DispersalDispersalLandscape Ecology

DefinitionsDefinitionsDispersal ◦Spreading of individuals away from

others

Migration◦Mass directional movements of large

numbers of species from one location to another.

Question/CommentsQuestion/Comments

Do all species disperse?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 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 Do animal moves randomly? randomly? RandomCorrelated random walkMemory – making a decision.Does it depend on patch type?

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

a group?

Examples – Fire AntsExamples – Fire Ants

European StarlingEuropean Starling

How to model this spread? 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 EquationIntegrodifference Equation

Types of model?Types of model?Scientific or Statistical?

Analytical or Simulation?

Static or dynamic?

Modified diffusion Modified diffusion equationequation

How to model this spread? How to model this spread? Diffusion equation?

2004 Distribution2004 Distribution

0 200 400 600 800 1000 1200

020

4060

8010

012

0

Distance to Great Lakes

Freq

uenc

y

2400

Reservoirs in OK and KS in Verdigis River

basin

Lake Mead & Havasu

Inland Lake Distance to Great Inland Lake Distance to Great LakesLakes

1700

Inland Lake Distance to 1993 Inland Lake Distance to 1993 DistributionDistribution

dijjii

K

iij DWOAU

1

Number of Boats

Area

Scaling Factor

Distance & coefficient

Gravity Models – Gravity Models – primary spread primary spread from the Great Lakesfrom the Great Lakes

Types of model?Types of model?Scientific or Statistical?

Analytical or Simulation?

Static or dynamic?

United States Gravity ModelUnited 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. 2007 Conservation Biology

United States Gravity ModelUnited States Gravity Model

From Bossenbroek et al. 2007 Conservation Biology

2007 Distribution2007 Distribution

Predict the spread of emerald Predict the spread of emerald ash borerash borer

Local DispersalHuman-mediated Dispersal

Yr 3Yr 2

Modeling Dispersal Modeling Dispersal

Natural Spread

Yr 1

Lin

ear

Dis

tan

ce

Time

Yr 3Yr

2

Modeling Dispersal

Long-distance spread

Yr 1

Lin

ear

Dis

tan

ce

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 ModelingDiffusion Modeling

€

VF = 4rD

Used a derivation of Skellam’s diffusion equation

€

∂N∂t

= f (N )+D∂ 2N

∂x2+∂ 2N

∂y2

⎡

⎣ ⎢

⎤

⎦ ⎥

2004

2005Can diffusion

explain this rate of

movement?

Toledo

Croskey 2009 - Thesis

Estimating Diffusion Model Estimating Diffusion Model ParametersParameters VF = 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

€

VF = 4rD

Croskey 2009 - Thesis

Diffusion Model Alone Diffusion Model Alone Cannot Explain EAB SpreadCannot Explain EAB Spread

When D is estimated (obs = 0.8 – 20 km/year) mean = 802.80 km/year

When r is estimated (obs = 0.1 – 9.0 ): mean = 76.04

Natural dispersal is not responsible for the rate at which the emerald ash borer

has spreadCroskey 2009 - Thesis

Predict the spread of emerald Predict the spread of emerald ash borerash borer

Develop models for both: ◦Local Dispersal◦Human-mediated Dispersal

Natural Natural (or local) (or local) Dispersal Dispersal of EAB in of EAB in OhioOhio

Prasad et al. 2010

Predict the spread of emerald Predict the spread of emerald ash borerash 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 Predict the spread of emerald ash borer:borer:Human-mediated dispersalHuman-mediated dispersal

dijjii

K

iij DWOAU

1

Campers with Firewood

Bossenbroek & Jerde – in review

Natural and Human-Mediated Dispersal of EAB in Ohio

Prasad et al. 2010

Compared model to known Compared model to known distributiondistributionExamined 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. 2010.

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