Microhabitat association of Plethodontidsalamanders in stream ecosystems along a

riparian land-cover gradient

Thilina Surasinghe & Robert Baldwin

School of Agricultural, Forest & Environmental Sciences,

Clemson University, SC

IntroductionWhat affects habitat associations?

Climate

Habitat availability & heterogeneity

Resource distribution

Natural disturbances

Anthropogenic disturbances

What about community interactions?

Predation

Intraspecific competition

Interspecific competition

• Exploitative competition

• Interference competition

• Apparent competition

Experimental Species Desmognathus quadramaculatus Black-bellied salamander (BB) Large bodied (SVL:80mm) Dominant Aquatic Disturbance sensitive

Desmognathus fuscus Northern Dusky salamander (ND) Small bodied (SVL:50mm) Subordinate Aquatic/semi-aquatic Disturbance adaptive

Objectives

Do human induced disturbances in the riparian zone provide competitive advantage for certain species of stream salamanders?

Are Black-bellied salamanders competitively dominant over Northern dusky salamanders in forested streams?

Experimental Setup

Artificial streams simulate four land-use types with replications: forested, agricultural, residential, urban + stock tanks

Artificial streams filled with stream substrate materials and water sand, sediment, rocks, gravel, and

woody debris

Substrate thickness: 4-5 cm in wetted channel; 15 cm in banks

Water depth: 8-10 cm

Air pumps maintain DO in field-equivalent conditions

Experimental Procedure

Capture animals from the wild

Acclimatize

Individuals of same SVL class (40-50 mm for D. fuscus; 80-90 mm for D. quadramaculatus)

3 phases in each replication

1. Both species introduced

2. Remove one species

3. Reintroduce removed species & remove the one retained

Each LU type replicated in the same tank, with introduction of different individuals of each species

Make observations in each phase

Making Observations

Daily, 20-min observations in every two hours (0900-0100 hrs)

Aggression

Use of microhabitats

All Animal sampling

Percent occurrence of a species at a given microhabitat type in a certain phase

Results & Conclusion – Forested streams

D. quadramaculatus microhabitat selection

Occupied bank crevices 96% and 94% of times in coexistence and isolation, respectively

D. fuscus microhabitat selection

Occupied channel bottom 100% of times in coexistence

Occupied bank crevices 65% of times under isolation

0

20

40

60

80

100

120

Bank Crevices Channel Bottom Channel-Bank Interface Bank Surface

Perce

ntage

Occu

rrenc

e

Microhabitat Types

Forested Riparian Land-Use

BB with ND

ND with BB

BB only

ND only

Results & Conclusion – Agricultural streams

D. quadramaculatus microhabitat selection

Occupied bank crevices 89% and 88% of times in coexistence and isolation, respectively

D. fuscus microhabitat selection

Occupied channel bottom 95% of times in coexistence

Occupied bank crevices and interface 60% of times under isolation

0

10

20

30

40

50

60

70

80

90

100

Bank Crevices Channel Bottom Channel-Bank Interface Bank Surface

Perce

ntage

Occu

rrenc

e

Microhabitat Types

Agricultural Riparian Land-Use

BB with ND

ND with BB

BB only

ND only

Results & Conclusion – Residential streams

D. quadramaculatus microhabitat selection

Occupied bank crevices 52% and 88% of times in coexistence and isolation, respectively

D. fuscus microhabitat selection

Occupied channel bottom 88% of times in coexistence

Occupied bank crevices and interface 56% of times under isolation

0

10

20

30

40

50

60

70

80

90

100

Bank Crevices Channel Bottom Channel-Bank Interface Bank Surface

Perce

ntag

e Occ

urre

nce

Microhabitat Types

Residential Riparain Land-Use Type

BB with ND

ND with BB

BB only

ND only

Results & Conclusion – Urban streams

D. quadramaculatus microhabitat selection

Occupied bank crevices 25% and 88% of times in coexistence and isolation, respectively

D. fuscus microhabitat selection

Occupied bank-channel interface 70% of times in coexistence

Occupied bank crevices 76% of times under isolation

0

10

20

30

40

50

60

70

80

90

100

Bank Crevices Channel Bottom Channel-Bank Interface Bank Surface

Perce

ntag

e Occ

urre

nce

Microhabitat Types

Urban Riparian Land-UseBB with ND

ND with BB

BB only

ND only

D. quadramaculatus

Occupied stream banks and chose rock crevices as their preferred microhabitat in each land-use simulation

Showed high site fidelity at each land-use simulation

Strong domination of microhabitat selectivity over D. fuscus in forested streams

Weak domination of microhabitat selectivity over D. fuscus in non-forested streams

Some reduction in use of bank crevices in non-forest streams

General Conclusions

General Conclusions

D. fuscus

Exclusively occupied the stream channel in the forested stream in coexistence

Marked increase in occupancy of bank crevices and interface in non-forest streams, which is prominent in the urban stream

Broad selectivity of interstitial spaces including beneath rocks and logs, leaf litter, sand and gravel

Low side fidelity

No aggression or predation was observed

D. quadramaculatus competitively displaced D. fuscus in forested

streams

D. fuscus shifted to the microhabitats previously occupied by D.

quadramaculatus once the later was experimentally removed

Marked change in the microhabitat selectivity of D. fuscus with

increasing disturbances in the riparian zone

The study is still continuing and more replications will be done

General Conclusions

Funded by….

Creative Inquiry Program

Numerous undergraduates in Dept. of Biological Sciences and School of Agricultural, Forest & Environmental Sciences

Dr. Mark Scott and SC stream bio-Assessment team, SC Dept. of Natural Resources

Dr. Bryan Brown, Dept. of Biological Sciences, Virginia Tech University

Dr. Michael Childress, Dept. of Biological Sciences, Clemson University

Acknowledgement