NSF REU Ecology Research InternshipBlandy Experimental Farm

June-August 2004

Contents overview

• What is Blandy Experimental Farm?

• What is their REU program?

• What did I do there?

• What was my research project?

Blandy Experimental Farm - background

• Graham Blandy donated 700 acres to UVa in 1962• Undergraduate ecology and environmental science

research since 1992• State Arboretum of Virginia

The internship

• 12 participants– $3000 stipend

– $750 for research equipment

– Housed in estate’s old slave quarters

• Carried out ecological research project with the help of a faculty mentor

• Possible career in ecological research

Structure

• Week 1: orientation and mentor selection

• Week 2: wrote and defended research proposal

• Weeks 3-9: experiment

• Weeks 10-11: analyzed data, wrote final paper, made presentation at forum, made poster

Fun stuff

• Weekly seminar and potluck dinner• Career talks• Smithsonian’s Conservation and Research Center• Mountain Lake Biological Station• Concerts• Kid’s camp• Canoe trip• Hiking

The highs and lows of ecological research

• Time intensive• Adverse conditions• Tedious• Physically taxing

• Get to spend all day in beautiful, fascinating ecosystems learning about organisms!

• What could be better?

Predator-prey interactions between dragonfly larvae and snails

Paige BarlowBlandy Experimental Farm

Research Experience for Undergraduates

Summer 2004

Background

• Importance of predator-prey interactions for community

• Lack of research on the possible interaction between dragonfly larvae and freshwater snails– Interaction is suspected

• Dragonfly larvae are opportunistic, polyphagous predators

• Common habitat

– Inconclusive results from studies of larval odonate diets

Freshwater snails

large Planorbella small Planorbella Physa

Giant water bug

• Belostoma flumineum• Known predator of

snails

Dragonfly larvae

• Anax junius • Pachydiplax longipennis

Dragonfly larvae as predators

• Methods– Ambush– Stalk

• Cues– Visual– Chemical– Tactile

http://www.fcps.k12.va.us/StratfordLandingES/Ecology/mpages/green_darner.htm

Response of snails to predator• Alter life history

– Reproductive output– Growth rate

• Importance of morphology– Shell length– Aperture width

• Perform avoidance behavior– Crawl-out– Surface– Bury into substrate– Hide in vegetation

Questions

1. How strongly does each predator prey upon different sizes and species of snail?

2. How do the different sizes and species of snail respond to the different predators?

a) Growth

b) Reproductive output

c) Avoidance behavior

Hypotheses1. Belostoma, large Anax, small Anax,

Pachydiplax, control have greatest predatory effect respectivelyPredation greatest for Physa, small Planorbella, large Planorbella respectively

2. a) Predator small aperture width; large wet mass, length, and width

b) Predator low reproductive output c) Predator avoidance behavior proportional to

risk: bury > surface > plant use > crawl-out

Methods• Set up mesocosms

– Sand

– Water• Well (9L)

• Filtered pond (1L) periphyton, algal community

– Microscope slides

• Three snail classes crossed with five predator treatments in a full factorial design with six replicates

• Collected invertebrates from ponds

Methods – snail measurements

• Wet mass (10 snails/tub)

• Shell dimensions– Aperture width

– Width

– Length with aperture

– Length without aperture (for Planorbella)

aperture width

width

length with aperture

length without aperture

Methods – mesocosms• Added vegetation and snails• Introduced predators 1 day later (1 predator/tub)

• Shade structures

Methods – data collection

• Made behavioral observations – 3 times daily, 4 times per week for 3 weeks (July 8-July 27)

• Removed slides to dry• Determined proportion

of snails surviving in each tub

• Measured surviving snails

Statistics

• Two-way analysis of variance– Survival– Mass– Growth

• Two-way repeated measures ANOVA – behavior • Proportional data (survival and behavior) were

angularly transformed to meet the assumptions of ANOVA

• Slides will be analyzed at a later date

Results – survival

• Low survival for Physa

• Low survival in large Anax treatments

Survival - predator treatment

00.20.40.60.8

Predator

Pro

po

rtio

n

Survival - snail class

0

0.5

1

Physa sm Planorbella lg Planorbella

Snail

Pro

po

rtio

n

p<0.001

p<0.001

Results – crawl-out

• Physa crawled out when exposed to small Anax and Pachydiplax

• Increased through day

Crawl-out - snail by predator interaction

00.050.1

0.15

Predator

Prop

ortio

n

Physa

sm Planorbella

lg Planorbella

p=0.022

Results - surfacing

• Physa surfaced in response to Pachydiplax presence

• Increased through day• Decreased through

experiment

Surfacing - snail by predator interaction

00.020.040.060.08

Belost

oma

lg Ana

x

sm A

nax

Pach

ydipl

axno

ne

Predator

Pro

po

rtio

n

Physa

sm Planorbella

lg Planorbella

Surfacing - predator treatment by time of day

0

0.05

0.1

morning afternoon evening

Predator

Pro

port

ion Belostoma

lg Anax

sm Anax

Pachydiplax

nonep=0.004

p=0.001

Results – burying

• Planorbella buried more than Physa

• Did not bury in presence of predator

• Little change through day

• Increased through experiment for Planorbella

Burying - predator treatment

00.020.040.06

Predator

Prop

ortio

n

p=0.004

Results – plant use

• Planorbella used plants more than Physa

• Increased through experiment, especially for Planorbella

Plant use - snail class

0.280.3

0.320.340.360.38

Physa sm Planorbella lg Planorbella

SnailPr

opor

tion

p=0.041

Results – growth

• Average size of Physa shells decreased

• Average size of Planorbella shells increased

Change in average width

-2

-1

0

1

Physa sm Planorbella lg Planorbella

Snail

mm

Change in average length with aperture

-5

0

5

Physa sm Planorbella lg Planorbella

Snail

mm

Change in average aperture width

-1.5

-1

-0.5

0

0.5

Physa smPlanorbella

lg Planorbella

Snail

mm

p=0.006

p=0.008

p=0.003

Limitations of the study

• Belostoma escaped from tubs

• Physa behavioral proportions may be inaccurate

• No egg masses found

• Wet mass by nature not very accurate

• Minute dimensional differences

Conclusion

Belostomalarge Anax small Anax Pachydiplax

Snail- Physa- large Planorbella- small Planorbella

?

Acknowledgment