

• Dispersal occurs among all patches

• Patch dynamics are asynchronous

• Ignore population dynamics within a patch

Extinction (E) and Colonization (C)

• E = probability that an occupied patch will go extinct.

• C = probability that an occupied patch will send a successful colonist to an unoccupied patch

Metapopulation Dynamics

• Balance between extinction (E) and colonization (C).

• % occupied patches (P) = 1 - E/C

• What happens if E > C?

What Influences Colonization?

• C increases as distance between patches decreases.– Conservation implication?

• Probability of colonization = C*P*(1-P)– Proportion of empty patches = 1-P– Should we maintain empty patches?

Role of Empty Patches• Habitat destruction = H, removes empty patches

• Proportion of available patches = 1-P-H

• Probability of colonization = C*P*(1-P-H)

• Habitat destruction decreases the effective colonization rate.

• Conserve empty patches!