Habitat degradation modifies spider diets and carbon flux

in riparian environments

Jamie-Lee Hunt

Co-authors: Neil Pettit, Harriet Paterson & Paul Close

Outline

Honours research thesis (2018)

Southwest WA, in the region surrounding Albany

Biodiversity hotspot

Multiple land use types:• Primary production• Tourism• Remnant bushland • National parks

ALBANY

Riparian zones: degradation is a major issue for freshwater ecosystems

Riparian Spiders

Abundant terrestrial predators

Important prey source

Understudied in Australia

Inform ecosystem function

Important link between aquatic and terrestrial food

webs

Common subsidies in riparian food webs

? ? ?

Research Questions

? ? ?

1. Are spider community dynamics affected by loss of habitat in the riparian zone?

2. Do riparian spiders feed more from aquatic or terrestrial food webs?

Q1 Methods : Spider community surveys

5 x Rivers

21 x 10m transects

n=7 n=5n=4n=5

Orb Weavers • Orb Weavers (Araneidae)• Long-jawed Orb Weavers

(Tetragnathidae)

Ambush Hunters• Crab Spiders (Thomisidae)• Sac Spiders (Clubionidae)

Cursorial Hunters• Fishing Spiders (Pisauridae)• Wolf Spiders (Lycosidae)

Space Weavers• House Spiders (Desidae)

• Comb-footed Spiders (Theridiidae)

• Money Spiders (Linyphiididae)*

Family Guild No. Morphospecies

No. spiders surveyed

% spiders surveyed

Araneidae Orb Weaver 20 160 38.65

Tetragnathidae Orb Weaver 3 183 44.20

Desidae Space Weaver 1 1 0.24

Linyphiidae Space Weaver 1 2 0.48

Theriididae Space Weaver 3 23 5.56

Clubionidiae Ambush Hunter 3 7 1.69

Thomisidae Ambush Hunter 3 4 0.97

Lycosidae Cursorial Hunter 7 13 3.14

Pisauridae Cursorial Hunter 4 21 5.07

Totals - 45 414 100

Summary of spider survey results

-0.5 0.0 0.5 1.0 1.5 2.0

-0.5

0.0

0.5

1.0

MDS1

MD

S2 GD1

GD2GD3

GD4

GD5

GD6

KA1

KA2

KA3KA4

KI1

KI2

KI3

KI4

KI5MA1

MA2YA1

YA2

YA3

YA4

A - Pristine

B - Slightly Disturbed

C - Some canopy, liimited erosion

D - No canopy, severe erosion

Spider community data mMDS

Riparian condition does not affect spider abundance

A B C D

510

15

20

25

30

35

ORB WEAVERS

Penn-Scott condition grade

Orb

weaver

abundance

A B C D

0.0

0.5

1.0

1.5

2.0

AMBUSH HUNTERS

Penn-Scott condition grade

Am

bush h

unte

r abundance

A B C D

01

23

4

CURSIORIAL HUNTERS

Penn-Scott condition grade

Curs

orial h

unte

r abundance

A B C D

01

23

45

SPACE WEAVERS

Penn-Scott condition grade

Space w

eaver

abundance

Morphospecies richness (p=0.72) and Shannon-Weiner diversity (p=0.67) were also unaffected by condition.

ORB WEAVERS (n=343) AMBUSH HUNTERS (n=11) CURSORIAL HUNTERS (n=34) SPACE WEAVERS (n=26)

Penn-Scott condition grade Penn-Scott condition gradePenn-Scott condition gradePenn-Scott condition grade

Orb

wea

ver

abu

nd

ance

Spac

e w

eave

r ab

un

dan

ce

Cu

rso

rial

hu

nte

r ab

un

dan

ce

Am

bu

sh h

un

ter

abu

nd

ance

Exploring ‘C’ grade habitats

A B C D

51

01

52

02

53

03

5

ORB WEAVERS

Penn-Scott condition grade

Orb

we

ave

r a

bu

nd

an

ce

p<0.01Low Cover (<9%) Mid Cover (10-49%) Dense Cover (>50%)

51

01

52

02

53

03

5

Understorey Coverage

Orb

We

ave

r a

bu

nd

an

ce

Sparse Canopy (<9%) Mid Canopy (10-49%) Dense Canopy (>50%)

51

01

52

02

53

03

5Canopy Coverage

Orb

We

ave

r a

bu

nd

an

ce

Understorey: test results

ANOVA p<0.01Mid v Dense (p<0.01)Low v Dense (p=0.12)

Mid v Low (p=0.26)

ORB WEAVERS (n=343)

Penn-Scott condition grade

Orb

wea

ver

abu

nd

ance

Canopy:marginal p-value

ANOVA p=0.07

Orb

wea

ver

abu

nd

ance

Orb

wea

ver

abu

nd

ance

Canopy Coverage

Understorey Coverage

Sparse(>10%) Mid(10-49%) Dense(>49%)

Sparse(>10%) Mid(10-49%) Dense(>49%)

? ? ?

Research Questions

? ? ?

1. Are spider community dynamics affected by the condition of the riparian zone?

2. Do riparian spiders feed more from aquatic or terrestrial food webs?

• Question 2 : SIA Methods

Q2 Methods: Spider diets using Stable Isotope Analysis

Spiders in degraded habitat ate more terrestrially derived prey

Pristine Degraded

-34-33-32-31-30-29-28-27-26-25

δ13C [‰ VPDB]

Degraded

Pristine

Orb weavers

Cursorial hunters

Orb weavers

Cursorial hunters

Degraded habitats diversify diet

Clustering of spider SI signals in Pristine vs Degraded habitat

? ? ?

Research Questions

? ? ?

1. Are spider community dynamics affected by the condition of the riparian zone?

2. Do riparian spiders feed more from aquatic or terrestrial food webs?

Sure is!Yum!

Conclusions

• Spider communities are not affected by riparian condition

• Diet becomes more terrestrial in degraded sites

• Habitat loss impairs ecological processes of carbon flow & nutrient cycling

• Foundation for future research into spider communities

Implications for

management

• Informs structural aspects of stream restoration

• Results provide another line of evidence to support riparian restoration & revegetation projects

• Spiders are not a useful indicator species to show riparian condition

Acknowledgements:

Ben Ford

Steve Janicke

Maddi Howard

Kyle Townsend

Kahree Garnaut

Susie Cramp

Sharon Rost

Ela Skrzypek

Greg Skrzypek

Kate Bowler

Doug Ford

Edith Easthope Scholarship

GSDC NRM Sustainability Research Scholarship

Property OwnersSonja Johnson ~ Graeme Pile

Peter Gilmour ~ Rebecca

Conclusions &

Implications

• Spider communities are not affected by riparian condition

• Diet becomes more terrestrial in degraded sites

• Implications for stream restoration

• Foundation for future research into spider communities

Degraded habitats diversify diet

Araneidae

Lycosidae

Pisauridae

Tetragnathids

BiofilmAlgae

Kikuyu

Fish

2nd Order Aq. Inverts

1st Order Aq. Inverts

1st Order Terr. Inverts

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

-47.00 -42.00 -37.00 -32.00 -27.00 -22.00 -17.00 -12.00

δ1

5N

[‰ A

IR]

δ13C [‰ VPDB]

Pristine Sites (Penn-Scott Grade = A)

Degraded habitats diversify diet

Araneidae

Fish

AlgaeBiofilm

Kikuyu

1st Order Aq. Inverts

2nd Order Aq. Inverts

1st Order Terr. Inverts

Lycosidae

Pisauridae

Tetragnathids

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

-47.00 -42.00 -37.00 -32.00 -27.00 -22.00 -17.00 -12.00

δ1

5N

[‰ A

IR]

δ13C [‰ VPDB]

Degraded Sites(Penn-Scott Grade = C & D)

Contribute to riparian

biodiversity

Possible value as indicator species

Cursorial hunters were more abundant on the Kalgan River

Goodga Kalgan King Marbellup Yakamia

01

23

4

River

Cu

rsio

ria

l h

un

ter

ab

un

da

nce

Goodga Kalgan King Marbellup Yakamia

05

10

15

RiverS

alin

ity (

PS

U)