Dispersal Landscape Ecology

Definitions Dispersal ◦ Spreading of individuals away from others Migration ◦ Mass directional movements of large numbers of species from one location to another.

Question/Comments

Do all species disperse? Yes… ◦ Some by choice, some by chance  Chance can be influenced by evolution.  E.g. dandelions sees are puffy for a “reason”.

Dispersal Why disperse? ◦ Escape immediate environment.  Relieve local congestion. ◦ Discovery Dispersal  1) Exploring, picking, then settling  2) Exploring, staying. ◦ Non-discovery dispersal  Matter of change, e.g. seeds.

Do animal moves randomly? Random Correlated random walk Memory – making a decision. Does it depend on patch type?

Do animal moves randomly? Usually no…. ◦ But that is as individuals, do they as a group?

Examples – Fire Ants

European Starling

How to model this spread? What do we need to know about a population? ◦ How far they move? ◦ How fast the population grows? ◦ Suitable Habitat?

Integrodifference Equation

Types of model? Scientific or Statistical? Analytical or Simulation? Static or dynamic?

Modified diffusion equation

How to model this spread? Diffusion equation?

2004 Distribution

2400 Reservoirs in OK and KS in Verdigis River basin Lake Mead & Havasu Inland Lake Distance to Great Lakes

1700 Inland Lake Distance to 1993 Distribution

Number of Boats Area Scaling Factor Distance & coefficient Gravity Models – primary spread from the Great Lakes

Types of model? Scientific or Statistical? Analytical or Simulation? Static or dynamic?

United States Gravity Model Basic Information - ◦ Based on 210 Watersheds ◦ Estimate # of boaters/watershed ◦ Sum lake area/watershed How to parameterize? ◦ Boat surveys ◦ Local information Primary Question – ◦ How many boaters from areas with zebra mussels are traveling to western waters?

From Bossenbroek et al Conservation Biology United States Gravity Model

From Bossenbroek et al Conservation Biology

2007 Distribution

Predict the spread of emerald ash borer Local Dispersal Human-mediated Dispersal

Yr 3 Yr 2 Modeling Dispersal Natural Spread Yr 1 Linear Distance Time

Yr 3 Yr 2 Modeling Dispersal Long-distance spread Yr 1 Linear Distance Time

Does natural dispersal account for the rapidity with which the emerald ash borer has spread, even at the county scale? Predict the spread of emerald ash borer

Diffusion Modeling Used a derivation of Skellam’s diffusion equation Can diffusion explain this rate of movement? Toledo Croskey Thesis

Estimating Diffusion Model Parameters V F = velocity of the invasion front ◦ Observed in Lucas County Ohio  16 – 40 km/year D = diffusion coefficient ◦ Reported movement capabilities of EAB  0.8 – 20 km/year r = intrinsic rate of increase ◦ r values for other beetles  0.1 – 9.1 Force the model to fit observations by solving for r and D Croskey Thesis

Diffusion Model Alone Cannot Explain EAB Spread  When D is estimated (obs = 0.8 – 20 km/year)  mean = km/year When r is estimated (obs = 0.1 – 9.0 ):  mean = Natural dispersal is not responsible for the rate at which the emerald ash borer has spread Croskey Thesis

Predict the spread of emerald ash borer Develop models for both: ◦ Local Dispersal ◦ Human-mediated Dispersal

Natural (or local) Dispersal of EAB in Ohio Prasad et al. 2010

Predict the spread of emerald ash borer Local Dispersal ◦ Flight (~2 km/yr) ◦ Local human spread (~20 km/yr) Human-mediated dispersal ◦ Campers moving firewood ◦ Hitchhikers on cars, trucks, etc.  i.e. road networks. ◦ Wood products industry

Predict the spread of emerald ash borer: Human-mediated dispersal Campers with Firewood Bossenbroek & Jerde – in review

Natural and Human- Mediated Dispersal of EAB in Ohio Prasad et al. 2010

Compared model to known distribution Examined the model predictions to the patterns of the human factors included. We examined 11 of the major routes from Detroit, MI, to major cities in Ohio ◦ And included one turn only onto an adjoining highway. ◦ Then buffered these highways at 1, 2, and 4 km. Results: ◦ 52% of the known locations of EAB fell within 1 km ◦ 64% fell within 2 km ◦ 81% fell within 4 km  these few roads that represent only 34.7% of the total road length used in the modeling. Prasad et al

 This result highlights the importance of the role of major highways that are in a connected road network in spreading the emerald ash borer.