Mechanisms driving nonnative plant-mediated change in small

mammal populations and communities

Dan Bachen

Approach and Methods

http://www.stolaf.edu/depts/environmental-studies/courses/es-399%20home/

es-399-05/Projects/Jared's%20Senior%20Seminar%20Research%20Page/htt.htm

Question 1Do invasive species alter the structure of the vegetation and the food resources within the

ecosystem?

• Answering question will provide:– What factors change• native vs. invasive dominated

– Quantifications of these changes• To answer:– Literature Review– Focused Research at Site

Types of factors:

• Vegetation• Food resources– Granivorous– Insectivorous– Herbivorous

Vegetation analysis

• Horizontal vs vertical

Measurement Techniques:Vegetation

• Horizontal Structure:• Techniques:– Quadrat

• % cover

– Stem/area

Measurement Techniques:Vegetation

• Vertical Structure• Techniques:– Sidelook

Measurement Techniques:Food Resources

• Grain• Techniques:– Count -> Density

• Biomass

http://www.nouriche.com/NutriorWheatProtein.html

Measurement Techniques:Food Resources

• Arthropods• Techniques:– Pitfall– biomass

Measurement Techniques:Food Resources

• Edible Vegetation• Techniques:– % cover– Clip-> dry weight– Biomass

Question 2 Is there evidence that small mammal communities and species abundance are influenced by the structure of their habitat’s vegetation and by the available food

resources?

• Answering question will provide:– Basis for asking future questions

• To answer:– Literature review• Established correlation

Question 3Can native plant communities be manipulated in such a

way that the alterations mimic those induced by the

presence of non-native plants?

• Answering question will provide:– Tested treatments of isolated factors

• To answer:– Use previous knowledge to ID important potential factors– Test treatments for factors– Confirm

Question 3

• Use previous knowledge to ID important potential factors– Question 1: All potential factors– Question 2: Factors previously correlated– Combination

Question 3

• Test– 10x10 m test plot(s)– Control– Quantify• Measurement methods used in Question 1

– Success of treatment based on ability to mimic characteristic of invasion

Question 4 Can the consequences of manipulating the

physiognomy of the vegetation and the available food resources be quantified in small mammal community structure and species abundance? If so what are the

effects? • Answering question will provide:

• To answer:– Treat plots– Assess:

• small mammal population demography • species abundance• Species richness• Vegetation

Experimental Design• Sample Plots– 1ha (100m x 100m)

• Selection– Random sampling– Randomization of treatments• Treatment plots • Control plots

• Grid numbers sampled– Replicate plots per treatment– Paired with 4 “control” plots

Experiment Design

– Trapping• Each plot trapped 5 nights• 10x10 grid of Sherman live traps

http://www.depauw.edu/univ/naturepark/classes/small%20mammals.asp

Capture Mark Recapture

• Marks– Ear tag– Sharpie marker

• Processing– Species– Age-class– Sex– Reproductive status– Weight

http://www.flickr.com/photos/captainschlumpy/3961667069/

Analysis of Data

• Species Abundance: estimate of number of animals per plot– Ideally by age class• Account for age-class heterogeneity

– CMR Data– Model in Program Mark– Results expected

Analysis of Data

• Species richness: Measure of number of species on each plot– Similar to CMR for species but uses species as

“individuals”• Accounts for species heterogeneity

– Analyzed in MARK– Expected Results

Analysis of Data

• Species demographics: The proportion of animals in a given age class in a population– Data from CMR– Analyzed in MARK– Expected results– Important Why?

Analysis of Data

• Method of comparison– Treatment vs Control– Two sample t-test– Significance level

Vegetation confirmation

• Re-sample vegetation– Confirmation of isolation of factor– If different provide opportunity to reassess

statistical methods

Question 4 Can the consequences of manipulating the

physiognomy of the vegetation and the available food resources be quantified in small mammal community structure and species abundance? If so what are the

effects?

Question 5 Is there a plausible explanation for how the treatments affected (or didn’t affect) the community structure and

species abundance of the small mammals? • Answering question will provide:– Confidence in results

• To answer:– Explore logical explanations

Summary

• Do invasive species affect habitat?• Does habitat affect small mammals?• Can I mimic the habitat alterations caused by

invasive plants?• What are the effects of the application of

these treatments on small mammals?• Do the effects seen make logical sense?

Questions?