Distribution of Tree Squirrels in California: A Species Distribution Modeling Approach to Analyzing

DataR. Garcia1 , A. Muchlinski2 , F. Shilling3 , H.L. Qiu1 , K.

Tiedeman3

1Department of Geosciences and Environment, California State University Los Angeles, CA2Department of Biological Sciences, California State University, CA

3Department of Environmental Science and Policy, University of California Davis, CA

Key Players

Western Gray Squirrel, Sciurus griseus

Eastern Fox Squirrel, Sciurus niger rufiventer

Western Gray Squirrel (Sciurus griseus)

• Found along the forested eastern slopes of the mountains from Washington to California, then westward (except for the California Central Valley) through the coast ranges.

Eastern Fox Squirrel (Sciurus niger)

• Found in much of the eastern and central United States extending northward into the southern prairie provinces of Canada.

Eastern Fox Squirrel (Sciurus niger rufiventer)

Distribution of Tree Squirrels

Wait…. The Eastern Fox Squirrel is here!

What is the big issue?• It has been shown that the non-native species

replaces (completely) the native species when the two come into contact.

Red Squirrel • The American Eastern Gray Squirrel has taken

over most of Europe and has mostly replaced the European Red Squirrel.

Hypothesis

• The non-native Eastern Fox Squirrel will have an increasing negative effect on the native Western Gray Squirrel in California.

Main Take-Home Points

• The Eastern Fox Squirrel will continue to expand its geographic range in CA

• There are populations of the Western Gray Squirrel “in the way” of continued expansion of the Eastern Fox Squirrel

• GIS & Remote Sensing are valuable tools to understand future “conflict” between Eastern Fox Squirrels and Western Gray Squirrels in CA

Goals for My Study

1: Gather data on the all-time distribution of the non-native and native species within the US2: Map the distribution of each species in CA3: Construct and Compare Ecological Niche Models for Each Species

Goal 1: Gathering Data, Achieved!

So Far: ~37,000 records, ~29,000 locations

Goal 2: Mapping Distribution, Achieved!

• Google Fusion Tables

Western Gray Squirrel

Eastern Fox Squirrel

Goal 3: Construct and Compare Ecological Niche Models for Each Species

• Use MaxEnt (Maximum Entropy Species Distribution Software) to find suitable habitat

• Use ESRI ArcMap to classify the habitat

Goal 3: Construct and Compare Ecological Niche Models for Each Species

Landcover gradient

Habitat model based on suitable landcover and altitude zones in combination with current observations.

Altitude gradient

Current Observation

Goal 3: Construct and Compare Ecological Niche Models for Each Species

BIOCLIM data• Altitude• Mean Annual

Temperature• Annual

Precipitation• Land Cover Type*• Imperviousness*• Tree Canopy*

Eastern Fox SquirrelCalifornia Sightings National Sightings

Eastern Fox Squirrel to Binary Ecological Niche Model

Apply Binary Threshold

Apply Binary Threshold

Apply Binary Threshold

S. griseus Model to Binary Ecological Niche Model

Apply Binary Threshold

Goal 3: Compare the Ecological Niche Models of the two species.

Western Gray SquirrelEastern Fox Squirrel

Overlap of Both Species

Unsuitable for BothSuitable for Both Suitable for S. niger onlySuitable for S. griseus onlyS. griseus will lose over 99% of its projected niche area

Validation with New Range Maps

Validation with New Range Maps

Future Work

• Analyzing the importance of certain biotic features that would aid in determining future range (Land Cover Type, Imperviousness, Tree Canopy, NDVI).

• Looking at how the model changes due to different time frames.

• Determining specific migration areas and rates over time.

Hypothesis – Supported!

• The non-native Eastern Fox Squirrel will have an increasing negative effect on the native Western Gray Squirrel in California.

Conclusions – Take-Home Points

• The Eastern Fox Squirrel will continue to expand its geographic range in CA

• There are populations of the Western Gray Squirrel “in the way” of continued expansion of the Eastern Fox Squirrel

• GIS & Remote Sensing are valuable tools to understand future “conflict” between Eastern Fox Squirrels and Western Gray Squirrels in CA

Acknowledgements• Dr. Alan Muchlinski, Dr. Qiu, Dr. Aguilar, Carly Creley, Ruby

Alvidrez• Sources of Data: Arctos, CDPH, California Living Museum,

California Wildlife Center, Critter Creek, Gold Country Wildlife Rescue, Lindsey Wildlife, Orange County Vector Control, Peninsula Humane Society, SPCA Monterey County, Shasta Rehab, Sonoma County, Squirrelmender, Stanislaus Wildlife Rehab, Suisun Wildlife, Sulphur Creek Nature Center, Tehama Wildcare, Wetlands & Wildlife Care Center, WildCare, Wildlife Center Silicon Valley

• Individuals: Fraser Shilling, Janel Ortiz, Julie King, Sheila Byrnes, and private citizens.

Questions?

facebook.com/californiatreesquirrels

Sciurus niger rufiventer Nationwide Population