Differential Seed Preferences of Tamias striatus and Neotamias minimus and their implications for the Great Lakes regionAmy Johnson, University of Notre DameMichael J. Cramer and David Flagel, University of Notre Dame Environmental Research CenterSamantha Driscoll, Syracuse University

Forest rodents serve two potential roles for plants

Seed dispersal through caching Seed predation

Many species eat seeds Potential for evolutionary responses

Size assortment Masting

Previous studies of closely related seed predators

Species are not always redundant Peromyscus: difference in foraging

preferences for maple seeds

Community Effects

Important members of forest communities

Prey for carnivorous species Dual role for many tree species

Seed predators – consume seeds Seed dispersers – move seeds away from

parent plant Species-specific foraging preferences Sciurids common seed

predators/dispersers Species ranges altered by climate change

Southern species moving north

Seed Predators

Chipmunks

Eastern Chipmunk (Tamias sciurus)

Least Chipmunk(Neotamias minimus)

Small body size Habitat specialist Seasonal torpor Scatter hoarder

Large body size Habitat generalist Active year-round Mostly larder

hoarder

Species-specific seed preferences demonstrated by other rodents

Laboratory experiments useful to quantify preferences

Cafeteria trails common experimental approach

Analysis of multiple food sources becomes problematic

Simplify analysis using index Selectivity indices work for pairwise

comparisons Statistical issue: multiple comparisons

Seed Preferences

Shannon Index Compare diversity of items in diet relative

to what is offered Includes analysis of number of types of

food items (richness) and relative abundance (evenness)

Conceptually simple Allows for multiple seed species to be

tested simultaneously Strong inference – hypothesis testing Useful for species comparisons Statistical power

New Approach: Diversity Indices

Determine chipmunk seed preferences for common trees

Sugar maple (Acer saccharum) Red maple (A. rubrum) Balsam fir (Abies balsalmea) Beaked hazelnut (Corylus cornuta) Pin cherry (Prunus pennsylvanica)

Compare preferences between chipmunk species

Hypotheses Smaller bodied Neotamias should prefer

smaller seeds (especially A. rubrum and A. balsalmea)

Tamias should have more generalized preferences

Objective

Chipmunks of both species captured in the wild

Tamias : 2012 Neotamias: 2013

Chipmunks kept in laboratory for 36 hours Fed sunflower seeds ad libitum during day

of capture Starved overnight (8 hours) Fed combination of seeds the following

day Tamias were fed 20 g of each seed type Neotamias were fed 10 g of each seed

type Seeds dried and weighed before and after

each trial Amount consumed recorded

Methods

Proportion eaten calculated for each seed type

Shannon Diversity Index calculated for each individual

Mean for each chipmunk species compared to null expectation

Assume all proportions 0.2 Hypothesis test: compare observed value

of Shannon Index to expected If significantly different, separate t-tests

compared proportions between the chipmunk species

Proportions logit transformed prior to analysis

Analysis

Do chipmunks demonstrate seed preferences?

T.str iatus N.minimus0.0

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Chipmunk species

shan

non

dive

rsity EQUAL PREFERENCES

t13 = -10.56, p < 0.001

t10 = -4.94, p < 0.001

Seed Preferences Vary by Chipmunk Species

SM6%

RM66%

BF12%

PC10%

HZ6%

Neotamias minimus

SM34%

RM4%BF

9%PC

18%

HZ34%

tamias striatus

Red Maple: t23 = 6.82, p <0.001Sugar Maple: t23 = -4.11, p < 0.001Hazelnut = t23 = -2.41, p = 0.02

Inconsistent Decision for Eastern Chipmunks

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00.0

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Tamias Striatus

Sugar Maple

Haz

elnu

t

Kendall’s correlationTau = -0.429, p = 0.04

Neotamias: prefer red maple over all others

Tamias: prefer sugar maple or hazelnut Why?

Size assortment Foraging decisions: eat it now or eat it

later? Implications?

Reduction in Neotamias, increase in Tamias

Potentially more red maple, reduction in hazelnut and sugar maple

Overall lower germination rates due to increased pilfering

Differences in Seed Preferences

Shannon Diversity Index useful to determine if preferences exist

Cannot determine where differences lie Possibility of using beta diversity to

compare seed predator species

Utility of Diversity Indices

Funding : University of Notre Dame Bernard J. Hank Family Endowment

(UNDERC) Glynn Family Honors Program

Field help (chipmunkies) Riley Parrott Matt Pfarr Lauren Eckert Chelsea Gyure

Thanks